Chapter 2: Q2.5-27Q (page 93)
27. Design two different ladder networks that each output 9 volts and 4 amps when the input is 12 volts and 6 amps.
Short Answer
The first ladder network is
Here, \[{v_1} = 12,{i_1} = 6,\] and \[{v_3} = 9,{i_3} = 4\].
The second ladder network is
Here, \[{v_1} = 12,{i_1} = 6,\] and \[{v_3} = 9,{i_3} = 4\].
Step by step solution
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Write the transfer matrices
The transfer matrices of the series circuit with resistance \[{R_1}\] and shunt circuit with resistance \[{R_2}\] are \[\left[ {\begin{array}{*{20}{c}}1&{ - {R_1}}\\0&1\end{array}} \right]\], and \[\left[ {\begin{array}{*{20}{c}}1&0\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&1\end{array}} \right]\], respectively.
Design the first ladder network
Consider the first ladder network as aseries circuitwith resistance \[{R_1}\], followed by a shunt circuitwith resistance \[{R_2}\]. Therefore, the transfer matrix for this network is
\[\left[ {\begin{array}{*{20}{c}}1&0\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&1\end{array}} \right]\left[ {\begin{array}{*{20}{c}}1&{ - {R_1}}\\0&1\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}1&{ - {R_1}}\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&{1 + {{{R_1}} \mathord{\left/
{\vphantom {{{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}\end{array}} \right]\].
To produce an output of 9 volts and 4 amps for an input of 12 volts and 6 amps, the transfer matrix must satisfy the equation:
\[\begin{array}{c}\left[ {\begin{array}{*{20}{c}}1&{ - {R_1}}\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&{1 + {{{R_1}} \mathord{\left/
{\vphantom {{{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}\end{array}} \right]\left[ {\begin{array}{*{20}{c}}{12}\\6\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}9\\4\end{array}} \right]\\\left[ {\begin{array}{*{20}{c}}{12 - 6{R_1}}\\{ - {{12} \mathord{\left/
{\vphantom {{12} {{R_2} + 6 + {{6{R_1}} \mathord{\left/
{\vphantom {{6{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}}} \right.
\kern-\nulldelimiterspace} {{R_2} + 6 + {{6{R_1}} \mathord{\left/
{\vphantom {{6{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}}}\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}9\\4\end{array}} \right]\end{array}\]
This implies that
\[\begin{array}{c}12 - 6{R_1} = 9\\6{R_1} = 3\\{R_1} = {1 \mathord{\left/
{\vphantom {1 2}} \right.
\kern-\nulldelimiterspace} 2}\end{array}\]
And
\[\begin{array}{c} - {{12} \mathord{\left/
{\vphantom {{12} {{R_2} + 6 + {{6{R_1}} \mathord{\left/
{\vphantom {{6{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}}} \right.
\kern-\nulldelimiterspace} {{R_2} + 6 + {{6{R_1}} \mathord{\left/
{\vphantom {{6{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}} = 4\\ - 12 + 6{R_2} + 6\left( {{1 \mathord{\left/
{\vphantom {1 2}} \right.
\kern-\nulldelimiterspace} 2}} \right) = 4{R_2}\\2{R_2} = 12 - 3\\{R_2} = {9 \mathord{\left/
{\vphantom {9 2}} \right.
\kern-\nulldelimiterspace} 2}\end{array}\]
Thus, the firstladder network is
Here, \[{v_1} = 12,{i_1} = 6,\] and \[{v_3} = 9,{i_3} = 4\].
Design the second ladder network
Consider the second ladder network as a shunt circuit with resistance \[{R_2}\], followed by a series circuit with resistance \[{R_1}\]. Therefore, the transfer matrix for this network is
\[\left[ {\begin{array}{*{20}{c}}1&{ - {R_1}}\\0&1\end{array}} \right]\left[ {\begin{array}{*{20}{c}}1&0\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&1\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}{1 + {{{R_1}} \mathord{\left/
{\vphantom {{{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&{ - {R_1}}\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&1\end{array}} \right]\].
To produce an output of 9 volts and 4 amps for an input of 12 volts and 6 amps, the transfer matrix must satisfy the equation:
\[\begin{array}{c}\left[ {\begin{array}{*{20}{c}}{1 + {{{R_1}} \mathord{\left/
{\vphantom {{{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&{ - {R_1}}\\{ - {1 \mathord{\left/
{\vphantom {1 {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}}}&1\end{array}} \right]\left[ {\begin{array}{*{20}{c}}{12}\\6\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}9\\4\end{array}} \right]\\\left[ {\begin{array}{*{20}{c}}{12 + {{12{R_1}} \mathord{\left/
{\vphantom {{12{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}} - 6{R_1}}\\{ - {{12} \mathord{\left/
{\vphantom {{12} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}} + 6}\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}9\\4\end{array}} \right]\end{array}\]
This implies that
\[\begin{array}{c} - {{12} \mathord{\left/
{\vphantom {{12} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}} + 6 = 4\\{{12} \mathord{\left/
{\vphantom {{12} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}} = 2\\{R_2} = 6\end{array}\]
And
\[\begin{array}{c}12 + {{12{R_1}} \mathord{\left/
{\vphantom {{12{R_1}} {{R_2}}}} \right.
\kern-\nulldelimiterspace} {{R_2}}} - 6{R_1} = 9\\3 + {{12{R_1}} \mathord{\left/
{\vphantom {{12{R_1}} 6}} \right.
\kern-\nulldelimiterspace} 6} - 6{R_1} = 0\\3 + 2{R_1} - 6{R_1} = 0\\{R_1} = {3 \mathord{\left/
{\vphantom {3 4}} \right.
\kern-\nulldelimiterspace} 4}\end{array}\]
Thus, the second ladder network is
Here, \[{v_1} = 12,{i_1} = 6,\] and \[{v_3} = 9,{i_3} = 4\].