Help to design a PCB for my PI design!

[Aziz]

But the diode in series with the MOSFET compensate it. Doesn't it?

1843

No, this wouldn't help much.

Try replacing the 7660 with a discrete BJT DC/DC converter or mosfet driver IC DC/DC converter. This will definitely help.
Aziz

[1843]

I found the best way! Using a totem-pole (same as the gate driver) DC converter instead of the backlight controller for supplying the preamp.
100% synced!


The backlight controller is not critical.

Best regards,
1843

[1843]

I tested the above circuit. Not real improvement I observed. The 7660 noise is still there...affecting the preamp.

Regards,
1843

[hobbes_lives]

Are you sure the noise is coming from the supply and is not from the micro? I had allot of problems with digital signal noise affecting the analog circuits in my design.

[1843]

Are you sure the noise is coming from the supply and is not from the micro? I had allot of problems with digital signal noise affecting the analog circuits in my design.

Yes! the noise is about 10KHz. BTW the before prototype PCB wasn't like this...
I will design a PCB... If I get free time.

Best regards,
1843

[porkluvr]

porkluvr,
Thanks a lot for the schematic.
There are some errors in the schmatic:
Best regards,
1843

I wasn't intending any components changes but It was late (and it's late now). No excuse, but I was tired.

About your voltage converter noise,
Try making a pi filter on the charge pump output by adding one L and one C, between charge pump and the 7805.
68uH and 220uF might work but the best combination would depend on your clock frequency and how much noise is too much. I can offer no mathematical analysis for selecting the best component values.

It's late again. (big yawn)

[1843]

OK porkluvr, I'm going to do some experiments...

Best regards,
1843

[Qiaozhi]

Yes! the noise is about 10KHz. BTW the before prototype PCB wasn't like this...
I will design a PCB... If I get free time.

Best regards,
1843

I doubt very much that the noise is due to the PCB layout.

Have you tried disconnecting the power supply circuit and hooking the PI up to a bench supply? Or you could simply disable the 7660, and feed the 7805s from a second 12V source. That will confirm if the noise is actually due to the 7660.
It the noise is still there, then it could be due to ground bounce caused by the ATMega8.

[1843]

Yes, I used a bench supply instead of the 7660. The noise faded away.But still the PI is somewhat instable even without coil.

The noise of 7660 doesn't affect the performance much. It's constant and averages out by the software.

The instability at the moment is most likely due to the PCB. I still need some more experiments...like disabling the sound...

Best regards,
1843

[Qiaozhi]

Yes, I used a bench supply instead of the 7660. The noise faded away.But still the PI is somewhat instable even without coil.

The noise of 7660 doesn't affect the performance much. It's constant and averages out by the software.

The instability at the moment is most likely due to the PCB. I still need some more experiments...like disabling the sound...

Best regards,
1843

Could you try adding a small wire jumper between pins 8 and 22 on the micro to improve the connection between the two ground pins?

[1843]

I found the problem of the instability.... 79L05...
It's very late here I cannot stay awake anymore...

...

[Götz von Berlichingen]

When using 78xx or 79xx, i always add 100nF Capacitors at Input and Output.
Without them, i get low Output Voltage or the Thing starts Oscillating.

[Qiaozhi]

When using 78xx or 79xx, i always add 100nF Capacitors at Input and Output.
Without them, i get low Output Voltage or the Thing starts Oscillating.

That's a good point. I always do the same.
In fact the datasheet states that the capacitor on the output improves stability and transient response.

[1843]

Hi all,

After a lot of experiments... the schematic was updated:



Because of using LP filters, the 7660 noise is reduced more than 50%.

Now you only need a PCB to build this PI.

Kind regards,
1843

[Unregistered]

Sync 7660 ; pin 7 to PB1 through some buffer.