I've placed 22-ohm 0805 resistors in series with the HV supply lines in the latest version of my easy-to-build AMP-62 high-voltage amplifier board. This version is often made with aggressive output current-limit values, e.g., 150mA. But it's intended that such currents last only a short time, e.g., to rapidly charge a capacitive load (during the rapid output slewing, the 22-ohms only drops 3.3 volts). By comparison, the original version of this board, as described in our x-Chapter book, has a wimpy 5mA current limit. But we assume that users of this amplifier version who need its extreme slewing capability understand the risks, when they select the 150mA current-limiting resistor values.
If the output were to be shorted, and draw 150mA from the supply, firstly it's hoped the supply voltage will soon fall dramatically, due to its own say 20mA current limit. Meanwhile the 22-ohm 0805 resistor would dissipate 0.5 watts, or
4x its rated power, and hopefully after a while it would fail open. But if it doesn't fail fast enough, one of the high-voltage MOSFETs, dissipating 40 watts, might short. At that point the current would increase further, and the 22-ohms would certainly fail, stopping the high power dissipation and removing the load from the supply.OK, I see I'm going to get roasted for this one.