Generating -3V from +10V Supply on PCB Without Additional Negative Supply

174 14

#1 21665303 15 Dec 2012 05:39

anupam shakya anupam shakya

Anonymous

Post #1
21665303 15 Dec 2012 05:39

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..
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#2 21665304 15 Dec 2012 05:57

Eugene Lisovy Eugene Lisovy

Anonymous

Post #2
21665304 15 Dec 2012 05:57

You can try some like this (see schematic diagram).
#3 21665305 15 Dec 2012 06:08

gurpreet Bhui gurpreet Bhui

Anonymous

Post #3
21665305 15 Dec 2012 06:08

you may use icl7660 chip refer datasheet
#4 21665306 15 Dec 2012 12:39

Stephen Van Buskirk Stephen Van Buskirk

Anonymous

Post #4
21665306 15 Dec 2012 12:39

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.
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#5 21665307 15 Dec 2012 16:19

Earl Albin Earl Albin

Anonymous

Post #5
21665307 15 Dec 2012 16:19

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.
#6 21665308 17 Dec 2012 05:09

gurpreet Bhui gurpreet Bhui

Anonymous

Post #6
21665308 17 Dec 2012 05:09

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
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#7 21665309 17 Dec 2012 06:42

Earl Albin Earl Albin

Anonymous

Post #7
21665309 17 Dec 2012 06:42

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.
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#8 21665310 17 Dec 2012 07:09

Earl Albin Earl Albin

Anonymous

Post #8
21665310 17 Dec 2012 07:09

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.
#9 21665311 17 Dec 2012 17:33

Steve Lawson Steve Lawson

Anonymous

Post #9
21665311 17 Dec 2012 17:33

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.
#10 21665312 17 Dec 2012 17:47

Earl Albin Earl Albin

Anonymous

Post #10
21665312 17 Dec 2012 17:47

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.
#11 21665313 20 Dec 2012 05:40

alpesh Patel alpesh Patel

Anonymous

Post #11
21665313 20 Dec 2012 05:40

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.
#12 21665314 20 Dec 2012 05:47

Earl Albin Earl Albin

Anonymous

Post #12
21665314 20 Dec 2012 05:47

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?
#13 21665315 27 Dec 2012 15:20

Eugene Lisovy Eugene Lisovy

Anonymous

Post #13
21665315 27 Dec 2012 15:20

One more schematic diagram.
#14 21665316 27 Dec 2012 15:34

Eugene Lisovy Eugene Lisovy

Anonymous

Post #14
21665316 27 Dec 2012 15:34

Schematic with MC34063A.
#15 21665317 27 Dec 2012 18:50

Mark Harrington Mark Harrington

Anonymous

Post #15
21665317 27 Dec 2012 18:50

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
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Topic summary

✨ The discussion addresses generating a -3 V supply from a single +10 V supply on a PCB without adding a separate negative power supply, sharing the same ground reference. Several solutions are proposed: using a charge pump IC like the ICL7660 voltage converter to invert the +10 V to -10 V and then regulating down to -3 V; employing a buck-boost (positive-to-negative) DC-DC converter module for efficient negative voltage generation; stacking regulators with careful current sinking and shunting considerations; and using isolated DC-DC converters combined with diode voltage drops and low dropout (LDO) linear regulators to achieve the desired negative voltage. The importance of load current specifications and thermal dissipation is emphasized. Some responses highlight the complexity of creating a negative rail from a single positive supply without isolation or additional components, noting that linear regulators alone cannot create a negative voltage relative to the same ground. Schematics involving the MC34063A switching regulator and charge pump ICs are referenced for practical implementation. Overall, the consensus is that a dedicated inverting DC-DC converter or charge pump IC is the most straightforward and compact solution for generating -3 V from +10 V with a common ground.

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Generating -3V from +10V Supply on PCB Without Additional Negative Supply

FAQ

TL;DR: Need -3V from +10V? A simple charge‑pump like ICL7660 delivers up to 40 mA; "IOUT is very low." Use buck‑boost or isolated DC‑DC for higher current. [Elektroda, Mark Harrington, post #21665317]

Why it matters: This FAQ helps PCB designers quickly pick a safe, space‑efficient way to create a -3V rail without adding a full negative supply.

Quick Facts

ICL7660/charge‑pump inverters suit light loads; expect approx. 40 mA max before regulation sags noticeably. [Elektroda, Mark Harrington, post #21665317]
MC34063A supports inverting topologies; example schematics show -V generation from +10V. [Elektroda, Eugene Lisovy, post #21665316]
Buck‑boost (positive‑to‑negative) modules are inexpensive and about ~1 sq in, making them a compact fix. [Elektroda, Earl Albin, post #21665307]
Isolated DC‑DC + diode/LDO can be referenced to ground to realize a regulated -3V rail. [Elektroda, Earl Albin, post #21665310]
Define load current and ripple early; missing specs block reliable solutions and can cause rework. [Elektroda, Earl Albin, post #21665312]

What’s the simplest way to get -3V from a +10V rail on my PCB?

Use a charge‑pump inverter such as the ICL7660. It needs only capacitors and can generate about −3V at light loads. Its practical output current is around 40 mA, beyond which voltage droop increases. Keep traces short and add low‑ESR caps near the IC. [Elektroda, Mark Harrington, post #21665317]

How do I build a quick -3V inverter with ICL7660 (3 steps)?

Drop or regulate a +3V node if needed, then feed the ICL7660 VIN.
Wire the ICL7660 in voltage‑inverter mode with the recommended flying and reservoir capacitors.
Take −VOUT as your −3V rail and tie circuit ground to the original board ground. “Refer the datasheet and feed it to ICL7660.” [Elektroda, gurpreet Bhui, post #21665308]

I need more than 40 mA. What should I use instead of ICL7660?

Pick a buck‑boost (positive‑to‑negative) DC‑DC module or controller. These regulate better at higher current and waste less power. As one expert put it: “A very simple slam dunk solution is to buy a buck‑boost.” Size around one square inch is typical for small modules. [Elektroda, Earl Albin, post #21665307]

Can I just shift ground with a linear regulator to get -3V?

Beware: when you stack regulators to move ground, the reference regulator must sink current. Many LDOs source only, so voltage rises and heat increases. Without proper sink/shunt capability, the scheme fails under load. This approach needs detailed current‑path analysis and thermal design. [Elektroda, Earl Albin, post #21665314]

Will two 3V LDOs in series give me -3V with respect to ground?

No, not reliably with standard LDOs. LDOs behave as current sources; driving current back into them forces their node upward unless they can sink. That creates instability and heat. Use a genuine inverting converter or an isolated supply referenced as negative. [Elektroda, Earl Albin, post #21665314]

Can I derive -3V from AC using rectifiers and filters?

Yes, but it’s bulky and unregulated. A simple AC/bridge/RC design needs heavy 120 Hz filtering and large capacitors. Regulation will vary with load. For compact, stable rails, a buck‑boost or inverting converter is the better fit on modern PCBs. [Elektroda, Earl Albin, post #21665307]

How do I use an isolated DC‑DC to create a clean -3V?

Use a small isolated 10–12V to 5V module. Reference its + output to your board ground through diode drops or an LDO to land near −3V at the board. Isolation lets you define the negative rail cleanly and regulate it if needed. [Elektroda, Earl Albin, post #21665310]

What frequency and noise should I expect from an ICL7660 inverter?

The internal oscillator runs at about 10 kHz. You can lower it to ~1 kHz by adding a 100 pF capacitor from pin 7 to supply. Lower frequency eases switching loss but increases ripple amplitude, so size capacitors accordingly. [Elektroda, Mark Harrington, post #21665317]

What is a charge‑pump inverter?

It’s a switched‑capacitor circuit that flips a positive input to a negative output using flying capacitors. The ICL7660 and MAX232 families use this method. It’s efficient for low current rails and requires few external parts. [Elektroda, Mark Harrington, post #21665317]

What is a buck‑boost (positive‑to‑negative) converter?

It’s a switching regulator topology that inverts voltage and regulates the negative output. It handles higher current loads than simple charge pumps and maintains regulation across varying loads. Many off‑the‑shelf modules implement this compactly. [Elektroda, Earl Albin, post #21665307]

Which design details must I specify before choosing a method?

State load current, allowable ripple, noise sensitivity, isolation needs, and available PCB area. Without these, proposals miss the mark and can fail under real‑world conditions. Document exact operating modes and duty cycle for worst‑case sizing. [Elektroda, Earl Albin, post #21665312]

Can MC34063A generate -3V from +10V?

Yes. Configure MC34063A in an inverting topology per shared schematics to produce a regulated negative rail. Select inductor, diode, and feedback resistors for −3.0 V and your load current. Validate ripple and stability on your PCB layout. [Elektroda, Eugene Lisovy, post #21665316]

Could I just use a 555 timer to drive a charge pump?

You can. A 555 can clock a discrete charge pump similarly to RS‑232 style inverters. Ensure the driver frequency, capacitor size, and diode selection meet your load current and ripple targets. Watch thermal limits at higher loads. [Elektroda, Mark Harrington, post #21665317]