Browse Prior Art Database

VOLTAGE CONTROLLED CURRENT SOURCE

IP.com Disclosure Number: IPCOM000007013D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-18
Document File: 1 page(s) / 53K

Publishing Venue

Motorola

Related People

Emilio Martinez: AUTHOR

Abstract

The purpose of this circuit is to provide an out- put current in response to an input voltage. The unique aspect of this circuit is that the output cur- rent is dependent solely on the applied input voltage and not on the system power supply or an external reference voltage. Therefore this circuit will provide accurate output currents in systems with poor power supply regulation.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 78% of the total text.

Page 1 of 1

0 M

MOTOROLA INC. Technical Developments Volume20 October 1993

VOLTAGE CONTROLLED CURRENT SOURCE

by Emilio Martinez

  The purpose of this circuit is to provide an out- put current in response to an input voltage. The unique aspect of this circuit is that the output cur- rent is dependent solely on the applied input voltage and not on the system power supply or an external reference voltage. Therefore this circuit will provide accurate output currents in systems with poor power supply regulation.

  The proposed circuit is shown in Figure 1. In this application the inputs to the circuit are the two current controlling voltages VI and V2. The fimc- lion of the first op-amp (Al) in conjunction with resistors Rl through R5 is to form a difference ampli- fier. The output ofthis amplifier will be:

V,,, = aVref - bVI - cV2

where the constants a, b and c are determined by the values of Rl through R5. This signal is then fed to the positive terminal of the second op-amp (AZ). The action of this second op-amp will be to adjust its output such that the voltage at the negative ter- minal will equal the voltage at the positive termi- nal. Therefore the voltage at the negative terminal

is also Vout. From Figure 1 it can then be seen that the voltage across R6 will be:

therefore VR6 = Vref- V,,,

VR6 = Vref - (aVref - bV1- cV2)

if the value of the constant "a" is constrained to the value of 1 then the voltage across R6 becomes:

V,, = Vref - Vref + bV1 f cV2

= bV1 + cV2

The current fl...