LM555 output frequency drops when supply voltage from the regulator


I'm using a LM555 timer to produce a frequency of 240KHZ & 50% duty cycle.

The circuit i'm using is Astable.
RA is 82ohm
RB is 200ohm
C is 0.01uF
RLs nothing

I built up this circuit and got nearly 240K frequency and 44% duty cycle

But when use a normal LM340T5 to produce a 5V to the LM555 timer...
The frequency immediately drop to 190KHZ
This cause my 3rd IC almost burn T^T

anyone can guide me to the solution?

Best Regards
Wan Xi

The LM555 Circuit which provide 240KHZ & 50% Duty Cycle:

The regulator Circuit:


  • sauravgoswami
    hey check your capacitor value,secondly somewere loading is goin on...
  • ahmed_hassan133
    first,be sure that your de voltage is 5v purly after loading,and also check this link for mor information


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