msansom wrote:...I remember that wall transformer putting out something like a smidge over 11 volts or so.
ZX81 PSU's often output around 11V
They are an "unregulated" type, so unless supplying the full rated output current, the output voltage will be above the "nominal" 9V. When not connected to a ZX81 / TS1000, the output voltage is between 14.5V and 16V.
Mark
Yep, you had the series resistance of the transformer secondary and the fact that in say the US, the mains voltage at the wall plug can range from around 106V to 127V. To ensure operation they had to design that wall transformer such that at full load at low line it would still make enough volts to satisfy the 7805 dropout voltage with a bit of margin. You can imagine that in a home where the AC mains is more towards the upper end of that range the output voltage is going to be rather high and that 7805 a bit toasty.
Regulated SMPS are really nice.
I'd like to say thank you on behalf of the group and ourselves and I hope we've passed the audition.
that 'high' 11v may be needed if the zx is used with some non sinclair rampacks as they derive the '12v' supply for the 4116's direct from the '9v' (11v) line....
gozzo wrote:that 'high' 11v may be needed if the zx is used with some non sinclair rampacks as they derive the '12v' supply for the 4116's direct from the '9v' (11v) line....
Ah, I see that the unregulated "9V" is indeed brought out to the edge connector. Kinda bad design practice to rely on that 9V being greater than 9V (or being any voltage in particular given that it's not regulated).
Do you know if the Sinclair 16k RAM packs used 9V for that purpose? I've never seen a schematic for one but they surely must be out there.
I'd like to say thank you on behalf of the group and ourselves and I hope we've passed the audition.
gozzo wrote:that 'high' 11v may be needed if the zx is used with some non sinclair rampacks as they derive the '12v' supply for the 4116's direct from the '9v' (11v) line....
Ah, I see that the unregulated "9V" is indeed brought out to the edge connector. Kinda bad design practice to rely on that 9V being greater than 9V (or being any voltage in particular given that it's not regulated).
Do you know if the Sinclair 16k RAM packs used 9V for that purpose? I've never seen a schematic for one but they surely must be out there.
Found a TS1016 RAM pack schematic. Looks like they do use the +9V, but they don't use it directly for +12. They have a crude switching power supply that makes both +12V and -5V. So should be ok with "only" 9V there.
Any other RAM pack that used the +9V directly for +12V on the ram chips would probably have a problem with people using lower voltage regulated supplies to make the 7805 run cooler.
I'd like to say thank you on behalf of the group and ourselves and I hope we've passed the audition.
genuine sinclair packs dont use it directly, memotech ones certainly do,and have a zener across the 11v ish 9v line, so dont stick more than 12v in or they'll be a bang, puff of smoke and 8 dead 4116s no idea what others do but i bet a lot of them did the same as memotech !
IIRC, Memotech, Panda and an uncased, and hence unbranded 16k RAM pack that I have ALL use the "9V" line to supply a "+12V" feed to the 4116 DRAM chips.
However, keep in mind that they all had an extra, large electrolytic "smoothing" capacitor across the "9V" line. And the specified tolerance for the "+12V" supply required by the 4116 DRAM chips is +/-10%.
So they should work okay within the 10.8V to 13.2V range.
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1024MAK wrote:IIRC, Memotech, Panda and an uncased, and hence unbranded 16k RAM pack that I have ALL use the "9V" line to supply a "+12V" feed to the 4116 DRAM chips.
However, keep in mind that they all had an extra, large electrolytic "smoothing" capacitor across the "9V" line. And the specified tolerance for the "+12V" supply required by the 4116 DRAM chips is +/-10%.
So they should work okay within the 10.8V to 13.2V range.
Mark
Don't know if it makes a difference re voltages Mark but the two Panda rampacks I have both have factory fitted MM5290 chips not 4116 chips and no extra large cap unless 10uf is considered as such.
EDIT
Just got off my lazy backside and looked up the mm5290chip data and it's a direct 4116 replacement, voltages being the same etc, so ignore my wafflings
no idea what others do but i bet a lot of them did the same as memotech !
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