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Skipping Chopper Cycles in Switching Regulator

IP.com Disclosure Number: IPCOM000085512D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Yeager, RC: AUTHOR

Abstract

It is usual for constant-frequency transistor switching regulators to have a pulse width control sensitive to the output voltage, to vary the "on" time of a series transistor switch or chopper in such a manner as to compensate for changes in the output voltage. This mode of control, known as pulse width modulation (PWM), can usually accommodate normal operating conditions. However, provision may be made to shut the regulator down upon the occurrence of a radically abnormal condition such as short circuit in the load, or other causes of overcurrent, undervoltage, or overvoltage.

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Skipping Chopper Cycles in Switching Regulator

It is usual for constant-frequency transistor switching regulators to have a pulse width control sensitive to the output voltage, to vary the "on" time of a series transistor switch or chopper in such a manner as to compensate for changes in the output voltage. This mode of control, known as pulse width modulation (PWM), can usually accommodate normal operating conditions. However, provision may be made to shut the regulator down upon the occurrence of a radically abnormal condition such as short circuit in the load, or other causes of overcurrent, undervoltage, or overvoltage.

Because there is a minimum practicable pulse width in the operation of the chopper, such shutdown may be required in response to a transitory fault of extreme operating condition which could have been survived, if a minimum pulse had not been required at every clock time of the system.

In the illustrated control, a sample pulse is provided in advance of each clock time, and a decision is made as to whether the "minimum" on-pulse for that clock time should be skipped.

In Fig. 1, a transistor or other on-off chopper 10 admits current pulses to filter inductor 12 in pulses at clock times 13 determined by oscillator 14. The width of each pulse passed by chopper 10 is determined by PWM control 16 responsive to the output voltage sensed at output 18 of inverter 20, or if desired, at the load.

Fault conditions in the load or in chopper 10 or inverter 20, or simply a no- load condition or an overvoltage in...