Temperature Sensitive MOSFET
designed by David A. Johnson, P.E.

Recently I was asked by a company to discover why one of their products failed to operate properly in cold temperatures.  A simplified version of the circuit is shown below.

Two n-channel MOSFETs and a few resistors are wired to form a flip/flop latch circuit.  Each time the pushbutton switch is pressed, the circuit changes state and remains in that state until another activation of the switch.