Power supplies

How it works On power-up Q1 and Q2 are off. There is no collector current so L1 is off. If the digital control input on the left is brought high (5 V) Q1 will turn on. Current will flow through L1, Q1 and R2. As the voltage drop across R2 increases to about 0.6 V Q2 … Continue reading "Simple constant-current driver"

The LM317 adjustable voltage regulator can be used to make a simple constant-current power supply. The device is over forty years old but is still very popular with beginners due to it’s low cost, availability and thousands of practical applications. LM317 datasheet. Constant current The LM317 regulates by adjusting it’s output until it is 1.25 V … Continue reading "LM317 constant-current power supply"

In certain circumstances the supply voltage is not high enough to light the LED – particularly with blue or white types which have a higher forward voltage. For example, a 3.3 V micro-controller will not light an LED that has a forward voltage of 3.6 V at 20 mA. We can get around this by using a voltage … Continue reading "GPIO voltage booster"

Many of the LED power supplies such as those by Mean Well, etc., offer three modes of control: output constant current level can be adjusted through the control input by connecting a variable or fixed resistance to the control terminals, using a 0 ~ 10 V DC control signal, using a 10 V PWM signal … Continue reading "Dimmable mains PSU control"

The AL5809 series of devices are a very convenient two-terminal constant current driver and ideal for many LED applications. The AL5809 turns on when the voltage between IN and OUT swings from 2.5V up to 60V enabling it drive long LED chains. The floating ground, 60V Voltage rating between Input and Output pins designed to withstand the high … Continue reading "AL5809 constant current driver"