Hi I wanted to desig a simple solenoid driver. The solenoid's operating voltage is 6V. The resistance is 20Ohm and inductance is around 60 mH. I want to operate it at 20 Hz 50% duty cycle. The input voltage will vary from 6V to 15V. So i am plannig to use 6V zener to clip the voltage first of all. And to drive the solenoid i am plannig to have astable multivibrator and a transistor driver for driving the solenoid. In that case how should i select the zener and the series resistor. I have done some rough calculation but the wattage seems to be higher. Could you help me in selecting the zener and resistor values?