I have a fairly simple 555 timer circuit. I am using either one Li-ion coil cell at 3V, two of them in series for 6V, or even 3 for 9V to power the design. The output is an LED meant to flash at the right timing. My output voltage is acting a bit odd. Regardless of if I use 3V, 6V, or 9V, my output voltage from pin 3 to ground is 1.8-2V. I am using the NE555 timer from TI. I thought the voltage drop would be less than 1V. Any ideas on why the output voltage is the same regardless of the input being 3-9V?

 

. Regardless of if I use 3V, 6V, or 9V, my output voltage from pin 3 to ground is 1.8-2V.

Is R1 402 ohms?
What else is pin 3 connected to (off the page)?

 

R1 - 1k ohm, R2 - 30k ohm. The there is a small 3V buzzer I've disconnected originally there

 

my output voltage from pin 3 to ground is 1.8-2V

It sounds like the LED is connected directly to pin 3 without the 1k resistor in series.

 

R3 is in series with the LED at 470ohm. I have even tried reducing to a 0 ohm to drive the voltage up on the LED all the way to 2V

 

Is your ‘555 a CMOS version?

What color is your LED and what size is it?

Unlesd your LED has an internal resistor you will need an external resistor in series.

 

Double check the output wiring.
It sounds like you have an error.

What is the output with the LED disconnected?

 

I have a fairly simple 555 timer circuit. I am using either one Li-ion coil cell at 3V, two of them in series for 6V, or even 3 for 9V to power the design. The output is an LED meant to flash at the right timing. My output voltage is acting a bit odd. Regardless of if I use 3V, 6V, or 9V, my output voltage from pin 3 to ground is 1.8-2V. I am using the NE555 timer from TI. I thought the voltage drop would be less than 1V. Any ideas on why the output voltage is the same regardless of the input being 3-9V?

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If you want to operate the circuit at 3v, use the CMOS version of the 555 (TLC555). The NE555 won't work.
It will also need a MOSFET drive transistor.

 

Double check the output wiring.
It sounds like you have an error.

What is the output with the LED disconnected?

interesting, the output of pin 3 is about 4.5V for a 6V Vcc when i disconnect everything from it. any ideas on what to do next?

 

interesting, the output of pin 3 is about 4.5V for a 6V Vcc when i disconnect everything from it. any ideas on what to do next?

You load is greater than you think.

Find the reason for that excess load and you will solve you problem.
Measure the output current from the 555 to the load with a multimeter (connect the multimeter current terminals in series between the output and the load).

 

Is your ‘555 a CMOS version?

What color is your LED and what size is it?

Unlesd your LED has an internal resistor you will need an external resistor in series.

It is an NE555 timer, not the CMOS (TLC555) timer. LED is just a kingbright high efficiency red LED. Attached the data sheet. I have a 470Ohm in series resistor on the LED, but with the voltage output of pin 3 being so low, I can drop the resistor completely and still drive it with the 1.7-2V coming out of the 555 timer

 

I have a 470Ohm in series resistor on the LED

From you problem, it seems more likely it is in parallel, not in series with the LED.

 

The resistor is definitely in series, the LED will not power on when i remove the resistor to swap out with a different one. Measuring from pin 3 to the LED positive side with a 0ohm resistor (instead of the 470 ohm), I am reading .35mA, and measuring from pin 3 to the negative side of the LED I am reading 55mA

 

I think that Crutschow’s analysis is probably correct. Check your connections.

 

Have you tried using a different NE555?

 

Disconnect one end of the 470 Ohm resistor and check its resistance to make sure it really is that; not 47 Ohm or less.

 

The resistor is definitely in series, the LED will not power on when i remove the resistor to swap out with a different one. Measuring from pin 3 to the LED positive side with a 0ohm resistor (instead of the 470 ohm), I am reading .35mA, and measuring from pin 3 to the negative side of the LED I am reading 55mA

You've cut off the right side of the schematic. Show the remainder of the circuit to the right...

 

One more thought:

Is you battery voltage what it is supposed to be? Some of those coin cells have pretty high internal resistance.