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High-gain High-stabiliy Feedback for Switching Power Supply

IP.com Disclosure Number: IPCOM000061406D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

MacInnis, AG: AUTHOR [+3]

Abstract

In a Switching Power Supply an Rc Network is Connected to the Input Side of the Lc Filter. This Rc Network is Used As the Feedback Means to Control And Regulate a Switching Power Supply.

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High-gain High-stabiliy Feedback for Switching Power Supply

In a Switching Power Supply an Rc Network is Connected to the Input Side of the Lc Filter. This Rc Network is Used As the Feedback Means to Control And Regulate a Switching Power Supply.

Referring to the drawing, the RC network is connected between the output rectifiers 1 and 2 and the filter choke 3. Resistor 6 and capacitor 7 filter out the large amplitude high frequency switching pulses to prevent their being fed back to the supply's modulator. It is not necessary and in fact undesirable that the filtering effect mimic the output filter. The DC level at the junction point of resistor 6 and capacitor 7 is used as the feedback point for control and regulation purposes.

In many cases where LC filters are used, the resonant frequency of the LC filter is very low, often near the line ripple frequency. To get good line ripple rejection, the gain of the feedback loop must be large enough to get the required ripple rejection, but this gain requirement causes stability problems with the conventional feedback connection.

The solution is to use the RC circuit ahead of the LC filter. Since the feedback circuit essentially sees only the single pole of the RC circuit rather than the double pole of the LC filter, it is possible to increase the gain of the feedback loop while still maintaining stability.

An ideal power supply would have a constant voltage source driving the output filter. If we were able to achieve a...