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To design and test switch mode power supply using ICs 78XX .

 

OBJECT: To design and test switch mode power supply using ICs.

Apparatus required

Transformer, diodes, capacitor, resistor, 7805 IC.

Theory

A switch mode power supply is a circuit that supplies a constant voltage regard of charges in load current. Although voltage regulator can be designed using op-amps, it is quicker and easier to use IC switch mode power supply. Furthermore, IC switch mode power supply are versatile & relativity inexpensive.

Switch mode power supply are commonly used for on – card power supply & laboratory- type power supplies. Almost all power supplies use  some type of switch mode power supply IC because switch mode power supply are simple to use, reliable, low in cost and above,all available in a variety of voltage & current rating.Positive switch mode power supply series with screw voltage options:-

The 7800/78Xxseries consist of terminal positive switch mode power supply with seven voltage option these ICs are designed as fixed switch mode power supply.A switch mode circuit is an indispensable, part of the power supply section of any electronics system. The contemporary regulator circuits are almost exclusively based on one or more than one IC’s known as IC switch mode power supply. IC switch mode power supply are available commercially in a variety of voltage, current and regulationSpecific to meet designers need. The IC switch mode being covered include the adjustable output precision switch mode type 723,the three terminal fixed output voltage positive and negative switch mode and the three terminal adjustable output voltage and negative switch mode.

 

General purpose precision IC switch mode power supply, Type 723.

IC 723/723c is a general purpose adjustable output switch mode power supply designed primavilyfor series positive switch mode power supply applied. But it is capable of operation or negative power supply as a series, shunt, switching or floating switch mode.

The IC 723/723c has a wide application range including series switch mode power supply, switching switch mode power , temperature controller and so-on. Each type may have certain variations. For instance, under series switch mode power supply, there are low switch mode power supply, high switch mode power supply etc. The IC 723 resembles IC 723c in all respects except for the operational temperature range. IC 723 has a military qualified operational temperature of -55 c to +a25 c while IC 723c has commercial operation temperature range of 0 c to +70 c.

Three Terminal (+ve) and  (-ve) switch mode power supply:-

In the basic operational mode,3 terminal switch mode require virtually no external components.

 

They are available in both fixed voltage as well as adjustable voltage type with current ratings of 100mA , 1.5A, 3.0A. The fixed types are (+ve) switch mode power supply LM78XX /MC78XX, LM78MXX, /MC78MXX series. LM78LXX /MC78LXX /LM140-XX, whereas adjustable type are of LM117 /LM217 /LM317 and LM317 /237 /337 series AND (-ve). Switch mode power supply are LM79XX /MC79XX /MC79MXX /LM79MXX /LM79LXX /MC79LXX and LM137 /LM237 /LM337 SERIES.

Circuit Application

 

Although 3- terminal switch mode power supply of LM78XX series and LM340-X series have been designed primarily as a fixed switch mode power supply these device can be used with external components to obtain adjustable voltage and currents. Same will be for negative switch mode power supply.

 

Specification of switch mode power supply devices:-

 

Device number

 

 

 

Vo(volt)

 

Io( mA )

Drop out(v)

voltage

Package

Type

General Remark

LM78L05

5.0

100

1.7

TO-5,

TO-39, and

LM7805, MC7805 has the MIL specified temperature. Rang whereas LM7805C, MC78L05C has commercial temperature rang.

LM78M08C

LM7805 /MC7805

5.0

1500

2.5 to 3.0

To -220 and To-3

To -3

LM7805, MC7805 has the MIL specified temp. Rangwhereas LM7805C, MC78L05C has commercial temp rang.

MC78TO8 /MC78TO8C

8.0

3000

2.5

TO-3

LM7805, MC7805 has the MIL specified temp. Rang whereas LM7805C, MC78L05C has commercial temp rang MC7805 has the MIL specified temp. Rang whereas LM7805C, MC78L05C has commercial temp rang.

 

MC7812 /MC7812C

12.0

1500

2.5TO 3.0

TO-220

And

TO-3

LM7805, MC7805 has the MIL specified temp. Rang whereas LM7805C, MC78L05C hascommercial temp rang MC7805 has the MIL specified temp. Rang whereas LM7805C, MC78L05C has commercial temp rang.

MC78T12 /MC78T12C

12.0

300

2.5

TO-3

LM7805, MC7805 has the MIL specified temp. Rang whereas LM7805C, MC78L05C has commercial temp rang MC7805 has the MIL specified temp. Rang whereas LM7805C, MC78L05C has commercial temp rang.

 

MC79LO5C

-5.0

100

1.7

TO-39 &

TO-92

0 degree to 70 degree

( commercial range )

 

LM7915C /MC7915C%

-15.0

1500

2.5

TO-220 & TO-3

0 degree to 70 degree

( commercial range )

 

LM140-5

 

5.0

1500

2.0

TO-220 & TO-3

Operational range

( -55 degree to 125 degree )

 

LM140-12

12.0

1500

2.5

TO-220 & TO-3

Operational range

( -55 degree to 125 degree )

 

LM340-18

18.0

1500

2.5

TO-220 & TO-3

Operational range

( -55 degree to 125 degree )

 

LM320K

-5,-12,

-15

1500

2.5

TO-220 & TO-3

Operational range

( -55 degree to 125 degree )

 

 

Precautions

   

  1. If large output capacitor is used (10MF), the momentary short circuit ass the input can damage the switch mode power supply as here the output capacitor and the stored charge may be large enough to damage the switch mode power supply. A fast diode may be connector to protect the switch mode power supply by passing bulk of the discharge current through it.

 

  1. Sufficiently strong transients exceeding the maximum Vi or going sufficiently below ground level are likely to damage the switch mode power supply. The solution is to use a large capacitor, a chockor transient suppressor or a combination of these.

 

  1. In case ground terminal becomes disconnected, the output apparatus the  un regulated causing damage to other circuit connected.

Result

We have designed and tested switch mode power supply use ICs.

Questions

  1. What is the difference between a topology and a configuration?
  2. What is an "inverting" configuration?
  3. What is really "ground" for a dc-dc converter?
  4. What is "ground" for the control IC?

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