PSU alternative?

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1024MAK
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Re: PSU alternative?

Postby 1024MAK » Tue May 12, 2015 2:17 pm

As I said above, you would need two transformers.
One with a 15V secondary - feed one wire to the QL via a fuse
The other wire connects to the 0V pin on the QL

The second transformer should have an output of 9V. This should then be full wave rectified. Then go to a simple "pre-regulator". Followed by a large electrolytic capacitor (smoothing) and then the output goes to the QL. Include a fuse.

The "pre-regulator" can be a power transistor (mounted on a heatsink) controlled by a resistor and Zener diode.

If you use a single 15V transformer and try to use this to feed the 9V DC supply, you will need a big transformer and an even bigger heatsink to get rid of the excessive voltage (power).

However you could use a "simple switcher" switch mode DC to DC converter to drop the rectified and smoothed 21V (that you would get from the 15V transformer) to 7.5V DC. See here for one of many available.

Mark


QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
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Lurch666
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Re: PSU alternative?

Postby Lurch666 » Tue May 12, 2015 3:06 pm

Now that doesn't look too difficult.
In reference to the DC to DC converter would this be better?

http://www.ebay.com/itm/DC-DC-Buck-Step-Down-Converter-Module-LM2596-Voltage-Regulator-Led-Voltmeter-M1-/291455750070?pt=LH_DefaultDomain_0&hash=item43dc1dcfb6

As it is a converter and voltage regulator?

I'm thinking I use a full rectifier bridge to convert the ac into dc,run it through this regulator and drop it down to 9v giving me the 15v ac and 9v dc?


Thanks for all the help dude.


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1024MAK
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Re: PSU alternative?

Postby 1024MAK » Tue May 12, 2015 3:56 pm

The one you linked to uses a LM2596 like the one I linked to. This chip does all the hard work, it is a switch mode regulator chip.
Up to you if you want a voltmeter. There are lots of these DC-DC converters on eBay. It does need to be a step down type though. Oh and remember to adjust the output before connecting to the QL!

I was thinking of a circuit like this:-
Replacement QL PSU e1.png

Because we are feeding the output of the secondary of the transformer to the QL and the QL uses the DC 0V / GND line as a common for the 15V ac as well, you cannot use a four diode full bridge rectifier.

Mark


QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
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Derek_Stewart
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Re: PSU alternative?

Postby Derek_Stewart » Tue May 12, 2015 4:23 pm

Hi,

I have fitted a TSR 1-2450 in place of the 7805 regulator. There is no heat from the TSR 1-2450, so no heat sink.

All work with QL-SD and Qubide Clone.


Regards,

Derek
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Lurch666
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Re: PSU alternative?

Postby Lurch666 » Wed May 13, 2015 12:16 pm

So being a collector of old computers I suddenly remebered having a simalar problem with my TRS-80.
I had a PSU for it but needed another for the expansion unit I got for it.I ened up using a USA one with a stop down transformer before I managed to get myself a U.K. one.
I still have the USA psu and its outputs might be usful for powering my Q.L.

http://www.trs-80.com/images/zaps-Model-I-Power-Supply-DIN-Pinout.png

Could I use the AC output as is and use a DC to DC converter to drop the 19v dc to 9v dc?


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1024MAK
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Re: PSU alternative?

Postby 1024MAK » Wed May 13, 2015 10:00 pm

Yes, but only if the AC and the DC outputs are not internally connected in the PSU. And if the DC output can safely supply the required current / power.

Mark


QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
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Lurch666
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Re: PSU alternative?

Postby Lurch666 » Fri May 15, 2015 10:00 pm

OK so I've copped out.

Managed to get a spares and repairs Q.L. with a working PSU so now I have my Q.L. running.
Just got to sort the microdrives out now.Will have a look and will maybe use some parts from the non-working Q.L. microdrive mechs to get a fully working one.

Thanks for all you help dudes.


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vanpeebles
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Re: PSU alternative?

Postby vanpeebles » Fri May 15, 2015 10:08 pm

What are your plans for the QL? :)


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Lurch666
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Re: PSU alternative?

Postby Lurch666 » Fri May 15, 2015 11:00 pm

Open it up.clean the heads on the microdrives to see if that fixes them.If that doesn't work look around on here and the 'net to find other solutions and if that doesn't work swap the microdrives from the spares Q.L. into the working one to see if they work.


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vanpeebles
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Re: PSU alternative?

Postby vanpeebles » Fri May 15, 2015 11:01 pm

What will you be using it for? :)



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