This is a multi-part message in MIME format. ------=_NextPart_000_0005_01C25C61.D4F3DD50 Content-Type: multipart/alternative; boundary="----=_NextPart_001_0006_01C25C61.D4F563F0" ------=_NextPart_001_0006_01C25C61.D4F563F0 Content-Type: text/plain; charset="windows-1250" Content-Transfer-Encoding: quoted-printable 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 ------=_NextPart_001_0006_01C25C61.D4F563F0 Content-Type: text/html; charset="windows-1250" Content-Transfer-Encoding: quoted-printable

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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