Oh, well, I have some 15 v baxck-to-back zeners extremely fast to help the
fuse out. In any case, the max current is limited by the power supply
Something can be worked out...
12 v actually limits the current through the coil(s) and heating even at
full on will not destroy anything. I'd probably use igbt transistors, I've
become quite fond of them :-) Note that the design will not deliver any
current through the coil if both gizzie outputs are either positive or
negative.
I'll bet there's a small half-bridge or full h-bridge that will work
extremely well, say sparkfun or the like. On fact, that's probably the best
way to go; as the h-bridges are designed to drive inductive loads. Neat, I'm
glad you kept my mind on task. A simple small motor driver will do the trick
nicely.
Doe to age, my current philosophy is <buy the biggest piece you can>
Don
----- Original Message -----
From: "Bruce Griffiths" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Sunday, August 08, 2010 5:22 PM
Subject: Re: [time-nuts] Regulating a pendulum clock
Mere fast blow fuses aren't usually precise enough to protect transistors
against over current unless one uses rather large transistors.
Overcurrent protected drivers are available and readily designed/built.
Protection against di/dt transients due to external events is also
advisable.
Minimising the parts count isn't necessarily conducive to improved
reliability when external hazards aren't taken into account.
Merely resonating the coil without other filtering doesnt necessarily lead
to low EMI when driving it with a voltage waveform having high edge slew
rates.
Some edge filtering to control the current flowing in the load capacitance
is also advisable.
Bruce
Don Latham wrote:
fast blow fuse, resonate the coil to the pwm frequency. Parts count
small,
tinkering in software instead of breathing lead fumes or whatever noxious
stuff the Europeans have forced us to use...
Don
Bruce Griffiths
No protection against external shorts or other undesired events.
Extensive analog filtering to avoid creating an effective radiator of
noise may also be necessary.
Simple analog techniques are probably simpler/cheaper once the necessary
filtering and protection are included.
Bruce
Don Latham wrote:
Hmmm lemme see. I think I'd use a 12 volt supply and two transistors
driven by two outputs on my Arduino,basic stamp,picaxe or other
whizzie.
I'd then implement a PID controller essentially using the 1 sec pulse
from
the pendulum and the 1 sec pulse from my Rb, satellite receiver,
crystal
clock, or whatever. The appropriate output pin will be brought to
ground,
and the other driven as a pdf with the rate given by the pid loop.
Temperature and even pressure corrections can be applied within the
gizzie
software. External parts, minimum. Opportunity to play with tuning,
maximum.
Don
Bruce Griffiths
J. Forster wrote:
You are picking very unimportant nits.
If there were a small noise spike from the opamp, it'd goose the
pendulum
a tiny amount. That would be corrected on the next swing.
Heuristic analysis of this type is counter productive.
You are turning a trip to the corner store into an Apollo Moon
Mission.
Reliability is paramount in a circuit that may be required to work for
decades.
BTW, since the =drive does not to be bipolar, one of the NPN and PNP
transistors can be deleted. They never turn on. So you are left with
two
opamsa, =each with a simple emitter follower.
The original request was for a bipolar drive.
The lack of short circuit protection is poor design practice when
driving an external load.
-John
==============
Bruce
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