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Power switch recommendation

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  • 3 months later...

What 3D package are you doing those in Justin?

I was messing around trying to figure out how to do voltage switching with 2 transformers, 1 using a relay to switch on (ala Amb e24), but handling voltage switching for 120/240. Does the below schematic look feasible?


power switch xfrmr.png

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Still using Kicad and its 3d libraries, haven't had time to look into Eagle again. 

Maybe I don't know how to read that schematic or maybe it's in a separate sheet but I am not seeing any relay drivers or 12V supply. The operation of the e24 seems to be a bit different as that is using a low voltage switch to turn on high voltage relays for line AC. The V&K voltage selector unit is already a line voltage switch and can handle 250VAC at (?) 5A, so however you would connect it to one transformer's primaries, just put the second one in parallel.

Edited by mypasswordis
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None of that shit is in yet, i was just messing around with doing the voltage switch and having AC relays in for the main transformer. I think I basically did just parallel the 2nd set of primaries with the first, with the relays after that. I realize that when switched to 240V both relay contacts are in series but as far as I could see, that is the only way to do it. Of course I could cheat and use something like a MeanWell for the relay/e24 thingie...

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  • 4 weeks later...

So, general features I am after are:

Momentary switch operation
Remote trigger input
Support for more than one temperature sensor (not thermal breakers)
Antiparallel bi-color LED indication
Support for AC-DC switcher and AC transformer footprints
High current relay control (mechanical and SSR, though I am done with SSRs)

Probably three PCBs - transformer, control and relay.

Other requests? Maybe IR control?

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  • 1 month later...
That looks pretty good Marc. Is your intent to support all 3 on a single board (single, dual and the LP2992)?


Exactly. I worked carefully with the do not allow traces regions on the switchers and they will work just fine and it turns out to be a useful little board.


I think I need to mirror V1 (MOV suggested for 220V operation), add an mains input label, and change the 5V output label to Vr (in case a 3.3V regulator or other fixed output regulator that works with low ESR caps, such as the LP2992, is used). A little bit more copper for the regulator would be nice as heat is dissipates through its pins. Also need to add polarity makers to the caps - I didn’t have this size in my library, oddly enough.


I will make the changes this afternoon and order 3 and make them up. I need to double check that the 20A relay I am eyeing will fit on the same dimensioned board. The other parts are all SMD, including the micro controller so they will fit in a square inch top and bottom.



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  • 2 weeks later...

Ok, here's the schematic for the control board. A few questions:

1.) I've never used a MOSFET pull-up in the manner described on the 1-Wire circuit. Does this look correct? I figured I might want a dozen or so external temperature sensors, so I wanted to beef this up

2.) In general, am I using the "right" uC pins? I tended to randomly assign them, but I know that there are specific pins suited for different things (ADC, D, UART, etc.). A pair of eyes on this would be great.

3.) I'd like to use this bootloader, https://github.com/micronucleus/micronucleus. Any reason to think this wouldn't be compatible? It looks like it might need an external crystal, I have that.

4.) Eyes on the MOSFET relay driver? I wanted to be able to drive high current things like SSRs, etc.

5.) Other features? Better name? :)


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Getting this on a two layer board the same size as the PS will be fun.

Any suggestions on a crystal that is smaller and perhaps doesn’t need external components?

Smaller opto isolator recommendation? Don’t need anything fancy will just accept DC voltage for the trigger input.

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More re-working the schematic, mostly around the USB input. The wrinkle is the 4DSystems OLED displays want 5V and I need 3.3V for USB compliance, while still supporting higher voltage relays. It should be a pretty flexible board when I am done. Now the main issue is dealing with the oh so large 0805 caps in high density trace regions. I see why Kerry used small caps (0603?) right around the uC in his photo above!

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