Michael Doogue Richard Dickinson INTRODUCTION adjust output range. exi

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Michael Doogue Richard Dickinson INTRODUCTION adjust output range. exi

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Using Allegro Current Sensors Dual Power Supply Applications Converting Sensed Currents into Peak Current Measurements
Michael Doogue Richard Dickinson INTRODUCTION adjust output range. existing application designs, such cases include replacing bulky current transformers more expensive dual-supply Hall-based sensors. system designs there other reasons adjusting output, such providing output centered expanding dynamic output range. This application note describes simple circuits, which applied with presently-available Allegro ACS704 bidirectional ACS75x current sensors. first circuit allows configuration gain sensor output signal configuration output voltage sensor shift from nominal) another level. This circuit could used with Allegro sensor replacement, example, sensor that requires dual power supply voltages. second circuit used current sensing applications, such where required input into controller peak value measured current. circuit only performs same functions first, also rectifies output signal from sensor. this analysis, circuits were implemented Allegro application board, shown figure These designs optimized development purposes: easily configurable user, provide maximum flexibility. Users adapt principals demonstrated with these circuits designs optimized meet their application requirements.
Current sensors manufactured Allegro MicroSystems powered single supply provide output voltages range between These features allow system designer avoid level-shifting sensor output before passing A-to-D converters, microprocessors, microcontrollers that also powered Further, they eliminate need additional voltage regulator power negative rail sensors that require dual positive negative voltage supplies. some instances, however, useful level-shift output Allegro current sen-
Figure Allegro sensors available variety configurations, such CB-PFF (A), used ACS75x families, (B), used ACS704s.
AN295034
Using Allegro Current Sensors Dual Power Supply Applications Converting Sensed Currents into Peak Current Measurements
INTERFACE CIRCUIT LEVELSHIFTING ACS7XX OUTPUT SIGNAL first circuit shown figure powered with supplies. voltage divider between supplies used output voltage when current flows through Allegro
sensor. When potentiometer nominal value, 15.3 output VOUT voltage circuit node VREF Node VREF buffered, output buffer into standard subtractor subcircuit formed operational amplifier with negative feedback. output subtractor subcircuit corresponds level-shifting circuit output, VAPP (mV), given following equation:
Figure Allegro Application Board. This board used constructing testing example circuits.
Where: VOUT output current sensor, VBUF output buffer. subtractor subcircuit used level-shift output Allegro current sensor also amplify gain. example, following resistor combinations yield circuit output gain,
Figure Level-Shifting Gain Amplification Example Circuit
AN295034
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Using Allegro Current Sensors Dual Power Supply Applications Converting Sensed Currents into Peak Current Measurements
GAPP times: different gain required, then values resistors changed. resistances calculated using following equation:
while primary sensed current, ramped increments from then down gain level-shift circuit confirmed times. This level selected order achieve sensitivity approximately mV/A, reached using following resistor combinations: 10.1 41.2 results shown figure Because output noise will also amplified, applications requiring high-resolution measurements suggested that low-pass filter inserted between level-shifting circuit. Various resistor combinations with fixed capacitor value were evaluated demonstrate
EXPERIMENTAL RESULTS LEVEL-SHIFTING CIRCUIT Allegro ACS704ELC-015 current sensor connected first circuit Voltages were applied circuit board,
ACS704
Level-Shifting Circuit
ACS704
Figure Output ACS704 Current Sensor, VOUT (Blue Trace) Level-Shifting Circuit, VAPP (Red Trace). These traces represent response level-shifting circuit ramp primary sensed current, order overlay signals easier comparison, oscilloscope adjusted offset trace ACS704 -2.5
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
AN295034
Using Allegro Current Sensors Dual Power Supply Applications Converting Sensed Currents into Peak Current Measurements
ACS704
ACS704
Level-Shifting Circuit
Level-Shifting Circuit
Filter Filter Figure Output Level-Shifting Circuit with Filtering. These panels show effects VAPP inserting low-pass filter between ACS704 current sensor input application board used experiments.
improved signal noise ratio adding filter. results shown figure INTERFACE CIRCUIT CONVERTING SENSED CURRENTS INTO PEAK CURRENT MEASUREMENTS This circuit adds diode bridge pass filter level-shift gain adjust circuit described above sections. expanded interface circuit shown figure designed rectify current measurements.
application board again powered with voltage divider between supplies node VREF used output voltage when current flows through Allegro sensor. ACS7xx output signal tracks sine wave, node rectified through diode bridge then filtered. configured figure combination pass filter break frequency This level attenuates ripple associated with rectification stage. offset rectified signal, measured node VREG when
Figure Signal Rectifying Example Circuit
AN295034
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Using Allegro Current Sensors Dual Power Supply Applications Converting Sensed Currents into Peak Current Measurements
potentiometer nominal value Both rectified output signal circuit node VREF buffered before being into subtraction subcircuit. output subtractor subcircuit corresponds positive peak ac-converting circuit output, VAPP (mV), given following equation:
EXPERIMENTAL RESULTS CONVERTING CIRCUIT Allegro ACS704ELC-015 current sensor connected second circuit Voltages were applied circuit board, while primary sensed current applied with varying amplitude. output rectifier stage circuit ramps proportion peak amplitude applied current. gain stage, which follows rectifier, confirmed times this circuit well. This level reached using following resistor combinations: 10.1 41.2 results shown figure
Where: VOUT output current sensor, VBUF1 output buffer power supply side. with basic level-shifting circuit, different gain desired then resistors altered select gain, using equation
ACS704 Rectified shifted output
ACS704
Rectified shifted output
Response during initial ramp,
Steady state output
Figure Output ACS704 Current Sensor, VOUT (Green Trace) Rectifying Level-Shifting Circuit, VAPP (Black Trace), Response Current. output current sensor (2.5 nominal).
AN295034
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com
Using Allegro Current Sensors Dual Power Supply Applications Converting Sensed Currents into Peak Current Measurements
CONCLUSION circuits described this note used develop optimized applications using Allegro family current sensors. Allegro sensors used sense both direct alternating currents. With galvanic isolation ACS704 family SOIC8 package, ACS75x families, these sensors make attractive substitute current transformers. applications, although demonstrated measurements, described circuit applied higher frequencies several kilohertz with significantly lower parasitic losses than those exhibited typical current transformers.
more information about circuits described this application note, including reference build materials, please contact your local Allegro MicroSystems sales office. Visit Allegro current sensor product pages Allegro site:
information included herein believed accurate reliable. However, Allegro MicroSystems, Inc. assumes responsibility use; infringement patents other rights third parties which result from use. Copyright 2005, Allegro MicroSystems, Inc.
ACS704
Shifted output
Figure Output ACS704 Current Sensor, VOUT (Green Trace) Level-Shifting Circuit, VAPP (Black Trace), Response Primary Sensed Current, This output produced using first circuits described this note. output current sensor (2.5 nominal).
AN295034
Allegro MicroSystems, Inc. Northeast Cutoff, 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com

Michael Doogue Richard Dickinson INTRODUCTION adjust output range. exi

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