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connecting 3 non-isolated DC to DC converter

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Member level 3
Jun 30, 2008
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Hello ALL,

I need 6A on the 5V rail, I found a DC to DC converter with an output current of 2 A@5V, is there any risk if I connect the output of 3 non-isolated DC to DC converter together to have 6A at 5V?

Thanks in advance,


That depends on whether you can count on -
- synchronization of phase & frequency
- match of through-delay on edges, to avoid cross-
- a single inductor good for 6A in the inductance value
you want

A current-share I/O if present, would at least make
sure one converter doesn't start hogging or loafing.

If you can use three inductors and construct a poly-
phase control then you can get to a 3X effective
frequency (ripple) at a 1X base frequency (switching

You have to get down to details.

POL (point of load) converter modules are available with output currents of 10 A and more, from various vendors. I previously used TI products. Without special means, most regulated power supplies are not suited for parallel operation. You may achieve e.g. overload and periodical shutdown of individual moduls, causing an overall supply failure. If modules offer paralleling options, you'll find a specification info.

The problem is that I have a single input voltage, I did not find any converter that supply 6A @ 5V with that input voltage. TI have some DC to DC converter with a specification info about parallel option but don't have the input and output voltage I need.

I am planning to use a output boost converter from 6V to 10 V per example, than another DC to DC converter from 9V to 5V. in this way I can find a converter that can supply 6A at 5V. does this work?



I don't understand the motivation for cascading converters. What's your input voltage specification?

The real situation is as follow (I have not describe it exactly because it is difficult to explain):

I am designing an daughter board that plug into a back plane, I have only 5V and 3.3V rails, and I need 3.8A at -5.2V.
I did not find any inverting DC to DC converter witch can supply this amount of current at -5.2V, especially that I only have 5V and 3.3V input voltage. I found on TI website the PTN04050A but the maximum output current is 1A. I also found some inverting DC to DC converter with an output current of 4A at -5.2V but the input voltage is 9V minimum. this is why I was thinking to use a boost converter from 5V to 9V and and inverting DC to DC converter from 5V to -5.2V

I'm pretty sure you could rig a positive PWM controller
to make a negative one, using a transformer based
(rather than inductor) design. I had occasion to do
one such converter IC (lower current) and the only
significant feature was an error amp that would take
a below-ground signal. I did this by using the bandgap
voltage against negative output voltage, and making
ground the "reference" point with a "single supply op
amp" error amp.

Yes, this works with any standard buck converter. The operation is almost identical to a 10V input 5 V output buck converter. But the controller loop is different and this may cause stability issues with some converters. I used a National Simple Switcher in this operation mode, they even have a respective application note **broken link removed**.

By the way, you didn't mention the intended invertíng converter operation in your previous posts, so the real problem wasn't understandable.

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