I'm trying to get 19V / 3.5A supply From 12V battey, I made a boost converter circuit using mc34063 ic, The simulation of the circuit was perfect and I got 19V/3.7A as output, This is my circuit enter image description here But the problem was in real time ... I made it but i couldn't get more than 600mA, I think there is two possibilities for that failure

  • Maybe R1 value .. Because I couldn't get a small resistance with value of 0.07ohm so I replaced with a wire
  • Or the inductor L1 which i used have a considered resistance

Please help me .. What is the problem and how to solve it

  • \$\begingroup\$ I would like your assistance. I am designing a similar circuit as yours only that am boosting voltage 5V to 12V and an output current of 2A. May you plese take me through on how your obtained the transistor and how it was able to boost current to the desired value using the MC34063 IC. \$\endgroup\$ – Emmanuel Shoombe Bonge Nov 23 '16 at 17:27
  • \$\begingroup\$ @EmmanuelShoombeBonge Please post that comment as a new independednt question. You can reference this and other questions if desired. MC34063 application note AN920 may provide all the help you need. \$\endgroup\$ – Russell McMahon Dec 28 '16 at 23:11

If the wire shorting out R1 is less than 0.07 ohms, that defeats the current limit function and should not be the source of the problem described.

The peak current through the inductor would be around 3 times the output current. That would be 10.5A. You need an inductor with saturation current rating higher than that. An undersized inductor could be a source of your problem.

In your schematic, there is nothing at the base Q1 to turn off the transistor. That is definitely an issue. The simplest thing you can put there is a resistor to ground.

I am curious on what do you use to simulate the circuit and where do you get the MC34063 simulation model. Also, I wonder why doesn't the simulation catch the lack of turn off on Q1.

The 180uH 10.5A saturation inductor is quite big. You can try to reduce its size by increasing the switching frequency and therefore reducing the inductance required.

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  • \$\begingroup\$ I use proteus 8 for simulation, it has the mc34063 model .. I would ask you if you have any information about inductor sizing , please share it with me. \$\endgroup\$ – Waleed Saydi Dec 27 '14 at 2:38
  • \$\begingroup\$ search result from an distributor with good inventories. No 180uH with the required spec available. Have only up to 120uH. \$\endgroup\$ – rioraxe Dec 27 '14 at 4:03

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