I have the following BJT inverter circuit and graphs of its electrical characteristics. I need to graphically find the DC response characteristics of this inverter but I don't know how to proceed.

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You have circuits equations: $$U_1 = R_1I_b+U_{be}\text{ (I)}$$ $$U_2 = U_{ce} = U_n - R_cI_c\text{ (II)}$$ and \$I_c = \beta I_b\$

Use the graph to determinate the value of \$\beta\$ and \$U_{be}\$. you have $$U_2 = U_n-R_c \beta I_b$$ so $$I_b = \frac{U_n-U_2}{\beta R_c}$$

Introduce \$I_b\$ in the equation (I) and you get: \$U_1=f(U_2)\$ with \$U_n\$, \$U_{be}\$ and \$\beta\$ constant.


Start with the bottom left graph - this tells you the relationship between applied volts across the BE junction and current into the base. You have to sort this out first so that you can then make a new graph of Ib against U1 (your real input). This is the hardest bit to sort out because things just aint linear. For instance, with U1 at 0.2 volts, current into the base will cause a volt drop across R1 leaving Ube across the base. Either derive a formula, use a spreadsheet or iterate to get this relationship correct. This is the difficult and tedious bit.

Once you have a relationship between U1 and Ib you can use the top right graph for predicting what Ic will be. Now you have a relationship between U1 and Ic. This relationship is altered by Vn (the power supply voltage) so a series of graphs at different voltage for Vn are required I reckon.

Good luck.


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