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I have two questions I CANNOT figure out. Please help.

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Kloop

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K - I've been stuck on these questions for two weeks now. The only two out of a 20 page assignment that is due soon. I'll even pay pal 15$ to who ever gets this done. my times running out :(

Can anyone take a stab @ them?


Or can someone add me on msn

Kloopsch@Hotmail.com


and maybe just give me a hand?

<3
 

I'll give it a shot;
the transformer reduces V by 1/4, so secondary has 20V. Since it's center tapped, it should put 10V across R. I believe peak V is square root of 2, X Vrms so 1.414 X 10 = 12.4V Pk V across R, So Pk I = 12.4/1K = 12.4 mA. I believe average I is .63 X PK so 12.4mA X .63 = 7.81mA. I think the peak inverse V across each diode would be 20V.
If C3 is 750 ohms and has 4mA thru it, the V drop is 3V, which would also be the V across C2 and VC1=5-3=2V. Using the reactance formula, Fr=1/(2Pi*Xc*C), the Freq = 141,471Hz. Xc2 would be 562.5 ohms and the current thru it would be 5.3 mA. So the current thru C1 is 4mA+IC2=9.3mA and it's dropping 2V. So Xc1= 215 Ohms, so it's value must be .005.2 uF. Pat
 

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    Kloop

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patweadock said:
I'll give it a shot;
the transformer reduces V by 1/4, so secondary has 20V. Since it's center tapped, it should put 10V across R. I believe peak V is square root of 2, X Vrms so 1.414 X 10 = 12.4V Pk V across R, So Pk I = 12.4/1K = 12.4 mA. I believe average I is .63 X PK so 12.4mA X .63 = 7.81mA. I think the peak inverse V across each diode would be 20V.
If C3 is 750 ohms and has 4mA thru it, the V drop is 3V, which would also be the V across C2 and VC1=5-3=2V. Using the reactance formula, Fr=1/(2Pi*Xc*C), the Freq = 141,471Hz. Xc2 would be 562.5 ohms and the current thru it would be 5.3 mA. So the current thru C1 is 4mA+IC2=9.3mA and it's dropping 2V. So Xc1= 215 Ohms, so it's value must be .005.2 uF. Pat
Click to expand...
U have an error Vpk=1.414*10=14.14V :)))) => Ipk=14.14/1k=14.14mA.
That 0.63 is confusing, u get it from 2/pi=0.63. When u calculate average of |sin(x)|

Dont hate electronics, its fun
 

Thank you, It's been a while since I've done anything like this, I'm 52 yrs old - school's been out quite a while. Pat

-actualy, I just looked it up, on several sites to be sure; Vavg does = .636xVpk? - I see, I made a simple arithmatic mistake, of course 10 X 1.4 =14, don't know how I did that (when I calc'd Vpk) - again, 52 yrs old....
 

    K

    Kloop

    Points: 2
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