Electric blanket thermostat circuit household appliance circuit

With the improvement of people's material life, household appliances have gradually entered every family. In winter, people like to use electric blankets to keep out the cold,
especially the elderly and children. However, if you accidentally forget to turn off the power and unplug the plug, it can easily cause the electric blanket to overheat and burn
the quilt, causing a fire accident. Such tragedies happen from time to time. For this reason, this electric heating thermostat is designed and made. When the temperature of the electric blanket reaches 50°C
, it will automatically turn off the power and stop heating. When the temperature of the electric blanket drops, the electric blanket fork can continue to heat. The circuit is shown in Figure 1-11.
    (1) Working principle: The thermistor is used as the temperature sensor, and the bridge circuit is used to detect the change of the thermistor. At the same time, a linear integrated operational
amplifier is used as the detector.
    The thermistor is made of semiconductor materials that are extremely sensitive to temperature. Its resistance value can change significantly with the temperature.
The working characteristics of the thermistor are divided into positive temperature coefficient and negative temperature coefficient. We use MF12 type Thermistor is a negative temperature coefficient thermistor
.
    5G24 is an integrated operational amplifier. When the voltages at its two input terminals are equal, the output is zero. When the voltages at the two input terminals are not equal, the output is not
equal to zero At this time, the output voltage is used as the bias current of the transistor VT to turn it on and then trigger it. Triacs enable electric blanket heating.
The resistance of the sensor-thermistor placed in the electric blanket changes as the electric blanket heats up, when it gradually approaches the original preset resistance of the potentiometer (
used to adjust the temperature). Make the voltage applied to the two input terminals of 5G24 equal, the output is zero, VT loses bias and is cut off, so that the bidirectional thyristor VTH is also cut off,
cutting off the power supply of the electric blanket, causing it to stop heating. When the temperature drops, the resistance cross of the bridge becomes unbalanced, the output has electricity again, the trigger tube
Vr triggers the bidirectional thyristor, and the electric blanket continues to heat.
    In Figure 1-11, EH is the load, which is the electric blanket , 0.47yF/lOOOV is the step-down capacitor, and 1N4001X2 is the rectifier. 100vF/1'6V is a filter
electrolytic capacitor, and 2CW56 is a voltage stabilizing tube. During assembly, the capacitor with a high voltage stabilizing value should be installed close to the input end of the DC power supply.