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Electronic Circuits

10CS32

UNIT – 7: Linear Power Supplies, Switched mode Power Supplies
7.1 Regulated power supply
The regulated power supply converts the standard 220 volts, 50 or 60 Hz AC available at wall outlets
into a constants DC voltage. It is one of the most common electronics circuits that we can find. The
DC voltage produce by a power supply is used to power all the types of electronic circuits, such that
television receiver, stereo system, CD players and laboratory equipment.
The regulated dual voltage DC power supply is to be used for the FM receiver. Two regulators, one
positive and the other negative, provide the positive voltage required for the receiver circuits and the
dual polarity voltage for the op-amp circuits.
The regulated power supply is to provide the necessary dc voltage and current, with low levels of ac
ripple and with stability and regulation.
There are various methods of achieving a stable dc voltage from ac mains. The two methods are more
commonly used. These are used;
(i) a linear voltage regulator and
(ii) A switching mode regulator.
Several types of both linear and switching regulators are available in integrated circuit (IC) form. By
using the linear voltage regulator method, we must get the regulated dual dc power supply.

I
P

TRANSFORMER
STEP-DOWN

FILTER
RECTIFIER
FILTER

+V
POSITIVE
REGULATOR
O
P
NEGATIVE
REGULATOR - V

Fig: (1) Block Diagram of the Regulated Dual Voltage DC Power Supply

7.2 POWER SUPPLY FILTER
A power supply filter ideally eliminates the fluctuations in the output voltage of a half –wave rectifier
and produces a constant-level dc voltage. The 60Hz pulsating dc output of a half-wave rectifier or the
120Hz pulsating output of a full-wave rectifier must be filtered to reduce the large voltage variations.
Fig: (4.1) illustrates the filtering concepts showing a nearly smooth dc output voltage from the filter.
The small amount of fluctuation in the filter output voltage is called ripple.
Vin
0V

Full-wave
Rectifier

0V

Filter

Vout
0

Fig: (4.1) Power supply filtering

Dept .of ISE, SJBIT

Page 147