Infrared dimming circuitb

 (1) Transmitting circuit The dimming transmitter circuit is shown in Figure 16-56a. It consists of a pulse square wave generator composed of a 555 timer, a driving amplifier
, an infrared light-emitting diode and other components. The pulse generator outputs a pulse square wave signal and is added to the base of the VTI via R3. When the pulse signal waveform
is high level "1", VT1 is saturated and turned on, and VT2 is also turned on, driving the light-emitting diode LED1 to emit visible light (red or green), indicating that
the transmitter circuit is working. The infrared light-emitting diode LED2 emits infrared light (invisible near-infrared beam). When the pulse signal waveform is low level "o"
, neither VT1 nor VT2 is conducting, and LED2 does not emit light. In this way, the emission of infrared light pulses can be achieved.
  LED1 is an ordinary light-emitting diode, LED2 is a TLN104 infrared light-emitting diode, and VT1 and VT2 are 3DG6. Other component parameters.
    (2) Receiving circuit When the infrared receiving tube receives the control signal from the transmitter, it will be processed by KA2184 and output low power from pin ⑦.
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 upper end of R. This
high level is added to the auxiliary input terminal (pin ⑥) of the dimming circuit LS7232 through the island as a dimming control signal.
    The circuit is shown in Figure LG-56b. It is an infrared dimming circuit . When its ⑥ pin inputs a trigger signal, its ⑧ pin will continuously
output control pulses that control the conduction angle of the bidirectional thyristor, so that the bidirectional thyristor The conduction angle is 41. N160. changes between. As the conduction
angle of the bidirectional thyristor changes, the light also changes from dark to bright or from bright to dark, thus realizing the dimming control of the light.
    During the dimming process, when the light needs to change from dark to bright, press and hold The transmit button of the remote control continuously sends 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
pressed continuously. The light will gradually dim from bright to dark until it goes out.
    It should be noted that LS7232 is a PMOS integrated circuit, so its power supply polarity is opposite to that of commonly used CMOS circuits, that is,
its Vm power supply terminal should be connected to the negative pole of the power supply, while Vss should be connected to the positive pole of the power supply.
    The power supply of this circuit still uses AC power supply, capacitor C7 step-down, and diode VDI half-wave 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 220pH 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. .