How does a variable power supply work

[ke7vvt]

How does a variable power supply work? I am thinking of the kind that have the knob to vary the current as well as the voltage. It is the current part I don't understand.

I am imagining my HT radio that wants ~13.8 VDC, if I hook it up to a power supply that doesn't have the current knob it will draw as much as it wants ~0.2A receiving. What would happen if I gave it 2.0A from one of the adjustable supplies?

What is the general purpose of telling a device how much current it is going to have?

Thanks!

 

[ken white]

How does a variable power supply work? I am thinking of the kind that have the knob to vary the current as well as the voltage. It is the current part I don't understand.

I am imagining my HT radio that wants ~13.8 VDC, if I hook it up to a power supply that doesn't have the current knob it will draw as much as it wants ~0.2A receiving. What would happen if I gave it 2.0A from one of the adjustable supplies?

What is the general purpose of telling a device how much current it is going to have?

Thanks!

The current knob is a set-point, limit or threshold level. Once the load starts to draw more current than the set-point, the power supply will typically start to lower the output voltage in an effort to reduce power ratings.

 

[Wire Weasel]

They use variable voltage regulators instead of fixed voltage regulators....and the extra parts that go along with them.

 

[Captain Kilowatt]

You cannot "give" a device more current than it wants to draw. A current control simply limits the amount a device can draw whether it wants more or not. A current limiting control sets the maximum current a device can draw at the designated voltage output. When the device attempts to draw more current than the supply is set to deliver, the power supply compensates by lowering the output voltage to whatever voltage is required to keep the current level at the set level. As voltage is dropped the current drawn is also lowered.Typically the way the current limit is set is by first adjusting the voltage to the desired output and then turning the current all the way down.As scary as it sounds, the next step is to actually short out the power supply + and - leads and adjust the current control for whatever current level you want. Remove the short and connect to the device. Max current available will now be whatever you set it at when the supply was shorted.

 

[ke7vvt]

Thanks, that makes perfect sense.