Need to convert 115V AC to 3.3V dc

Hello All,

I purchased these in the link below the price and size are correct. for the life of me I can't figure out how this thing works.

AC DC Power Supply Buck Converter Step Down Module

I was reading that a simple voltage divider could do this but I believe that was higher voltage dc to lower voltage dc not AC

This device is sufficiently cheap and small enough for me. I want to add it to a pcb with wire terminals for the ac input and then I need to route the lower voltage. (for the life of me I don't see an in or out on this thing)

I would not mind building my own circuit if it's cheaper or smaller.

Please let me know

Mark

I some times buy from AliExpress

This product looks similar and is very cheap.

mtalent: for the life of me I can't figure out how this thing works.

The mains electricity supply is not something you should play about with unless you really know what you are doing.

All sorts of unwanted excitement could ensue... sparks, fire, shocks, death and so on.

If you need a 3.3v supply for an arduino, buy a ready-made power supply.

Yours, TonyWilk

mtalent: Hello All,

I purchased these in the link below the price and size are correct. for the life of me I can't figure out how this thing works.

AC DC Power Supply Buck Converter Step Down Module

I was reading that a simple voltage divider could do this but I believe that was higher voltage dc to lower voltage dc not AC

This device is sufficiently cheap and small enough for me. I want to add it to a pcb with wire terminals for the ac input and then I need to route the lower voltage. (for the life of me I don't see an in or out on this thing)

I would not mind building my own circuit if it's cheaper or smaller.

Please let me know

Mark

Since you received no schematic with these boards and no user manual as to how to use them I would suggest that you not use them.

You could attempt to draw the schematic by going by the traces on the PCB. The PCB may only be front and back and not have more layers internally.

If you happen to have an oscilloscope and a good voltage meter you could take voltage measurements and look at the various signals present on the board to determine if they are indeed worth using.

In looking at these more closely there is one piece of information that is absent, How many amps can this provide?

There is no amperage rating. It is a glaring omission. If you can return to amazon and find a wall wart for the arduino.

It is a switch mode power supply. A diode and capacitor convert incoming AC to DC at a rather high voltage, then a switch mode controller IC converts it down to 3.3V using controlled pulse width. Isolation is provided by using a small transformer (that black block in the center) and an optoisolator for feedback with isolation.

You cannot build this yourself.

With your knowledge level, no offense meant, just buy an enclosed power supply.

They sell these with the assumption that you'll know how to use them. The boards are labeled with AC inputs and DC outputs. The ratings are arranged horribly, but since the 5V module is rated at 1A, I expect the 3.3V is rated at least 1A output.

I'm not happy with the lack of isolation of the primary from the secondary.

Thanks all,

I have a small enclosure that the pcb w/chip will go into. The enclosure has 115V already in it, so I just need to convert it to 3.3.

polymorph has the the right idea I think just buy one thats enclosed and basically drop in and solder. they are 3 times as much I was hoping that these might be user friendly.

Anyhow thanks all

Mark

mtalent: Thanks all,

I have a small enclosure that the pcb w/chip will go into. The enclosure has 115V already in it, so I just need to convert it to 3.3.

polymorph has the the right idea I think just buy one thats enclosed and basically drop in and solder. they are 3 times as much I was hoping that these might be user friendly.

Anyhow thanks all

Mark

With further digging of the 4 devices listed on amazon at the URL that you gave originally. two of them do have current ratings.

The 3.3v version is not given The 5v version is 700mA. The 9v version is not given The 12v version is 400mA.

In the image below:

The two solder holes on the left hand side are for the AC power input. I doubt that these devices care about which is neutral and which is hot.

The two solder holes on the right side toward the center of the board are the DC output. As to which is + and which is - you would have to check with a volt meter.

I still recommend that you return these to amazon.

I doubt that these devices care about which is neutral and which is hot.

If a device actually did cair about it then it would fail safety standards.

I bought a high voltage leakage tester just to test things like this. Not a comprehensive test, but better than nothing.

Grumpy_Mike: If a device actually did cair about it then it would fail safety standards.

The electrical engineer in me, (B.S.E.E. University of Illinois, Urbana-Champaign, IL, many decades ago. ) just shutters thinking about these devices. It reminds me of a company that was around when I was growing up. The company would take another company's product, typically a television or radio, would start removing parts until the device no longer worked. They would than put the last part removed back in.

This was when the televisions had the huge transformers to drive the valves/tubes, resistors rated in Watts, and can capacitors. The discharge from the CRT could bounce you across the room. Much worse than getting hit by the old car coils.

That is what these devices remind me of. The minimal parts to make it sort of work.

Shudders.

polymorph: Shudders.

you have to love those automatic software spell checkers. ;-)

why would it change "shudder" to "shutter" ? depending on ones pronunciation they may sound alike. it is spelling them phonetically?

:stuck_out_tongue_closed_eyes:

inexpensive power supply enclosed and certified

In case someone reads this having the same problem I was here is what I think will work best.

I found this one it seems like a lot less trouble and it's drop and solder and only $3.83

Thanks again all for the help

Mark

Do not use that device it is a Non-Isolated AC/DC Converter you will get electric shocks and potentially more.

Grumpy_Mike:
Do not use that device it is a Non-Isolated AC/DC Converter you will get electric shocks and potentially more.

Study the data sheet!

You still need to supply 1/2 wave DC to the device.

Paul

Yes but it is not isolated so that means anything connected to it is directly connected to the mains. Yes we haven’t been told about the application but the OP’s posts so far does not fill me with confidence that he knows the implication of not being isolated.

Stefflus: OP, have you considered that a 5V phone charger and a 3.3V linear regulator might be both safe and cheap?

I am trying to remain as small as possible and it seems that might be a bit too big.

As for the others point taken not as great as I thought. Actually since I posted I have decided to go smd double sided for size and have begun to try to find an smd version of a safe power system.

here is what I found -- IRM-01-3.3S $5.40

Link to Power supply description

Grumpy_Mike: Yes but it is not isolated so that means anything connected to it is directly connected to the mains. Yes we haven't been told about the application but the OP's posts so far does not fill me with confidence that he knows the implication of not being isolated.

Yes my Grumpy friend you are very correct I am not an electrical engineer I'm a programmer by trade. I had to do one project involving this kind of work and well I liked it. However one of the main reasons I like this forum is you guys are a lot smarter than me.

thanks again

Mark

I am running one 3.3 volt synapses sm220uf1 rf chip.