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Old 3rd April 2005, 03:35 PM   #1
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Default UC2577T power supply

I know I've asked about simple PSUs for car amps before, but I think I may have finally found one that would work, a UC2577T-ADJ. I have some of them, and according to the datasheet, http://focus.ti.com/lit/ds/symlink/uc2577-adj.pdf, they can operate from 12VDC and output up to 60VDC at 3A.

I know little to nothing about switching PSUs, so I have no clue where to start with building this. Can anybody help me design a schematic for this so I can make a PCB and build it?

I don't know if I can use two of them to make a split suppy, but if I can I want to set the power of each around 28-29VDC, otherwise I want to set it at 56-58VDC.

Can this be done? If so, would somebody please help me figure how how?

Thanks,
Mike
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Old 3rd April 2005, 04:08 PM   #2
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Hi Mike

You can use it for a flyback converter.
Then +/- 28V are possible.

Check for a similar, but little more powerful device
from National.
The data sheet also contains schematics for flyback.
In figure 9 you can see a flyback which delivers pos and neg output voltages.
http://www.national.com/pf/LM/LM2587.html
In flyback topologies, take care for leakage inductance of the transformer and proper snubber for the switch.


Good luck
Markus
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Old 3rd April 2005, 04:26 PM   #3
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uhhhps...
Figure 10 & 11 of the LM 2587 data sheet, of course.
Figure 9 is a single output.....
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Old 3rd April 2005, 05:09 PM   #4
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Thank you.

Are the two chips interchangeable, so I can use the schematic from National for the TI chip? I have that one and would like to use it.

Also, the transformer used in that circuit, do I have to wind one myself. Can I just use a torrid core and wind until I get the voltage I want? Or will I have to change something on the chip so it knows I am running 28V not 12V in the feedback.

And, will I be able to get the full 3A, or because of the step-up transformer, will I be trading voltage for current.

Finally, can I parallel more than one of the chips to get more current? For example, if I were to get 4 of the National Semiconductor ones, could I parallel their outputs to get 20A going into the transformer?

Thanks so much for the help,
Mike
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Old 3rd April 2005, 05:48 PM   #5
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Join Date: Dec 2003
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The chips are not interchangeable without circuit adjustments.
BTW: 3A in the data sheet means the max. current of the switch
in the data sheet. The possible output current to 60V DC rail
will be MUCH less ! Best case in a boost arrangement, when operating
from 12Vdc input will be about an output of 60V / 300mA. More realistic 250mA. Also is 60V output voltage of a boost converter to close to the max. operating of 65V of the switch. If you go for
flyback you can handle this by a suitful transformation ratio, but
this will again reduce the possible output current.
Simple paralleling is also not fortunate... except for blowing it.
Just "pick a torroid and wind".... oh, oh... well somtimes it looks
like this if you watch experts. But it isn't that easy.

For higher power car smps, you should consider a push pull converter anyway.

You have two options:
A:
Search the WEB and the this forum for fundamentals about flybacks (or for push pull) and then rebuild a design that is close to your requirements. When it works, slowly start to modify to the direction you need.
B:
Search a proven SMPS design (including PCB) that exactly
matches to your requirements and hope that it will work.
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