Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

problem with duty cycle for given diagram

Status
Not open for further replies.
rajaram04

rajaram04

Advanced Member level 3
Advanced Member level 3
Joined
Jun 17, 2012
Messages
871
Helped
6
Reputation
12
Reaction score
5
Trophy points
1,298
Location
earth
Activity points
7,687
Hello sir
After reffering to many areas i got a circuit for 555 as astable with this diagram below
555astable.gif

here with R1=1.2k , R2=1k , C= .01 mf , im getting results with online calculator as 45 Khz
but the duty cycle is 68.75 % as it is showing here

So if i want to get 50 % with same frequency out , what measures i ve to take please responce
i completed to many practicals but still having problem in that
thanks
 

If you want an exact 50% duty-cycle then operate the 555 at double the desired frequency and run it through a ÷2 flip-flop.
 

sir would you please let me have a circuit diagram or circuitry idea about how to run it through a ÷2 flip-flop. please . . . thanks
 

The circuit in post #1 can't achieve 50% duty cycle by nature. There's apparently a problem with the said online calculator or a misunderstanding. A 50% duty cycle circuit is shown in the 555 datasheet. Another popular circuit uses a single resistor between output and capacitor.
 

kkk sir in that case is there any resistor between +ve & pin 7 of the i.c. as we do in general ?
please comment
 

rajaram04 said:
sir would you please let me have a circuit diagram or circuitry idea about how to run it through a ÷2 flip-flop. please . . . thanks
Click to expand...
Use a D type flip-flop such as a CD4013. Connect the /Q (Q not) output to the D input of one of the flip-flops. Connect the 555 output to the FF clock input. The Q output will be 1/2 the 555 frequency with exactly 50% duty-cycle.

You can also use a JK FF such as the CD4027. Just tie the J and K inputs to the V+ voltage and the 555 to the clock input. Again, the output will be 1/2 the 555 frequency.

Note: Make sure you tie all unused inputs of both FFs to ground.
 

hmm okk i got it but sir tell me please about the frequency responcing limits for this 4027 etc
cause i hv listened about 555 that it has good responce upto 100 KHgz
so if i need a 50 Khz 50% duty cycle out using filp flops then i ll have to make 100 Khz on 555 timer

& too a problem is here that if i ve to make final output of flip flop to 100 Khz then i hv to make frequency of 200Khz on 555 timer which is practically i guess not possible

so please help
 

rajaram04 said:
hmm okk i got it but sir tell me please about the frequency responcing limits for this 4027 etc
cause i hv listened about 555 that it has good responce upto 100 KHgz
so if i need a 50 Khz 50% duty cycle out using filp flops then i ll have to make 100 Khz on 555 timer

& too a problem is here that if i ve to make final output of flip flop to 100 Khz then i hv to make frequency of 200Khz on 555 timer which is practically i guess not possible
Click to expand...
According to this (pg. 7, FAQ 2), you can use a 555 up to about 500kHz. The CMOS circuits will work above that frequency.
 

ok sir tell me its perfect nmber code so that i may choose from the given

currently we have NE555 in market & now a days only this series is avaliable for 555 so please help me so that i can place order there
 

rajaram04 said:
ok sir tell me its perfect nmber code so that i may choose from the given

currently we have NE555 in market & now a days only this series is avaliable for 555 so please help me so that i can place order there
Click to expand...
I don't understand your question. Are you asking about where and how to order a 555? Since I don't know where on "earth" you live, I can't really help you there. (Now if you were on Mars, I may know a place. :wink:)
 

hahaha :D no no actually i am asking the proper number or say a code including the 555 labelled on tha i.c. . . Are all 555 i.c.s available in market relating CMOS family ?
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top