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Help needed in designing power source

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Sonia123

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Hello there folks,

I a supposed to design a power source device. And this is what has been done in multisim so far, am falling short of time but I really want to know valuable suggestions of the experts over here since I really want to make this design final and robust. Also sine am a beginner in electronics, please can someone direct me on the attachment of oscilloscope and voltmeter to test.
Waiting or your replies.
Thank you
 

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That looks to be a perfectly reasonable -11.4V power source, with the current limited to ~ 300mA.
As for attaching the scope and voltmeter, what are you interested in measuring? At the very least I presume you want to test the output voltage. To do that, connect the voltmeter (set for 20V DC range, or the next highest range your meter has) negative probe to the junction of C1 and C4, and connect the positive probe to circuit ground.
 
Alright, but now I have one more problem. I need a voltage outlet of 220Vac which is capable of supplying fixed or variable DC voltage. I am confused as to how would I make this happen. Thanks alot for your response.
 
I need a voltage outlet of 220Vac which is capable of supplying fixed or variable DC voltage. I am confused as to how would I make this happen.
We're all confused! What is going to power this 220V AC? Battery? Mains? What is your local mains voltage? What fixed voltage do you want? What range of variable voltage do you want? What maximum currents will be drawn from the different voltage sources?
 
You need a larger value for C2.

When you are taking 300 mA, C2 has to provide the current for just under half a mains cycle.

The charge is 0.3 * 1/120 = 0.0025 coulombs. The voltage drop for a 220 uF capacitor would be

0.0025/0.00022 = 11 V,

That is not a very accurate calculation, as the time will be a bit less than 1/2 cycle, and the value of the capacitor has a large tolerance on it, and the current might well be less.

You should aim for about 2 V drop each half cycle, so you need around 1000 uF or more.
 
Mains are going to power this 220Vac and the local main voltage is 220V. The maximum output current can be either 1.5A or 2A and the fixed voltage can be either 5V or 12V, so just forget about variable voltage since am planning for fixed one now.
 
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The zener diode needs at least 5mA and the base of the TIP42 transistor needs at least 10mA for an output of 300mA. Then R1 must supply at least 15mA.
But R1 has such a high value (10k) that it supplies only 0.4mA.
 
The circuit in post #6 seems to relate to a different power supply altogether, which has been discussed in another thread.
 
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