bridge rectifier error?!
Moderators: Altitude, adafruit_support_bill, adafruit, phono, mome rath

bridge rectifier error?!

by evostars on Mon May 28, 2012 12:01 pm

I just started building the power supply, and I saw strange voltages.
After inspecting the schematic I saw the bridge rectifier is incorrect!

The AC is bypassing the rectifier, and going straight to the -pole of c5; the+ of c3 ;and INput of 7805
... that's messed up. I'm reading voltages of 30V over 16V rated condensators...

So I will correct the rectifier. See pictures....

Any comments?
Attachments
bridge original.jpg
bridge original.jpg (45.6 KiB) Viewed 2578 times
bridge modded.jpg
bridge modded.jpg (46.7 KiB) Viewed 2578 times
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm

Re: bridge rectifier error?!

by evostars on Mon May 28, 2012 12:52 pm

this should fix it.
It connects - of C5 to ground,
and connects the + of C2, c3 c4 7805 and 7806 to +C5

This way the rectifier works proper...
Attachments
cut and retrace.jpg
cut and retrace.jpg (114.5 KiB) Viewed 2575 times
cut trace.jpg
cut trace.jpg (99.2 KiB) Viewed 2575 times
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm

Re: bridge rectifier error?!

by gompie on Mon May 28, 2012 2:44 pm

I came to the same design change earlier this year, because I was not happy with the voltage over the 25V spect C's.

I thought it was a fault in the schematics, but I actually went back to the original design (so I undid the applied changes, the changes you show in your foto's)

It occurred to me that the reason of the two separate outputs of the rectifier instead of one is the following:
IC23 has a max Vcc of 32 Volts. My guess is that the designer of the 303 wanted to be close to that voltage.
To get to this voltage with just a 9V AC power supply is done by stacking two C's on top of each other.
The C's I mention are C3 and C5. If you measure those separately, you see the same voltage over them.
Since they are on top of each other (only one is connected to ground) the voltage is doubled.

Now, the voltage over C8, C7, and C5 should indeed not be higher than what they were designed for.
What could be wrong? The only variable I could think of is the chinese power supply I got with my kit.
This power supply says 9V AC. I measured this and found that it was actually close to 11.
Then take into account that the voltages are doubled after the rectifier because of the design, and you end up with a way to high voltage over the mentioned C's!

The thing I changed was my AC power supply. I found a transformer (8,5V) to check my theory, and all voltages are within limits.

I am not saying you did anything wrong by applying the change you mentioned, I just think the 'fault' in the design was intended.

Take care that the IC23 needs at least 14V (considering possible power fluctuations) to get to the 12V output (2Volt drop) and the 5.333V which is responsible for the tuning (!!!). You don't want to affect the tuning unwillingly (I recon)....

If you have any trouble with the 5.333V, let me know, I've got a theory about why some kits are off tune.
I fixed mine anyways.

Good luck with the rest of the build!

Cheers
gompie
 
Posts: 28
Joined: Mon May 28, 2012 2:07 pm

Re: bridge rectifier error?!

by machine.cuisine on Mon May 28, 2012 2:47 pm

wow. I have not built an x0xb0x, but this does seem strange. are you referring to a classic 'diode bridge'? like this:
diode bridge w cap.PNG
diode bridge w cap.PNG (6.55 KiB) Viewed 2563 times


if so, it would appear that you are correct in that the x0xb0x does not follow this design.

what voltages were you reading at top and bottom of C5?
machine.cuisine
 
Posts: 9
Joined: Tue May 15, 2012 6:59 pm

Re: bridge rectifier error?!

by machine.cuisine on Mon May 28, 2012 2:54 pm

gompie wrote:I came to the same design change earlier this year, because I was not happy with the voltage over the 25V spect C's.

I thought it was a fault in the schematics, but I actually went back to the original design (so I undid the applied changes, the changes you show in your foto's)

It occurred to me that the reason of the two separate outputs of the rectifier instead of one is the following:
IC23 has a max Vcc of 32 Volts. My guess is that the designer of the 303 wanted to be close to that voltage.
To get to this voltage with just a 9V AC power supply is done by stacking two C's on top of each other.
The C's I mention are C3 and C5. If you measure those separately, you see the same voltage over them.
Since they are on top of each other (only one is connected to ground) the voltage is doubled.

Now, the voltage over C8, C7, and C5 should indeed not be higher than what they were designed for.
What could be wrong? The only variable I could think of is the chinese power supply I got with my kit.
This power supply says 9V AC. I measured this and found that it was actually close to 11.
Then take into account that the voltages are doubled after the rectifier because of the design, and you end up with a way to high voltage over the mentioned C's!

The thing I changed was my AC power supply. I found a transformer (8,5V) to check my theory, and all voltages are within limits.

I am not saying you did anything wrong by applying the change you mentioned, I just think the 'fault' in the design was intended.

Take care that the IC23 needs at least 14V (considering possible power fluctuations) to get to the 12V output (2Volt drop) and the 5.333V which is responsible for the tuning (!!!). You don't want to affect the tuning unwillingly (I recon)....

If you have any trouble with the 5.333V, let me know, I've got a theory about why some kits are off tune.
I fixed mine anyways.

Good luck with the rest of the build!

Cheers


the power configuration of the x0xb0x wasn't in the original 303. It used DC from an external transformer/adapter (or DC from batteries).

I'm not following your 'stacked capacitor' bit.

and every AC transformer (that I've ever looked at) puts out an unloaded voltage greater than what it's rated at. also, the 9V rating is an RMS value. if you multiply 9V by the square root of 2, you will get your measured 11V (roughly). actually it should be more like 12.5 VAC peak.
machine.cuisine
 
Posts: 9
Joined: Tue May 15, 2012 6:59 pm

Re: bridge rectifier error?!

by evostars on Mon May 28, 2012 3:37 pm

I do follow the stacked c story, but it seems no good.
Ac is bleeding through...
My 16V caps had 18V over it ... Now its around 14. Better in my eyes.

The adaptor has a 220V rating but we have 235V from the wall... So the 9V is actually 11.4VacI will buy a 230 V 9V ac adaptor to save my elco's.

Anyway I did the mod, and tested it. Everything seems fine now. Still bit vlose to max V for the caps, but the new adaptor will fix that.

Actually I had a 5.333V problem, but i fixed it by replacing R5 with a wire.

The 6562 opamp now gets 14.35V. This will drop with a new adaptor. ... Maybe keep this adaptor...

Hmm this isn't perfect yet
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm

Re: bridge rectifier error?!

by evostars on Mon May 28, 2012 3:43 pm

C5 has 14.75v dc over it. Its rating is 16v. Its close. And i preffer 70% of the max V. But i guess I'll keep it like that, or maybe change them voor 25v rating....
That would be the best solution, but size does matter.
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm

Re: bridge rectifier error?!

by machine.cuisine on Mon May 28, 2012 3:45 pm

concerning transformers/adapters:
Are you measuring RMS AC or peak AC? Because peak will always be 1.4 times greater than the rated V RMS. And when it's loaded, it will be a bit less (like you're seeing 11.someting)

I don't think a 230V vs a 220V will make a difference. Like I said, make sure you know what you're measuring. And remember that an unloaded voltage will be greater than a loaded one.

regarding the circuit, I think that you're right - there is something wrong with the schematic/layout. C5 is merely in parallel with a diode and is seeing the respective 'negative' side of the AC. the other caps and the regulator are seeing this AC, too. I don't think this is proper circuitry.
Last edited by machine.cuisine on Mon May 28, 2012 3:51 pm, edited 1 time in total.
machine.cuisine
 
Posts: 9
Joined: Tue May 15, 2012 6:59 pm

Re: bridge rectifier error?!

by evostars on Mon May 28, 2012 3:51 pm

machine.cuisine wrote:concerning transformers/adapters:
Are you measuring RMS AC or peak AC? Because peak will always be 1.4 times greater than the rated V RMS. And when it's loaded, it will be a bit less (like you're seeing 11.someting)

I don't think a 230V vs a 220V will make a difference. Like I said, make sure you know what you're measuring. And remember that an unloaded voltage will be greater than a loaded one.

Yes rms, tested with the wall outlet, 233V ac...
And adaptor is 11.3 V ac under load of the regulators and the opamp
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm

Re: bridge rectifier error?!

by machine.cuisine on Mon May 28, 2012 4:04 pm

before modified, what was the voltage at the input of the 5V regulator IC20?
machine.cuisine
 
Posts: 9
Joined: Tue May 15, 2012 6:59 pm

Re: bridge rectifier error?!

by evostars on Mon May 28, 2012 4:24 pm

machine.cuisine wrote:before modified, what was the voltage at the input of the 5V regulator IC20?

Around 18 but im not sure, could be 22
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm

Re: bridge rectifier error?!

by gompie on Mon May 28, 2012 4:36 pm

evostars wrote:I do follow the stacked c story, but it seems no good.
Ac is bleeding through...
My 16V caps had 18V over it ... Now its around 14. Better in my eyes.

The adaptor has a 220V rating but we have 235V from the wall... So the 9V is actually 11.4VacI will buy a 230 V 9V ac adaptor to save my elco's.

Anyway I did the mod, and tested it. Everything seems fine now. Still bit vlose to max V for the caps, but the new adaptor will fix that.

Actually I had a 5.333V problem, but i fixed it by replacing R5 with a wire.

The 6562 opamp now gets 14.35V. This will drop with a new adaptor. ... Maybe keep this adaptor...

Hmm this isn't perfect yet


I read in another post that you changed the 25V caps to 16V, why would you do that??
The walloutlet voltage could be the cause for a higher output voltage on a adapter that was designed for 220V, good thinking!
14,35V is a bit low on the opamp. if you take a look at the specs of the opamp, you see that there is a 2V difference between the power supplied to the opamp and its output.
Since you need the 12V on the output of the opamp, 14,35V is quite critical.
gompie
 
Posts: 28
Joined: Mon May 28, 2012 2:07 pm

Re: bridge rectifier error?!

by gompie on Mon May 28, 2012 4:45 pm

evostars wrote:I do follow the stacked c story, but it seems no good.
Ac is bleeding through...
My 16V caps had 18V over it ... Now its around 14. Better in my eyes.

The adaptor has a 220V rating but we have 235V from the wall... So the 9V is actually 11.4VacI will buy a 230 V 9V ac adaptor to save my elco's.

Anyway I did the mod, and tested it. Everything seems fine now. Still bit vlose to max V for the caps, but the new adaptor will fix that.

Actually I had a 5.333V problem, but i fixed it by replacing R5 with a wire.

The 6562 opamp now gets 14.35V. This will drop with a new adaptor. ... Maybe keep this adaptor...

Hmm this isn't perfect yet


AC is bleeding through? Thats not because of the voltage doubler (stacked C's). The problem is the too high voltage over the Elco, it cannot simply do it's work its meant to do. Please try a new adapter/transformer.
gompie
 
Posts: 28
Joined: Mon May 28, 2012 2:07 pm

Re: bridge rectifier error?!

by gompie on Mon May 28, 2012 4:48 pm

evostars wrote:
machine.cuisine wrote:before modified, what was the voltage at the input of the 5V regulator IC20?

Around 18 but im not sure, could be 22


any voltage above 5V will do. the regulator will put the rest into heat anyways...
gompie
 
Posts: 28
Joined: Mon May 28, 2012 2:07 pm

Re: bridge rectifier error?!

by evostars on Mon May 28, 2012 4:51 pm

Change 16v to 25v c's i meant.
Ac bleed: i mean its connected straight to the ac of the adaptor.
evostars
 
Posts: 110
Joined: Sun May 13, 2012 8:35 pm