###### Asked in Car Electronics and LightsElectronics Engineering

Car Electronics and Lights

Electronics Engineering

# What is transition and diffusion capacitance?

## Answer

###### Wiki User

###### November 18, 2008 5:43PM

**Diffusion capacitance** is the capacitance due to transport
of charge carriers between two terminals of a device. - Amog This
diffusion capacitance is due to depletion capacitance which is a
function of forward bias applied to emitter junction of a
transistor and due to diffusion capacitance which a function of
transconductance of the transistor. Its value is 100 pF. Tirupanyam
B.V

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### What is meant by transition and space charge capacitance of a diode?

space charge region in a diode or say a bjt for better
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c= (epsilon*A)/d ;
where ... c is capacitance
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and d is the depletion width
the other type of capacitance is the diffusion capacitance
c= (T*I)/(n*V)
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me
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Transition capacitance : A reverse biased PN-junction has a
region of high resistivity (depletion layer) sandwiched in between
two regions of relatively low resistivity. The P-N regions act as
the plates of a capacitor and the depletion layer acts as the
dielectric This is known as the transition capacitance or depletion
capacitance.
Diffusion capacitance : It is the capacitance due to transport
of charge carriers between two terminals of a device like the
forward biased PN junction. In a semiconductor device with a
current flowing through it (for example, an ongoing transport of
charge by diffusion) at a particular moment there is necessarily
some charge in the process of transit through the device. If the
applied voltage changes to a different value and the current
changes to a different value, a different amount of charge will be
in transit in the new circumstances. The change in the amount of
transiting charge divided by the change in the voltage causing it
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### What is the effects of capacitance in a diode?

Any variation of the charge within a p-n diode with an applied
voltage variation yields a capacitance wich must be added to the
circuit model of a p-n diode. The capacitance associated with the
charge variation in the depletion layer is called the junction
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### What is diffusion capacitance in pn junction?

A capacitor is a device that stores charge. Therefore any device
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capacitance.
When a PN diode is forward biased, a current flows due to the
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charges in motion. This is dynamic charge. The capacitance due to
storage of dynamic charge is called the diffusion capacitance.
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charge also increases exponentially . Hence the diffusion
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### Why is that a space charge region in a pn junction at equilibrium is often made small?

The space charge region in a pn junction at equilibrium is often
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to obtain a high junction capacitance;
since the junction capacitance is inversely proportional to the
width of the space charge region, the smaller the width, the larger
the junction capacitance.
to ensure easy diffusion of charge carriers;
if the space charge region is made small, that is, the width is
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The charge inside of a p-n diode with a connected voltage
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diode. The capacitance connected with the charge variety in the
exhaustion layer is known as the intersection capacitance, in the
same process capacitance connected with the abundance bearers in
the semi impartial district is known as the dissemination
capacitance.