XL6007 used as dual rail supply without transformer

[HSPalm]

Hello,
I'm looking into making a dual rail supply which is only powering a PWM signal of +/-12V with very limited current needs.
This circuit seems to far exceed my demands but I wonder how it works?
https://www.aliexpress.com/store/product/No-Pin-3-11V-Positive-Negative-Boost-Converter-Step-Up-Power-Supply-Module-12V-Output-ADC/1829717_32826939640.html?spm=2114.12010615.0.0.10118ef6KFWVqA

The datasheet of the controller IC has an example of a dual rail supply configuration on page 7, but it includes a transformer with dual secondary taps. The circuit in the store only has a single power inductor.

I will most likely buy a +/- 15V version and trace the circuit. I will use linear regulators on the outputs for better regulation.

[Buriedcode]

On that page you linked, you'll notice the asymmetrical current of the positive and negative outputs (700mA for positive, 150mA for negative) that tells me the output is from a charge pump, driven by the switching node.   Its quite a common way to add a negative rail to a boost converter, as it only really requires two diodes and two caps, with an output of roughly the positive rail -2Vf where Vf is the forward bias drop of the diodes used, ~0.3V for shottky, and ~0.65V for silicon.

It'll have an output resistance much higher than the positive rail, and won't be tightly regulate... so if you pull say 50mA from it, and your positive rail is set to 12V, you won't get -12V more like -9 (all depends!).
But for low currents, its a fairly simple and clean way to get a negative voltage form a boost converter.  At that price I don't think it will hurt to get one and test it.

So, the short answer is, "charge pump", with an output of -12V - 2*-0.3V = -11.4V.

Edit: fixed typo's, because otherwise I can't sleep!

[HSPalm]

Aha, so that's what all the extra capacitance and the extra diodes are for. Thank you Buriedcode.

[Skidlz]

Sorry, I know this is a very old thread. It showed up on google when I was trying to find more info about making dual rails with this chip though. So maybe others will stumble on it too.

I drew a schematic for a similar board (DD1912PA) that uses this same XL6007 chip, and I figured something out about the transformer. It's not really a transformer! Or it doesn't have to be.
You can use 3 separate inductors. Then it follows the generic SEPIC design: https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter

I've attached the schematic I drew. It's basically the datasheet design.