Browse Prior Art Database

Electronic Load

IP.com Disclosure Number: IPCOM000090416D
Original Publication Date: 1969-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 56K

Publishing Venue

IBM

Related People

Bengner, LH: AUTHOR

Abstract

This device provides a programmable regulated load current and is capable of modulation of up to 100 kc with a wide operating range of 100 amps at 1.2 volts to 10 amps at 100 volts in milliampere steps, with a precision of within one per cent. In order to achieve these broad limits, it is necessary to minimize the series impedance in the device. As a corollary, it is desirable to provide power dissipation limiting safety features which conform to the maximum safe load characteristic of the series control elements utilized.

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Electronic Load

This device provides a programmable regulated load current and is capable of modulation of up to 100 kc with a wide operating range of 100 amps at 1.2 volts to 10 amps at 100 volts in milliampere steps, with a precision of within one per cent. In order to achieve these broad limits, it is necessary to minimize the series impedance in the device. As a corollary, it is desirable to provide power dissipation limiting safety features which conform to the maximum safe load characteristic of the series control elements utilized.

The load has input terminals 10 and 12 which connect to the external device from which power is to be drawn such as, for example, a power supply under test. The main series circuit between such terminals comprises a group of pass transistors 14 each provided with an emitter resistor 16 for balancing the current flow in the parallel arrangement. The main series path is completed by current sensing shunt 18 which, like resistors 16 and the saturation resistance characteristics of transistors 14, is kept at as low an impedance value as is practicable. Of these three impedance areas, resistor 18 offers the possibility for the greatest saving in impedance because compensating amplification can be provided. Thus, a resistor 18 value of two milliohms provides a workable signal when utilized in combination with a highly temperature stable integrated circuit differential amplifier 20. One side of resistor 18 is connected via 22 to a common t12 volt line. The other side is connected via line 24 through passive mixer circuit 26 to one input 28 of amplifier 20. Mixer 26 has a low impedance AC input 30, 60 ohm coax, by which a modulating signal can be superimposed upon the signal on line 24.

The reference input of amplifier 20 is obtained through a binarily weighted ladder 32 from a stabilized source 34. Ladder 32 has a control input 36 operable by a card reader or manual switches or interface from a processor for programming the load. The output of amplifier 20 connects through driver 38 to the control input 40 of transistors 14.

Overpower and undervoltage prote...