SCR circuit 1

[RICH535]

I am looking for a circuit to control a high current (40 amps) demagnetizer coil using the 60Hz line. We have used SCRs and high current diodes in the past that have become obsolete. The gate control circuitry for the SCRs is also outdated being designed with discrete transistors, etc. I would like to "modernize" both. Any ideas where to look?

 

[MacGyverS2000]

What do you hope to "modernize"? Unless you believe the gate driver can be made better or with fewer components than the current design, why screw with it? It's not like you need a micro to take care of it, so "modern" is a somewhat pointless term.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

Demagnetisation works best with AC, so maybe use a triac instead of an SCR.

With respect to specific parts becoming obsolete, there should be close replacements available. The requirement for these sorts of parts isn't going to go away.

 

[Comcokid]

I would think you could make it really simple by buying a solid-state relay. Zero turn-on crossing, pre-made, bolt it to a suitable heatsink and go. I've not looked into these for some time, but they may have zero turn-off versions as well - ideal for demagnetizing.

 

[electricuwe]

I've some doubts if a zero crossing solid state relay will do a good job in a demagnetizing circuit. Usually demagnetizing requires the magnetic field to be reduced gradually to cope with the remanenz effect in magnetic material (current zero not equal to magnetic field zero).

As Triacs for 40 A RMS are a rare species, the approach with two SCRs connected antiparallel is well suited for this application.

If it is useful to redesign the discrete control circuit to integrated or even microcontroller control depends on two issues:

- complexity
- added benefits

If complexity is low and a more advanced technology does not provide added benefits, I'd just convert the old discretes to more recent types.