bridge rectifier error?!
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Re: bridge rectifier error?!

by aminoacid on Fri Jun 01, 2012 10:53 am

input voltage offset..?

or maybe the multimeter is to low impedance to get a right reading from there.
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Re: bridge rectifier error?!

by MMM on Fri Jun 01, 2012 11:01 am

evostars wrote:Its wired as a buffer. Cant be right to put 5.2 in and get 5.33 out.


But it's what is happening here. It's an error of around 2.5%.

I'm doing all measurements directly on IC23, pin 4 as ground.

#1
pin 5: 5.18v
pin 7: 5.33v

#2
pin 5: 5.20v
pin 7: 5.33v

#3
pin 5: 5.19v
pin 7: 5.32v

#4
pin 5: 5.32v
pin 7: 5.33v

#5
pin 5: 5.23v
pin 7: 5.33v

To me, it's quite obvious.
I don't know if this is inherent in the opamp design (is a 2.5% error acceptable or not? I don't know...).
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Re: bridge rectifier error?!

by MMM on Fri Jun 01, 2012 11:13 am

aminoacid wrote:input voltage offset..?

or maybe the multimeter is to low impedance to get a right reading from there.


Or perhaps this is the result of running the opamp from a single side supply? Doesn't opamp precision depend on the symmetrical power supply?
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Re: bridge rectifier error?!

by aminoacid on Fri Jun 01, 2012 12:37 pm

the datasheet says input offset is between 2mV and 7mV @ 5V Vcc single rail if i get it right.

but you are seeing a differance by 133mV.

what happens if you hook up one multimeter to the input of the opamp and one to the output at the same time? and then disconnect the meter from the input.
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Re: bridge rectifier error?!

by evostars on Fri Jun 01, 2012 3:26 pm

ah as long as it gives 5.333V guess
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Re: bridge rectifier error?!

by MMM on Sat Jun 02, 2012 12:50 am

aminoacid wrote:what happens if you hook up one multimeter to the input of the opamp and one to the output at the same time? and then disconnect the meter from the input.


I only have one multimeter.
However, using an oscilloscope and two probes shows that the voltage on input and output is identical. So the "low impedance" theory is probably right.

http://www.ladyada.net/make/x0xb0x/fab/powersupply.html suggests that the 5.333v should be achieved even before IC23 is soldered in. If the builder has a multimeter like mine he could try to hunt down a problem that doesn't even exist.
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Re: bridge rectifier error?!

by aminoacid on Sun Jun 03, 2012 9:41 pm

im still thinking about getting a zener after the voltage doubler to work.

reading this thread, perhaps confirms that the voltage is set by a 15V zener and one voltage drop from a transistor that helps regulate the voltage before the transformer in the 303.

viewtopic.php?f=13&t=8613&p=43181&hilit=power+supply+mod#p43181

i would like to find a ac adapter that gives about 7Vac. that would prob work for the 6V and the 5V line, the 5Vreg would be having less voltage to dispose like gompie was talking about, and giving a doubled voltage close above 16V that could be fixed to about 15.7V by a zener and a diode.

i wonder if it will work better with the zener regulation when using a lower voltage adapter... since my earlier attemt gave a result of about 1V perhaps and slowly rising some...
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Re: bridge rectifier error?!

by aminoacid on Tue Jun 05, 2012 6:17 pm

or that maybe a coil in a rather then a transformer .... :)
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Re: bridge rectifier error?!

by evostars on Tue Jun 05, 2012 6:30 pm

aminoacid wrote:or that maybe a coil in a rather then a transformer .... :)

inductor?
http://pdf1.alldatasheet.com/datasheet- ... C-102.html
Can be used as DC-DC converter transformer
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Re: bridge rectifier error?!

by aminoacid on Thu Jun 07, 2012 12:32 pm

to bad the datasheet doesnt reveal stuff for a substitute...

and the pinouts cant work with the pin out of the 303 and 606 schemtics...

i have a 606. but i dont have instruments for measuring the coil...
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Re: bridge rectifier error?!

by evostars on Thu Jun 07, 2012 1:01 pm

aminoacid wrote: but i dont have instruments for measuring the coil...

Buy one! Ive got one that measures c 's as well.
Straight from china :-)
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