How to distinguish the three working states of the transistor

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There are three main working states of transistors. 1. As of the state. When the transistor transmitting junction is back-biased and the collector junction is back-biased, the working state of the triode will enter the cut-off state.

This is equivalent to a closed faucet, and the water in the faucet cannot flow.

2. Amplified state. When the transistor transmitting junction is positively biased and the collector junction is reversed, it will cause the transistor to be amplified. It is equivalent to a controlled faucet, and the size of the water flowing out of the faucet is controlled.

3. Saturation state. When the transistor transmitting junction is positively biased, and the collector junction is positively biased, it will lead to a saturation state, which is equivalent to when the switch is turned on again, the outflow of water will not become larger.

To determine the working state of the transistor, it can be detected by a variety of methods. The following will introduce some commonly used methods to determine the working status of the transistor.

1. Introduction to transistors:

A transistor is a semiconductor device that consists of a base, emitter, and collector.

The working state of the transistor includes three states: cut-off, amplification and saturation.

2. Measurement cut-off status:

Use a multimeter or ammeter: Connect the test pin to the corresponding triode pin, if no current passes through the transistor and the meter shows a current close to zero, it is in a cut-off state.

Using an oscilloscope: Connect the test pins to the emitter and collector of the transistor and be cut off if the oscilloscope shows a low signal.

3. Detection amplification status:

Use Voltage Measurement: Connect the test pin to the base and emitter, measure the voltage between them, if the voltage is greater than the diode voltage drop between the base and emitter, indicating that the triode is amplified.

Using an oscilloscope: Connect the test pins to the base and collector of the transistor and be amplified if the oscilloscope displays an amplified signal waveform.

4. Detect saturation state:

Use voltage measurement: Connect the test pin to the collector and emitter, measure the voltage between them, if the voltage is close to zero, the transistor is saturated.

Using an oscilloscope: Connect the test pins to the base and collector of the transistor and be saturated if the oscilloscope shows a flat waveform in saturation.

5. Precautions:

Maintain the correct test circuit: Connect the test pins correctly to ensure the accuracy of the test circuit.

Confirm the suitability of the test signal: Select the appropriate test signal and voltage according to the type and characteristics of the transistor.

By using a multimeter, an ammeter, an oscilloscope, and an appropriate test circuit, the working state of the transistor can be determined. When conducting the test, it is necessary to pay attention to the correct connection of the test pins and the selection of the appropriate test signal and voltage.

In addition, referring to the transistor's data sheet can provide more accurate information on the operating status. When judging the working status of the triode, the safety operation procedures should be followed to prevent accidents such as circuit short circuit or current overload.

The three working states of the transistor are the cut-off state, the amplified state, and the full spine and conduction state.

Transistor amplification circuit (signal transistor):

The most typical feature of the transistor amplification circuit is that the IC max > IB, that is, no matter how the IB current changes, *IB never exceeds the maximum value of the IC, and the state at this time is the amplification state.

First of all, it is clear that when the transistor is saturated and conducted, vbe=, vce=, because it will change with temperature, humidity, etc., so it is assumed that the pants are =100 for easy calculation.

Then IC max=(5V-VCE) R1, first determine the current required on the IC according to the load to determine what R1 is.

Assuming that IC needs 47mA, then IC max=(5V-VCE) R1=47mA, VCE can reach the maximum current value when IC is the youngest hour, that is, IC max=(,R1=100, after determining the IC current value and R1 resistance value, take a look at how IB calculates, because =100, IC= *IB, you can calculate IBMAX=47mA 100=, that is to say, IB "when the transistor is in an amplified state.

Determine the resistance of R2, because when the transistor is turned on, VBE=, and the input is a 3V square wave signal, IB Max=(3V-VBE) R2=, and R2=The triode is in a critical saturation state.

We choose a commonly used nominal resistance of 10k, i.e., r2=10k, actual ib=(3v-vbe) r2=(, and ib*

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Analysis: Three working states of a transistor.

Cut-off state: When the voltage added to the transistor transmitting junction is less than the on-voltage of the pn junction, the base current is zero, the collector current and the emitter current are zero, the triode loses the current amplification effect, and the gap between the collector and the emitter is equivalent to the disconnection state of the switch, we call the triode in the cut-off state.

Amplification state: when the voltage added to the transmitting junction of the triode is greater than the conduction voltage of the pn junction and is at an appropriate value, the transmitting junction of the triode is positively biased, and the collector junction is reversed biased, at this time, the base current plays a controlling role in the collector current, so that the triode has a current amplification effect, and its current amplification factor is δic δib, and the transistor is amplified at this time.

Saturation on-state: when the voltage applied to the transistor emission junction is greater than the on-voltage of the p-n junction, and when the base current increases to a certain extent, the collector current no longer increases with the increase of the base current, but does not change much near a certain value, then the triode loses the current amplification effect, the voltage between the collector and the emitter is very small, and the conduction state between the collector and the emitter is equivalent to the switch. This state of the transistor is called the saturation conduction state.

According to the potential of each electrode when the triode is working, the working state of the triode can be judged, therefore, in the maintenance process, electronic maintenance personnel often have to take more meters to measure the voltage of each foot of the triode, so as to judge the working condition and working state of the triode.