On 02/17/2012 07:11 AM, Jim Brain wrote: > Looking over the Cassette motor circuit on the various Commodore units, > I noticed Commodore used a few different drive circuits through the > years. My transistor theory is very rusty, and I'm hoping someone else > can shed some light on the differences: > > All of them implement a similar circuit. > > An initial circuit flips the logic level of the MOTOR signal. > THe second circuit bleeds 9-12VDC via a resistor into the base of a > power NPN, while tying the Collector to the voltage, and the Emitter to > the cassette motor. A Zener on the drive's base holds the voltage from > getting too high. That circuit is a voltage regulator (power transistor, resistor and zener diode) with a switch to turn it off. The circuit will supply you with about 6V unless you use the 7406 stage or transistor to short the zener diode to ground. > The VIC uses a 2sc1815 for the first stage and a 2sd880 for the driver, > no darlington, and the zener goes from 7.5V to 6.8. Yes, since you only have one base-emitter stage now, you need a 6.8V zener to get the 6V output. > To me, that implies the 8296 cassette motors run > overvoltage. From what I remember, those motors were also meant to be run in battery powered equipment and don't care too much as long as the voltage doesn't get too high. > http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/plus4/c116-251239-1.gif > > The +4 keeps the 2sd880 drive, but uses a 7406 for the first stage I have a C16 with a TIP29 instead of a 2SD880 and a +4 with a 2SD313. So it looks they again used what was handy... > * The 2n3904/2n2222 circuits have a 10K to ground on the first stage > transistor base. I assume this weakly holds base at GND until a > signal appears. This does not show on the VIC,64. Why not? You sure? My schematics for a 250407-board show R3, a 10K resistor to GND on the first stage. And a photograph of such a board also shows that resistor being present. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2012-02-17 18:00:04
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