QUESTION THREE

$(20$ Marks$)$

$($a$).$ What is safe operating area $($SOA$)$ of power semiconductor devices.

$($b$).$ Sketch the curve of safe operating area $($SOA$)$ of power semiconductor and explain the various limitations of the device.

$($c$).$ Sketch the switching characteristics curve of Insulated Gate Bipolar Transistor $($IGBT$)$ and indicate on the curve the switching ON and OFF.

$($d$).$ Consider the switching waveform for power semiconductor device if the load is resistive show that, the total switching dissipation is given by;

$W_{on}=\frac{V_{\text{b}\text{u}\text{s}}{I}_{\text{l}\text{o}\text{a}\text{d}}(t_{on}+t_{\text{o}\text{f}\text{f}})f}{6}$

Figure $1.$ Switching wave form for power semiconductor device.

QUESTION FOUR

$($a$)$ Sketch and explain the circuit and waveforms of a single $-$phase full bridge inverter

$($b$)$ Construct a table to indicate the following on it for both positive and negative cycle

$($i$)$ Load voltage, current and conducting devices

$($c$)$ A single$-$ phase half rectifier feeds a $15$ resistance. The supply voltage is $230$ V $($ rms $).$ The firing angle is $\frac{}{2},$ find $($i$)V_{dc},I_{dc},V_{rms}$ and $I_{rms}$