I heard that DC power supplies have a pulldown circuit at their output. When the output is disconnected (turn-off), the output port is internally pull-down to ground. And it’s not a simple short to ground nor connecting to ground through a resistor, but an active pulldown with a constant current.
To verify this, I ganged two DC power supplies together, set output voltage to 10V for them. I turned on one power supply, I can see 20mA current; then I turn on the other one, the current are 0s for both. After that, I turned off the first one, and the other power supply shows 20mA current. At last I increased the output voltage to 20V, the current is still 20mA.
Seems there is an active pulldown circuit.
Does active pulldown circuit exist on all kinds of power supplies, including SMU (Source Measurement Unit) and ATE VI (Automatic Test Equipment Voltage and Current Source)?
What's the purpose of the pulldown function?
Is there any example of active pulldown circuit diagram?
Thanks.