Reducing And Converting 120AC to 10-15VDC

[Molimo]

Anyone here that might know how to build a circuit to reduce and convert 120VAC to 10-15VDC

I know I could easily use a Transformer but the problem with that is our project is limited to a size of 1 x 2 Inches. so the transformer that I have takes all the space so there is no way I could use it.

I've Tried calculating with a Voltage Divider But I need at least 100mA at the end and with the It's wither 1-10mA Max or I start using 5=10W Resistors which I dont Have

Any Help is Appreciated

Thanks

Marc

 

[dknguyen]

Aside from the safety issues about not using a transformer...

if you can't get ahold of large power resistors (which are relatively easy to get compared to other components), how do you expect to get the parts for other methods? Also, a couple of 5 or 10W resistors also easily take up the space of 1x2 inches.

I would say a capacitive divider possibly followed by a diode rectifier. THe capacitors might be small enough. But I doubt it. THe problem is that you don't seem to have space/experience to use switching or transformer methods. So the only thing left is linear methods. (120V-15V) * 0.1A = 12W that you have to burn off. So the resistor size (or capacitor size) all sound about right. Can't get around the laws of physics.

But the only way may be a switching converter. THe easiest thing is to buy a premade one (and these ones also have isolation transformers so they are safer).

Like these from Digikey:
**broken link removed**
**broken link removed**

But remember, no transformer means no isolation means lethal shocking potential. ANd using dividers of any kind also makes for poor output voltages that can swing wildly on load changes.

 

[Ubergeek63]

Or you could do a non isolated buck switcher with a single inductor.

 

[ericgibbs]

hi.

Get the following two application notes from Microchip Technology Inc. - a Leading Provider of Microcontroller and Analog Semiconductors

AN954 & TB008

 

[petrv]

Hi Marc,

transformerless (resistive or capacitive) power supplies are used if you don't need that much current - it is Ok for a few milliamps but 100 mA is too much. You will end up with very big resistors or very big capacitors. If you don't want to use a classical transformer you can use a switched power supply (for example TinySwitch from Power Integrations) but it still needs a transformer (but much smaller) and it is not a beginner project.

Petr

 

[Hero999]

Another option is to use a wall plug power supply.

 

[Willbe]

A series diode gives you ~50vdc, then (50-15)/0.1 = 350Ω. For the wattage value you need the RMS value of a half-wave rectified waveform.

 

[Hero999]

A Black regulator?

Official Home Page of Roman Black

It needs a bit of tweaking and a high voltage transistor but it might work.

 

[Ubergeek63]

grrrr why is everyone conspiring to piss me off?!?

Power Itegrations USED to have an app note about simple inductor buck regulators. I will post it from work since I have it saved locally there.

 

[Hero999]

Perhaps you should take one of these.

**broken link removed**

 

[Ubergeek63]

Perhaps you should take one of these.

no lie!

 

[carmusic]

i would go also with the v-infinity dc converter very simple and pretty cheap and very small

 

[Ubergeek63]

Digi-Key - 495-2748-ND (EPCOS Inc - B82722J2302N1) for an inductor and

Digi-Key - 596-1144-5-ND (Power Integrations - TNY377PN) for a switcher.

It is easy to hook that up for a unisolated switcher.... I will upload the appnote that appears to no longer be on the Power Integrations site

EDIT: the app note. there are other tricks that can be added, the most obvious gets rid of the optocoupler.

 

[Molimo]

Just to let everyone up with the current situations. We went with the AN954, Using a 5W ressitive load in series with a Recitifer. On the other end of the rectifier, a 5.1V Zener with a Capacitor. Everything went smooth and since we didnt have a small enough transformer for our project. This did the job and took alot less space.

Just to clarify a few things for the project. the dimensions of the board was a MAJOR thing. And we couldnt go around that. but eveything went well with the AN952 Datasheet and Thanks for all the help.