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Browse Prior Art Database

LOAD DUMP SUPPRESSION IN A SWITCH FOR ELECTRICALLY HEATED CATALYST

IP.com Disclosure Number: IPCOM000007814D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-25
Document File: 1 page(s) / 56K

Publishing Venue

Motorola

Related People

John Qualich: AUTHOR

Abstract

In a switch for a catalytic converter heater used in an automobile, it is possible to minimize the energy dissipation of a transient suppressor (Dl) by dissipating a large portion of the load dump energy in one ofthe switching transistors (Ql). This allows use of a smaller, and less expensive, transient sup- pressor Dl.

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Technical Developments

LOAD DUMP SUPPRESSION IN A SWITCH FOR ELECTRICALLY HEATED CATALYST

by John Qualich

  In a switch for a catalytic converter heater used in an automobile, it is possible to minimize the energy dissipation of a transient suppressor (Dl) by dissipating a large portion of the load dump energy in one ofthe switching transistors (Ql). This allows use of a smaller, and less expensive, transient sup- pressor Dl.

  One method of quickly heating an automotive catalytic converter is with a resistive heater (Rl) that is powered by the vehicle's alternator. Switches comprised of large power MOSFETs (Ql and Q2) connect the alternator output to either the vehicle electrical loads (including battery) or to Rl. The sizes of transistors Ql and Q2 are selected to switch currents of lOOA. To minimize current through Rl, the alternator is allowed to operate at an output voltage of 40V when Q2 is 'on' and Ql is 'off: When the alternator's output is connected to the vehicle electrical system (Ql 'on' and Q2 'off), it operates at 14V

  Should current demand of the vehicle electrical system suddenly decrease, a transient high voltage (SOV) (called a Load Dump transient) can be gener- ated by the alternator. Transient suppressor Dl is used to limit the voltage at the vehicle electrical system to a safe value, in this case 36V During a load dump transient, zener diode D2 will break down and cause transistor 43 to conduct which will decrease the gate voltage of Ql. The volta...