Bjt Analysis And Biasing Practice Questions

In the circuit shown, the identical transistors Q1 and Q2 are biased in the active region with $\beta=120$ . The Zener diode is in the breakdown region with $\mathrm{V}_{\mathrm{Z}}=5 \mathrm{~V}$ and $\mathrm{I}_{\mathrm{Z}}=25 \mathrm{~mA}$ . If $\mathrm{I}_{\mathrm{L}}=12 \mathrm{~mA}$ and $\mathrm{V}_{\mathrm{EB} 1}=\mathrm{V}_{\mathrm{EB} 2}=0.7 \mathrm{~V}$ , then the values of $R_{1}$ and $R_{2}$ (in $k \Omega$ , rounded off to one decimal place) are __________ , respectively.

In the voltage regulator shown below, $V_l$ is the unregulated at 15 V. Assume $V_{BE}$ = 0.7 V and the base current is negligible for both the BJTs. If the regulated output $V_O$ is 9 V, the value of $R_2$ is ________ $\Omega$ .

For the BJT in the amplifier shown below, $V_{BE} = 0.7 V, kT/q = 26 mV$ . Assume the BJT output resistance ( $r_o$ ) is very high and the base current is negligible. The capacitors are also assumed to be short circuited at signal frequencies. The input $v_i$ is direct coupled. The low frequency gain $v_o/v_i$ of the amplifier is

In the figure shown, the npn transistor acts as a switch For the input $V_{\in}(t)$ as shown in the figure, the transistor switches between the cut-off and saturation regions of operation, when T is large. Assume collector-to-emitter voltage saturation $V_{CE(sat)}=0.2V$ and base-to-emitter voltage $V_{BE}=0.7V$ . The minimum value of the common-base current gain ( $\alpha$ ) of the transistor for the switching should be _________.

In the circuit shown, transistors $Q_{1}$ and $Q_{2}$ are biased at a collector current of 2.6mA.Assuming that transistor current gains are sufficiently large to assume collector current equal to emitter current and thermal voltage of 26 mV, the magnitude of voltage gain $V_{0}/V_{s}$ in the mid-band frequency range is _____________ (up to second decimal place).

Consider the circuit shown in the figure. Assume base-to- emitter voltage $V_{BE}$ =0.8 V and common base current gain $(\alpha)$ of the transistor is unity. The value of the collector- to - emitter voltage $V_{CE}$ (in volt) is _______.

For the DC analysis of the Common-Emitter amplifier shown, neglect the base current and assume that the emitter and collector current are equal. Given that $V_{T}=25mV,V_{BE}=0.7V$ , and the BJT output resistance $r_{0}$ is practically infinite. Under these conditions, the midband voltage gain magnitude. $A_{c}=|V_{0}/V_{i}|V/V$ , is _________.

The Ebers-Moll model of a BJT is valid

Resistor $R_1$ in the circuit below has been adjusted so that $I_{1}$ = 1 mA. The bipolar transistors Q1 and Q2 are perfectly matched and have very high current gain, so their base currents are negligible. The supply voltage $V_{CC}$ is 6 V. The thermal voltage kT/q is 26 mV. The value of $R_{2}$ (in $\Omega$ ) for which $I_{2}$ =100 $\mu$ A is ________

Consider the circuit shown in the figure. Assuming $V_{BE1}=V_{EB2}$ = 0.7 volt, the value of the dc voltage $V_{C2}=$ (in volt) is __________

In the circuit shown in the figure, the BJT has a current gain ( $\beta$ ) of 50. For an emitter-base voltage $V_{EB}$ = 600 mV, the emitter-collector voltage $V_{EC}$ (in Volts) is _______.

In the circuit shown, $I_{1}$ = 80 mA and $I_{2}$ = 4 mA. Transistors $T_{1} \; and \; T_{2}$ are identical. Assume that the thermal voltage $V_{T}$ is 26 mV at $27^{\circ}C$ . At $50^{\circ}C$ , the value of the voltage $V_{12} = V_{1} -V_{2}$ (in mV) is_______.

In the ac equivalent circuit shown, the two BJTs are biased in active region and have identical parameters with $\beta \gt \gt 1$ . The open circuit small signal voltage gain is approximately _______.

A good current buffer has

A cascade connection of two voltage amplifiers A1 and A2 is shown in the figure. The open-loop gain $A_{v0}$ , input resistance $R_{\in},$ and output resistance $R_{o}$ for A1 and A2 are as follows : $A1=A_{v0}=10 \; R_{\in}=10k \Omega \; R_{0}=1k \Omega$ $A1=A_{v0}=5 \; R_{\in}=5k \Omega \; R_{0}=200 \Omega$ The approximate overall voltage gain $v_{out} / v_{\in}$ is______.

In the circuit shown, the silicon BJT has $\beta =50$ . $V_{BE}=0.7 V \; and \; V_{CE(sat)}=0.2V$ . Which one of the following statements is correct ?

An increase in the base recombination of a BJT will increase

If the emitter resistance in a common-emitter voltage amplifier is not bypassed, it will

A BJT in a common-base configuration is used to amplify a signal received by a 50 $\Omega$ antenna. Assume kT/q = 25mV. The value of the collector bias current (in mA) required to match the input impedance of the amplifier to the impedance of the antenna is_____.