Q2GATE 2023MSQ

A semiconductor switch needs to block voltage $V$ of only one polarity $(V \gt 0)$ during OFF state as shown in figure (i) and carry current in both directions during ON state as shown in figure (ii). Which of the following switch combination(s) will realize the same?

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Q3GATE 2022MCQ

A charger supplies 100 W at 20 V for charging the battery of a laptop. The power devices, used in the converter inside the charger, operate at a switching frequency of 200 kHz. Which power device is best suited for this purpose?

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Q4GATE 2020NAT

A resistor and a capacitor are connected in series to a 10 V dc supply through a switch. The switch is closed at $t=0$ , and the capacitor voltage is found to cross 0 V at $t=0.4 \tau$ , where $\tau$ is the circuit time constant. The absolute value of percentage change required in the initial capacitor voltage if the zero crossing has to happen at $t=0.2 \tau$ is _______ (rounded off to 2 decimal places).

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📖 Explanation

If initial charge polarities on the capacitor is opposite to the supply voltage then only the capacitor voltage crosses the zero line.

\begin{aligned} V_{c}(t) \; \Rightarrow \;& \text{Final value} \\ &+ (\text{Initial value - Final value}) e^{-t/\tau }\\ 0&=10+(-V_{0}-10)e^{-0.4} \\ 10&=(V_{0}+10)e^{-0.4} \\ V_{0}&=4.918 V \\ \text{Now, } t&=0.2\tau \\ 0&=10+(-{V_{0}}'-10)e^{-0.2} \\ {V_{0}}'&=2.214 \\ \%\text{change \in voltage} &= \frac{4.918-2.214}{4.918}\times 100 \%\\ &=54.99\% \end{aligned}

Q5GATE 2020NAT

A single-phase inverter is fed from a 100 V dc source and is controlled using a quasisquare wave modulation scheme to produce an output waveform, $v(t)$ . as shown. The angle $\sigma$ is adjusted to entirely eliminate the $3^{rd}$ harmonic component from the output voltage. Under this condition, for $v(t)$ , the magnitude of the $5^{th}$ harmonic component as a percentage of the magnitude of the fundamental component is _______(rounded off to 2 decimal places).

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📖 Explanation

Using result,

\begin{aligned} V_{n}&=\frac{4V_{s}}{n\pi }\cos n\sigma\\ \text{For, } V_{3}=0\\ \cos 3\sigma &=0 \\ 3\sigma &=\frac{\pi }{2} \\ \sigma &=\frac{\pi }{6}\\ \text{Now, } \frac{V_{5}}{V_{1}}&=\frac{\cos 5\sigma }{5\cos\sigma }\\&=\frac{\cos 5\pi /6}{5\cos \pi /6}=-\frac{1}{5} \\ \% \left | \frac{V_{5}}{V_{1}} \right |&=\frac{1}{5}\times 100=20\% \end{aligned}

Q6GATE 2020MCQ

A non-ideal diode is biased with a voltage of -0.03 V, and a diode current of $I_1$ is measured. The thermal voltage is 26 mV and the ideality factor for the diode is 15/13. The voltage, in V, at which the measured current increases to 1.5 $I_1$ is closest to:

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📖 Explanation

\begin{aligned} I_{1}&=i_{0}\left[ e^{\frac{0.03}{15/13\times 26mV}}-1 \right]\$ \\ V_{D}&=\text{ -ve '1' can not be neglected}\\&\text{\in diode current equation} \\ I_{1}&=I_{0}\$[e^{-30mV/30mV}-1]\$ \\ &=I_{0}\$[e^{-1}-1]\$ \\ &=-0.64\: I_{0} \\ 1.5I_{1}&=I_{0}\$[e^{V_{D}/30mV}-1]\$ \\ -1.5\times 0.64 I_{0}&=I_{0}\$[e^{V_{D}/30mV}-1]\$\\-0.96&=e^{V_{D2}/30mV}-1\\1-0.96&=e^{V_{D2}/30mV}\\0.04&=e^{V_{D2}/30mV}\\ 30 mV \ln (0.04)&=V_{D}\\ V_{D}&=-0.09 V \end{aligned}

Q7GATE 2018MCQ

Four power semiconductor devices are shown in the figure along with their relevant terminals. The device(s) that can carry dc current continuously in the direction shown when gated appropriately is (are)

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Q8GATE 2017MCQ

For the power semiconductor devices IGBT, MOSFET, Diode and Thyristor, which one of the following statements is TRUE?

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Q9GATE 2016NAT

The voltage ( $v_{s}$ ) across and the current ( $i_{s}$ ) through a semiconductor switch during a turn-ON transition are shown in figure. The energy dissipated during the turn-ON transition, in mJ, is _______.

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📖 Explanation

\begin{aligned} \text{Energy}&=\int_{0}^{T_1}V\cdot i dt+\int_{0}^{T_2}V\cdot i dt\\ &=V\left[ \frac{1}{2}IT_1 \right]+I\left[ \frac{1}{2}VT_2 \right]\\ &=600\left[ \frac{150}{2}\times 1 \times 10^{-6} \right]\$\\ &+100\left[ \frac{1}{2} \times 600 \times 1 \times 10^{-6} \right]\$\\ \text{ Energy}&=75mJ \end{aligned}

Q10GATE 2016NAT

A steady dc current of 100 A is flowing through a power module (S,D) as shown in Figure (a). The V-I characteristics of the IGBT (S) and the diode (D) are shown in Figures (b) and (c), respectively. The conduction power loss in the power module (S,D), in watts, is ________.

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📖 Explanation

No current flows through IGBT. So current flows only in diode. Equivalent circuit of diode is as shown below,

\begin{aligned} V&=IR+0.7\\ &=(100 \times 0.01)+0.7\\ V&=1.7V \end{aligned}

Power loss during conduction,

\begin{aligned} P&=V \times I\\ &= 1.7 \times 100=170W \end{aligned}

Q11GATE 2015NAT

The circuit shown is meant to supply a resistive load $R_{L}$ from two separate DC voltage sources. The switches S1 and S2 are controlled so that only one of them is ON at any instant. S1 is turned on for 0.2 ms and S2 is turned on for 0.3 ms in a 0.5 ms switching cycle time period. Assuming continuous conduction of the inductor current and negligible ripple on the capacitor voltage, the output voltage $V_{0}$ (in Volt) across $R_{L}$ is ___________.

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📖 Explanation

$S_1$ is turn ON for 0.2 ms $S_2$ is turn ON for 0.3 ms. Switching cycle time period is 0.5 ms. the output voltage $V_0$ across $R_L$ is

\begin{aligned} V_0&= \frac{1}{0.5 \times 10^{-3}}\left[ \int_{0}^{0.2}10dt +\int_{0.2}^{0.5}5 dt \right]\$\\ &= \frac{1}{0.5 \times 10^{-3}} [10(0.2)+5(0.5-0.2)]\\ &=\frac{1}{0.5 \times 10^{-3}} \$[2 \times 10^{-3}+1.5 \times 10^{-3}]\$ \\ &= \frac{3.5 \times 10^{-3}}{0.5 \times 10^{-3}}=7V \end{aligned}

Q12GATE 2014MCQ

Figure shows four electronic switches (i), (ii), (iii) and (iv). Which of the switches can block voltages of either polarity (applied between terminals 'a' and 'b') when the active device is in the OFF state ?

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Q13GATE 2012MCQ

The typical ratio of latching current to holding current in a 20 A thyristor is

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Q14GATE 2011MCQ

A voltage commutated chopper circuit, operated at 500 Hz, is shown below. If the maximum value of load current is 10 A, then the maximum current through the main (M) and auxiliary (A) thyristors will be

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📖 Explanation

When main thyristor (M) is turned on, an oscillatory current in the circuit C, M, L and diode is set up and it is given by $i_c(t)=V_s\sqrt{\frac{C}{L}} \sin \omega _0 t$ Peak value of current through capacitor $I_P=V_s\sqrt{\frac{C}{L}} =200 \times \sqrt{\frac{0.1 \times 10^{-6}}{1 \times 10^{-3}}}=2A$ Current through main thyristor $i_m=I_0+I_c(t)=I_0+I_P \sin \omega _0 t$ So maximum value of $i_m=I_0+I_P =10+2=12A$ When auxiliary thyristor (A) is turned on, capacitor voltage applies a reverse voltage across main thyristor and main thyristor is turned off. The load current is now carried by C nad auxiliary thyristor . Current through auxiliary thyristor, $i_A=I_0$ maximum value of $i_A$ = maximum value of $I_0=10A$ .

Q15GATE 2011MCQ

Circuit turn-off time of an SCR is defined as the time

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Q16GATE 2010MCQ

The L-C circuit shown in the figure has an inductance L=1mH and a capacitance C= $\mu$ F. The L-C circuit shown above is used to commutate a thyristor, which is initially carrying a current of 5A as shown in the figure below. The switch is closed at t=0. If the forward drop is negligible, the time taken for the device to turn off is

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Q17GATE 2010MCQ

Figure shows a composite switch consisting of a power transistor (BJT) in series with a diode. Assuming that the transistor switch and the diode are ideal, the I-V characteristic of the composite switch is

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Q18GATE 2009MCQ

An SCR is considered to be a semi-controlled device because

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Q19GATE 2009MCQ

The circuit shows an ideal diode connected to a pure inductor and is connected to a purely sinusoidal 50 Hz voltage source. Under ideal conditions the current waveform through the inductor will look like.

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📖 Explanation

Frequency of the voltage source, f=50Hz Time period, $T=\frac{1}{f}=\frac{1}{50}=20ms$ During positive half cycle of the source voltage, $0 \lt t \lt \frac{T}{2}$ , energy is stored in the inductor and current increases. During negative half cycle of the source voltage, $\frac{T}{2} \leq t \leq T$ , current decreases and energy stored in the inductor is delivered to source.

Q20GATE 2009MCQ

Match the switch arrangements on the top row to the steady-state V-I characteristics on the lower row. The steady state operating points are shown by large black dots.

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📖 Explanation

Device-A: When diode is forward baised (ON state), $V_s=0, i_s \gt 0$ diode is reversed baised (OFF state) $V_s \lt 0, i_s = 0$ : when thyristor is in reverse blocking mode, $V_s \lt 0, i_s = 0$ thyristor is in forward blocking, $V_s \gt 0, i_s = 0$ thyristor is in forward conduction mode, $V_s=0, i_s \gt 0$ When device is ON, $V_s=0, i_s \gt 0$ The device is OFF, $V_s\gt 0, i_s = 0$ Reverse current can flow through the diode so $i_s \lt 0$ and $V_s=0$ During ON state of the device $V_s=0, i_s \gt 0$ During OFF state of the device, $V_s=0, i_s = 0$

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