inductors 41 and 42 the output of the filter 12 is fed to the voltage limiter 13 that is utilized for surge conditions when the input voltage rises above 45 volts the voltage limited output of the limiter 13 is then supplied through the schottky diode 14 to the low voltage emi filter 21 and then to the d c to d c converter 22 due to the use of the diodes 35 and 36 short duration voltage spikes present on the power inputs are clamped so as not to exceed 150 volts consequently this permits the use of low voltage capacitors for the capacitors 37 40 to provide higher capacitance per unit volume and a greater attenuation of electromagnetic interference and also permits the use of lower voltage components in the voltage limiters 13 and 19 the voltage limiter 13 includes an rc timing path with a resistor 46 and a capacitor 47 so that as voltage is applied to the limiter 13 the capacitor 47 is charged through the resistor 46 until the gate to source threshold voltage of a mos field effect transistor 48 is reached and it begins conducting the limiter 13 further includes a 45 volt zener diode 49 to limit the voltage applied to subsequent stages of the circuit 10 this limiting action begins as the input voltage of the limiter 13 rises above 40 volts because the diode 49 allows only a 5 volt gate to source voltage which forces the operation of the transistor 48 into the linear region thus during any voltage surge the difference between the applied voltage to the limiter 13 and 45 volts appears.