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FLYBACK VOLTAGE DETECTOR

IP.com Disclosure Number: IPCOM000007129D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2002-Feb-27
Document File: 1 page(s) / 51K

Publishing Venue

Motorola

Related People

Michael S. Kemmet: AUTHOR

Abstract

In many applications, when driving inductive type loads, it is necessary to detect faulted load condi- tions. There are a variety of faults that can occur, such as faults to ground, to power, or a shorted load. The impedance of these faults can range From near zero ohms (hard short) up to higher levels that are still less than the circuit impedance (sot? shorts). In various applications, different types of faults may require a different type ofcorrective action. In these situations, detection ofover current alone cannot be relied upon to identify the exact type of fault. For these applications, a flyback voltage detector can be advantageous.

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MO-LA Technical Developments Volume 21 February 1994

FLYBACK VOLTAGE DETECTOR

by Michael S. Kemmet

  In many applications, when driving inductive type loads, it is necessary to detect faulted load condi- tions. There are a variety of faults that can occur, such as faults to ground, to power, or a shorted load. The impedance of these faults can range From near zero ohms (hard short) up to higher levels that are still less than the circuit impedance (sot? shorts). In various applications, different types of faults may require a different type ofcorrective action. In these situations, detection ofover current alone cannot be relied upon to identify the exact type of fault. For these applications, a flyback voltage detector can be advantageous.

A flyback voltage detector, as the name implies, detects the presence or absence of the flyback volt-

age that is produced by an inductive load. The cir- cuit below is shown using two internally clamped insulated gate bipolar transistors (ICIGBT) as out- put drivers. The gates of the ICIGBTs are diode cou- pled to a single comparator. The basic circuit con- cept is to detect the flyback voltage by monitoring the gate voltage. When the ICIGBT gate control signal is driven low, by either the normal drive cir- cuitry or an over current protection circuit, the ICIGBT is put in a linear mode by the presence of the flyback voltage. The comparator is biased up, so that it will be high when the ICIGBT's gate voltage rises and is put in...