Parallel BJT with constant DC supply

[AshwinNambiar]

I'm trying to simulate a BJT circuit on MULTISIM(BC635) .What i require is to provide an input DC voltage of 50V ,create a BJT circuit such that my voltage at the output is stepped down or rather the current at output > current at input.SO essentially if i want to build a circuit where i want my current to increase it will be in parallel .
My questions are :
1.How do i connect two BJT s in parallel i.e calculating the impedance values and providing bias?
2.Is it possible to develop a design using BJT s where i get an exponentially decaying curve of an increasing current to a decreasing voltage.
Also point out if i'm going wrong in my approach
Thanks

 

[chuckey]

" the current at output > current at input ". To get this you need some form of convertor which in essence is a DC transformer. The conservation of power must hold, so if the input is 50 V at 1A (50 W), you can only get 50W out, i.e. 5 V at 10 A. These circuits convert the input DC into an AC, then transform it to another AC voltage then convert it back to DC.
To feed two transistors in parallel, feed each base via a resistor to the input voltage and include a low value resistor in series with each emitter before they are connected together. This resistor should drop .2 -> .5V at the working current. This will help to ensure that the current is shared equally between the transistors. The collectors can be connected together.
Frank

 

[crutschow]

If you describe what you will be using this for, it would help in discussing the design.

To have the output current greater than the input current will require some sort of switching regulator or conversion circuit as chuckey described.

 

[AshwinNambiar]

I'm trying to create an electronic circuit based on the property of
ELECTRIC ARC (DC)which exhibits a decrease in voltage with an increasing current.The power is to be conserved,
SO trying to design a circuit where i give a constant DC supply and enable the circuit design such that my output current is greater than the input ,thus lowering my voltage at output which can hence give me a characteristic as desired.

 

[crutschow]

So you need a DC-DC converter.
What maximum output current and voltage do you require?

 

[asdf44]

I'm trying to create an electronic circuit based on the property of
ELECTRIC ARC (DC)which exhibits a decrease in voltage with an increasing current.The power is to be conserved,
SO trying to design a circuit where i give a constant DC supply and enable the circuit design such that my output current is greater than the input ,thus lowering my voltage at output which can hence give me a characteristic as desired.

Yeah that's a DC-DC converter and it's going to require switching and magnetics.

Look up "buck converter".

There is literally no way to do this without a switching supply. It sounds like you were looking at BJT current curves trying to make it add up - that's a dead end path. Linear components can't create more current or voltage than they're supplied. Only reactive components that can cyclically (with switching) store energy and then release it can achieve this.

 

[AshwinNambiar]

Well for a 1kw design ,100V and 10A at the input,so at the output say around 20 A and 40V ;the power is to be conserved.Is the power conserved in a DC-DC converter???