Class E power amplifier

[sinato]

I want to know what is the relation between the transistor size and dc current in class E power amplifier, what is Imax and how I set the DC current ??

 

[barry]

I want to know what is the relation between the transistor size and dc current in class E power amplifier, what is Imax and how I set the DC current ??

The relation is : Bigger transistor<==>more current.

I'm not sure I understand the second part of your question. I don't know what Imax is, either. Could you give us some context?

 

[sinato]

the problem is when I want to increase the output power , I try to increase this dc current by increasing size but neither the measured output power nor the power consumption increase !!

 

[barry]

Size doesn't matter. (except for power handling capability). If you want more output current, you need to increase the voltage.

 

[sinato]

@barry could you please explain what do you mean by "power handling " , also if i want to increase the output power without increasing voltage what shall I do ...as a power converter the power amplifier converts Idc*Vdc to Irf*Vrf how can i control Idc ???
@BigBoss I really appreciate your help ,but could you talk more about junction temperature because i didn't understand the last line

 

[BigBoss]

@barry could you please explain what do you mean by "power handling " , also if i want to increase the output power without increasing voltage what shall I do ...as a power converter the power amplifier converts Idc*Vdc to Irf*Vrf how can i control Idc ???
@BigBoss I really appreciate your help ,but could you talk more about junction temperature because i didn't understand the last line

What type of transistor do you use ??

 

[sinato]

it is Mosfet

 

[barry]

You need to understand how a class E amp works. Basically, the MOSFET is either fully on or fully off-it's working as a switch. I'm not an expert on Class E amps, but I believe they are only used for RF, but you're talking about increasing DC current; I'm not sure I understand. Do you just mean the ON current of the device? As I said before, the only way to increase that is to increase the supply voltage (or the load) since the MOSFET is already being driven fully on. I guess if you got a MOSFET with lower on resistance that would increase your current a bit.

 

[sinato]

thaaaaanks

 

[vfone]

Switching Class-E amplifiers use the transistor capacitance in parallel of the switch. When the switch is closed, all the current flows through the switch. When is open, this same current must flow through the capacitor.

Best Class-E efficiency requires an upper limit of the transistor capacitance, and also have to increase the device size until the switch capacitance equals the total capacitance at the output of the PA.

 

[sinato]

thanks vfone, I'd like to know the meaning of this sentence (the transistor should bear imax,(which is the maximum current)) .how can I fulfill this condition?

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Also , the only way to increase output power , is increasing Vdd or decreasing load, right ??

 

[barry]

You also control power with your pulse-width, right?

 

[sinato]

I think it only changes the optimum design parameters (capacitor size,....etc)