# Primary analog circuit: 8-4 controlled source circuit

Time：2020-10-26

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With the characteristic that the output of ideal operational amplifier can output any voltage and any current, we can use ideal operational amplifier to build a variety of controlled power supply. Of course, in practical use, the output of op amp should not exceed the maximum value given in its data manual.

## 1. Voltage controlled voltage source (VCVS)

Both the inverted amplifier and the in-phase amplifier can build a voltage controlled voltage source. Taking the in-phase amplifier as an example, we redraw the circuit diagram as follows:

Figure 8-04.01

The output voltage is expressed as follows:

Its output voltage is voAnd input voltage ViIt is linear, and can be configured by RfAnd r1To adjust the coefficient K value of the controlled voltage source.

## 2. Voltage controlled current source (VCCS)

The circuit diagram of voltage controlled current source is shown in the following figure:

Figure 8-04.02

Its load RLDirectly connected to the feedback path, the output current flowing through the load is expressed as follows:

Its output current is IoAnd input voltage ViIt is linear, and can be configured by R1To adjust the coefficient K.

## 3. CCVs

The circuit diagram of the current control voltage source is shown in the following figure:

Figure 8-04.03

The output voltage expression is as follows:

Its output voltage is voAnd input current IiIt is linear, and can be configured by R1To adjust the coefficient K.

## 4. CCCS

The circuit diagram of the current source is shown in the following figure:

Figure 8-04.04

The analysis of its work is as follows:

The in-phase input of the circuit is grounded. According to the virtual short characteristic of the ideal operational amplifier, the reverse input is also zero potential. Input current IiFlow through R1After that, the potential at point a is negative, so R2The current direction in the is from left to right and flows through the load RLThe output current expression is as follows:

Its output current is IoAnd input current IiIt is linear, and can be configured by R1And r2To adjust the coefficient K.

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