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Description: DC to DC converter/regulator MC34063A.  Has an input range of 3V to 40V, output switch current of up to 1.5 amp.  Step up, step down and invert capability.  This is the unit we used in the high voltage ringer circuit for the port-o-rotary phone!

Documents: MC34063 Datasheet

Comments 28 comments

  • More helpful then the datasheet would be this document
    http://www.onsemi.com/pub/Collateral/AN920-D.PDF
    which explains the theory of operation, and also has the mathematical equations to calculate the necessary component values for any desired output voltage.

  • What a great little chip. With ~5 external passive components, you can make a switched-mode power supply that will give you lower, higher or opposite polarity DC from DC input. You can also use an external power transistor to deliver way more than the ~500ma the chip alone will supply (I’m currently using it in this configuration to power a ~3a 5v load from a 20v rechargeable battery pack.)
    Not to mention that unlike a linear regulator, you can power loads over a hundred mA or so without burning yourself or having a completely ridiculous heatsink.
    Best design resource I found was http://www.nomad.ee/micros/mc34063a/index.shtml… it’s a javascript calculator for the component values in the basic circuits presented in the datasheet given your application parameters (VIN, VOUT, IOUTmax, etc.)

    • How did you configure the transistor to increase the current? Can you show me a picture or schematic?

    • Best design resource I found was http://www.nomad.ee/micros/mc34063a/index.shtml
      I’m pretty sure there is an error calculating Ct, it is off by a factor of 10. I could be wrong but it is best to double check yourselves. Try it, put in the example initial values found in the AN920-D reference sheet.
      I just sent a email to the author, looks like it was written a long time ago. In any case it is best to double check the values yourself.

  • I was looking into using this switching regulator for 5V –> 3.3V step-down for an XBee but was told by Digi that switching frequencies below 500kHz might interfere with the XBee. Does anyone know if that is true or not?

  • I can use it for Step up 1.2v to 5v?

  • Hi everybody, I’m looking for some help using this IC as a step up switching regulator with the following specs:

    Vin = 3.60 V Vout = 5.00 V Iout = 300.00 A Vripple = 0.10 V Vin min = 3.24 V Ct = 165.00 pF Ipk = .60 A Rsc = 0.00 Ω Lmin = 0.01 µH (using 390UH) Co = 198,367.35 µF (using 2000UF) R1 = 1.00 kΩ R2 = ((Vout - 1.25) / 1.25) * R1 = 3.00 kΩ

    Under no load I get a perfect 5V on the output. However when under a .3A load the output voltage drops to 2.5~3.0 Volts.

    Anybody have any idea’s what i’m doing wrong? I’m trying to use this chip to step up the voltage on a 3.6volt LIPOLY battery to 5 volts.

    Thanks for any help.

  • I’m choosing between this and lt1303 form digikey: http://www.digikey.sg/product-detail/en/LT1303CN8%23PBF/LT1303CN8%23PBF-ND/889063. which do you think would give more amps with the same configuration?

  • Can anyone tell me maximum output voltage of this thing? Right now I’m using a TL499a to stepup 6v to about 26v at 10mA… would this chip be able to do the same job? I’ve looked thru the datasheet and the application note and I can’t find this info anywhere, what am I missing?

  • I’ve used the online calculator available here: http://www.bobtech.ro/mc34063a-online-calculator
    there is also a very comprehensive video tutorial about MC34063A. I’ve used this as a current mode power supply for 4 HB LEDs.

  • Btw, for a guy relearnig his HS electronics after 30 years, what is Vripple and Fmin?
    thx again,
    Barry

    • From the Datasheet:
      Vripple(pp) − Desired peak−to−peak output ripple voltage. In practice, the calculated capacitor value will need to be increased due to its equivalent series resistance and board layout. The ripple voltage should be kept to a low value since it will directly affect the line and load regulation.
      fmin − Minimum desired output switching frequency at the selected values of Vin and IO.

  • Will this chip let me step up 5V input from a USB jack to 12.6V that I need to have to charge 3 LI cells in series? I know its not ideal but need to be able to show as proof of concept
    Tia,
    Barry

      1. This product WILL boost 5V to 12V
      2. You still do not want to charge multiple LI packs in series unless you are very certain that they have the same characteristics including their discharge. I.e. if one pack is discharged more than the other, you’re going to run into problems. You might want to look at parallel charging instead. Hit Google :)
  • Ideally, if I put in 10V at 1A max, can I get 5V at 500mA max, and vice versa?

  • Will this chip work at 2.4v input? I want to power an ATmega328 with 2 x 1.2v AA batteries.

  • SparkFun should sell switching regulator modules that are pin-for-pin replacements for 780x series linear regulators, like this, but cheaper: http://www.dimensionengineering.com/de-sw050.htm

    • I just bought one of these, seems like that’s the sort of thing you’re looking for.

      • That whole family on DK is great for that kind of thing, I’ve used a V7805 in the past when I had a normal 7805 running too hot for my tastes, worked like a charm.

  • Could I use this to power an ATTiny with 1.5V OR 9V?
    EDIT: Never you mind, I’m going to power it with a definite 3V (coin battery).
    EDIT: You may mind again… although I don’t need an answer anymore.
    EDIT: Never mind again, this is not suitable for my purposes.

  • So I just built a circuit using one of these to step up voltage from 3.3V to 5V (one of the sensors I am using is 5V while the Arduino Pro is 3.3).
    It is almost working, but when I supply power from the Arduino board the voltage (on the arduino line) fluctuates from 3.3 V to around 2.5 V, constantly, and the output voltage is not stable either. I’m not sure what I did wrong here…I used the javascript calculator posted above with the following values:
    Vin: 3.3
    Vout: 5
    Iout: 16.5
    Vripple: 0.25 mV
    Fmin: 43 kHz
    I was given the following values:
    Ct: 444 pF (used 2 220 pF in parallel)
    Rsc: 4.752 Ohm (used 2 10 Ohm in parallel)
    Lmin: 404 uH (used 400 uH)
    Co: 6593 uF (Believe this is a calculation error; used 1000 uF)
    R: 180 Ohm (used 180)
    R1: 1k
    R2: 3k
    I used a 1N5819 diode and a 180 uF input capacitor.
    Any ideas what could be wrong? Why is the supply voltage fluctuating so much?
    EDIT: Nevermind…check your circuits! I had one of the grounds connected to pin 3 rather than pin 4.

  • Hey, i see in the Sparkfun eagle library there is a 34063 SMD part, but no PTH. Is this part an SMD?
    Thanks

  • Of the two I just got form Sparkfun, the markings say:
    ST CHN
    063EC
    KK2736
    I assume these are the correct ICs - why was the MC34 -part left off?

  • un1tz3r0:
    Thanks for that link. That was really helpful for getting the components right. Far easier than dealing with the math myself. :) I did spot check it, but it worked fine. I built it, and my first switching regulator works great. 14V to 3.3V step down, now on to the XBee modules.. :)

    • That is the exact power supply that I’m looking to build, for the same purpose of powering XBees. I’m a bit unsure what I should have for Vripple and Fmin. Can you tell me which components you used?


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