Looking for a "reverse amplifier" circuit - Electronic Circuits Projects Diagrams Free

delambo · 11th September 2007, 07:47 PM

I am looking for a circuit (or some advise) on how to drop a high voltage signal by a given percentage accurately - like an amplifier only in reverse!

I wish to have a switchable scale to reduce by 5000% (50 volts to 1 volt), 2000% (20 volts to 1 volt) 500% (5 volts to 1 volt) and straight through, ie to supply my curcuit board with 1 volt direct from the supply.

I am currently doing this using the voltage divider method with 2 resistors, but I looking for something a little more accurate and pleasing to the eye!

I am currently switching between the scales with 4 push to make switches (one for each scale), a pic controller and 4 relays, but I open to more suggestions on this.

Any help appreciated,

Thanks.

delambo · 11th September 2007, 08:42 PM

whoops sorry for the double post.

Leftyretro · 11th September 2007, 08:54 PM

You seem to be on the right path. Attenuation is the more proper term for your reverse amplifier term (that I have also seen used for special application using an active amplifier, but forget it's details). You can design a switchable attenuator that will allow a specific reduction of gain you seek depending on the switched attenuator you switch into the signal path. You will need to use double pole switches that will route both the input and output signal to selected attenuator, or you could use a single multi-pole multi-position rotory switch.

To do it accurately you will need to know the impedance of the source and load to calculate the individual attenuator stages.

Here is one on-line attenuator calculator aid, but there are many on line and in reference manuals.

http://chemandy.com/calculators/pi_a...calculator.htm

Good luck

Lefty

delambo · 11th September 2007, 09:01 PM

Thanks leftyretro. Now you mention attenuator I remember, its been a while since I studied electronics and I forget the stuff I dont use evry day!

delambo · 11th September 2007, 09:25 PM

...and on closer inspection that is pretty much what I am already doing only without the first shunt resistor!

mcs51mc · 12th September 2007, 06:31 AM

Is your voltage AC? Why not using a transformator with multiple primary and secondary windings?

Is your voltage DC? Why not using PWM, % duty cycle is % attenuation, and low pass filter?

Hero999 · 12th September 2007, 08:29 PM

What load are you driving?

You might need a buffer amplifier on both the input and output to isolate it from the source and load impedance but this is only normally necessary if the input or load can be a variety of different things; i.e. if your attenuator is going to be a piece of test equipment.

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11th September 2007, 07:47 PM	(permalink)
delambo	Looking for a "reverse amplifier" circuit I am looking for a circuit (or some advise) on how to drop a high voltage signal by a given percentage accurately - like an amplifier only in reverse! I wish to have a switchable scale to reduce by 5000% (50 volts to 1 volt), 2000% (20 volts to 1 volt) 500% (5 volts to 1 volt) and straight through, ie to supply my curcuit board with 1 volt direct from the supply. I am currently doing this using the voltage divider method with 2 resistors, but I looking for something a little more accurate and pleasing to the eye! I am currently switching between the scales with 4 push to make switches (one for each scale), a pic controller and 4 relays, but I open to more suggestions on this. Any help appreciated, Thanks. Last edited by delambo; 11th September 2007 at 08:40 PM.

11th September 2007, 08:42 PM	(permalink)
delambo	whoops sorry for the double post.

11th September 2007, 08:54 PM	(permalink)
Leftyretro	You seem to be on the right path. Attenuation is the more proper term for your reverse amplifier term (that I have also seen used for special application using an active amplifier, but forget it's details). You can design a switchable attenuator that will allow a specific reduction of gain you seek depending on the switched attenuator you switch into the signal path. You will need to use double pole switches that will route both the input and output signal to selected attenuator, or you could use a single multi-pole multi-position rotory switch. To do it accurately you will need to know the impedance of the source and load to calculate the individual attenuator stages. Here is one on-line attenuator calculator aid, but there are many on line and in reference manuals. http://chemandy.com/calculators/pi_a...calculator.htm Good luck Lefty

11th September 2007, 09:01 PM	(permalink)
delambo	Thanks leftyretro. Now you mention attenuator I remember, its been a while since I studied electronics and I forget the stuff I dont use evry day! __________________ Southern Auto Problem Solutions

11th September 2007, 09:25 PM	(permalink)
delambo	...and on closer inspection that is pretty much what I am already doing only without the first shunt resistor! __________________ Southern Auto Problem Solutions

12th September 2007, 06:31 AM	(permalink)
mcs51mc	Is your voltage AC? Why not using a transformator with multiple primary and secondary windings? Is your voltage DC? Why not using PWM, % duty cycle is % attenuation, and low pass filter?

12th September 2007, 08:29 PM	(permalink)
Hero999	What load are you driving? You might need a buffer amplifier on both the input and output to isolate it from the source and load impedance but this is only normally necessary if the input or load can be a variety of different things; i.e. if your attenuator is going to be a piece of test equipment. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.