I want to make a variable power supply using a thyristor full wave rectifier bridge into a capacitor filter into some sort of regulator but I'm not totally sure how to go about it, in large part due to the fact I'm new to thyristors and I can't get LTspice to simulate a thyristor model properly.
Can someone give me an example of such a supply? At least the variable rectifier bridge >capacitor part. I would greatly appreciate it.
I intend for the power supply to run at a bit over 2 amps DC with 6 amp AC peaks with an output between 250v and 25v.
Thanks in advance.

 

You may realize that your circuit needs transformer isolation for the safety of the circuit and you.

Your topology should be similar to a buck converter. Insert a large inductor (value depends on how much current it will handle and how much smoothing you need) between the output of the bridge and the filter capacitor. A freewheeling diode from the output of the bridge to common would catch any back EMF from the inductor as the thyristor(s) turn off. The inductor is needed otherwise the circuit's range of adjustment would be impaired be cause a bridge directly into a capacitor is a peak detector.

Surprisingly I could not locate a schematic of this circuit using SCRs or Thriacs on the web. Maybe this is not a popular technique. I used the technique twice about 30 years ago, but high powered off-line switchers were more expensive and delicate than they are today. Be prepared to use a lot or iron and copper in the transformer and choke. If you go to a higher frequency you can use a MOSFET and follow an existing off-line switcher design.


Just substitute your triac or SCR circuit along with the rectification in place of TR1.

 

I don't think that will suit my needs, I need it to be small and cheap and I need the output of the power supply to have an output impedance of <1 miliohm 10hz-20khz.
I need a simple resistor value to determine the output voltage of the regulator

The inductor is needed otherwise the circuit's range of adjustment would be impaired be cause a bridge directly into a capacitor is a peak detector.

Seems to work in LTspice

Phase angle control is allowing me to adjust the voltage via capacitor. Unfortunately the thyristor model I'm using will not seem to function when I try to use it for negative current flow which is something I need for a full wave bridge rectifier. I don't know if I'm doing something wrong or if the model won't work but I ran out of ideas.

Just substitute your triac or SCR circuit along with the rectification in place of TR1.

The biggest problem I'm having at the moment is that I don't know how to make the SCR circuit.

 

How much adjustment range do you get past 90°?

 

Try using a Triac instead, they conduct on both cycles, a Thyristor only conducts on the positive cycle.

 

There's a million and 1 examples like this on the internet though

Unfortunately none of them tell me what circuit to connect to the gates but none of them use triacs.
I should be able to alternate between activating Q1/Q4 and Q3/Q2 on each half cycle but unlike a normal diode it will not pass negative voltage in my simulations.

How much adjustment range do you get past 90°?

I seem to be getting the full range.

 

Any advice?

 

Any advice?

I think you either need a transformer with another winding so you can sync up with the line. Or a zero cross detector and something like a micro so you can step (time wise) across a cycle.

 

Yep, You need line synchronization plus some form of gate triggering delay and a feedback loop that integrates the output voltage into the gate triggering deadly cycle.

Synchronization can be taken from the AC side of the bridge easily enough and as for your SCR bridge you only really need two of the four devices to be SCRs (Q3 and Q4) and the other two (Q1 and Q2) can be normal diodes.

This circuit is pretty close to what I think you are looking for except that the positive lead off the center tap would be replaced with the appropriate two diodes and a few other components may not be needed or would need their values or equivalent components parts switch with whatever would fit you application parameters.



I believe the two LF442 Op-Amps can be replaced with most any other decent dual Op- Amp IC.

 

I want to make a variable power supply using a thyristor full wave rectifier bridge into a capacitor filter into some sort of regulator but I'm not totally sure how to go about it, in large part due to the fact I'm new to thyristors and I can't get LTspice to simulate a thyristor model properly.
Can someone give me an example of such a supply? At least the variable rectifier bridge >capacitor part. I would greatly appreciate it.
I intend for the power supply to run at a bit over 2 amps DC with 6 amp AC peaks with an output between 250v and 25v.
Thanks in advance.

Around the late 80s; quite a few UK tv sets used a crude form of SCR regulator - there are various archives of old service manuals that should provide some instruction. None of these PSUs were isolating - if you want to pursue this line on this forum; you must specify a mains isolating transformer. There's no reason why you couldn't scale down one of these circuits to regulate the output from a step down transformer - but stay under 48V if you can.