# Can you use a switching regulator from 120 V AC (house power), 5 A to output 5 V DC, 5 A?

I am looking to power my high-powered LEDs. If I can switch from 30 V DC to 5 V DC with a switching regulator, can I skip over using a power supply and just connect a switching voltage regulator directly to the 120 V AC? When doing this, and I may need to convert AC to DC by using a full bridge rectifier, would it work?

EDIT:

I've been using buck switching voltage regulators to step down voltages from 30 V DC to 5 V DC at low current with little to no issues. They have a limit of 400 mA or so and I now need to switch voltages from 120 V to 5 V AC or DV, then convert to DC if it's AC. What can I use for bringing down the voltage? I prefer to use the buck switching voltage regulator because I have experience with them.

My load is 5 A when it's 5V DC, so my question is: can I use the buck converter (if I find one that can do 5 A) to convert to 5 V AC without it burning up? What alternative is there? Is this a time when only a transformer will do? I prefer not to use a transformer because they are big and weighty on a PCB. Also I have seen phone chargers and even the Raspberry Pi charger put out 3.5 A from a wall wart in a very small space.

• Only if the 5V output switching regulator can accept 120VAC. Commented May 21, 2020 at 23:34
• would it work? Sure. Would it be safe? who knows. I don't recommend doing anything mains-voltage if you're sufficiently inexperienced that you have to ask questions like this. Commented May 21, 2020 at 23:34
• connecting directly to AC is an almost sure way to build a deadly device ... if you have to ask, then you are not qualified to build it Commented May 21, 2020 at 23:37
• So you want to build a DC power supply instead of buy one, even though DC power supplies are one of the most commodity things on earth, and you can get a perfectly safe UL listed one for a few bucks? Commented May 21, 2020 at 23:46
• Saying "using a full bridge rectifier" is vague. If you're talking about a common design RC rectifier, you'll have to do more than just something like this. Is it possible? Sure, a lot of things are as long as you abide by the laws of physics... but I wouldn't recommend it. There are already certified devices out there that can do what you're looking for so I don't think there's a need to reinvent the wheel.
– user103380
Commented May 21, 2020 at 23:50

Sure, check out an ATX power supply for a PC computer. They are powered by 120VAC or 240VAC. Pins 21-23 are 5Vdc at near 30A (in parallel). So I guess the only thing left is to current regulate the LEDs. But at least now you are in the safe voltage range if you need to roll your own.

Pinout Reference for ATX 24 pin 12V Power Connectors

Pin Name Wire Color Description

1 +3.3V Orange +3.3 VDC

2 +3.3V Orange +3.3 VDC

3 COM Black Ground

4 +5V Red +5 VDC

5 COM Black Ground

6 +5V Red +5 VDC

7 COM Black Ground

8 PWR_ON Gray Power Good

9 +5VSB Purple +5 VDC Standby

10 +12V1 Yellow +12 VDC

11 +12V1 Yellow +12 VDC

12 +3.3V Orange +3.3 VDC

13 +3.3V Orange +3.3 VDC

14 -12V Blue -12 VDC

15 COM Black Ground

16 PS_ON# Green Power Supply On

17 COM Black Ground

18 COM Black Ground

19 COM Black Ground

20 NC White -5 VDC (Optional - Removed in ATX12V v2.01)

21 +5V Red +5 VDC

22 +5V Red +5 VDC

23 +5V Red +5 VDC

24 COM Black Ground

UPDATE: Here are a few tags from actual power supplies showing the currents available. The last one does show lower current (15A) on the 5V rail, so your mileage may vary.

• "Near 30A", that's unlikely. "Modern" PSUs have most (almost all) of their capacity on the 12V rails. A 20+ year-old PSU has a lot more capacity on 5V and 3.3V. Commented Aug 14, 2022 at 22:09
• @OskarSkog added images from power supplies. Looks like you could be right for some of them. Commented Aug 15, 2022 at 12:41
• Those seem pretty ancient. Most of the load is on the 12V rail since Pentium 4 got a CPU only power connector and GPUs have extra PCIe power connectors. And -5V hasn't been part of the standard for quite a while. // In older copmuters, 12 V is used mostly by motors (harddrives and fans). Commented Aug 15, 2022 at 13:06
• @OskarSkog That last one is 54A on 12V and only 22A on 5V. It is currently for sale on Amazon, so as you say, the ATX supplies are changing over time. Either way, the OP was only looking for 5A at 5V. So whether he buys a new one, or finds an old one, he's good to go. Commented Aug 15, 2022 at 13:12