In-circuit transistor beta test and method

An in-circuit test device for testing the gain of a transistor comprising:

• constant current source means coupled to the emitter of said transistor for generating first and second bias currents sufficient to forward bias the base/emitter junction of said transistor;
• operational amplifier means having a first input coupled to ground potential, a second input coupled to the base of said transistor and feedback resistance coupled to said second input and the output of said operational amplifier means such that output voltages are produced at said output of said operational amplifier means in response to said first and second bias currents which are substantially proportional to the current flowing through the base of said transistor and the voltage at the base of said transistor is maintained at approximately ground potential;
• means for coupling the collector of said transistor to ground potential so that the collector/emitter voltage is substantially equal to the base/emitter voltage to prevent said transistor from going into saturation;
• whereby the difference in said output voltages divided by said feedback resistance provides an indication of the gain of said transistor when compared to the differences in said first and second bias currents.

A method of in-circuit testing to determine the beta of a transistor comprising the steps of:

• connecting the collector of said transistor to ground potential;
• generating a first and second constant current level in the emitter of said transistor sufficient to forward bias the base/emitter junction of said transistor;
• maintaining the voltage of said base of said transistor at approximately ground potential such that the voltage drop between said collector and said emitter is approximately equal to the voltage drop between said base and said emitter;
• measuring the base current of said transistor by detecting the voltage drop across a resistance coupled to said base of said transistor;
• determining the difference between base currents measured for each of said first and second constant current levels generated in said emitter lead of said transistor;
• determining the difference between said first and second constant current levels generated in said emitter lead of said transistor;
• comparing said the difference between said base currents and said difference between said first and second constant current levels to determine the beta of said transistor.

A method of in-circuit testing of a transistor comprising the steps of:

• maintaining the voltage between the collector and emitter of said transistor at a level sufficiently high to prevent saturation;
• generating a first and second constant current in said emitter of said transistor;
• measuring first and second base currents of said transistor for said first and second constant currents generated in said emitter;
• determining the difference between said first and second base currents and the difference between said first and second emitter currents;
• and
• calculating the beta of said transistor from the difference between said base currents and the difference between said emitter currents.

A process of in-circuit testing to determine the gain of a transistor which is coupled to other components in a circuit and to eliminate the effects of said components comprising the steps of:

• providing at least two levels of d.c. signal to the emitter of said transistor;
• measuring at least two levels of base signal corresponding to said at least two levels of d.c. signal provided to said emitter lead;
• determining the difference between said at least two levels of d.c. signal provided to said emitter lead to produce an emitter difference signal;
• determining the difference between said at least two levels of base signal to produce a base difference signal;
• comparing said emitter difference signal an said base difference signal to determine the gain of said transistor.

An in-circuit test device for testing transistors in which the base, emitter and collector leads of said transistor are connected to various components on a circuit board under test comprising:

• means for biasing said transistor through said emitter lead at a predetermined emitter current level;
• means for maintaining said collector lead at a first predetermined voltage level;
• means for maintaining said base lead at a second predetermined voltage level so that a preselected voltage transition is produced between said collector lead and said emitter lead;
• means for determining the current level in said base lead to calculate the gain of said transistor by comparing the predetermined emitter current level with the current level in said base lead.

A method of in-circuit testing to determine the beta of a transistor comprising the steps of:

• maintaining the voltage level of the base of said transistor at approximately ground potential;
• generating a first and second constant current level in the emitter of said transistor sufficient to forward bias the base/emitter junction of said transistor;
• maintaining the voltage level of the collector of said transistor at a first predetermined potential such that a voltage drop between said collector and said emitter is sufficient to prevent said transistor from saturating;
• measuring the base current of said transistor by detecting a voltage drop across a resistance coupled to said base of said transistor;
• determining the difference between base currents measured for each of said first and second constant current levels generated in said emitter of said transistor;
• determining the difference between said first and second constant current levels generated in said emitter of said transistor;
• comparing said the difference between said base currents and said difference between said first and second constant current levels to determine the beta of said transistor.