Request: Power Supplies UK700 vs UK1200 Schematic diagrams (and why does my UK1200 sup run much hotter under same load?)

Discussions about Sinclair ZX80 and ZX81 Hardware
sP1d3r
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Re: Request: Power Supplies UK700 vs UK1200 Schematic diagrams (and why does my UK1200 sup run much hotter under same lo

Post by sP1d3r »

1024MAK wrote: Mon Jul 18, 2022 1:59 pm There are no transistors in any of the Sinclair 9V PSUs as used with the ZX80, ZX81, ZX Spectrum 16K/48K/+, 128K or the +2 (grey). All these computers use a 7805 (or higher current version) series pass voltage regulator (which is also often described as “linear”).
I noticed a step-down transformer, two large capacitors and a full wave bridge rectifier inside the UK1400 but obviously this is only part of the conversion and regulation process so although the UK1400 supplies unregulated DC, the regulator circuits in the ZX81 could make the larger supply unsuitable for a particular reason, so I thought I'd ask never having seen a ZX81 PSU.

I got on a Electrical/Electronic principles course a long time ago but only got as far as trying to get to grips with Thevenin, Kirchoff and Fleming before I had to drop out, unfortunately and I've not so far managed to catch up with my studies.
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1024MAK
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Re: Request: Power Supplies UK700 vs UK1200 Schematic diagrams (and why does my UK1200 sup run much hotter under same lo

Post by 1024MAK »

sP1d3r wrote: Wed Jul 13, 2022 6:29 pm :?: Would it be ok to use a UK1400 PSU with a suitable connector for a ZX81, I wonder.
bola_dor wrote: Wed Jul 13, 2022 6:59 pm Yes
Just double check polarity
I concur :D
sP1d3r wrote: Mon Jul 18, 2022 5:40 pm I noticed a step-down transformer, two large capacitors and a full wave bridge rectifier inside the UK1400 but obviously this is only part of the conversion and regulation process so although the UK1400 supplies unregulated DC, the regulator circuits in the ZX81 could make the larger supply unsuitable for a particular reason, so I thought I'd ask never having seen a ZX81 PSU.
Yes, it does not appear to be “common sense”, but a UK1400 PSU is actually no worse for a ZX81 compared to a UK700 or a UK1200.

This is due to larger mains iron transformers having better secondary voltage regulation (the difference between the open circuit/no load voltage and the voltage at the rated output current is smaller).

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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sP1d3r
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Re: Request: Power Supplies UK700 vs UK1200 Schematic diagrams (and why does my UK1200 sup run much hotter under same lo

Post by sP1d3r »

1024MAK wrote: Mon Jul 18, 2022 10:12 pm Yes, it does not appear to be “common sense”, but a UK1400 PSU is actually no worse for a ZX81 compared to a UK700 or a UK1200.

This is due to larger mains iron transformers having better secondary voltage regulation (the difference between the open circuit/no load voltage and the voltage at the rated output current is smaller)
It's good to know that it'll be alright.

Using a PSU that's too big with an ATX motherboard means that the PSU works with a low efficiency, ideally the typical working current requirement should be 50-60% of the rated output of the PSU or the MTBF won't be likely.
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1024MAK
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Re: Request: Power Supplies UK700 vs UK1200 Schematic diagrams (and why does my UK1200 sup run much hotter under same lo

Post by 1024MAK »

1024MAK wrote: Mon Jul 18, 2022 10:12 pm Yes, it does not appear to be “common sense”, but a UK1400 PSU is actually no worse for a ZX81 compared to a UK700 or a UK1200.

This is due to larger mains iron transformers having better secondary voltage regulation (the difference between the open circuit/no load voltage and the voltage at the rated output current is smaller).
See my corrected earlier post.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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