Abstract: A heater control circuit functions in conjunction with a suitable heating coil to provide precision, automatic temperature regulation. The combination of heating and temperature sensing functions into a single system results in a two-wire heater regulator control circuit in which a continuous excitation voltage and a power voltage can be simultaneously present at the heater coil. Temperature of the heater is established by continuous excitation and sensing independent of the occurrence of power for heating. A short circuit protection circuit is responsive to an electrical short in the heater coil (which significantly changes its resistance with temperature) and disables the power voltage.

Abstract: A low-level voltage clamp circuit drives its active components with the fault voltage of a main circuit being protected which main circuit operates at about one volt DC or less. The clamping circuit senses voltages in excess of a predetermined limit and effects the sinking of increasing levels of fault current in order to hold the voltage of the main circuit at the predetermined clamp limit.