Amplifier configurations (setup)

Thread Starter

captoro

Joined Jun 21, 2009
176
Hello,,

So far I only had to use simple ON-OFF mosfet.
I have a project that needs to make amplify a 1v signal to 50v Sine wave signal. From 0 to 4Mhz bandwidth
I did a simple a CS MOSFET amplifer. But that didn't work well.
Anyone can guide towards the right direction ?
SHould I use multistage ? ( I read it would decrease the bandwith)
Type of configuration (CS, CG...) ? Type of MOSFET to use ?
My classes in amplifers is very far away.
Anything can be helpful

Ken
 

LowQCab

Joined Nov 6, 2012
2,512
DC to 4-Mhz ..........
Good Luck with that,
I'll be watching to see what You come up with.

It would help tremendously if You would explain why You need
such an Amplifier and especially what its ultimate purpose is intended to be.

4-Mhz is a Radio-Frequency-Transmitter, why does it need DC-response ?
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Audioguru again

Joined Oct 21, 2019
5,202
An amplifier has a certain load impedance or resistance then the output current and output power can be calculated.
How much distortion can be tolerated?
 

Thread Starter

captoro

Joined Jun 21, 2009
176
An amplifier has a certain load impedance or resistance then the output current and output power can be calculated.
How much distortion can be tolerated?
Dont mind a little distortion.
I can also have two or three different circuits so it can handle all the frequency range
 

LowQCab

Joined Nov 6, 2012
2,512
It would help tremendously if You would explain why You need
such an Amplifier and especially what its ultimate purpose is intended to be.
.
.
.
 

Thread Starter

captoro

Joined Jun 21, 2009
176
It would help tremendously if You would explain why You need
such an Amplifier and especially what its ultimate purpose is intended to be.
.
.
.
I want to study the effect ( if any) of a air coil to materials witin a feet.
Yes its within a faraday cage.
 

DickCappels

Joined Aug 21, 2008
9,332
That performance is within the capability of consumer color televsion receiver video output stages.

What you intend to do is not very hard, but I think that you would be better off with a bipolar transistor than a MOSFET for a couple of reasons.

Run-of-the-mill MOSFETs have high internal capacitances.
Bipolar transistors have a much higher Gm (output current change for a given change in input voltage.

To do this one usually uses a common emitter configuration, sometimes with an output buffer, and sometimes feedback -that would take care of most of your linearity problem.

The key component is the transistor used in the common emitter stage. We already have an idea of the desired bandwidth and output amplitude, and the selection of the transistor in the gain stage is greatly affected by the load and the power supply voltage available.

Can you tell us the available power supply voltage and describe the load? What is very important is the load capacitance - if you don't know, describe it and estimate the capacitance to ground.

This might take a couple of watts and probably the purchase of a transistor you don't already have.
 

Thread Starter

captoro

Joined Jun 21, 2009
176
That performance is within the capability of consumer color televsion receiver video output stages.

What you intend to do is not very hard, but I think that you would be better off with a bipolar transistor than a MOSFET for a couple of reasons.

Run-of-the-mill MOSFETs have high internal capacitances.
Bipolar transistors have a much higher Gm (output current change for a given change in input voltage.

To do this one usually uses a common emitter configuration, sometimes with an output buffer, and sometimes feedback -that would take care of most of your linearity problem.

The key component is the transistor used in the common emitter stage. We already have an idea of the desired bandwidth and output amplitude, and the selection of the transistor in the gain stage is greatly affected by the load and the power supply voltage available.

Can you tell us the available power supply voltage and describe the load? What is very important is the load capacitance - if you don't know, describe it and estimate the capacitance to ground.

This might take a couple of watts and probably the purchase of a transistor you don't already have.
Hello,

The source of the DC a a from a regulated power supply with 10A min . no issue there.
My load is a 0.04mH coil.
hope that helps
 

LowQCab

Joined Nov 6, 2012
2,512
Hey
LowQcab , any thoughts now ?
Only that what You are thinking about doing is extremely dangerous,
and not likely to be much more than a "novelty" display,
( which could be very interesting none the less ).

Is there some practical use for what You have in mind ?
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DickCappels

Joined Aug 21, 2008
9,332
A large coupling capacitor, which would simplify the circuit a lot by allowing AC across the coil without the need for a direct coupled approach.

What power supply voltages do you have available?
 

Thread Starter

captoro

Joined Jun 21, 2009
176
A large coupling capacitor, which would simplify the circuit a lot by allowing AC across the coil without the need for a direct coupled approach.

What power supply voltages do you have available?
Right know I have a 40v power supply .
Here is my schematic so far. there is a coupling capCommon drain.jpg
 

Thread Starter

captoro

Joined Jun 21, 2009
176
Only that what You are thinking about doing is extremely dangerous,
and not likely to be much more than a "novelty" display,
( which could be very interesting none the less ).

Is there some practical use for what You have in mind ?
.
.
.
Hi,

there is no practical use for now. Its for a halloween thing if you must know.
I dont know what that has to do with helping to build an amplifier . So many people here ask question In what occasion is it used for, when why how.... It has nothing to do with electronics
regards
 

DickCappels

Joined Aug 21, 2008
9,332
The reasons we ask so many questions about the use of these projects is that there are many ways that electronics can end up hurting somebody or damaging property. We would rather guide you through doing something safely than for you to have an unfortunate accident. Besides, this is also referred to in the User Agreement.

It is ok if one end of the inductor is connected to another amplifier rather than ground? <=== Big question!

1662309482002.png
Full bridge amplifier implemented for audio.

If you want to get 50V P-P while using a single 40V power supply you will need to use a full bridge configuration. I am currently looking at transistors used in color CRT television sets to see if we can find something that is both fast enough and can swing much V P-P. One possibility is the CR2424 hybrid amplifier which can get you more than enough bandwidth and more than 50 V P-P if used in a bridging configuration (one amplifier for each end of the load) but I really doubt it can drive 50 ma into a load. Maybe with output buffers.

Also, while at it, one way to generate a lot of voltage (and therefore current) is to drive a series tuned circuit at or near resonance. The current drawn would be very large, limited primarily by the resistance of the circuit + driver. It would use less expensive and exotic parts.

Pulse generator ==> Capacitor ==> Inductor ==> Ground. Either the frequency or the series resistance could be adjusted to obtain the desired current.
 

Thread Starter

captoro

Joined Jun 21, 2009
176
The reasons we ask so many questions about the use of these projects is that there are many ways that electronics can end up hurting somebody or damaging property. We would rather guide you through doing something safely than for you to have an unfortunate accident. Besides, this is also referred to in the User Agreement.

It is ok if one end of the inductor is connected to another amplifier rather than ground? <=== Big question!

View attachment 275613
Full bridge amplifier implemented for audio.

If you want to get 50V P-P while using a single 40V power supply you will need to use a full bridge configuration. I am currently looking at transistors used in color CRT television sets to see if we can find something that is both fast enough and can swing much V P-P. One possibility is the CR2424 hybrid amplifier which can get you more than enough bandwidth and more than 50 V P-P if used in a bridging configuration (one amplifier for each end of the load) but I really doubt it can drive 50 ma into a load. Maybe with output buffers.

Also, while at it, one way to generate a lot of voltage (and therefore current) is to drive a series tuned circuit at or near resonance. The current drawn would be very large, limited primarily by the resistance of the circuit + driver. It would use less expensive and exotic parts.

Pulse generator ==> Capacitor ==> Inductor ==> Ground. Either the frequency or the series resistance could be adjusted to obtain the desired current.
Hello,

I am trying to avoid the negative pulse.
My source is a 120VAC to 35VAC (200 VA) transformer, so this will give me 50v (not 40 v as I previously mentionned) DC as my DC source.
My AC source is from an LM7171 with positive output.
I can go in a different method, if its easier
 

Thread Starter

captoro

Joined Jun 21, 2009
176
It is ok if one end of the inductor is connected to another amplifier rather than ground? <=== Big question!
I rather not, I probably be increasing the voltage afterwards, so I better let the coil be grounded or connected to the source if using a common source type amplifier.
 

LowQCab

Joined Nov 6, 2012
2,512
Hi,

there is no practical use for now. Its for a halloween thing if you must know.
I dont know what that has to do with helping to build an amplifier . So many people here ask question In what occasion is it used for, when why how.... It has nothing to do with electronics
regards
.
Yes, we all must know.
It has everything to do with everything ........
The are at least a million ways you can pursue a given project,
999,987 of them have been proven over and over again to NOT WORK,
or to be extremely dangerous, or to be very costly, or impractical, in some other way.

All Electrical-Circuits are designed around achieving a desired, overall end result,
not a particular "Voltage-number".
Everything is speculation until a "desired end-result" is described in detail,
with that done, You are likely to receive at least 2 valid approaches here,
and maybe even 4 or 5 different ways to achieve that same end-result.
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