Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Active Clamp Circuit

IP.com Disclosure Number: IPCOM000114156D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Ackerman, JE: AUTHOR [+6]

Abstract

An active clamp circuit with sharp turn-on characteristics, tightly controlled, trimmable clamp levels, and low leakage in the region of operation is disclosed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Active Clamp Circuit

      An active clamp circuit with sharp turn-on characteristics,
tightly controlled, trimmable clamp levels, and low leakage in the
region of operation is disclosed.

      The active clamp is achieved with two operational amplifiers
and a resistor ladder to set the clamp levels; for this application,
the clamp levels were set to 1V and 2V.  The clamp is shown in Fig.
1.

      The reference voltage levels are set by running a fixed current
through the known resistors of the ladder.  The ladder is then used
as a tap line with a center tap, a 1V tap, and a 2V tap.  The 1V
reference is then input to the low level clamp, and the 2V reference
is input to the high level clamp.  A 1.5V tap is provided as a no
load reference to the clamped circuit.  Note that the reference
levels need not be set by current and resistor combinations; they may
be generated by zener diodes, bandgap reference circuits, or any
other scheme the designer wishes to use.

      The low level clamp is shown in Fig. 2.  The 1V reference is
level-shifted up by source-follower T0 then input to Q0 of the
emitter-coupled pair.  The clamp node is also level-shifted up and
input to Q2 of the emitter-coupled pair.  Two diodes connect the
inputs to prevent the circuit from reaching an undesirable and
irrecoverable state.

      The differential currents from the emitter-coupled pair are
mirrored with gain by T13, T1, T5, and T10; the difference current at
T7 is then amplified through two stag...