In figure , the \(V_{\mathit{BB}}\) supply can be varied from \(0 \;V\) to \(5.0\;V\) . The Si transistor has \(\beta _{\mathit{dc}}=250\) and \(R_B=100\;k\Omega ,R_C=1\;KV_{\mathit{CC}}=5.0\;V\) Assume that when the transistor is saturated, \(V_{\mathit{CE}}=0\;V\) and \(V_{\mathit{BE}}=0.8\;\mathit{V.}\) Calculate the minimum base current, for which the transistor will reach saturation. Hence, determine \(V{_1}\) , when the transistor is switched on.
Answer
Given at saturation \(V_{\mathit{CE}}=0\;V,V_{\mathit{BE}}=0.8\;V\) \(V_{\mathit{CE}}=V_{\mathit{CC}}-I_CR_C\) \(I_C=\frac{V_{\mathit{CC}}}{R_C}=\frac{5.0\;V}{1.0\;k\Omega} =5.0\;\mathit{mA}\) Therefore \(I_B=\frac{I_C}{\beta }=\frac{5.0\;\mathit{mA}}{250}=20\mu A\) The input voltage at which the transistor will go into saturation is given by \(V_{\mathit{IH}}=V_{\mathit{BB}}=I_BR_B+V_{\mathit{BE}}\) \(=20\mu A\times 100k\Omega +0.8V=2.8V\)
In figure , the \(V_{\mathit{BB}}\text{ supply can be varied from }0\) V to \(5.0V\) . The Si transistor has \(\beta _{\mathit{dc}}=250\) and \(R_B=100k\Omega ,R_C=1KV_{\mathit{CC}}=5.0V\) Assume that when the transistor is saturated, \(V_{\mathit{CE}}=0V\) and \(V_{\mathit{BE}}=0.8\mathit{V.}\) Find the ranges of \(V{_1}\) for which the transistor is 'switched off and 'switched on'.
For a CE transistor amplifier, the audio signal voltage across the collector resistance of \(2.0\;k\Omega \) is \(2.0\;V\). Suppose the current amplification factor of the transistor is \(100,\) What should be the value of \(R_B\) in series with \(V_{\mathit{BB}}\) supply of \(2.0\;V\) if the de base current has to be \(10\) times the signal current. Also calculate the do drop across the collector resistance.
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