Obsolete SES C230E SCR Thyristor Replacement

[bookaboo]

Hi,

I've been handed a very old motor speed controller to repair. I've narrowed it down to this thyristor but it's obsolete,








SES C230E Datasheet:
http://www.alldatasheet.com/datasheet-pdf/pdf/579002/DIGITRON/C230E.html


I'm looking for a suitable alternative available from stock from Farnell/RS/Mouser/Digikey but I'm not all that familiar with SCR specification.
So far the parameters I'm searching by are
Peak repetitive off state voltage >= 500v
Peak non-repetitive reverse volatge >= 600v
Forward current RMS >= 25A
Peak Surge Current >= 250A
Forward "on" voltage <= 1.9v
Gate Trigger Current < 25mA
Gate Trigger Voltage <1.5V
Holding Current <50MA
Turn On Time  ~1uS
Turn Off Time ~23-35uS

I found this one, its a little physically larger (I have room) and the Forward Current is 63A, but I figure the bigger the better there right?
http://docs-europe.electrocomponents.com/webdocs/0a35/0900766b80a35a6a.pdf
The only thing is that it has a holding current of 100mA, I'm not sure if that matters or not.

If I stick to the 50mA max holding current I can't find anything in a stud mount format, that doesn't bother me as there's a large heatsink to mount to anyway.  The best I can find is
http://www.mouser.com/ds/2/240/Littelfuse_Thyristor_Sxx35x-63752.pdf



So can anyone tell me if I'm on the right lines and what are the key specifications to look out for when replacing obsolete SCRs?

[T3sl4co1l]

Turn off time (t_q) is much shorter on the original part, it's probably an "inverter grade" device, or something near that.  Well.. maybe not that much.  It's not guaranteed, nor is critical dV/dt.

That S6035 is probably a good idea.  It's even available (well, they make it in... not that you'll necessarily find it in stock at a distributor) in wire lug format.

Tim

[SeanB]

Gate voltage and gate current are more important. The one you want to buy will need a little more current, but as you are using a transformer to drive it it probably has a low enough output impedance to trigger it. Only way is to try, or use a TO220 device with a current rating of around the same level. With lower current the gate drive should reduce though, so it likely will work.

Why do you think it is the SCR, they typically fail as short or open, or with a gate current that needs to be in the amp range to turn it on.

[bookaboo]

Thanks guys, I'm getting a dead short between Anode and Gate on the old one. I'm doing some cold tests on the rest of the circuit to see if it was anything in the driver side that caused it.
The motor etc. is apparently all fine (according to the site technician)
The drive works off a tacho so I can't test here except the old "turn on and hope for no smoke".

[wraper]

First variant ixys scr is a no go as it have 10 times higher max gate trigger current, second choice is closer but have 4 times higher Igt too, so unless you use exemplar with much lower Igt than maximum allowed, it is much better to find another replacement.

[SeanB]

True, but most devices are a little more sensitive than the spec, and most drivers use a higher current to drive them, unless you are limited in power. Pulse drive will typically use a high current to do it, so likely here it will work, as the currents are within the spread of values, and the drive transformer likely does give enough current to the gate.

[bookaboo]

The lowest Igt I could find was the CS19-08ho1, but it's only 28mA which isn't all that different.

So if I'm understanding correctly too high a value of "Igt" means the thyristor will fire later in the cycle given the same drive circuitry?

[wraper]

The lowest Igt I could find was the CS19-08ho1, but it's only 28mA which isn't all that different.

So if I'm understanding correctly too high a value of "Igt" means the thyristor will fire later in the cycle given the same drive circuitry?

It depends on control circuity. If current is enough from the beginning it will simply fire. If there is some current ramp and not enough from the beginning, then it could fire with a delay. If there is not enough current, it will stay closed.

[bookaboo]

Thanks to all, I'm going to try a S6035 in as a replacement and see what happens.

[bookaboo]

Just a quick update, just spoke to the service engineer who informs me that repair has been working perfectly with the S6035 as a replacement. Many thanks again to all.