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Jeremys LED Lighting Page.pdf


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Resistive Current Regulators
A one amp constant current source can be constructed for less than a euro that only requires 0.6
volts overhead, and occupies less space than a decent eraser. It contains just 4 components and can
be made dimmable by the addition of 3 more. The circuit is as follows for the strait 1A version:

LED3 Z-LED P4
LED2 Z-LED P4
R2 100k
LED1 Z-LED P4
T1 IRFU8729 or similar

Battery, 11.7 to 14.5 volt
T2 BC546B

R1 600m

R1 (0.6Ω) sets the current when matched to the 0.6 volt drop across the base of the BC546 (my
standard general purpose npn bipolar – cost 4p). R2 turns on the MOSFET (T1) until the current
produces 0.6 volts on the 0.6Ω resistor and T2 starts to turn on and stop T1 turning on any more.
Different currents can be achieved by changing R1, eg 1.2Ω gives ½ A output.
The dimmable version is as Follows:

LED3 Z-LED P4
LED2 Z-LED P4
R3 100k

R2 100k

LED1 Z-LED P4
T1 IRFU8729 or similar

Battery, 11.7 to 14.5 volt
Pot1: 10k

T3 BC546B

T2 BC546B

R1 600m

In this version, R3 and T3 create a reference voltage 0.6V above the current sense voltage and Pot1
sweeps from that reference - turning current-limiting T2 on with no current flowing - to the current
sense voltage, meaning that the full 1A must flow before current limiting activates.