Temperature control alarm circuit

The temperature control circuit is composed of a dedicated intelligent temperature sensing integrated circuit. It has high and low temperature light alarm function, no mechanical contacts, and
a wide temperature control range. Safe and reliable, with high temperature control accuracy.
    (1) Circuit composition and working principle The circuit composition is shown in Figure 13-30, which mainly consists of rectifier filter, temperature control circuit 1C1, optocoupler
IC2, bidirectional thyristor VTH and heater RT.
    When the power is turned on, the T-secondary winding of the transformer passes AC 220V, and the secondary output is 12V AC voltage, after bridge rectification and filtering. The
electronic temperature control circuit IC1 is provided . There are RP1 and RP2 potentiometers on pins 1, 2~3, and 4 of IC1 respectively to set the constant temperature. When the ambient temperature
is lower than the set temperature, the ⑥ pin of the temperature control Icl outputs a high level , and the infrared light-emitting diode flashes, causing the photosensitive
bidirectional to conduct, and the internal LED light of IC2 is lit, triggering the thyristor VTH Turn on, heater RT starts heating. When the ambient temperature exceeds the set temperature
, the ⑤ pin of the circuit IC1 jumps from high level to low level, causing the optocoupler bidirectional switch of the output stage to turn off, the LED light goes out, and the VTH
bidirectional transistor cuts off, so the The heater stops heating when the power is cut off. At this time, the @ pin of IC1 will always remain at a low level. Only when the ambient temperature drops
below the set temperature, will it output a high level , thus enabling the heater to be powered on. In this way, the above control process is continuously repeated to achieve
the purpose of automatically controlling the temperature.
   The medium resistance Rz is used to limit the current flowing to the light-emitting tube.