I am working on an RF energy harvesting circuit. Problem is that the charge slowly builds up in the capacitor and the output voltage from the DC boost increases slowly. The output voltage is being used by an RF chip. I want the RF chip to turn on only when the output voltage reaches 3 to 3.3V. Now if the RF chip is on it will start draining the voltage right when the output voltage reaches 1.8V. I do not want my RF circuit to turn on when the output voltage is 3V. Now there is a voltage indicator pin of the DC boost that turns high when the voltage reaches 3V. So can I use a NPN or PNP transistor circuit and use this voltage indicator pin to turn on the RF chip when the output voltage reaches 3V? Is a PNP better or an NPN?