Infrared remote control dimming circuit a

 (1) Infrared emission circuit The infrared emission circuit is shown in Figure 18-la. A
multivibrator is composed of transistors VT1, VT2 and resistor-capacitor components . The working principle of the multivibrator is: Kun and brother are the base bias resistors of VT2 and VT1 respectively.
After closing the switch SA and adding the power supply voltage, VTZ is turned on first, and its collector is at low level "O". This low level is coupled to the base of VT1 via VD2 and C3, causing VT1 to be cut
off. After VT2 is turned on, R4, VD2 and VT charge G. The result of charging is that C is charged with left positive and right negative charges, so that the base potential of VT1
begins to increase. When the base voltage rises to a certain value, VT1 is turned on, and the lower jump level of its collector is added to
the base of VT2 through VDI and island, causing VT2 to change from conduction to cutoff. After a while, rr and 1 turn off, and VT2 turns on. vri and VT2 are turned on and off alternately,
and the cycle continues. So it is called astable multivibrator.
    Its oscillation frequency mainly depends on the charge and discharge time constants R, G and Ra, island.
    After VT1 and VT2 start to oscillate, they are turned on and off alternately, and LED2, LED3 and LED1 connected to their collectors alternately emit infrared light and red
light. The visible light of the LED is used to monitor whether the oscillator is working properly, that is, to indicate the working status.
    (2) Infrared receiving circuit When the infrared receiving tube receives the remote control signal from the transmitter, the ⑦ pin outputs
low level after being processed by KA2184. This low level is directly added to the base of VT to turn it on, and the current output by its collector forms a high level output at the top of the island
. This high level is added to the auxiliary input terminal (⑥ pin) of the wither circuit LS7232 through ‰. As a control signal for dimming.
    The receiving circuit is shown in Figure 18-lb. It is an infrared remote control dimming circuit . When its ⑤ pin inputs the trigger signal, its ⑧ pin will
continuously output control pulses that control the conduction angle of the bidirectional thyristor, causing the bidirectional thyristor to The conduction angle is 41. —160. changes between. With bidirectional thyristor.
As the conduction angle of the tube changes, the light also changes from dark to bright or from bright to dark, thus achieving dimming control of the light.
    During the dimming process, when you need the light to change from dark to bright, you can press and hold the transmit button on the remote control to continuously send control signals. At this time, you can see that
the lamp is gradually getting brighter. When the required brightness is reached, immediately release the emission button, and the brightness of the lamp will stay at this position. If
connected continuously, the light will gradually dim from bright to dark until it goes out. .
    It should be noted that LS7232 is a PMOS type integrated circuit, so its power supply polarity is reversed from that of commonly used CMOS circuits, that is,
its Vm power supply terminal should be connected to the negative pole of the power supply, and the iris terminal should be connected to the positive pole of the power supply.
  The power supply of this circuit still uses AC power supply, capacitor G for step-down, and diode VD1 for half-transition rectification. Different from other capacitor step-down power supply circuits
, the step-down capacitor G of this power supply is connected in parallel with a 220vH inductor. Its function is to absorb the harmonics generated by the LS7232 and prevent
it from interfering with other electrical appliances through the power line. .