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Subject: Re: How to get CMOS counter to drive a relay?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 18 Oct 2002 13:44:58 GMT
NNTP-Posting-Date: Fri, 18 Oct 2002 09:44:58 EDT
Organization: Cox Communications
"Fred Bloggs" wrote in message
> GPE wrote:
> > Just look at what the pinball people did. Lots of coils. Early on
> > they used transistor pairs to drive these. Some of the latter ones
> > to simple MOSFETs and the reliability increased tremendously.
> Just exactly how were the transistor pairs configured to drive the
I'm not too good at ASCII logic diagrams - so I scanned some partial
Here's how the transistor pair did it --
Logic on left was 74LS154, first transistor was part of CA3081 transistor
array, final transistor was TIP102 equivalent. Coil diode was located on
coil. This method worked quite well but sometimes load was too great for
TIP102 - they'd get pretty hot sometimes and those solenoid coils took a
heft chunk o' current.
> Was there something else that accompanied the transition to
> MOSFET drive like direct microprocessor I/O control?
Here's how the MOSFET's did it --
Simpler, no two stage. In this case, coil diode was located on board.
These MOSFETS seldom fail.
In both cases, transistor failures were usually caused as a result of coil
Coils failure was somewhat rare in either configuration - normally caused by
transistor failure (see last previous sentence) or when controlling CPU
would lock up and not clear 74HC273 register using a software timer - the
big coils (solenoids) were only meant to be left on for a brief period of
time usually to kick a ball. A relay uses far less current - smaller MOSFET
can be used and don't have to worry about coil burn if left on.
> The pinball machine
> "coils" should be mostly solenoids, right? I can see where conversion to
> microprocessor supervision would enable economical
> pulse-width-modulation of the coil voltage, and this would definitely
> make for a big improvement in solenoid lifetime because the heat
> dissipation could be nearly halved.
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