PCB problem with voltage

sparky 1

Joined Nov 3, 2018
500
The PCB could be alright maybe.
Working with the decoupling caps would begin to show certain wave shaping.
the blue might be acceptable possibly more capacitance would be going beyond what was needed
in this example for the given load.

image_2021-03-19_100410.png
 

Thread Starter

camerart

Joined Feb 25, 2013
2,436
The PCB could be alright maybe.
Working with the decoupling caps would begin to show certain wave shaping.
the blue might be acceptable possibly more capacitance would be going beyond what was needed
in this example for the given load.

View attachment 233160
Hi S,
Can you clairify please?
Are you talking about PCB6 that the initial question is about? So If I added the suggested decoupling capacitors, then it whould work.
NOTE: I made two PCB6s. The one with the fault, and one I abandoned for some reason? previously, which worked ok, and didn't have any Capacitors on yet (But it's not going to be used) as I'm adding the suggested Caps, on PCB7.
C
 

Thread Starter

camerart

Joined Feb 25, 2013
2,436
If that is true, the 5V reg needs a heatsink with less than 10C/W thermal resistance.
The copper pad on the PCB is not enough.
Hi E,
The 7805s I have just received are TO220 through the hole types, so I can add any heatsink necessary.
Thanks.
C
 

sparky 1

Joined Nov 3, 2018
500
Hi S,
Can you clairify please?
Are you talking about PCB6 that the initial question is about? So If I added the suggested decoupling capacitors, then it whould work.
NOTE: I made two PCB6s. The one with the fault, and one I abandoned for some reason? previously, which worked ok, and didn't have any Capacitors on yet (But it's not going to be used) as I'm adding the suggested Caps, on PCB7.
C
The power supply that I was looking at starts with 9V ...
https://ww1.microchip.com/downloads/en/DeviceDoc/Explorer_16_32_Schematics_R6_3.pdf

I looked briefly at the two commercial development boards for the old 18F4 series 40 pins very complex.

I was hoping the picture could be compared to what you had PCB6 but I see you are moving a fast pace.
it is not easy to talk about either of those boards without a detailed study and history, a lot of work.
The 4431 secondary internal osc 125kHz might be problem I am really not sure.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,436
The power supply that I was looking at starts with 9V ...
https://ww1.microchip.com/downloads/en/DeviceDoc/Explorer_16_32_Schematics_R6_3.pdf

I looked briefly at the two commercial development boards for the old 18F4 series 40 pins very complex.

I was hoping the picture could be compared to what you had PCB6 but I see you are moving a fast pace.
it is not easy to talk about either of those boards without a detailed study and history, a lot of work.
The 4431 secondary internal osc 125kHz might be problem I am really not sure.
Hi S,
"Fast pace" Your the first person to say that :)

I looked at your PDF, but could see anything that would change things, but I'm not best at circuits.

I think one of the PCB6, had a fault, I can't remember what it was, and it maybe on the 18LF4620 PIC side, leaving the 4431 working ok, as previous messages, and it was scrapped anyway. The second, which is the one that caused this thread also has a fault, so after all the above tests, it's better to make another PCB, (7) with the suggestions on. It should work ok, so best wait till I get results. I'm just finalising the SCH, then I'll make one.
Thanks,
C
 

sparky 1

Joined Nov 3, 2018
500
The pdf ( one of microchip's) later power supply designs reflects design changes for later chips.
You still have to work backwards correcting for all the old chips so having feelings of disgust and frustration
at times using a coping strategy of starting fresh. The other comments on thermal and load are good
possibly improvement on the latest power supply design will be a decision of cost and PCB improvement.
The numbers of layers and parts density would be a different department.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,436
The pdf ( one of microchip's) later power supply designs reflects design changes for later chips.
You still have to work backwards correcting for all the old chips so having feelings of disgust and frustration
at times using a coping strategy of starting fresh. The other comments on thermal and load are good
possibly improvement on the latest power supply design will be a decision of cost and PCB improvement.
The numbers of layers and parts density would be a different department.
Hi S,
None of the previous 6PCB iterations, had this latest fault, so for now, I'll put it donw tomy poor etching, and we'll see if it occures again.

I think I'm following that PDF information, from all of the suggestions.

I don't get so frustrated, lately, it's just a hobby, so to start a new one with all of the ideas, I get from this and other forums, is great, so I don't think too much about it.
Cheers, C
 

Danm1

Joined Jul 19, 2010
69
Hi D,
Why do you say that?
C
Hello C,

I just looked at the initial scope screen and the thought came to mind, I admit I did not read all the other replies nor is my comment one arrived at thru careful analysis. It was off the cuff.
Sorry for not offering a better analysis,
D
 

Thread Starter

camerart

Joined Feb 25, 2013
2,436
Hello C,

I just looked at the initial scope screen and the thought came to mind, I admit I did not read all the other replies nor is my comment one arrived at thru careful analysis. It was off the cuff.
Sorry for not offering a better analysis,
D
Hi D,
Fine, thanks.
C
 

Thread Starter

camerart

Joined Feb 25, 2013
2,436
Hi,
Regarding the comments on heatsinks etc.
I watched a video about Thermal jumpers: https://www.electronicproducts.com/thermal-jumper-reduces-component-temperature-by-over-25/ which was interesting, especially if there is little space. These components, have almost no resistance, meaning that they can go through slots in the PCB and connect layers together thermally. 'Say' a hot voltage regulator head pad, down to the GND plane.

As I have space, and noting the 1oz 2oz comments, I can add a heatsink to a small pad around the 3.3V REGs, if necessary.
C.
 
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