power loss in 7805 used as current regulator

[Spehro Pefhany]

On Sun, 21 Mar 2004 20:27:30 GMT, the renowned Fred Bloggs
<nospam@nospam.com> wrote:

Maybe you can use required ON time and voltage to gauge the required
battery technology and package based on their energy density ratings.
It's moot point- OP is evidently here to ask pointless questions.

Hey, symbiosis.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[John Woodgate]

I read in sci.electronics.design that Walter Harley
<walterh@cafewalterNOSPAM.com> wrote (in <c3l634$5vh$0@216.39.172.65&gt
about 'power loss in 7805 used as current regulator', on Sun, 21 Mar
2004:

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:En3kPqCWoVXAFwRx@jmwa.demon.co.uk...
If the OP doesn't know how to run an LED from a linear regulator, how do
you think he is going to cope with a far more complex switcher?

Well, at least he knew a current regulator from a voltage regulator, which
some of the respondents didn't seem to...

That should have been in the message text, as well as, or instead of, in
the subject line.

but mainly, I was trying to give
him a bit of perspective on what the options were.

The Roman Black circuit

I thought that was a font. (;-)

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Spehro Pefhany]

On 21 Mar 2004 22:48:04 GMT, the renowned "Walter Harley"
<walterh@cafewalterNOSPAM.com> wrote:

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:En3kPqCWoVXAFwRx@jmwa.demon.co.uk...
If the OP doesn't know how to run an LED from a linear regulator, how do
you think he is going to cope with a far more complex switcher?

Well, at least he knew a current regulator from a voltage regulator, which
some of the respondents didn't seem to... <snip

Well, the only thing that made sense with a 7805 and 100R was a
voltage regulator and dropping resistor, which effectively *is* a
current regulator for constant Vf (a reasonable approximation for
fixed If). It works if Vf for the LED is 3V, which is quite typical
for a blue or white LED. Nothing else really works, as Fred's analysis
pointed out so nicely. ;-) And the energy vs. power issue..

The Roman Black circuit is pretty darn simple - even someone as ignorant as
me can get it to work And the one-chip solutions are simple too. At
this low power level, it's easy to get a simple switcher to work and be
reasonably reliable even with off-the-shelf components; the problem is
getting it to be efficient.

Sure, and there are an amazing number of expensive purpose-built chips
for LED backlights that would work.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Walter Harley]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:En3kPqCWoVXAFwRx@jmwa.demon.co.uk...

If the OP doesn't know how to run an LED from a linear regulator, how do
you think he is going to cope with a far more complex switcher?

Well, at least he knew a current regulator from a voltage regulator, which
some of the respondents didn't seem to... but mainly, I was trying to give
him a bit of perspective on what the options were.

The Roman Black circuit is pretty darn simple - even someone as ignorant as
me can get it to work And the one-chip solutions are simple too. At
this low power level, it's easy to get a simple switcher to work and be
reasonably reliable even with off-the-shelf components; the problem is
getting it to be efficient.