PCB Relay for switching on ATX power supply?

You are presumably aware that the ATX switch is only a 5v logic signal, so can be driven directly from a simple CMOS gate. Also that the signal only wants to be 'momentary on' to switch on the supply. Your existing 'momentary on switch closure', is exactly what the ATX supply needs to turn on already...

Best Wishes

*Relays* don't do that normally. I seem to recall that there are such things as bistable relays but they're rare and it's simpler just to make your own support circuitry to do the same thing.

You could google "bistable relay" and see what's out there of course.

Graham

Good point. He might not have realised that.

It just needs a normally open switch to control an ATX supply.

Graham

My experience is that the PS is only on for the duration of the switch closure, and the line in question is activated by grounding.

I have about 10 ATX supplies loose around the shop, and that's how the one I just tested worked.

Here's a relevant reference:

"you can power up an ATX power supply by shorting the green wire with any black ground wire"

It's pretty standard to test ATX supplies by this means:

"...use a bent paper clip and insert one end in the green wire connector and bend it around and put it into a black wire connector."

Actually, its easier to bend the clip right before you insert it. ;-)

I'd like to see a working plan to do that.

How do you propose to turn the PS off with the same SPST NO switch and no other circuitry?

BTW, if you have a steady source of power its no problem to cobble up a latching relay from a standard DPDT relay. The usual implementation uses a second pushbotton for power off.

I'm sure the desired function can be obtained with one 4xxx or LSxxx chip that RS has in stock... ;-)

Roger,

An ATX PS requires that the signal remain on, a momentary signal will not turn on the PS unless you continue to hold the button down. I do not want to use a on/off type switch because they require more space and a longer button travel to operate. I already use a tactile switch control with my other cases that have motherboards so I want this HDD case (with no MB) to have the same type of switch action.

I want to simulate what the MB is doing. The MB looks for a momentary signal and locks the signal 'ON' to the PS until the button is pressed again, then it releases the signal and the PS turns off.

I don't know what you mean by a CMOS gate?

Graham,

I'll take a look at the bistable relay. I would rather use readily available parts. Perhaps it can be done using two relays? Or maybe some other type of circuit that uses a IC chip? I am open to anything I just don't know what kind of chip to look for. Digi-key probably sells it, but they provide no information to design it. The fact that the same momentary signal must turn off and then turn on the PS is making it more complicated than I first thought.

Thanks, Glenn

A C Graham,

I think you're looking for something like this, except you don't want the timeout feature:

If you ground pin 10; and leave out the capacitor, the diode, and the resistor, the time-out feature should be gone.

You power this circuit off the ATX lead that has +5 volts whenever its plugged in, per the other web page I referenced elsewhere in this thread.

Because the control lead needs to go low rather than high, connect the ATX control wire to pin 12 not pin 13.

Anybody feel free to comment.

Probably the same way I do with my PC - hold the button down until it turns itself off (2-5 sec.).

Cheers! Rich

That's a motherboard function, not a power supply function. That button is attached to the MB, not directly to the PS. Most motherboards let you program at least two different functions for this action.

Hint. What do you think a motherboard has in it. It doesn't have a relay... CMOS, is a 'name' for a generic type of semiconductor fabrication process used now for most logic components. For simple logic, the commonest family, are descendents of the old '4000' series, which provides a whole range of simple logic 'gates' in standard packages for a few pence each. What you need is effectively an /2 counter, which can be built out of any one of about twenty different members of this family (includin a couple of versions that actually contain this operation 'pre-built'. The output of the counter feeds the PSU active input. The counter itself is powered of the 5vSB line, and it's clock input connects to +5v via a resistor, and to

0v via your switch. Press the switch, and the counter 'counts', changing state on the output, and turning the PSU on. Press the switch again, and it counts again, turning the PSU off. I'd probably add a capacitor to the signal to 'debounce' the switch. Total cost a few pence/cents, power consumption, uW, and parts count perhaps one capacitor, one IC, and a couple of resistors.

Best Wishes

Any toggle switch will turn on the first time you push it (up) then turn off the next time you push it (down). If you're intent on pushing (in), they make mechanically toggling push switches. If you want to do it the hard way, they make latching relays. OR if you want the harder way, you can build some logic to do it.

mike

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A bounceless pushbutton and a flip flop to turn the supply on or off.

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Michael A. Terrell
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Arny and Roger,

That looks like what I will need. I did some searching and found this list of flip-flop chips. Is there one that has the basic functions I need?

Could this basic 5-pin single gate chip work?

Here is the data sheet for the 4013 used in the circuit Arny posted:

I'd like to keep the design as simple as possible to minimize assembly time on the PCB. I need to study these sheets and pick up a few chips to play with.

Working with IC chips is new to me. I have a lot of experience with industrial controls. I spent ten years designing theme park attractions for companies like Universal Studios. Some of the control boxes were the size of two refrigerators. With 100?s of sensors, digital and analog input/outputs. All the logic was done with PLC?s, which I also programmed, everything from simple stand-alone PLC?s using Basic or C, to complex modular controllers that were programmed with Allen-Bradley ladder logic. It would be easy for me to design the function with a PLC, but that is way beyond the scope of what I need.

Thanks, Glenn

Note that

provided a circuit based on a 74HCT74 chip.

In a non-critical application just about any chip that was of type that followed the pattern:

74 74 would probably work.

That means

74H74 74L74 74C74 74LS74 74VC1G74 74ABT74 74AHC74 74AHCT74 ...

would probably work.

In that neighborhood, I'd stick with a 74AHCG74.

Yup, and maybe a piece of proto-board. A meter or other logic state indicator.

You're working at a more basic level than you are used to! ;-)

Old-timers like me started out making flip-flops out of tubes and transistors. Now that is basic!

Then came hybrid circuitry with flip-flops the size of sugar flat cubes.

Then came 74xx ICs.

I am mind blown at the many permutations of the basic 7474 that the Phillips page shows. At the gross simple level we are working they are all probably the same.

Exactly.

I have some unwelcome news for you (and the follow up posters)

1. any reasonable simulation of a momentary switch will start the PS.
2. the ATX class power supplies will turn them selves off if they do not receive a power good signal back from the board electronics.
3. many of them have minimum load requirements for +5 main, +3.3 main and +12 main More info here:
   formatting link

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JosephKK