hi, friends...I'm currently working on my Final Year Project to construct a plasma needle and facing problems in construct my RF supply. I'm using MOSFET IRF540N in my circuit as switching device and got some question here:

1) Does this IRF540N actually require Vgs of 15V to on/off it instead of the 2.5V shown in the datasheet?

2) The current instrument available for me only manage to provide a 13.56Mhz, Vpp of 2.5V square wave to my MOSFET, and it is a function generator. Is it possible for me to amplify the signal to Vpp of 15V?? what circuit needed to do it??

3) Any gate drive circuit available to provide a Vpp 15V, 13.56Mhz square wave if it is impossible to amplify the signal from function generator?

I'm really in need of your kind help and run out of time, so please help me

 

hi, friends...I'm currently working on my Final Year Project to construct a plasma needle and facing problems in construct my RF supply. I'm using MOSFET IRF540N in my circuit as switching device and got some question here:

1) Does this IRF540N actually require Vgs of 15V to on/off it instead of the 2.5V shown in the datasheet?

Neither. Vgs of 15 V is not needed to turn it off. Vgs of 10V is needed to turn it on fully. The datasheet is correct. You apparently don't understand what V threshold means.

2) The current instrument available for me only manage to provide a 13.56Mhz, Vpp of 2.5V square wave to my MOSFET, and it is a function generator. Is it possible for me to amplify the signal to Vpp of 15V?? what circuit needed to do it??

Yes. You had better check the switching times for that mosfet. It may not operate too well at that frequency. Here is a discussion on design of high-speed drives and limitations: http://focus.ti.com/lit/ml/slup169/slup169.pdf

3) Any gate drive circuit available to provide a Vpp 15V, 13.56Mhz square wave if it is impossible to amplify the signal from function generator?

Yes. Although, most gate drivers do not generate the actual driving frequency. They simply produce the current and voltage needed. Some drivers are designed to produce both top and bottom drive signals for an H-bridge from a single input.

I'm really in need of your kind help and run out of time, so please help me

When is it due?

John

 

jpanhalt, thank you so much for the reply...I'm sorry for din't notice it since no email was send to notify me

http://images.elektroda.net/28_1297149430.jpg
this is the ideal output i want to get, the MOSFET available in this simulation is IRF530N. However, the input from XFG1 is only a 13.56Mhz, 2.5Vp square wave and it works perfectly well. Why it comes to a problem when test in real practice?


http://images.elektroda.net/42_1297149430.jpg
btw, i tried to amplify the voltage from the output of function generator and that's what i get. I was manage to amplify it from Vp of 2.5V to 10V now but it's still useless when come to connect the C2 to the gate of MOSFET. Can any1 tell me why it failed??

http://iopscience.iop.org/1367-2630/6/1/149 is what I was trying to achieve but my deadline is end of March. Right now I'm just looking for any circuit that can help me to produce the plasma, I mean I'll be really satisfied as long as i can see the purple glow on the needle neglecting its characteristic

 

Alright, I'm not sure is it a good news or bad news. My instructor finally agreed to buy some component for my project, but the budget can not be too high. 2 things i need now are IXYS RF-DEIC420-IC,DRIVER,MOSFET DE275 and IXYS RF DE275-501N16A, if I can only choose one, which one is most needed in my project?

1) Is it possible to generate the plasma by using the DEIC420 to drive the IRF540N MOSFET? i heard that a RF MOSFET like DE275 series is more suitable in generating plasma but the problem is out of budget. The MOSFET is even expensive than the MOSFET driver...any suggestion please?? thank you...

 

A couple of observations. The simulation for your driver shows the effects of capacitance and resistance. Essentially, your output at 13 MHz is at 500 Ω into 0.1 uF. That is a lot.

As for driving that mosfet at 13 MHz, you should review how gate drivers work. Here is a relevant excerpt from good review:

Source: http://www.irf.com/technical-info/appnotes/an-937.pdf

11. RESONANT GATE DRIVE TECHNIQUES
As indicated in Section 14, gate drive losses in hard switching are
equal to Qgs x Vgs x f. An IRF630 operated at 10 Mhz with a
gate voltage of 12 V would have gate drive losses of 3.6 W,
independent from the value of the gate drive resistor. Clearly, to
achieve hard switching at this frequency, the resistance of the gate
drive circuit is limited to whatever is associated with the internal
impedance of the driver and with the gate structure of the device
itself. Furthermore, the stray inductance of the gate drive circuit
must be limited to tens of nH. The design and layout of such a
circuit is not an easy task.
An alternative method to drive the gate in such an application is
to design a resonant circuit that makes use of the gate capacitance
and stray inductance as its reactive components, adding whatever
inductance is necessary to achieve resonance at the desired
frequency. This method can reduce the peak of the gate drive
current and losses in half, while simplifying the design of the gate
drive circuit itself. Since the gate charge is not dissipated at every
switching transition, but stored in a reactive component, the gate
drive losses are proportional to the resistance of the gate drive
circuit, rather than being independent from it. More information
on this gate drive method can be found in an article by El-
Hamamsy: Design of High-Efficiency RF Class-D Power
Amplifier and in references at the end of this article (IEEE
Transactions on Power Electronics, May 1994, page 297).

Second, it would be helpful if you could give more detail about what you have done and what you mean by it "not working."

Finally, please post your images on the local server. Going off site can create unnecessary delays and other problems.

John

 

John, can you please show me any circuit can be use to ON/OFF a MOSFET?? I got no idea how to do it even after read many articles/datasheet @.@

All i got is a function generator can output a 2.5Vp square wave and its obviously not enough to turn On the MOSFET as other people do...I know that a oscillating Vgs =10V and -10V needed to do it but i just don't know how....please help me...