Electronics > Beginners
SCR Gate Drive Transformer
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ZeroResistance:

--- Quote from: T3sl4co1l on June 08, 2018, 08:07:04 pm ---You can also use a reverse diode on the secondary side, for the same reason: this allows more flux so the flux discharges faster than when using a diode on the primary side.  (You'd still want some damping on the primary side, to deal with leakage inductance -- an R+C across the primary should do fine here.)

Tim

--- End quote ---

So a R in series with the primary should be okay for currrent limiting on the primary side right? You say R + C across the Primary instead of the free wheeling diode, also Hero999 said he used a cap across the primary. What is this cap or R + C meant for?


--- Quote from: T3sl4co1l on June 08, 2018, 08:16:28 pm ---Is the SCR ready to fire (V_AK positive)?  If so, a few microseconds at, say, 10 * I_gt will do.

--- End quote ---
So for the SCR i'm using that comes to around 150mA, for a few 10's of microseconds. Question is, how do I validate that my GDT can supply 150mA to the gate. Do I measure the current in the gate of the SCR when I trigger it or will the Volt second rating of the GDT give an estimate of the secondary drive?
T3sl4co1l:
Take small-signal measurements of your transformer, and toss together a representative schematic.  We can walk through all of these figures as a design-time matter.  Then if you like, you can take measurements as well to see how it works out. :)

Tim
Zero999:

--- Quote from: ZeroResistance on June 09, 2018, 06:15:38 am ---
--- Quote from: T3sl4co1l on June 08, 2018, 08:07:04 pm ---You can also use a reverse diode on the secondary side, for the same reason: this allows more flux so the flux discharges faster than when using a diode on the primary side.  (You'd still want some damping on the primary side, to deal with leakage inductance -- an R+C across the primary should do fine here.)

Tim

--- End quote ---

So a R in series with the primary should be okay for currrent limiting on the primary side right? You say R + C across the Primary instead of the free wheeling diode, also Hero999 said he used a cap across the primary. What is this cap or R + C meant for?
--- End quote ---
Sorry, I didn't make myself clear. I put the capacitor in series with the primary, not in parallel.

How are you driving the transformer? Are you just using microcontroller IO pin, a signal generator or a single transistor?

I just connected the transformer to a constant voltage power supply, via a capacitor and push-button switch, to see if my pulse transformer worked. I know this isn't ideal: there will be switch bounce and the capacitor will only discharge via its internal leakage. Unfortunately the project got shelved, so I didn't do any more scientific tests.
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