LM25184-Q1: LM25184-Q1 (LM25184QNGURQ1), Data Sheet, Typical Applications - Design1- Recommended Transformers

Cvetan Marinov

Part Number: LM25184-Q1
Other Parts Discussed in Thread: LM25184

Hello Dear TI Team,

In Data Sheet of LM25184-Q1 device (SNVSBJ6A – MARCH 2020 – REVISED AUGUST 2020, https://www.ti.com/lit/gpn/lm25184-q1),

in subsection 8.2 Typical Applications, 8.2.1 Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 12 V, 1 A, Table 8-2. specifies three suitable transformers:

COILCRAFT ZA9672-BE

SUMIDA 12387-T162

WUERTH 750318701

The following questions occurred:

1. Are the transformers from Table 8-2 most efficient and suitable for the case when Vin_nom=24V?

2. Do you recommend the same transformers as per Table 8-2 for the case when Vin_nom=12V?

The overall design goal is to use one and the same transformer for the full range Vin=6V to 42V, while Vout=12V and Iout_max=1A.

3. Are the transformers from Table 8-2 tested by TI?

3.1. On what Board have these transformers been tested?

3.2. Did the test include high ambient temperature or the tests had been performed at room temperature only?

10 months ago

0 Frank De Stasi 10 months ago

TI__Guru 57555 points

Hello

Your application is the same as shown in figure 8.1 of the data sheet. The BOM is shown in figure 8.2.

Any of the transformers listed in those table will work. They have all been tested.

Also, the EVM for the LM25184 is configured for your application. That is the test bench that was used by TI.

Testing was done at room temperature only.

Keep in mind that you will not be able to get the full 1A at 6Vin.

I have attached the calculator tool for this device as well as the user guide for the EVM for your convenience.

Thanks

4300.snvu680.pdf

6354.LM(2)518x PSR flyback converter quickstart tool revB.xlsx

0 Cvetan Marinov 10 months ago in reply to Frank De Stasi

Prodigy 50 points

Hello Dear Frank,

Thank you a lot for your response and for provided files!

Of course I had them previously.

Yes, sure, it is clear that I_Load=1A cannot be achieved at Vin=6V, not at all.

The main issue remains that the flyback transformer generates heat in excess and

considering that the operating temperature is around 95-120 Degrees Celsius.

Best regards,

Cvetan Marinov

0 Frank De Stasi 10 months ago in reply to Cvetan Marinov

TI__Guru 57555 points

Hello

You will need to find out from the transformer vendor what temperature rise you can

expect and see if it will work with your ambient.

Thanks

0 Cvetan Marinov 10 months ago in reply to Frank De Stasi

Prodigy 50 points

Hello Dear Frank,

Regarding LM25184-Q1 application with single output transformer, there is a heat issue with the primary winding zener clamp diode.

The operating conditions are as follows

Vin=12V

Vout_set=11.5V (RFB=120k)

I_out=0.4A

Tamb=25 Deg C

Transformer: 7uH, 0.6uH (leakage), 1:1, DCR _Pri=56mOhm, DCR_SEC=65mOhm

Cin=100uF ALU

Cout=47uF ALU

Dclamp (Transformer primary winding clamp) - TVS: Vbr=18.8V to 22V, DO-219AB similar, Ppeak=200W,

In series to Dclamp there is 60V 3A Schottky Diode in DO-214AC package

Dclamp is dissipating in excess - over 100 Deg C

Could you suggest any reason for such overheating of Dclamp diode?

Best regards,

Cvetan Marinov

0 Frank De Stasi 10 months ago in reply to Cvetan Marinov

TI__Guru 57555 points

Hello

What is the normal flyback voltage across the primary ?

It may be that the diode needs more heat sink.

Be sure that the diode and TVS are oriented correctly.

Thanks

0 Cvetan Marinov 10 months ago in reply to Frank De Stasi

Prodigy 50 points

Hello Dear Frank,

Thank you!

Regarding the voltage across the primary transformer winding - I will share the value next Week, hopefully.

Regarding the TVS diode insufficient cooling there is the same feeling here - the current-in-use TVS clamping diode (Dclamp) in not being cooled down effectively, so I am thinking to replace it with 18V-20V power (>1W) Zener Diode as you recommend in the LM25184-Q1 Data Sheet as well as in the LM252184 EVM User Guide.

Clamping Diode and clamping TVS are connected correctly, even there is a RC snubber circuit in parallel to them: 91Ohm 330pF.

Best regards,

Cvetan Marinov

0 Frank De Stasi 10 months ago in reply to Cvetan Marinov

TI__Guru 57555 points

Hello

I think it is a good idea to replace with a Zener.

Thanks

0 Frank De Stasi 9 months ago in reply to Frank De Stasi

TI__Guru 57555 points

Hello

I will close this post due to inactivity.

Thanks

0 Cvetan Marinov 9 months ago in reply to Frank De Stasi

Prodigy 50 points

Hello Dear Frank,

The measurements with the new components (arrival expected the next days), including a new transformer, are still forthcoming. Probably you could hold a little bit the closure procedure?

Best regards,

Cvetan Marinov

0 Frank De Stasi 9 months ago in reply to Cvetan Marinov

TI__Guru 57555 points

Hello

I will assign this to the engineer in charge of E2E for July.

Thanks

0 Cvetan Marinov 9 months ago in reply to Frank De Stasi

Prodigy 50 points

Ok.

Dear Frank, Thank you a lot, for your high level of expert support!

Best regards,

Cvetan Marinov

0 Ryan Wicklund 9 months ago in reply to Cvetan Marinov

TI__Intellectual 1360 points

Hello Cvetan,

Due to the US holiday, responses may be delayed. Our team will get back to you soon.

0 Cvetan Marinov 9 months ago in reply to Ryan Wicklund

Prodigy 50 points

Hello Ryan, Happy 4th of July!

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LM25184-Q1: LM25184-Q1 (LM25184QNGURQ1), Data Sheet, Typical Applications - Design1- Recommended Transformers