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Old 14th May 2005, 05:38 PM   #1
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Join Date: Mar 2004
Location: Jakarta
Question Is my DIY PS proper for powering CDROM drive?

Hi DIYers,

I need your advice...

I have an old CDROM drive with analog audio out (no digital out, though) that I'm thinking to use it as a cd-player to burn other equipment (to keep my main player life longer).

The CDROM drive need +12VDC (1A) and +5VDC (0.5A), both to the same single GND reference..

I have a spare transformer with 32-25-18-15-CT-15-18-25-32VAC/3Amp secondary, some bridge rectifier and some capacitors of various values.

If I add some 78xx regulators to make a power supply like the attached drawing, will it be proper for the CDROM drive?

Regards,
---
David
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Old 15th May 2005, 01:32 PM   #2
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Join Date: Apr 2005
Location: Tallinn
Yes, probably...

But then the 15 volt regulator should be able to supply about 2 Amperes, and the 12 Volt regulator should be able to supply 1,5 Amperes. So both must be mounted on a proper heat sink.

The efficiency of the schematic will lack though, because of the high voltage drop on the regulators. Your CD-ROM can consume max. 14,5 W of energy (12 * 1 + 5 * 0,5), but the whole circuit will draw about 25W (15 * 1,75). The efficiency will be then about 60%, which is not very good.

If I were you, I'd use a conventional step-down converter (which can be made using the same 78xx regulators - have a look at their datasheets) or use a trafo with 0-6-13 outputs to power the regulators separately.
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Old 16th May 2005, 02:35 AM   #3
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Hi Harroth,

thanks for your reply...

I'll check the 78xx datasheet then...

The main idea to use 15VAC source is to use existing transformer that I already have...

REgards,
---
David
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Old 16th May 2005, 03:30 PM   #4
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Join Date: Apr 2005
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You should also check the LM257X series step-down regulators. They tend to cost more, than the 78xx series, but they don't require so many external components, have higher efficiency, and lots of other pro's.

And you should probably be warned, that the main disadvantages of switching regulators are less stability in dynamic mode and different kinds of noise emission.
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Old 17th May 2005, 04:26 AM   #5
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Join Date: Mar 2004
Location: Jakarta
Hi Harroth,

thanks for your advice... :-)

Are you sure that LM257X circuit will be more compact then 78XX? I check on it's datasheet, it still require some components which about the same as 78XX.

Other thing is, yesterday I bought some 7812 and 7805 (each less then @US 0.25). And at the same time the shop owner told me (and even show me) that he use the configuration that I made to power his own CDROM drive. The difference is he use only 7812 and 7805, without 7815, and got the circuit powered by car battery. So, I'm convinced that it will works... :-) Of course, noise is different issue, I will check whether it is acceptable or not...

Regards,
---
David
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