linux-kernel - Re: [PATCH] leds: driver for ab5500 high voltage leds

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Date:	Wed, 07 Dec 2011 20:01:46 +0200
From:	Denis Kuzmenko <linux@...onet.org.ua>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Linus Walleij <linus.walleij@...ricsson.com>,
	Richard Purdie <rpurdie@...ys.net>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Shreshtha Kumar Sahu <shreshthakumar.sahu@...ricsson.com>
Subject: Re: [PATCH] leds: driver for ab5500 high voltage leds

On 12/07/2011 04:07 PM, Linus Walleij wrote:
> On Sat, Dec 3, 2011 at 11:49 PM, Denis Kuzmenko <linux@...onet.org.ua> wrote:
> 
>> (snip)
>>> diff --git a/drivers/leds/leds-ab5500.c b/drivers/leds/leds-ab5500.c
>> (snip)
>>> +/*
>>> + * Driver for HVLED in ST-Ericsson AB5500 analog baseband controller
>>> + *
>>> + * This chip can drive upto 3 leds, of upto 40mA of led sink current.
>>
>> Can't get these are High Voltage or High Current LEDs?
>> If Voltage why haven't you wrote about supplied voltage but wrote about
>> max. current?
> 
> The three channels are indeed high-voltage LEDs, they supply
> up to 20V from a supply voltage of some standard mobile handset
> battery at say 3.8 V or so. But there is no register to control the
> voltage or anything like that.
> 
> My naive understanding is that you set the current limit and then
> the HV transformer (I guess this is a buck converter of some kind)
> will raise the voltage level until it either (A) cannot raise it any more
> at c:a 20V or (b) the current limit is reached.
> 
> I suspect this is because for LEDs of this type you get a
> specified current but the voltage just has to be "high enough"
> to break through some diode barrier threshold or so. After
> that intensity is controlled by limiting the current.
> 
> Does this suffice as explanation...?
> 
> Yours,
> Linus Walleij

Yeah, It does, thank you.
Does it worth to make additional comment in code to avoid further questions?

-- 
Best regards, Denis Kuzmenko.
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