Getting -5V In A Circuit

Thread Starter

PIC-User

Joined Sep 25, 2015
38
Hi,

I have a project where I'm using the power from a USB port. That would be ground (0V) and 5VDC. There is a chip that I'm using where I need to have -5V, 0V, and 5V. How can I get -5V from 5V? I don't need much current only a few mAmps. Is there a voltage regulator that would let me do this?

Thank you,

Robert
 

WBahn

Joined Mar 31, 2012
25,918
You need a DC-DC converter. There are some chips on the market that will produce specific output voltages from a single input voltage. A Google search from something like: DC-DC converter -5V will probably get you off to a good start. That's assuming that you are primarily interested in an off-the-shelf solution so that you can move forward with your project as opposed to being more interested in building the circuit yourself.
 

jpanhalt

Joined Jan 18, 2008
9,740
Based on your user name, if you have a microcontroller with a spare pin, you can generate the -5V from the MCU with a charge pump like this:
upload_2016-2-29_13-29-9.png

As for off the shelf, I have used the MAX851, MAX1680, and ICL7660. I am not sure which, if any are still available.

John
 

Thread Starter

PIC-User

Joined Sep 25, 2015
38
Thank you all.

jpanhalt, very interesting idea! I assume that the MCU pin connection would be at V1. Is that right? Where do you see the -5V in this circuit?
 

jpanhalt

Joined Jan 18, 2008
9,740
Yes to V1. I have used that circuit to provide negative bias to a GLCD. It is actually in some Microchip document. You probably have at least one PWM channel that you can use.

John
 

AnalogKid

Joined Aug 1, 2013
8,488
USB +5V has a tolerance built into the USB spec. Does your -5V have to track the +5V for balance, or do you just need something negative? If you need a regulated output, there are simple non-isolated dc/dc converters in SIP packages.

ak
 

Thread Starter

PIC-User

Joined Sep 25, 2015
38
USB +5V has a tolerance built into the USB spec. Does your -5V have to track the +5V for balance, or do you just need something negative? If you need a regulated output, there are simple non-isolated dc/dc converters in SIP packages.

ak
I just need to pull-down some resistors down to -5V, so some MOSFETs I have in my circuit can work properly. The load should be a few mAmps.
 

cmartinez

Joined Jan 17, 2007
7,015
As several people have already said, the ICL7660 will do the job nicely. Just copy the circuit shown in fig 14 of the attached datasheet and you should be fine.
 

Attachments

ian field

Joined Oct 27, 2012
6,539
Hi,

I have a project where I'm using the power from a USB port. That would be ground (0V) and 5VDC. There is a chip that I'm using where I need to have -5V, 0V, and 5V. How can I get -5V from 5V? I don't need much current only a few mAmps. Is there a voltage regulator that would let me do this?

Thank you,

Robert
You can drive a diode/capacitor charge pump with a 555 - if you only need low current, a CMOS 555 will probably do.

There are also various off the shelf "flying capacitor" chips made for the job - I think the ICL7660 might be one example.
 

cmartinez

Joined Jan 17, 2007
7,015
I think the ICL7660 might be one example.
Actually, I speak from personal experience. I've used the exact circuit I mentioned in my previous post to help power the negative side of an ADC converter, and it worked wonderfully.

Word of advice for @PIC-User, though. The 7660 is capable of delivering only a very limited amount of current. I suggest you double check your requirements and compare them to the datasheet. Otherwise a more complex circuit might be needed.
 
Top