Sound and light controlled LED lighting based on emitter output shutdown

1 Sound and light controlled switch circuit based on 220 V AC power supply

Figure 1 shows a circuit diagram of a sound and light controlled switch based on a 220 V AC power supply. In the rightmost part of the circuit, the 220 V mains power is output (marked 1 and 3 in the figure) and then rectified by a bridge, and then connected in series with an incandescent lamp of less than 100 W. The pulsating voltage with zero crossing (marked 2 and 4 in the figure) output after rectification is connected to the anode of the thyristor, and the brightness of the incandescent lamp is controlled by the on and off of the thyristor.

Figure 1 Sound and light controlled switch circuit based on 220 V AC power supply

The main current loop of the general sound and light controlled switch is mainly controlled by thyristor. Since the conduction of thyristor is related to the applied voltage and trigger voltage, there must be a minimum maintenance current after conduction. The working current of energy-saving lamps and LED lighting lamps is a discontinuous pulse mode. Since the thyristor is continuously and erratically turned on and off, the light flickers. The thyristor has poor voltage and current impact resistance, and it is fully turned on at non-zero voltage. It generates serious heat when working with large current. In this regard, the application range of the controlled load is relatively small.

If the object of sound and light control is changed to a high-brightness white LED lamp, and the circuit is not connected to the 220 V mains but powered by a DC power supply, there is no need for a pulsating AC switch output after bridge rectification to control the on and off of the thyristor.

2 Sound and light controlled LED lamp based on emitter output shutdown

An acoustic and optical switch based on the shutdown of the emitter follower is used to control the operation of the LED lighting lamp, which is used for lighting in special public places without a 220V mains power grid, as shown in Figure 2.

Figure 2: Sound and light control LED lamp based on emitter output shutdown

2.1 Voice Control Principle

Microphone MIC1 (receives audio signals such as speech and footsteps) and VT1, R1~R3, C1 are the sound pickup amplifier circuit. In order to obtain higher sensitivity, the current amplification factor β of VT1 is greater than 100; MIC1 uses a high-sensitivity microphone; R3 should not be too small, otherwise the circuit is prone to intermittent oscillation. If the sound disappears, the electronic switch VT1 will automatically turn off. C2, D1, D2, C3 are voltage doubler rectifier circuits, which convert the low-frequency sound signal into a DC control voltage.

2.2 Light control principle

When light shines on the negative photoresistor R8, its resistance value becomes smaller (i.e., the voltage divider is small), which greatly attenuates the DC control voltage, causing the electronic switch (VT2, R6, VT3, D3) to be cut off. There is no charge on the charge and discharge circuit C4, causing D4 to be reverse biased and cut off. The emitter output devices VT4 and VT5 are reverse biased and reliably cut off, and the LED lamp does not light up [3-4].

When no light shines on the negative photoresistor R8, its resistance value becomes larger (i.e., the voltage division is large), and the attenuation of the DC control voltage is very small. The electronic switch (VT2, R6, VT3, D3) is turned on to charge C4 forward, causing D4 to be forward biased and turned on. The emitter followers VT4 and VT5 are forward biased and saturated, and the LED lights up.

Through experimental measurements, it was found that when the lamp is on, the current passing through the lamp is about 16 mA, the voltage across the lamp is about 5.8 V, and the energy consumption of the lamp is about 93 mW, with significant energy-saving effects.

The circuit is powered by a DC power supply with high stability, which prolongs the life of the LED lamp.

The object of sound and light control is a high-brightness white LED lamp working under DC state, which has good light color, energy saving, long life, no flicker, and improves the comfort of users.