|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
26th Dec 2018, 6:50 pm | #1 |
Hexode
Join Date: Aug 2009
Location: Liverpool, Merseyside, UK.
Posts: 254
|
Choosing a Thyristor
I wonder does anyone know which thyristor type would be a suitable replacement for a CRS1/40 400 p.i.v. 1A thyristor. It requires a 3V trigger and about 50mA holding current. This appears to be an obsolete type and the only ones which I have found are at silly prices.
Thanks.
__________________
Geoff. (BVWS Member) |
26th Dec 2018, 9:54 pm | #2 |
Hexode
Join Date: Feb 2014
Location: Southampton, Hampshire, UK.
Posts: 419
|
Re: Choosing a Thyristor
Hi,
one way is to use the thyristor search and filters on RS or Farnell and just filter on the specs or close to them and all the nearest type numbers pop up. Pete |
26th Dec 2018, 10:27 pm | #3 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
|
Re: Choosing a Thyristor
This is close, you won't need a heatsink at 1A;
https://uk.farnell.com/littelfuse/2n...220/dp/9556753 |
27th Dec 2018, 11:33 am | #4 |
Hexode
Join Date: Aug 2009
Location: Liverpool, Merseyside, UK.
Posts: 254
|
Re: Choosing a Thyristor
Thanks for that, I can get on with the job now, no excuses!
Best Wishes, Geoff.
__________________
Geoff. (BVWS Member) |
27th Dec 2018, 6:26 pm | #5 |
Hexode
Join Date: Aug 2009
Location: Liverpool, Merseyside, UK.
Posts: 254
|
Re: Choosing a Thyristor
I have been looking at, and comparing data sheets for the thyristor suggested (2N6397G) and I notice that the maximum trigger voltage is 1.5V.
When using an SCR1/40 a pulse of greater than 3V is required to trigger it. The pulse generator in the circuit I want to build is designed to produce such a pulse (circuit included) ie. greater than 3V. Will this damage the 2N6397G ? If so, can anyone suggest a way out of this difficulty which does not include forking out a fortune for an obsolete SCR1/40 ? The transistor in the trigger circuit is a unijunction TIS43.
__________________
Geoff. (BVWS Member) |
27th Dec 2018, 6:42 pm | #6 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
|
Re: Choosing a Thyristor
I think damage is unlikely, you could insert a resistor or 2 x silicon diodes in series with the to gate to drop voltage, or connect 2 x silicon diodes in series from gate to ground
to act as a 1.2V zener, cathode of one diode to ground of course. |
27th Dec 2018, 6:46 pm | #7 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
|
Re: Choosing a Thyristor
I'd regard it as good practice to include a low value resistor - 10Ω or so - in series with the thyristor gate.
With the circuit as it is, there is virtually nothing to limit the gate current when the TIS43 avalanches. The timing capacitor (one of C3-C6), the bottom half of the unijnction's channel, the 0.1μF coupling capacitor, and the thyristor gate-cathode are effectively all in series, forming a pretty low-resistance discharge path. But adding a small resistor will I limit the current to under an amp, which everything will be happy with, without interfering with how it's supposed to work. |
27th Dec 2018, 7:30 pm | #8 |
Hexode
Join Date: Feb 2014
Location: Southampton, Hampshire, UK.
Posts: 419
|
Re: Choosing a Thyristor
Intrigued as to what the rest of the circuit is doing now! I built something like this many years ago to fade disco lights in and out by varying the pulse frequency around the mains frequency.
Extract from the gate limits attached. (Farnell/Littlefuse) Last edited by G4_Pete; 27th Dec 2018 at 7:31 pm. Reason: added data source. |
27th Dec 2018, 8:17 pm | #9 |
Hexode
Join Date: Aug 2009
Location: Liverpool, Merseyside, UK.
Posts: 254
|
Re: Choosing a Thyristor
That's brilliant, thank you so much for the advice. The thyristor is used to trigger a gas discharge tube (Ferranti NSP2) acting as a stroboscope with a range of 10Hz to 250Hz.
__________________
Geoff. (BVWS Member) |
28th Dec 2018, 1:44 pm | #10 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Choosing a Thyristor
Quote:
Also I don't recognize that UJT, but a good one for the job is a 2N3980. Last edited by Argus25; 28th Dec 2018 at 1:53 pm. |
|