Regulatory diode tester ----- zener test circuit

Keywords: diode test circuit The instrument can check if the voltage regulator diode up to 200V is working properly. And can find the reverse breakdown voltage of the regulator diode (note that the voltage regulator is only 2V to 5.6V, more than 5.6V strictly speaking "snow" collapsed diode "). The voltage stability of the regulator diode is determined. The internal resistance and temperature coefficient. The above value is measured at different currents for this tester. The internal resistance formula RINT = DV / DI, DI is the difference between the two currents (such as 10 mA and 5 mA. Difference 5 mA), and test the voltage under two currents (such as 6.6V and 6.3V) can be determined. DV (6.6V-6.3V = 0.3V) thus calculates the value of RINT (0.3 / 0.05 = 60Ω). The temperature coefficient of the regulator diode is related to the reverse voltage: a diode below 5.6V. The temperature coefficient is negative, equal to 5.6V diode temperature coefficient is 0, and more than 5.6V is positive (not all varieties). The method of measuring the temperature coefficient is to measure the voltage on the diode. The diode is passed through a constant current (10mA). Temperature of the diode. Tester has three small transformers. There are two voltages: 0V ~ 20V and 0V to 200V, and additional transformer TR3 is used to generate DC 5V power supply to supply digital voltmeter components. Switch S2.A-S2. D is the four-knife voltage selection switch, the intermediate position is "shutdown". 1.20V voltage block The transformer TR1 is powered by the 20V blocking bridge rectifier of the switch S2.a. Generate a 32V DC voltage. The BD244 transistor constitutes a constant current source generator, and the switch S1.A changes the emitter resistance. To produce three currents of 5 mA, 10 mA and 50 mA. The current generated by the BD244 can be applied by the following formula: iconst = V2 (3.4V) -vee (0.6V) / emitter resistance. S2.c is also in 20V. 2.200V voltage block The switch S2a is rotated to a 24V AC voltage winding of the transformer TR2. The voltage rose from 24V to 230V. That is, a usual 230 / 24V transformer. Its bridge rectifier generates 250V DC voltage, and the BF470 transistor also constitutes a constant current source output. The same S1.B also changes the emitter resistance. Generate three currents: 1 mA, 5 mA and. 10mA (see the above calculation), at 10 mA and 200V. It means that BF 470 must dissipate 2W power (for 200V regulator tubes) when the BF 470 outputs short-circuit. The tester can also measure the insulation of ordinary diodes and inflatable regulator tubes. The digital voltmeter gives the temperature drift of the voltage stabilizer voltage and the voltage. The voltage range selection switch S2.D converts the decimal point of the voltmeter in 19.99V and 199.9V.

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