How much sagging in an unregulated DC-DC converter? - diyAudio
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Old 26th November 2004, 09:13 AM   #1
space is offline space  Norway
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Join Date: Jan 2004
Location: Oslo - Norway
Default How much sagging in an unregulated DC-DC converter?

I'm working on a SMPS for a car amp, and planning on using the ESP project 89. Elliot states that there is almost no sagging on the supply voltages during load. How much is "almost no sagging"?
I'm planning on +/-40V.

I have built a working prototype of the p89, but got unsatisfactory results. On my prototype, (was exactly that, a prototype), the output sagged about 10% with a 100W load. (Taking into account the drop at the 12V input) Is this normal? What can I expect from a well built unit?

Some details of my prototype:
Input caps: 2x4700uF
Output caps: 2x2x2200uF
Core: Edt49
Windings: pri: 3x1mm2 Litz, sec:1x1mm2
MOSFETís: IRFZ48V (72A, 60V, 12mohm)
While running a 100W load there was very little heating, just some inn the MOSFETís.

Iím planning on getting about 400W max. (Yes, like Eva and others pointed out, the edt49 is overkill, I bought it thinking bigger is better, but anyway that is what I've got at the moment.)


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Old 1st December 2004, 07:55 AM   #2
ssanmor is offline ssanmor  Spain
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Join Date: Jan 2002
Location: Madrid
I am the designer of that project.

Well, the power supply has quite good load regulation, but how much is the "shagging" depends on your components and transformer, as well as the regulation of your 12v source.
Anyway, you can implement feedback so the supply is regulated to improve that. For that, you need to put the output inductors (about 47microH per rail should be ok) and a feedback scheme. If you want to keep your primary and secondary grounds separated (good in a car to avoid ground loops), you need an optoisolator to close the loop.

I recommend that you wind your own toroidal transformer instead of an ETD. Magnetics INC have a bunch of them. But have in mind that you need ferrrite cores, not powder!

My experience is that in a car you don't need regulation, anyway, and it can complicate things quite a bit. I would operate at full (almost) 50% duty-cycle. Regulation could be necessary only if your amplifier has very bad supply rejection, IMHO.

Have luck.
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