Trying to figure out this DJIA thing!?!? - Page 5 - Mercedes-Benz Forum

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post #41 of 47 (permalink) Old 09-17-2008, 06:22 AM
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You got the half wave right but then you mess up with you voltage assessment, you still kept the output at 20Vpp. Yes, you will get a 1.7V drop due to two diodes for each half cycle but that would be subtracted from 10Vpp
I agree, don't use a resistor based voltage divider because you will be consuming energy at no load. Remember that a current will be going through R1 and R2 of said divider and your output impedance is low anyway which can be a problem once you plug in a load. Next, your best bet is to use the large enough resistor value with a capacitor at each end of the output of the bridge rectifier. That would filter the signal and you got your analysis correct about what could happen with the balance if you use too large or too low of a value. The simplest way to obtain the 8Vdc after that is to use a Zener diode but Op amps are better like you mentioned but to a certain degree, that is how much current do you want this "power supply" to output? You have to figure that automotive applications require much higher currents than say, an audio amp or some control circuitry.

Right, but why is it your wife still complains you can't fix the light next to the bed?
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post #42 of 47 (permalink) Old 09-17-2008, 06:32 AM
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God Damn the Dow just dropped 200 points within 3 minutes of the opening bell...........
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post #43 of 47 (permalink) Old 09-17-2008, 07:20 AM
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Right, but why is it your wife still complains you can't fix the light next to the bed?
With me being on BWOT so much I guess she forgot to unplug her vibrator hence there is no power to the table lamp, besides that's a dedicated 240V line anyway
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post #44 of 47 (permalink) Old 09-17-2008, 12:36 PM
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You got the half wave right but then you mess up with you voltage assessment, you still kept the output at 20Vpp. Yes, you will get a 1.7V drop due to two diodes for each half cycle but that would be subtracted from 10Vpp
I agree, don't use a resistor based voltage divider because you will be consuming energy at no load. Remember that a current will be going through R1 and R2 of said divider and your output impedance is low anyway which can be a problem once you plug in a load. Next, your best bet is to use the large enough resistor value with a capacitor at each end of the output of the bridge rectifier. That would filter the signal and you got your analysis correct about what could happen with the balance if you use too large or too low of a value. The simplest way to obtain the 8Vdc after that is to use a Zener diode but Op amps are better like you mentioned but to a certain degree, that is how much current do you want this "power supply" to output? You have to figure that automotive applications require much higher currents than say, an audio amp or some control circuitry.
I never said anything about it being 20V out of the rectifier did I? Oh maybe you meant because of the rating I chose for the IC voltage regulator. That has to be at least as high as the fullwave PP incase of reverse voltage breakdown of the diode occurs. Otherwise you are replacing the IC when you get voltage spikes on the input side of the rectifier.
post #45 of 47 (permalink) Old 09-17-2008, 01:23 PM
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Drew and Heddi ya'll are pretty smart. I read your posts and such. Some times I wish I could hop in your conversation and add to it but all it ends up doing is making







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post #46 of 47 (permalink) Old 09-17-2008, 01:32 PM
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I hate voltage spikes on the input side of my rectifier. Try explaining those marks to your wife.
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post #47 of 47 (permalink) Old 09-17-2008, 01:40 PM
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I hate voltage spikes on the input side of my rectifier. Try explaining those marks to your wife.






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