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I'm trying to create a power supply for a project I'm working on. It will need to be able to convert 120VAC from the wall to 24VDC and be able to take around 15 amps of current draw (it's driving some pretty powerful stepper motors). Finding transformers and components that were rated for that amount power draw seemed impractical, especially considering how high the capacitance values had to be in order to smooth out the rectified AC at that current. I was wondering if I could then have multiple transformers in parallel, spreading the current out across them? After rectifying the output of each of the transformers, they'd be fed into a buck converter, and the PWM would be synced across the parallel lines, before they're brought back together to form the since high amperage power rail to power what I need. Would this be a sensible way to do this? Is there a simpler solution I'm missing?

enter image description here

This is a bit of an aside, but even without that, I was wondering how the PWM controller of the buck converters should be powerered? I was thinking of just putting another transformer that would have a much higher winding, rectifying it, and feeding it into a linear regulator to get a 5V rail to power the logic. This feels weird to me, so I was wondering if there's another way to do that.

Anyways, I kind of asked two questions, but if you have any advice, that would be greatly appreciated!

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  • \$\begingroup\$ that's exactly how all power outlets and light bulbs are connected in your house \$\endgroup\$
    – jsotola
    Nov 1, 2023 at 1:12
  • \$\begingroup\$ newark.com/mean-well/hrp-300-24/power-supply-ac-dc-24v-14a-rohs/… I would buy one not make it. Your idea of paralleling the primary if a transformer is good. Use the exact same part every time. \$\endgroup\$
    – user338146
    Nov 1, 2023 at 1:15
  • \$\begingroup\$ even paralleli the secondaries (after rectification) will work pretty well, but just buy a power supply \$\endgroup\$ Nov 1, 2023 at 3:11

2 Answers 2

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The schematic, you have referred to, is not relevant to a switch mode power supply.

It pertains to a linear DC power supply.

Here's the block diagram of a linear DC regulated power supply.

enter image description here

It is quite bulky owing to its large 50 / 60 Hz step-down transformer, pass transistors and heat sinks.

The switch mode power supply, however, is compact with a much smaller 50 kHz step-down transformer minus pass transistors and heat sinks.

enter image description here

Designing and building an SMPS is not going to be easy.

It would be worth your while to buy a sleek SMPS, available off-the-shelf, at a reasonable price.

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  • \$\begingroup\$ So I truncated my schematic to only show how I was planning to hook up the transformers, since that's what I wanted to double check. But yeah, I'm not actually making an SMPS like I thought, I'm just using multiple buck converters in parallel. \$\endgroup\$ Nov 1, 2023 at 13:14
  • \$\begingroup\$ Hi Arthur, In that case, you do need to edit your question to make it more relevant. \$\endgroup\$
    – vu2nan
    Nov 1, 2023 at 14:40
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As for paralleling transformers off of an AC feed, take a look out of your window and you will see an endless quantity of utility transformers being fed in parallel off of a single AC feed. Connecting the outputs in parallel is also OK, the rectifiers don't know who is contributing what to the load, and even imbalances tend to even themselves out when the transformers are close.

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    \$\begingroup\$ Are you sure transformer outputs can be put in parallel? What if they have say 5% of tolerance and you might have slightly different output voltages. Usually, unless explicitly accepted by the transformer manufacturer, you would not parallel transformer secondaries. \$\endgroup\$
    – Justme
    Nov 8, 2023 at 19:49
  • \$\begingroup\$ I had to check your profile, and yup, USA. Seeing transformers 'in the wild' where I live are rare. \$\endgroup\$
    – MiNiMe
    Nov 8, 2023 at 19:49

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