DES PRELAB

III Semester 2013-2014

RESISTORS

• The first band gives the first digit. • The second band gives the second digit. • The third band indicates the number of zeros. • The fourth band is used to shows the tolerance (precision)

of the resistor, this may be ignored for almost all circuits but further details are given below.

• Tolerance of resistors (fourth band of color code):• A special color code is used for the fourth band tolerance:

silver ±10%, gold ±5%, red ±2%, and brown ±1%. If no fourth band is shown the tolerance is ±20%.

RESISTORS

RESISTORS• Power Ratings of Resistors:• The power, P, developed in a resistor is given by: • P = I² × R

or

P = V² / R• Where:• P = power developed in the resistor in watts (W)

I = current through the resistor in amps (A) R = resistance of the resistor in ohms ( ) V = voltage across the resistor in volts (V)

Voltage Source & Current Source

AC from a power supply

Steady DC

Smooth DC

Varying DC

• Amplitude is the maximum voltage reached by the signal. It is measured in volts, V.

• Peak voltage is another name for amplitude. • Peak-peak voltage is twice the peak voltage

(amplitude). When reading an oscilloscope trace it is usual to measure peak-peak voltage.

• Time period is the time taken for the signal to complete one cycle. It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (µs) are often used. 1ms = 0.001s and 1µs = 0.000001s.

• Frequency is the number of cycles per second. It is measured in hertz (Hz), but frequencies tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. 1kHz = 1000Hz and 1MHz = 1000000Hz. frequency = 1 time period

• Timeperiod = 1 frequency

• Mains electricity in the UK has a frequency of 50Hz,

so it has a time period of 1/50 = 0.02s = 20ms.

Root Mean Square (RMS) Values

• VRMS = 0.7 × Vpeak and Vpeak = 1.4 × VRMS

• The RMS value is the effective value of a varying voltage or current. It is the equivalent steady DC (constant) value which gives the same effect.

• What do AC meters show, is it the RMS or peak voltage?

• What does ‘230V AC' really mean, is it the RMS or peak voltage?

COILS & INDUCTORS

Symbol used to denote an inductor

CAPACITORS

Polarized capacitors (large values, 1µF +):

Circuit symbol:

Electrolytic Capacitors:

Unpolarised capacitors (small values, up to 1µF):

Circuit symbol:

CAPACITORS

Color CodeColor NumberBlack 0Brown 1Red 2

3Yellow 4Green 5Blue 6Violet 7Grey 8White 9

Capacitor Number Code:

A number code is often used on small capacitors where printing is difficult: The 1st number is the 1st digit, The 2nd number is the 2nd digit, The 3rd number is the number of zeros to give the capacitance in pF. Ignore any letters - they just indicate tolerance and voltage rating.

Capacitor Color Code:

CAPACITORSVariable capacitors:

Variable Capacitor Symbol

Trimmer capacitors:

POTENTIOMETERS (VARIABLE RESISTORS)

Rheostat:

Potentiometer:

Presets:

Multiturn presets:

Preset(open style)

Presets(closed style) Multiturn preset

PN JUNCTION DIODE

TRANSISTORS

JUNCTION FIELD-EFFECT TRANSISTOR

MOSFET

P-channel

N-channel

JFET MOSFET enhMOSFET

dep

LIGHT-EMITTING DIODES