Using LEDs to drop voltage in a variable current circuit?

Can an LED be used to drop a few volts (whatever the voltage drop of the particular LED is) in a circuit where the current may vary a little bit (but within the LED's Imax)?

For instance:

(10V supply)-------|>------(load never exceeds 10mA)-------(GND)

Does the LED still need a current limiting resistor if it's looking into a load that won't ever draw more than 10mA?
Will the LED still try to consume as much current as possible until it dies?

I'm guessing yes?  Unless I find a way to limit/regulate a constant current?

you can use LED's to drop voltage at 10 ma no problem.

whatever is drawing 10 ma is the current limiting resistor for the LED's so no extra resistor needed.

10 ma will make modern day LED's light up like a torch, so maybe use blue if you are  using these as a pilot lamp also.

get a jumbo LED so it won't burn out, steal a traffic light and you are set for life as far as inventory, lets see, red, yellow, or green...   

i use Lincoln Navigator tail lights,  ;D

shop at midnight auto,  :

Thanks CJ!

Still showing me which end of the iron to hold after all these years!  ;D

I did exactly that in a kit design back in the early 80's. I needed a couple volt drop and zeners that low were not common. I thought it was cool to have a red LED inside making light for no reason.  

The alternative for drops larger than 0.5V are a Vbe multiplier ( a transistor with a voltage divider feeding the base).  But one LED was simpler than a transistor and two resistors.

JR

Just make sure you don't hold the tip end. ;D

If you want to pm me your address I can send you some old 5mm Red LEDs that have 20mA forward current.

@John: Thanks for the real-world example!

@Sahib: Thanks for the LED offer, but I'm still trying to figure out what to do with the reel of 5000 "vintage" LEDs that I bought on ebay for $20.  ;D

Ha ha ha.

I actually have five large drawers full of various shapes and colours that I bought from a surplus supplier way before e-bay.

Ethan said:

... but I'm still trying to figure out what to do with the reel of 5000 "vintage" LEDs that I bought on ebay for $20.  ;D

Click to expand...

Umm ... use them to decorate the website next December?

You can solder long strings of them in series and power them from the mains voltage, to make christmas lights.. Just don't put it on an aluminum tree... 8)

JR

i have the Vistalight schemo if you want to make some tail lites for the mtn bike,

however, since you can buy one already made for $11.99, why bother?

you could mark the rocks for cruise ships, each rock gets an flashing LED,

There's enough slack in your question to make me wonder exactly what your "circuit where the current may vary a little bit" is.

If it is, say, a guitar-pedal opto-compressor taking 3mA idle and 13mA slammed, OK (if you can spare the voltage loss).

If you added a mini-motor on a "12V" battery which is really 9V-15V, and see 10mA steady current on test, you might not notice that the STARTing current of a motor may be 10 times higher than the running current.

> Will the LED still try to consume as much current as possible until it dies?

_OR_ until the voltage across it falls below ~~1.6V. So 12V and 1K, it sucks 10mA but 10.4mA will starve the LED for voltage and it stops sucking. It actually balances around 10.2mA.

Variable semi-constant current sources do the same, except it balances at whatever the s-CCS sucks (and the LED glows more/less as the s-CCS varies).

OTOH: Just Do It. What is the cost of failure? Ten Cents? Oh wait: "5000..for $20". Half-cent of pre-spent cash, and you can make 4,999 mistakes for zero additional dollars.