How many ways can I judge whether a transistor is good or bad?

Electrical and electronic knowledge points, the simplest way to judge the quality of the transistor, simple and easy to understand.

1. Insert a successful circuit into the trial, 2. Use a multimeter to measure its open circuit and short-circuit pins, 3. See whether there are major defects in the appearance. 4. Test with a simple circuit: put your finger on the BC pole (the dry finger is a little wet), string a light-emitting diode in the E pole, and use DC5V for the power supply voltage, which can be estimated.

First, a simple way to judge the quality of the triode: first look at the type of triode, judge whether it is a silicon tube or a germanium tube, according to the characteristics of the type of triode, use the unidirectional conductivity of the pn junction in the triode, use the instrument universal meter, check the forward and reverse resistance of the pn junction between the poles, if the difference is large, the tube is good, if the forward and reverse resistance is large, it means that there is an open circuit inside the tube or the performance of the pn junction is not good. If the forward and reverse resistance is small, it means that the tube has a short circuit between the poles or a breakdown.

Give Lichai a picture to you again, and you'll understand.

Because the input of the TTL gate is input from the emitter, if it is floating, the triode at the input is cut-off, which is the same as the input high level (i.e. 1), which is equivalent to input 1. If you look at the internal circuit of the TTL inverter, you will know the limb belt type.

The quality of the transistor can be judged by other measurement methods such as DC parameter measurement method and AC parameter measurement method.

DC parameter measurement method is a common triode measurement method, which carefully judges the working state and quality of the transistor by measuring its current and voltage parameters. The AC parameter measurement method is a method used to test the amplification performance of a triode, by inputting an AC signal and measuring the output signal to evaluate the quality of the transistor. In addition to DC and AC parameter number measurements, there are a number of other methods that can be used to detect the quality of a triode, including:

Short circuit test, open circuit test, insulation test.

The three working states of the transistor

1. Cut-off status

When the voltage of the transmitting junction is less than the on-voltage of the PN junction, the base current is zero, the current flowing through the collector and the emitter is zero, and the transistor does not have the effect of amplifying the signal. When the transistor is used as a switch, it is in the open state, that is, it works in the cut-off state. The shape and working area of the transistor are shown in the figure below.

2. Amplified state

When the voltage of the transmitting junction is greater than the on-voltage of the pn junction, the transmitting junction of the triode is in the forward bias state, and the collector junction is in the reverse bias state, and the current flowing through the collector of the triode has a certain relationship with the base current: IC= *ib, where is the current amplification factor. The transistor plays a role in amplifying the base current, and this state is called the amplification state of the transistor.

In this state, the transistor has three types of circuits, namely common base amplifier circuit, common emitter amplifier circuit and common collector amplifier circuit.

3. Saturation state

With the continuous increase of the base current, the collector current IC no longer increases with the increase of the base current IB, then the triode loses the current amplification effect, and the collector and the emitter are in a conduction state, which is the saturation conduction state of the triode. When the transistor is used as a switch, it is in the on-state, that is, it is working in the saturated state-on.