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Current Limitation and Over Current Protection in Direct Mode DC/DC Converters

IP.com Disclosure Number: IPCOM000051109D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Azzis, D: AUTHOR [+3]

Abstract

In direct-mode, DC-DC converters, the output current is reflected in the switching transistors which thus may pass a current as high as required by the load without any control; this may damage the switching transistors. This article describes a direct-mode DC-DC converter which includes a current limiter and a fast over-current protection mechanism which turns off the supply when destruction is endangered.

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Current Limitation and Over Current Protection in Direct Mode DC/DC Converters

In direct-mode, DC-DC converters, the output current is reflected in the switching transistors which thus may pass a current as high as required by the load without any control; this may damage the switching transistors. This article describes a direct-mode DC-DC converter which includes a current limiter and a fast over-current protection mechanism which turns off the supply when destruction is endangered.

The circuit shown in the figure comprises a conventional direct-mode converter (outside dashed lines), a current limiter and an over-current protection (OCP) mechanism. The current limiter operates as follows. In steady state, the voltage at node A is controlled by the output from amplifIer 10. When the output DC current exceeds a predetermined current limit (200 mV across shunt resistor
11), the voltage at node A is pulled down and the width of the pulses which drive switching transistors T1 and T2 is reduced. The output voltage is no longer controlled and drops down. Current limitation so obtained takes time (filter time constant is about a few milliseconds), and does not provide protection against excessive switching transistor currents.

Efficient protection is provided by the OCP mechanism which operates as follows. Switching transistor current is sensed across shunt resistor 12 at each cycle. When the current is above a predetermined level, which is equal to 20 A in the example...