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Output Voltage Control by Varying Over Current Control Level

IP.com Disclosure Number: IPCOM000089282D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Hoffman, HS: AUTHOR

Abstract

In output voltage regulation, the output is compared to a reference voltage, and thus controls a factor such as the ON time of a series switch to correct the error. The switch current is also monitored for an over-current condition to prevent damage to equipment.

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Output Voltage Control by Varying Over Current Control Level

In output voltage regulation, the output is compared to a reference voltage, and thus controls a factor such as the ON time of a series switch to correct the error. The switch current is also monitored for an over-current condition to prevent damage to equipment.

Inductance effectively in series with the switch (e.g., in an output filter or, in the case of a flyback regulator, in the output transformer) imparts a ramp shape to the switch current. The output voltage can be controlled by controlling the flow of current by an intercept with that ramp. To implement this, advantage is taken of the fact that this current is also sensed for over-current protection purposes.

This over-current sensing technique utilizes a measurement of the current, converted to a voltage 10, and compared to a value provided by voltage divider 12, 14 connected to a reference voltage 16. For adding output voltage control, part of the current flowing in leg 12 of the divider is made to flow to an external sink 18, whereby the effective ratio of the divider is changed.

To provide this control, the output 20 of a comparison of the output voltage 22 of the regulator and the reference 24 is used to create a variable current sink for the divider. Operational amplifier 26 provides this comparison. The voltage at 20 varies inversely by a multiple of the amount that 22 exceeds 24. Thus, when 22 is high, 20 feeds less current through diode...