18-06-2012, 05:52 PM
PRACTICAL ELECTRONICS HANDBOOK
[attachment=24758]
INTRODUCTION:
MATHEMATICS CONVENTIONS
Quantities greater than 100 or less than 0.01 are usually expressed in the
standard form of A × 10n, where A is a number, called the mantissa,
less than 10, and n is a whole number called the exponent. A positive
value of n means that the number is greater than unity, a negative value
of n means that the number is less than unity. To convert a number into
standard form, shift the decimal place until the portion on the left-hand
side of the decimal point is between 1 and 10, and count the number of
places that the point has been moved. This is the value of n. If the decimal
point has had to be shifted to the left the sign of n is positive; if the decimal
point had to be shifted to the right the sign of n is negative.
RESISTORS
Passive components
Passive components are those that need no power supply for their operation
and whose action will dissipate power, though in some cases the amount of
dissipation is negligible. No purely passive component can have an output
that supplies more power than is available at the input. Active components,
by contrast, make use of a power supply, usually DC, so that the
signal power output of an active component can be higher than the signal
power at the input. Typical passive components are resistors, capacitors and
inductors. Familiar active components are transistors and ICs.
All components, active or passive, require to be connected to a circuit,
and the two main forms of connection, mechanical and electrical, used in
modern electronic circuits are the traditional wire leads, threaded through
holes in a printed circuit board (see Chapter 18) and the more modern
surface mounting devices (SMDs) that are soldered directly on to the tracks
of a board. Both passive and active components can use either type of
connection and mounting.
Thermistors
Thermistors are resistors made from materials that have large values of
temperature coefficient. Both PTC and NTC types are produced for applications
that range from temperature measurement to transient current
suppression. Figure 1.14 shows some representative types. Miniature thermistors
either in bead form or in glass tubes are used for temperature
measurement, using a bridge circuit (Figure 1.15), and are also used for
timing circuits and in stabilizing the amplitude of sine wave oscillators (see
Chapter 7).
[attachment=24758]
INTRODUCTION:
MATHEMATICS CONVENTIONS
Quantities greater than 100 or less than 0.01 are usually expressed in the
standard form of A × 10n, where A is a number, called the mantissa,
less than 10, and n is a whole number called the exponent. A positive
value of n means that the number is greater than unity, a negative value
of n means that the number is less than unity. To convert a number into
standard form, shift the decimal place until the portion on the left-hand
side of the decimal point is between 1 and 10, and count the number of
places that the point has been moved. This is the value of n. If the decimal
point has had to be shifted to the left the sign of n is positive; if the decimal
point had to be shifted to the right the sign of n is negative.
RESISTORS
Passive components
Passive components are those that need no power supply for their operation
and whose action will dissipate power, though in some cases the amount of
dissipation is negligible. No purely passive component can have an output
that supplies more power than is available at the input. Active components,
by contrast, make use of a power supply, usually DC, so that the
signal power output of an active component can be higher than the signal
power at the input. Typical passive components are resistors, capacitors and
inductors. Familiar active components are transistors and ICs.
All components, active or passive, require to be connected to a circuit,
and the two main forms of connection, mechanical and electrical, used in
modern electronic circuits are the traditional wire leads, threaded through
holes in a printed circuit board (see Chapter 18) and the more modern
surface mounting devices (SMDs) that are soldered directly on to the tracks
of a board. Both passive and active components can use either type of
connection and mounting.
Thermistors
Thermistors are resistors made from materials that have large values of
temperature coefficient. Both PTC and NTC types are produced for applications
that range from temperature measurement to transient current
suppression. Figure 1.14 shows some representative types. Miniature thermistors
either in bead form or in glass tubes are used for temperature
measurement, using a bridge circuit (Figure 1.15), and are also used for
timing circuits and in stabilizing the amplitude of sine wave oscillators (see
Chapter 7).