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Short Protection Circuit for DC/DC Converter

IP.com Disclosure Number: IPCOM000110524D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 4 page(s) / 69K

Publishing Venue

IBM

Related People

Terazawa, S: AUTHOR

Abstract

Disclosed is a short protection circuit which has a self-recovering function for non-isolated step-up DC to DC converters with transistors and resistors.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 57% of the total text.

Short Protection Circuit for DC/DC Converter

       Disclosed is a short protection circuit which has a
self-recovering function for non-isolated step-up DC to DC converters
with transistors and resistors.

      The output current foldback short protection circuit is shown
in Fig. 1. Output characteristic curve is shown in Fig. 2.

      To explain the circuit, let us begin with a simple circuit.

      Fig. 3 shows an over-current protection circuit. The
characteristics of output current (Io) versus output voltage (Vo) is
shown in Fig.  4. This circuit works as follows,
       When Io < VBEon / Rsc,  Io depends on load.
            Io > VBEon / Rsc,  Io = constant.
But when output is shorted, and Vo comes to be less than (Vcc VD1
VBEon), this circuit does not work.

      VBEon is the base-emitter forward-biased voltage, typically 0.7
volt.

      Fig. 5 shows the short protection circuit which is added P-MOS
FET to the circuit in Fig. 3.
      When V2 - Vg > VGon, FET is ON.
   (So, Vg and FET should satisfy the following condition, Vo - Vg >
VGon.)
      When the output is shorted, Io is limited to VBEon / Rsc (=
IoL).

      In this circuit, the maximum ratings of FET1 must be considered
as follows,
      a) The power dissipation of FET1 is IoL * VDS'.
      Fig. 6 shows output to GND short schematic.
      VGS' = Vg - (V2 - VBE2)

      V1  << V2, Tr2 is non-saturated.  So the drain curr...