Temp. control circuit for heating element - has temp. dependent resistor controlling pulse generator that triggers thyristor

摘要

The temp. control circuit has a pulse generator (8) producing the triggering pulses for the thyristor (Thy) or triac, etc. that connects the heating element to its ac supply. The thyristor is shunted by a series circuit comprising a first capacitor (C1), a resistor (R5) and a second capacitor (C3). The first capacitor is shunted by a zener diode (D3) in series with two diodes (D1, D2). The temp. dependent resistor (Rt) is in series with a fixed (R2) and a variable (R1) resistor across these two diodes. The pulse generator's input is connected to one end of the temp. dependent resistor. The advantage lies in fewer components and greater reliability.