Lowest draw "power on" indicator?

K

Ken

Guest
What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?

I need an indicator for a circuit that itself only draws 20mA.


Ken
(to reply via email
remove "zz" from address)
 
"Ken" <cprstn54zz@att.net> wrote in message
news:aki5u0hktlc1f3uqcm7lm29n80jgagbm1d@4ax.com...
What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be
reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?
I need an indicator for a circuit that itself only draws 20mA.

Ken
Click to expand...
I often use LEDs at as little as 1mA for indicators. Just aren't
as bright!
 
On Mon, 10 Jan 2005 14:25:18 -0800, Jamie
<jamie_5_not_valid_after_5_Please@charter.net> wrote:

Ken wrote:

What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?

I need an indicator for a circuit that itself only draws 20mA.


Ken
(to reply via email
remove "zz" from address)
you could try running the LED in series with the Power source if your
circuit does draw that much,.
you will get a slight drop in voltage how ever if that is not a problem.
Click to expand...
How is that brainwave going to save on power?
 
On Mon, 10 Jan 2005 14:25:18 -0800, Jamie
<jamie_5_not_valid_after_5_Please@charter.net> wrote:
you could try running the LED in series with the Power source if your
circuit does draw that much,.
you will get a slight drop in voltage how ever if that is not a problem.
Click to expand...
Won't the drop be 2 volts?

Assuming I can make this work, how much power in milliwatts will the
LED actually consume?


Ken
(to reply via email
remove "zz" from address)
 
On Mon, 10 Jan 2005 13:37:15 -0500, Ken <cprstn54zz@att.net> wrote:

I need an indicator for a circuit that itself only draws 20mA.
Click to expand...
There are LEDs that will require only .5mA to 2mA with decent appearing light.
You could try those high-efficiency red types. A few discretes could achieve
the blinking (two BJTs and three or four passives come to mind.)

And in no way is the 3909 *worth* $5 -- cripes!

Jon
 
if you want to go mechanical, power ON-OFF switches are avaiable
with an indicator which changes color depending on whether it's ON or
OFF. Zero power required for the indicator.
John Fields
Click to expand...
The ones I've seen are push-on/push-off
with 2 dayglow green (or yellow) bits that come together like eyelids.
 
On Mon, 10 Jan 2005 14:32:09 -0500, Ken <cprstn54zz@att.net> wrote:

Won't the drop be 2 volts?
Click to expand...
Yes.

Assuming I can make this work, how much power in milliwatts will the
LED actually consume?
Click to expand...
20mA * 2V or 40mW.

Probably, this series deal isn't a good idea. The use of a high-efficiency red
led is probably much better. You can tweak it's current down to say .5mA and it
will probably look okay. Another option would be to add the few discrete parts
it would take to blink the LED to further reduce the average current. (I've got
the schematic for a duplicate of the 3909, for example.)

The simplest is probably the high-efficiency red led, though.

Jon
 
On 10 Jan 2005 11:44:38 -0800, "JeffM" <jeffm_@email.com> wrote:

if you want to go mechanical, power ON-OFF switches are avaiable
with an indicator which changes color depending on whether it's ON or
OFF. Zero power required for the indicator.
John Fields

The ones I've seen are push-on/push-off
with 2 dayglow green (or yellow) bits that come together like eyelids.
Click to expand...
---
Exactly! I've got one on my TEK 2465A.

--
John Fields
 
On Mon, 10 Jan 2005 19:19:41 GMT, "Clarence_A" <no@No.com> wrote:

"Ken" <cprstn54zz@att.net> wrote in message
news:aki5u0hktlc1f3uqcm7lm29n80jgagbm1d@4ax.com...
What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be
reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?
I need an indicator for a circuit that itself only draws 20mA.

Ken

I often use LEDs at as little as 1mA for indicators. Just aren't
as bright!
Click to expand...
---
Sorry to hear that. Perhaps if you read a little more???^)

--
John Fields
 
Ken wrote:

What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?

I need an indicator for a circuit that itself only draws 20mA.


Ken
(to reply via email
remove "zz" from address)
you could try running the LED in series with the Power source if your
Click to expand...
circuit does draw that much,.
you will get a slight drop in voltage how ever if that is not a problem.
 
Ken wrote:

On Mon, 10 Jan 2005 14:25:18 -0800, Jamie
jamie_5_not_valid_after_5_Please@charter.net> wrote:

you could try running the LED in series with the Power source if your
circuit does draw that much,.
you will get a slight drop in voltage how ever if that is not a problem.


Won't the drop be 2 volts?

Assuming I can make this work, how much power in milliwatts will the
LED actually consume?


Ken
(to reply via email
remove "zz" from address)
like i said, you will get a drop in voltage to your circuit, but since
Click to expand...
i don't know your circuit totally i am only guessing that you could
recalucate for that problem.
 
John Fields <jfields@austininstruments.com> writes:

Also, if you want to go mechanical, power ON-OFF switches are avaiable
with an indicator which changes color depending on whether it's ON or
OFF. Zero power required for the indicator.

--
John Fields
Click to expand...
For safety reason, I think mechanical indication is required on line powered
equipment.
--
Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
 
John Fields <jfields@austininstruments.com> wrote:

On 10 Jan 2005 11:44:38 -0800, "JeffM" <jeffm_@email.com> wrote:

if you want to go mechanical, power ON-OFF switches are avaiable
with an indicator which changes color depending on whether it's ON or
OFF. Zero power required for the indicator.
John Fields

The ones I've seen are push-on/push-off
with 2 dayglow green (or yellow) bits that come together like eyelids.

---
Exactly! I've got one on my TEK 2465A.
Click to expand...
Or a simple toggle labeled ON / OFF. (Optional extra: colour the
labels.)

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
On Mon, 10 Jan 2005 17:44:20 -0600, John Fields
<jfields@austininstruments.com> wrote:

[snip]
So, Einstein, since 0.16W < 0.4W, there's your answer.
Click to expand...
Thanks, knob-head.
 
On Mon, 10 Jan 2005 13:37:15 -0500, Ken <cprstn54zz@att.net> wrote:

What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?

I need an indicator for a circuit that itself only draws 20mA.
Click to expand...
---
High efficiency LEDs are available with a rated current of 2mA which
are clearly visible with less than 1mA going through them. High
intensity LEDs are also available which should give you a nice output
for much less than that.

Also, if you want to go mechanical, power ON-OFF switches are avaiable
with an indicator which changes color depending on whether it's ON or
OFF. Zero power required for the indicator.

--
John Fields
 
Ken wrote:
What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?

I need an indicator for a circuit that itself only draws 20mA.

Ken
(to reply via email
remove "zz" from address)
Click to expand...
You usually do not need 20 ma to have a useful power on indicator.
And the main claim to fame of the 3909 was that it could boost a low
voltage high enough to light the LED, as well as flash it. You can
use an LMC555 as a flasher, and put the LED in series with the
discharge pin to give a flash often enough to indicate power on with a
sub milliamp average drain and much less than $5 price tag. This
assumes that you have more than about 4 volts to work with.

--
John Popelish
 
On Mon, 10 Jan 2005 19:31:40 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Mon, 10 Jan 2005 14:25:18 -0800, Jamie
jamie_5_not_valid_after_5_Please@charter.net> wrote:

Ken wrote:

What "power on" indicator consumes the least current?

An LED draws 20 mA. In a flasher circuit (LM3909) this can be reduce
to 0.4 mA, but at an expense of around $5 in components.

Is there anything in between?

I need an indicator for a circuit that itself only draws 20mA.


Ken
(to reply via email
remove "zz" from address)
you could try running the LED in series with the Power source if your
circuit does draw that much,.
you will get a slight drop in voltage how ever if that is not a problem.

How is that brainwave going to save on power?
Click to expand...
---
Well, my boy, first consider:


+V
|
+------+--E1
| |
| [RS]
| |
[RL] +--Eled
| |
| [LED]
| |
+------+
|
GND

E1˛ (E1 - Eled)
Pd = ----- + E1 * -------------
RL RS


Assuming that +V is 10V, that RL is the load, (which draws 20mA at
10V) that Eled is 2V, and that the LED draws 20mA, if we plug in those
numbers we'll have:


10˛ (10V - 2V)
Pd = ------ + 10V * ------------ = 0.4W
500R 400R




Then, if our circuit becomes:


+V
|
+--------E1
|
[RL]
|
+--------Eled
|
[LED]
|
GND


We'll have:


E1 - Eled
Pd = E1 * -------------
RL


Now, keeping everything as it was before and assuming that the
circuitry represented by RL can work with 8V across it, if we plug in
the numbers, this time we'll have:


10V - 2V
Pd = 10V * ---------- = 0.16W
500R



So, Einstein, since 0.16W < 0.4W, there's your answer.

--
John Fields
 
"Steven Swift" <novatech@eskimo.com> wrote in message
news:crvei5$8sf$1@eskinews.eskimo.com...
For safety reason, I think mechanical indication is required on line
powered
equipment.
Click to expand...
'Required?' There's tons of common household equipment that uses pushbutton
switches that have no mecahnical indication of their powered/unpowered
state. (In fact, I have a monitor where this is actually kinda annoying...
the power LED changes color depending on the mode, and it can be hard to
tell red's 'off' from orange's 'on, but in power save mode' at times!)

The original poster might want to go a Google news groups search for the
thread about ultra-low power LED flasher circuits some months back.
Winfield Hill had plenty to contribute to it, which is a pretty good
indication that the results were high quality and robust!
 
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