Thyristor based power supply for Gailcone

[yusuf]

Anyone tried Thyristor (SCR) based power supply for Gailcone.

I guess thyristor will enable making compact regulated PSU using less components but appears to be not a popular choice.

Please provide inputs.

Yusuf

[Electrone]

Hi Yusuf, it reminds me of something like Bob Carver may have tried probably a long time ago. It seems like a rather interesting idea. You would want isolation still and need a power transformer, albeit a smaller one than otherwise required since you would need to limit the conduction angle to a certain maximum number degrees at the end of each half of the AC cycle. But your hum would still be at 50 or 60 Hz, making a switchmode power supply operating at ultrasonic frequencies, the present standard for audio, more desirable, I'd say. Yet, the transformer may be able to ring at a higher frequency if it is able to resonate with a suitable capacitance. Something this way would work better with a triac instead of an SCR, I think.

If you used an SCR, you would need to either use a regular sized transformer after which one SCR were used in half wave rectification, maybe along with a second for full wave, or maybe it could excite some tank circuit on the primary side comprising a smaller transformer and a suitable capacitance. You'd then have to rectify the ringing waveform on the secondary side of the transformer.

In both cases, the fundamental switching frequency at the mains line frequency might still be audible as switching spikes. You would need to filter them extra. One reason why thyristors are not as popular these days may be that they are limited in switching ability. Their turn-on and turn-off characteristics are restricted to a rather narrow range. I have done some experimentation with SCR rectification after a regular transformer over ten years ago, but I have not tried anything I speculated about above other than that rather simpler way to use SCRs as rectifiers after the standard line-operated power transformer.

There may be someone who has a circuit for using a thyristors in one of those ways or another which I missed mentioning. I think it could be an interesting project, though I am not sure if is as practical as more standard switching methods using higher fundamental frequencies.

[yusuf]

Thanks Electrone for your detailed reply.

Morever, I was looking from perspective of removing bulky transformer. Any inputs of how will it compare against linear power supply we typically see as diy choice.

[Electrone]

You're welcome Yusuf.

I think it is possible to use a transformer that is about 75% smaller. But I am just guessing with that regard. I am not really sure how easy it would be to do. I recall that the triggering of the SCRs I used in my old project was rather jittery. I think another drawback is that the peak currents drawn from the power line would greater, too. You might like to do some experimentation to get an idea of its feasibility.

[yusuf]

How about using thyristor instead of regulator and use feedback loop to trigger thyristor to get regulated output without any linear regulators (like LM338 or LT1083). I think it would be better to control waveforms at transformer secondary instead of primary to avoid transfer heating. Its been long I worked on thysristor. Any low volatge thyristor option avaiable?

Thanks

[dnsey]

Thyristor regulated supplies were used in TV set sfor a number of years, but were criticised as one of the main culprits for introducing noise to mains supply lines.
For this reason, I'm not sure that they would be a good choice for hi-fi use.

[yusuf]

dnsey, can you help me any reference design of Thyristor regulated supplies.

Thanks
Yusuf

[megajocke]

Those TV sets used a thyristor as the rectifier and regulator I think, so they would draw half-wave rectified current from the mains, which isn't very good...

[Electrone]

Hi,
I took an old battery charger I had made with negative output resistance and made an educated guess at how to convert it to a more simple regulated power supply. I tried to simulate it, but I don't know what is wrong with the SCR model. There are six 1N4148 diodes.

One disadvantage of this method is that the switching noise will have a low fundamental frequency which will need extra filtering. But it still has some interesting attractive features.

[theChris]

SCRs are not ideal for capacitive loads. you must ensure that the device can withstand the repeated inrush currents as the current can be even harsher then diode bridges.

alternatively, you can place some inductance in the circuit in order to prevent current from building up to high levels while the devie is switching.