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posted by  AJECE on 10/31/2009 8:33:55 PM  |  status: Live  |  Earned Karma: 25

a full wave center-tapped transformer

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Electrical Engineering Microelectronic Circuits (5th) by Sedra, Smith N/A N/A 11/1/2009 at 4:00:00 PM
Question Details:
a full wave center-tapped transformer rectifier in a power supply provides an average dc output voltage of 14 v on which a maximum ripple of +,-0.5 volt is allowed.Diodes have a 0.7 volt drop when conducting.Assuming a resistive load of 120 ohm, a line voltage of 120 v rms@ 60Hz through a transformer,
a) Sketch the circuit diagram for the rectifier
b) what is the rms voltage across the transformer secondary?
c) Determine the size of filter capacitor required.
d) Assuming 50% safety maegin, what diode PIV rating is appropriate?
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posted by Tachyon12 on 11/2/2009 4:35:12 AM  |  status: Live
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Response Details:

b) The average DC voltage across RLOAD = 14V
The diode has a voltage drop of 0.7V
So the voltage before rectification by diode is 14.7V
∴ The voltage on the secondary terminal of CTT is 14.7x 2 = 29.4˜30V
c) The capacitor value is given by
       C= IDC/2.f.ΔV
where frequency(f)= 60
          Current through RLOAD (IDC)= 14/120 =0.117A
          ΔV = 0.5 - (-0.5) = 1V

That gives a Capacitance of about 0.98mF

d) Maximum voltage across the diodes = 14- (-14.7) =28.7
If i want to keep a 50% safety margin i would choose a diode with PIV of 60V.
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