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Power supply for FEZ Cobra II + CP7 display


#1

I have a FEZ Cobra II + CP7 as my display. I wonder what should be the power supply. I am looking at buying a power adapter.
I read on various discussion about power supply and concludes it needs a 6V. How about the current rating? Will it matter?

http://www.radioshack.com/product/index.jsp?productId=3802150 - 6V/300mA
http://www.radioshack.com/product/index.jsp?productId=3839138 - 6V/800mA
http://www.walmart.com/ip/ProForm-6-Volt-AC-Power-Adapter/16472415 - 6V/2A

Will any of these fit? will it caused overheating or device burning issue?

If I connect power supply adapter and usb mini(for debugging purpose), will it work?

Thanks!


#2

current rating is CRITICAL and is the key factor. Using the 300mA one is not going to work. The 800mA might work (probably might, but might give you intermittent issues). One with 2000mA will be the best option (not so sure that the one you linked to is what I would buy though - it isn’t stated clearly that the output is 6vDC, it actually says AC too many times for me to say yes buy it).

But personally, I would ask why you’ve decided on 6V? I personally typically look at 7V or 7.5V adapters, because a Voltage regulator on board the DP module or the Cobra II onboard regulators will drop the voltage by 1.2-1.5V, which means if you start from 6v you have under 5v available.


#3

Hi Brett,
Thanks for the quick response.
I got the idea of using 6Vdc as I refer to this discussion http://www.tinyclr.com/forum/topic?id=574.
As well this, http://www.ghielectronics.com/downloads/FEZ/Cobra/Broch_FEZ_Cobra.pdf

I thought of using 9Vdc or 12Vdc in the first place because they are common and can get anywhere else. After browsing through the forum, I found out the suggestion are most likely on 6Vdc. It worries me that beyond 6Vdc will burn the device. I don’t want to take the risk and so, I created this topic to get suggestions.
How about a device like this - http://www.radioshack.com/product/index.jsp?productId=11343870

thanks.


#4

All of that supporting material is for Fez Cobra, not Fez Cobra 2. And you’re talking CP7, not the old original display the Cobra came with.

I’ve just looked on the silkscreen printing on my Cobra2, and it says 7v to 12v.

The Cobra2 has a Micrel 4680 switch-mode buck converter, to bring power down to 5v level. It then has a standard low-drop-out voltage regulator to drop the 5v to 3v3. This arrangement is much better from a heat dissipation perspective than the original Cobra.

The CP7 uses 700mA from 5V (and 50mA from 3v3) according to http://www.ghielectronics.com/catalog/product/376. And the Cobra2 docs say you need an 800mA capable supply. So looks to me like you need 1.5A (1500mA) at least.

That last link seems like it could be suitable, but the confusing thing to me is that it says the battery option can deliver 14.8V but that’s not listed on the tech specs as an output voltage. Just seems somewhat, strange, to quote this info in this way.


#5

Okay. I will look into it. Highly appreciate your details explanation. Getting a variable output seems to be the best solution at this point.
Thank you.