What Is a Bullet-Type LED Diode?
A bullet-type LED diode is a type of light-emitting diode (LED: Light-emitting diode) device package that is cylindrical with a hemispherical top. It is named “bullet-type” because of its resemblance to a bullet.
It is also called “through-hole mounting type” or “lead frame type” because the LED leads are passed through the component insertion holes on the printed circuit board and mounted by soldering.
The bullet-type LED diode is the oldest type of LED element package. Currently, surface-mount LEDs are the mainstream, and the number of bullet-type LEDs in the market is decreasing year by year.
Uses of LED Diodes
An LED diode has the characteristic of emitting light far in the forward direction and almost none in the side direction. Therefore, taking advantage of the feature of emitting light in one direction, they are used in various places, such as indicators, signs, signals, billboards, and information displays.
The bullet-type LED Diode was often used for general lighting in the past. However, when the surface-mount type LED appeared, the surface-mount type replaced the bullet-type LED as the mainstream for general lighting because it is brighter and has better heat dissipation performance than the bullet-type LED.
Principle of the Bullet-Type LED Diode
A bullet-type LED diode consists of a lead frame with a 0.3mm LED element of each size fixed to it, the anode (positive) terminal, and the LED element connected by bonding wire, and then sealed with a bullet-shaped encapsulating resin. The cathode (negative) terminal comes directly from the lead frame.
The bullet-shaped encapsulating resin not only protects the LED diode but also allows adjustment of the emission color by mixing phosphors in the resin and also serves as a lens. The size of a bullet-type LED Diode is indicated by the diameter of the lens portion, which is generally 3mm or 5mm.
An LED diode is a two-terminal device consisting of an anode terminal and a cathode terminal. The anode terminal is slightly longer than the cathode terminal to help identify the terminals. The anode side is connected to the positive side of the power supply and the cathode side to the negative side. The LED will not light up when connected in reverse.
LEDs are characterized by their low heat generation compared to light emitters, such as light bulbs. Although energy that is not converted into light is still released as heat. Since the LED diode only propagates the heat released by the LED element via a thin lead frame, it has poor heat dissipation and cannot conduct a large current.