Micro footprint 90-240 VAC to 5VDC converter

Thread Starter

nekojita

Joined Nov 19, 2010
156
Hi,

For a project I am working on, I need a 90-240VAC to 5V offline converter. The converter would preferably be isolated, with overcurrent protection. Maximum current is 300mA at 5V.

I have bought several ac/dc modules meeting these requirements but the problem is size. I ordered some of these:

https://www.ebay.com/itm/192612896363

These are quite compact, but still larger than my target footprint of less than 0.75 x 0.75x 0.75". Definitely the capacitors are a challenge for keeping the size in this footprint.

What would be the best of all worlds, would be the circuit schematic and magnetics detail of a working circuit so that I can integrate this into my PCB layout and hopefully adjust footprint as needed.

I've done a lot of searching, but micro size doesn't seem available.

Does anyone in the Forum have a source for a small module meeting the size requirements or even better, a circuit design that could be made to fit in this footprint?

Any help, comments or suggestions are welcome and appreciated.

Thanks,

Neko
 

Papabravo

Joined Feb 24, 2006
16,086
Your output power is 1.5 Watt and you want that in 0.42 in^3. Your requirements are probably impossible to meet unless you contract for a custom transformer, and put components on both sides. You might also be needing a heat sink.
 

Thread Starter

nekojita

Joined Nov 19, 2010
156
Hi Papabravo,

Thanks for your response and comments. Yeah, probably a tall order given the space/^3 requirements. Custom transformer- I can do this. The PCB has two component sides- so no problem with double sided. If I need a heat sink, could make do with a large copper pad on one or more layers. Can be a 4, 6, layer board if needed using pads on layers as heat sinks. Have done this before.

Do you have an example circuit that you can post that I can work with?

Thanks,

Neko
 

Papabravo

Joined Feb 24, 2006
16,086
Hi Papabravo,

Thanks for your response and comments. Yeah, probably a tall order given the space/^3 requirements. Custom transformer- I can do this. The PCB has two component sides- so no problem with double sided. If I need a heat sink, could make do with a large copper pad on one or more layers. Can be a 4, 6, layer board if needed using pads on layers as heat sinks. Have done this before.

Do you have an example circuit that you can post that I can work with?

Thanks,

Neko
When I mentioned components on both sides it had nothing to do with how the board is fabricated. When you have a board with a mixture of SMT and thru-hole components, you can arrange the fabrication process to put through hole components on both sides. Most components will not survive a wave solder process that will immerse them in molten metal. This process cannot be automated and has to be done by hand. It is more expensive and is generally avoided.

You have not given us a schematic of a design or even an adequate set of requirements to see if proposed components are compatible.
 

Thread Starter

nekojita

Joined Nov 19, 2010
156
When I mentioned components on both sides it had nothing to do with how the board is fabricated. When you have a board with a mixture of SMT and thru-hole components, you can arrange the fabrication process to put through hole components on both sides. Most components will not survive a wave solder process that will immerse them in molten metal. This process cannot be automated and has to be done by hand. It is more expensive and is generally avoided.

You have not given us a schematic of a design or even an adequate set of requirements to see if proposed components are compatible.
Hi Papabravo,

I spent quite a bit of time looking at offline converter circuits; didn't post one because if I wanted my wish list of features, there were always too many components to fit in my volume. Need to do this with minimal parts count.

So, what do I give up? Not too much with the very basic design at the link below and it's only a handful of components:

http://www.discovercircuits.com/H-Corner/Mini 5v power supply.htm

The DC/DC converter has good line and load regulation, just no active over current or short protection. The LTSPICE simulation looks good with no components being over stressed at the 400mA maximum current.

Please take a look at the link and sim and see what you think. The circuit is shown below:

1612141613686.png

Thanks,

Neko
 

Attachments

Papabravo

Joined Feb 24, 2006
16,086
Hi Papabravo,

I spent quite a bit of time looking at offline converter circuits; didn't post one because if I wanted my wish list of features, there were always too many components to fit in my volume. Need to do this with minimal parts count.

So, what do I give up? Not too much with the very basic design at the link below and it's only a handful of components:

http://www.discovercircuits.com/H-Corner/Mini 5v power supply.htm

The DC/DC converter has good line and load regulation, just no active over current or short protection. The LTSPICE simulation looks good with no components being over stressed at the 400mA maximum current.

Please take a look at the link and sim and see what you think. The circuit is shown below:

View attachment 229213

Thanks,

Neko
Sorry. I'm not comfortable helping you with such an amateurish and inherently unsafe design. Maybe another member is willing and able to help.
 

Sensacell

Joined Jun 19, 2012
2,819
I am also in the middle of a project requiring 5V @ 100 Milliwatts DC from 230VAC 50 Hz mains, also in the smallest form factor.

The capacitor dropper design is problematic, - the mains rated X type capacitor is highly stressed- it's got to be massively de-rated if you hope to get reasonable reliability.
It's also a giant pig, around 0.366 cubic inches for the capacitor ALONE.

What you really need is the same guts as a USB charger, these designs are highly optimized, but require custom magnetics.
There are some other clever concepts- like the Microchip SR087, and the TI -TPS7A7850 both of which are NON-ISOLATED, but could provide power to a DC-DC module.

Be careful with "isolated" DC to DC modules, they might not provide safety isolation meeting regulatory standards.
 

Attachments

Thread Starter

nekojita

Joined Nov 19, 2010
156
Hi Sensacell,

Thanks for your response and comments. In all the searching that I did, I never ran across those three chips. What a treasure trove. :) Best I found was the NCP 1060 which can be configured in both isolated and non-isolated configurations. Please see attached.

So the dilemma for me is isolated vs. not. This supply will be part of a commercial product where the user has no access atoll to the 5V supply.

If I did go with isolated, I like the simplicity of the basic circuit for the VIPER06, Figure 1 shown below. Yes, it has magnetics but since it's a simple 1:1 winding, I should be able to find a commercially made small outline transformer. See below:

1612150623617.png

Comments, thoughts?

Thanks,

Neko
 

Attachments

Sensacell

Joined Jun 19, 2012
2,819
Hi Sensacell,

If I did go with isolated, I like the simplicity of the basic circuit for the VIPER06, Figure 1 shown below. Yes, it has magnetics but since it's a simple 1:1 winding, I should be able to find a commercially made small outline transformer. See below:



Comments, thoughts?

Thanks,

Neko
The example shown is NOT isolated, the output shares ground with the input.
This can be solved via optoisolation, additional feedback windings, etc.

Additionally, it's not a 1:1 ratio- it's custom for the output voltage and power level- you will never find this off the shelf.

The best idea is to look to China- the same people making zillions of transformers for USB chargers.
 
Last edited:

Thread Starter

nekojita

Joined Nov 19, 2010
156
The example shown is NOT isolated, the output shares ground with the input.
This can be solved via optoisolation, additional feedback windings, etc.

Additionally, it's not a 1:1 ratio- it's custom for the output voltage and power level- you will never find this off the shelf.

The best idea is to look to China- the same people making zillions of transformers for USB chargers.
Hi Sensacell,

Yah, transformers can be tricky business. Been there. You said in your first post that you were were trying to accomplish a similar endgame.

What did you circuit did you finally go with? Or is the jury still out?

-Neko
 

Danko

Joined Nov 22, 2017
1,079
Does anyone in the Forum have a source for a small module meeting the size requirements or even better, a circuit design that could be made to fit in this footprint?
I guess you can short footprint area, using single 90-240VAC to 5VDC+2*±15VDC converter instead two (90-240VAC to 5VDC and 5VDC to 2*±15VDC) converters.
ADDED:
It is what I told about:
1612213530525.png
 
Last edited:

Thread Starter

nekojita

Joined Nov 19, 2010
156
I guess you can short footprint area, using single 90-240VAC to 5VDC+2*±15VDC converter instead two (90-240VAC to 5VDC and 5VDC to 2*±15VDC) converters.
Hi Danko,

When I started the layout and did a reality check for space, I realized that the circuit board and line to 5V module, (the black block in the photo) it was not all going to fit in a single gang NEMA box.

I will be using your ± 15V design; the largest component there is the transformer. See photo. Hopefully Sensacell can come up with a smaller footprint for the line to 5V converter.

Neko

1612206423333.png
 

schmitt trigger

Joined Jul 12, 2010
438
You may want to open up an Apple Iphone charger to see how they done it.. They are the smallest volume chargers on the market and easily exceed the 1.5 watt output.

But I suspect that they will have very customized magnetics and silicon devices.
 

Thread Starter

nekojita

Joined Nov 19, 2010
156
You may want to open up an Apple Iphone charger to see how they done it.. They are the smallest volume chargers on the market and easily exceed the 1.5 watt output.

But I suspect that they will have very customized magnetics and silicon devices.
Hi Schmitt Trigger,

That's a good suggestion but like you say, custom magnetics and quite possibly custom silicon. Maybe with some poking around I can find a teardown. I wouldn't be to hopeful that component identities would be readily available.

Back in the day on DIP chips, we used a solvent to wipe off the chip identity. :)
Neko
 

Danko

Joined Nov 22, 2017
1,079

Attachments

Last edited:

Thread Starter

nekojita

Joined Nov 19, 2010
156
Hi Schmitt Trigger,

That's a good suggestion but like you say, custom magnetics and quite possibly custom silicon. Maybe with some poking around I can find a teardown. I wouldn't be to hopeful that component identities would be readily available.

Back in the day on DIP chips, we used a solvent to wipe off the chip identity. :)
Neko
I found this Apple charger teardown: https://www.ifixit.com/Teardown/Apple+Wall+Charger+Teardown/120511
That little cube is fully packed! Below is a photo of a teardown I did on a standard USB wall charger cube; it's a little smaller the the Apple unit and a little smaller than the off-the-shelf unit (black):

1612221756189.png
The tallest components are the transformer, cap, and the USB connector.
 

Thread Starter

nekojita

Joined Nov 19, 2010
156
I guess you can short footprint area, using single 90-240VAC to 5VDC+2*±15VDC converter instead two (90-240VAC to 5VDC and 5VDC to 2*±15VDC) converters.
ADDED:
It is what I told about:
View attachment 229269
Hi Danko,

Two comments

• All the apps circuits on the VIPER06 datasheets have many more components; this circuit may need more
• From the TDK datasheet, the bobbins for those cores appear to have 6 pins maximum- did I miss something

Neko
 
Top