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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: SSR question
Date: Sat, 14 Sep 2024 02:53:38 +0200
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On 13-09-2024 19:47, john larkin wrote:
> On Thu, 12 Sep 2024 20:09:31 -0000 (UTC), piglet
> <erichpwagner@hotmail.com> wrote:
> 
>> john larkin <JL@gct.com> wrote:
>>>
>>> Given a power supply that needs 120 volts AC input, I'd like to use a
>>> small front-panel power switch at some low voltage, not run the AC
>>> line up to the front panel.
>>>
>>> Do people make SSRs that would do that, accept a low-voltage switch
>>> closure to switch AC?
>>>
>>>
>>
>> I think Piotr Wyderski posted a cool looking circuit using a small hf pulse
>> transformer as isolation and coupling. Shorting the isolated LV side loaded
>> or stopped an oscillator or something.
>>
>> The 1960s GE SCR manual showed ways to do that too but using 50/60Hz
>> transformers which are now not cost effective.
> 
> Some people sell a small potted PCB-mount brick that's an AC-line
> powered power supply. But I'd have to design a PCB and run line
> voltage into it.
> 
> Some biggish universal-input metal-box power supplies have a
> contact-closure enable input. May as well use one of those, even
> thought I only need a few watts.
> 
> The product is a high-voltage pulse generator, probably a detonator or
> something. We don't know.
> 
> 
> 
One thing to look out for, is the robustness against spurious turn-on 
(add snubber).

Also, if you draw more than just low power, look out for the zero 
crossing distortion. That might result in failing to comply with 
conducted emission tests.

I did a design on a 650W heater with several outputs, and in that one we 
had to roll our own driver, to make sure the Triacs was kept on during 
the zero crossing. One design implementation had back to back FETs.