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Reply to "Decoders, Smoke, and Couplers"

DarrellR posted:
In regards to my first question regarding the PWM-compatible "relay," I came across some Omron Solid State Relays G3MC-202PL-DC5 (w/o zero crossing) and G3MC-202P-DC5 (w zero crossing), and MOS Trigger Switch Driver Module FET PWM Regulator High Power Electronic Switch Control Board (cheap, $2.94). The latter claims a PWM bandwidth of 0 to 20kHz. I have purchased all of these for testing, but I would, of course, welcome anyone's comments on the suitability of the devices for PWM of the smoke heater. The zero-crossing capability of an "AC Relay" is discussed at this site, where the relay is controlled by the "ESU Version 4" to modulate AC power to the smoke heater. I suppose the zero crossing capability is useful for preventing output surge currents on the heater, but it would not work if the power to the smoke heater was DC, as it might be for dead-rail applications.

Again, thanks to Sinclair and Jonathan.

Hate to be the bearer of bad news, but...

The data sheets for those SSRs suggest switching times of around 1ms. This is far too slow for typical PWM use.

Consider: 20kHz PWM means a full duty cycle takes 50us. If you want, say 10% duty cycle, like for a dim light, that means the on-time of the signal is 5us. For that 5us pulse to be meaningful, the switching times need to be a small fraction of that. So the max switching times that will be feasible in that case will be less than 1us. (For comparison, the switching times of the MOSFET I use on my boards are around 10ns.)

The FET driver module is triggered by a high logic input. This is not readily compatible with the decoder output, which will float when off, and be low when on, as I describe above. If you can find a p-channel version of it, you may be in luck.

These are just the sorts of issues that led me to cook up my own board.  

Last edited by thor73
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