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TPS55010 power consumption issue with custom transformer

Peter Isza
Prodigy 30 points
Other Parts Discussed in Thread: TPS55010EVM-009, TPS55010

Hi all,

I am trying to use TPS55010EVM-009 with a custom transformer. I need 50mA output @ 5V. My problem is that the circuit consumes 60mA with no load, compared to 10mA with the original transformer. However, it still works, and I can get my 50mA @ 5V, but then the input supply goes up to 110mA (which is kind of understandable, since it was 60mA without load).

I have no clue what causes this excess consumption. It is definitely not the Zener diode on the secondary side.

I have changed two things on the board:

  1. Added the protection diode discussed here:http://e2e.ti.com/support/power_management/isolated_controllers/f/188/t/138227.aspx after wrecking 3 eval boards. The diode doesn't affect the power consumption characteristics with the original transformer, I have measured it.
  2. Replaced the transformer with the custom one.

The insulated wire is pretty thick compared to the core, and I can't have many turns. Here are the parameters of my transformer:

Core type NiZn ring core
Core sizes

Outer diameter: 6.23 mm
Inner diameter: 3.25 mm
Height: 1.62 mm
Relative permeability 125
Resistivity 10^8 Ohm*cm
Frequency 0.1 MHz - 10 MHz
B_saturation 220mT
# of primary turns 7
# of secondary turns 19

These are the parameters that I have calculated:

Primary inductance 1.15 uH
Maximum current through primary winding

1.5A
Maximum magnetic field

110mT

According to my calculations, the transformer should be similar to the original one. I can't imagine what the difference is. The core shouldn't go into saturation, and the IC doesn't report anything on the FAULT pin either.

Could you please help me figure out where the excess power consumption comes from?

Best Regards,
Peter Isza

  • 0
    Prodigy 30 points

    Here's an update. I have measured the no-load power consumption (mA) versus the frequency (kHz).

    Now this makes me think that the primary inductance is not enough for 350 kHz.

  • 0 in reply to Peter Isza
    Prodigy 30 points

    I have tried increasing the inductance. I think this was the case.

    If you can suggest anything else to increase efficiency at 350 kHz, please do.

    Thanks.

  • 0 in reply to Peter Isza
    TI__Mastermind 35115 points

    Hi Peter,

    I think the higher inductance helped in this case because the TPS55010 had to sink less current during each switching cycle. This lowers conduction losses on the low-side FET.

    Another tip to boost the efficiency with the TPS55010 is to ensure there is enough leakage inductance in the transformer to allow zero voltage switching to reduce switching losses. When the low-side FET turns off there is some delay until turn on of the high-side FET. The leakage inductance causes the SW node to ring. With enough leakage energy it will ring up to the input voltage the same time the high-side FET turns on.

    Best Regards,
    Anthony