WBCHSE HS Vocational Electronics flashcards

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

Ohm's law

The current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, expressed as V = IR.

Resistor colour code

Bands on a resistor encode digits and multiplier: first two bands are significant digits, third is the power-of-ten multiplier, fourth gives tolerance such as gold for plus or minus five percent.

Capacitive reactance

The opposition a capacitor offers to alternating current, given by X_C = 1/(2πfC). It falls as frequency or capacitance rises, so a capacitor blocks steady direct current.

Potential divider

Two resistors in series across a supply give an output voltage V_out = V_in times R2 divided by the sum of R1 and R2, valid when the tap draws negligible load current.

Depletion region

The zone near a p-n junction depleted of free carriers, leaving fixed ions. It widens under reverse bias and narrows under forward bias, setting the barrier potential.

Bridge rectifier

Four diodes arranged so both half-cycles of the input are rectified. It gives ripple frequency twice the supply, efficiency about 81 percent, and peak inverse voltage equal to peak input.

Ripple factor

The ratio of ripple rms voltage to direct output voltage. It is about 1.21 for half-wave and 0.48 for full-wave rectifiers; a smaller value means smoother output.

Zener diode

A heavily doped diode operated in reverse breakdown, where voltage stays nearly constant over a wide current range. A series resistor limits current in voltage-regulator circuits.

Transistor current gain beta

The ratio of collector current to base current in a bipolar transistor, written beta = I_C/I_B. It relates to alpha by beta equals alpha divided by one minus alpha.

Common emitter amplifier

A bipolar transistor stage with the emitter common to input and output. It gives high voltage gain, moderate input impedance and inverts the signal by 180 degrees.

Class B amplifier

Two transistors conducting on alternate half-cycles, giving efficiency near 78.5 percent. It suffers crossover distortion unless biased into Class AB operation.

Darlington pair

Two transistors cascaded so the emitter of the first drives the base of the second. Overall current gain is roughly the product of the two betas, giving very high input impedance.

Universal gates

NAND and NOR gates are called universal because either one alone can implement AND, OR and NOT, and therefore any combinational logic function.

Exclusive OR gate

A two-input gate whose output is one only when the inputs differ. Its Boolean expression is A'B plus AB', and it forms the sum output of a half adder.

Half adder

A combinational circuit adding two single bits. The sum is the XOR of the inputs and the carry is their AND product; it cannot accept an incoming carry.

Flip-flop

A bistable latch storing one bit. Types include SR for set and reset, JK which toggles when both inputs are high, D for data and T for toggle.

Voltmeter connection

A voltmeter measures potential difference and is connected in parallel with the component. It must have very high resistance so it draws negligible current from the circuit.

Cathode ray oscilloscope

An instrument displaying voltage against time. Vertical volts per division times height gives amplitude, and time per division times width gives period.

Lissajous figures

Patterns formed on an oscilloscope when sine waves drive both axes. The ratio of horizontal to vertical tangencies equals the ratio of the two frequencies.

Multimeter sensitivity

The ohms-per-volt rating of an analog meter, equal to full-scale resistance divided by full-scale current. A higher figure means the meter loads the circuit less.

Barkhausen criterion

The condition for sustained oscillation: the loop gain magnitude of amplifier times feedback must be at least one, with total loop phase shift of zero or 360 degrees.

Three-terminal regulator

An integrated series regulator such as the 7805 giving a fixed positive output. The input must exceed the output by roughly two to three volts for proper regulation.

Colpitts oscillator

An LC oscillator using a capacitive divider to feed back a fraction of the tank voltage. Its frequency is set mainly by the inductor and the series combination of the two capacitors.

Filter capacitor ripple

In a full-wave supply the ripple voltage is approximately load current divided by twice frequency times capacitance, so larger capacitance or lighter load reduces ripple.

Amplitude modulation

A process varying carrier amplitude in step with the message. Bandwidth equals twice the highest modulating frequency, and a modulation index above one causes overmodulation distortion.

Superheterodyne receiver

A receiver mixing the incoming signal with a local oscillator to a fixed intermediate frequency, typically 455 kHz for AM, before detection and audio amplification.

Nyquist sampling rate

To reconstruct a signal without aliasing, it must be sampled at least twice the highest frequency present in its spectrum.

Microcontroller

A single chip containing processor, memory, timers, input-output ports and serial interfaces, designed for dedicated embedded control rather than general-purpose computing.

ADC resolution

The smallest voltage change an analog-to-digital converter can distinguish, equal to reference voltage divided by two raised to the number of bits.

Pulse width modulation

Switching a supply on and off rapidly and varying the on-time fraction. Average output equals duty cycle times supply, used for motor speed and lamp dimming.

Good solder joint

A connection where the iron heats the joint until solder melts and flows, producing a shiny concave fillet. Dull lumpy joints indicate cold soldering and unreliable contact.

Project block diagram

A drawing showing each functional stage of a project as a labelled block with signal flow arrows, prepared before the detailed circuit diagram and layout.