EEVblog #273 – Power Factor Correction with the MC34262

This was supposed to be a small side piece in the Manson PSU Teardown, but it was almost 10 minutes, so I decided to separate it out to keep the teardown as short as possible. You should watch the PSU teardown to get the context of this where the chip is used.

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    • PChi

      Hi Dave,
      Thanks for the teardown video. As you were saying we didn’t bother with PFC even in the eighties when the 800 W power supply / charger that I worked on took abot 18 A peak from the 240 V mains despite being close to 90 % efficient.
      The input and output Electroltyics in the Manson power supply don’t look very big. I wonder how long they would last at the full rated power?

      • Niklas Jansson

        With the PFC circuit you can actually decrease the amount of output capacitance compared to a rectifier only-solution. The boost converter refills the output capacitor more often, actually several thousands of times per second. We had 3*470 uF before PFC and just 1*470 uF after we introduced PFC in a 1kW rated frequency inverter. The EMC filters was not so small though, adding a lot of BOM cost for an additional differential mode choke and extra filter capacitors.

    • JRR

      Thanks for this. I didn’t know what power factor correction was, this explained it nicely.

    • tchicago

      This should also carry some efficiency loss. It makes the whole thing a double-conversion PSU.

    • Wartex

      Dave sounds sick, throat full of snot. Eww that was hard to listen.

      • Yes, I’ve not been good for the last week or so.

    • Luciano

      The chip is (was) also used as preconverter in the electronic ballast of fluorescent lamps.

      Electronic Lamp Ballast Design:

      Motorola, Inc. 1996 Rev 1:

    • allan

      I hadn’t heard of PFC until now. I gather that this device’s purpose is similar to that of an antenna tuner used with an amateur radio transmitter. The function of the antenna tuner is to zero-out the antenna’s imaginary reactances (capacitive and/or inductive) so that the antenna appears to be a purely resistive load.
      Applying this analogy, I infer that this device is helpful in minimizing electrical energy consumption in driving a load with either capacitive and/or inductive reactances.

    • Leslie Green

      Did you spot the dumb ass circuit diagram in the data sheet where on a MAINS circuit they EARTH the output of the bridge rectifier? These circuit diagrams need to come with a public health warning:
      “WARNING: Whoever drew this circuit diagram doesn’t realise that the safety Earth symbol should NOT be used for a 0V reference that clearly is not anywhere near Earth potential. If you connect your scope earth to that point you will get a big BANG!”

    • Luciano

      @Leslie Green:

      Grounding: Terms and Symbols

      Three diagonal lines from a horizontal bar represents earth or chassis ground.

      Three decreasing-length parallel lines represents analog or circuit ground.

      The hollow triangle usually means digital ground, but is often used as a reference ground.

      * * *

      See also the schematic of the Manson 9400 power supply: (EEVblog #272).

      Best regards,


    • Indeed, this device is helpful in minimizing electrical energy consumption

    • Jay

      I’ve often wondered if it’s worth it to do PFC on an automotive alternator/generator or some other power source that has variable frequency. It seems to me that the windings would run a bit cooler. Automotive alternators feed a battery so the PF is quite high. Apparantly the chip makers don’t think it’s worth the bother. The PFC chips I’ve found all work at a fixed frequency.

    • PeterK

      PFC can indeed be used (and there is active research being done) for variable frequency applications (most often wind) where you want to decrease the harmonic losses in the windings. In a car it is less of an issue. These applications often have other control logic involved (MPPT, etc) which lend them to custom microcontroller control rather than ICs

    • c srinivas


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