Resistance Between VCC and GND – Why Does It Drop to 3k Ohms?

currentpcbpowerpower supplyvoltage

I am kind of lost because of this problem.

When my board is connected to my power supply and up and running the resistance between VCC and GND is at about 18M-Ohms.

As soon as I power the board off, and it's no longer running, the resistance between VCC and GND drops slowly to about 3k-Ohms, then stays there.

What could be causing this?

Best Answer

What could be causing this?

When the board is off this is a little unusual because most often the leakage current through transistors or loads when the power is off is in the 1-100kΩ range for most of the boards I have with voltage regulators on them. If you had something with a high side switch or a relay this could explain why the numbers are so high.

When the board is on, it really matters how your meter is measuring current, and often doesn't make sense. If you really want to find the equivalent load, measure both voltage and current going into the board with a nice digital power supply or a power supply and a multimeter to measure current. Then use this equation.

\$ R_{eq}=V/I\$