Hello, can somebody check my transistor amplifier schematic?

  • #1
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Main Question or Discussion Point

Hi, can somebody tell me how to connect some component in this picture, i draw it but is not working because i have no bfg520 transistor, look this picture maybe i make mistake
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  • #2
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Can you provide some context here? What is the circuit for?

What did you replace the BFG520 transistor with? It seems you need to find an equivalent transistor or one that's similar and adjust the other compoenets as well.

I'm not skilled in electronics per se and can't comment beyond this. However, I figured other PF members would need to know what I'm asking here.

It seems thay are still selling this transistor:

https://www.nxp.com/products/rf/rf-discrete-components-low-power/rf-wideband-transistors/6-ghz-10-ghz-rf-wideband-transistors/npn-9-ghz-wideband-transistor:BFG520
 
  • #3
434
19
Can you provide some context here? What is the circuit for?

What did you replace the BFG520 transistor with? It seems you need to find an equivalent transistor or one that's similar and adjust the other compoenets as well.

I'm not skilled in electronics per se and can't comment beyond this. However, I figured other PF members would need to know what I'm asking here.

It seems thay are still selling this transistor:

https://www.nxp.com/products/rf/rf-discrete-components-low-power/rf-wideband-transistors/6-ghz-10-ghz-rf-wideband-transistors/npn-9-ghz-wideband-transistor:BFG520
one question, can you compare with mine circuits is everything ok, except transistor?
lllllllllllllp.png
 

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  • #4
berkeman
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Both schematics look basically okay to me. Is L1 supposed to be coupling to an antenna as the signal input?

When you say the circuit "is not working", what do you mean? Can you plot the DC solution? Are you trying to run a transient analysis? If so, what is your input signal?
 
  • #5
434
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Both schematics look basically okay to me. Is L1 supposed to be coupling to an antenna as the signal input?

When you say the circuit "is not working", what do you mean? Can you plot the DC solution? Are you trying to run a transient analysis? If so, what is your input signal?
:headbang::headbang::headbang:, I forgot to add signal, but if i put 1 v output is 313mV is okej?
 
  • #6
berkeman
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but if i put 1 v output is 313mV is okej?
No, this is an AC amplifier, with an assumed input source somewhere around L1.
 
  • #7
berkeman
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The 2V DC bias source is for setting the capacitance of that varacter diode, to make the input LC tank circuit resonate at the frequency of interest... It is not a signal input source.
 
  • #8
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The 2V DC bias source is for setting the capacitance of that varacter diode, to make the input LC tank circuit resonate at the frequency of interest... It is not a signal input source.
Sorry one more question, is not working so good varactor because, in document the say min 0.8v and max 6V to change resonance, i dont undrestand, so input frequency must be 100MHZ right?
 
  • #9
berkeman
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is not working so good varactor because, in document the say min 0.8v and max 6V to change resonance
And the 2V bias is right in the middle of that range, right? You will fine-tune that input DC voltage to get the right LC resonance...
so input frequency must be 100MHZ right?
That's about what the output filter is tuned for, so yes.
 
  • #10
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Sorry one more question, is not working so good varactor because, in document the say min 0.8v and max 6V to change resonance, i dont undrestand, so input frequency must be 100MHZ right?
input si
And the 2V bias is right in the middle of that range, right? You will fine-tune that input DC voltage to get the right LC resonance...

That's about what the output filter is tuned for, so yes.
Please sorry, for what we use te varactor? to tune from 88mhz to 108mhz right of not? why i cant change the frequency, can you explain more clear please, what input dc voltage you mean for varactor diode to change capacitance to tune to another station, because i read varactor with dc input increase and decrase the capacitance of varactor, and i put to 2v , do i need to put potentiometer to connect with varactor, of, how suppose to be working like this?, to change frequence
 
  • #11
berkeman
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This is a similar
Please sorry, for what we use the varactor? to tune from 88mhz to 108mhz right of not?
Yes, the reverse bias voltage of any diode changes its capacitance (because it changes the width of the depletion layer). The higher the reverse bias voltage, the wider the depletion layer and hence the lower the capacitance of the diode.

https://en.wikipedia.org/wiki/Varicap

You could use a hand-turned variable capacitor for that input tuning stage, or you can use a voltage-controlled varactor diode to change the input capacitance to fine-tune the input resonant frequency.

So L1 is part of the antenna input circuit, right?
 
  • #12
434
19
This is a similar

Yes, the reverse bias voltage of any diode changes its capacitance (because it changes the width of the depletion layer). The higher the reverse bias voltage, the wider the depletion layer and hence the lower the capacitance of the diode.

https://en.wikipedia.org/wiki/Varicap

You could use a hand-turned variable capacitor for that input tuning stage, or you can use a voltage-controlled varactor diode to change the input capacitance to fine-tune the input resonant frequency.

So L1 is part of the antenna input circuit, right?
But i use already varacator(voltage-controlled varactor), what i have to do more, because i want to use varactor, there is not more in use so much variable capacitor, what i need to change to work varactor can you help me,the L1 is part of oscillator, and i put signal between L1 and Right leads of capacitor C3
 
  • #13
berkeman
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But i use already varacator(voltage-controlled varactor), what i have to do more, because i want to use varactor, there is not more in use so much variable capacitor, what i need to change to work varactor can you help me
Sorry, I'm not able to understand what you said. It sounds like you have used varactor diodes before, and now you need to use one in this circuit. It is shown correctly in the circuit, as far as I can tell.
L1 is part of oscillator, and i put signal between L1 and Right leads of capacitor C3
If L1 is the secondary of a tuned antenna transformer, then coupling the input signal into the circuit single-ended with a connection between L1 and C3 does not work the same way. It's better to use a transformer for L1 to couple the input signal in differentially across L1.
 
  • #14
434
19
Sorry, I'm not able to understand what you said. It sounds like you have used varactor diodes before, and now you need to use one in this circuit. It is shown correctly in the circuit, as far as I can tell.

If L1 is the secondary of a tuned antenna transformer, then coupling the input signal into the circuit single-ended with a connection between L1 and C3 does not work the same way. It's better to use a transformer for L1 to couple the input signal in differentially across L1.
L1 is part of oscillator? i dont know rely:sorry:, if i know i will tell you, me i just take from that picture, wich i post it:sorry:, i think is part of oscillator
 
  • #15
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why in document this circuits works, what i make mistake
 
  • #16
berkeman
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Can you post a copy of your simulation schematic with the DC bias points labeled? Which version of SPICE are you using to simulate your circuit?
 
  • #17
berkeman
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L1 is part of oscillator? i dont know rely:sorry:, if i know i will tell you, me i just take from that picture, wich i post it:sorry:, i think is part of oscillator
Is the circuit meant to be part of a radio receiver or a radio transmitter? Can you show us where you got the circuit from?
 
  • #18
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Can you post a copy of your simulation schematic with the DC bias points labeled? Which version of SPICE are you using to simulate your circuit?
Is party of local oscillator in fm supere heter receiver, he do simulation ind ads2011
 
  • #19
berkeman
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Is party of local oscillator in fm supere heter receiver, he do simulation ind ads2011
Please provide a link to where you got it. Thanks. :smile:
 
  • #22
berkeman
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Ah, it's a Clapp oscillator, not a receiver amplifier. Got it. I haven't used SPICE to simulate oscillators in the past, but I'm guessing you need to find the DC bias points with the oscillator part disabled, and then let it run starting at that DC bias point. It might take an initial (small) impulse input to start the oscillation going, though.

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...
 
  • #23
434
19
Ah, it's a Clapp oscillator, not a receiver amplifier. Got it. I haven't used SPICE to simulate oscillators in the past, but I'm guessing you need to find the DC bias points with the oscillator part disabled, and then let it run starting at that DC bias point. It might take an initial (small) impulse input to start the oscillation going, though.

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...
But i build in multisim, but is no problem i will build also in LTSPICE
 
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  • #24
434
19
Ah, it's a Clapp oscillator, not a receiver amplifier. Got it. I haven't used SPICE to simulate oscillators in the past, but I'm guessing you need to find the DC bias points with the oscillator part disabled, and then let it run starting at that DC bias point. It might take an initial (small) impulse input to start the oscillation going, though.

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...
Hello i start to build in LTSPICE so first i put varactor, but there is no bby40, i have only that in multisim
what do you think why is not working in multisim
 
  • #25
berkeman
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I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...
The search comes up with lots of useful ideas. Here's the google hit list:

https://www.google.com/search?q=spice+simulation+tips+for+transistor+oscillators&ie=utf-8&oe=utf-8&client=firefox-b-1

And this PDF has a nice idea for the forcing function to use to "kick start" the oscillator:

https://m.eet.com/media/1148991/22768-52799di.pdf (see page 110 in the PDF version)

They use a damped oscillator input signal to kick start the oscillator and then let the oscillator circuit continue on its own after the exciting waveform dies out. Nice idea... :smile:

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