We have considered the operating principle and circuitry of voltage kacher converters (KVC) a little earlier. In this note, we will consider a KVC cascade with a common emitter, but we will choose a MOSFET transistor as the active element. Just like a bipolar transistor, it is capable of effectively generating short high-voltage pulses, while providing high conversion efficiency.

The circuit diagram of such a KVC is shown in Figure 10. Here, resistors R1 and R2 provide the operating point for stable pulse generation by transistor VT1. Elements C1-L1 form a circuit for exciting the avalanche mode of the transistor, and ZN1 serves to protect its gate. Next, from oscillogram 13 it will be clear how the amplitude is limited at this output. Capacitor C2 is responsible for smoothing the pulsations, and L2 is a pulse-setting choke. The amplitude of the output pulse and its length depend on it. Let us just recall that L1 and L2 are independent and are not inductively connected to each other in any way.

Any inductance in the range of 0.5..2 mH is suitable as L2, and this can be either a choke or the primary winding of a transformer. In the second case, it is advisable to add an RC circuit to the drain of the VT1 transistor for more stable operation of the device, as is done in the circuit in Figure 10b (R3C3). The smaller this inductance, the shorter the pulse will be, and the greater its amplitude will be.

The following oscillograms examined a circuit in which the inductance of L2 was 1.5 mH, which gave an output pulse amplitude of about 540 V. But if it is halved, then their amplitude increases to 670 volts, and the pulse width decreases to 1 μs. Also, when the inductance of L2 decreases, the circuit consumption increases, which is usually about 10..15 mA (without load).

It is clear from the oscillograms that the pulses at the output of the circuit are unipolar, and without a tail of damped oscillations. Photo 13 shows how the non-polar suppressor ZN1 limits the amplitude of the master oscillations on the gate of VT1 to 33 volts.

Almost any MOSFET transistors are suitable for this circuit, but the output voltage will depend on their maximum working voltage. If the transistor is rated for 100 V, the output voltage will be about 80 V or less. If the transistor can withstand 1000 V, the output voltage will be about 800 V or less. Some IGBT transistors are also suitable for this circuit, but they must be selected with care.

The following transistor brands have been tested in practice and worked well: FCH47N60, IRFPG50, FCA22N60, FS7KM, and with the latter - it is possible not to use the ZN1 suppressor.

The ZN1 suppressor must be non-polar with a limiting voltage of 15-18 volts, for example, 1.5KE18CA. The capacitors can be any, the main thing is that they can withstand a voltage of at least 50 volts. The L1 and L2 chokes can be wound by yourself, but it is better to use industrial ones, for example, 4.7 mH and 1.5 mH.

The trimmer resistor R2 should be in the lowest position (according to diagram 10). After power is supplied to the circuit, the value of this resistor is gradually increased until stable oscillations appear at the X1 pin. That's all the setupand it ends.