# Tekpower TP-3003D Switch Between Constant Current and Constant Voltage

I understand that the Tekpower TP-3003D power supply has two modes: constant current and constant voltage. There is no switch or button or anything obvious to select one mode over the other. How is this done?

It appears to be stuck in constant current mode. With no load on the supply, I set the voltage to 12 volts. Once a load is put on, the voltage drops to around 9 volts and the current is around .47 amps. Adjusting the voltage while there is a load on the supply does nothing; the voltage remains unchanged.

• Adjust the current... it will voltage limit at 12v if used as above. Feb 23, 2017 at 7:19

A lab power supply like the Tekpower TP-3003D usually behaves like this:

If the load is lower than the set maximum current, provide a constant voltage. If the load is higher than the set maximum current, reduce the voltage so that the set maximum current is flowing.

There are some others which will switch off the voltage completely if the load is higher than the maximum current, but modern ones have the constant current mode.

So in your situation, the load at 12 V is higher than the set maximum current (0.47 A), so the voltage is reduced to a point where just this current can flow. In your case that is around 9 V.

In order to get the voltage up, increase the current limit, not the voltage. As you allow more current, the internal regulator will increase the voltage to get that current flowing. But it will not exceed the set voltage once it reaches that level.

Usually you can see the set maximum current if you turn off the output, adjusting voltage and current while the output is active should be performed carefully. Especially don't change the voltage when in constant current operation, you won't see what voltage you set, if you turn up the maximum current, you might have set the voltage too high and damage your device.

Also make sure that your device is connected the right way, if it isn't supposed to take so much current, you can easily have a short circuit somewhere or hooked it up with reverse polarity. The current limit of my bench supply saved quite a few electronics from premature death...

# specs

Output: 0-30 volts DC adjustable with both coarse and fine controls for precise settability. 0-3 amps with excellent current settability and meter resolution.

If it shows meter current >0 with no load, there is a fault. Try a load cap. V ought to be adjustable if current limit is increased to expected load.

Check internal caps for replacements.

http://tekpower.us/tp3003d.html