Digital multimeter to judge transistor type and DC magnification
The transistor has two PN junctions, which are the same as the unidirectional conduction characteristics of the diode. When using a multimeter to detect the transistor, the transistor can be regarded as two common-base diodes, and the NPN type can be regarded as a common-cathode double diode, as shown in the figure .
Of course, the transistor is not a simple structure as shown in the figure, because it has a current amplification effect, which is significantly different from the finished common anode (or cathode) diodes on the market, because the latter is two common anode (or cathode) diodes. The diode explained has no current amplification capability. In engineering practice, the two PN junctions of the transistor are often measured with a digital multimeter "diode", and the type of the transistor is judged according to the value displayed on the LCD. The specific steps are shown in the figure:
Steps to judge the transistor type with a digital multimeter:
At present, there are common anode and common cathode diodes on the market. Although the above test methods can determine the diode inside the device, it cannot be determined as a transistor. Therefore, using this method, it cannot be determined that the 3-pin component containing two PN junctions must be a transistor.
Warm reminder: In the above steps of judging the transistor type, the silicon tube is between 500 and 700, and the germanium tube is between 200 and 300. This value represents the forward conduction voltage of the PN junction inside the transistor, in mV.
Measure the DC magnification of the transistor with a digital multimeter:
Although the above test methods and steps can determine whether a transistor is a PNP type or an NPN type, it cannot determine which is the collector and which is the emitter. Using the "hFE" block function of the digital multimeter, while measuring the DC magnification of the transistor, the name of each pin can be determined, which can be described as "killing two birds with one stone".
Common small-signal transistors S8050 and S8550, S1815 and 1015 are paired transistors. The method for measuring the DC amplification factor is simple:
①Turn the rotary dial to "hFE" gear;
②Insert the transistor correctly into the jack next to the "hFE" block, and the LCD reading is the DC amplification factor: that is, the β value of the transistor.
It should be pointed out that there are currently two main schools of transistor pin ordering in the world: one is the American order; the other is the Japanese order. As far as small power tubes are concerned, the American sequence of the three pins of the transistor is e-b-c, and the Japanese sequence is e-c-b. Regardless of the ordering, when the transistor pins face down and the text faces the viewer, the pins on the left are e-pins.
