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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Prefix for testing transistors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur [an error occurred while processing this directive] The idea of using diode bridges in measuring technology, known from publications in the journal, allowed the author of the proposed article to develop a simple prefix - a kind of switching unit for controlling the parameters of bipolar and field-effect transistors of almost all types. The prefix is used in conjunction with a multi-limit DC milliammeter and an autonomous power source. It allows you to measure many parameters: the static current transfer coefficient of bipolar transistors in a circuit with a common emitter at a fixed value of the base current (10, 30, 100, 300 μA; 1,3, 10, 30 mA); initial drain current of field-effect transistors with p-n junction or built-in channel; drain current of field-effect transistors with an induced channel at a gate voltage equal to half the drain-source voltage; the steepness of the characteristics of field-effect transistors with two gates for each of them; the steepness of the characteristics of field-effect transistors when using the output of the substrate (case-substrate) as the second gate. The idea of this prefix is borrowed from [1]. Schematic diagram of the set-top box is shown in the figure. Transistor VT1 and resistors R1-R8 form a stable current source to power the base circuit of the bipolar transistor under test, the outputs of which are connected to the X1-X1 sockets. The current value is set by switch SA5. Diodes VD6, VD14 and resistor R9 determine the bias in the source circuit of the field-effect transistor. Dividers R10, R11 and R13-R31 provide bias on the first (32) and second (XNUMX) gates.
The voltage at the first gate (socket X5) must be equal to the voltage drop across the diodes VD5, VD6. The same voltage should be at the connection point of resistors R12, R13. The polarity of the supply voltage, depending on the type of bipolar (field-effect channel) transistor, is set by switch SA2. At the same time, thanks to diode bridges on diodes VD1 - VD4 and VD7-VD10, it was possible to do without polarity switching in the base and collector (drain) circuits of the transistor under test. Switch SA1 - biscuit, SA2 - type P2K or similar for two positions with two groups of contacts. Buttons SB1-SB3 - MP9 or others. Diodes VD1-VD4 can be any silicon with a maximum forward current of 40-60 mA and a reverse voltage of at least 30 V, VD5-VD10 - also silicon, designed for forward current up to 1 A with a reverse voltage of at least 30 V. Diodes VD1-VD4 and VD7-VD10 can be replaced with blocks of the KTs402-KTs405 series corresponding in parameters. The transistor (it can be, in addition to that indicated on the diagram, KP302V, KP302G) must be installed on the heat sink, since when checking powerful transistors or setting the base current to 30 mA, significant power will be dissipated on it. The measuring device connected to the attachment is multi-range of any type with a maximum current from tens to hundreds of milliamps. The power supply must provide a constant voltage of 4 V and a current of up to 5 A - in case of controlling high power bipolar transistors. To control field-effect transistors with an induced channel, the supply voltage must be 1 ... 9 V, therefore, it is necessary to install an output voltage switch in the power supply, which, by the way, does not have to be stabilized at all. Setting up the set-top box begins with the selection of resistors R1-R8, controlling the current between the sockets X1 and X1 and setting the movable contact of the SA10 switch to the appropriate position. The selection of each resistor is completed if the current does not differ by more than 10% from the desired one. After that, resistors R13, R5 are selected with such resistance that the voltage across them is equal to or slightly less than the voltage drop across the diodes VD6, VDXNUMX. To make it convenient to connect the tested transistors to the attachment, it is necessary to make adapter panels with flexible leads ending in plugs inserted into the attachment sockets. For power transistors, single conductors should be made with alligator clips and plugs. Before connecting the transistor for control, it is necessary to set the structure (channel type) with the switch, connect a milliammeter with the maximum measurement limit, turn on the power source. The base current value of 10 and 30 mA should be set with the SA1 switch only at the time of measurements with the SB 1 button pressed, and the milliammeter measurement limits should be switched when this button is released. Bipolar transistors are tested in the following sequence. 1. Switch SA2 to set the desired structure - p-n-p or n-p-n. 2. Connect the milliammeter, power supply and transistor to the appropriate sockets. 3. Switch SA1 to set the required base current. 4. Press the SB1 button and determine the collector current on the milliammeter scale, and then calculate the base current transfer coefficient using the formula h21E = Ik / Ib. If the pinout of the transistor pins is unknown, you must first determine the base and structure of the transistor using an ohmmeter using a well-known method. The conclusions of the emitter and collector are determined by the maximum value h21E. But what is the sequence of checking field-effect transistors. 1. Switch SA2 to set the type of channel. 2. Connect milliammeter and power supply. 3. MIS transistor with a built-in channel or a transistor with a p-n junction, connect to the corresponding sockets: source - with socket X7 ("I"), substrate (case-substrate) - with X8 ("P"), gate - with X5 ( "31"), stock -cX4 ("C"). 4. Press the SB1 button and determine the value of the drain current by the deviation of the milliammeter needle - it must correspond to the Ic parameter given in the reference books. 5. Press the buttons SB1, SB2 simultaneously and determine the new value of the drain current. 6. Calculate the slope of the characteristic according to the formula S = lc / U, where lc is the difference between the currents measured according to paragraphs 4 and 5, mA; U - voltage drop across the resistor R10, V. Compare the obtained value with the reference data. 7. Connect the shutter output to the X5 socket, and the substrate (substrate case) output to the XXNUMX socket. 8. Press the SB1 button and determine the drain current, then press SB1, SB2 simultaneously and determine a new current value. 9. Calculate the slope value along the substrate using the formula sn = Ic/u, where Ic is the difference between the currents measured according to clause 8, mA; U - voltage drop across the resistor R10, V. In [2], the issues of using a substrate (substrate body) as a second shutter are considered, but this parameter is not given in reference books. When checking the MIS transistors with an induced channel, make the connections as in the previous case, but connect the gate output to socket X6 ("32"). Measure the drain currents by first pressing the SB1 button, and then simultaneously pressing the SB1 and SB2 buttons. Calculate the value of the slope for the first gate, given that U is the voltage drop across the resistor R13. To determine the slope on the substrate, this pin must be connected to socket X5 (31). As in the previous case, first press the button SB1, and then simultaneously on SB1 and SB2. After that, the slope value is calculated, given that U is the voltage drop across the resistor R10. When controlling transistors of this type, it should be remembered that the drain current measured according to the first point must correspond to the current determined by the family of drain-gate characteristics given in reference books (Usi - supply voltage; Usi = 0,5 Usi). To control double-gate field-effect transistors, you must first set the channel type with the SA2 switch, and then connect the transistor outputs to the console in the following order: source, first gate, second gate, drain. By manipulating by pressing the buttons SB1, simultaneously on SB1 and SB2, simultaneously on SB 1 and SB3, measure the drain currents and calculate the value of the gate slope. Checking such transistors is possible only in enrichment mode. Literature
Author: V.Kalendo, Minsk, Belarus
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