Basics of Bypass Capacitor, Its Functions and Applications

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Basics of Bypass Capacitor, Its Functions and
Applications
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Basics of Bypass Capacitor, Its Functions and
Applications
Introduction

• The Bypass capacitors are applied between the
  power supply pins VCC and GND of integrated
  circuits. They reduce both the power supply noise
  and the result of spikes on the supply line. They
  also provide immediate current demands of an
  integrated circuit whenever it switches.
• An application note describes the different
  properties of the bypass capacitors and provides
  a guide of their use. This article discusses
  about a bypass capacitor, its functions and
  applications.

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Basics of Bypass Capacitor, Its Functions and
Applications
What is a Bypass Capacitor?

• The bypass capacitor is a capacitor that shorts
  AC signals to the ground.
• In a way that any AC noise that present on a DC
  signal is removed producing a much cleaner and
  pure DC signal.
• A bypass capacitor basically bypasses AC noise
  that may be on a DC signal.
• Filtering out of AC so that a clean, pure DC
  signal goes through without several AC ripples.

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Basics of Bypass Capacitor, Its Functions and
Applications
What is a Bypass Capacitor?
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Basics of Bypass Capacitor, Its Functions and
Applications
What is a Bypass Capacitor?

• A capacitor employed to conduct an alternating
  current around as a component or group of
  components.
• Regularly an AC is  removed from an AC/DC
  combination.
• the DC is then freed to pass through the bypassed
  component.

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Basics of Bypass Capacitor, Its Functions and
Applications
Emitter Bypass Capacitor

• When an emitter resistance is added in a CE
  (Common Emitter) amplifier.
• Its voltage gain is reduced, but the input
  impedance increases.
• Whenever bypass capacitor is connected in
  parallel with an emitter resistance.
• The voltage gain of CE amplifier increases.
• If the bypass capacitor is removed, an extreme
  degeneration is produced in the amplifier circuit
  and the voltage gained will be reduced.

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Basics of Bypass Capacitor, Its Functions and
Applications
Emitter Bypass Capacitor
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Basics of Bypass Capacitor, Its Functions and
Applications
Cathode Bypass Capacitor

• A cathode resistor in a typical triode preamp is
  bypassed within a large capacitor to eliminate
  negative form of feedback is called as the
  cathode degeneration, which significantly
  increases gain.

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Basics of Bypass Capacitor, Its Functions and
Applications
Cathode Bypass Capacitor

• When a capacitor is large enough, it acts as a
  short circuit for audio frequencies.
• It eliminates the negative feedback, but acts as
  an open circuit for a DC, thereby maintaining the
  DC grid bias. 
• A treble boost can be introduced by using a lower
  capacitor value.
• The one that acts as a short circuit for the high
  frequencies but allows a negative feedback to
  attenuate bass.

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Basics of Bypass Capacitor, Its Functions and
Applications
Cathode Bypass Capacitor

• This is often done in the preamps bright
  channel.
• If the extra gain is unwanted, based on the
  amplifiers overall gain from the input jack to
  the power amp,
• The capacitor can be eliminated completely.

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Basics of Bypass Capacitor, Its Functions and
Applications
How to Calculate Bypass Capacitor Value

• We need to find out the appropriate value of the
  capacitor to use it for a particular device.
• The characteristic values are considered for
  bypass capacitors include 0.1 µF and 1 µF. 
• The higher the frequency, smaller the value
  while the lower the frequency, the larger the
  value is.
• ffrac12tR
• Here tR rise time

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Basics of Bypass Capacitor, Its Functions and
Applications
How to Calculate Bypass Capacitor Value

• The most significant parameter to select as an
  appropriate bypass capacitor.
• Its capacity to supply the immediate current when
  it is needed.
• In order to select a capacitor size for the
  particular device, we include the following
  methods

• Firstly, the bypass capacitor size can be
  calculated using the following equation

• Cfrac1NDeltatdeltaV

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Basics of Bypass Capacitor, Its Functions and
Applications
How to Calculate Bypass Capacitor Value

• I amount of current required to switch one
  output from a low to high
• N switching the number of outputs
• ?t time required to charge the line by the
  capacitor
• ?V tolerated drop in VCC
• The values are given in the formula should be 
  known, where ?t and ?V can be assumed.

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Basics of Bypass Capacitor, Its Functions and
Applications
How to Calculate Bypass Capacitor Value

• One more way to find out the bypass capacitor
  size is by the calculating its maximum current
  with the specified highest pulse slew rate.
• The greatest pulse slew rate is in place set by
  several capacitor manufacturers.

• ICfracdVdt

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Basics of Bypass Capacitor, Its Functions and
Applications
Bypass Capacitor Functions

• Bypass capacitor is used as a bypass AC signal to
  ground.
• A capacitor is connected between the ground and
  the wire.
• For an AC signal, the capacitor performs short
  and bypasses it.
• The DC  gone through the capacitor  behaves as an
  open for DC.
• DC is supplied directly to the IC.

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Basics of Bypass Capacitor, Its Functions and
Applications
Bypass Capacitor Functions

• The necessary characteristics of a bypass
  capacitor are
• It has low impedance.
• It electrifies an electric current is well.
• It capably grounds the noise current.
• It effectively decreases the noise current.

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Basics of Bypass Capacitor, Its Functions and
Applications
A Bypass capacitor is used in

• Power conditioning and Power factor correction
• Real time clock calendar with EEPROM
• DC/DC Converter    
• Voltage Reference    
• DSL Amplifiers    
• Signal coupling and Decoupling    
• High pass and Low pass filters

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Basics of Bypass Capacitor, Its Functions and
Applications
Conclusion

• Bypass capacitors help filter the electrical
  noise out of your circuits. They do this by
  removing the alternating currents caused by
  ripple voltage. Most digital circuits have at
  least a couple of bypass capacitors. A good rule
  of thumb is to add one bypass capacitor for every
  integrated circuit on your board. A good default
  value for a bypass cap is 0.1uF. Higher
  frequencies require lower valued capacitors.

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