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Constant Current Load With Resistive Turn On Turn Off Characteristics

IP.com Disclosure Number: IPCOM000085864D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Gillespie, ND: AUTHOR [+2]

Abstract

In the circuit of the drawing, a power transistor 2 and a resistor 3 form a test load for a power supply 4 under test. A signal I SET on a line 5 controls transistor 2 to draw a load current that is set by the voltage on line 5 and the value of resistor 3. In the normal operation of the tester, the analog signal on line 5 is transmitted to the base terminal of transistor 2 through a differential amplifier 6, a circuit 7 that combines the output of differential amplifier 6 with a signal on a line 8, and amplifiers 9 and 10.

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Constant Current Load With Resistive Turn On Turn Off Characteristics

In the circuit of the drawing, a power transistor 2 and a resistor 3 form a test load for a power supply 4 under test. A signal I SET on a line 5 controls transistor 2 to draw a load current that is set by the voltage on line 5 and the value of resistor 3. In the normal operation of the tester, the analog signal on line 5 is transmitted to the base terminal of transistor 2 through a differential amplifier 6, a circuit 7 that combines the output of differential amplifier 6 with a signal on a line 8, and amplifiers 9 and 10.

As the circuit has been described so far, transistor 2 operates as a constant- current source, and it may overload the power supply 4 during turn on while the voltage at the output of the power supply rises to its operating value. During turn on it is desirable for the test load to appear as a linear resistor so that the load current rises with the power supply voltage.

A voltage V MIN on a line 12 is set to represent the normal output voltage of the power supply 4 under test. A divide circuit 13 and a differential amplifier 14 cooperate to produce a signal on a line 15 that represents the quotient I SET/V MIN. The signal on line 15 has the dimensions of conductance and represents this characteristic of the test load, when it draws the load current I SET at a voltage V MIN. A multiply circuit 16 and a differential amplifier 17 receive the voltage at the output of the power su...