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Electronics => Best WORKING circuits for WFC => Topic started by: Steve on May 12, 2008, 00:42:28 am

Title: Frequency generator with gating option
Post by: Login to see usernames on May 12, 2008, 00:42:28 am
Hi,

This schematic is the one from Dave Lawton.
I think we all build this one of these... ;)

br
Steve
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on May 12, 2008, 10:45:18 am
Another schematic of this with layout of a print.

br
Steve
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on May 12, 2008, 10:52:28 am
Here another one. Not like Dave's but with other chips on it.
This one is looking better to me.

br
steve
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on May 13, 2008, 00:00:18 am
Ahhh,,, i think i understand what your asking,, a frequency generator with Gating, very well put!

Stevie, if i get time tonight i will try and surf the net for more schematics on how to create a much better Frequency "With Gating." i do agree that dave lawtons circuit could have been a bit better. But as of right now the 555 timer is the best you can get for generating a frequency isn't it?
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on May 13, 2008, 00:08:16 am
I have been doing some thinking, and Dave Lawtons circuit Sends Square Waves to the fet, so it switches the fet either ON or OFF really fast.

I've looked into Pulsing a Transformer, i have seen that when you pulse a transformer with a 555 timer and a fet that the mosfet will send a Square Wave to the primary side of the transformer.

PROBLEMS, well, for one when you switch a fet like that on really fast when driving a transformer IT's on really Fast, this should Be Fixed, In other words you don't want a Square wave Driving the fet if you're using it to pulse a transformer, its less efficient! you need a Sine wave Driving the fet wich powers the Transformer! Why? well fast on switching of the fet is on really fast, if you use a sine wave gating then the fet is not on, its slowly coming on to its peak. so this way you get what looks to be the first LEFT HALF of the sine wave, and the fet shall not quickly Switch OFF. If the fet switches off fast then the second RIGHT HALF of the sine wave from the secondary side of the transformer will not look like a sine wave but will look like a capacitor discharge wave! for this you also need to have a sine wave DISCHARGE the fet from the coil.

when you pulse 1 side of the primary in this manner it is more effecient than dave lawtons setup. On the oscilloscope you will learn that you now see a full sine wave and not just half of one, but to get the AC sine wave you must then pulse in the opposite direction.
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on July 15, 2008, 16:35:19 pm
Hi,

To make life a bit easier, i redesigned today the Dave lawton circuit.
I used the 556 timer in stead of 2 pieces 555 timer.

Output can be put into a mosfet, or transitor .......

br
steve
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on July 20, 2008, 04:52:20 am
Stevie,

You say output can be put into a mosfet or a transistor.  Which would you recommend?  I'm a beginner in electronics.  Thanks.
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on July 20, 2008, 10:05:40 am
Stevie,

You say output can be put into a mosfet or a transistor.  Which would you recommend?  I'm a beginner in electronics.  Thanks.

At these frequency's both are possible.
Mosfets are preferred but are very sensitive and blow up easy.
A 2n3055 transitor is very robust and works too.

I run at this moment a BUZ11 mosfet and it holds with my single cell test setup, but i also have bigger Fets on stock.
You just have to look at the amps and voltages that a specific fet or transistor can handle and take a big marging.
Also use a coolingblock on all your fets and transistors.
And do not forget the diode between the transistor/fet and the +
Coils do give back a puls when you take the power of it. Bemf as we name it. Without the diode, you hit your fet or transistor with that BEMF pulse and you destroy it.

br
Steve
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on July 20, 2008, 13:27:19 pm
Steve,

Thanks very much for the clarifications.
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on March 24, 2009, 09:06:41 am
And this one is also nice.
It keeps the frequency the same, but can change the gating.

br
Steve
Title: Re: Frequency generator with gating option
Post by: Login to see usernames on September 14, 2011, 03:41:18 am
I have a question - might seem a bit silly but here goes:
With the lawton circuit - it uses square waves. The 8xa circuit on the drawing shows it uses a sine wave. Is there any difference in the response in the VIC or driving a cell directly through a bifiliar coil as in the lawton diagram whether a square wave or sine wave is used.?