From: Enric Balletbo i Serra <enric.balletbo@collabora.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: linux-pm@vger.kernel.org, sre@kernel.org,
Sameer Nanda <snanda@chromium.org>,
bleung@chromium.org, rjw@rjwysocki.net, gwendal@chromium.org,
linux-kernel@vger.kernel.org, Len Brown <len.brown@intel.com>,
groeck@chromium.org, Adam.Thomson.Opensource@diasemi.com,
kernel@collabora.com
Subject: Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property
Date: Tue, 16 Apr 2019 10:42:30 +0200 [thread overview]
Message-ID: <8d1f70a7-46d6-f278-f58c-6a7e7a644d46@collabora.com> (raw)
In-Reply-To: <20190416071941.GB14538@amd>
Hi Pavel,
On 16/4/19 9:19, Pavel Machek wrote:
> Hi!
>
>> This patch exposes a new property, similar to input current limit, to
>> re-configure the maximum voltage from the external supply at runtime
>> based on system-level knowledge or user input.
>
> Well, and I suspect it should expose input power limit, not input
> voltage limit.
>
Oh, ok, I thought we were agree that input voltage had sense after had some
discussion in v3. Seems that no, let me try to give you another example...
> DC-DC convertor efficiency normally does not much depend on input
> voltage....
>
> Pavel
>
As we said we have a heat "problem" due the internal voltage conversions.
Lets assume you have a linear regulator instead with a Vin range from 5V to 9V
and we want an output of 3.3V/1A
For 9V:
Input power : P(in) = 9V x 1A = 9W
Output power: P(out) = 3.3V x 1A = 3.3W
Regulator power dissipated: P(reg) = P(in) - P(out) = 9W - 3.3W = 5.7W
For 5V:
Input power : P(in) = 5V x 1A = 5W
Output power: P(out) = 3.3V x 1A = 3.3W
Regulator power dissipated: P(reg) = P(in) - P(out) = 5W - 3.3W = 1,7W
In the first case the regulator needs to dissipate more power, hence the
temperature is greater than the second case.
Thanks,
Enric
next prev parent reply other threads:[~2019-04-16 8:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-15 22:00 [RESEND PATCH v3 1/2] power: supply: add input voltage limit property Enric Balletbo i Serra
2019-04-15 22:00 ` [RESEND PATCH v3 2/2] power: supply: cros: allow to set input voltage and current limit Enric Balletbo i Serra
2019-04-16 7:19 ` [RESEND PATCH v3 1/2] power: supply: add input voltage limit property Pavel Machek
2019-04-16 8:42 ` Enric Balletbo i Serra [this message]
2019-05-02 21:01 ` Sebastian Reichel
2019-05-02 21:12 ` Pavel Machek
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