• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 20 subscribers
  • Views 179 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LM555: LM555 Circuit Connections

LM555: LM555 Duty Cycle Issue

Kami Huang60
Genius 3830 points
Part Number: LM555

Dear Sir/Ms.

My client uses LM555 to generate 40% Duty but his actual result is 60% Duty. The customer said that he adjusted the resistance ratio of RP1 to RP2, the maximum duty is only 50%. The customer's schematic is like an attachment, can you help the customer to see if there are design errors?

SCHEMATIC1 PWM & 3_3V circuit.pdf

Best Regards,

Kami Huang

  • 0
    TI__Guru*** 140126 points

    Hello Kami,

    The formula in the LM555 data is duty cycle, but it is the low time duty cycle. Notice that the numerator is RB which is proportional to low time. For high time duty cycle the numerator will be RA + RB. In the basic a-stable configuration high duty cycle must be greater than 50%.

    There is an a-stable timer FAQ with a three timing resistor method for getting 40% high duty cycle. FAQ

    Diodes can also be used to create high duty cycles less than 50% (also in the FAQ)