Hello, i'm in the process of this creating this design and is requires 120 AC to be transformed down to 24VDC.

I've been told to transform the 120AC to a lower Voltage then use a bridge to convert to DC.This is the part were i'm getting stuck.

The power consumption is very low about 5Ws.
Isolation rating is 2500VRMS
Also this is very small form factor so i have a height limit of 24mm

 

Hello,

Hello to you.

 

Hello to you.

Accidentally posted without my full questions woops

 

Hello, i'm in the process of this creating this design and is requires 120 AC to be transformed down to 24VDC.

I've been told to transform the 120AC to a lower Voltage then use a bridge to convert to DC.This is the part were i'm getting stuck.

The power consumption is very low about 5Ws.
Isolation rating is 2500VRMS
Also this is very small form factor so i have a height limit of 24mm

The solution depends on the end usage and application of the device. Is this "one of" or a production item?
I would just go out and buy a 120VAC to 24VDC power adapter.

 

The solution depends on the end usage and application of the device. Is this "one of" or a production item?
I would just go out and buy a 120VAC to 24VDC power adapter.

More of a production item

 

Is this school work? If not, why is the height limitation 24mm? It immediately rules out using a conventional power transformer.

 

I've been told to transform the 120AC to a lower Voltage then use a bridge to convert to DC.This is the part were i'm getting stuck.

What current do you need? The transformer would likely cost more than a secondhand laptop supply.

More of a production item

I'd still buy an adapter. It will already have the required approvals (e.g. UL).

 

https://www.amazon.com/dp/B0897G5KP1/ref=sspa_dk_detail_3

 

Why design your own? This would do the job:
The shortest dimension is 16.3mm and the price will not break the bank.

 

Why design your own? This would do the job:
The shortest dimension is 16.3mm and the price will not break the bank.
View attachment 326461

I've looked into these modules but I need to have an operating voltage range of 60VAC - 135 VAC

 

Two things you need to know about transformers:

1. When transforming voltage from one level to another you need to account for wattage. That's to say that 120VAC at 2A is 240W. Transforming that down to 24VAC (I know you want DC, bear with me) 240W ÷ 24V = 10A. That's not MORE power, that's the same amount of power at a lower voltage and higher amperage. You still have 240 watts. BUT WAIT! That's assuming the transformer is 100% efficient. And transformers are not 100% efficient. You WILL have losses. So if your final output is 5 watts then 5 ÷ 24 = 0.208 Amps (208mA). Assume an 80% efficiency you would need a small transformer rated for 120VAC @ 6.25W minimum. It's always recommended you use at least 50% more than you need. Many here will tell you double. I'm suggesting 9W, others will suggest 12.5W. Either way - you want the extra headroom to cover unexpected conditions.
2. The second thing you need to know about converting AC to DC using a transformer and full wave bridge rectifier is this: You can expect approximately 1.414 times the AC voltage when filtered through a cap. That is to say 24VAC rectified and filtered is going to be nearly 34 volts DC. (24VAC • 1.414 = 33.936VDC when properly filtered).

Filtered? you ask? AC will hum or cause interference with your circuit. Filtering is important if you need a pure DC sine. Not sine wave, DC is steady. Even filtered there will be some ripple.

Add to your complexity you're looking for something just under 1 inch (Yankee terms). 25.4mm is equal to 1". That's not a lot of room to work with. And here's another thing you need to consider - "Heat Management". In a small area you can expect heat to build. If not vented it will shorten the life of your project or product.

 

I've looked into these modules but I need to have an operating voltage range of 60VAC - 135 VAC

That's not going to be easy to find. 100 to 240 VAC is common. The reason why 100VAC is because some countries run on a 100VAC system. A lot run on 120VAC and many run 240VAC. 60VAC may be something you need to forget about. And if your input range is 60 to 135 VAC then a transformer is not the way to go. There's just too much variation in the input to maintain a 24VAC output.

 

And one other point. If this is a production item you will require UL certification and this is costly.
The sealed AC to DC adapter is already UL certified or should be UL certified. Check before buying.

 

If you start with 60VAC and transform down to 24VAC that's 1 : 0.4 ratio then 135VAC at that ratio would be 54VAC output. IF you regulate it down to 24VDC you're going to be wasting 30 volts as heat energy. That's going to be a whole lot of heat wasted energy. Heat management will become critical long before you get very far in your project. So a transformer is not the way to go. At least that's my opinion on the subject.

 

If you start with 60VAC and transform down to 24VAC that's 1 : 0.4 ratio then 135VAC at that ratio would be 54VAC output. IF you regulate it down to 24VDC you're going to be wasting 30 volts as heat energy. That's going to be a whole lot of heat wasted energy. Heat management will become critical long before you get very far in your project. So a transformer is not the way to go. At least that's my opinion on the subject.

For the most part all the IC's run off the 3.3VDC rail, pulling about 250mA

So doing my calculation I'm getting about 1.5W and 0.0625A at 24VDC (With the 1.2 Efficiency taking into account) I said 5Ws just for a standard number but it wont be that high.

Yeah that's why i'm kinda stuck at the moment on what to do. The 60VAC is tripping me up.

 

The wall-wort type supply, as shown in Post #8 is external, so the size limitation is not a consideration.
Also, you don't have to design protection for high AC line voltage inside the device.

 

I've looked into these modules but I need to have an operating voltage range of 60VAC - 135 VAC

THIS is absolutely what you want, for $2.98:

 

Danko, it seems that, no matter what circuit one requires, there will already be something ready-to-use on Ebay or Aliexpress, and at a far cheaper price than the cost of the individual components.

 

Danko, it seems that, no matter what circuit one requires, there will already be something ready-to-use on Ebay or Aliexpress, and at a far cheaper price than the cost of the individual components.

That is the modern electronic reality. We might as well tear up our diplomas and go into real estate.

 

Danko, it seems that, no matter what circuit one requires, there will already be something ready-to-use on Ebay or Aliexpress, and at a far cheaper price than the cost of the individual components.

Yes. it is!

That is the modern electronic reality. We might as well tear up our diplomas and go into real estate.

We are guilty. It is progress, in which we participated (participate) too.