Author Topic: Split rail Power supply using coupled inductor  (Read 1161 times)

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Offline tip29Topic starter

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Split rail Power supply using coupled inductor
« on: December 18, 2019, 04:19:15 pm »
Hello guys,

So I recently built a split rail power supply using TPS560430 fixed frequency switcher and a coupled inductor following the topology as shown below. (TPS560430 doesn't require a catch diode)



I designed it to output +6V -6V. The result I got was an uneven split from the ground. Like +9V -3V. More positive than negative.
If I load + and - terminals the split starts improving. And, across the + and - terminals the switcher IC regulates the output of 12V perfectly.
If I increase the input voltage to the IC the split starts getting worse (uneven).

Is there anything I can do to get close to even split without loading the power supply?

Thank you.
 

Offline capt bullshot

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Re: Split rail Power supply using coupled inductor
« Reply #1 on: December 18, 2019, 04:49:47 pm »
The positive side rectifies the coupled inductor ringing if unloaded, and the negative side is loaded by the switcher IC, so this circuit can't produce evenly split output if unloaded.
This circuit requires some substantial and best case evenly distributed load to produce an even split. There's some other tricky circuits available that regulate the positive side and provide the negative side unregulated, using an AC coupling capacitor and an additional (non-coupled) inductor. It's similar to the SEPIC auxiliary described here: https://www.maximintegrated.com/en/design/technical-documents/tutorials/3/3740.html but the inductors don't need to be coupled.

Here's an example for the "charge pump" method: https://www.analog.com/media/en/reference-design-documentation/design-notes/dn47f.pdf

Edit: If you simply want to split your supply to half (midpoint @ 1/2 Vin), use a synchronous half bridge buck converter driven by a 50% duty signal, and its output as the virtual GND.

« Last Edit: December 18, 2019, 04:54:06 pm by capt bullshot »
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Offline David Hess

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Re: Split rail Power supply using coupled inductor
« Reply #2 on: December 19, 2019, 01:08:49 am »
Good tracking between the supplies requires the switching regulator to be in continuous conduction mode which requires a minimum load on the main output.

 
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Offline tip29Topic starter

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Re: Split rail Power supply using coupled inductor
« Reply #3 on: December 19, 2019, 10:35:55 pm »
Thanks for the links.
 


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