Current Switch
Current Switch
(OP)
Hi-
I need to perform a current test that will apply a 40A, 6.25 ms current pulse every 5 seconds to a transformer. My first thought was to trigger a device that would deliver the current, but could be gated with the desired pulse. An SCR would be close, but it wants to stay "on" once gated. I need something that will shut off when the trigger finishes its 6.25 mS pulse. Any suggestions? Maybe there's a much easier way to do this.
Thanks!
I need to perform a current test that will apply a 40A, 6.25 ms current pulse every 5 seconds to a transformer. My first thought was to trigger a device that would deliver the current, but could be gated with the desired pulse. An SCR would be close, but it wants to stay "on" once gated. I need something that will shut off when the trigger finishes its 6.25 mS pulse. Any suggestions? Maybe there's a much easier way to do this.
Thanks!





RE: Current Switch
RE: Current Switch
RE: Current Switch
There are power MOSFETs that can handle that current in a single device if the voltage is 60V or less. Or you can use an IGBT and get up to 600Volt capability.
No you can't drive the gates of IGBTs from a 555 timer. You don't have enough current drive capability. For that much amperage in a FET type device, you are going to need at least 250ma to get the part to saturate rapidly. Otherwise, your current pulse is going to look like a triangle waveform.
Elantec makes a nice driver, EL7155C which takes a TTL level input, but has an output supply pin which can go up to 18V, for rapid gate switching.
RE: Current Switch
dydt
RE: Current Switch
TTFN
RE: Current Switch
RE: Current Switch
Warm regards.
RE: Current Switch
Also, it sounds like you are trying to operate these IGBT in a push-pull configuration. Obviously, you know that IGBT's are are succeptable to "slow" turn off times due to the gate capacitance of the front end FET. This means that they turn on much faster than they turn off unless your circuit has a good biasing resistor network on the front end.
LEWISH, I have read many of your posts and they are always very technically sound. I just saw a small inconsitency between what was posted and what I have successfully designed too and I wanted to pass along some of my experience.
RE: Current Switch
I too, have driven big MOSFETs and IGBTs with digital on the gate, but it always leaves the parts at less than full saturation. The original poster was looking to switch a 40Amp pulse into some type of transformer, so I assume he wants the current to be limited by the inductance of the transformer rather than the resistance of the switching device because the switch changed states slowly. Thus, I advise using a gate driver and at least 15 volts from gate to emitter at turn-on. This will ensure maximum turn-on rate is achieved.
I wish you Best Success.