Issues in my design

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Hi,

There seems to be some issue with our design Could you guide me in the resolution. We didnt get the correct output on 12V5A-18V2A SMPS. In 12V side we are getting 2.1V to 2.2V(varying) In 18V side we are getting 0.5V to 3.5V(Varying) The Sch doc and transformer winding details are attached. In our analysis the problem appears to be with the transformer. I Hope you can give me a correct solution.

 

Transformer: 18V2A12V5A

Items used: 1) Bobbin: EI35 (v) 12 Pins 2) Core: HP400 or equivalent Winding 

Testing specifications: 1) Inductance (at 1kHz/0.3V) : Pins :1-3/L=290uH+/-10%

 

 

Winding

Start pin

Finish pin

 Turns

No of wires.

Wire size(mm)

Direction of wdg

Tape

(No. of layers)

Remarks

W1

3

2

16

2

24AWG

C.W

3

 

W2

5

4

03

2

25AWG

C.W

3

 

 

                   3MM MARGINE TAPE

3

 

W3

8,9

10

03

4

24AWG

C.W

3

 

W4

11

8,9

01

3

26AWG

C.W

3

 

W5

2

1

15

2

24AWG

C.W

3

 

 

Attachmentサイズ
Sch design587.5 KB

Dear Nandu,

Thank you for using power integrations.

Please clarify what IC you are using.
Also, we encourage you to make use of our online tools as these are the most updated.
We have not rolled out updates on our standalone PIXls for quite some time now.
It will also help if this comes with a schematic.
From you illustration, it seems like this one is an AC-stack design.
We need to see the IC you are using. What semiconductors you are using in your schematics
and how they are connected.

https://piexpertonline.power.com/site/login
In as much as we would like to help, we need inputs from you as well.

Regards,
Thorin

You mentioned that the problem appears to be with the transformer - can you provide us details about this? I would recommend the following troubleshooting steps.
1. Make sure that the voltage across the input capacitor is correct
2. Are the transformer pins soldered properly - if yes, does the input capacitor voltage appear across the drain-source pins of the TOPSwitch?
3. Is there switching on the TOPSwitch drain-source terminals?
4. Make sure that the V-pin is not floating
5. The C-pin should have a voltage between 4.8-5.8V for the TOPSwitch to function properly
6. Do you see an Auto-Restart? (Refer to the datasheet for description)
7. Ensure proper polarity of the components
8. Is the problem load-dependent?

We noticed that the transformer winding description has 2 less turns on the primary winding as compared to the recommendation provided by PI Expert. This is just an observation and unlikely the issue causing failure to regulate.