GB1508774A - Apparatus for testing voltage regulators - Google Patents

Abstract

1508774 Testing electrical apparatus LUCAS ELECTRICAL Ltd 14 April 1975 [20 April 1974] 17430/74 Heading G1U In testing a voltage regulator, an increasing voltage is supplied thereto and at the operating point, when a semi-conductor switch in the regulator turns off, a switch in the test apparatus prevents further rise in the voltage which is indicated. The automobile voltage regulator, Fig. 1 (not shown), has three terminals +, -, F, normally connected to an alternator. These are connected to terminals 11a, 12a, 13a in the test apparatus. If the voltage supplied to the regulator at terminal 11a is below its operating point, terminals 12a, 13a are connected together through a transistor (19) in the regulator. Thus, transistors 27, 28 are off, allowing capacitor 29 to charge towards the voltage (45 volts) or line 23 derived from an A.C. rectified supply 25, 26, 20. At the switching voltage, the path from 12a to 13a is opened and the regulator oscillates providing a current through resistor 36 (simulating the alternator field winding) to turn on transistor 27, 28 allowing the capacitor 29 to discharge and causing the voltage at terminal 11a to fall. Thus the voltage supplied to the regulator oscillates about a mean level close to the operating voltage of the transistor switch (19) in the regulator. This voltage is passed to a meter 45 which because of its inertia, indicates the mean level. Zener diode 52 has a 15 volt threshold, thus if a correctly operating 12 volt regulator is being tested, the diode remains non-conducting, ensuring that transistors 55, 56 are off. In this state base current for transistor 61 flows through lamp 58 (which does not glow at such a low current) and the transistor turns on, breaking down the 12 volt Zener diode 46 and turning on transistor 43. The regulator voltage is thus transferred to the meter 45 via transistor 61, diode 46 and transistor 43 with a 12 volt back-off. Adjustment of resistor 47 calibrates the meter. If a 24 volt regulator is tested, the voltage at terminal 11a rises above the breakdown voltage of Zener diode 52 and the transistors 55, 56 are turned on, illuminating the lamp 58 and turning off transistor 61. A second 12 volt Zener diode 41 is now introduced between the meter 45 and the terminal 11a, providing a total 24 volt back-off. Resistor 42 is used to calibrate in this case. The meter 45 thus is required to indicate only the excess of the operating voltage above the nominal values 12 volts or 24 volts and consequently measures the same order of voltage in both cases, ensuring similar sensitivity.