What Is a Constant Current Driver?
A constant current driver is an electronic circuit designed to output a stable current, unaffected by changes in supply voltage, temperature, or load. It achieves this by controlling the collector current of a transistor or the drain current of a MOSFET through the base current and gate voltage.
Various circuit methods are employed, including those using Zener diodes or operational amplifiers, and some utilize switching methods like PWM (Pulse Width Modulation) control.
Applications of Constant Current Drivers
Constant current drivers are primarily used in LED driver circuits, where they are often referred to as LED drivers. Since LED brightness is determined by the current, these drivers help maintain consistent brightness by compensating for power supply voltage fluctuations and temperature changes. This control not only stabilizes LED characteristics but also enhances efficiency and longevity.
Another common application is in motor drive circuits, where they provide a constant current for consistent torque output.
Principles of Constant Current Drivers
One circuit approach involves a Zener diode connected to a transistor’s base, an emitter resistor, and a load connected to the collector. The Zener diode, which is also connected to the power supply via another resistor, ensures a constant voltage at the transistor’s base regardless of supply voltage changes. This setup results in a self-regulating mechanism where any fluctuation in collector current alters the emitter resistor’s voltage drop, thereby adjusting the base current to stabilize the collector current to the load.
In operational amplifier methods, the collector current stabilization is achieved by connecting a Zener diode to the non-inverting input, a transistor’s emitter to the inverting input, and its base to the output.
For the switching method, PWM control is used to maintain an average constant collector current by toggling the transistor on and off.