Electric blanket automatic protection constant temperature circuit

Published:2011/3/21 1:33:00 Author:Allen | Keyword: Electric blanket, automatic protection, constant temperature | From:SeekIC

Currently, many electric blankets temperature control use manually switch, which adopts a fast and a slow thermal step for temperature control, so that the internal temperature of electric blanket is difficult to control at a constant temperature to work, as a result, a lot of trouble is brought. This paper introduces a electric blanket automatic control circuit, which can not only work at a predetermined temperature, but also play a role in self-locking power and over voltage protection. The circuit principle is shown in figure 1. It consists of power-failing and self-locking circuit, overvoltage protection and automatic constant temperature control circuit. When the button switch S2 is pressed, 220V AC is used for relay J after passing capacitor C2 step-down voltage, V6 and V7 regulator rectifier and C3 filter, then J powered on and normally open contact J1 connected make the circuit self-locking. At this time, it can maintain power to the electric blanket and the relay J, even if the button switch S2 releases. When encountered power outage in the use of electric blanket, the relay J powers off and release, normally open contact J1 powers off, so the electric blanket does not work. When the power grid restores power supply, the relay and electric blankets can not automatically power on, only press s2 again, and the relay J pull, so electric blankets will be re-energized work. Rt is a positive temperature coefficient thermistor. Its internal resistance varies with the high and low temperature, that is, at high temperature, the internal resistance increases, and vice versa. The electric blankets constant temperature control circuit is composed of the rectifier diode V2 ~ V5, one-way thyristor SCR, two-way trigger diode V1, positive temperature coefficient thermistor Rt, capacitor C1, RP potentiometer. The control process is: AC turns into DC by V2 ~ V5 bridge rectifier, charge to C1 by RP and Rt, when the voltage of C1 reaches a certain value, the bi-directional trigger diode conducts and breakdowns in a discharge state. At this point, one-way thyristor SCR is triggered and powered on, which make the blanket work. When internal temperature in the electric blanket rises a certain value, the internal thermistor resistance Rt is great, but the voltage of C1 is small, which can not make V1 breakdown, so the SCR turn-off. Relatively, the electric blanket is off and does not work, it is in a cooling state. When the electric blanket temperature drops to a certain value, then repeat the control process, so keep the cycle, and make the blanket temperature at a constant value. If the grid appears over voltage, varistor MY internally (ie in-state) is short circuit, and quickly burn out fuse RD, and thus play a role in over-voltage automatic protection. Figure 2 is the device's printed circuit board assembly drawing.



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