BJT amp

[jack23]

Hello all,

I have a simple Common-Emmitter BJT Amplifier circuit in a Voltage Divider Bias configuration with a Source and Load Resistor. The question is:

1) Show that the ICQ that produces the largerst AC output voltage swing is given by ICQ = VCC / Rac + Rdc, where Rac is the AC resistance and Rdc is the DC resistance, and -1/Rac = slope of ac load line
-1/Rdc = slope of dc load line

The circuit does not have a specified value for VCC.

The way I was thinking of going about this problem was to draw the AC and DC load lines on the characteristics graph and show the best ICQ that gives the largers signal swing. But, since there is no VCC given, I can't go about this method.

Does anyone know how I can go about solving this problem

 

[rupertherbert11]

hello jack23

If it is a multi stage amplifier it is very difficult to predict the Vcc. But if it is a single stage amplifier it is somewhat simple. I think you know about the gain of the transistor Hfe. assume that no input is given and eliminate all the capacitor with open circuit. find out the relation for the output voltage. and put output voltage = Vcc/2. then solve the equation then you can get the Vcc.

 

[ericgibbs]

hi Jack,
If its a college type question, you are not being asked to give a numerical value, but to 'show' ICQ = VCC / Rac + Rdc.

You can draw the load line graph without knowing the Vcc.