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What Is a Coreless Motor?

A coreless motor is a small motor without an iron core.

It is also called an iron coreless motor. The advantage of coreless motor is that there is no loss due to iron loss because there is no iron core. There is no vibration due to cogging, and the motor operates quietly.

However, the torque is lower because the magnetic force generated is weaker than that of a normal motor.

Uses of Coreless Motors

Coreless Motors are used in vibration motors that vibrate cell phones and servo motors for radio-controlled vehicles and robots, taking advantage of their small size and low vibration, noise, and electromagnetic interference.

Because of their excellent responsiveness and controllability, they are also used in surveying instruments, camera lens motors, ultrasonic endoscopes, surgical drills, etc., making them indispensable motors, especially for medical applications. Each manufacturer is developing its own unique coil winding method and materials.

Principle of Coreless Motors

An ordinary motor consists of a coil wound around an iron core, with a magnet placed outside the coil. Electric current flows through the coil, and the magnetic field generated by electromagnetic induction is used to cause the magnet to rotate.

In a coreless motor, on the contrary, a permanent magnet is placed inside and the coil is wound around the outside of the magnet in a cup shape using resin or other material, thereby eliminating the iron core. When an electric current is applied to the coil, the coil rotates, subject to Fleming’s left-hand rule. Since the coil rotates, it is called a rotor.

1. Response to Current

Coreless motors have low inductance in their windings and are highly efficient. The electrical time constant of the motor is a parameter that indicates the characteristics of the rising current in relation to the input voltage.

It indicates the time it takes for the current to reach 63.2% of its peak value. Since the electrical time constant is relatively low for coreless motors, the current responds very quickly.

2. Acceleration/Deceleration Response

Coreless motors are motors with low inertia due to their reduced weight. Inertia refers to the moment of inertia, which increases in proportion to the mass.

Inertia is proportional to the acceleration/deceleration torque, which is the torque required to accelerate or decelerate to a given rotational speed. In other words, the acceleration/deceleration torque is also smaller in coreless motors, making them suitable for rapid acceleration and deceleration.

The use of powerful rare earth magnets, such as neodymium magnets for the internal magnets, has led to further miniaturization and increased torque. They help reduce size, thickness, and weight.

Other Information on Coreless Motors

1. Efficiency of Coreless Motor

A coreless motor does not generate iron loss. Iron loss consists mainly of hysteresis loss and eddy current loss. The energy loss caused by a change in the magnetic field report of the iron core is called hysteresis loss.

In addition, changes in the direction of the magnetic field generate electric current inside the iron core. The generated electrical energy is converted to heat and escapes to the outside, and this loss is called eddy current loss.

In the case of coreless motor, the above-mentioned iron loss does not occur, so the motor can operate at high efficiency even at high speeds. Each company’s technology is reflected in the way the coils are wound to minimize waste and increase efficiency. 

2. Difference Between a Coreless Motor and a Brushless Motor

A coreless motor is a motor that does not use an iron core (core) but consists of coils and magnets. A motor with coils wound around a general iron core is called a cored motor.

A brushless motor is a motor that does not use brushes and is rotated by controlling the direction of the electric current by an electronic circuit. DC motors (direct-current motors) are classified according to whether they are controlled by electronic circuits or commutators and brushes, as they need to periodically reverse the direction of the current to keep rotating.

Coreless motors come in two types: brushed and brushless. A motor that is coreless and brushless is called a coreless brushless motor. For brushed motors, the rotor is a coil, and the stator is a permanent magnet. For brushless motors, the rotor is a permanent magnet, and the stator is a coil.

3. Advantages and Disadvantages of Coreless Motors

Advantages

• Small size and lightweight
• High-speed rotation is possible
• High efficiency and low current consumption
• Cogging-less

The iron core accounts for most of the weight of a motor. The absence of an iron core in a coreless motor allows it to be smaller and lighter. They also have a small moment of inertia (inertia), resulting in excellent responsiveness and controllability, as well as high motor efficiency and high-speed rotation.

In the case of cored motors, the iron core and magnet repeatedly move closer together and farther apart, each time causing cogging, or magnetic force trapping. Coreless motors, however, have the advantage of smooth and quiet rotation because cogging does not occur.

Disadvantages

• Low torque
• Insensitive to heat
• High price

The disadvantage of coreless motors is that they generally have low torque. The amount of torque is proportional to the current value. To achieve high torque, a large current must be applied, but because the copper wire is thin and there is no iron core, the coil is mechanically weak and a large current cannot be applied.

If a large current is applied to a coreless motor with a small allowable current value, the heat may deform the coil and lead to motor failure.

What Is a Fuse?

A fuse is an electrical/electronic component that prevents electrical fire or spillover to upper circuits in the event of an overcurrent.

When an abnormality such as a short circuit or overload occurs in an electric circuit, an overcurrent occurs, in which the current value exceeds the designed value of the circuit. Overcurrents not only lead to failure of the equipment itself on the electric circuit, but can also cause fires due to abnormal heat generation or ignition.

There is also a high risk of voltage drops and other abnormalities occurring in the upper circuits on the power supply side. Fuses are incorporated to protect against these hazards from overcurrents. When connected in series with a circuit, they act as conductors that carry current during normal operation. When an overcurrent occurs, the conductor in the fuse melts, thereby interrupting the power supply to the load-side circuit.

Uses of Fuses

Fuses are used in a wide range of applications in industry.

Specific applications are as follows:

• For protection of instrumentation and control circuits
• For protection of automotive control parts
• For protection of OA equipment such as printers and multifunctional machines
• Protection for white goods such as TVs and air conditioners
• Short-circuit protection for transformers in high-voltage power transmission and distribution networks
• Short-circuit protection for high-voltage motors

In the past, no-fuse breakers were used in many home switchboards, but in recent years, no-fuse breakers have become more popular than fuses, which need to be replaced once they blow.

However, Fuses are still used in automobiles to protect electrical systems and prevent vehicle fires. They come in a variety of shapes depending on their application and include plate fuses and blade-type fuses.

Principle of Fuses

The basic principle of a fuse is that it self-blows due to heat generated by an overcurrent. Fuses are mainly composed of a mouthpiece, fuse element, and housing.

1. Mouthpiece

The mouthpiece is the metal part that connects the fuse to the electrical circuit. Fuses with Y-terminals or blade type fuses are also available. 

2. Fuse Element

The fuse element is the part of the fuse that melts in the event of an overcurrent. When current flows through the fuse element, Joule heat proportional to the square of the current value is generated. If the current is less than the rated current, heat dissipation is superior to the temperature rise associated with the Joule heat generation, so fusing does not occur. When the rated current is exceeded, the temperature rises and the current is cut off by melting. In general, the fuse is irreversible and must be replaced before it can be restored to its original state.

3. Housing

The housing is the part that supports the element and mouthpiece of the fuse. It is made of insulating materials such as glass, porcelain, or resin. Fuses whose housings are made of glass tubing are called glass-tube fuses.

How to Select a Fuse

Fuses are selected primarily by their ampere rating. The key point is to select a fuse with a rated current that is less than or equal to the rated current value of the components on the circuit, while ensuring that there is no circuit breakage due to malfunction.

Currents to be considered in selection include steady-state current and inrush current. The steady-state current is the current value that flows when the circuit actually used is stable, while the inrush current is the high starting current that occurs when the power is turned on to the circuit. The inrush current does not cause the device to melt, but it is selected so that it will melt when the inrush current exceeds the steady-state current during steady-state operation. The protection conditions are examined by combining the breakdown-time characteristic and the rated current.

The melt-time characteristic is the characteristic of the magnitude of the current and the time it takes to be interrupted. The inrush current is selected so that the device will not melt during the duration of the inrush current and will melt immediately in the event of a short-circuit accident. Another important item to consider when selecting fuses is the ambient temperature, where the circuit will actually be used. Fuses are designed to blow due to heat, so they are affected by the ambient temperature of the area around the equipment.

Types of Fuses

Fuses come in a variety of shapes and sizes to suit the type of circuit and environment in which they are mounted.

Typical types are as follows:

• Fuses for mounting on electronic circuit boards
• Thermal Fuses
• Glass-tube Fuses
• Blade fuses
• Current-limiting Fuses for high-voltage circuits

If the type or shape of a fuse you want to use is not available in the off-the-shelf products, some manufacturers will accept special orders. Most fuses are power fuses that interrupt at overcurrent, but there are also thermal fuses that interrupt at temperature.

Because they detect a rise in ambient temperature and blow, they are often used in appliances that generate heat, such as hair dryers. The elements of thermal cutoffs have low resistance and generate almost no heat due to the current.

What Is a Pushbutton Switch?

There are two types of pushbutton switch: one for power and the other for operation. The power pushbutton switch is a button that directly inputs power into the motor. Once it is turned on, the power remains on even if the user removes their hand from the button. To turn off the power, press the off button. The operating pushbutton is used to operate the electromagnetic contactor or electromagnetic switch. Once the button is turned on, the power is turned off by removing your hand from the button.

Basically, this switchgear has a robust exterior to withstand both outdoor and indoor use. It is sturdier than a household switch box and is available in an exposed type for indoor use and a rainproof structure for outdoor use.

Uses of the Pushbutton Switches

Pushbutton switches switches are installed in various industrial machines, such as woodworking machines, machine tools, and food processing machines, to switch them on and off.

For operation, they are used as pushbutton switches for electromagnetic switches and electromagnetic contactors for hoists, cranes, pumps, heaters, etc.

Pushbutton switches for large currents and waterproof or dustproof types with the button part covered with a special resin are also available to meet the needs of special environmental applications, such as outdoors and in factories. There is also switchgear with an overload protection device and an adjustment knob.

Principle of the Pushbutton Switches

The pushbutton switch consists of a push button attached to an electromagnetic switch with a case and an electromagnetic contactor. Some types of pushbutton switch have the operating circuit wiring already connected, but if not, make sure to connect the wiring correctly. Check the contact configuration as it varies from product to product.

The direct-in starting method using an operating pushbutton switches are often used in the circuit to start an electric motor. Connect a thermal relay and an electric motor to the main contacts of the electromagnetic switch. The thermal relay is used to protect the equipment. Pushbutton switches are connected to the electromagnetic switch, and the switch starts the motor. Use within the range of the rated current and voltage specified by the product. Some products are equipped with an interlock to prevent opening and closing while the switch is turned on.

ABS resin is often used for the outer plastic case of the pushbutton switches; ABS resin is lightweight, has good insulation properties, and can be used outdoors. Some pushbutton switches are made of impact-resistant steel.

What Is an Ammeter?

An ammeter is an electrical meter used to measure the magnitude of an electric current. It is a measuring instrument with small internal electrical resistance. The circuit at the point of measurement is disconnected, and the ammeter is connected in series between them. Inside the ammeter, a low resistance is inserted into the circuit, and the voltage at both ends of the resistance is measured and converted to a current value.

A current shunt or current transformer is used to measure large currents. An ammeter is broadly classified into a DC ammeter and an AC ammeter. An ammeter is available in two display types: analog and digital.

In industrial applications, an ammeter is more accurate than multimeters and clamp meters and can measure minute currents.

Uses of Ammeters

Ammeters can be used in laboratories where electricity is used for precise measurements, or they can be fixed to control panels as monitors. There are also cases where the current is checked using a simple tester. Ammeters in multimeters, clamp meters, etc., are used to check power distribution and transmission in homes and buildings.

Some automobile instrument panels are equipped with DC ammeters. A positive reading indicates the battery is charging and a negative reading indicates it is discharging. Ammeters are commonly installed in switchboards of factory equipment, buildings, and power generation equipment. School science experiments teach how to measure current. In laboratories, the current is often measured precisely.

Fine ammeters and totalizing ammeters are also used for plating and surface treatment with fine currents, which require measurement of fine currents.

Principle of Ammeters

Ammeters are connected in series to a circuit. Analog ammeters use a pointer to indicate the current value. The needle of the permanent magnet moves in response to changes in the magnetic field caused by the current flowing through the internal coil. DC ammeters are of the moving coil type and consist of a permanent magnet and a coil. For large current measurements, a current divider is used to extract a portion of the current for measurement.

Ammeters for alternating current are mainly moving iron strip-type instruments and are used to measure commercial frequencies of about 45 to 65 Hz. When measuring current, voltage drops at the connection terminals and indication errors due to heat generation and magnetic fields may occur. Measuring a current greater than a certain value will result in a larger error. To improve the accuracy of current measurement, current dividers are used for DC and current transformers are used for AC.

Ammeters with digital displays use current dividers, current sensing resistors, and AC current sensors. The fine voltage at both ends is then digitized and used as the current measurement value. In addition, an integrating ammeter is used at plating sites. It is possible to measure the totalization of the current that has flowed over a certain period.

Other Information on Ammeters

1. How to Use an Ammeters and Precautions

Ammeters are a measuring instrument that measures the current flowing at a certain point in a circuit. It is made so that its internal resistance is low and does not affect the current flowing in the circuit. When connecting ammeters, insert the ammeters in series with the circuit whose current is to be measured. Connect the higher potential of the circuit to the + side of the ammeters and the lower potential of the circuit to the – side of the ammeters.

There are generally several terminals on the (-) side of the ammeters. If the measurement range is known, select the appropriate range; if not, start with a large range and work down to the appropriate range. If you start with a small range, you may destroy the ammeters when a current greater than the range is applied. Some ammeters are protected by an internal fuse.

A similar instrument is the voltmeter. A voltmeter is connected in parallel to a circuit and measures the voltage between two points. Connecting ammeters to measure voltage in the same way as ammeters is very dangerous because it is the same as shorting the power supply. Therefore, extreme caution is required. 

2. Multimeter

There is a useful instrument called a multimeter or tester. They can measure not only current but also basic electrical characteristics such as current, voltage, and resistance, regardless of whether it is AC or DC. There are digital and analog types. They are mainly handy types that can be easily carried around and used.

Current is displayed by measuring the voltage at both ends of a micro resistor inside the instrument and converting it to current. DC voltage is displayed by amplifying the voltage between two probes or by attenuating it through an attenuator. AC voltage is displayed by converting AC voltage to DC voltage through a rectifier circuit.

What Is a Voltmeter?

A voltmeter is a device that measures the voltage between two points to be measured. They are mainly classified into digital and analog voltmeters. Digital voltmeters use an A/D converter to convert the input voltage to a digital value and display it numerically, enabling highly accurate measurements.

Analog voltmeters, on the other hand, are a combination of ammeters and voltage dividers and are characterized by the ability to determine the voltage value from the position of the meter pointer roughly. AC voltmeters usually convert alternating current to direct current using a rectifier circuit and measure and display the voltage. The measurement of distortion waves is less accurate than that of sine waves.

Uses of Voltmeters

Voltmeters are used in a wide variety of applications, including adjustment and inspection in production lines, monitoring the operating status of various facilities, and measuring temperature and humidity in combination with sensors.

Each model of voltmeter has a defined measurement voltage range, so it is necessary to select the appropriate model according to the purpose of use. Depending on the measurement target, the input impedance of the voltmeters may affect circuit operation, resulting in measurement errors, so careful consideration is required.

It is especially important to clarify the performance requirements of the voltmeters and select voltmeters that meet them, such as voltmeters with measurement accuracy, that is one order of magnitude higher than that required for accurate measurement.

Principle of Voltmeters

The operating principles of digital voltmeters and analog voltmeters are described below.

1. Digital Voltmeters

Digital voltmeters consist of an input converter, an A/D converter, and a display. The input converter consists of an amplifier and voltage divider to adjust the voltage to be measured between two points to an appropriate voltage within the input voltage range of the A/D converter.

In other words, the amplifier amplifies the measured voltage when it is small and the voltage divider divides the measured voltage when it is high so that the A/D converter can convert it to a digital value with high accuracy. The digital value converted by the A/D converter is displayed as a voltage value on the display after converting the effects of the amplifier and voltage divider.

Since the input impedance of the input converter can be set relatively high, the effect on the circuit to which the voltmeters are connected is small, enabling highly accurate voltage measurement.

2. Analog Voltmeters

Analog voltmeters consist of an ammeter and a voltage divider. When the probes of the voltmeter are connected to two points on either side of the circuit element to be measured, the current is obtained by dividing the voltage between the two points by the sum of the resistance of the voltage divider and the internal resistance of the ammeter flows into the ammeter. The meter pointer will oscillate according to the current value and show the voltage value obtained by multiplying the current value by the sum of the voltage divider resistance and the internal resistance of the ammeter.

The meter pointer can be read visually only about 1% of full scale, which is much less accurate than a digital voltmeter that can measure with an error of 0.1% or less. Ammeters used in analog voltmeters are mainly of the movable coil type using permanent magnets, but the movable iron strip type using electromagnets is also used in some applications. The movable iron strip type has the advantage of being able to measure the RMS value of the alternating current without a rectifier circuit.

How to Use Voltmeters

Voltmeters must be connected in parallel to the circuit under test to measure voltage. In the case of DC voltage measurement, by placing the Hi terminal probe on the high potential side and the Lo terminal probe on the low potential side, the Hi terminal voltage concerning the Lo terminal potential is displayed. With analog DC voltmeters, connecting the low potential side to the Hi terminal and the high potential side to the Lo terminal will drive the meter in the opposite direction and may break the meter, so be very careful.

On the other hand, when measuring AC voltage, both digital and analog voltmeters convert the voltage to DC voltage via a rectifier circuit, so there is no need to be aware of the Hi and Lo terminals. Analog voltmeters also require attention when measuring high voltages. If a voltage exceeding the measurement range is applied, not only will the meter pointer swing out of alignment, but the meter itself may burn out due to the large current flowing through it, or its fuse may blow, if a fuse is part of the voltmeter.

If the voltage value of the circuit to be measured is unknown, measure at the maximum voltage range to determine the appropriate measurement range, and then switch to that measurement range for a new measurement. Digital voltmeters are designed to withstand high voltages and are equipped with an auto-range function that automatically sets the appropriate range.

What Is a Die Casting Machine?

A die casting machine is a piece of equipment that melts a metal or alloy at high speed and pours it into a mold for casting.

Die casting machines can mass-produce products of the same shape with high precision, thus reducing the workload of workers. They are also effective when using low-melting-point metals such as aluminum and zinc, since low-melting-point metals are easy to melt and pour into the die.

However, it is difficult to use die casting machines for metals with high melting points, necessitating the use of other casting methods. Another advantage of die casting machine casting is that the surface of the product is very smooth, so the polishing process can be omitted.

Omission of the polishing process leads to reductions in product manufacturing time and cost.

Uses of Die Casting Machines

Die casting machines are used in a variety of industries. Specifically, they are used in the manufacture of automotive parts, electronic devices, and construction materials. Recently, die casting machines have been developed that use environmentally friendly materials to reduce product waste and increase sustainability.

1. Automotive Parts

In automotive, aluminum is used to manufacture a wide variety of parts, from engine blocks, cylinder heads, and other components to emblems, door handles, and other small decorative items. In particular, the use of lightweight and highly rigid aluminum alloys can improve vehicle fuel efficiency and safety.

2. Electronics

In electronics, aluminum alloys are used to manufacture metal parts used in smartphones, tablet devices, and digital cameras. Examples include camera lens holders, shutter buttons, and aluminum frames for smartphones.

3. Building Materials

In building materials, die-casting machines are used to manufacture small to large and complex shaped parts such as door knobs, handles, shutter hinges, and curtain walls and facade panels that decorate the exterior of buildings.

Principle of Die Casting Machines

The principle of making a product with a die casting machine consists of creating a mold that matches the shape and pouring liquid metal into it. Die casting machines use pistons that utilize hydraulic pressure, which must be above a certain level.

Liquid metal such as aluminum alloy, called molten metal, is poured into the die connected to the die casting machine. Since the die into which molten metal is poured is subject to internal pressure, care must be taken to ensure that the die is not tightly sealed or the molten metal may leak from the gaps in the die.

For example, a die casting machine during casting will hold the mold under high pressure. When the liquid metal poured into the mold is cooled, a hardened product conforming to the shape of the mold is completed.

Types of Die Casting Machines

Die casting machines are classified into two types:

1. Hot Chamber Type

The hot chamber system is named after the injection section, which injects molten metal, and the molten metal storage furnace, which are integrated into a single unit, and the injection section is constantly heated. Since the injection part is always heated, it is used for casting materials with low melting temperatures from the viewpoint of safety and durability of parts. The major advantage is that molten metal can be injected efficiently.

2. Cold Chamber Method

The cold chamber system is named after the fact that the injection section, where molten metal is injected, and the molten metal storage channel are separated and the injection section is not heated at all times. Since the molten-metal storage furnace is independent, it is used for casting materials with high melting temperatures; molten-metal injection is required for each product, and the production time tends to be long.

Other Information on Die Casting Machines

Die Casting Machine Molds

Die casting machine molds are mainly responsible for determining the shape and changing the temperature.

1. Shape Determination
Since products are manufactured according to the die, the die determines the general and detailed shape of the product, as well as small grooves and holes. The accuracy of the mold’s shape is an important point because it directly affects the quality of the product.

The position of the gate for pouring molten metal and the flow of molten metal in the mold are determined according to the shape of the product and the number of products to be manufactured at one time. If the mold is in the way and the product cannot be taken out, a mechanism is added to move the mold at an angle or a hydraulic cylinder is pushed out to take the product out.

2. Temperature Change
Die-cast products are manufactured by cooling and solidifying molten metal. The die, which determines the quality of the product, is a very important component of the die casting machine. In addition, the creation of a die takes months and the cost of creating a die is a large part of the manufacturing process.

If a die fails or is damaged during mass production, production must be halted. It is important to note that along with a significant reduction in production capacity, there are additional costs associated with mold maintenance.

What Is a Diode Rectifier?

A diode rectifier is a semiconductor device that rectifies the alternating current of a commercial power supply in a power circuit to obtain a pulsating current.

Compared to ordinary small-signal diodes, rectifier diodes are characterized by their large size, high current capability, high withstand voltage, and robust structure. Bipolar tubes, which are vacuum tubes, are also called diodes and were once widely used as rectifiers, but since they are now limited to special applications, this paper is limited to semiconductor elements.

Uses of Diode Rectifiers

Diode rectifiers are always used in the rectifier circuits of power supplies that produce DC power from commercial power sources. In circuits that rectify high-frequency alternating current, such as switching regulators, fast recovery diodes with short reverse recovery times and Schottky barrier diodes with low losses are used, which are also considered to be a type of rectifier diode.

Principle of Diode Rectifiers

In a diode rectifier, the P-type terminal side is called the anode and the N-type terminal side is called the cathode, and near the PN junction, N-type electrons and P-type holes cancel each other out, creating a depletion layer. When a forward voltage is applied between anode and cathode, holes are injected into the P-type area and electrons into the N-type area, thus narrowing the depletion layer and allowing current to flow from P-type to N-type.

When a reverse voltage is applied, electrons are injected into the P-type area and holes into the N-type area, causing the depletion layer to expand and no current to flow. This indicates that in a diode, current flows only in the P-type to N-type direction. From the above, when an alternating voltage is applied from the anode to the cathode of a diode, current flows only in the forward direction, and no current flows in the reverse direction. This is the principle of rectification.

A rectifier diode by itself is a half-wave rectifier, and current is output for only half a cycle of alternating current. On the other hand, a bridge connection using four diodes results in full-wave rectification, which has the advantage of providing a large current and reducing ripple, so diodes connected in a bridge are commonly used.

Types of Diode Rectifiers

There are three main types of diode rectifiers:

1. Silicon Diodes

This is one of the most widely distributed PN-junction diodes. The term diode rectifier usually refers to a silicon diode. Germanium diodes were once used, but they are rarely used anymore because of their poor heat resistance and difficulty in carrying large currents.

2. First Recovery Diode

A carrier trap is created in the N-type semiconductor region of a PN junction diode by heavy metal diffusion or electron beam irradiation to trap carriers during switching. The reverse recovery time can be improved to 1/100 to 1/1,000 of that of a normal diode, but there is the disadvantage of a larger forward voltage.

Fast recovery diodes are used in switching power supplies that require high-speed operation, because diodes with short reverse recovery times are advantageous.

3. Schottky Barrier Diode

These diodes utilize the “Schottky effect” caused by the junction of a metal and a semiconductor. The Schottky effect creates a barrier (Schottky barrier) that prevents current flow unless a certain voltage is applied, and this is used to achieve rectification. Since the forward voltage becomes small, the loss due to the diode becomes small, but the drawback is that the withstand voltage is low.

Other Information on Diode Rectifiers

How to Use Diode Rectifiers

There are two procedures for converting commercial power to direct current, and there is a diode rectifier suitable for each. One is to connect a diode rectifier directly to the commercial power supply line to extract a pulse current with a peak value of about 140 V (in Japan), convert it to DC with a smoothing circuit, and then convert it to the desired voltage with a switching regulator or the like.

In this method, the power supply for the entire device is concentrated in a set of rectifying diodes, so large-current/high-voltage diodes are generally used. On the other hand, in the method of converting the voltage from the commercial power supply to near the desired voltage via a transformer, and then connecting the diode rectifier to the output of the transformer to convert the voltage to DC, the withstand voltage performance becomes lower and the current becomes higher because the voltage to be handled is lower.

Devices with low forward voltage, such as Schottky barrier diodes, are advantageous, especially since losses due to the forward voltage of the diode affect energy efficiency.

What Is a Small Signal Diode?

A small signal diode is a diode that operates with a relatively small current of a few hundred mA or less.

They are used in rectification and switching to convert alternating current to direct current, and in the generation of constant voltage. The most well-known application is demodulation.

Demodulation is the process of combining a high-frequency carrier signal with a low-frequency audio signal and using the diode’s ability to detect only the low-frequency signal to output the radio signal as an audio signal to an audio output device.

Uses of Small Signal Diodes

Small signal diodes are used in electronic products that handle small signals and perform electrical operations, especially in high-frequency applications such as electrical equipment, precision instruments, and radio receivers, as well as in switching operations.

When selecting a diode, the maximum rating and the bias that can be applied to the diode should be taken into consideration due to its small signal operation. If there is a possibility of excessive current flow, a protection circuit must be installed to prevent excessive current flow to the diode.

Principle of Small Signal Diodes

The principle of small signal diodes is based on a unique circuit operation that utilizes the rectifying effect that occurs in the forward and reverse directions of the I-V characteristics, using physical phenomena that occur at the PN junction interface of a semiconductor diode or at the junction interface between a metal and a semiconductor.

The operation of small electrical circuits is divided into their typical functions: switching operation, rectifier circuit, and constant voltage generation.

1. Switching Operation

When voltage is applied to a diode, it is serves as a switch using its ability to allow current to flow in only one direction. When a voltage is applied in the forward direction, current flows, which is called the on-state operation, and in the reverse direction, current does not flow even if a voltage is applied, which is the off-state operation.

Schottky barrier diodes and PIN diodes are capable of high-speed switching at small currents, so they are used as diodes for the function of switches with relatively high operating frequencies.

2. Rectification Circuit

Rectification is a circuit operation that converts alternating current to direct current by utilizing the diode’s property of current flow in only one direction. Normally, the current is a half-frequency current that does not pass in the negative direction, but when diodes are connected in a bridge circuit, the negative portion of the AC current is converted to positive and energized, making it possible to convert the current into a full-frequency DC current.

3. Constant Voltage Generation

This is a circuit operation in which a zener diode is often used. A zener diode is a diode that can generate a constant voltage over a certain range regardless of the reverse current. These diodes are used in circuits that generate constant voltages and are also used as protection circuits.

Other Information on Small Signal Diodes

1. Examples of Small Signal Diode Structures

Small signal diode structures can be broadly classified into planar and mesa types.

Planar Type
The planar type is the most commonly used semiconductor structure, in which an impurity diffusion layer is formed near the oxide film on the silicon semiconductor surface to create a PN junction for the diode. This structure can be widely used as a circuit block inside an IC in addition to discrete small signal diodes.

Mesa Type
The mesa type has the feature of forming the PN junction in a vertical mountain-like shape, and in particular, the area of the N-type part can be made large due to its structure, enabling a relatively large reverse withstand voltage. This structure is often used in small signal diodes for rectification.

2. Array-Type Small Signal Diodes

When small signal diodes are used in various circuits, multiple diodes may be used. Array-type small signal diodes are suitable in such cases.

Products that integrate multiple small signal diodes in a single package or, for example, a composite array of Zener diodes and Schottky barrier diodes, are also available. These products are useful when you want to use different Vf voltages for different diodes in a circuit.

What Is an Optical Sensor?

An optical sensor, also called a light-receiving element, is also a semiconductor device. It is one of the auxiliary devices that detects various light properties by converting them into electrical signals and is an accessory device that makes up a machine. The technology of optical sensing is used as a method of sensing light. And there are various types of light sensors for all kinds of situations. A wide range of sensors have been developed, from those that detect whether a light object is within a specified value and pass if it is ON and fail if it is OFF, to types that provide notification and highly sensitive sensors that can detect single photons.

Optical sensor is also used in motion sensors for automatic doors. The sensor’s response is fast, so there is no extra time lag. In addition, because they operate by detecting light, they do not require contact with people or objects, and they do not lead to contamination of the objects they detect. Therefore, the sensor can be used with peace of mind. For these reasons, an optical sensor is used in industrial and consumer applications.

Light includes visible light and invisible light, such as ultraviolet and infrared rays. Therefore, when selecting an optical sensor, it is necessary to choose a sensor that is appropriate for the wavelength.

There are two types of light sensors: those using semiconductors such as photodiodes and those using photomultiplier tubes.

Uses of Optical Sensors

In recent years, the automation of devices in our daily lives has been increasing, and the applications of optical sensors are expanding. Typical examples are remote controls for TVs and audio equipment. These remote controls move in response to infrared rays, so optical sensors for infrared rays are used. They are also used in camera autofocus and image sensors. Other light sensors are also used in washbasin faucets, which automatically switch on and off when they detect a person’s hand.

Once you step out of your house, light sensors are used everywhere in our daily lives.

In automated teller machines (ATMs), optical sensors are used for “card detection,” “bill detection,” and “internal mechanism detection.” In ticket machines, they are used for “coin detection,” “ticket detection,” and “bill detection.” A motion sensor is used to turn on the lighting when someone enters the restroom and to turn off the lighting when no one is in the restroom, contributing to energy saving.

Optical sensors are also used to test the sugar content of fruits, and demand is increasing because they can measure sugar content without damaging the fruit. Sugar content can also be measured by applying the principle that the more sugar and acid components dissolved in fruit juice, the greater the refractive index of light.

They have also been applied to astronomy. In the past, astronomical images were recorded on photographic dry plates, but since the 1990s, charge-coupled devices (CCDs) have been adopted.

Optical Sensors Technology

In recent years, optical sensor technology has made remarkable progress. In the industrial field, nondestructive testing is an inspection method that can examine the status of an object without destroying it. In this inspection method, an object is exposed to radiation or ultrasonic waves to determine the degree of damage without destroying the object. Optical sensors employ a method called near-infrared spectroscopy, which is similar to this type of inspection method. Near-infrared spectroscopy is used in near-infrared spectroscopic sensors and is a mechanism that does not affect the object being observed. Infrared rays are classified into “near-infrared rays,” “mid-infrared rays,” and “far-infrared rays,” of which near-infrared spectral sensors handle near-infrared rays.

Near-infrared spectroscopic sensors can observe a wide range of materials, from inorganic materials to organic materials. For example, they are used in conjunction with machine learning to check the deterioration of concrete in inorganic materials, and in organic materials to observe the amount of fat in the bodies of people and fish.

In this way, the technology of optical sensors is still evolving, not only in one field but also by incorporating additional technologies.

Principle of Optical Sensors

There are many detection methods for optical sensors. The two main types are the transmission type and the retro-reflection type. The transmissive type requires a light-emitting projector and a light-receiving receiver and reacts when there is an obstruction between them. In the retro-reflective type, the projector and receiver are integrated into a single unit, and the light emitted from the projector is detected when it is interrupted by a reflector bouncing back.

In principle, there are also two types of sensors, one using the internal photoelectric effect and the other using the external photoelectric effect.

Internal Photoelectric Effect

This type of sensor uses semiconductors, as typified by photodiodes, and utilizes the photovoltaic or photoconductive effect. Silicon cells cover the visible light range, while germanium cells cover the UV to IR wavelengths. CCDs often used in cameras are in the visible light range.

External Photoelectric Effect

When light is irradiated, electrons are ejected from the cathode and collected on the anode for amplification and detection. Sensors using photomultiplier tubes can detect a wide range from the vacuum ultraviolet region to 1700㎛. Sensors using phototubes can also detect from ultraviolet light to visible light.

Features of Optical Sensors Products

Optical sensor products are available in the following types, which are designed to match the detection target and have features in the optical path.

1. Transmissive Photo Sensor

The light emitted from the light-emitting element has a U-shaped structure with both elements facing each other so that light emitted from the light-emitting element hits the light-receiving element with a certain distance between them. The light emitted from the light-emitting element is measured at the output of the light-receiving element, which changes depending on the obstruction. 

2. Separate Photo Sensor

The light emitting element and the light receiving element are separated in a package, and the distance between the long sensors can be realized to allow any desired setting.

3. Reflective Photo Sensor

Light emitting and light receiving elements are aligned in the same direction or mounted at a certain angle. Light from the light-emitting element is shone on a certain detectable object, and the light reflected from it is measured by the light-receiving element.

4. Prism Photo Sensor

Light emitting and light receiving elements are aligned in the same direction and mounted on a prism between the light emitting and light receiving elements to make measurements.

5. Actuator Photo Sensor

By combining a transmissive photo sensor with an actuator (lever) that rotates, the sensor is shut off by the lever to perform mechanical discrimination.

What Is a PCB?

PCB is essential components for electrical engineering.

It is possible to fabricate electronic circuits by placing transistors, resistors, and other components on a mainly copper wiring pattern on the surface of an insulator (plastic) and soldering them together. PCB is used in almost all electronic devices (TVs, PCs, smartphones, home appliances), and the electronic circuits built into devices are operated by PCB.

Japan was the first country in the world to obtain a patent for PCB around 1936, and the development of the technology has been progressing. As a result, Japan was the world’s largest producer in terms of production value around 1990. In recent years, production of electronic devices has shifted to China and Asia, and large quantities are produced in China and Asia.

Uses of PCBs

PCBs are used as wiring boards for PCs, televisions, and electrical equipment as well as for electronic construction.

The PCBs for these particularly precise electrical devices already have the necessary circuit patterns formed on the board itself, and electronic circuits are completed simply by placing components on them. For even higher density, there are also multilayer boards with multiple layers of circuits on a single board, which are used in electronic equipment such as PCs and smartphones.

There are also many types of materials and hundreds of varieties, depending on the application. Generally, rigid materials are the main materials used, but in recent years, flexible materials (films) are increasingly being used for smartphones and other mobile applications, with many soft flexible substrates being used.

Printed Circuit Board Manufacturing Methods

PCBs are made by drilling small holes in an insulating board and plating the holes with copper or other materials. (called through holes or via holes). By soldering electronic components and wires to the small holes, a circuit can be built by allowing electricity to flow through them. In the case of a multilayer board, signals in the board are connected to other layers through holes and via holes.

PCBs can be single-sided, double-sided, or multilayered. The more layers there are, the more circuits can be built, which saves space.

Materials Used

For home appliances (refrigerators, washing machines), paper phenol substrates made of paper impregnated with phenol resin are the main materials used as substrates for PCBs. For PCs, smart phones, automobiles, measuring equipment, etc., where reliability is required, glass epoxy substrates (glass cloth impregnated with epoxy resin) are used.

Aluminum substrates with good heat dissipation are sometimes used where heat dissipation is required. Recently, demand for these substrates has been increasing due to the trend toward EVs, which require higher current.

Flexible substrates made of thin polyimide or polyester film have also emerged. While flexible substrates have low mechanical strength, they are flexible and can be bent. The materials used for these substrates are required to be flame-retardant (i.e., they do not burn easily even if set on fire). For this reason, halogen-based substances are used, and some customers require halogen-free materials for environmental reasons.

In recent years, circuit patterning methods have become more automated, and products are being developed to accommodate smaller size and higher density.

Structure of PCBs

There are several types of PCBs, each with a different structure, material, etc., depending on the purpose.

Single-sided substrate

A substrate with copper foil only on the patterned side. Only relatively simple patterns can be realized. It is the cheapest type of printed circuit board to manufacture and is the most commonly used type for self-made PCBs.

Double-sided PCBs

PCBs with copper foil on both the front and back sides. Patterns can be drawn on the front and back sides, and more complex patterns can be realized than on a single-sided board. Although it is a bit more advanced, it is also possible to make it yourself. Be careful of pattern misalignment between the front and back sides. Solid ground pattern boards also require through holes.

Multilayer Substrate

Used for complex patterns that cannot be realized with double-sided boards (computer boards, etc.) or when patterns need to be stacked due to board size restrictions (cellular phones, portable audio equipment, etc.). Multilayer substrates with up to 8 layers are used. For boards that require mass production, it is necessary to combine equipment costing hundreds of millions of yen per unit to manufacture several hundred thousand boards per month, making it an equipment industry.

Materials of PCBs

There are several types of printed circuit board materials, each with different properties. Select the one that matches your purpose.

Paper Phenol Substrate

Paper is used as the base material, and the adhesive resin is phenolic resin. Also called “Bake substrate” or “Bakelite.” It has been used for a long time. It is inexpensive and easy to process, but the substrate easily warps and has poor heat resistance and moisture absorption. It also has poor insulation resistance and high-frequency characteristics, and through-holes cannot be formed.

Paper Epoxy Substrate

This substrate uses paper as the base material and epoxy resin as the adhesive resin. It has characteristics intermediate between paper phenol substrate and glass epoxy substrate. It is made as a single-sided substrate. It has superior heat resistance, moisture absorption, and electrical characteristics compared to paper phenol substrates, but is inferior to glass epoxy substrates.

Glass Epoxy Substrate

This is a printed circuit board manufactured by glass fiber containing epoxy resin. Currently, the most widely used type, most multilayer boards are glass epoxy boards, which are used in a wide range of applications, from thin boards as thin as 0.2 mm to boards up to 2.4 mm in thickness for power equipment, motherboards, etc. They have low dimensional change and excellent durability. It also has good electrical and mechanical properties. However, workability is poor, and special tools are required. Although the cost is higher, functionality is improved.

As described above, there are various types of PCBs, and various materials are used. Design rules differ greatly depending on the type of printed circuit board, so please contact a specialized manufacturer if you have any problems.