How do I convert a Normally Open switch to normally closed?

Tonyr1084

Joined Sep 24, 2015
7,852
Do you have an old computer mouse? There are microswitches inside those that you can use. Something like one of these will do. Just wire the C and the NC to your power/ground circuit and when you want to do a reset just push the button on the microswitch.
 

Thread Starter

ssr215

Joined May 15, 2021
12
Surely a transistor and 2 resistors will do the same thing? If I understand the requirement, PS_ON needs to be kept grounded except when a reset is necessary. ssr215 do you have any transistors? A BD139 or similar? Within reason, anything will do.
I have transistors, but only BJTs.
 

Ya’akov

Joined Jan 27, 2019
9,069
None of the active solutions are going to help you unless you power them from some other source. At that point, buy a new switch!
 
Last edited:

Ya’akov

Joined Jan 27, 2019
9,069
Give us some of the types that you have - BJTs are fine. As I recall, ATX PSUs have a permanent +5v available to enable the Mobo to power up (am I wrong?) that could be used?
The reason he needs the switch is to reset the supply if it shuts down. It might keep the 5V going but it seems unlikely.
 

old_beggar

Joined Jan 29, 2021
39
I want to make a "Reset" button for my repurposed ATX PSU that cuts the jump between PS_ON and GND when pressed (to reset protection mechanisms). How do I do so?
Just to be clear, you want the ATX psu to be on all the time, but if it DOES trip out for some reason, you want to be able to press a normally open push button (NOPB) switch to turn it back on - is that correct?
 

Tonyr1084

Joined Sep 24, 2015
7,852
Just to be clear, you want the ATX psu to be on all the time, but if it DOES trip out for some reason, you want to be able to press a normally open push button (NOPB) switch to turn it back on - is that correct?
Understood. Actually, I knew that was what you wanted from the very start.

As for the switch, you have it backwards. You want a "Normally Closed" switch. That way it just looks like a connection to the PS. When you push the button it breaks the circuit and shuts the PS down. When you release it - it starts back up.

I have a similar setup. Only, mine has a switch. I use that switch to turn the PS on and off. IF I overload the PS I just have to toggle the switch. Little more bother than just a pushbutton, but I rarely OL the PS.
 
Top