Author Topic: 24V  (Read 5320 times)

lrlr

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24V
« on: November 17, 2013, 01:42:34 am »
does anyone use Digispark with 24V ?

mine get very hot, naked digispark use 500mW ??? with 24V

(5V powerd use 200mW)

is this correct?

« Last Edit: November 17, 2013, 01:54:18 am by lrlr »

Bluebie

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Re: 24V
« Reply #1 on: November 17, 2013, 03:07:36 am »
The linear regulator on the digispark would be getting uncomfortably hot at those voltages. It works by simply throwing away the extra 19 volts as heat. You can get more efficient switching regulators if you're concerned about the heat or need to draw more current or just want to be more efficient (if using batteries this is important).

Something like http://www.hobbyking.com/hobbyking/store/__10312__Turnigy_5A_8_26v_SBEC_for_Lipo_.html would do the job well, while providing much more amperage than the normal regulator built in to the digispark. If you don't need to power devices aside from the digispark you can surely find something smaller and cheaper than the one I linked. When using an external regulator power the digispark from it's 5v output through the digispark 5v pin rather than VIN, to skip it's built in regulator.

lrlr

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Re: 24V
« Reply #2 on: November 17, 2013, 04:24:21 am »
so my "works up to 36V digispark" does not work (well) with 24V ...


> get more efficient switching regulators

somthing like  Recom RI-2405 . 87 %Efficiency ??

the "onboard" one seems to have 40% Efficiency @24V  ??


for my (current) use,  99% sleep + 1% work would also be OK
is there a (effectiv) sleep mode?



« Last Edit: November 17, 2013, 04:35:56 am by lrlr »

digistump

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Re: 24V
« Reply #3 on: November 17, 2013, 01:37:27 pm »
so my "works up to 36V digispark" does not work (well) with 24V ...
Yep that is why the product description reads:
"Power via USB or External Source - 5v or 7-35v (12v or less recommended, automatic selection)"

It works up to 35v, as you have seen it does work at 24v, but additional cooling might be needed - hence 12v or less is recommended. If you put it on a big heatsink it will run happily at 24v.

> get more efficient switching regulators

somthing like  Recom RI-2405 . 87 %Efficiency ??

the "onboard" one seems to have 40% Efficiency @24V  ??
Recom RI-2405 would work.

The onboard regulator is a linear regulator and so the efficiency decreases as voltage increases. Given the price of a switching regulator it was impractical to include one on the Digispark.
Here is a cheaper, albeit larger option as well: http://www.ebay.com/itm/5V-USB-Output-Converter-DC-7V-24V-to-5V-3A-Step-Down-DC-DC-Buck-KIS3R33S-Module-/291015794725?pt=LH_DefaultDomain_0&hash=item43c1e4a025

lrlr

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Re: 24V
« Reply #4 on: November 17, 2013, 02:14:18 pm »
thank you

>cheaper

yes, but my experiense tells me, not to buy cheap chinese things...




what about the "sleep mode" ?



digistump

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Re: 24V
« Reply #5 on: November 17, 2013, 11:24:44 pm »
AVR sleep modes work - but the USB and power LED still sue power - to get started:
http://digistump.com/board/index.php/topic,951.0.html
Might not apply perfectly to attiny85/digispark: http://playground.arduino.cc/Learning/arduinoSleepCode
http://www.insidegadgets.com/2011/02/05/reduce-attiny-power-consumption-by-sleeping-with-the-watchdog-timer/

Lots more if you google "Arduino attiny85 sleep"

lrlr

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Re: 24V
« Reply #6 on: November 19, 2013, 12:46:19 pm »
with:

http://www.insidegadgets.com/wp-content/uploads/2011/02/ATtiny85_watchdog_example.zip

9mA (200mW) @ 24V

seems to be OK now (doesn't get too warm anymore..)