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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Speed control for small d.c. motors
<3D8B6E81.6CC64148@worldonline.fr> <3D8BB559.9DDA2099@webaccess.net> <firstname.lastname@example.org>
Date: Sat, 21 Sep 2002 13:23:06 GMT
NNTP-Posting-Date: Sat, 21 Sep 2002 06:23:06 PDT
Tony Williams wrote:
> I think you are right. Since this is a Philips circuit
> it may be the one in the original Philips speed-control
> patent, that Bill Sloman mentioned a few months back.
As an aside, on a customer evaluation board that I designed, I use 4
LM1877 stereo power amplifiers and a couple of LT1215 opamps for motor
power drivers for small motors. Two are configured as transconductance
amplifiers (current feedback) to drive linear voice coil motors. One is
configured as a voltage driver (output voltage proportional to input
voltage). The last is jumper configurable as a voltage amp, a
transconductance amp or a BEMF driver. Each LM1877 is connected as an
"H" driver to get 20 volts p-p available for the motors. The BEMF driver
configuration adds two resistors to complete a bridge in which the motor
and the resistor used for current sense in transconductance mode form
one leg. Two jumpers are used to change the configuration of the
(1/2)LT1215 feedback amplifier/level shifter since the sign of the
feedback changes between transconductance configuration and BEMF
configuration. There is a third jumper which disconnects the (1/2)LT1215
output for voltage drive configuration. Voltage mode also requires a
change in the local feedback on the "master" side of the LM1877 "H"
power amp. Note that the goal of the evaluation board is to allow
customer evaluation of a set of ASIC chips in a fully operational system
configuration including customer provided electromechanical and other
parts. The various configurations of the one amplifier are needed to
support mechanics we have seen.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com
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