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UCC24630EVM - no load power consumption and FCC approval

Other Parts Discussed in Thread: LM5023

Hi,

I recently received a.m. EVM.

Trying to verify the efficiency data given in the manual on page 12 (table 4, no load, VIN = 230 V) I could NOT measure/confirm the given results. While table 4, line 1, states a "no load" Pin of 0.060 W. Measuring power at the input with a lost cost energy meter shows a value of approx. 0.8 W. and a current flow of 19 mA. Verifying this result with a more expensive/accurate DMM confirms a current flow of 18.9 mA with no load.

Any idea how to explain this difference?

By the way: all other data can be measured/verified with differences < 1%

On the pcb you find a note " not FCC approved ..."

What is missing on the EVM in order to meet FCC approval?

Chris

  • You will not be able to measure no load power with a low cost power meter-its just not accurate enough for these power levels. The data in the UCC24630EVM User Guide was taken with a Yokogawa WT210 Digital Power Meter and it was set up as shown in Figure 2 of the document. Measurements for power were taken with the instrument set for a long integration time.

    Also you cannot correlate input current with power. The input current may well be 19mA ( this is not documented in the test results of the User Guide) but it cannot be used to calculate power.

    The note " not FCC approved..."  is a legal disclaimer that is used on all of the Texas Instruments EVM's. This EVM passes the conducted emission limits of FCC but it has not been formally tested and certified. You would only go through the expense of this process with a final product that is in an enclosure and is powering a real load (instead of a resistor).This might be one of the final steps before releasing a product to market

  • Hi John,
    thanks for answering my questions. I understand the cost saver with respect to FCC approval.

    I know that measuring AC input voltage and current does not give you a correct power level/product. I furher agree that a low cost meter will be quite inaccurate. It still gives you more than a good indication. Comparing several wall adapters during the last months, at least I was able to figure out which consumes more power with no load and which consumes less. Differences range from 0.6 W to 1.3 W with tolerances of about 20 - 30% (comparing my "results" with those given in data sheets.
    In case of the UCC24630EVM I did not expect to measure something around 0.065 W or less (this would definitely be beyond the resolution of my equipment). But something around 0.1 - 0.2 W (or even 0.0 W) would have beeen a good indication.
    Reading something around 0.8 W (sorry, instead of integrating over a long period I simply stare at my equipment) is not what I expected.

    How can I figure out whether your UCC24630EVM is better (means drawing less energy) without spending a lot of money for a simple evaluation?

    Chris
  • Hi Chris,

    It is indeed very difficult to measure power in the sub 100mW region. The LM5023 used on the UCC24630EVM goes into a "skip cycle" mode at light loads so the EVM does not behave like a fixed resistive load.This makes it important to get an average value for power input.

    You could try this experiment:

    (1) Remove the EVM and connect 230Vac to the power meter

    (2) Measure input power

    (3) Repeat test with EVM connected.

    (4) Subtract the offset , (3)-(2)

    Or you could try running the systems on DC and compare the average input currents at no load.

    Regards,

    John