High Voltage Switching Regulators

kt88seamp

I am looking for switching·regulator devices that can take the mains voltage rectified and step it down to 3.3 volts and 5 volts. The devices with the highest input·voltage I found were 100 volts. Many of these devices look easy to work with. I have a basic understanding of switched mode power supplies. So are there·IC·regulator type·devices that can take·120 volts and step it down without have to use a transformer?

Post Edited (kt88seamp) : 10/16/2009 6:18:46 PM GMT

Mike Green

You need a transformer for safety purposes. With switching regulators designed for mains use, the transformer operates at the switching regulator's frequency (usually 10's to 100's of KHz) and can be quite small. There are some circuits that take 120V and, using a capacitor as the impedance, drops the line voltage to something that can be managed by a linear regulator. These are always low power and can only be used when isolation is not an issue.

kt88seamp

Are those transformers used for isolation purposes only or do they step down the voltage as well?

kwinn

Re: "Are those transformers used for isolation purposes only or do they step down the voltage as well?"

Depends on the design of the supply. In most cases the transformers provide isolation and step down in one unit to save cost. For multiple output voltage supplies that require isolation, isolation from line noise, and tight regulation there may be an isolation transformer providing an intermediate voltage and a transformer/regulator for each output voltage. This is expensive, so it is not common.

HollyMinkowski

My advice is find a supply of cheap 5v switching wall power supplies and use a 3.3 linear to get
both 3.3 and 5v.

I have 60 of them I recently acquired while converting some cameras for use in a project at work.
They are 330ma units and are meant to charge a lion battery in the cameras...they terminate in a
mini usb plug. I tried using one to power a test board with a prop and some 5v chips and they seem ideal.
I have not cracked one open but they weigh nearly nothing and probably contain a tiny board that could
be mounted in a case easily. 120vac in and 5v dc out and seems to be zero heat generated.

I suppose you could drop the 5v to about 3.3 using diodes in place of a linear regulator but not
sure if this would be good for the prop? Mike Green would probably know....there might be transitory
periods when the prop would get greater than 3.3v doing this?

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mctrivia

Just so you know rectified 120v ac is about 160vdc

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kt88seamp

I found this device.

http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/28830d1241249029-relay-noise-resets-microcontroller-5v-power-supply-pi.png

Here is its datasheet:

http://www.es.co.th/Schemetic/PDF/LNK304-306.PDF