supply voltage

I have a +10 V supply in my PCB . I need a -3 V supply But I dont want to add a negative power supply in addition. Can any body give me an idea so that i can make a -3 V supply from +10 V supply with same ground..

You can try some like this (see schematic diagram).

you may use icl7660 chip refer datasheet

I interpreted this differently

. If you mean the pcb makes 10VDC from a higher voltage, such as 120VAC, then it is pretty easy to make a separate 120VAC to -3V supply. Alternately you could have an isolated 3VDC supply and connect +3VDC to the board ground. Then the -3VDC supply ground would be -3VDC with respect to 0VDC on the board.

If you mean you have regulated +10 VDC to the card that is being converted to lower voltages on the board that is much different. If you do have 10 VDC and it's being reduced to +5 VDC or +3.3VDC on board , there may be a simple way. You don't' mention the current.

If you mighe be able to put a +3v regulator between the card ground and in comming +10VDC power ground. Then there'd be +7 VDC ton the card, still enough to make +5VDC or +3.3VDC and the power ground would be -3VDC referenced from the card ground.

Obviously you are going to have to add something. You don't make any mention of how configurable the +10V supply is. For instance if you could convert the 10V to say 13V, you could use a linear regulator to convert the +13 to +3V. That node would be your reference ground. Now converting 13V to 3V if there is much current will make lots of heat, something to consider.

The difference between the +13V and the +3V (reference ground) is +10V. There is a problem with this method if your +10V uses much current is that the +3V will start to increase unless you shunt it with additional load, that is more load on the +-3V supply rail.

A very simple slam dunk solution is to buy a regulator known as a buck-boost, which is actually a positive to negative converter. You can get theses cheap, a few bucks. This is what I would do. It takes up perhaps 1 square inch of board space.

The AC/DC solution with bridge diodes will work except it isn't regulated and requires a lot of 120Hz filtering, big bulky components.

dear sir ,
pls refer icl 7660 (voltage convertor) make +3v from +10v using zener regulator you will get +3v feed it to icl7660
pls refer datasheet that i have attached

If you are going to stack the regulators and use the +3V are return, that regulator must be able to SINK current as well as shunt current, which means a lot of heat for one. If it shunts/sources and gets rid of the heat it should work.

Draw the schematic showing the current paths.

Here is what you can do as an alternative:

On ebay a company that sell isolated 12V to 5V converter. So if you are using 10V that would give you 4.1V out that you can configure negative. That's too high so in the +5Vout side place 2-20V 2A Schotkey diodes in series to drop the voltage down to 3V. If this isn't regulated well enough you can always use a simple linear regulator to drop the 1.1V, except it needs to be of the LDO type (low voltage dropout tripe)

http://www.ebay.com/itm/DC-DC-1W-isolated-con...909?pt=LH_DefaultDomain_0&hash=item20c7490915

http://www.ebay.com/itm/DC-DC-1W-isolated-con...773?pt=LH_DefaultDomain_0&hash=item1e6be6445d

The other type will give you these same output as input, in this case an isolated 10V, which you canmake into a regulated -3V with a standard linear regulator.

These modules are very small & efficient.

Guys, he's asking for -3V (i.e. NEGATIVE not POSITIVE).

Bhui's solution has merit, but might require an additional linear regulator (or zener) depends on the load requirement on that -3V supply (unspecified and yet, oh so important ;)

Lisovy's solution assumes access to an AC source.

The problem is not enough design details have been supplied so as to propose a solution that would meet the requirements, that's the problems.

The problems isn't a lack of ideas, just absolute missing design details of the existing circuit and the requirements that must be met.

you may use two 3V LDO or any Switching regulator and connectto both supply output in series as per below Image. take -3.0 Volt WRT GND.

This is simply not true. LDO regulators are current sources. Therefore when you source current into them the voltage increases, which means the regulator has to shunt current as well. This is the case when you are using one voltage source for two outputs and no isolation. There is another way that I have use that uses two negative regulators, whereby one regulator is in the return side, the other regulator is on the -3V rail. This will work I know because I have tried it.

There are too many people on this who don't understand linear regulators and how to connect them.

The battery you have sources current but is a very low impedance to sinking current and lso constitutes a SEPERATE voltage rail.

This person doesn't have it, they just have one 10V rail and DOES not want to add anything except wants a free -3V rail. Also provides virtually no helpful information.

Go figure?

One more schematic diagram.

Schematic with MC34063A.

Hi according to the datasheet this is all you have to do using the ic youve quoted but IOUT is very low max 40ma into 60 ohm load.

The frequency of the oscillator is set to 10khz internally If you want to lower this you can to 1khz by adding a 100 pico farad cap btw pin 7 and the supply although id leave this at 10khz

In fact this is so funney because you might as well have used a 555 timer or But ill let you think this one out

It shows you how to achieve this in the datasheet

This ic is truthfully only intended for cmos to ttl conversion ie. RS232 communications A max 232 is more or less the same type of function comprising a charge pump to perform similar functions

See attached