Electronics > Beginners

constant current constant voltage power supply circuit

**franksterb92**:

im messing around with a circuit based on the HP E3631A Power supply circuit and had a question about the current limit part i understand essentially its taking the voltage drop across R66 but when i build the circuit it doesn't seem to work the voltage part works but not the current could anyone point me to maybe a formula to calculate the current out from the voltage drop and more info on the topology of this current limit circuit or maybe explain more about how it works thanks

**TimFox**:

As posted, I can't read what is on the far left and the right of that resistor.

The current through R66 can be calculated directly from Ohm's law and the (relatively small) voltage measured across it: I = V/R.

In use, the feedback voltage from R66 only controls the output voltage when the current through your external load exceeds the current setpoint; otherwise, the voltage setpoint controls the output voltage.

**franksterb92**:

here is what i built up

**TimFox**:

No filter capacitor after the rectifier bridge?

Where is your current sense resistor, equivalent to R66?

**franksterb92**:

No I didn't put the caps on cause of safety as I have this hooked to a mains transformer but it's the low side 0.2ohm one R1 it is

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