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555 Timer Output in Cold Temperatures

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kringen

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Hello,

Has anyone had any issues with a 555 timer output dropping in cold temperatures?

I am using an IR emitter/detector circuit with the IR LED's tied to the output of the 555 timer.

Under normal operating temperature (70 deg F or 21 deg C), the output signal is around 38Khz with enough power to light up the IR LED's.

However, I've noticed that when I store my robot in my garage, where the temps are around 50 deg F (10 deg C), the output of the 555 timer drops completely (around 0.1V). When I bring it back inside, it works perfectly when it warms back up to room temperature.

Here's a short summary of the circuit:

5V -> 555 Timer
R1 = 22K 1/4W resistor
R2 = 10K trimpot (103)
C1 = 0.001 uF (102)

Any help is appreciated!

Thanks,
Erik
 

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  • 38Khz IR Emitter Detector.pdf
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I am using a similar circuit for LED's I am using a power mosfet to turn on the LED's but I am using a TS555IN by STmicroelectronics. It has a temperature range from -40° to 125° C. It is CMOS so the output sink and source current is less than the 555, but it doesn't matter in my circuit as the power mosfet drives the LED's fine.
 
Thanks for the reply. I like the idea of a transistor or a mosfet so I'm not dependent upon the 555 output current.
 
What is the forward voltage drop of the IR emitter you are using? With only 5V on the 555, I'm guessing that there is not enough head room between the Vf of the emitter and the Voh of the 555. What is the voltage drop across the resistor in series with the LED?
 
What is the forward voltage drop of the IR emitter you are using? With only 5V on the 555, I'm guessing that there is not enough head room between the Vf of the emitter and the Voh of the 555. What is the voltage drop across the resistor in series with the LED?

Hi Mike,

I believe the voltage drop of the LED's are 1.7V and there are 2 of them sharing the 555 timer output. The resistor used is 180 ohm.

I wonder if at room temperature the LED's are getting JUST enough current and storing in the cold does something to the duty cycle to the point where they aren't getting enough power.

I like k7elp60's idea of using some sort of transistor. I'm thinking I should leave well enough alone on this project since it seems to work just right at room temperature. Maybe supplying more current will make them work TOO well. I'll give the transistors a shot on the next project.
 
An ordinary 555 with a 5V supply has an output high (low current) of only 3.7V, not 5V.
If the current is high then the output is only 2.5V.

The datasheet also shows what happens to the output when the IC is cold.
 
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