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Refrigerator thermostat circuit diagram analysis

Date: 2013-11-29
Viewed: 59
案例名称: Refrigerator thermostat circuit diagram analysis
冰箱温控器电路图解析


The TC4011BP (Q801) is connected to two RS flip-flops. Among them, RS1 is used to control the operation of the compressor, and RS2 is used to control the defrosting work. The working process is as follows: when the RS11 pin is low


When 3 feet are high level, Q81I is turned on, RY01 is closed, and the compressor is turned on; when RS16 pin is low level, 3 feet is low level, QS11 is cut off, RY01 is released, and the compressor is stopped. When pressing the 'Defrost Start' button on the panel, the SET terminal, that is, the input pin 13 of RS2 is grounded, which is low level. At this time, the RS2 output terminal 11 is high level, Q812 is turned on, and RY02 is connected. The defrosting heating wire is energized to defrost. At the same time, because the Q812 collector is low, through the diode


D803, the Q811 is cut off, RY01 is released, and the compressor is forced to stop. ;


When the refrigerator freezer temperature is higher than 8.5 °C, or when the 'Defrost Stop' (STOP) button is pressed, the RS2 pin 8 is low.


The output terminal (11) is low level, Q812 is off, its collector is high level, RY02 is released, and the defrost is finished. If the 3 pin of RS1 is high at this time, Q811 is turned on and the compressor is running. ;


The three op amps (A1, A2, A3) in the TA75339P (Q802) are connected to three voltage comparators to detect the change in resistance of the temperature-controlled thermistor. In phase of A1


The input terminal 5 has a 4V reference voltage UR1, and the inverting input terminal 4 has a temperature-controlled thermistor.


Temperature sensing component consisting of R806. When the temperature inside the box rises to a certain value (about 3.5 ° C), the resistance of the temperature-controlled thermistor drops (about 6.7kΩ), the voltage of the 4-pin rises (about 1V), and the 2 pin of the A1 output becomes Low level. This low level is applied to the RS11 pin, so that the 3 pin is high and the compressor is turned on.


  ; ; ; Comparator A2 Inverting Input 6 is equipped with an adjustable reference voltage UR2, the maximum voltage is about 2.2V (about 1.5v when adjusted to the 'winter' side). In phase of A2


The input terminal 7 is also connected to the temperature control thermistor. After the boot for a period of time, the temperature inside the box drops, the temperature-controlled thermistor


The resistance becomes larger and the voltage at pin 7 decreases. When the reference voltage UR2 is lower than the 6 pin setting, the output pin 1 of A2 becomes low level.


This low level is added to the 6 pin of the RSI, so that the 3 pin of the RS1 output terminal is low level, and the compressor is stopped, thereby realizing the automatic temperature control function.


  ; ; ; A3 and RS2 together to complete the semi-automatic defrost control function, its in-phase input terminal 9 is connected with a reference voltage of about 4.4V (by R808, R809 partial pressure), inversion


Input pin 8 is connected to the voltage divider composed of the defrost thermistor and R810. After the defrosting starts, the temperature inside the box gradually rises. When it rises to about 8.5 °C, the defrosting thermistor


The resistance decreases (about 5.4kΩ), and the 8-pin voltage gradually rises. When the 4.4V is higher than the 9-pin, the A3 output 14-pin is high.


It goes low, Q812 is cut off, and the defrost is terminated. When pressing the 'Defrost Termination' button on the panel, input a low level directly to the RS28 pin, or force the defrost to be aborted.


  ; ; ; When the control function is not normal, try to unplug the temperature control thermistor. At this time, A15 pin and A27 pin are low level.


Therefore, the A12 pin should be high, and the A21 pin should be low; otherwise, the TA75339P is damaged (peripheral components are good). Remove the TA75339P and check the TC4011BP by: putting the multimeter


(voltage setting


Block) Connect the RSl output terminal 3 to the ground, and short-circuit the 6-pin to the ground. If it is normal, the 3 pin should be low; then try to short-circuit 1 pin and ground, 3 feet should be high; otherwise, TC4011BP damage.


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