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How to design a triode amplifier circuit



Analysis Design Requirements

How to design a triode amplifier circuit

The voltage gain can be used to calculate voltage gain, maximum output voltage can be used to set the power supply voltage.

How to design a triode amplifier circuit

The emitter current can be calculated from output power, frequency characteristics should be paid attention to when choosing a transistor.


Determine supply voltage

The first figure shows that maximum output voltage amplitude is 5V, and triode output voltage amplitude is determined by Vc pole voltage, and Vc terminal voltage should be set to about 1/2. supply voltage.

Here we set power supply voltage to 15V. To make positive and negative signal have a symmetrical change space, when there is no input signal, that is, input signal is 0, assuming that Uce is half of power supply voltage, we take it beyond horizontal line used as a reference point.

How to design a triode amplifier circuit

When input signal increases, Ib increases and current Ic increases, then voltage U2=Ic×R2 of resistor R2 increases accordingly, and Uce=VCC-U2 decreases. Theoretically, U2 can reach a maximum equal to VCC, and Uce can reach a minimum of 0 V. That is, as input signal increases, maximum change in Uce is from 1/2 VCC to 0 V.

Similarly, when input signal decreases, Ib decreases, and current Ic decreases, then voltage U2=Ic×R2 of resistor R2 decreases accordingly, and Uce=VCC-U2 increases. When input signal decreases, maximum change in Uce is from 1/2 VCC to VCC. Thus, when positive and negative changes occur within a certain range of input signal, if Uce is based on 1/2VCC, there will be a symmetrical range of positive and negative changes.


Choose a crystal diode

Things to pay attention to when using a triode:

1) Is withstand voltage sufficient

2) Is load current large enough?

3) Is speed fast enough (sometimes slow)

4) Is there enough current to control pole B?

5) Sometimes power problems can occur

6) Sometimes it is necessary to consider problem of leakage current (can it be "completely" cut off)

7) In general, gain is not considered large (my application has not yet required a high level of this parameter)


Determining emitter current Ie

By relationship between frequency response of radiator and frequency response of radiator. The emitter current of a low-signal common emitter ranges from 0.1 to several milliamps.


Determine Rc and Re values

Usually Vce is set to half VCC, Vce=Ic*(Rc+Re), Rc and Re refer to increase.


Determine value of underlying bias chain R1 and R2

We know value of Ic from Ic=β*Ib (β is usually assumed to be 100) and then we estimate current value flowing through R1, which is usually about 10 times greater than Ib. Calculate R1 and R2.

R1 and R2 are DC bias resistors of triode V1. What is DC bias? In other words, you need food to work. In order for a triode to work, certain operating conditions must first be provided, and electronic components must require power, otherwise it is not called a circuit. In working requirements of circuit, first condition must be stable, so power supply must be a DC power supply, so it is called DC bias. Why power is supplied through a resistor A resistor is like a faucet in a water supply that is used to regulate current. Therefore, three operating states of stop, saturation, and gain triode are determined by DC bias, in Fig.Unke 1 it is determined by resistors R1 and R2.


Identify coupling capacitors C1 and C2

C1 and input impedance, C2 and terminating resistor connected to output end respectively form a high pass filter. It is necessary to obtain values ​​of C1 and C2 by calculating center frequency.

C1 and C2 are coupling capacitors. Communication is transmission of signals. Capacitors can transmit signal signals from front stage to back stage because voltage at both ends of capacitor cannot change dramatically. Since voltage cannot change suddenly, voltage at output terminal will change along with input AC signal at input terminal, thereby coupling signal from input terminal to output terminal. But it should be noted that voltage across the capacitor cannot change suddenly, but it is not impossible to change either.