52
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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/...
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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 ...
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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 ...
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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 ...
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 ...
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 ...
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 ...
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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 ...
- 180k
9
votes
SCR not latching when triggered
The datasheet specs a Holding Current of 115 mA. With your 1k resistor R23, you only have at most 45 mA
.
Another issue with the circuit is that you should add a resistor between the collector of Q10 ...
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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 ...
- 38.5k
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 ...
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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 ...
- 81.4k
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 ...
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 ...
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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 (...
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 ...
- 45.6k
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 ...
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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 ...
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 ...
- 100k
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 ...
- 180k
5
votes
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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 ...
5
votes
Accepted
What type of vintage semiconductor device is this? Is it an SCR?
It matches rectifier Case 175-03 or 253-03 used on SCR's with an obsolete P/N made in 1987 week 39 (8739). Appears to be rated for about 25A with 4 switches to serve as 2 half-bridges for 2 loads ...
- 148k
5
votes
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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" ...
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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 ...
5
votes
Accepted
Why does adding an LCD to my Arduino project break the controlling of the SCR?
The modified code improves upon the original by addressing timing issues caused by LCD updates. In the original code, the LCD update (lcd.print()) happens in every iteration of the loop(), which ...
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
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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 ...
- 48.8k
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, ...
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 ...
- 38.5k
4
votes
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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 ...
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