Skip to main content
52 votes

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

Mechanical relays won't last long if forced to switch at 5 Hz, but solid state devices (thyristors, triacs or transistors) are perfect for your task. Instead of coming up with your own thyristor/...
jms's user avatar
  • 8,651
31 votes

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

Three major issues here. The first is that you don't seem to be aware that you're effectively building a dimmer circuit when you start using electronic switching. If you Google "theatre light dimmer ...
Graham's user avatar
  • 6,170
28 votes

Can a thyristor be built from two transistors?

There are two easy kinds of thyristors made out of two BJTs. One is the SCR and the other is a PUJT. (The PUJT will use the base of \$Q_2\$ instead of the base of \$Q_1\$ as the gate -- see circuits ...
jonk's user avatar
  • 78.1k
22 votes

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

Your best bet is probably to use SSRs (solid state relays) which include drive and isolation circuitry in one package. They also include a thyristor and usually a heat spreader to interface with a ...
Spehro Pefhany's user avatar
21 votes

Can a thyristor be built from two transistors?

Yes, it's easy. You would typically want to add base-emitter resistors to one or both transistors to control the trigger and holding current. Here's a simulated SCR that triggers at about 400uA gate ...
Spehro Pefhany's user avatar
15 votes

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

You can't switch mains. First you shouldn't switch it because mains power is dangerous, and you should not be running it through a homebrew gadget (it violates the electrical code and will void ...
Harper - Reinstate Monica's user avatar
11 votes
Accepted

Why do NPNP thyristors remain on but NPN transistors don't after gate voltage is removed?

First of all: It is gate current (or base current in the case of a bipolar transistor) and not voltage that matters. An NPN transistor can be regarded as a current controlled current source. It ...
kruemi's user avatar
  • 3,099
9 votes
Accepted

What does 'not controllable' mean in power electronics?

simulate this circuit – Schematic created using CircuitLab Figure 1. (a) A diode will conduct if it is forward biased. There is no control pin on it. It is not controllable. Figure 2. The ...
Transistor's user avatar
  • 176k
8 votes
Accepted

Series thyristor circuit

You'll need equalisation for both static and dynamic behaviour. As all of us are aware, the I-V and reverse recovery characteristics of the same brand/model SCRs are similar but not equal due to ...
Rohat Kılıç's user avatar
7 votes

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

Relays are bad for that sort of thing because every opening of the circuit will arc which will burn the contacts and wear them out. OK, so you are switching A/C so sometimes you'll catch it at the ...
Anthony X's user avatar
  • 485
7 votes
Accepted

What distinguishes an ordinary thyristor from a GTO thyristor?

Interesting question! Let's start with how we typically use a Thyristor. The Cathode will usually be connected to Ground and the Anode to supply via the load: simulate this circuit – Schematic ...
Bimpelrekkie's user avatar
6 votes
Accepted

Replacement for tube-based trigger switch (Thyratron) in high-voltage supply

A thyratron (especially a large one) is an example of a pretty rugged device that is quite expensive and difficult to replace with a solid-state device. For example, these hydrogen thyratrons will ...
Spehro Pefhany's user avatar
6 votes
Accepted

Parallel RC filter on SCR gate

R2 is a "gate-cathode resistor". Visually, the schematic makes it look like R2 is about C2, but it's really about the SCR's performance. A gate-cathode resistor allows some of the SCR anode current ...
Bob Jacobsen's user avatar
  • 1,880
6 votes

How does a TRIAC work?

The two-SCR model is not very helpful in understanding how a triac works. It's correct in that there are two parallel inverse PNPN structures that carry the current, but the triggering mechanisms (...
Spehro Pefhany's user avatar
6 votes

Series thyristor circuit

I randomly have a Velonex 510 Ring Generator, which uses an SCR stack. Here's an internal view: As you can see, they have a stack of six (optionally seven in another model, it would seem) SCRs in ...
Tim Williams's user avatar
  • 35.8k
6 votes
Accepted

How to interpret critical rate of rise of on-state current in a thyristor datasheet?

Turning to ON state doesn't happen uniformly inside the thyristor. It starts somewhere and spreads gradually to the whole area of the semiconductor. Current growth rate limit is specified to prevent ...
arnold8a's user avatar
  • 141
5 votes

Replacement for tube-based trigger switch (Thyratron) in high-voltage supply

So looking at this: What the Pre-Ionized Gap (PIG) and the Thyratron (T) form is a spark-gap flyback impulse generator. Pretty much the same kind of deal that Hertz used to prove the existence of ...
Marcus Müller's user avatar
5 votes
Accepted

Replacement Triac

The proposed replacement is 25x more sensitive with regard to trigger current in the relevant quadrants. Current rating is probably okay. Voltage rating is similar (and not very generous for 220V ...
Spehro Pefhany's user avatar
5 votes
Accepted

Is this thyristor model or circuit wrong?

As far as I understand when the thyristor is triggered it should turn on and remain on unless negative voltage applied to its gate. No, it remains on after the trigger has been removed until the ...
Transistor's user avatar
  • 176k
5 votes
Accepted

Thyristor SCR gate trigger

It does not say that you should apply 30V to the gate- it says the drive circuit should produce at least 30V with the gate disconnected. A current source with 30V compliance would satisfy that, and a ...
Spehro Pefhany's user avatar
5 votes
Accepted

What is the reason of difference in distributed gate thyristor design

See first this link ... See the "spreading speed" of 30-100 um/us ... Semikron application manual Power Semiconductor, 2015, § 2.2.2.4 As long as the device engages in a "regular" ...
Antonio51's user avatar
  • 13.7k
5 votes
Accepted

Why is the SCR in this circuit switching off even though current is still above th holding current?

Here is an example of what Dave is talking about in the above comment (my choices may not exactly represent your setup). Unfortunately Circuitlab does not have a simulation SCR model so I've ...
Spehro Pefhany's user avatar
4 votes

Thyristor gate voltage at "on" state

simulate this circuit – Schematic created using CircuitLab Figure 1. (a) Bad circuit. (b) Good circuit. I think Figure 1a shows what you did. This is bad for two reasons. 9 V is too much for ...
Transistor's user avatar
  • 176k
4 votes
Accepted

Triggering a Thyristor

It looks like your voltage source is backwards for the gate drive to the SCR, the gate voltage for an SCR needs to positive, you are giving it a negative voltage. Here is a good reference for SCR's
Voltage Spike's user avatar
  • 83.1k
4 votes
Accepted

Inner Resistance of TRIAC

When in any doubt, read the datasheet! Fig. 12 gives the (typical, not guaranteed) I/V characteristics. From this you can see that the triac in the on-state for currents >= 200 mA behaves like a ...
Wouter van Ooijen's user avatar
4 votes

Thyristor latching current and holding resistance

No there is no formula, it's a characteristic of the device and some guidance can be found in the datasheet (eg. 2N5064 datasheet). As always, there can be considerable variation from unit to unit, ...
Spehro Pefhany's user avatar
4 votes

How does a TRIAC work?

So if I understood correctly, you are confused about the SCR model of TRIAC, and specifically why the right-hand side SCR has its gate from N material while the left-hand side does from P material, as ...
Rohat Kılıç's user avatar
4 votes
Accepted

Floating high-side thyristor switch is destroyed by massive gate voltage undershoots

Upon further investigation, the problem has been solved with a rather anticlimactic conclusion. The isolated power supply design itself is pretty solid, the true culprit is a basic and unforgivable ...
比尔盖子's user avatar
  • 7,138
4 votes

Thyristor blowing up in a coilgun

While this isn't a conclusive answer (and, it doesn't look like there is a conclusive answer given current information), here are some things to consider: As raised by Spehro in a comment, trigger ...
Tim Williams's user avatar
  • 35.8k

Only top scored, non community-wiki answers of a minimum length are eligible