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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: Hard drive motor question
References: <31pr9.4557$46.3661@fe01> <3DAF56FE.481B9324@webaccess.net> <3DB0AAE2.779D40DF@webaccess.net> <0Cgs9.5787$46.2303@fe01>
Date: Sat, 19 Oct 2002 18:59:02 GMT
NNTP-Posting-Date: Sat, 19 Oct 2002 11:59:02 PDT
> Here's the location of the data sheet:
> This one is pretty representative of Philips' other similar chips. The
> small schematic in the data sheet definately gives the impression that aside
> from a few cap's, not much else is needed to run these motors. No sensors
> are needed here......the ST data sheets and other similar ones DO indicate
> that Hall effect sensors are needed.....but I would prefer to stay away from
> these methods which seem to over-complicate the situation.
This motor controller will do the trick. The capacitor used in the
starting circuit will have to be decided based on the inertial load on
your motor. The commutation delay capacitors are a bit less critical.
The driver assumes that the center of a "Y" wound motor is available to
connect. If the center of the "Y" is not available (typical of small
motors), a "Y" of equal value resistors will give you the center voltage
so the driver should still work. The full data sheet has an example of
using the the uncommitted transconductance amplifier for motor current
control. In normal operation, this amplifier would be driven by a DAC on
> I'm not sure though, how run speed (rpm) is determined. Not that it is a
> big deal to me, but I'd be interested to know if speed can be adjusted using
> this type of driver.
The FG output is defined to be a square wave at half the comutation
frequency. In a disk drive, FG would be timed by a timer in an MCU and
the MCU would compute a current drive for the transconductance amplifier
connected as in the scanner example. A disk drive will typically switch
to timing some other internal event such as servo sectors for speed
control after servo header acquisition.
To use FG for speed control, a one shot such as a 555 can be connected
to produce a fixed pulse width from FG. The pulses can be filtered to
produce a voltage proportional to speed. An opamp can be used to compare
the speed voltage with a reference you provide and the output of the
opamp can drive the transconductance amplifier connected as in the
scanner example. This configuration is stable unless the gain is too
high or the filter time constant to obtain the speed voltage too long.
Read the full data sheet and try the minimum circuit configuration that
is also given in the data sheet.
If you do not know which coil was connected to which output of the
driver for your motor, you have to experiment. Two of the six possible
connections will work. You can use either. The two configurations that
work rotate the motor in opposite directions.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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