# DC Power Supply

Discussion in 'Homework Help' started by Ahmed Zafar Khan, Feb 18, 2016.

1. ### Ahmed Zafar Khan Thread Starter New Member

Feb 18, 2016
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I have designed a 5V ,350mA fixed power supply with a 12 Vrms step down transformer. the voltage across filtering capicitor should be almost peak value i.e 15V or 16V . but I am getting 12 volts acrossthe capacitor why is it so.

2. ### AnalogKid Distinguished Member

Aug 1, 2013
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Schematic.

Is the supply loaded at 350 mA when you are measuring the voltage?

Schematic.

What is the size of the filter capacitor?

Schematic.

ak

3. ### Ahmed Zafar Khan Thread Starter New Member

Feb 18, 2016
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YES IT IS WHEN THE CIRCUIT IS LOADED .

Last edited by a moderator: Feb 18, 2016

Jun 22, 2012
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Feb 18, 2016
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image

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6. ### crutschow Expert

Mar 14, 2008
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We mean the schematic.

Sep 17, 2013
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Feb 18, 2016
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MAY IT WORK

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9. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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NO, you have resistors in series with the output supply, and the zener is pulling too much current through the resistors, i would use a lm7805 regulator instead of the resistors and zener.

10. ### Ahmed Zafar Khan Thread Starter New Member

Feb 18, 2016
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SIR THIS IS OUR LAB PROJECT USING ZENER MY QUESTION IS WHY VOLTAGE DROPS ACROSS CAPACITOR THEORY BASED ANSWER NEEDED

Apr 5, 2008
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12. ### ronv AAC Fanatic!

Nov 12, 2008
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The capacitor gets charged by the peaks only so the charge current is quite high. This makes the drop across the 1 ohm and the diodes higher than you think.

13. ### WBahn Moderator

Mar 31, 2012
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What is the average current through the 15 Ω resistor between the cap and the zener?

What fraction of the time do the diodes spend conducting?

What is the average current through the 1 Ω resistor between the bridge and the cap?

What is the average voltage drop across that 1 Ω resistor?

14. ### WBahn Moderator

Mar 31, 2012
18,089
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Typing in all caps on a forum (or e-mail) is considered the equivalent of shouting and it is also considered quite rude. Please refrain from the practice (except, of course, when your intent is to shout and be rude).