FSK , FM DEMODULATOR & VOLTAGE REGULATOR ICS

Application of PLL in FSK & FM demodulation three terminal regulator ics.

Adjustable output voltage regulator LM 317, LM 337 & LM 340 series power supply ics.

Basic design considerations for designed regulated power supply

CONTENTS

FREQUENCY MULTIPLIER USING PLL

A divide by N network (frequency divider) is connected externally between the VCO output and phase comparator input.

Since the output of the divider network is locked to the input frequency fs, the VCO actually operates at a frequency which is N times higher than fs.

fs = N fs

The multiplying factor can be obtained by proper selection of the scaling factor N of the frequency divider.

FM DETECTION USING PLL

The FM signal which is to be demodulated is applied at the input of the PLL.

As the PLL is locked to the FM signal, the VCO starts tracking the instantaneous frequency in the FM input signal.

The error voltage produced at the output of the amplifier is proportional to the deviation of input frequency from the center frequency FM.

Thus the ac component of the error voltage represents the modulating signal.

Thus at the error amplifier output we get demodulated FM output.

FSK demodulator using PLL

FSK is used in computer peripherals and radio communication of binary data or codes.

The carrier frequency is shifted to either fH or fL depending on whether a binary “1” or “0” is to be transmitted respectively.

Thus if a “1” is to be sent, the transmitter will transmit a signal at frequency “fH” and if a “0” is to this FSK signal can be demodulated by using PLL as shown in fig.

THREE TERMINAL IC REGULATORS

The discrete component regulator circuit such as the zener voltage regulators are not much used in practice.

Now a days the voltage regulator circuits are available in the IC from and the IC regulators are widely used.

Advantages of IC regulators:1. The power supply design becomes easy & quick.2. Cheap & easily available.3. small hence they reduce the size of the power supply.4. They are easy to use.5. IC regulators are versatile.

78XX series are three terminal ,positive fixed voltage regulators. Here XX indicate the output.

These regulators are available in seven different output voltage option, such as 5,6,8,12,15,18 and 24.

Thus if we select a regulator IC numbered “7812”, it provides us a 12 V regulated output voltage.

78XX SERIES VOTAGE REGULATOR

ADJUSTABLE VOLTAGE REGULATOR USING 78XX SERIES

Even though the 78XX series is fixed voltage regulator series it is possible to obtain a variable output voltage using it.

The arrangement for obtaining a variable output voltage is as shown in fig.

The output voltage is varied by varying the variable resister R2.

Expression for output voltage :

BLOCK DIAGRAM OF LM 317

The block diagram shows that LM 317 is a series regulator and a Darlington pair acts as a series pass element.

The output voltage is compared with the internally generated voltage reference to produce an error voltage which drives the Darlington transistors to regulate the output voltage.

RLIMIT is an internal sensing resistance. The voltage across it is proportional to load current.

This voltage is applied to the internal protection circuitry. If the load current exceeds beyond its maximum value, the Darlington pair will be automatically turned off to protect the IC.

Its o/p is adjustable over a range of 1.2 V to 37 V.

BLOCK DIAGRAM OF LM 337

The block diagram shows that LM 337 is a series regulator and a Darlington pair acts as a series pass element.

The output voltage is compared with the internally generated voltage reference to produce an error voltage which drives the Darlington transistors to regulate the output voltage.

RLIMIT is an internal sensing resistance. The voltage across it is proportional to load current.

This voltage is applied to the internal protection circuitry. If the load current exceeds beyond its maximum value, the Darlington pair will be automatically turned off to protect the IC.

Its o/p is adjustable over a range of -1.25 V to -37 V.

BLOCK DIAGRAME OF LM 340

LM 340XX

These regular Ics are available in plastic power package as shown in fig.

It is three pin regulator with input, ground and output terminals.

The sequence of input, ground and output pins is same as that of the 78xx IC.

E draw max (for drawing)

Analog Electronics (J. S. Katre)

REFRENCE

Thank You……