Power Switching Device

I guess you could take a look at IGBTs. They are very easy to control and very resistant. But it depends on what do you need it for...is it a rectifier? I used full-bridge of IGBTs for a rectifier with grid interface, it worked fine!

http://pt.farnell.com/fairchild-semiconductor/fgh50n6s2d/igbt-n-to-247/dp/1095034

Hey Pedro, thanks for the reply.

No, this is not a rectifier. The AC would need to pass through the device unmodified (60Hz). It also shouldn't be amplified. I just need it switched on or off.

I didn't actually know about IGBT's until you mentioned them and looked them up. Are they widespread? Do you know where they are used?

See attached, quick sketch of possible configuration of the device. Gate voltage of 5V. Any thoughts?

Attachments:

schematic2.pdf

Many cicuits switch mains loads.

You could use a simple 5V Coil relay such as G5LE (farnell part number 1333640) which easily be switched by 5V (use NPN transistor such as 2N3904 to switch the coil, and protect the circuit with a didode such as 1n4004 reversed across the coil)

You could also use an SSR (solid state relay) such as S21601F (farnell 1618479) - which gives a very neat solution - you must add a snubber circuit (Resistor + Capacitor) to prevent accidental switching.

Note that this SSR requires a control current of 50ma, so don't drive it direct from a processor pin, again use something like an NPN transistor to switch it.

Thanks Kenny.

The coil sounds like a good idea. Since it is simple, I could probably start there and try another method if I am successful. Just wondering, how does placing a dioide across the coil protect the circuit? I drew a simple circuit. Does it look right?

A Triac sounds like it could also do the trick, and as you mentioned would probably need a transistor for the higher gate current capabilities.

Thanks for your input.

Duncan

Attachments:

Schematic3.pdf

The circuit is pretty much ok, but I'd probably use a small series resitor inline with the base of the transistor, say 820 Ohm.

Current flowing through a relay coil creates a magnetic field which collapses suddenly when the relay is switched off. This sudden collapse of the magnetic field induces a brief high voltage across the relay coil. The diode feeds the current back through the coil (and diode) so the magnetic field dies away over a short time rather than instantly. This prevents the induced voltage becoming high enough to cause damage.

Yeah, I think there needs to be that series, gate resistor present. Not sure why I didn't include it.

Ok I see how it works. I have seen the diode present in motor control devices and wasn't quite sure the use for it. (Of course motors are just inductive loads.)

I realize now that the switching frequency of the relay may be up to 10Hz so that might be a little fast for a mechanical switch. In this case a SSR would work (using a Triac). I plan on testing the circuit at a lower frequency, 1Hz, so I will still likely try using the mechanical relay first.

Thanks for the input.

Think you are looking for a Solid State Relay.

A while ago i found one with 3 - 9Vdc control voltage.

Just search it on the net.

Rick

Some time ago I uset a optotriac. It is like a optoinsulator, but with a small triac in output. You can use this small triac to drive a more powerful triac. Two components, optoinsulation and a drive current of few milliamps..... Zero corossing for the less noise.

Regards.

Franco Vecchi