General > General Technical Chat
How hard can it be to find a 9,8V, 75W PSU?
Zero999:
--- Quote from: Emo on January 01, 2022, 10:06:19 am ---Hi,
The 12V LRS Meanwell supplies can be adjusted from as low as 10.2V So by just adding a diode in series the output will drop within the desired range.
Eric
--- End quote ---
That will work, but might not be accurate enough, as the diode drop will vary with the current.
A low drop-out regulator could be used to reduce the output voltage to 9.8V
http://ww1.microchip.com/downloads/en/DeviceDoc/MIC29712-7point5A-Fast-Response-LDO-Regulator-DS20006068A.pdf
https://www.analog.com/media/en/technical-documentation/data-sheets/108345fh.pdf
--- Quote from: madires on January 02, 2022, 07:28:48 pm ---Take the next best 12V power brick and modify the voltage divider for the feedback?
--- End quote ---
Yes, the typical feedback circuit uses the TL431, with an opto-coupler for feedback. Changing the feedback resistors normally works, but you might also need to alter the resistor in series with the emitter, as 9.8V will lower the forward current, and there's a chance of instability, in which case a compensation capacitor will need to be added/changed.
In this case 9.8V is only a little lower, so just changing the feedback will probably work. Here are a few links.
https://www.instructables.com/Changing-the-output-voltage-of-a-cheap-power-suppl/
https://www.homemade-circuits.com/how-to-make-variable-current-smps/
https://www.onsemi.com/pub/Collateral/TND381-D.PDF
BrokenYugo:
I'd regulate down a common 12V supply or fix the existing one, looks like something on the secondary side popped?
thm_w:
I assume they are using Q1 to regulate the voltage into a 2S Lipo. So 7.4V termination voltage.
I doubt the input voltage is that critical. Maybe if its too high, Q1 will heat up.
In that case, putting in a series diode or two on a tweaked 12V supply is a complete non-issue. Even 9V supply may work.
This page says 10V input: https://www.sepura.com/accessories/1-1-desktop-charger
oh2ftu:
Here's a short follow up.
As I have an extra charger which I intended to make use of, I decided to check it out.
Good thing I did, the charger pcb's inside are gone (corrosion).
also, before that, I contacted powersolve which would've been able to supply the correct PSU for about 200 eur including shipping and taxes.
At least they are available..
madires:
A Meanwell 12V 100W power brick is EUR 41. This reminds of a friend who lost the charger for his Bosch cordless screwdriver. 28 bucks for a 5V 400mA wall wart. WTF! Next best mobile phone charger from the box full of old PSUs plus some unsusual sized barrel plug for EUR 2.80 (incl. shipping) and the problem is solved.
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