| 摘要 |
PURPOSE:To execute efficiently an in-circuit test by providing a controlling circuit for controlling the base potential of an output TR of an emitter coupling circuit having an emitter follower output stage. CONSTITUTION:The base potential of output TRs 25, 26 is controlled by providing a voltage controlling circuit 40. At the time of a test, when a voltage for turning on a TR34 is applied to a control signal input terminal 37, as for a current of a differential input amplifier 1 for executing a logical operation, in addition to a current of a usual time, a current flowing into a low potential power source VEE6 through the TR34 and a resistance 35 from a high potential power source VCC24 is applied, and a large voltage drop is generated in resistance 9, 10. As a result, the output TRs 25, 26 are both turned off, and both logical outputs of output terminals 8a, 8b become logic '0'. Accordingly, when testing other logical output connected to the terminals 8a, 8b, an output state of this logical output exerts no influence on the test.
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