What Is a Constant-Current Power Supply?
A constant-current power supply is a circuit that controls and delivers a steady output current. It is sometimes referred to as a constant-current source or a constant-current stabilized power supply. While DC constant-current power supplies are more common, AC versions are also available.
Uses of Constant Current Supplies
1. LEDs:
Used for powering LEDs, as their brightness is determined by the current. A stable current supply prevents brightness fluctuations and flickering.
2. Rechargeable Battery Charging:
Essential for charging rechargeable batteries, like lithium-ion batteries in smartphones, where a constant current is needed regardless of voltage variations.
3. Power Supplies for Sensor Signals:
Employed in powering sensor signals, converting resistivity changes into voltage changes for CPU interpretation. Examples include piezoelectric elements and resistance thermometers.
Principle of Constant Current Supply Devices
According to Kirchhoff’s law, in a circuit with a power supply of electromotive force E and internal resistance r connected to a variable resistor R, the current value I is given by I = E / (R+r). A constant-current supply achieves a stable current (I ≈ E / r) by having an internal resistance r significantly larger than R.
Additionally, voltage and current sources are equivalently convertible. An ideal voltage source with electromotive force E and internal resistance r in series can be equivalent to a current source with the same internal resistance r in parallel.
Types of Constant Current Supplies
Stabilized DC Power Supply:
Includes regulated DC power supplies with the ability to switch between constant voltage and constant current modes. Control methods vary between series regulators and switching power supplies, the latter being more efficient but generating more noise.
Others:
There are also output-isolated constant-current supplies, AC constant-current units, and AC-regulated power supplies, each suited for specific applications.