I am trying to design a solar charge controller to charge a 12V battery, my solar panel is made of 9 cells that are 5W and 0.5V per-cell. I would like to make a booster circuit to get the voltage up to 13-14 in order to charge the circuit.

I am planning on using a MC34063A for this and I found multiple examples of what I am trying to do.

  1. The first arrangement I have tried was Here, but when I get the components into LTSpice and try and simulate it, I get very different results than what I am expecting.

  2. The second is here, but again when I get the components into LTSpice I am getting very different results than what I am expecting to see.

I got the spice model for the MC34063A from this post

Here is a picture of my current spice model, which is representative of the second configuration. Circuit

Here is the picture of the results of the simulation. results

I am hoping to see 12V at C3 and currently, I am getting the source voltage. Just over 5V.

If someone is able to show me the errors of my ways I would be greatly appreciative for the help

  • 3
    \$\begingroup\$ It would help a lot if you edit your question to tell us what you are expecting, and what you are seeing. \$\endgroup\$
    – TimWescott
    May 21, 2019 at 15:57
  • \$\begingroup\$ And, in the absence of PTT, as a start you probably want to design the circuit to regulate the panel input voltage to 0.5V/cell, rather than regulating the output voltage. (You really want to have some priority regulator that says more or less "first keep the panel voltage above this limit, then keep the battery current below this limit, then keep the battery voltage below this limit" -- if I got that right (meaning, if you get your diodes pointed the right way in your regulator) then you should end up with something that charges the battery pretty good. \$\endgroup\$
    – TimWescott
    May 21, 2019 at 16:00
  • \$\begingroup\$ And -- 12V battery, but what chemistry? Lead-acid? \$\endgroup\$
    – TimWescott
    May 21, 2019 at 16:01
  • \$\begingroup\$ @TimWescott I have changed it so that I mentioned what I would like to see and I added a picture of the simulation currently. \$\endgroup\$
    – laxer
    May 21, 2019 at 16:04
  • 1
    \$\begingroup\$ For some reason you're not turning Q1 on. What's going on at the base of Q1? What's your PWM frequency? It should be PWM-ing and (T'oh) you should have a current-limit resistor in there. The circuits that I've seen that use an external transistor with the 34063 have a circuit with two or three transistors to actively drive the base of the main transistor. Without those you should probably have a series pass resistor from pin 2 to the base, and a resistor from base to ground. \$\endgroup\$
    – TimWescott
    May 21, 2019 at 17:23

1 Answer 1


DC-DC converter not simulating correctly

I think you'll find that the simulation is correct.
The datasheet for the MC3046A shows the schematic (9.1.1) you require when using an external transistor:

enter image description here

Without the Base/Emitter resistor the capacitance of the Q1 junction (both EB and CB) will cause your Q1 to switch off very slowly. This will decrease the backemf you get from the series inductor so limiting the voltage output.


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