Solve 555 Timer Problem - Get 100kHz & 95% Duty Cycle

[N468989]

[SOLVED] help 555 timer problem

hi all, i am designing a 555 on astable mode. it is designed to operate at 100kHz with a duty cycle of 95% ( and i get 48Khz and duty cycle 93.5%).

i calculated all the values necessary:

Ra = 12.987 kOhm
Rb = 721.5 Ohm
C = 1nF
F = 1.44/ ((Ra + 2Rb)*C)


i used thes formulas :

tH = 0.693*(Ra + Rb)*C
tL = 0.693*(Rb)*C

T = tH + tL


i searched everywhere and found out the max frequency is 500Khz so I am not sure where the problem is...i need the 100kHz because i am designing an infrared modulator and the central frequency for my filters is 100kHz


can anyone help me thanks.

 

[mgb_phys]

1nF is a bit small, capacitors this small aren't very accurate and the effects of stray and gate capacitance start to matter, you might want to redesign it with at least 10nF.

 

[N468989]

just tested with 10n and 100n ...got 40Khz this time...ive double checked everthing.


i just simulated it on multisim and i got 45.9kHz ...but by my calculations it should be 100kHz

any ideias? i think this is very odd

 

[N468989]

--SOLVED--

the multsim 555 design wizard is not correct. there is a problem with it... in the lab i changed the IC (it was a bit damaged) and i managed to adjust it to my desired frequency / dutycycle.

btw... thanks for trying to solve my problem