555 Timer voltage drop issue

Thread Starter

kjglennon1

Joined May 9, 2024
6
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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Thread Starter

kjglennon1

Joined May 9, 2024
6
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
 

DickCappels

Joined Aug 21, 2008
10,247
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.
 

eetech00

Joined Jun 8, 2013
4,056
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?

View attachment 321992
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.
 

crutschow

Joined Mar 14, 2008
34,857
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).
 

Thread Starter

kjglennon1

Joined May 9, 2024
6
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
 

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Thread Starter

kjglennon1

Joined May 9, 2024
6
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
 

Alec_t

Joined Sep 17, 2013
14,417
Disconnect one end of the 470 Ohm resistor and check its resistance to make sure it really is that; not 47 Ohm or less.
 

eetech00

Joined Jun 8, 2013
4,056
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...
 
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