CS amp using IRFZ44N

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Thread Starter

captoro

Joined Jun 21, 2009
126
Hello,

I am having issues with a common source amplifier using a NPN MOSFET.
Attached is my simulation and its output. Its the best i can do after tweeking the resistances values, I was hoping to get +/- 9 v.

Ken
 

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ScottWang

Joined Aug 23, 2012
7,065
Do you want to change Rc to 1.2K and change Re to 1K, if you want the result to close you want then just change the vlaues of two resistors.
 

sparky 1

Joined Nov 3, 2018
580
I purchased some P-Channel IRF9540 for a Current Source project that never was built.
I looked for that circuit (think it was the CS for a Hakko soldering iron controller) It used an AD823 op amp for low noise.
From reading different projects it was without much complaint and reported back ok, the lower Vgs FETs are popular.
I think the mid sized CS projects get interesting, they can do some serious work and accurate control that are often neglected.
With informative reporting more applications can be built.

edited
Woops sorry for thinking current source here. Common source amplifier.
 
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Ian0

Joined Aug 7, 2020
3,275
I was always told the IRFZ44N is for switching applications and not sine wave amplification. Am I wrong?
All MOSFETs have a linear region where they can act as amplifiers, but you would be correct in thinking it was primarily designed for switching applications.
 

Audioguru again

Joined Oct 21, 2019
3,544
Even though the IRFZ44 Mosfet is rated to pass 30A to 50A when its Vgs is 10V, like most ordinary Mosfets its threshold Vgs is 2V to 4V when its Vgs is only 0.25mA and it is barely turned on and is almost turned off.
 

Thread Starter

captoro

Joined Jun 21, 2009
126
Even though the IRFZ44 Mosfet is rated to pass 30A to 50A when its Vgs is 10V, like most ordinary Mosfets its threshold Vgs is 2V to 4V when its Vgs is only 0.25mA and it is barely turned on and is almost turned off.
Even if I have over 4v for Vgs, I assume its turned on completely. Why dont I full voltage at output. if I reduce Rc, I get lower voltage. I will eventually have my load at RCc. Rc will eventually be a coil I want to drive. But if I cant get a simulation to work, no point of adding my coil. Unless there is another way to pulse a coil ?
 

sparky 1

Joined Nov 3, 2018
580
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Thread Starter

captoro

Joined Jun 21, 2009
126
Exactly how does the coil need to be pulsed?
What do you mean how ? I dont mind how. I just need to put 600V / 2A.
Basically like a big coil antenna. The source is AM signal that has been pre amplified. The last stage (the circuit I am having issues here) is to put that signal (amplified) into the air coil mentionned above.
 

Audioguru again

Joined Oct 21, 2019
3,544
You showed the high power Mosfet with a 20V supply and a 33k ohms load driven from 1kHz. Now you say 600V, 2A and 1000kHz which is a completely different circuit.
Since the IRFZ44 Mosfet you showed has a maximum allowed voltage of 60V then you need a high voltage amplifier to replace it.
 

Ian0

Joined Aug 7, 2020
3,275
So finally after 14 posts, a clue. . . .
I suggest you start looking up AM transmitter circuits. A Class-A amplifier with a maximum efficiency of 25% probably isn't the way to go, unless you can afford a really big heatsink.
 

Thread Starter

captoro

Joined Jun 21, 2009
126
You showed the high power Mosfet with a 20V supply and a 33k ohms load driven from 1kHz. Now you say 600V, 2A and 1000kHz which is a completely different circuit.
Since the IRFZ44 Mosfet you showed has a maximum allowed voltage of 60V then you need a high voltage amplifier to replace it.
Ya let's start from the basic. If I can't get my MOSFET going with high resistive load . Which is a very common configuration, I won't get a more complicated circuit going. But. If there is a better approach then I ask and you can reply here. I am not changing the parameter of the circuit. I am slowly building up from my simple CS amplifier.
 

Thread Starter

captoro

Joined Jun 21, 2009
126
And if my approach is not the best way. Then I will start a new thread because I initially thought I could replace Rc with my air core inductor once I get the circuit going. .. yes change the MOSFET. But the MOSFET I want to use is not on LTspice and I have lots of IRFZ44N
 

Audioguru again

Joined Oct 21, 2019
3,544
First, you need to learn about how an AM radio transmitter works and about all the circuit sections (oscillator, modulator, RF amplifier, antenna) it needs.
Second, design and build a legal low power transmitter, not the 1200W one.
Have you selected a radio frequency for it?

Your new thread says you want to put an AM signal into a 90 ohms, 2H coil using a 600V/2A power supply. Then it will not be an AM radio transmitter, instead it might be an electric/mechanical buzzer.
 
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