# regulated power supply

Discussion in 'Homework Help' started by darkknight, Oct 26, 2013.

1. ### darkknight Thread Starter Active Member

Oct 7, 2009
41
0
hi,

I have to build a regulated power however i am quite confused with the specs requisition and was hoping that someone could help me. these are the specs

D.C. Output is 10 V
Load Variation is 300  9000ohms
Ripple Factor has to be Less than 0.1% for 1900ohms load
Load Regulation has to be better than 4 mV for a 1 mA change in load current
Line Regulation has to be better than 4 mV for a 1V change in line voltage

i am stuck on the regulation portion of it, how would i calculate the rs and rl?

2. ### #12 Expert

Nov 30, 2010
17,293
8,137
There is no Rs. Rl is given in the instructions.

3. ### darkknight Thread Starter Active Member

Oct 7, 2009
41
0
dont i need an rs to drop the extra voltage from the zener diode? i have trouble "translating those specs to their terms such as rl, so i guess the rl is the load variation where i can pick from 300 to 9000?

4. ### #12 Expert

Nov 30, 2010
17,293
8,137
Why not just pick the right voltage zener diode?
You pick all the values from 300 ohms to 9000 ohms. The circuit has to work at both of those loads and everywhere in between.

5. ### darkknight Thread Starter Active Member

Oct 7, 2009
41
0
im sorry im still quite a newbie, this is my first project, could you elaborate more?

6. ### #12 Expert

Nov 30, 2010
17,293
8,137
If you want 10 volts, choose a 10 volt zener diode.
Why would you choose an 11 volt zener diode and then add a resistor?
The Rl is given as 300 ohms to 9000 ohms.
Now it is time for you to post your effort to design the circuit, or do calculations, or something.
This is the Homework forum. It is YOUR homework.
Do something besides repeating the same question.

7. ### WBahn Moderator

Mar 31, 2012
19,129
5,172
If you have an ideal voltage supply, does the load voltage change if the load current changes?

If you have a real voltage supply, does the load voltage change if the load current changes?

If you have a real voltage supply, how much does the load voltage change by as a result of a change in the load current?

What parameter describes this relationship?

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8. ### anhnha Well-Known Member

Apr 19, 2012
776
48
May I try to answer these questions? I still don't understand all the specs above.
No, it doesn't.
Yes, it does.
Let's call the internal resistance of voltage supply, load resistance are Rs and RL respectively. Vs is the voltage of ideal voltage supply and IL is the current flowing through the load.

$V_{ R_{L} } = V_{s} - I_{L}. R_{s}$

$\Delta V_{ R_{L} } = - \Delta I_{L}. R_{s}$

This means that with 1 mA change in load current, the voltage across the load has to be less than 4 mV, right?

$\Delta V_{ R_{L} } \leq 4mV$

$\Delta I_{L} = 1mA$

From this we have constrain for the internal resistance:

$R_{s} \leq \frac{ \Delta V_{ R_{L}}}{ \Delta I_{L}} = \frac{4mV}{1mA} = 4 \Omega$

Here is my understanding about other parameters.
Not sure how to use the load variation spec.
From load range, I calculated current range: 10V/9000Ω to 10V/300Ω
The maximum current is 1/30A => Rs < 30S*Vs = 300Ω

Is that correct?

And what does this spec mean?

9. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,082
1,149
Your answer looks good. Except I don't understand what are you doing here
As for Line Regulation - if voltage at regulator input change be 1V. The regulator output voltage cannot change more then 4mV.

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10. ### anhnha Well-Known Member

Apr 19, 2012
776
48
How would you use the spec?
I also don't know how to use this. Any clue?

11. ### Jony130 AAC Fanatic!

Feb 17, 2009
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this spec inform as how the load will change nothing more.

http://www.ittc.ku.edu/~jstiles/312/handouts/Line Regulation.pdf

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12. ### anhnha Well-Known Member

Apr 19, 2012
776
48
Well, I didn't know that we have to use the regulator with Zener diode like that.

I got stuck with that circuit. How can I use this information.

13. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,082
1,149
But for any voltage regulator circuit we can find Line Regulation and Load Regulation

But you already did that correctly. Then for a given voltage regulator, you need to find Rout and and ensure that Rout < 4mV/1mA = 4Ω

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14. ### anhnha Well-Known Member

Apr 19, 2012
776
48
In the circuit Rout = rz || R?

15. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,082
1,149
Yes, Rout = rz || R

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16. ### WBahn Moderator

Mar 31, 2012
19,129
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In general, it would be better if you held off and gave the OP a chance to see them and ponder them and attempt to answer them. After all, this is THEIR thread and the primary purpose should be to maximize the help to THEM. The point of the questions is to get them to THINK about the concepts and draw upon THEIR understanding of the material to form conclusions. That process is largely (but not totally) defeated if someone else does the thinking for them.

If they don't answer after a few days, then it becomes fair game.

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Apr 19, 2012
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