Browse Prior Art Database

Voltage Ramp Circuit for Current-Mode Controlled Regulators

IP.com Disclosure Number: IPCOM000105349D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Daun-Lindberg, TC: AUTHOR [+2]

Abstract

A voltage ramp circuit for current-mode controlled regulators is disclosed. This circuit provides noise rejection and stability at light loads while maintaining equal current sharing between multiple regulators at heavier loads.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 76% of the total text.

Voltage Ramp Circuit for Current-Mode Controlled Regulators

      A voltage ramp circuit for current-mode controlled regulators
is disclosed.  This circuit provides noise rejection and stability at
light loads while maintaining equal current sharing between multiple
regulators at heavier loads.

      The circuit in the Figure shows the components necessary to
implement the voltage ramp in association with an integrated
pulse-width modulated (PWM) control module.  Average current-mode
control is assumed in this design but other methods of current
feedback may also work with the voltage ramp circuit.  Details of the
average-current sense signal are not discussed (C1/R3 are part of
this average current sense circuit).

      Transistor Q1 is configured as an emitter follower which
buffers the sawtooth voltage ramp created internally by the PWM
module.  Resistors R1 and R2 sum the ramp waveform at the emitter of
Q1 with the sensed current signal and are sized to provide a suitable
ramp input signal at minimum regulator output loading.  This combined
current/voltage ramp signal is fed to the current ramp input to the
PWM module and used to control the duty cycle.

      At light output loads, the sensed current is small compared to
the voltage ramp, thus the signal fed to the PWM control module
consists mostly of the voltage ramp for stability and noise
rejection.  The regulator can be considered as operating in voltage
mode at light loads.  As output loa...