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Bootstrap Bias Power Supply

IP.com Disclosure Number: IPCOM000112802D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Ahladas, SJ: AUTHOR [+3]

Abstract

Disclosed is a bootstrapped bias power supply circuit used to provide control and drive voltages for off-line power converters. The circuit utilizes a unique method for starting the bias power supply and maintaining operation over all worldwide (200-480V 50/60Hz) input voltages. The circuit is applicable to three phase or single phase input voltages as well.

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Bootstrap Bias Power Supply

      Disclosed is a bootstrapped bias power supply circuit used to
provide control and drive voltages for off-line power converters.
The circuit utilizes a unique method for starting the bias power
supply and maintaining operation over all worldwide (200-480V
50/60Hz) input voltages.  The circuit is applicable to three phase or
single phase input voltages as well.

      In the Figure, input VAC voltage to the power converter is
full-wave rectified by the rectifier bridge.  The rectified voltage
VR is used for the input voltage of the AC/DC stage.  This stage
produces a regulated high DC intermediate bus voltage VB that the
DC/DC stage converts to an isolated output(s) VO.  Capacitor(s) CB
provide buffering for input VAC disturbances.

      The bias control and drive voltages VBIAS for the power stages
are provided by the bias power supply.  Because the bias voltages
need to be present before the power stages are on, the bias power
supply needs to be started with only input VAC present.  This is
achieved by charging capacitor C from VR via positive temperature
coefficient(PTC) resistor RT, resistor R and diode CR1.  When the
voltage VC on capacitor C reaches a preset value, the bias power
supply will turn on.  VC is also the initial DC source for the bias
power supply that will be converted to VBIAS.  Capacitor C is sized
to provide VBIAS for only the time necessary for the AC/DC stage to
turn on and provide the voltage VB.  Diode CR2 isolates VC from VB
until this occurs.  Once VB is at its fina...