Patent GB-944385-A (GB)
Title: Improvements in and relating to apparatus and methods for testing transistors
IPC: G01R31/26
Filed: 1960-05-09
Abstract: 944,385. Transistor testing- PHILCO CORPORATION. May 9,1960 [May 8,1959], No. 16295/60. Heading G1U. A transistor test apparatus comprises means for biasing the transistor to non-linearity between an applied harmonic-free alternating signal and the resultant collector signal, and for comparing and/or determining the respective components of base current and collector current at second or higher harmonics of the input current as a measure of the beta or current amplification factor of the transistor; means also being provided for establishing continuity test circuits for detecting base to emitter or emitter to collector shortcircuits and for measuring the collector current I CB0  at a given base to collector bias with the emitter open circuited. In Fig. 2 the base of a PNP type test transistor (not shown) which may be incorporated in a printed circuit is connected through contact a of switch 50 and resistor 24 to harmonic free oscillator 20 of low impedance having variable output control 22; whose other terminal is connected through contact a of switch 52 to the emitter and through the contact c of switch 50 and contact a of changeover switch 56, contact b of switch 52, and capacitance shunted resistor 60 to the arm of switch 54 selecting alternative positive bias voltages over resistors 62, 64 from source 28; returned to the collector of the transistor through contact b of switch 56, contact b of switch 50, and resistor 30. The junction of resistors 60 and 62 or 64 is connected to the base of transistor 66, whose emitter is returned to the bias taps of resistors 62 or 64 over arm b of switch 54 and whose collector is connected through indicator lamp 70, resistor 72 or 74, and arm c of switch 54 to the negative pole of source 28. An emitter to collector shortcircuit of the test transistor develops a voltage across resistor 60 and 62 or 64 to open transistor 66 and light the lamp. Switch 32 enables amplifier 34 tuned to the second harmonic of the oscillator frequency and detector 38 to be connected alternatively across collector and base load resistors 30, 24, and the detector output is connected over arm d of switch 54 and contact d of switch 52 to meter 40 earthed over contact c of switch 52, so that the ratio of the collector to base load voltages at the second harmonic of the input frequency generated in the test transistor due to its biased nonlinear condition is a measure of its beta value (Fig. 1, not shown). The oscillator output may be adjusted to give full scale reading for collector load voltage, so that the meter may be calibrated directly to read beta values on base load voltage measurement. To test for base to emitter shortcircuits, switch 50 is changed over to disconnect the base from resistor 24 and oscillator 20 and connect it over contact c of the switch 50, contact a of switch 56 and contact b of switch 52 to resistor 60 while contact b of switch 50 connects the emitter to negative bias over contact b of switch 56, so that no current normally flows in resistors 60, 62, but on a shortcircuit between base and emitter an appreciable current will flow so that the voltage drop opens transistor 62 and lights lamp 70, (Fig. 3 not shown). For measurement of I CB0 , the collector current for given base to collector bias with emitter open circuited. switch 50 is restored and switch 52 is changed over so that the emitter circuit is broken at contact a while contact d connects the meter directly to the base over contact a of switch 56, contact c of switch 50, the oscillator output circuit, resistor 24, and contact a of switch 50. Contact c of switch 52 connects the meter in series with resistor 80 and contact b of switch 52 to one end of resistor 60, (Fig. 4 not shown) so that the meter reads I CB0  directly for an increased base to collector bias in the third position of switch 54. This switch may have additional positions for selecting further values of bias for beta measurement, for disconnection of bias, and for checking the several bias voltages using meter 40. Switch 56 may be changed over for testing NPN type transistors.