This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MC33063A: Power consumption in idle mode

Part Number: MC33063A


I need help to reduce power consumption of the attached MC33063A Circuit.

I am measuring current as shown in the image and it is ~6-7mA. No load condition.

Nothing else is connected except relay coil positive terminal at +12V. Relay is OFF.

Rectifier Output: 32VDC

Is the 6-7mA current consumption expected when there is no load except 5V LDO connected at it`s output?

Any help on this circuit would be really helpful.


  • Hello,

    Thank you for posting.  6~7mA sounds big.  Please double check the LDO datasheet which seems having remarkable quiescent current.


    Youhao Xi, Applications Engineering

  • Thank your for your quick reply.

    I have removed the diode to disconnect the 5V LDO power. And disconnected the relay power as well.

    Now the no-load current is 5.2mA and that is from MC33063A only.

    I have replaced the MC33063A IC as well but the behavior is same.

    Any change in timing capacitor will help?

  • 5.2mA also sounds large.  Could you double the timing resistor and see if there is any improvement?  Another question is, what is your spec limit for the quiescent current? Are you open to change to a different IC?

  • Thanks for your reply.

    Tried 1nF timing capacitor, no difference.

    If I reduce output voltage to 7V then, that quiescent current goes to ~2.5mA.

    I cannot change part as of now, but please suggest alternative for the next revision. Acceptable quiescent current is ~2mA.

    Thanks again.

  • If lower the output voltage helps, you may consider to lower it to 6V and short out D8 to your LDO to gain back the headroom voltage.  You may meet your 2mA spec.

    Regarding alternative device, would you please take a look at the LM51571, which was recently released and the quiescent current is less than 1mA.

    Thank you and good luck!


  • May I assume the issue has been resolved hence I can close this thread?  You are welcome to re-open it by adding a new post.