Application and working principle of silicon controlled rectifier in infrared remote control switch
There are two ways to turn off the unidirectional thyristor: one of them is well known, that is, when the anode potential of the thyristor is lower than the cathode potential or the anode current is less than the maintenance current, it can be turned from on to off. The other is to short the control pole of the thyristor to ground, which can also be turned off. The one-way thyristor has the function of realizing self-locking at the touch of a button. I made use of its characteristics to make the following simple infrared remote control switch circuit, as shown in Figure 1.
1. Working principle
220V AC voltage is stepped down by capacitor C1, VD1, VD2, C2 are rectified and filtered, and VD3 outputs 12V DC voltage after voltage stabilization to supply power to this circuit. The 12V DC voltage is further stabilized and filtered by R2, VD4, and C3, and then it is used as a power supply for the infrared receiving head HRM.
Turn-on process: the pulse amplifying tube is in a saturated state at static state, and the collector outputs a low level of 0.1V. At this time, the thyristor trigger circuit does not work. Instantly press the remote control (all kinds of color TV and VCD remote controls are acceptable), the receiving head receives the infrared remote control signal, and its output terminal outputs the demodulated sequence command pulse, and the signal amplified by V1 is divided into two channels: one channel is transmitted to C6 via R6 Charging, don’t charge C5 through R5 all the way, because the capacity of C5 is much larger than that of C6, so the charging speed is slow, and V2 cannot be turned on, and the instantaneous pulse voltage charged on C6 is enough to trigger the conduction of the thyristor SCR. The relay K is energized, the normally open contact CJ1 is closed, and the load in the socket CZ is energized to work. LED is used for working status indication.
Closing process: When the remote control button is pressed again for more than 3 seconds, the voltage charged on C5 is enough to make V2 enter the conduction state from cut-off, thereby short-circuiting the thyristor control pole to ground, the thyristor is turned off, and the relay fails. Electricity, electric shock is disconnected, and the negative cut-off stops working. Then the voltage charged on C5 is quickly discharged through the collector and emitter of R5 and V1, and the circuit enters a waiting state.
2. Component function and parameter selection
1. The model of the integrated infrared receiver used in the circuit is HRM380017, which can receive infrared remote control signals emitted by various remote controls, and output demodulated sequence command pulse signals. Readers can choose other different types of infrared receivers according to the conditions. Most of the functions are the same and they can be interchanged with each other, but the pin arrangement will be different. Be careful not to connect the power terminal and ground terminal of the receiver wrongly, otherwise it will easily cause damage. The receiving head is damaged. 22. In order for V2 to reliably enter the saturated conduction state from the cut-off state, to ensure that the thyristor is turned off, R5 must satisfy that the resistance of R5 is less than the product of β of V2 and the resistance of the relay coil, otherwise the thyristor cannot be turned off. The relay model in this circuit is JZC-23F, and its coil resistance is about 400Ω, so according to the requirements, R5 shall not be greater than 10KΩ (set V2’s β=100).
3. One-way thyristor can choose MCR100-6, its maximum operating current (1A) and maximum operating voltage (600V) can fully meet the needs of this circuit, the gate current is between 10μA-30μA, so the trigger sensitivity is very high. In the production process, it will be found that even if C6 is omitted, the thyristor can still be triggered and turned off normally, but the anti-interference performance of this circuit will deteriorate, and it is very easy to be misconducted by external interference, so C6 must not be omitted .
4. If it is found that the time required to turn off the SCR is too long, it can be adjusted by appropriately reducing the capacitance of C5.
