Grr... high frequency square wave - Electronic Circuits Projects Diagrams Free

dandare99 · 22nd January 2007, 07:01 PM

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

evandude · 22nd January 2007, 07:17 PM

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).

**Nigel Goodwin** · 22nd January 2007, 10:13 PM

For a start, what are you trying to do?.

Analog · 22nd January 2007, 10:39 PM

describe what it looks like.

dch222 · 23rd January 2007, 04:40 PM

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.

**Nigel Goodwin** · 23rd January 2007, 05:18 PM

Quote:

Originally Posted by dch222

You cannot quite get a 50% duty cycle with a 555,

Yes you can, and either side of it as well!.

dandare99 · 23rd January 2007, 07:40 PM

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.

Roff · 23rd January 2007, 09:12 PM

Quote:

Originally Posted by dandare99

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

I can't find any reference to a part named TL5100.

k7elp60 · 24th January 2007, 02:07 AM

Quote:

Originally Posted by evandude

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 don't need and inverter with a D flip flop, just connect the Q(_) to the D.

Russlk · 24th January 2007, 09:58 PM

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.

Hero999 · 27th January 2007, 09:53 PM

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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22nd January 2007, 07:01 PM	#1
dandare99	Grr... high frequency square wave 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

22nd January 2007, 07:17 PM	#2
evandude	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). __________________ EEgeek.net

22nd January 2007, 10:13 PM	#3
Nigel Goodwin	For a start, what are you trying to do?. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

22nd January 2007, 10:39 PM	#4
Analog	describe what it looks like. __________________ "Everything that is done in the world is done by hope." -Martin Luther "There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."-Albert Einstein

23rd January 2007, 04:40 PM	#5
dch222	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.

23rd January 2007, 07:40 PM	#7
dandare99	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.

24th January 2007, 09:58 PM	#10
Russlk	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. __________________ see my website: www.geocities.com/russlk

27th January 2007, 09:53 PM	#11
Hero999	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 __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.