Power supply

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mk79
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Power supply

Postby mk79 » Sat Aug 08, 2020 6:25 pm

As many here are not member of the QL facebook group I relay Charlie Ingley's new power supply prototype. Looks to cool to not share ;)

ql_power.png


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bwinkel67
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Re: Power supply

Postby bwinkel67 » Sat Aug 08, 2020 7:38 pm

Will the 50Hz screw up 60Hz QL's? It looks like from what I read it should be fine for electronics as long as the voltage is but what about things that require timing like microdrive motors or the oscillator?


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mk79
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Re: Power supply

Postby mk79 » Sat Aug 08, 2020 8:23 pm

Timing is not derived from the AC voltage, that is all from the crystal.


stephen_usher
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Re: Power supply

Postby stephen_usher » Sun Aug 09, 2020 9:55 am

Indeed, you can never rely upon the mains frequency, which is at best approximate, so no-one does.


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Pr0f
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Re: Power supply

Postby Pr0f » Sun Aug 09, 2020 2:33 pm

In the UK the national power company used to adjust it - so long term it could be relied on for driving those early digital clocks.. - more accurate than pc clocks, but clearly the radio clocks, internet and gps are a much better bet these days


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Ruptor
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Re: Power supply

Postby Ruptor » Sun Aug 09, 2020 11:16 pm

Pr0f wrote:In the UK the national power company used to adjust it - so long term it could be relied on for driving those early digital clocks.. - more accurate than pc clocks, but clearly the radio clocks, internet and gps are a much better bet these days
yes I had a Philips mains motor clock that ran for twenty years and was always accurate to the nearest minute never needing adjustment until it died so I can testify that the UK 50 Hz is ace. I guess I was just tight to buy a new digital clock but why change something that works? The digital replacement keeps resetting on mains brown outs making it totally unreliable and I can't see it in daylight. :x


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bwinkel67
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Re: Power supply

Postby bwinkel67 » Sun Aug 09, 2020 11:52 pm

I recall in the 90's, besides changing the crystal on some computers, you could replace the power supply and it would increase the overall speed by playing around with some frequency it was delivering. But that was on the DC end I suppose. I had some info at the time for my Mac IIsi which I sped up by de-soldering the crystal and adding in a slightly faster one. I think it was a kit you could buy online. Anyone recall what I'm talking about?


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Re: Power supply

Postby stephen_usher » Mon Aug 10, 2020 9:24 pm

It probably just overclocked the CPU a bit.


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Dave
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Re: Power supply

Postby Dave » Tue Aug 11, 2020 4:48 pm

In the QL, the AC feed is immediately rectified into DC. This derives +12V and -12V. The DC feed is immediately regulated to 5V for running the system. There's nothing in the QL that relies on the AC frequency. A QL will happily work on AC from about 38 Hz up to around 225-260Hz without problems.

Charlie Ingley's solution is interesting. It creates a modified sine wave, even though there's no need to do so. An AC square wave would be more efficient. However, a modified sine wave raises the noise floor of the switching frequency above anything that might push through the elderly caps on the QL.

His goal price is VERY reasonable.


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bwinkel67
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Re: Power supply

Postby bwinkel67 » Tue Aug 11, 2020 8:17 pm

From Facebook:

...the ‘modified sine wave’ [used] is basically square but with an extended zero crossing duration.



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