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I am currently working on a PCB design that will be using 12VDC to power all of its components. It will be mounted on a vehicle, which is powered by an external power supply, which supplies the average voltage of 375VDC. I want to make the board bullet proof, and design it so that it can take up to 700VDC before bad things happen, and using the flyback converters is not an option. Most of buck converters have the maximum input lower than 100VDC.

The only solution I can think of, within my knowledge, is to use a voltage divider to bring the voltage down first, and then use a buck converter chip to get 12VDC. Would it be a valid option? Could anyone suggest better ways to solve this problem?

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  • \$\begingroup\$ "using the flyback converters is not an option" that's sad, because that's the type of DC/DC converter you would use in this case (unless you lead a lot of current from your 12 V rail). However, you're not giving any requirements for the 12 V rail, nor about why you can't use a flyback converter. \$\endgroup\$ – Marcus Müller Nov 2 '19 at 0:17
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    \$\begingroup\$ and if you're asking whether a voltage divider is a viable power supply approach: You should not be building electronics for 375 V or more. \$\endgroup\$ – Marcus Müller Nov 2 '19 at 0:18
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    \$\begingroup\$ Exactly why is a flyback converter not in the cards? \$\endgroup\$ – TimWescott Nov 2 '19 at 1:06
  • \$\begingroup\$ @MarcusMüller I apologize for the lack of details in my question. The goal is to get 5-10W from the 12V rail, although 5W will probably do it. My manager told me to see if I can come up with something without using the flyback converters, but I suppose it is the only way to go in this case. Thanks for your comment! \$\endgroup\$ – HumbleBumble Nov 2 '19 at 3:21
  • \$\begingroup\$ @TimWescott My manager told me to see if I can come up with something without using the flybacks, so I've been trying to stay away from those. \$\endgroup\$ – HumbleBumble Nov 2 '19 at 3:23
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using the flyback converters is not an option.

Why?

Most of buck converters have the maximum input lower than 100VDC.

Buck converters work well for input/output ratios up to 10:1 or a bit more, but 700V/12V is 58:1 which is definitely "not the ideal use case" for a buck, in the same way that using a hammer to drive a screw is "not ideal".

What you need is a transformer based converter, either flyback or push-pull, or other high current topology if you need the amps. This will have high efficiency.

Since 375V DC is lower than the peak voltage of three phase 400V AC, you should be able to use an industrial switching converter that takes 400V AC input. Most AC-DC switching converters will work fine with DC input. Check the documentation.

The only solution I can think of, within my knowledge, is to use a voltage divider

No... Try to calculate the power loss in the resistors, it will be obvious why this is a bad idea.

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  • \$\begingroup\$ Thank you for the AC-DC converter idea, I will check it out. My manager asked me if I could stay away from the flyback converters, probably for the sake of my education, because he makes me dig around a lot quite often. \$\endgroup\$ – HumbleBumble Nov 2 '19 at 3:30
  • \$\begingroup\$ Sounds like weird advice from your manager... \$\endgroup\$ – peufeu Nov 2 '19 at 12:42

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