This be 8A Solinoid coil driver circuit. Which use mosfet number IRF150 2 amounts, be important equipment , it performs to drive Solinoid coil. Which be valuable low resistance, use current the plentiful. By use the way encourages of input model PWM make use current , share lower, mosfet not very hot. Unless R16 still use fine but current adjust and R15 use fine decorate Release Adj as well .
(PWM duty cycle) D = Vout/Vin , want about 3V, D = 3/12 = 0.25 etc. , want about 9V, D = 9/12 = 0.75. The R16 take keep fine topmost trend has depend upon a kind of solenoid.
The R16 , can fine get from 4A trends arrive at 9A. The D1 help cover up something current flow turn back from solenoid coil. The C1 use increase efficiency of the circuit. The detail is other, please see in the circuit.