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adjustable amplified BJT circuit..help

ahndy05

Sep 30, 2011
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pls help me to my circuit project.. I need to know the computation of the value of those unknown resistor.. The output voltage are 2.5V minimum at 4.5V maximum... TNX.:D
 

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ahndy05

Sep 30, 2011
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adjustable amplied BJT circuit

somebody help me to my circuit project.. I need to know the computation of the value of those unknown resitors..with the output voltage of minimum of 2.5v and maximum of 4.5v..tnx:)
 

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TedA

Sep 26, 2011
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ahndy05,

Can you provide some more information? What sort of transistor? What's the temperature? Where is the output voltage found? Are the 2.5V and 4.5V values not-to-exceed values, or are they values that must be reached within the adjustment range?

Are you looking for some values to actually use in a circuit you are building, or for help in showing how one might choose the values?

Note that choosing values does involve calculation, but also requires "engineering judgement". There is not one single set of values that is correct.

Ted
 

ahndy05

Sep 30, 2011
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Sep 30, 2011
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TED,

the transistor I need to use is H1061C with Hfe min 100 and Hfe max 300,, temperature = -55 to 150 degree celsius.. The value 2.5 and 4.5v are the values that I need to reached from Vab.. pls.. I really need the calculation of those unknown resistors.. Tnx..

ahndy05
 

duke37

Jan 9, 2011
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You have not specfied where the output is. I assume that it is across the 10k load resistor.
I do not see how to calculate the resistors, it could be done if you have a resistor in the emitter connection of the transistor. Have you got the circuit right?
 

TedA

Sep 26, 2011
156
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Sep 26, 2011
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ahndy05,

Thanks for your reply. We still need some clairification.

I will try to find your transistor later, but the "H1061C" P/N is not immediately familiar. Do you have a manufacturer for it, so I'll know where to look? A link to the transistor's data sheet is always a useful thing to include in your post, so we can all be looking at the same information.

What is Vab? I don't see any such label on the schematic.

Pending confirmation, I'm assuming that the "output" is across RL in the schematic.

The temperature is important, because the output will vary with the temperature. The temperature dependance is a vital characteristic of this circuit in its usual application. Over the -55C to +150C range, the output may vary over a range of around 2V. Do we really need to consider this entire temperature range?

I was not sufficiently clear about what I meant about the adjustment range. I'll try to do better:

The range adjustment you will actually get, with a circuit made from real parts, will depend on those particular parts, and as I said, the temperature. So I was trying to find out if the endpoint values you gave for the adjustment, 2.5V and 4.5V, are values that should be inside the adjustment range in every case and over the temperature range. Such a design will result in the endpoints of the adjustment range usually being well outside the specified 2.5V and 4.5V levels.

Have you figured-out how the circuit works? Can you tell us the practical application for this circuit?

Again, can you give us some idea why you are asking this particular question?

I hope this is of some help to you.

Ted
 

ahndy05

Sep 30, 2011
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oh I'm sorry I forgot to put the label of voltage out :D.., node A is above the collector and B was located under the emitter.. My prof. said that "He will test it inside the aircon room with temperature of 18degree celsius... And also said that when he rotate the potentiometer ( R2 ) to the min. the voltage output will be 2.5v and in max. the voltage output is 4.5v...

My prof. also said that the transistor we need to use have a value of 100 beta...but H1061C was only available transistor that I bought...:(
 
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