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# 555 timer question

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#### batman

##### New Member
I have a 555 in astable mode pulsing an IR LED at 10 kHz. THe supply voltage is 5.2 V. I measured the voltage across the LED in DC mode and it says .97V. Can someone show me a schematic to get the voltage across it to just under 2V, like 1.9V? Thank you

Uhhh... do you have a resistor before the LED, if you do, try dropping it by about 1/10th the resistance, and slowly test it until it's voltage goes up.

I do not have a resistor in front of it.

What's the voltage and draw of the LED ?

forward current = 150mA
forward voltage = 1.3V

It'd be cool if i could get as close to 1.3V as possible.
Thanks

Hmmm... lemme think a bit...

Yeah, you don't really need a resistor, it's only about a 32 ohm variance, so that's not the problem.

A 555 timer will be able to sustain a 9v battery, try that, and put in a 100 ohm resistor before the LED.

That should get the IR LED a bit closer to 1.9v

By the way, what's this for, may help a bit better.

If you're having a problem with extending the range, try using a better IR LED

I'd prefer to use the 5.2V supply. Is there a way to use a transistor to get the LED at a higher voltage?

The specs i posted are wrong, sorry. This is all the info i have on the LED:
Max forward current 80mA continuous. Max reverse Voltage =2VDC

batman said:
I have a 555 in astable mode pulsing an IR LED at 10 kHz. THe supply voltage is 5.2 V. I measured the voltage across the LED in DC mode and it says .97V. Can someone show me a schematic to get the voltage across it to just under 2V, like 1.9V? Thank you
You have probably got it right already.
Don't forget your 555 in astable mode will have its output high for only 1/2 its time; the other 1/2 it is at 0v. A meter set to DC range will read the average over time, so the average voltage of 1.9v on for 1/2 its time is .95v

yes, u can use an NPN transistor to "boost" the power, thouhg what type will be up to your research. a 2n3904 is a simple one. you hook the (B)base to the output of the 555 (pin 3?) and the (E)emmiter to ground, then connect the led to your powersource, with a resistor to limit the 5V down to 1.9 or what voltage u want, and connect that, to the (C)collector. then it should work all good... otherwise if want to use a higher frequency, you will probably need to use a mofset and connect it the same idea, but with the gate connected to the output of the 555... ask somone else though about that as iv dont rember how.

Jaw174 said:
yes, u can use an NPN transistor to "boost" the power, thouhg what type will be up to your research. a 2n3904 is a simple one. you hook the (B)base to the output of the 555 (pin 3?) and the (E)emmiter to ground, then connect the led to your powersource, with a resistor to limit the 5V down to 1.9 or what voltage u want, and connect that, to the (C)collector. then it should work all good... otherwise if want to use a higher frequency, you will probably need to use a mofset and connect it the same idea, but with the gate connected to the output of the 555... ask somone else though about that as iv dont rember how.
If you use this method you need a resistor in series with the base, or else you'll pop the transistor - they don't like 5V applied between B and E!

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