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Hi folks, I'm working on a power supply design for a project I'm going to build:

Currently I have a couple of things I'm not sure about.

1) I'm trying to use the mosfet in the tube power amp supply as an on/off switch for the amp. It's gate will be attached to a pin the Raspberry PI which will either be high (3.3V) or low (0V). When I simulate, though, the amp is on regardless of the voltage on the gate. Is my design flawed, or is there some issue in what/how I'm trying to simulate?

2) I'm using a linear voltage regulator on the Raspberry PI supply, with a circuit pretty much straight out of the datasheet. Isn't really working in the sim. Again, is the design wrong, or something else with the simulation?

Thanks! Chris

I figured out 1. I failed to keep straight the virtual ground of the load and the actual ground node that returns to the power transformer.

The regulator has a 2.5V dropout voltage and you also have a roughly 1.4V drop from 5Vrms*sqrt(2) out of the transformer due to the bridge rectiifer drop.

I think the lin reg is not regulating because the DC input to it is too low.

Reducing the turns ratio of the 117V/5V transformer to 117/10 will work.

However, you'll also find that:

(i) the 0.1 Ohm R_O of the model drops about 0.2V

and

(ii) you may see spikes dropping down well below 4.8V. These are almost certainly solver artefacts and can be avoided by reducing the Time Step. Reducing the Stop Time by the same ratio will obviously maintain the overall simulation time.

I've come back to play with it after some time away and I can't get a transient simulation to run on anything, period. I get no data. Is something hosed in the simulation engine?

You've added the two resistors, Htr1 and Htr2 with 6V3AC+ and 6V3AC- connections which are floating.

CL's error messaging is poor to non-existant but that's what is breaking the simulation.

Remove or add the 6V3AC+ and 6V3AC- labels to the 6.3V transformer secondary and it'll run.

BTW: rather than increasing the 117/5 transformer to 117/10, you could try reducing the V_DO (dropout voltage) parameter on the linear reg to simulate a low dropout (LDO) type and/or increase C6 to reduce the ripple and so raise the trough voltage.

Yep, that was it! Thanks for your help. I'm trying to keep the sim parameters close to real life. I think the upshot is what I have now just isn't going to work. The linear regulators I looked at all want an input voltage of 7.5-8V. And I looked up the specs on the actual transformer and R_sec is worse even than I'm simulating.

If my goal is to try to run everything off of the one Hammond transformer, I can look into a DC-DC converter for the 5V supply. Or I can just add another transformer for the Raspberry PI supply, which is probably the easiest/sanest thing to do. I was just trying to get clever and run it all off the one tube amp power transformer.