Author: Liu Jing
The DC amplification coefficient of the crystal triode is an important parameter indicating its enlargement. According to the working current requirements of the triode in the circuit, the HFE of the triode is selected, which is conducive to the full use of the triode and the normal operation of the circuit. Small power triode HFE can be easier to measure, but the measurement of medium-high power triode HFE is not easily done. The author makes an adjustable power supply, add a multi-block IC current, the HFE measuring circuit under the IC current, which is successfully solved the HFE measurement problem of large medium and small power crystal triodes, especially high-power crystal triodes, and the selection of crystal triodes when electronic production It is convenient to provide. Its circuit main feature is: (1) IC current is divided from 3mA to 3A, and the current span is 1: 3 to 3.3, and the uniformity of IC current is improved. (2) When the header is full of HFE, the supply voltage is 10V; when the supply voltage is 5.3V (silicon tube) and 5.1V (tube), the header is full of HFE is 600; when the supply voltage is 19.4V (Silicon tube) and 19.8V (tube), the header is full of HFE is 150. (3) The same crystal triode is subjected to the size of the HFE at a multi-stop current, which can be roughly judged. (4) The dial scale of the header is 30 or 300, which is conducive to Fe and current reading. As shown in Figure 1, it mainly has three parts of the power supply portion, the measuring circuit of the HFE and the base bias resistance. The following is a presentation.
I. Regulated power part
1. Make a steady power supply board as shown in Figure 2 and assemble the components in accordance with the requirements.
2. The power transformer power is 100W, the core section is 28mm × 40mm, the primary 220V uses φ0.47mm ~ 0.51mm enameled wire by 990, secondary 30V with φ1.2mm enameled wire by 143.
3. Tripartic regulator integrated circuit LM317 and high power tubes are mounted on the heat sink, and the LM317 is mounted on the printed circuit board copper foil surface.
Be
HFE measuring section
1. Measurement of the internal resistance of the meter can be used inside the high-precision digital multi-purpose table test head, and the internal resistance can also be measured according to the shunting method shown in Figure 3. The podium potentiometer RP makes the header indicate fullness, and then cooperate with the switch S, rotate the variable knob on the resistor box, so that the measured watch head finger should be stopped at 1/2, and the resistance box resistance value of this at this time is measured in the measurement of the head-in-headed Ri.
2 Measuring the sensitivity of the header Measures the header sensitivity IM as shown in Figure 4.
3. Current split by closed-circuit tap is convenient to calculate, here is a mesh sensitivity IM = 1mA, ie 0.001A, head head total resistance Rm = 400Ω, current is 7 stops: 3A, 900mA, 300mA, 90mA, 30 mA , 9mA, 3 mA, expressed in I1 to i7, respectively. The deer is shown in Figure 5, which is as follows:
Because I7 = IM + ISIS = I7-IMIN × RM = RS (I7-IM) (1) RS = IM × RM ÷ (I7-IM) = 200Ωr1 (I1-IM) = IM (RM + RS-R1) I1RI = IMRM + IMRS (3) will be (1) into (3):
I1R1 = RS (I7-IM) + IMRSI1R1 = RSI7R1 = (RS × I7) ÷ I1 = 200Ω × 0.003A ÷ 3A = 0.2ωR1 + R2 = RS × I7 ÷ I2 = 0.6 ÷ 0.9 = 0.67Ω Similarly, can be obtained The resistance of R3, R4, R5, R6, R7 is:
So R2 = 0.47Ω R3 = 1.33Ωr4 = 4.67Ω R5 = 13.3Ωr6 = 46.7Ωr7 = RS- (R1 + R2 + R3 + R4 + R5 + R6) = 133.3Ω 3. Determination of the silicon tube of base bias resistance Vbe = 0.6V 锗 管 VBE = 0.2V When the head is full of HFE = 3003A gear test silicon tube RB = (VC-VBE) ÷ IB = 10-0.6 ÷ 3/300 = 940Ω (IB = Ib / hfe) The rest Site is 3.13K, 9.4K, 31.3K, 94K, 313K, 940K mean tube RB = (Vc-Vbe) ÷ IB = 10-0.2 ÷ 3/300 = 980Ω The rest of the gear is 3.26K, 9.8K, 32.6K , 98K, 326K, 980K regulator power part components have no special requirements, and can be selected according to the map. The HFE measuring section, the current meter shunt resistor applies a manganese copper resistance wire to be wound, preferably a multi-purpose bridge to measure the resistance to ensure that each gear current error is less than 3%. Each transistor bias resistor application 1 / 4W metal film five-ring precision resistance. The gear selection switch should select three knives seven rotary switches.
PNP, NPN conversion switch, with double knife double throwing button switches. Silicon, germanium conversion with single knife double throw button switches. When the actual measurement, the small power pipe is measured, and the high power pipe is measured. When the small power pipe is used to measure the large current gear measurement, the transistor will cause the transistor to be burned, and the high power pipe is measured, it will not be correct. HFE value. The circuit sets the ICEO measurement button switch S3. This switch is a normally closed switch. When the Iceo is measured, the switch reading is ICEO. Braztees are required to subtract their values in the IC because the Iceo is very large and accurately testing HFE. To simplify the circuit, when the NPN tube is measured, the head string is power supply positive extreme, and the current is IC + IB. When the PNP tube is measured, the head is string into the emitter, the display current is IE, due to IE = IC + IB, the sensing NPN, the PNP measurement result is consistent, the measured HFE value does not care, the reading is minus 1.
When using a regulated power supply, the circuit current can be displayed directly. At this time, it is necessary to pay attention to the position of the current subtocial switch should be appropriate, and the anti-burn-up header (generally should be put first in the maximum current gear).
Our other product:
