Help for design calculation!

[zawminoo]

Help me for design calculation.

This circuit is to generate high voltage at an instantaneous time.
Firstly, when give pulse to MOSFET, It will switch close and IGBT's gate will ground.
So if no gate voltage,it disallow current to flow through it.
But I can't calculate by equations.
Please help me if you can.


Z

 

[leotim]

Let us define these variables:

(1) fs: frequency of switching = 333 Hz

(2) Ts: period of switching = 1/fs = 3 ms

(3) Vg_th: threshold voltage on IGBT gate to be turned on = suppose 5 Volts

(4) vg(t): Voltage of IGBT gate after Q1 is turned off = vc1(t) =
12 * (1 - e^(-t / (R1 * C1)))

(5) t1: time at which IGBT is turned on (after Q1 is turned off).
vg(t1) = Vg_th
=> 12 * (1 - e^(-t1 / (R1 * C1))) = 5
=> t1 = 0.539 µs

(6) tg_off: off-time of IGBT in each period of switching = Ts/2 + t1 = 2.039 ms

(7) tg_on: on-time of IGBT in each period of switching = Ts/2 - t1 = 0.961 ms

(8) Ipk: maximum current of L1: If L1 current before IGBT is turned on was 0, then we can calculate Ipk using this formula:
Ipk = tg_on * 12 / L1 = 11.532 kA!!! But L1 will not reach this current because of L1 resistance and V1 internal impedance and IGBT saturation and presence of R2. If we only take the effect of R2, Ipk will be about 12 / R2 = 545A.

(9) EL1_pk: The Energy stored in L1 at peak current = ½*L1*Ipk^2 = 0.1485 J

(10) VC2_peak: Maximum voltage on C2: If we neglect the R3, we have:
VC2_peak = √(2 * EL1_pk / C2) = 545V.

Maximum output voltage is about 545 V

Now, you yourself can calculate for arbitrary Vg_th or other parameters.