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impedance matching

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Oh my. I did misunderstand. Okay. This 3-5 mA current you want. It is a constant DC current, or can it vary sinusoidally between +/- 3-5 mA? I understand the 5-10vpp across the capacitor. That is clear.

Edit. And must this 3-5 mA current flow through the capacitor, or is that the load current you want to draw from the signal generator?
 
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i want AC current and flow through the capacitor (as i said i have two electrode inside the salt water)....
 
i want AC current and flow through the capacitor (as i said i have two electrode inside the salt water)....
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I don't see how you can have such a high capacitance with such a setup. If that is only two plates that far apart, I don't see how you can get 27uF of capacitance.
 
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when placed in salt water capacitance will be high, Meanwhile 12 of these electrodes are parallel.
 
Skeptical, but I take your word for that. Anyhow, I'm sorry, but I don't think I can help you immediately. You're asking for a big ripple voltage across a large capacitance at a high frequency and only want a little current to flow through it. I was thinking this could be done by resonating it with a parallel coil, but the practical amount of Q turns out to be so low that the generator would be loaded too much, even at resonance, to provide the voltage you want. Capacitors do not use any real power, so the output power of your generator is not an issue, theoretically. I am sitting on this problem for now.
 
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That was why I asked you whether it is possible to control current and voltage simultaneously?
if not possible i Must consult with my teacher and choose one of them(current or voltage).
plz help....
 
I suggest you consult your teacher on that. I don't think it's possible to achieve what you are asking for.
 
i did a test with another signal generator (vo=20vpp, Ro=50 ohm) and result is as follow:
load voltage drop to 5vpp i am not sure about current, What is your opinion?
 
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That was why I asked you whether it is possible to control current and voltage simultaneously?

In the business of electronics, we often use so-called two terminal devices, such as resistors, capacitors and inductors. The very nature of two terminal devices is that they enforce a relationship between the voltage across the terminals (two of them) of the device, and the current through the device. The relationship between current and voltage is an intrinsic property of the device. You cannot independently control the voltage and current present in a two terminal device. Your load is such a device, hence current and voltage cannot be controlled independently.
 
hi again,
review:i have a load(two electrode inside the salt water) that want to drive with 20vpp .i did a test with a signal generator (vo=20vpp, Ro=50 ohm) and load voltage drop to 5vpp,
Consultation with my teacher: Since the load impedance can not be precisely measured we decided to apply the voltage 10 vpp, regardless of the current how can i do this without dropping voltage?
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Consultation with my teacher: Since the load impedance can not be precisely measured we decided to apply the voltage 10 vpp, regardless of the current how can i do this without dropping voltage?

You can buffer the output of your signal generator so that the output of the buffer is capable of supplying the required current while maintaining the required voltage across the load. Your going to need a pretty stiff buffer and operating at 300 KHz to boot.
 
hi,
can you introduce me an op amp with very low output impedance, each opamp that i know have output mpedance about 70 ohm, i want it be lower than 50ohm, as you know my signal genarator has 50 ohm output impedance thai voltage drop across load,
 
Hi. An op amp to deliver the power you need is going to be very expensive. The attached circuit should be useful. Use the transistor part numbers in blue font, or equivalent. Heat sink them if operating the circuit continuously for more than a few minutes, or they will overheat.
 

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hi,
i used your proposed circuit, can you change it for 100 ohm impedance of signal generator instead of 50 ohm.
 
I can only assume that you couldn't achieve the output voltage across your load that you wanted with the circuit. Would that be correct?
 
i used the circute with 100 ohm signal generator then voltage drop before 0.1uf capacitor. 50 ohm is not available today.
 
I have since simulated the circuit with good models I found for the BD transistors and found that those transistors are barely adequate for the job with a 50 ohm generator because of their cutoff frequency (my apologies). Can you use different transistors?
 
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