SEPIC converter possible design?

Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
hi,
It is looking close to being finished.
Check what the switcher datasheet says about linking the SS pin
The component drill thru hole should be 1mm dia

For the switcher and surface mount components, how do you intend making the track contact from non side to comp side.???
Corrected the SS pin link.

E
EDIT: the usual way is a pad on both sides, with a1mm dia hole, solder in a copper wire link thru.

When doing PCB design layout you should have 3 dimensional model in your mind.
Hello E,

Is the SS pin necessary? The datasheet says for normal operations, I can either tie it to Vin or leave it floating. At the moment, i just have it floating.

All the components and traces i have on the layout are placed on the top layer of the PCB. There are no traces on the other side. I plan to put the through hole components in their respective slots and solder them in from under the board.
Am i missing something? o_O

J
 

ericgibbs

Joined Jan 29, 2010
18,993
hi J,
I assume that the Blue track is on the component side of the PCB and the Green track is on the non component side.?
Which means all the through hole components can soldering at the non comp side.?


Hi Eric,
Oh yes, all through holes will be soldered from the bottom layer of the PCB. ( All components are placed on top layer )

Hello E,
All the components and traces i have on the layout are placed on the top layer of the PCB. There are no traces on the other side. I plan to put the through hole components in their respective slots and solder them in from under the board.
Am i missing something? o_O
hi J,
If the pad holes are not plated thru [PTH] how will you be sure that when you solder the component wire, on the non component side, that the solder will make an electrical contact with the component side pad.????? which has the component side track connected to it.

In my experience it will not.

Look at this link.
https://electronics.stackexchange.com/questions/232595/why-are-through-holes-plated-in-pcbs
 
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Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
hi J,
If the pad holes are not plated thru [PTH] how will you be sure that when you solder the component wire, on the non component side, that the solder will make an electrical contact with the component side pad.????? which has the component side track connected to it.

In my experience it will not.

Look at this link.
https://electronics.stackexchange.com/questions/232595/why-are-through-holes-plated-in-pcbs
Hi E,
Ah okay. I can't seem to add pads on the bottom layer of the board, i'm getting errors in DRC.

I've updated the PCB design with track width of 1mm for all power traces and 0.5mm for signal traces.

J
 

ericgibbs

Joined Jan 29, 2010
18,993
Ah okay. So if i were to route all the through hole components using bottom layer trace, that would be easier?
hi J,
It would be easier and more reliable.
Don't forget to put some round thru hole pads on the PCB, that can be used to link one side/face of the PCB track to the other, thats for the surface mount components.
Do you follow OK or do want a sample image.?
E

EDIT:
I see that you are trying to use the small RED pads to do that.

EDIT2:
If those large copper areas are for heat sinking, ensure that the wire link thru does not cause an air gap.
 
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Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
hi J,
It would be easier and more reliable.
Don't forget to put some round thru hole pads on the PCB, that can be used to link one side/face of the PCB track to the other, thats for the surface mount components.
Do you follow OK or do want a sample image.?
E

EDIT:
I see that you are trying to use the small RED pads to do that.

EDIT2:
If those large copper areas are for heat sinking, ensure that the wire link thru does not cause an air gap.
Hi E,

Actually i just realized that was a mistake, i tried to flip the board, but it flipped all the components and added vias underneath.
Is this what you meant?

J
 

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ericgibbs

Joined Jan 29, 2010
18,993
hi,
That should do it.
The other small point is the SMD caps will not look 'neat' on top of wire link thru.
Are you planning to fill the untracked area of the non component side with copper.?
If so, leave a gap along side the non ground track and the fill copper.

Always double check the schematic against the copper track, its easy to make a mistake while you have been adjusting the track layout.
E
 

Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
hi,
That should do it.
The other small point is the SMD caps will not look 'neat' on top of wire link thru.
Are you planning to fill the untracked area of the non component side with copper.?
If so, leave a gap along side the non ground track and the fill copper.

Always double check the schematic against the copper track, its easy to make a mistake while you have been adjusting the track layout.
E
Hi E,

All my caps are through hole. If it isn't necessary, i don't plan to.
I hope this does it.

J
 

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Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
Hi J,
Let us know your project final test results.

E
Hey Eric,
Hope you're doing fine. My PCB is being manufactured and i have a few questions regarding my circuit.

I realised that i miscalculated the inductance needed, i have 10uH on L1 and L2. and after i recalculated using the guide from http://www.ti.com/lit/an/slyt309/slyt309.pdf . I need 80uH instead. What changes would happen if i changed my inductors to 100uH ones?

Also, during the time of testing with varying load, to obtain 9Vout, my potentiometer was set to 45K.
However in the test using LTspice, to obtain 9Vout, the potentiometer had to be 33K.
What could be the reason?

I have attached the files showing the differences.

Regards,
J
 

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ericgibbs

Joined Jan 29, 2010
18,993
However in the test using LTspice, to obtain 9Vout, the potentiometer had to be 33K.
What could be the reason?
hi J,
This could be due to the LTSpice simulation model parameters not being exactly the same at the actual switcher.
In most IC circuits, like the LT1370 the datasheet quotes min/typical/max parameters in the electrical characteristics.

I will run some LTS sims using 100uH inductors.
E

EDIT:
Initial checks with 100uH inductors shows little difference, do you have the inductor coil resistance.??
 
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Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
hi J,
This could be due to the LTSpice simulation model parameters not being exactly the same at the actual switcher.
In most IC circuits, like the LT1370 the datasheet quotes min/typical/max parameters in the electrical characteristics.

I will run some LTS sims using 100uH inductors.
E

EDIT:
Initial checks with 100uH inductors shows little difference, do you have the inductor coil resistance.??
Hi E,

I have the datasheet. I'm thinking of replacing it with this 100uH ones, just so when i write my report, i have the calculations to back up the decision. Would this one do?

My test comparing the 10uH and 100uH only shows differences in the current going through it. With the 10uH, i get a sinusoidal wave of +0.3A to -0.9A.
With the 100uH, it goes from +3A to -3A.

J
 

Attachments

ericgibbs

Joined Jan 29, 2010
18,993
hi,
This what I get using 10u, 80u and 100uH inductors, with a 0.79R internal resistance. [from d/s]
Using a 36R load for 250mA Iout.
Looks fine to me.
I will check the actual current waveforms later.
E

EDIT:
This 2nd sim shows the current thru the inductor L1 for the 3 coil inductance values.
 

Attachments

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Thread Starter

Senorjohnny

Joined Feb 18, 2018
47
hi,
This what I get using 10u, 80u and 100uH inductors, with a 0.79R internal resistance. [from d/s]
Using a 36R load for 250mA Iout.
Looks fine to me.
I will check the actual current waveforms later.
E

EDIT:
This 2nd sim shows the current thru the inductor L1 for the 3 coil inductance values.
Hi Eric,

Wow thank you for the help. I will replace my 10uH inductor in this case.
I will update you with the final results when my pcb arrives.

Regards,
J
 
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