How can i build a boost DC/DC Converter that can boost from 24 to 96V without the output voltage depending on the load?

Why? Because i need to charge a battery system that has already been designed and i cant know what is the load resistance...

Basically, i need to charge some batteries using a solar panel to get the energy, it is for charging an electric car, and i cant find a charge regulator for the panels that outputs the 96V needed, i also cant change the battery system in the car to meet the 24V i get from the charge regulator, so what i thought about was this type of converter that would probably reduce the maximum output current but i dont really care, because it doesnt matter how long it takes to charge, it just matters that it charges something so we can use the sun as a power source, anything is better than nothing, which is our current setup.

How would i proceed with the calculations? I've designed some boost/buck converting systems before, but none where i dont know the load resistance, but im assuming there is a way of making the output voltage the same or with a reduced change depending on the load...

  • \$\begingroup\$ This is a very advanced thing to do as a novice. You apparently don't seem to know about switching boost converters, but want to build one that can feed off solar panels (which in itself is already pretty hard, you need a maximum power point tracker for that to be of any use). I don't think we will be able to help you here, a comprehensive answer would require too much space in the SE format. \$\endgroup\$
    – user36129
    Nov 12, 2013 at 10:51
  • \$\begingroup\$ I know something about switching boost converters, i know how they work and i know theoretically and made some exercises in electronics class, what i've never done is building one from scratch, i asked my teacher about it and what he told me was that one of the steps was getting the resistance of the load so i could then decide on a ripple current and calculate both the inductor and capacitor for the system, i have already decided that the switching frequency must be around 30kHz (non audible) and i am thinking of using a 555 timer to build the oscillator, what i need to know is if i can* \$\endgroup\$ Nov 12, 2013 at 11:12
  • \$\begingroup\$ *calculate the remaining components without knowing the output load's resistance, like if i was to build a fixed voltage output for a bench supply, i wouldnt know what kind of load would be connected... As for the solar system, the panel supplier will get me the MPPT systems for outputting 24V, so im guessing i only need to work from there, as it would output fixed 24V \$\endgroup\$ Nov 12, 2013 at 11:14
  • \$\begingroup\$ More parameters: what sort of batteries? What charge current? What's the terminal voltage when fully charged (will be more than 96V!) Is this connected to an existing battery charging system in the car or the raw batteries? TI have various boost converter design help tools, e.g. ti.com/tool/pmp8913 is almost exactly what you want - at low current. \$\endgroup\$
    – pjc50
    Nov 12, 2013 at 11:50
  • \$\begingroup\$ Thats the sort of help i was seeking, i needed someone to tell me what info i need to gather in order to build this, i was kind of lost... but thank you for that TI link, it seems a really good system and will probably fit my needs, thank you very much :) If you want to add that as an answer, i will up vote it and will be registered in case someone else runs into this :) \$\endgroup\$ Nov 12, 2013 at 12:41

1 Answer 1


If you are looking for a general tool or guide to switch mode power supply design, there are several on the net, as well as free online design tools on the web sites of manufacturers such as:

These tools require information about input supply (AC or DC, voltage range) and output requirements (Voltage, acceptable ripple, current rating), and provide suitable part numbers and computations - evidently favoring the respective manufacturer's products, of course.

Many of these tools go as far as providing a schematic, a bill of materials, performance parametrics and even design simulation, all for free.

A boost regulator design does not need the load resistance to be known in advance: There would be a minimum load current specified for stability in many designs, and of course a maximum current rating depending on the switching devices used (internal MOSFETs in the boost controller, external power MOSFETs etc). As long as the load is within those two limits, the boost regulator would supply the desired voltage to the load.

Note: I've already checked with TI WeBench Power Designer but it cannot find a suitable solution to your requirements, so perhaps you can skip that one and try the others.

  • \$\begingroup\$ thank you very much for your help, thats a start, way more than i had before posting this question :) \$\endgroup\$ Nov 12, 2013 at 12:43

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