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PTH08T240W: Relation about efficiency and transformer

Satoshi
Guru 19485 points
Part Number: PTH08T240W

Customer is testing PTH08T240WAZ for 33℃ condition by thermostatic chamber.

In the case of output current, ①2.33A and ②1.36A.

(Vin: 12V→Vout:5V)

Customer is measured temperature to transformer by thermocouple.

(Condition is continuous 3 hour) 

As a result, ② is increased higher than ①.

⇒①：58℃ and ②：62℃

My question is, please let me know about technical reason for ② higher temperature.

I think that larger current should increase higher temperature.

I want to know why temp result became reverse. 

（Lower Iout, Higher transformer heat?）

Best regards,

Satoshi

  • 0
    TI__Mastermind 28020 points

    You are correct, the device with higher current should run hotter as long as the layout is the same and the ambient is the same.

    Do both sockets have the same layout? Are they both on the same board?

    Another reason for the difference in temperatures could be the thermocouple connection. Make sure both connections are the same and making good contact.

  • 0 in reply to J Arrigo
    Guru 19485 points
    Arrigo-san

    Thank you reply,

    I confirmed to customer below;
    ・These socket are same layout and circuit.
    ・Thermocouple contact is good, and accuracy is 1%(T-type).

    I calculated power dissipation(Pd) below, it feel Pd difference are very small.
    ※Efficiency is referenced by datasheet graph.
    ①Iout: 2.33A
    Vin: 12V → Vout: 5V
    Pin: 13.24W ～ eff: 88% ～ Pout: 11.65W
    ⇒ Pd: 1.59W

    ②Iout: 1.36A
    Vin: 12V → Vout: 5V
    Pin: 8.3W ～ eff: 82% ～ Pout: 6.8W
    ⇒ Pd: 1.5W

    Sorry for additional question, above efficiency is 25℃ condition.
    Customer condition is 33℃ and I guess efficiency is change depend on temperature.
    Is there relation data(graph) for efficiency and temperature?

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    Guru 19485 points
    Any update on this for additional question?
    Is is better if I make new thread on E2E?

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Mastermind 28020 points
    The efficiency does change over temeprature, however from 25C to 33C I do not expect a noticable change. The typical characteristic graphs in the datasheet are accurate for these conditions.