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Olin Lathrop wrote:
>=20
> An LED is specified at a particular current, not voltage,=20
> usually 20mA for common LEDs. =20
.
.
> I don't like putting 20mA thru a port pin because it is=20
> getting close to the spec limit. For simple circuits,=20
> I usually just run LEDs at 10mA. There are also ways=20
> of making an external transistor do the heavy lifting,=20
> but that is a bit advanced for where you are now.
=20
With mighty LEDs one can use DC/DC converters as=20
shown in attached .gif from National =93LM2704.pdf=94.
(LM2704 is limited to 7v input voltage).
=20
Mike.
-------
The LM2704 is a micropower step-up DC/DC in a small
5-lead SOT-23 package. A current limited, fixed off-time
control scheme conserves operating current resulting in high
efficiency over a wide range of load conditions. The 21V
switch allows for output voltages as high as 20V. The low
400ns off-time permits the use of tiny, low profile inductors=85
Features
- 550mA, 0.7W, internal switch
- Uses small surface mount components
- Adjustable output voltage up to 20V
- 2.2V to 7V input range
- Input undervoltage lockout
- 0.01=B5A shutdown current
=20
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Olin=
Lathrop
wrote:
>=
>=
An LED
is specified at a particular current, not voltage, =
>=
usually 20mA for common LEDs.=A0
.
.
>=
I don't
like putting 20mA thru a port pin because it is =
>=
getting
close to the spec limit.=A0 For =
simple
circuits,
>=
I usually
just run LEDs at 10mA.=A0 There are also ways =
>=
of making an external transistor do the heavy =
lifting,
>=
but that is a bit advanced for where you are =
now.
=A0With mighty LEDs one
can use DC/DC converters as
show=
n
in attached .gif from National =
=93LM2704.pdf=94.
(LM2=
704 is
limited to 7v input voltage).
=A0Mike.
----=
---
The =
LM2704
is a micropower step-up DC/DC in a =
small
5-le=
ad
SOT-23 package. A current limited, =
fixed
off-time
cont=
rol
scheme conserves operating current resulting in =
high
effi=
ciency
over a wide range of load conditions. The =
21V
swit=
ch
allows for output voltages as high as 20V. The =
low
400n=
s
off-time permits the use of tiny, low profile =
inductors=85
Feat=
ures
- =
550mA,
0.7W, internal switch
- =
Uses small
surface mount components
- =
Adjustable
output voltage up to 20V
- =
2.2V to 7V
input range
- =
Input undervoltage lockout
- 0.01=B5A shutdown current
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