Transformer Heating and 5V Output Drop

Question

Subject: Transformer Heating and 5V Output Drop in Eval Board Design 
 Hi everyone, 
 I am using a 500 kHz transformer with 5v 2A output (Part #:750315945) instead of T2 in the evaluation board schematic design. 
 I noticed the following behavior:

The transformer gets noticeably hot.

The 5V output drops when the LCD current exceeds approximately 0.45 A.

The transformer also generates audible noise.

I would like to understand:

What could be causing the transformer heating and output voltage drop?

Is the audible noise related to transformer saturation, switching frequency, or another issue?

Could this indicate that the selected transformer is not suitable for this operating condition?

Any guidance would be appreciated.

charlyelkhoury · Accepted Answer

The behavior your are describing (transformer heating, output voltage drop above ~0.45A, and audible noise) strongly indicates that the transformer is being operated outside its intended magnetic limits—most likely approaching core saturation. In a forward converter using the MAX17599, the transformer must be specifically designed for the operating conditions (input voltage range, duty cycle, switching frequency, and active-clamp reset). If parameters such as turns ratio, magnetizing inductance, or core size are not properly matched, excessive magnetic flux can occur. This leads to: Increased magnetizing current and losses → heating Loss of efficient energy transfer → output voltage droop Mechanical vibration of the core/windings → audible noise Based on these symptoms, it is very likely that the selected transformer is not suitable for this application or operating point. A transformer designed specifically for this topology and power level (such as the one used in the evaluation board) is recommended to ensure proper performance and reliability.)

charlyelkhoury · Answer

The behavior your are describing (transformer heating, output voltage drop above ~0.45A, and audible noise) strongly indicates that the transformer is being operated outside its intended magnetic limits—most likely approaching core saturation. In a forward converter using the MAX17599, the transformer must be specifically designed for the operating conditions (input voltage range, duty cycle, switching frequency, and active-clamp reset). If parameters such as turns ratio, magnetizing inductance, or core size are not properly matched, excessive magnetic flux can occur. This leads to: Increased magnetizing current and losses → heating Loss of efficient energy transfer → output voltage droop Mechanical vibration of the core/windings → audible noise Based on these symptoms, it is very likely that the selected transformer is not suitable for this application or operating point. A transformer designed specifically for this topology and power level (such as the one used in the evaluation board) is recommended to ensure proper performance and reliability.

charlyelkhoury · Answer

Do you mind sharing your schematic with me? 
 Did you try the eval board to see how it works in your application: MAX17598EVKIT 
 Charly

MaryKordi · Answer

5858_maxrefdes115_SCH_RA.pdf 5858_MAXREFDES115_BOM_RA.pdf Please see the specifications of T2 on the BOM list and the schematic.

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Transformer Heating and 5V Output Drop

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