Electronics > Beginners

Howto make 10.4V out of 4xAA batteries?

(1/3) > >>

OE2WHP:
Hi,

I want to build a LCD backlight into my metal detector. I already have a suitable (sizewise) backlight panel that I could use. Only problem is, its running at nominal 12-14V but the metal detector runs on 4 AA batteries.  I already did some tests with the backlight and found that at 10.4V the brightness would be right at the level I'm aiming for. Current is somewhere at 2mA

What I'm searching for is a small dc/dc converter that steps the voltage up to 10.4V, with an input voltage ranging from ~4.5V to 6V depending on battery level.
Important to know, the detector runs at 12.8 - 13.4kHz, thus beeing very sensitive to EMI at that frequency range. So the converter must not make any noise there.

I would be very happy if someone could point me in the right direction or give hints which converters could do the trick.

Thanks

Buriedcode:
At <10mA a charge pump doubler could work, although many tend to have a max input of 5.5V I'm sure there are still some of the older ICL7660A types.  The trouble with those is the low switching frequency - often as low as 10kHz.  The more modern ones can switch into the MHz range, but might not get more than 10.4V out (5.5V doubled, minus losses of two diodes = 11v - 2*0.3V = 10.4).

These tend to have lower EMI than magnetic switchers with perhaps increased ripple on the output, and often have a very low part count - some require two diodes and two caps for doubling (they were designed for inverting) others just require two caps as they are meant for doubling.

I'm sure searching your local distributor you'll get a list of candidates that meets requirements.

OE2WHP:
Thanks for your post.

any suggestions for a converter that does not work below or near 14kHz and where the output can be adjusted to stable 10.4V regardless of the battery level (within reasonable range)
Could I use this one?: http://www.ti.com/product/lm27313/description


Thanks


Giaime:

--- Quote from: OE2WHP on August 03, 2018, 08:33:39 am ---Could I use this one?: http://www.ti.com/product/lm27313/description


Thanks

--- End quote ---

Looks good!
Look for converter ICs that DON'T go in "pulse skipping mode" at low loads, but allow for DCM operation. This one you linked seems ok in this regard.
This is important because pulse skipping could lead to a skipping frequency near your "no noise" band.

Zero999:
You don't want a constant out voltage converter, but a constant current output, to drive LEDs.
http://www.ti.com/lit/ds/symlink/lm3410.pdf
http://www.mouser.com/pdfDocs/STMicro_LCD_BACKLIGHT_A.pdf

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod