Grr... high frequency square wave

D

dandare99

New Member
hi

i wonder if anyone can give me some help on my problem. im trying to generate a 100 - 150 kh square wave using a 555 timer. although i am able to generate perfect square waves at 50 - 70 Khz, i cant seem to be able to get a perfect square wavon the output a higher frequencies. can anyone help me figure this out. im not very experienced in using electronic components. maybe my supply voltages have something to do with this as i am using the correct resistora and caps according to the furmulas.

also can someone help me with a circuit using a tl5100cp as its supposed to be able to create output frequencies of between 20kHz and 500 kHz
 
If you're highly concerned about getting a perfect 50% duty square wave, then perhaps you should instead generate a signal twice the desired frequency and pass it through a divide-by-2 (such as a D flip flop with an inverter between Q and D).
 
You cannot quite get a 50% duty cycle with a 555, but almost, provided the discharge resistor (between pins 6 and 7) is much larger than the charge resistor (between pin 7 and Vcc). eg 1M and 1K. Trouble is for the high frequency tou are looking for you would then need a mighty small cap.
Haven't done the sums.
 
Thank you guys

it a part of a driver circuit for an induction heater. The rest of the circuit works fine at lower frequencies. i use a 2nF cap.
 
I can't find any reference to a part named TL5100.
 
evandude said:
If you're highly concerned about getting a perfect 50% duty square wave, then perhaps you should instead generate a signal twice the desired frequency and pass it through a divide-by-2 (such as a D flip flop with an inverter between Q and D).
Click to expand...
You don't need and inverter with a D flip flop, just connect the Q(_) to the D.
 
For induction heating, you want an AC signal. A single transistor driver will be very inefficient; use a push pull circuit. A D type flip flop and AND gate can make the push pull drive which does not have to be (does not want to be) 50% duty cycle because you need some dead time while the transistors are switching.
 
Where was the duty cycle mentioned?

Use a TS555 because they're more stable at higher frequencies.

The circuit for 50% duty cycle is on the datasheet.

What sort of driver are you using?

I recommend adding a capacitor in parallel with the coil to provide a resonant circuit which will boost the efficiency
 
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