This might be like a stupid question? But how come, in DC power supply, such as this one, you can set 5 mA, and 25V?

Shouldn't it be either just current or voltage? And then you only connect one wire to the circuit.

Say you connect this power supply to proto-board, and you simply have one resistor of 1k -> GND.

Does it mean there's gonna be 5 mA flowing in this simple circuit? or by ohm's law: \$ \frac{25V}{1K} = 25 mA \$


Am I missing something? But doesn't voltage in itself has the idea of current? Like if you have 25 Voltage you can't have no current through a resistor?

Yet you can set 25V and 0mA on the DC power supply linked above.

  1. And also another related "stupid" question, in solar panel

When the cells are exposed to sunlight, photons from the sun interact with electrons in the upper silicon layer, basically knocking them loose from their associated atoms. The loose electrons are attracted to atoms in the lower layer of silicon and travel through the wire to get there. This movement of electrons from one side of the cell to the other through the wire is electrical current. (c)

So the electrons never leave the solar panel, hence, no current can flow out from the solar panel! So solar panel only outputs voltage? But if you have a wire from the solar panel, and that wire is connected to some circuit, can't that circuit draw current from solar panel? I mean, if output of solar panel is some voltage, then by having a simple resistor the circuit can make the electrons flow towards the circuit and away from solar panel, no? Explain!

  • \$\begingroup\$ "And also another related... question, in solar panel" - Solar cells work on a different principle to a variable power supply, so this question is not related. Please remove it from here and put it in a new question. \$\endgroup\$ Commented Feb 17, 2018 at 7:38

1 Answer 1


On a bench power supply, such as the one in your link, the voltage and current settings are maximums.

Normally, you would want a constant voltage supply, so you would set the desired voltage, and set the current limit to more than you expect your circuit to draw. If the circuit draws more than the set limit, the supply will reduce its output voltage to keep the current below the set limit.

In your simple circuit with a 1K resistor, with the supply set to 25 volts and the current limit set to 5 mA, the supply would reduce its output voltage to 5 volts, to limit the current to 5 mA.


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