CHSE Odisha Elective Electronics flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

For a resistor at constant temperature, voltage equals current times resistance, V = IR; power dissipation is P = VI = I^2R = V^2/R.

Series resistor equivalent

Resistors in series carry the same current and add directly: R_eq = R1 + R2 + ...; the total voltage divides in proportion to each resistance.

Capacitor current relation

The current through a capacitor equals capacitance times the rate of change of voltage, i = C dv/dt; in steady DC a capacitor behaves as an open circuit.

RC time constant

For a series RC circuit the time constant is τ = RC. After one τ, capacitor voltage reaches about 63.2 percent of its final step value.

Depletion region

A PN junction forms a region depleted of mobile carriers near the boundary. Its built-in potential is about 0.7 V for silicon and 0.3 V for germanium.

Zener diode regulation

A reverse-biased Zener diode maintains an almost constant breakdown voltage. A series resistor drops the difference between input and Zener voltage while limiting current.

Half-wave rectifier output

A half-wave rectifier conducts for one half-cycle. With a sinusoidal peak Vm, ideal average DC output is Vm/π and ripple frequency equals supply frequency.

Bridge rectifier

A bridge rectifier uses four diodes and conducts on both half-cycles. It gives full-wave output, ripple at twice supply frequency, and needs no center-tapped transformer.

BJT current relation

In a bipolar junction transistor, emitter current equals base current plus collector current: IE = IB + IC. Current gain beta equals IC/IB and alpha equals IC/IE.

BJT active region

In active mode the base-emitter junction is forward biased and the base-collector junction reverse biased. The transistor then acts as a current-controlled current source.

JFET square law

For an n-channel JFET in saturation, drain current is ID = IDSS(1 - VGS/VP)^2, where VP is pinch-off voltage and IDSS is maximum drain current.

MOSFET threshold

An enhancement MOSFET conducts strongly only when gate-source voltage exceeds its threshold voltage. Below threshold it is essentially off, giving voltage-controlled switching.

Negative feedback effect

Negative feedback reduces overall voltage gain by the factor 1 + Aβ. It also widens bandwidth, reduces distortion and noise, and changes input and output impedance.

Inverting op-amp gain

For an ideal op-amp inverting amplifier, voltage gain equals negative feedback resistance divided by input resistance: Av = -Rf/Rin. The input node is a virtual ground.

Class B efficiency

A Class B push-pull stage conducts for 180 degrees per device. Its maximum theoretical efficiency is about 78.5 percent, but crossover distortion occurs unless biased into Class AB.

Barkhausen criterion

An oscillator sustains oscillation when loop gain magnitude equals one and total loop phase shift is 360 degrees, equivalent to zero degrees, at the oscillation frequency.

Wien bridge frequency

A Wien bridge oscillator with equal resistances R and capacitances C in its frequency-selective network oscillates at f = 1/(2πRC) and needs amplifier gain of at least three.

Monostable multivibrator

A monostable multivibrator has one stable state. An external trigger produces one output pulse whose width is set by an external RC time constant, then it returns stable.

Zener series resistor

For a shunt Zener regulator, Rs = (Vin - Vz)/(Iz + IL). The resistor drops excess input voltage while supplying both Zener current and load current.

Voltage regulation percent

Percent voltage regulation equals no-load voltage minus full-load voltage, divided by full-load voltage, multiplied by 100. Smaller values mean better regulation.

78xx regulator

A 78xx series integrated regulator provides a fixed positive output voltage; for example 7805 gives 5 V. It needs adequate input voltage and usually decoupling capacitors.

Ripple factor

Ripple factor is the RMS ripple voltage divided by average DC output. Ideal half-wave rectifier ripple factor is about 1.21 and full-wave about 0.48.

De Morgan's laws

De Morgan's laws state that the complement of A AND B equals A' OR B', and the complement of A OR B equals A' AND B'.

Half adder outputs

A half adder adds two bits. Its sum output is A XOR B and its carry output is A AND B; it cannot accept an incoming carry.

JK flip-flop

A JK flip-flop toggles when J and K are both high, sets when J is high and K low, resets when K high and J low, and holds otherwise.

Multiplexer

A multiplexer selects one of 2^n data inputs using n select lines and routes it to a single output. A demultiplexer performs the reverse operation.

AM modulation index

Amplitude modulation index m equals peak modulating voltage divided by carrier voltage. For undistorted AM, m must be between zero and one.

AM bandwidth

An amplitude-modulated wave with highest modulating frequency fm has upper and lower sidebands. Its total bandwidth is twice fm, or 2fm.

Carson's rule

Carson's rule estimates FM bandwidth as twice the sum of peak frequency deviation and highest modulating frequency: BW ≈ 2(Δf + fm).

PMMC instrument

A permanent-magnet moving-coil meter deflects in proportion to average coil current. It measures DC directly and needs a rectifier for AC measurement.

Thermistor behavior

A negative-temperature-coefficient thermistor decreases resistance as temperature rises. It is a passive resistive transducer used for temperature sensing and compensation.

LVDT

A linear variable differential transformer converts small linear displacement into an AC voltage proportional to core position. It is a passive inductive transducer with good linearity.