Browse Prior Art Database

Fast Restart Circuit for Switching Power Supplies

IP.com Disclosure Number: IPCOM000103040D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 41K

Publishing Venue

IBM

Related People

Celenza, N: AUTHOR

Abstract

This article describes a circuit topology which generates a reset signal every time AC power is switched OFF and then ON again, independent of the rectified line voltage level still present in the power supply.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Fast Restart Circuit for Switching Power Supplies

      This article describes a circuit topology which generates a
reset signal every time AC power is switched OFF and then ON again,
independent of the rectified line voltage level still present in the
power supply.

      In low-cost switching power supplies, the control IC
(Integrated Circuit) is usually powered from the rectified line
voltage (Vb) or a low voltage derived from Vb.  When a power supply
output fault occurs, sense circuitry turns off the control IC by
setting a latch.  A desired way to power up again is to turn OFF/ON
input AC power, but the IC will remain latched off until Vb
discharges to a voltage usually below 7 volts.  For Vb to discharge
from the usual 300 volts to 7 volts, it normally takes over 10
seconds, an excessive time to wait.

      The figure shows a circuit topology where Q1 and R1 form a
current source which turns ON Q3 through R5, thus generating a low
voltage (reset signal) until C1 charges up and turns ON Q1.  With Q1
turned ON, Q3 turns OFF, thus leaving the reset line free to set
again if an output fault occurs.

      Since the voltage for the Q1 R1 current source is taken
directly off the AC input, the reset pulse generation is independent
of the value of Vb; thus, a power supply fault latch now can be reset
as fast as one can turn OFF/ON the AC input power switch.

      Disclosed anonymously.