APD Bias Supply and Current Monitor

This circuit is consists of two circuit but in the figure this circuit is combines. This is the figure of the circuit.

The programmable APD bias supply is as before, except that feedback comes via A2. A2, sensing after the 1kW current shunt, isolates the R1-R2 path loading, preventing it from influencing the shunt’s voltage drop. A2’s action also insures tight output regulation, despite the current shunt’s presence. The current monitor, measures across the 1kW current shunt, presenting its output in Q1’s drain line. As shown, the output has about 1kW output impedance, although either of the circuit output options may be employed.

When considering circuit operation, note that both amplifiers are powered by the charge pump’s high voltage output, with their V– pin returned to the “2/3 VOUT” point. This biasing permits the amplifiers to process high voltage signals, although the voltage across them never exceeds 30V.