Triode 8050 is a very common NPN crystal triode. It is often seen in various amplifier circuits. It is widely used in high frequency amplification. It can also be used as a switch circuit.

### working principle

Triode 8050 is a control element, mainly used to control the size of the current, there are three poles, respectively called collector C, base B, emitter E. Taking the common emitter connection method as an example (the signal is input from the base, output from the collector, and the emitter is grounded), using the 8050 triode working principle, when the base voltage UB has a small change, the base current IB will also have a small change. Under the control of the base current IB, the collector current IC will change greatly. The larger the base current IB, the greater the collector current IC, On the contrary, the smaller the base current, the smaller the collector current, that is, the base current controls the change of collector current.

But the change of collector current is much greater than that of base current, which is the amplification effect of triode. The ratio of IC change to IB change is called the transistor amplification factor β (β = Δ IC / Δ IB, Δ is the change) The amplification factor β of triode is generally in the tens to hundreds of times. When the triode amplifies the signal, it must first enter the conduction state, that is to establish a suitable static working point, also known as the establishment of bias, otherwise it will amplify distortion.

A resistor is connected between the collector and the power supply of the triode 8050 to convert the current amplification into voltage amplification: when the base voltage UB rises, IB increases, IC also increases, and the voltage drop of IC in the collector resistance RC is greater, so the collector voltage Uc of the triode will decrease, and the higher the UB, the lower the UC, Δ UC = Δ UB. To understand the amplification effect of triode, remember one thing: energy will not be generated for no reason, so the transistor will not generate energy, but the powerful place of triode is that it can control large current through small current.

## Circuit diagram of 8050 transistor switch (1)

1. The circuit diagram of LED controlled by NPN triode is as follows

2. Generally control LED, considering that when the voltage input is increased, the power is abundant, so that the LED is luminous, and the power consumption is saved when the input voltage is low. 10K sampling potentiometer can adjust the voltage to be controlled at will, and all resistors will be changed according to the supply voltage to make the circuit work normally.

3. The output terminal is reserved for reverse control (input high, output low).