In-Circuit Transistor Leakage Current Testing

An instrument capable of measuring leakage current of transistors while the trarisistor remains in the circuit was developed. This instrument gives an accurate leakage current measurement in a large variety of circuits as well as being simple to operate, lightweight, battery powered, and portable for use in the field. This was accomplished by the measurement of the transistor leakage current ICBX, which is the collector current when both the collector and emitter junctions of the transistor are reverse biased. This particular leakage current was chosen because it is nearly independent of the gain parameters of the transistor and a very close approximation to the fundamental leakage current ICBO. The present instrument measures leakage currents as low as 1 µa with a collector load resistance down to 500 Ω. At present, an accurate instrument is not commercially available for measuring transistor leakage current in the circuit. The results presented in this paper indicate a method for adding the capability of measuring in-circuit transistor leakage current to future transistor testers.