The two functions of the DC power supply in the amplifier circuit
The DC power supply in the amplifying circuit is one of the most basic conditions for the working of the amplifying circuit. The establishment of the working point required for the working state and the power required for the amplified signal during amplification. If there is no DC power supply, no matter how good the amplifier is, it will not produce any effect. , almost like the relationship between fuel and internal combustion engine, if there is no fuel internal combustion engine can only be a static display.
There are two main functions:
1. Establish a suitable quiescent operating point for the transistor
As we all know, the basic task of the amplifier is to amplify the signal without distortion. To prevent the signal from being distorted, a suitable working area must be selected. Although the triode has three working states, the amplification state, the cut-off state, and the saturation state. But only when working in the amplified state, the base current Ib can control the collector current Ic, Ic=βIb, in the cut-off state, the triode does not work and no current flows through the three poles. When it is saturated, although the three electrodes have current but At this time, the collector current is approximately equal to Vcc/Rc. If the base current cannot control the collector current, the signal cannot be amplified. Then, in order for the amplifier to amplify normally, the tube must first be in the forward biased state of the emitter junction and the reverse biased state of the collector junction. Otherwise, when working in the other two states, the model will be distorted.
2. The load connected to the amplifier needs to consume energy, and the energy cannot be provided by the signal source, but must be provided by an external circuit. On the other hand, the amplifier circuit itself will also consume energy, resistance PN junction, etc., and the DC power supply acts as a provider of energy.
Since it is an amplifying circuit, it is accompanied by current amplification or voltage amplification or both voltage and current amplification, that is, the power is also enlarged, where does the energy come from? Of course it is provided by the DC power supply!
In order to amplify the positive and negative half cycles of the AC signal without distortion and prevent crossover distortion, the DC power supply must provide a suitable static operating point for the amplifying circuit, that is, provide a suitable initial bias (requires the cooperation of resistors, diodes and other components) .
In short, whether it is a discrete transistor or an integrated op amp, it is an active device. Without a DC power supply, it is like a car without gasoline!
