Self Switching Power Supply

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Self Switching Power Supply
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Self Switching Power Supply
Introduction

• Embedded system requires a regulated power
  supply. This power supply circuit gives a
  variable regulated supply and switches off in no
  load condition.
• Through an arrangement of voltage regulator 7805
  and a potentiometer the output voltage is varied
  from 3.7V to 8.7V. Another feature of this power
  supply is, when no load is there it automatically
  switches off. It is achieved through an
  arrangement of transistors and relay.

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Self Switching Power Supply
Block Diagram
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Self Switching Power Supply
Hardware Requirements

• Transformer
• Rectifier
• Filter
• Regulator
• Relay
• Transistor (BC 547 BC 557)
• Resistor
• Capacitor
• 1n 4007

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Self Switching Power Supply
Power Supply
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Self Switching Power Supply
Step down Transformer

• Its secondary voltage is less than its primary
  voltage.
• It is designed to reduce the voltage from the
  primary winding to the secondary winding.
• The transformer converts high-voltage,
  low-current power into low-voltage, high-current
  power.

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Self Switching Power Supply
Rectifier

• A bridge rectifier is an arrangement of four or
  more diodes in a bridge circuit configuration
  which provides the same output polarity for
  either input polarity. It is used for converting
  an alternating current (AC) input into a direct
  current (DC) output.

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Self Switching Power Supply
Filters

• A filter is a capacitor which filters out a
  certain frequency or range of frequencies from a
  circuit.
• Usually capacitors filter out very low frequency
  signals.
• These are signals that are very close to 0Hz in
  frequency value.
• These are also referred to as DC signals.

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Self Switching Power Supply
Voltage Regulator (LM 7805)

• A voltage regulator is designed to automatically
  maintain a fixed voltage level.
• 7805 is a voltage regulator integrated circuit.
• It is a member of 78xx series of fixed linear
  voltage regulator ICs.
• The xx in 78xx indicates the fixed output voltage
  it is designed to provide.
• 7805 provides 5V regulated power supply.

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Self Switching Power Supply
Relay

• A relay is an electromagnetic switch operated by
  a relatively small electric current.
• The purpose of relay is to control the movement
  of the gate ( whether to open or close).
• Relay is used to control the Electrical Devices
• A relay is able to control an output circuit of
  higher power than the input circuit.

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Self Switching Power Supply
Working Principle

• A regulated power supply circuit that though a
  fixed-voltage regulator U1-LM7805 not only gives
  a variable but also auto switch off features This
  is achieved by connecting a potentiometer between
  common terminal of regulator IC and ground. For
  every 100-ohm increment in the in- circuit value
  of the resistance of potentiometer RV1, the
  output voltage increases by 1 volt.
• Thus, the output varies from 3.7V to 8.7V (taking
  into account 1.3-volt drop across diodes D7 and
  D8). 
• Another important feature of the supply is that
  it switches itself off when no load is connected
  across its output terminals.

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Self Switching Power Supply
Working Principle

• This is achieved with the help of transistors Q1
  and Q2, diodes D7 and D8, and capacitor C2. When
  a load is connected at the output, potential drop
  across diodes D7 and D8 (approximately 1.3V) is
  sufficient for transistors Q2 and Q1 to conduct.
• As a result, the relay gets energized and remains
  in that state as long as the load remains
  connected. At the same time, capacitor C2 gets
  charged to around 7-8 volt potential through
  transistor Q2. But when the load( a lamp here in
  series with S2 ) is disconnected, transistor Q2
  is cut off. However, capacitor C2 is still
  charged and it starts discharging through base of
  transistor Q1.

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Self Switching Power Supply
Working Principle

• After some time (which is basically determined by
  value of C2), relay RL1 is de-energized, which
  switches off the mains input to primary of
  transformer TR1.
• To resume the power again, switch S1 Push button
  should be pressed momentarily. Higher the value
  of capacitor C2 more will be the delay in
  switching off the power supply on disconnection
  of the load, and vice versa.

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Self Switching Power Supply
Working Principle

• A transformer with a secondary voltage of 12V-0V,
  250mA was used, it can nevertheless be changed as
  per users requirement (up to 30V maximum. and
  1-ampere current rating). For drawing more than
  300mA current, the regulator IC must be fitted
  with a small heat sink over a mica insulator.
  When the transformers secondary voltage
  increases beyond 12 volts (RMS), potentiometer
  RV1 must be re-dimensioned. Also, the relay
  voltage rating should be predetermined.

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Self Switching Power Supply
Advantages

• Used as protector for electronic Circuits
• Can obtain different voltages
• Act as protector for monitors
• Less costly

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Self Switching Power Supply
Disadvantages

• If once the supply breaks then it is powered on
  manually.

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Self Switching Power Supply
Applications

• This circuit is used in different electronic
  circuits, electronic equipment's.
• This circuits is used for damage less uses.
• By this circuit we can produces various voltages.
• It can be used as supply voltage for different
  electronic equipment's.

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Self Switching Power Supply
Conclusion

• Almost all electronic equipements include a
  circuit that converts AC voltage of main supply
  into DC voltage. This part of the equipments is
  called power supply. In General, at the input of
  the power supply, there is a power transformer. A
  diode circuit called rectifier follows it. The
  output of the rectifier goes to a smoothing
  filter and then to a voltage regulator circuit.
  The rectifier is the heart of the power supply.
• This power supply is used as a variable one. In
  laboratory applications we need variable voltages
  in different level. So this circuit is very much
  helpful in electronic experimental applications.
  Also the auto switching facility less the energy
  wastage.

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