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From a wall power supply of 12V (I'm planning to use the PSU), I would like to boost the voltage to 22V at 9A to power some heating foil. These heating foil requires about 130W and I need at least a 22V power supply. Do you know any best way to boost the output without much loss of efficiency? I thought about step up, boost converter and even SEPIC. In some documents I found about of using the DC switching converter together with a low dropout regulator (LDO) in order to have a stable voltage...

I also found about Webench power designer tool from Texas Instrument, where I can insert the input and output voltage and output current, and then it generates the full design with the all elements required as you can see from the image below. For example in the schematic below uses the boost converter LM5022.

enter image description here

But when I look on the datasheet, I can't find information relating the maximum tolerated output current of boost converter. How can I be sure if the following converter is suitable for my intended application without damaging the component?

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  • \$\begingroup\$ I'm uncertain what you are looking for in the linked data sheet. Please explain what this means --> maximum tolerated output current and also explain what you mean by "relating" in the same sentence. I mean... "relating" to what? Please be clear. It seems your load need 6 amps and not 9 amps. Can you explain the discrepancy please? \$\endgroup\$
    – Andy aka
    Commented Apr 25, 2023 at 8:28
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    \$\begingroup\$ So you say you need 130W, but 22V at 9A is 198W. Also computer power supplies are bad as general purpose supplies for arbitrary loads. You also won't find the currents in the data sheets, because the chips are only controllers for external switching FETs, so the data sheet can't contain the information. \$\endgroup\$
    – Justme
    Commented Apr 25, 2023 at 8:43
  • \$\begingroup\$ @Justme Based on calculation, I need exactly 97W to heat at certain temperature a chamber. During the design phase I need to oversize the power at least of 30% factor and also the current.... So that's why I considered 22V voltage to reach a power of 128W. \$\endgroup\$
    – stefyanna
    Commented Apr 25, 2023 at 13:39
  • \$\begingroup\$ @Andyaka I mean the maximim tolerated current output from the boost converter LM5022. You're right. I need 22V and 6A to power the heating foil, but in design phase I need to oversize power by a factor of 30% and current by a factor of 1.5. That's why I considered 128W (130W) and 9A. \$\endgroup\$
    – stefyanna
    Commented Apr 25, 2023 at 14:00

2 Answers 2

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The best solution in your case would be to buy a power supply which can supply AT LEAST 12A at 24V (even better, go to a 15A or 20A model to give you some overhead and a longer-lasting supply) and then adjust or modify it to give you 22V.
Then you use step-down or buck converters to get other, lower voltages from the 22V.

PC power supplies are not good for simple loads on a single line and even if they are efficient, some of that efficiency is lost by not using other voltage rails.

However, to answer the question about boost converters:

  • the IC merely controls the output MOSFET, the output current doesn't go through it and that's why its maximum output current is not mentioned;
  • your MOSFET choice dictates the maximum output current and voltage, and the amount of its own heating (wasted power dissipation) or the converter efficiency - in your case a 30V MOSFET might be damaged by voltage peaks;
  • to increase boost converter efficiency, you need a controller which also has "synchronous rectification" which uses a MOSFET as an active diode and gives a much lower voltage drop and thus wastes less energy on the conversion - a diode would waste about 5W to 10W if it has 0.5V to 1V forward voltage drop across it.
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  • \$\begingroup\$ Actually I also need the other voltage rails. I need the 5V and 3.3V to power sensors and actuators and not only the 12V. By the way what do you mean with simple loads? \$\endgroup\$
    – stefyanna
    Commented Apr 25, 2023 at 13:50
  • \$\begingroup\$ @stefyanna By simple loads, I mean a single voltage rail used intermittently (sometimes full load, sometimes zero load). By comparison, a computer mainboard uses all voltage rails (maybe not the negative voltages) more or less, and always has some load on them when it's on. Computer power supply has internal load resistors ensuring a minimum required load to keep voltages within limits, and you're typically wasting a few watts just on those resistors. As for other voltages, just use smaller buck converters to drop the 24V down to 3.3V and 5V. \$\endgroup\$
    – Edin Fifić
    Commented Apr 25, 2023 at 17:58
  • \$\begingroup\$ When you say that I'm wasting watts on those resistor, it's not clear for me. Maybe I was not clear. I actually I have a bunch of sensors and actuators and must work continuously depending on some parameters. For instance, the temperature must always be constant. Therefore, the heating foil are always on. I tried to search other wall power supply, but the problem is that at high voltage, like 20V cannot exceed more than 13A of current. For my system I actually need a minim currebt of 11-12A, then considering a factor of 1.5, I need at least 16A. That's why I considered the PC power supply. \$\endgroup\$
    – stefyanna
    Commented Apr 26, 2023 at 7:13
  • \$\begingroup\$ @stefyanna There are usually load resistors of at least 1W and sometimes up to 3W on 3.3V, 5V and 12V, ensuring a minimum load, and each one of them use 1-2W of power whenever the power supply is on. If you only use 12V, those 3.3V and 5V (as well as -5V and -12V) rails are unused and their load resistors and the rest of the regulating circuitry are wasting a few watts unnecessarily, compared to just plain single voltage output power supply. \$\endgroup\$
    – Edin Fifić
    Commented Apr 26, 2023 at 8:24
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    \$\begingroup\$ In the meantime I restudied the voltage and current requirements increasing the heating time. So now I need 12V to power those heating foils. Therefore, I don't need anymore the power supply unit of 300W, but just a ac/dc power supply (digikey.ch/en/products/detail/xp-power/ALM150PS12C2-8/10059521) and use some buck converter or step down to to generate other voltage. Thanks for the advices. By the way the heating foils resistor are around 7-7.5 Ohm. \$\endgroup\$
    – stefyanna
    Commented May 7, 2023 at 9:18
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These heating foil requires about 130W and I need at least a 22V power supply.

together with a low dropout regulator (LDO) in order to have a stable voltage...

Heating elements do not need a stable voltage unless you are pushing it to the edge of burning out. A switching supply is good if built right. The switching supply will have some high frequency ripple on its output. Ripple at 100khz will not effect on the heat. Many heaters are run at 60hz AC not DC.

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  • \$\begingroup\$ I need a stable voltage of 22V because to warm a chamber at certain temperature it requires 128W. \$\endgroup\$
    – stefyanna
    Commented Apr 25, 2023 at 13:42

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