Boost MC34063

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I use MC34063 as a boost converter I need to convert 24V to 48V 1.5A. This regulator cannot deliver all current without external MOSFET as a result I drive IRF540 by chip to increase its current. I use 24V 10A as a power supply everything is ok and circuit do its operation well I measure that its input current peak is around 7A link below as a online tools is also result same.

http://www.nomad.ee/micros/mc34063a/

 

In my design unfortunately the power supply is current limited as a result after adding those resistive loads the voltage is drop to 33V instead of 48V. I try to add some capacitors in the input of the circuit (1000uF, 3300uF) the voltage is drop more surprisingly.

 

Any Idea to reduce peak current that get from the input power supply?

Should I decrease the switching frequency down to 50KHz to ensure that those capacitors have enough time to recharge?

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Do you have access to an oscilloscope? It is really hard to diagnose these circuits without one.

 

You MAY be saturating the inductor. They typically take a current rating of more than twice the load current. Does it get warm when you add the load resistors? When the inductor saturates,  not only does it get warm or hot, but the input current becomes higher than expected.

 

Jim

 

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Thu. Jan 23, 2020 - 11:38 PM
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sounds like your inductor is not correct. You probably need more inductance, or the inductor is saturating, thus causing peak currents.

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The MC34063 is ?, as seen on one of my circuits.

 

https://github.com/epccs/Driver/...

 

If you need to use an external MOSFET, please consider something (anything) else, for example, this new chip (note it does not have to drive LED).

 

https://www.diodes.com/assets/Da...

 

update: PC
update^2: that was not PC

Last Edited: Fri. Jan 24, 2020 - 12:07 AM
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I wouldn't say the 34063 is junk - it was good for it's time, but there are much simpler and better solutions these days. It's only advantage is it's cheap and widely available. Something like a UC3842 is also common- you'll find it in vga monitors, laptop power supplies etc. It has a mosfet driver, so that makes the circuit simpler. Nevertheless, with switching supplies, component selection and layout are critical.

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MC34063 follow-on is NCP3063 at twice the price; 1.5A peak absolute max so add a jelly bean power transistor to meet alex20's requirement.

NCP3063: Boost / Buck / Inverting Converter, Switching Regulator, 1.5 A

...

  • Cycle-by-Cycle Current Limiting
  • Improved protection capability over MC34063

...

due to

e2 PowerEdgeTM Economic Energy using Low VCEsat BJT’s

[bottom of page 8]

NCP3063 Buck reference designs

NSS40500UW3: Low V<sub>CE(sat)</sub> Transistor, PNP, -40 V, 5.0 A (6A peak)

https://www.mouser.com/Search/Refine?Keyword=slf12575t-470 (47micro-Henry 2.7A saturated)

 

"Dare to be naïve." - Buckminster Fuller

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With all those alternatives, the inductor choice may still be incorrect.

 

As some have noted, you need to pay attention to more than pure inductance value. Peak current rating REALLY is also critical. Don't ask me how I know!

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Thanks to Jim, Kartman and all other who response to this post. The circuit now is working properly by increasing the inductance and also changing the boost conveter power supply wires which play an important role apart from the circuit PCB Layout that should be taken into account.

 

Thanks again.