Hi All, This is my fisrt post, glad to join your group. I have built a circuit to sense an input voltage threshold based on a PNP transistor + zener as seen below: https://www.circuitlab.com/circuit/b34595/transistor-zener-10v-voltage-sensor/ the sensing level is given by: Vs = [(R2+R1)/R2] *Vz + Vbe (SAT) whereas the output is: LOW : Vout = Vin - Vz - Vce(off) = Ico*R3 HIGH: Vout = Vin -Vce(sat) = Ic*R3 The output of the circuit is limited to ~5.1V by using a resistor-zener (5.1V) combination. Therefore the circuit produces ~5.1V (HIGH) and ~ 0.2V (LOW) according to the sensing level. Vin can be anything from 0v -> 40V. Although the circuit works as expected , I noticed that for input voltages >20V resistors R3, R4 were getting hot.. I used 1/4W Resistors which is probably the case as I hadnt thought about the power dissipation.. So I need some guidance regarding the power dissipation on the resistors as I am not sure: According to my calculations, R3 max dissipation is 1.6W (max Ic 40mA), whereas changing R4 to 200Ω will dissipate 7W. R1, and R2 will stay 1/4W. Any ideas/help will be appreciated. George ps: had to limit the header to 20 chars..