Re: C64 9VAC any use?

So if no userport peripheral minds. It should be possible to drive the 9V
AC
input with an +12V square pulse that vary between 0V and +12V ..?

The CIA TOD input of 9VAC runs though a 74LS08 which is higher than spec to
begin with. I wouldn't put 12V pulses on mine.

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.A-left.gif

If you check this schematic at C44, CR6, U23. You will see that the 9VAC is
connected via a current limiting resistor of 560 ohm to a 3V Zener.
This means that for the positive half the zener will prevent any voltage
above 3V. And thus as long as the zener+resistor can take it the voltage
will remain below 3V. Giving a positive "1" to U23.
For the negative half the zener will supply a limited current. That protects
the U23 from negative voltage and it will only see a "0".
U23 is an inverting schmitt trigger connected to both TOD inputs on the
6526 chips.

The maximum voltage to this circuit is dependent mainly on:
* Current capability of CR6.
* Heat dissipation limit of the resistor.

If only the heat dissipation of the resisitor is taken into account as the
current limit of zener CR6 is not specified. The maximum voltage at 9 VAC is:

Umax = Uz + sqrt(R * Pmax) = 3 + sqrt(560 * 0.25) = 14.8 V

Uz = Zener voltage (which lessens the voltage seen by the resistor)
R = Resistor used as current limiter.
Pmax = Maximum power dissipated over the resistor.


You haven't told us what you want it for. :)

Replacement for the C64 power supply brick. Esp as an DC/DC converter that
can make use of battery power. But will not limit the functionality.

If it's just a power supply, it may be easier to just build one from
scratch.

That's what I'm proposing ;)
But need to have it clear what's the minimum specifications for such device.
Currently it seems a normal +5V DC and +12V "AC" square wave will do.

.

Relevant Pages

  • Re: He who laugh last, laughs loudest, was Re: Wet your pants funny-- A.J. as an EE
    ... if you look at the LM675 spec sheet it shows 90db of power supply ... If the power supply voltage varies ... going to get 60 volts peak-to-peak out, which is about 20 volts RMS ... So this added resistor has used up all the IC's power ...
    (rec.audio.tubes)
  • Laughing even louder at the "engineers", thanks Old Hack Re: He who laugh last, laughs loudest, was
    ... if you look at the LM675 spec sheet it shows 90db of power supply ... If the power supply voltage varies ... going to get 60 volts peak-to-peak out, which is about 20 volts RMS ... So this added resistor has used up all the IC's power ...
    (rec.audio.tubes)
  • Re: He who laugh last, laughs loudest, was Re: Wet your pants funny-- A.J. as an EE
    ... if you look at the LM675 spec sheet it shows 90db of power supply ... If the power supply voltage varies ... going to get 60 volts peak-to-peak out, which is about 20 volts RMS ... So this added resistor has used up all the IC's power ...
    (rec.audio.tubes)
  • Re: LED lights in coach
    ... voltage rating. ... RV's batteries, but when on shore power, it is not uncommon, (and ... It seems that the module is the LED and a current limiting resistor. ... Figure out where you can put the test fixture for a couple of days. ...
    (rec.outdoors.rv-travel)
  • Re: Interesting dimmable CFL
    ... that time, could not measure the DC component of the power line current, ... Although an incandescent lamp with a diode has a DC voltage component ... that the voltage coil in an electric meter does not see and so the ... resistor with a diode in series with it will have its ...
    (sci.engr.lighting)