Thyristor or SCR on the output of a power supply why?

[Simmon]

What does using a Thyristor or SCR in parallel with the filter caps on the output of a power supply do?

They use a Thysistor or SCR instead of a zener diode to do the voltage regulation? but why? what is the advantage?

It's a 2N2325 Thysistor

 

[(*steve*)]

google "crowbar protection"

 

[Simmon]

A crowbar circuit is distinct from a clamp in that, once triggered, it pulls the voltage below the trigger level, usually close to ground. A clamp prevents the voltage from exceeding a preset level

Is there any other theory about a crowbar circuit? how is works and operates?

So when there is an overvoltage before the Thysistor , the Thysistor gate will be triggered and Short out the power supplies output close to zero volts

Is this how is work?

 

[(*steve*)]

Well, you haven't shown us a circuit, but I assume that's what you meant, and yep that's what it does

Tthe over voltage doesn't necessarily have to be "before" the SCR, and it may be other than an overvoltage, but in most cases a crowbar circuit shorts out the probably malfunctioning power supply to protect the electronics. Hopefully the fuse fails PDQ.

 

[Simmon]

How does CR17 thyrsitor work with the RC network? R29 and C25 is a RC delay for the thyristor?

 

[(*steve*)]

I see no thyrsitor [sic].

 

[Simmon]

sorry here is the real schematic

 

[(*steve*)]

How does CR17 thyrsitor work with the RC network? R29 and C25 is a RC delay for the thyristor?

No, that resistor simply limits the gate current.

The dynamic resistance of the zener and the other resistor in parallel with the capacitor determine the time constant.

Can you think why you might need a time constant?

 

[Simmon]

Can you think why you might need a time constant?

No I can't, why is there one?

Why do you need to limit the gate current?

The Gate has a threshold voltage or threshold current? once you exceed above the threshold it triggers the gate ?

 

[(*steve*)]

Can you think why you might need a time constant?

No I can't, why is there one?

Then you need to think about the purpose of the circuit, and why you wouldn't want it acting the instant the voltage rose above the limit?

Why do you need to limit the gate current?

What might happen if the current was not limited?

The Gate has a threshold voltage or threshold current?

Yes

once you exceed above the threshold it triggers the gate ?

Yes

Why don't you go back to your Danny Davis account?

 

[Simmon]

why you wouldn't want it acting the instant the voltage rose above the limit?

Do most crowbar protection circuit has an RC network or RC time constant?

The dynamic resistance of the zener

What do you mean by the dynamics resistance of the zener?

Do you measure the resistance of the zener diode?

 

[(*steve*)]

Consider the questions I asked, do not quote them and pose different questions.

You need to learn to think for yourself.