adding a "power output button" to a cheap bench power supply

Question

I've an old and cheap Atten TRP3005T Take a look at atten site

I have seen more expensive device that had a specific button that always disable the current emission every time you power off the device.

This is a security feature to avoid disastrous error when you attach a device to the power supply when the power supply is off and has been left to wrong settings (happen to me.. but without consequences... 15 volts on an Arduino when I want to use only 9 volts to test it)

Is there a way to add the same feature to my power supply ?

I think that I need to build a circuit with a dual mosfet but I'm not enough skilled to design it by myself... Also I'm not sure if this option draws power from the power supplier and can make some strange side-effects to power output like wrong value for voltage.

Answer 1

If you can figure out the internals of your power supply, adding a relay and a momentary push-button is a fairly simple task, perhaps with an added LED for feedback. (Or an illuminated momentary push button I guess.)

^{simulate this circuit – Schematic created using CircuitLab}

Once it's on it would stay on till you turn off the supply though, but you can add a second, normally closed button to disconnect.

Answer 2

If the Lab supply has a large storage Cap that floats when AC is switched off, you want an LED charge indicator which also slowly discharges the cap. Choose 40mA for 30V with a couple UB LEDs White and Red using 2 current limiting Rs=1.4k .

Or better if you actually want an active Low to ground to enable a High Side 30V Smart switch. (this one may not be reliable << 5V although it has a charge pump for Vgs.)

Answer 3

The simplest solution that I can think of, using switched AC inside PSU with Relay and Lamp mounted inside.

^{simulate this circuit – Schematic created using CircuitLab}