Posted: 02 Sep 2010 08:29 PM PDT

Hello, this is my first post here.

I am currently working with a Wheatstone bridge containing 1 JFET to sense atmospheric static fields, and the circuit is working. However, having 4 sensors in a bridge gives a signal 4 times as big. I think I have found a way to connect 4 JFETs so they are all operated by a single antenna wire and their resistances will (hopefully) rise and fall appropriately to give me a larger voltage drop across the bridge.

I don't expect all the FETs to react to the same extent, but I thought there would be some changes in the right directions. I know the circuit is not perfect, but I don't care. Just looking for a varying DC voltage across the bridge proportionate to the voltage sensed by the antenna.

You'll notice that there are no bias resistors in the circuit. This is common in many static sensing circuits so I kept up the tradition. The FETs are simply acting as voltage controlled resistors anyway, passing DC only. There is no AC signals involved.

Brief explanation of operation:
The gate of T1 senses a positive voltage, for example, so it becomes more conductive. The drain side of T1 becomes more negative so the gates of T3 and T4 become negative and they conduct less. Meanwhile, T2 gate is more positive than T3 and T4 so it conducts more, just like T1. And vice-versa.
The result is 4 changing resistances instead of one so more signal output.
T1 and T2 work together and T3 and T4 must work together but opposite to T1 and T2.

The purpose of this circuit is to get away from using resistors. I have a working circuit now with just T1 as the only FET and 3 resistors. But if the resistors can vary, like T1, the bridge output will be greater.
One reason I don't have bias resistors is that the extra resistance will increase the total resistance of the bridge, and it is most sensitive to small signals picked up by the antenna when the bridge has a small resistance.

I've checked this using the Wheatstone Bridge calculator I found online at:
Wheatstone Bridge Calculator

The FET connected to the antenna is outdoors with only the source and drain wires coming indoors. The rest of the circuit can be built indoors and connected to my current circuit.

I would like some opinions about whether or not you think this circuit would work. If not, where did I go wrong?
Please keep the explanations simple, this is just a hobby and I'm not familiar with using transistors.

Thanks

Syncro geared ac motor

Posted: 02 Sep 2010 11:44 AM PDT

ٌWhat is it?
and where we can use it ?

Why Frequency In some Countries is 60 Hz??

Posted: 02 Sep 2010 08:21 AM PDT

As per my record their are some countries in which power is transmitted @ 60Hz but with a voltage of 110V...

Please tell me why is it so????

Will it result in increase in increase Efficiency???
Or
Will it reduce the conductor requirement???
Or
Something else???

If somebody know this Please provide me the full information......
If you have any *.pdf Copy please provide it to me.........

Note: How to Upload A PDF copy here???
Answer: 1. Register Here
2. Upload your attachment their by Logging In....
3. Copy the Provided link and paste that link here......

I know, me giving you more trouble bye telling you to do this.......
But please do this, cause this question is giving much more Headache to me.....
Please help me.....
I will be very thankful to you.....

Regards,
VIPUL

Thevenin maximum power transfer theorem

Posted: 02 Sep 2010 03:52 AM PDT

In Thevenin maximum power transfer theorem it state that the load resistance,RL must be equal to internal resistance of the source,Rin. However, the efficiency of the circuit is just 50%. At here, can i say i use power source in a more effective way if be able to have an output of higher efficiency and at the same time considerable high output voltage but this output voltage will be slightly lower abit than when RL=Rin. The efficinecy will be higher alot if using RL>>Rin but the amount of output voltage will be extremely low. So in order to choose a load resistor give optimization to power saving and total output power, can consider it as a product of efficiency and total oputput power?

here i let X=efficiency*output power and consider a voltage source connected in series with an internal resistance and a load resistance,nRin where n is the value to be find.

efficiency=Pout/Pin=V^2[(nRin)/(Rin+nRin)^2]/V^2(nRin+Rin)=n/(1+n)
output power=v^2(nRin)/(n+1)^2Rin^2)=(V^2/Rin)(n/(n+1)^2)

hence X=n^2/(n+1)^3[V^2/Rin]
differentiate it with respect to n using UV method will finally get
dx/dn=[n/(n+1)^3][2-[3n/(n+1)]]
when dx/dn=0 n=0(rejected) and n=2
so at here, can i say if i take into consideration of power saving and the amount of output power dissipated, taking n=2 will give me what i want? a desirable high efficinecy and high output power.

Crazy Engineers .CoM

Friday, September 3, 2010

CrazyEngineers Forum - Electrical & Electronics Engineering

CrazyEngineers Forum - Electrical & Electronics Engineering

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