Another mains controller…

I’ve designed and built a few control boards for switching on mains (e.g. this and this), because it tends to be a thing that many of my projects need. Good (and good looking!) mains switches are hard to come by, especially for higher currents, so it makes sense to use a lower-voltage switch combined with a relay or an SSR for this duty. An obvious downside to the relay-based approach is that a standby voltage is needed to control the relay, but as described in a previous post there are now several types of switching AC-DC converters able to do that job very cheaply and reliably.

However, more often than not I have found that I prefer to keep the standby PSU separate and so this addition to the control-board portfolio was delberately made smaller and to fit my usual 2”x2” format to make it stackable with my softstart-board. For anything with a large transformer in it, this is a combination that is very useful.

Another addition is an external trigger input (isolated with an optocoupler) which I don’t often use to be honest, but which I could see some potential in anyway. To make this feature a bit more versatile I have opted for the “deluxe-version”, by feeding the optocupler from a constant-current source made from an LM317L. This should mean that it’s not just the usual “12V-trigger” input, but actually it would work with any voltage between app. 3-30V and draw less than 20mA from the triggering device.

“In flight” (or at least on the way) are boards for a matching standby PSU based on the Mean Well IRM power modules – when everything is here and tested I’ll publish some files and more pictures 🙂

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JLH Evo Update

All right, no more moaning about lack of build time (at least not for now 😉 )

Managed to do a little work on the mechanics of my “JLH evo” concept allowing you to get an idea of what the end result will look like (when it’s eventually finished…).

I’m still figuring out a final chassis design so I may well leave it in this state for quite a while, but at least the mechanics seem to fit together as planned and there’s enough room to run the wires. The baseplate size is app. 170 x 230 mm per mono block.

The extra PCB is a CRC-regulator stage that I will add to reduce the noise and ripple from the switching PSU (a Mean Well EPP-150-27). The advantage here is that the ripple frequency from a switching power supply is very high (typically 65-100 kHz) so the attenuation is much, much greater than at the normal 100/120 Hz ripple from a linear supply – meaning in other words that it’s possible to get away with much smaller filtering caps than a usual class A amp.

This should therefore reduce the highish app. 240mV ripple that’s specified in the data sheet for the supply that I am using down to something much, much less. Any HF-noise on the output should be well attenuated as well. Not sure what effect it really has but that’s part of the experiment 😀