EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Alex Eisenhut on April 27, 2016, 11:42:29 pm
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The Commodore 64 requires a floating (transformer isolated) 9VAC supply as well as a 5V DC rail. Usually the 9V is done with big iron 60Hz transformers.
Can this be done using a Class-D amplifier, fed a suitable signal, driving a smaller high frequency transformer and a filtering network after the transformer?
Behold this NASA-level sketch:
(http://i63.tinypic.com/21jyhoi.png)
The linear supply could be the 12VDC part of a PC power supply, or maybe even off-line.
The class-D could be anything from a one-chip solution to maybe discrete parts.
Now the question is, could using a smaller high frequency transformer work to provide the isolation? What kind of filter will I need? The red feedback part will be optically isolated and whatever is driving the 60Hz (or 50Hz) signal will be driven by the feedback loop.
What do you think?
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I have a number of IR half bridge drivers, a HV 555 with power fet. this could be a use feeding a cap and a transformer. Want to do a shout out for these if you haven't noticed them. http://www.ebay.com/itm/DC-AC-Pure-Sine-Wave-Inverter-SPWM-Board-EGS002-EG8010-IR2110-Driver-Module-HK-/262348487870?hash=item3d15303cbe:g:qHkAAOSwZ8ZW8fo9 (http://www.ebay.com/itm/DC-AC-Pure-Sine-Wave-Inverter-SPWM-Board-EGS002-EG8010-IR2110-Driver-Module-HK-/262348487870?hash=item3d15303cbe:g:qHkAAOSwZ8ZW8fo9)
Add a minimum of two FET and all problems solved for $6.
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This smacks of "using a sledgehammer to squash a flea".
I used to have a book with a full schematic of a C64,but I think I threw it out as well when I sent the cursed thing to the landfill.------Do I not sound like a fan? ;D
I seem to recall that the 9v AC went to a conventional switchmode supply on the main board.
These usually have a bridge rectifier at the input,so will operate happily on a suitable DC supply.
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This smacks of "using a sledgehammer to squash a flea".
I used to have a book with a full schematic of a C64,but I think I threw it out as well when I sent the cursed thing to the landfill.------Do I not sound like a fan? ;D
I seem to recall that the 9v AC went to a conventional switchmode supply on the main board.
These usually have a bridge rectifier at the input,so will operate happily on a suitable DC supply.
This might help
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/ (http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/)
The only caution I would give is that on the two diagrams I looked at the 9V AC feeds the user port, so while you might be able to get away with a suitable DC feed for the C64, you also need to look at what peripherals are being used.
The first diagram I saw had some parts using "unregulated 9v" coming from a BR+Cap, and other parts fed from a regulator - one diagram had a basic "zener+transistor+2 resistor" regulator, the other had a 7805 fed normally from a bridge rectifier, and a 7812 fed from what looks like a diode pump circuit.
Personally I'd just use a transformer with two separate windings - one to feed the 9VAC, the other feeding a suitable 5v regulator module. If the regulator module was isolated, I'd use a single winding transformer and feed both the module and the 9VAC.
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Sigh. There's no switcher in the 64, and if I could get away with DC, why would Commodore have put 9VAC there in the first place?
The AC not only feeds peripherals on the user port, but the 50/60Hz sine wave drives the TOD clock with interrupts. And you need a floating supply for the SID chip. Don't ask me why, I didn't design the stupid thing. So worst case, common DC on the 9VAC lines risks frying the 64; or best case software that relies on the TOD incrementing will fail.
I want to get away from the 60Hz magnetics because they're big and getting harder/expensive to find. It's 30$ for a Hammond part that's only 500mA. I think I could throw together a hack for less than that.
It's not just the 64 that uses this, but the SX-64 and the 128.
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Sigh. There's no switcher in the 64, and if I could get away with DC, why would Commodore have put 9VAC there in the first place?
So they could put the DC power supply in the main case----not uncommon in the 1980s.
The AC not only feeds peripherals on the user port, but the 50/60Hz sine wave drives the TOD clock with interrupts. And you need a floating supply for the SID chip. Don't ask me why, I didn't design the stupid thing. So worst case, common DC on the 9VAC lines risks frying the 64; or best case software that relies on the TOD incrementing will fail.
OK,I was wrong,--long time ago,& I never was that enthusiastic!
I want to get away from the 60Hz magnetics because they're big and getting harder/expensive to find. It's 30$ for a Hammond part that's only 500mA. I think I could throw together a hack for less than that.
It's not just the 64 that uses this, but the SX-64 and the 128.
Why buy a Hammond part?
I've never had anything to do with them,but they have a reputation for being costly.
In Oz,you can buy a transformer from Jaycar for $A11.95 which would probably do the job ---It's almost certainly Chinese,but what the heck? So is everything. ;D
Surely there is something similar in your part of the world?