I'm designing a 555 timer circuit where I want to control the brightness of an LED array. There is a minimum lux requirement for the array so I need to know the output current when I have a 4.8 V source.

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This is a similar diagram. The only difference is I have a 4.8 V source and an LED array instead of an LED.

Without the 555 chip (simple circuit with 7 LEDs and resistors connected in parallel) I have about 140mA current going to the array. I would like to know if the values of resistor and potentiometer at pins 6 and 7 will affect the output current. I don't have tools to measure lux so my only guidance is 140mA current output.


  • \$\begingroup\$ Well there are a lot of 555s to choose from, I am pretty sure at least one of them can source 140mA, head on over the Digikey or where ever, maybe a TI SE555. \$\endgroup\$
    – Tyler
    Commented Oct 3, 2015 at 1:36
  • 1
    \$\begingroup\$ Answer should be in the data sheet. Question should be closed. \$\endgroup\$ Commented Oct 3, 2015 at 1:49
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    \$\begingroup\$ While the answer you've chosen is correct, your schematic is not a great idea. The LEDs should have current limiting resistors, and the 555 output will not drive full current at full voltage. The NE555, for instance, with a 5 volt supply, is only guaranteed to put out 3 volts with a 100 mA current. \$\endgroup\$ Commented Oct 3, 2015 at 3:25
  • \$\begingroup\$ I bought some capacitors and tested the circuit with and without the resistor. I can't see the flashing LED with the resistor. I removed the resistor and the LED is now blinking and its frequency determined by the potentiometer. I know this isn't a good practice as you said. \$\endgroup\$
    – Alp
    Commented Oct 3, 2015 at 9:02
  • \$\begingroup\$ Why do you have resistors in parallel with LEDs? \$\endgroup\$ Commented Oct 3, 2015 at 11:58

1 Answer 1


The current coming out of pin 3 is not affected in any way by whatever current may be flowing into or out of pins 6 and 7. Pin 3 is essentially the output of an S-R latch, which draws it's output current from the voltage rail in parallel with the comparators.


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