A programmable controller with overcurrent latch for constant primary peak current in capacitor-charging FET switcher for Nova

The flashlamps supply for the 10 mm laser amplifiers must be repeatable. Therefore, a constant current, linearly charging power supply was designed. Since it is a capacitor, the load varies throughout the charge cycle. At first the load is great, and di/dt of load current is at a maximum. As the capacitor charges the initial conditions for each cycle change, the power supply in effect sees a smaller capacitance, and di/dt decreases. A way of gradually increasing the on-time of the current pulses so that the transistors in the power pridge are turned off when they reach their maximum peak current is needed. The normal current sense response of the control chip is not fast enough to be useful for the present application. The deadtime, or the time that all the bridge transistors are turned off, is fixed so that as the pulse width varies so does the period. The end result is a constant peak current, switching power supply with frequency varying from 50 khz to 20 hz. An overcurrent latch protects the transistors from bridge or transformer faults.