Circuit diagram of 8550 transistor switch (1)

This paper introduces a three transistor audio amplifier which is based on 8050 and 8550.

The circuit is shown in the figure. The working voltage of the base of the input pole (9014) is equal to the neutral point voltage of the two output triode transistor. The stability of the voltage is controlled by two diodes on the base of the output triode. The 3.3 ohm triode diode resistor is connected in series with the emitter of the output triode to stabilize the bias current. In order to reduce the influence of ambient temperature and different device parameters (such as diode diode, input transistor diode and output transistor diode) on the circuit. When the bias current increases, the voltage between the emitter and the base of the output transistor will decrease to reduce the bias current. The input impedance of this circuit is 500 ohm, and the voltage gain is 5 when using 8 ohm loudspeaker. The figures are as follows.

Circuit diagram of 8550 transistor switch

When the circuit outputs 50MW power without distortion, there is about 2V voltage swing on the loudspeaker. The output power can be increased by increasing the voltage of the power supply loudspeaker, but the heat dissipation of the output transistor should be paid attention to at this time. When the power supply voltage is 9V, the power consumption of the circuit is about 30mA. It should be noted that the magnification of the two output power tubes should be close. Other device parameters can be selected according to the figure.

Circuit diagram of 8550 transistor switch (2)

Circuit diagram of 8550 transistor switch

Circuit diagram of 8550 transistor switch (3)

Circuit diagram of 8550 transistor switch

FM is a buzzer, 8550 is a PNP type triode, C-terminal is grounded, b-terminal is controlled by MCU, e-terminal is connected to VCC through FM. According to the direction of the arrow, when the e terminal has high voltage, when the B terminal is also high voltage, the E and C are disconnected; when the B end is low voltage, e and C are directly connected to realize the function of switch. Simple technique: as long as the diode in the direction of the arrow on the triode is on, then the triode can be turned on up and down.

Circuit diagram of 8550 transistor switch (4)

Circuit diagram of 8550 transistor switch

For PNP type triode, when it is used in the switching state, it is generally connected according to Fig. 2: the emitter is connected to the high level; when the base receives the low-level signal, the triode is on, that is, the current flows from the emitter to the collector.

If the voltage applied to the three terminals of the triode is incorrect, the triode will be damaged. There are parameters marked with breakdown voltage in the datasheet of the triode

Circuit diagram of 8550 transistor switch

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