One of the thermostatic control circuits using operational amplifiersb

The constant temperature control circuit using operational amplifier as the control element has high temperature control accuracy and stable performance.   The circuit is shown in Figure 11-46. These three circuits all use operational amplifier A as the control element and the thermistor R. #Temperature sensing element . The difference is that the power supply part in Figure 11-46 (a) is the simplest, using a capacitor to reduce the voltage, eliminating a transformer; Figure 11-46 (b) uses a transformer to reduce the voltage; Figure 11-46 (c) uses a transformer to reduce the voltage And series type regulated power supply, with better voltage stability. In addition, Figure 11-46 (a) and Figure 11-46 (b) directly control the triac to heat the electric heater, while Figure 11 6 (c) controls the electric heater through the relay KA. The working principles of these three circuits are basically the same.   The thermistor Rt, together with the resistor Rz and the potentiometer RP, provide a comparison voltage for the operational amplifier A.   Thermistor Rt can be selected from MF11 type or MF53 type, lOkfl, 0.25W.