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INDUCTIVE FLYBACK CLAMP CIRCUIT WITH REVERSE POLARITY PROTECTION

IP.com Disclosure Number: IPCOM000006968D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-13
Document File: 2 page(s) / 84K

Publishing Venue

Motorola

Related People

Edward Liccar: AUTHOR

Abstract

When driving inductive loads such as motors, dissi- When a reverse battery condition occurs there is a pating the inductor's flyback energy is a design consid- current path through the intrinsic diode of the driving era&n. A common practice is to connect a reversed device and the flyback diode. The current through this flyback diode across the inductor to provide a current path is limited only by the resistance of the diodes and recirculation path when the motor current is interrupted. the circuit wiring. This condition will ultimately cause In some applications this scheme is impractical as with irreversible damage to one or both of the electronic automotive electronics which must be protected against devices. reverse battery connections. Figure la illustrates com- monly used high and low side motor driving devices.

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MOlOROLA INC. Technical Developments Volume 19 June 1993

INDUCTIVE FLYBACK CLAMP CIRCUIT WITH REVERSE POLARITY PROTECTION

by Edward Liccar

  When driving inductive loads such as motors, dissi- When a reverse battery condition occurs there is a pating the inductor's flyback energy is a design consid- current path through the intrinsic diode of the driving era&n. A common practice is to connect a reversed device and the flyback diode. The current through this flyback diode across the inductor to provide a current path is limited only by the resistance of the diodes and recirculation path when the motor current is interrupted. the circuit wiring. This condition will ultimately cause In some applications this scheme is impractical as with irreversible damage to one or both of the electronic automotive electronics which must be protected against devices.
reverse battery connections. Figure la illustrates com-
monly used high and low side motor driving devices.

i & .b qr ; 1

IS)

* lb1

Figure 1

  The circuit of Figure lb will conduct to provide a flyback recirculation current path but will not conduct during a reverse polarity occurrence. The concept of the circuit is to allow the SCR to conduct only when the inductive load voltage reverses polarity within a period of time after the load was normally energized.

  When the load is normally energized, capacitor Cl is charged to the supply voltage Vpwr through Rl. and Dl. When power to the motor is interrupted, the motor vol...