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I am looking for a smart way to regulate my input power Vin = 12-24V to a stable Vout = 12V; Imax = 3A- Usual I use the TI Workbench but this time it makes really complex designs. On the Load side there are DC Motors and Sensors - The supervisor wants low noise so I thought about using a Linear Regulator but I read that Vin needs to be at least 1-2V higher than Vout and an LDO doesn't work if the input voltage is already at 12V I would need a boost which would make everything even more complex. There is only 1 Vin and I don't know if the user uses 12 or 24V.

After I regulate it to 12V I would like to use a Buck (TPS56339) for getting it down to 5V and power up an ESP. Further I need to regulate it down to 3V3 to power up some IC's which I would make over a linear from 5V to 3V3 because the current needs to be higher than from the ESP32 3V3 pin.

The only step I am really stuck on is a good way to regulate the first step from 12/24V to 12V. If possible I would like to internally read the voltage level and if it's already on 12V, skip the first regulation. If it's at 24V put it into a linear to get it down to 12V (36W should be doable?).

A good idea how to do that? Thanks!

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  • \$\begingroup\$ Is there any reason why you do not want to use a buck regulator whose supply voltage range supports already 12V-24V ? \$\endgroup\$
    – vtolentino
    Commented Apr 10, 2021 at 9:39
  • \$\begingroup\$ The Buck generates noise and the supervisor wants low/stable output voltage. I found a Buck with 30mV. But I dont know if that would be okay for motors/sensors. who need 12V \$\endgroup\$
    – Daniel Do
    Commented Apr 10, 2021 at 10:08
  • \$\begingroup\$ Motors don't care about having low noise supplies, can you power them separately and make a lower power supply with low noise for the sensors? \$\endgroup\$
    – Finbarr
    Commented Apr 10, 2021 at 10:17

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You could use a linear supply, but wasting 36W means a sizeable heatsink. You don’t mention environmental factors like size and operational temperature range.

You could use a buck to get 12V from 24V and use a relay to bypass the buck if the input voltage is less than, say 13V.

Another option is to use a dc/dc converter with a suitable input range and 12V output.

Like most engineering decisions, list down your criteria and apply values to them. Eg cost: 1..2$ 1000 off. Size, weight, temperature range, allowable heat rise, input range, output tolerance and so on.

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  • \$\begingroup\$ I would like to avoid huge heatsinks. I dont have any data of operational temperature but it should be around 90° with a ambient temp of max 40° to get a maximum temp of 130°C . Size should be as small as possible as big as needed. The Buck from 24 to 12V sounds good - How does it work with bypassing via a relay ? Any tutorial online there ? As for a DCDC I would need to talk to my supervisor first. \$\endgroup\$
    – Daniel Do
    Commented Apr 10, 2021 at 11:59
  • \$\begingroup\$ Running devices at 130C affects reliability and is a burn hazard. This is something you want to avoid if possible. Size up a 1K/W heatsink and decide if it is too big. The buck doesn’t work if you bypass it with a relay - that is the intention! The relay simply connects the output to either the dc input or the output of the buck. Each solution has its pros and cons - you need to resolve these and choose the most appropriate solution based on your specs. Expect to have compromises. \$\endgroup\$
    – Kartman
    Commented Apr 10, 2021 at 13:12

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