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Simple switching +-5v supply

CommanderLake

Oct 2, 2012
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I need a symmetric 5v supply for 2x PGA4311's and a 14M2 Picaxe and another for 2x 5v relays, the supply is +-30v so linear regulators would be very hot and inefficient so I need help finding the right IC's for a switching supply and I need them to be easy to solder so if they are surface mount packages I would prefer a package with widely spaced easy to solder pins.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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You might like to investigate the LM2576HVT-ADJ

Alternatively, there re a large number of SMPS modules on ebay for prices that make building a low power DC-DC converter hardly worth the effort.
 

CommanderLake

Oct 2, 2012
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What about the negative side? I found the TL2575-05 for the positive.
By SMPS module do you mean a separate board because this is for an all in one 7.1 amplifier board?
 

(*steve*)

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Do you want -5V from +30V, or do you have a -30V supply as well?

You could use something like these. (I say "like" because they only have a max input voltage of 17V).

However some are made with higher input voltage ranges.

If you want -5 from +30, that's also achievable, but I've not seen any simple modules. However there are a number of devices that can do it.

I've got to disappear now...
 

(*steve*)

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Back again...

Here is the sort of module I was talking about.

But they're only easily available with +ve input and output.
 

CommanderLake

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The main supply on the amplifier is symmetrical.

Yea I dont want a module I want everything on 1 PCB.
 

(*steve*)

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This article should give you some ideas.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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These are close to what you need, but your input voltage is right on the limit.

This expands on the article I mentioned above. Note that you will probably want a HV variant of the regulator to work from a -30V input.
 

CommanderLake

Oct 2, 2012
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I asked for help on the TI community forum and Anston Lobo a TI employee came up with THIS

I just wanted to see what you think?
 

(*steve*)

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It looks fine, however you need to note that the -5V rail is not well regulated (I think).

As long as the current drawn from both rails is similar, the -5V rail should remain close to -5V

If this is important it may be useful to go back and enquire about it.
 

CommanderLake

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Using the falstad circuit simulator I can see an oscilation on the positive outout created by the capacitors and inductors when its powered on then fades away and the negative voltage is reduced by the forward voltage of the diode.

This seems to be turning into a wild goose chase.

Ah ha! If I put a diode after the inductor on the positive side it compensates for the drop on the negative side and eliminates the oscillation!
 
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(*steve*)

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For a given collector current the power dissipated is almost completely determined by the voltage across the collector/emitter.

I can't really figure out what you're asking.

As for the inverting regulator question (I've already pointed you to how to get -5 from -30 using a +ve reg), you might want to look at this.
 

CommanderLake

Oct 2, 2012
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Actually going back to my BJT question, a lower Pd for a given DC collector current does mean its more efficient because the collector emitter saturation voltage is lower, take this for example: nxp.com/documents/data_sheet/PBSS4041NZ.pdf
they have an extremely low Vcesat making them cooler at a given load current.
 
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