220DC dropout

[MSPLife 2]

Hi everyone,

I use a Diode Bridge to convert 220AC to 220DC, how I can dropout to a low voltage about 12 VDC - 10A ?

Thanks in advanced

[enl 227]

There are a bunch of issues here. I'll address a couple.

 

First is the issue of isolation: In general, it is a good idea to isolate derived low voltage from the high voltage source

 

Second is regulation: if the target required reasonably well regulated voltage, then some means is needed to ensure he regulation

 

These lead to the commonly applied options (there are others, but they really shouldn't be implemented by someone that isn't quite conversant with power supply design and safety): Transformer voltage conversion and isolation, followed by regulation.

 

 

The two traditional methods (over the last 50 years) are to use a transformer to reduce the potential, filter with a capacitor, then use either a linear or a switching regulator to produce the output voltage. Today, there are integrated switching solutions that make this the preferable method for currents greater than maybe half an amp. TI, National, Maxim, and pretty much every other manufacturer of power supply IC's have reference designs for such applications, and these should be implemented directly for reliable service.

 

Rectification at high voltage (220V, in your case) will produce high, unisolated, voltage (300VDC or more in your case) that requires an experienced designer to safely deal with. DO NOT DO THIS. If you need to ask the question, you are 1) not ready to handle this, and 2) smart enough to realize that you are not yet ready to handle this. Good for asking. There are solutions for HV rectification (and many commercial supplies use them)  but they require good understanding of switching supply design to implement with proper isolation for safety.

 

 

If I was going to make a recommendation, I would say transformer to 12VAC to 24VAC, rectify and filter (producing about 15 to 17VDC for 12v V or 30 to 34VAC for 24V transformer,with some ripple with the appropriate filter cap) and use a switching reg running at 100KHz or so. I am a few years out of date on this so don't know what the best choice today is. There are several TI options, as well as from other manufacturers. The last time I dealt with this was about 6 years ago, and the design was roughly 500W, converting -38VDC to +12VDC. Used a National 5pin switcher, which required a hand wound toroidal. Design was close to reference design from the data sheet. The topology you are looking for is a buck converter. These can be very efficient, even with low voltage drop, and provide very high current outputs.

 

I would NOT recommend that you do this without more experience, but if I needed to do this without a transformer, I would use one of the available buck converter IC's designed for high voltage input. They are available, but come with some real risks for damage to equipment or personal injury/death if not imlemented correctly.

 

EDIT: elaboration last two paragraphs

[MSPLife 2]

My ideal as below, I think dividing resistor is not a optimal method, could you and anyone can suggest me some ways?

Thanks!

[zeke 693]

@@MSPLife,

 

@@enl has already made some excellent suggestions for you. 

 

I've drawn attention to them for you below.

 

 

The two traditional methods (over the last 50 years) are 1) to use a transformer to reduce the potential, 2) filter with a capacitor, then 3) use either 3a) a linear or 3b) a switching regulator to produce the output voltage. 

 

Keep asking questions! We are here to help :-)

[dubnet 238]

Joining the chorus in saying this is a really dangerous idea. Also, from a design standpoint, resistively dividing down this much voltage at 10A would require resistors that could dissipate a couple thousand watts. Not only is this very inefficient (in that the majority of your power is lost as heat) but a shorted resistor would put the mains voltage at the output. What is it that you are trying to power?

[Fred 453]

What you trying to make is a DC power supply. I'm sure it's well within your capabilities (if you follow the suggestions above) but it's been done many times before. Unless you have a particular interest in designing a power supply I'd suggest that you just buy a suitable one and spend your time on more interesting things.

[MSPLife 2]

I'm try to dropout a high voltage to lower for using Ti's power IC.

Thanks all.

[asgard20032 9]

I recently had similar requirement (120v AC -> 3.3v DC) for a project. I simply bought a fully integrated power supply in a small package (small compared to big power block, but still require some pcb space) on digikey. It costed me about 14$, but i have the assurance it work and its safe. Can draw about 500 mA. It has the size of a relay.

[enl 227]

As a side note: I grab supplies from desktop computers on a regular basis. Modern ones generally provide 12V@5 to 15A (or more), as well as 5V@10A (or more) and 3.3V@10A (or more). They are often free from machines that have some other failure, such as hard drive, or so full of dust as to overheat the processor to failure.