[Prev][Next][Index][Thread]
Re: Sam's HIGH POWER Ignition Coil Driver. Record pulses, driver dead:-(
> Does anyone have a good diagram for a SCR trigger circuit that will
>trigger larger SCRs (I have a 20mA gate current one now, moving onto
>100mA gate current) at a wide, adjustable frequency range?
Check out http://home.HIWAAY-dot-net/~eburwell
This circuit as shown was delivering about 2000ma peak into the gate. I
just upped that on my prototype probably to about 4000ma. This is the rated
max peak gate current for my SCR.
If you have questions about this circuit feel free to ask!
> How can I get SCRs to work at higher voltages? I can't find anything
>larger than 600V 50A here. The 50A are more than enough, but I would
>like at least 1000V for my next design.
>
Most SCRs don't self trigger until some voltage well above their rating.
You could use a series pair of SCRs. To do this you would need a well
isolated trigger transformer and some components to ensure voltage sharing
between the SCRs. A simple way to encourage voltage sharing would be a pair
of MOV picked to start conducting at 600V.
> If I put a 50A SCR and a 50A diode on the driver, will the higher
>resistance of them cause loss of input? Should I try to keep their
>values as low as possible (within working limits) to maximise
>efficiency or can I make them bigger?
>
Bigger SCRs and diodes are no problem. They are usually rated for higher
pulse currents. A significant portion of the losses in a SCR occur during
the turn on period (with any size SCR). After they are turned on they seem
to have about a 3V drop across them. The size of the SCR (within reason)
should not have a large impact on efficency.
If you want efficiency try resonant charging!
> How about the Diode snubber network? I heard someone used it to
>protect the SCR but I don't quite see how it would work and be used.
If your load is inductive (as the coil probably is) some amount of reverse
charge will be left on the cap after each discharge pulse . An anti-parallel
diode will give the reverse voltage left on the cap a discharge path. In my
setup this allows ringing between the primary cap and the primary turn of my
step up transformer. A RC snubber would not matter on your setup because
reverse voltage on the cap is probably commuting your SCR off. If you have
an anti-parallel diode there will be no voltage (aside from your charging
circuit) across the SCR when all the ringing has stopped. The SCR will turn
off when it is good and ready. A RC snubber is usually used with back to
back SCRs for phase control of inductive loads. In this case when one SCR
cuts off there will be a rapidly rising voltage (due to the nature of
inductive loads) which tends to turn on the other SCR.
Eddie Burwell