Triode measurement has many applications in life, and many friends are confused about triode measurement and cannot make relevant progress in triode measurement. This article will summarize the triode measurement experience from five aspects. If you are interested in triode measurement methods, you may continue to read the text.

1. On-circuit voltage detection and judgment method

(1) In practical applications, low-power transistors are mostly directly soldered on the printed circuit board. Due to the high installation density of the components, it is troublesome to disassemble. Therefore, the DC voltage block of a multimeter is often used to measure each transistor under test. The voltage value of the pin is used to infer whether it is working normally, and then to judge whether it is good or bad.

(2) Detection of high-power transistors. Various methods of using a multimeter to detect the polarity, tube type and performance of medium and low-power transistors are basically suitable for detecting high-power transistors. However, because the working current of the high-power transistor is relatively large, the area of its PN junction is also relatively large. If the PN junction is larger, its reverse saturation current will inevitably increase. Therefore, if you use the R×1k block of a multimeter to measure the resistance between the electrodes of medium and low-power transistors, the measured resistance value will inevitably be very small, like a short circuit between the electrodes, so you usually use the R×10 or R×1 block. Detect high-power transistors.

(3) Detection of ordinary Darlington tube The detection of ordinary Darlington tube with a multimeter includes identifying electrodes, distinguishing PNP and NPN types, and estimating amplification capabilities. Because there are multiple emission junctions between the E-B poles of the Darlington tube, the R×10K block that can provide a higher voltage with a multimeter should be used for measurement.

(4) Detection of high-power Darlington tube The method of detecting high-power Darlington tube is basically the same as that of ordinary Darlington tube. However, since the high-power Darlington tube is equipped with V3, R1, R2 and other protection and leakage current components, the impact of these components on the measurement data should be distinguished in the detection volume to avoid misjudgment. Specifically, it can be carried out according to the following steps: Use a multimeter to measure the resistance of the PN junction between B and C at the R×10k block, and it should be obvious that it has unidirectional conductivity. There should be a big difference between the forward and reverse resistance values. There are two PN junctions between the high-power Darlington tube B-E, and resistors R1 and R2 are connected. When using a multimeter to detect electrical blocking, when measuring in the forward direction, the measured resistance is the result of the BE junction forward resistance in parallel with the resistance of R1 and R2; when measuring in the reverse direction, the transmitting junction is cut off, and the measured resistance is ( R1+R2) The sum of the resistances is about several hundred ohms, and the resistance is fixed, and does not change with the change of the electrical barrier. But it should be noted that some high-power Darlington tubes also have diodes on R1, R2, and what is measured at this time is not the sum of (R1+R2), but (R1+R2) and two The parallel resistance value of the sum of the forward resistance of the diode.

2. Detection and discrimination electrode

(1) Determine the base. Use the multimeter R×100 or R×1k to measure the forward and reverse resistance values between every two of the three electrodes of the triode. When the first test lead is connected to an electrode, and the second test lead touches the other two electrodes successively and low resistance values are measured, the electrode connected to the first test lead is the base electrode b. At this time, pay attention to the polarity of the test lead of the multimeter, if the red test lead is connected to the base electrode b. When the black test lead is connected to the other two poles, the measured resistance is small, then the tested transistor can be judged to be a PNP type tube; if the black test lead is connected to the base b and the red test lead is in contact with the other two electrodes, the measured value is If the resistance is small, the tested transistor is an NPN tube.

(2) Determine the collector c and emitter e. (Take PNP as an example) When the multimeter is set to R×100 or R×1K, the base of the red test lead b, and the black test lead is used to touch the other two pins respectively, the two measured resistance values will be one larger , A smaller one. In a measurement with a small resistance value, the pin connected to the black test lead is the collector; in a measurement with a larger resistance value, the pin connected to the black test pen is the emitter.

3. The performance of the known model and pin arrangement of the transistor can be judged according to the following methods

(1) Measure the resistance between electrodes. The multimeter is placed in the R×100 or R×1K gear and tested according to the six different connection methods of the red and black test leads. Among them, the forward resistance values of the launch junction and the collector junction are relatively low, and the resistance values measured by the other four connection methods are all very high, about several hundred kiloohms to infinity. But whether it is low resistance or high resistance, the inter-electrode resistance of a silicon triode is much larger than that of a germanium triode.

(2) The value of the penetrating current ICEO of the triode is approximately equal to the product of the multiple β of the tube and the reverse current ICBO of the collector junction. ICBO increases rapidly with the increase of ambient temperature, and the increase of ICBO will inevitably cause the increase of ICEO. The increase of ICEO will directly affect the stability of the pipe work, so in use, ICEO pipes should be selected as small as possible. By directly measuring the resistance between the ec poles of the transistor with a multimeter, the size of the IEO can be estimated indirectly. The specific method is as follows: The range of the multimeter resistance is generally R×100 or R×1K. For PNP tubes, the black meter tube is connected to e Connect the red test lead to the c electrode. For the NPN transistor, connect the black test lead to the c electrode and the red test lead to the e electrode. The larger the measured resistance, the better. The larger the resistance between e and c, the smaller the ICEO of the tube; on the contrary, the smaller the measured resistance, the larger the ICEO of the tube under test. Generally speaking, the resistance of medium and low-power silicon tubes and germanium-based low-frequency tubes should be hundreds of kiloohms, tens of kiloohms, and more than ten kiloohms respectively. If the resistance is very small or the pointer of the multimeter shakes back and forth during the test , It shows that the IEO is very large and the performance of the tube is unstable.

(3) Measurement amplification capability (β). At present, some models of multimeters have scale lines and test sockets for measuring the triode hFE, which can easily measure the magnification of the triode. First set the multimeter function switch to the? Position, set the range switch to the ADJ position, short-circuit the red and black test leads, adjust the zero adjustment knob so that the multimeter pointer indicates zero, and then set the range switch to the hFE position and make the two short Separate the connected test leads, insert the tested transistor into the test socket, and then read the magnification of the tube from the hFE scale line. In addition: there are medium and small power transistors of this model, the manufacturer directly marked different color points on the top of the tube shell to indicate the tube's magnification β value, the corresponding relationship between the color and β value is shown in the table, but pay attention , The color code used by each manufacturer is not necessarily the same.

4. Distinguish between high frequency tube and low frequency tube

The cut-off frequency of the high-frequency tube is greater than 3MHz, while the cut-off frequency of the low-frequency tube is less than 3MHz. Generally, the two are not interchangeable.

5. Detection of line output transistor with damping

Place the multimeter in the R×1 gear and measure the resistance between the electrodes of the damped line output transistor separately to determine whether it is normal. The specific test principles, methods and steps are as follows: connect the red test lead to E and the black test lead to B. At this time, it is equivalent to measuring the resistance value of the equivalent diode of the BE junction of the high-power tube and the protection resistor R in parallel. The directional resistance is small, and the resistance value of the protection resistor R is generally only 20-50, so the resistance value of the two in parallel is also small; on the contrary, reverse the test leads, that is, connect the red test lead to B and the black test lead to E. The measured value is the parallel resistance value of the equivalent diode of the BE junction of the high-power tube and the protection resistor R. Since the equivalent diode reverse resistance value is relatively large, the measured resistance value at this time is the protection value. The value of resistance R, this value is still small. Connect the red test lead to C and the black test lead to B. At this time, it is equivalent to the forward resistance of the equivalent diode of the high-power tube BC junction in the measuring tube. Generally, the measured resistance value is also small; swap the red and black test leads, that is, the red test lead Connecting to B and connecting the black test lead to C is equivalent to measuring the reverse resistance of the equivalent diode of the BC junction of the high-power tube in the tube. The measured resistance is usually infinite. Connect the red test lead to E and the black test lead to C, which is equivalent to the reverse resistance of the damping diode in the measuring tube. The measured resistance is generally larger, about 300～∞; swap the red and black test leads, that is, connect the red test lead to C, Connecting the black test lead to E is equivalent to the forward resistance of the damping diode in the measuring tube. The measured resistance is generally small, about a few to several tens.

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