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13.5Mhz Class E amplifier

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Bikram

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Hi,
I am new in this forum so not sure where to post this question. Anyway, I have been trying to design a 13.5Mhz, 30Watt Class e amplifier. The class e amplifier seems to work very well according to the simulator, in the class e amplifier design I used two irf 520 in parallel.In simulator I have been driving these IRF520 using signal generator. In practice I intend to drive this mosfets using DEIC420.

In the datasheet of DEIC 420 there is a test circuit shown with all the bypass capacitors and resistances. According to this diagram 4 1/2 watt ferrite beads with a resistance of 7ohms are required in series with the power supply to the DEIC 420.


Now the questions are
1-the datasheet is little bit unclear to me whether the beads are 7ohms or 70 ohms?
2-In digikey ferrite beads are sold according to ampre rating;for example I have brought 7ohm 3amps ferrite beads.So far I have not seen any watt rating for the beads.So I am not sure if the beads are correct.

sorry for the long question.Please give me some advice if anyone here has any experience with DEIC420.
 
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I do not see why you think those beads are rated at 7 ohms. I see no such rating. I only see a reference designator called R7, a value of 0 (which is the generic ideal value for a bead), and a notation of 4 beads 1/2W. Since all the DC power is going through these beads and this power might involve up to 20 amps, it would not be wise to include a 7 ohm DC resistance, or for that matter four times 7 ohms resistance, in series with the supply since the resulting voltage drop will be extremely large and the circuit will not work. In addition, the beads will probably burn up immediately. You may have found a part that has 7 ohms of impedance at a specific high frequency, that might be a bit better, but still not what they mean. I suspect the description "1/2 watt" merely describes the size of package the part has (like a 1/2 watt resistor size).

Those beads are included for suppression of RF currents on the wire attached to E9 TP so to avoid radiating and coupling RF to other circuits and to avoid other RF currents getting into this circuit. They are not included to assist the performance of the driver amp. Its too bad they do not provide a part number, but I think that we can choose a reasonable substitute.

You can choose a bead that is rated for high current, such as a suitable tubular bead that goes around a short length of wire, or even better, you should use a common mode choke which requires that you pass both the + wire and the ground wire through it. This type of choke works well for common mode noise in circuits that take high DC currents. For example, a part like this one (digikey pn 240-2487-ND), rated at 20 A is suitable:

**broken link removed**
 
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Are you sure that the IRF520 mosfet is fast enough to switch at 13.5MHz? Your desired swithcing period is 74nsec. I just took a quick look at the datasheet and the combined rise time and fall times of the gate/drain (total time from gate turn on to full saturation and vice-versa) is nominally about 82nsec (sum total of td(on)+tr+td(off)+tf). Granted, the mfg's testing conditions are not going to be the same conditions in your amplifier, but using them as a guideline, I would think that the fet will always be in transition and never really on.
 
Are you sure that the IRF520 mosfet is fast enough to switch at 13.5MHz?

That was what I was going to post this morning - I've used the IRF540 a lot and its not particularly fast. I wasn't in the mood for reading through datasheets this morning though (kind of on my honeymoon :p)
 
That was what I was going to post this morning - I've used the IRF540 a lot and its not particularly fast. I wasn't in the mood for reading through datasheets this morning though (kind of on my honeymoon :p)

Your new wife has my permission to give you a 'good slapping' for posting here on honeymoon! :p
 
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