Temperature Control Combining Magnetic Logic with Silicon-Controlled Rectifiers

This paper describes a temperature control using SCR ON-OFF zero switching. The heart of the logic circuitry is a transformer wound on a square-loop core. It makes use of the basic constant-volt-second principle. The transformer performs the dual role of providing isolation from the sensor to the line and supplying isolated gate pulses to a pair of inverse parallel SCR's. It is designed to operate with a positive temperature coefficient resistance PTCR as the sensing element which results in a very narrow ON-OFF temperature band. A negative temperature coefficient resistance can be used by adding a few additional components.