Keywords: back pressure test circuit diagram
Author: Wang Fan
Here is a small instrument that can measure the reverse breakdown voltage of the transistor using a normal meter, which measures the range of 0 to 1000V and can meet the general measurement requirements. Circuit principle
The circuit of the transistor reverse breakdown voltage tester is shown below. The circuit can be seen as a high-voltage constant current source to the feed to the tube, and use the multimeter to directly read the reverse breakdown voltage of the tube. The circuit is essentially a feedback DC converter that converts the 3V DC voltage to the main high voltage direct current of about 1200V. After the circuit is powered, since the coupling feedback between the windings N1 and N2 of the transformer T is strongly oscillated, the oscillating voltage is boosted by the Wound Group N3, and the VD2 is rectified to the capacitor C2, so that the C2 can obtain approximately 1200V DC high pressure. This high pressure is applied to the high value resistor R2 to the pending tube, so that the pipe is broken, and the multimeter at both ends of the tube to be tested can directly read the reverse breakdown voltage of the tube. Since the R2 resistance value is large, it plays a constant current source, and the current is small when breakdown, and does not damage the tube to be tested.
2. Component Selection and Making VT use v (br) CEO ≥ 60V, ICM ≥ 0.8a silicon NPN triode, such as 2Scl008, etc., β≥50. VD1 can be used in a common 1 N4148 type silicon switching diode, and VD2 requires a quick recovery diode having a back pressure greater than 1500V, such as FRL08, and the like. Rp is WSW type organic solid core fine-tuning potentiometer, R1 is RTX-1kΩ / 0.125 W carbon film resistor, R2 RJ 1mΩ / 1W metal film resistor. C1 is a CD11-100μ / 16V electrolytic capacitor, C2 with a high pressure wafer capacitor with 1000 pF / 2 kV. The transformer T requires self-made: with an EE20 core with an initial magnetic magnetic rate of 1500 or 2000, a supporting skeleton is wound, and N1, N2, and then wound N3. N1, N2 with φ0.35mm enameled lines around 10, central tap; N3 with φ0.17mm high-strength paint wiring around 260. The layer must be an insulated tape to prevent internal voltage breakdown. Since the circuit operating current is small, the number of coil turns is small, there is no magnetic saturation problem, so the magnetic core is not needed. When winding and wiring, you should pay attention to the same name end of the winding, that is, the coil end (the "•" · "terminal in the figure), and the same name is not reversed when wiring. After the magnetic core is wound, we wrap two laps with a tape. X1 ~ X4 is 4 terminals, X1, X2 for receiving tube, X3, X4 used to serve the 10,000-purpose table. The printed circuit board of the tester is shown below. The printed circuit board is 50 mm × 30 mm. The power source g is used in two sections of the 5th, and the case enclosure is preferably made of organic glass plate. When debugging, in X3, X4 pick up the DC 2500V file of the 500-type meter, the power switch S is closed, and the secondary screwdriver is fine-tuned RP to make the readings of the multimeter at around 1200V. At this time, the collector current of the triode VT is about 200 mA. If the voltage is only about 100V, it means that the coil is connected to the same name, as long as the two ends of the winding N3 are called. When measuring, as long as the tube to be tested from X1, X2, the number of tables is shown in the x3, X4 terminals, the number of tables is the reverse breakdown voltage of the tube. Use this device to measure the reverse breakdown voltage of the crystal diode, the reverse breakdown voltage of the crystal triode. Such as: V (br) CEO, V (Br) CEO, etc.
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