Hi,
I'm experimenting with using a capacitance multiplier as a noise filter. It seems to work rather well, but one thing that I'm not sure about is if it is necessary to protect the NPN transistor from negative Emitter-Collector voltages. According to the DS, the maximum Emitter-Base voltage is 6V, which will be exceeded when removing the battery or if there is a large negative "spike" on "+Batt". However, only very little current can flow in these situations, as the total capacitance on the "V_BATT_FILT" net is in the order of 10uF.
Will removing the battery or negative spikes damage the NPN transistor over time and is it necessary to protect it using a diode? If so, what diode would be best? Ideally, it should start conducting at a few volts in forward direction and the reverse voltage should be in the order of 40V.