In an RF amplifier for more output, generally speaking, using two NPN transistors in a push pull configuration is it really push pull ?

Thread Starter

yourownfree

Joined Jul 16, 2008
99
I have a couple questions, a few I guess. With an NPN and PNP transistor you can have a push pull amp. What is it called when you use two NPN transistors in the same configuration? I suppose the best you could do is class B amp only for this configuration using two NPN transistors, is this correct?
Also will the two NPN configuration get rid of even harmonics or do you really need an NPN and a PNP transistor push pull circuit to do that?
Can Mosfets be used efficiently to amplify digital television transmitter output to increase the power? Say two IRF 510's ? The amplifier I want to design is for 69 MHz and will amplify a digital TV transmitter signal. One of low power in case you were wondering, to about 3-5 watts output. Input to this amp will be about .5 watts maybe less. It will run on 28 volts. Do I really need to run a digital TV signal through a class A amplifier? I know class B does work but I am wondering how well. Any insight into this will help me. I am new to amplifying digital signals and can't seem to find the info I need to read about it. I cant determine what class of amplifier I need for digital television. Yes I'm an old timer needing to fire up a new fire in my brain when I thought it was over. Yes I feel stupid asking and I can take criticism, but looking for some brilliant person to discuss this for me. Explain away, as I love picking others brains.
 

Irving

Joined Jan 30, 2016
796
I have a couple questions, a few I guess. With an NPN and PNP transistor you can have a push pull amp. What is it called when you use two NPN transistors in the same configuration? I suppose the best you could do is class B amp only for this configuration using two NPN transistors, is this correct?
Also will the two NPN configuration get rid of even harmonics or do you really need an NPN and a PNP transistor push pull circuit to do that?
Can Mosfets be used efficiently to amplify digital television transmitter output to increase the power? Say two IRF 510's ? The amplifier I want to design is for 69 MHz and will amplify a digital TV transmitter signal. One of low power in case you were wondering, to about 3-5 watts output. Input to this amp will be about .5 watts maybe less. It will run on 28 volts. Do I really need to run a digital TV signal through a class A amplifier? I know class B does work but I am wondering how well. Any insight into this will help me. I am new to amplifying digital signals and can't seem to find the info I need to read about it. I cant determine what class of amplifier I need for digital television. Yes I'm an old timer needing to fire up a new fire in my brain when I thought it was over. Yes I feel stupid asking and I can take criticism, but looking for some brilliant person to discuss this for me. Explain away, as I love picking others brains.
Can you post example circuits? Its hard to discuss without being on the same page...

I think the configuration you describe is cascode, but a schematic will confirm...
 

Thread Starter

yourownfree

Joined Jul 16, 2008
99
Hello,

Have a look at some datasheets of dual RF power mosfets.

Bertus
I love datasheets as I don't have to re-invent the wheel and I think most people just either use them as they are or modify them rather than build and design from scratch. The circuitry is great on these you have sent! Quite the power output though. I don't need 100 watts or even 50, although this will come in handy for other projects and this one as well. I will look for a lower powered dual transistor datasheet and modify the output matching transformer to match the impedance of the transistor. Although I could run these transistors at a lower capacity to stay cool but would still have to match the output impedance. For this project I am working on the source power is only about 28 volts at about 1 amp. It is ran by a propane thermocouple generator. So I am limited on what power that I can put out. Maybe get 5-7 watts of digital video if I'm lucky, that would be pushing it.
Thank you for your time to help me out here, I appreciate it.
Oh I enjoyed your quote. Made me laugh. Brought back a memory. My uncle used to tell me that if you don't talk and let the other person do all the talking
you'll know twice as much as them. You'll know what you know and what they know too. I think he told me that to get me to shut up when I was a kid. There is truth to it though. Never forgot that. I was always a quiet kid after that until I found out it wasn't getting me anywhere.
 

Janis59

Joined Aug 21, 2017
1,187
Strong speaking push-pull always is complementary pair. However, the trick is to substitute the upper shoulder by Darlington and lower shoulder with Sziklai. Then voila! - You got a complementary overall structure but output transistors are both identically equal.
 

Ylli

Joined Nov 13, 2015
965
Strong speaking push-pull always is complementary pair. However, the trick is to substitute the upper shoulder by Darlington and lower shoulder with Sziklai. Then voila! - You got a complementary overall structure but output transistors are both identically equal.
Commonly referred to as "Quasi-Complementary".
 
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