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Browse Prior Art Database

IMPROVED CHARGE PUMP

IP.com Disclosure Number: IPCOM000007776D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-23
Document File: 3 page(s) / 118K

Publishing Venue

Motorola

Related People

John Pigott: AUTHOR [+2]

Abstract

This new circuit replaces one of the diodes with a transistor acting as a switch or active rectifier. The drive circuitry for this switch is very simple, and so is easy to implement.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 3

M-LA Technical Developments

IMPROVED CHARGE PUMP

by John Pigott and Randy Gray

INTRODUCTION:

NEW SOLUTION:

  This new circuit replaces one of the diodes with a transistor acting as a switch or active rectifier. The drive circuitry for this switch is very simple, and so is easy to implement.

  The output voltage from simple charge pumps is reduced by the voltage drop across the rectifying diodes (7).

An ideal single-stage charge pump has an out- put voltage oftwice the input voltage

V ,=2x v,M

Simple circuits give only V ,=2x v,,v-2Y

because of the voltage drop across the rectifying diodes.

  This circuit eliminates these drops and ap- proaches the ideal by replacing the diodes that cause the j loss with transistor switches.

V om- 2 x WIN - E), or V oLIT- n x (P, - E) in a multi-stage configuration

Improved Charge Pump

HOW IT WORKS:

  The drive circuit for the transistor switch con- sists of a very small capacitor and an additional diode. The transistor looks nearly like an ideal switch and the voltage drop reduces from VBE to VCE(SAT).

  The capacitor only supplies base current to the switch, and so only needs to be l/b the size of main charge pump capacitor!

  Here, Ql acts as the transistor switch and CPUMPI is the charge pump capacitor. Additional components Q5 and CBASE drive the base of Ql. CBASE is driven out of phase with respect to CPUMPl.

m m

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cl 1

f

+

PULSE

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Simple Charge Pump Circuit

PRIOR ART:

  Existing circuits use diodes as the rectifiers. There is a one-j voltage loss because the charge-pumping capacitor can only charge to the supply minus the voltage drop across the diodes. There is an addi- tional voltage drop because ofthe output rectifier.

0 Momola. 1°C. 19% 98 August 1996

[This page contains 15 pictures or other non-text objects]

Page 2 of 3

M-LA Technical Developments

the 0.6V higher output voltage achieved with the use of the new circuit.

ADDITIONAL FEATURES:

  The other rectifiers in the circuit can also be replaced with this active rectifier in a similar con- figuration. This allows the output voltage to approach the ideal nx Yin a multi-stage charge pump.

  An important advantage of this circuit is that it allows the maximum output voltage of the charge pump to be limited.

  The top of CPUMP in the above...