A variable frequency sine/triangle wave generator

[user1453]

Hi

I need either a square to sine wave convertor or a sine/triangle wave generator with variable frequency adjustment

The problem is the range needs to be about 0-2mhz if possible

The sine/triangle wave will be used with comparitors to generate a duty cycle to control 4 mosfets in a full bridge arrangement.

I want to use a sine/triangle wave as my timing mechanism because it will allow me to adjust the duty cycle of the mosfets by adjusting the reference voltage connected to the comparators.

The device is for the control of a small solid state tesla coil

the frequency range is large because I am unsure what the resonant frequency will be required

Does anyone know of a good way to generate a variable frequency sine wave?

 

[_nox_]

buy a waveform generator - or build it.
What about googling first ? There're myriads of hobby projects covering wave generation, sines, and such stuff

 

[user1453]

I have googled it, most wave generators seem to be limited to 100khz

 

[HackinBlack]

try these for starters,50khz to 500khz,is the range you're looking for apparently..
**broken link removed**

 

[_nox_]

he's not looking for teslacoils... he wants to build a sort of controller, which allows him to modify the coils frequency, i assume.

 

[user1453]

the sine/triangle wave is to set the frequency that the mosfets switch at some tesla coils work on 4Mhz resonance.

I want a large frequency range because this controller may be used with several different coils

 

[poopeater]

To convert a square wave to a sine wave, can't you just use a low pass filter? It will give you an approximate sine wave anyway, depending on the quality and complexity of the filter.

 

[zachtheterrible]

I believe that a 555 timer can kick out 2MHZ in a squarewave or triangle wave. and just add a lowpass filter like poopeater said.

 

[user1453]

how do you get a 555 to output a triangle wave

All I need i a triangle or sine wave, if a 555 can prioduce a triangle wave then that will solve my problem

do you have a circuit diagram for a 555 outputing a triagular wave, I've only been able to find 555s producing square and saw tothed waves

 

[audioguru]

Maxim has a MAX038 function generator IC that has sine, square and triangle wave outputs up to 20MHz.

 

[jrz126]

what kind of solid state TC are you building? Class E? Dual Resonant? off-line? Vac. Tube?
How small is small?

You dont need a freq. generator that runs in the high kHz range. You design the primary ckt. to resonate at the same frequency of your secondary. Then you just switch the primary circuit at about 100-1000Hz (commonly referred to the break rate). This may change based on the type of SSTC you're building, but this is how the off-line TC operates.

I'm currently building an off-line TC.
The igbt and cap bank: **broken link removed**
The secondary: (12" dia by 35"h) **broken link removed**

Take a look at www.4hv.org, and Steve Conner's site: www.scopeboy.com

 

[user1453]

It will be a dc solid state tesla coil with 4 mosfets in a full bridge arrangement
similar to this one
**broken link removed**

my controller circuity once finalised will be something like this
http://i73.photobucket.com/albums/i228/user1453/diagram.gif

Is there a way of calcularting the resonant frequencys before buildning the coils?

 

[Hero999]

A low pass filter will only work with a small frequency range.

I've done a Google search and **broken link removed** I can find.

Here are some other interesting links:
**broken link removed**
**broken link removed**

 

[user1453]

I've found a ressonance calculator and the ressonance of the coil I intend to build is around 20khz so If I can find a wave generator at about that frequency then I am set

edit: could I just add an integration circuit onto a 555 timer circuit to convert the square wave to a triangle wave?

 

[jrz126]

Looks like a Dual Resonant design. I think you'll want to go with a PLL (phase locked loop) design. I'm not too familar with the DRSSTC design, but they can be quite complicated. Steve Ward has some good info...https://stevehv.4hv.org/drsstc_design.htm

What are the specs of your coil/topload? 20 khz seems kinda low. My 12"X35" coil will resonate at about 40-50khz. What are the specs on your mosfets?

 

[zachtheterrible]

I'm sorry I was mistaken, a 555 will not produce a triangle wave. I was looking at the datasheet, and on a graph, I saw a triangle wave, but didn't realize that it was actually the RC network charging and discharging.

BUT, I see no reason why you couldn't use the RC network as an output. Of course it wouldn't be a perfect triangle wave, as a capacitor charges very fast at first, then slower. It would also have to be buffered, as any load would change the value of the RC network.

Or I'm sure there's an easy way of taking the square wave output of the 555 and changing it to a triangle wave. Whichever is less complicated.

 

[audioguru]

You could use an opamp as an integrator to convert a square wave to a triangle wave. Then you don't even need a 555 as an oscillator, just use an opamp as a Schmitt trigger with positive feedback from the output of the integrator.

 

[mister_e]

MAX038 do everything

 

[audioguru]

Digikey doesn't have any MAX038's. When they get some it sells for more than $23.00US.

 

[user1453]

I will use a 555 to generate a 50% duty cycl at a variable frequenct, this output will then be put through an intergrator and then do through a series of op amps and comparators to acheve a variable duty cycle, wariable frequency square waves for conttroling the gate drivers, I'll post a block diagram soon (once I've completed it)

the specs on the coils, it will be a table top unit with a goal of 200w

a small 3 by 18 inch secongaty with a small topload

the mosfets have 2ot yet been chosen nore have the gate drivers been designed yet
I'll probably go for 400v 10a n mosfets
I'm just designing the electronic control first it will probably be used on multiple coils

It is just a normal sstc using a h-bridge to double the voltage swing, it is not a drsstc because there is no tank capacitor