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I need to supply a uC from 42V power source (battery). The uC controlls a buck converter to 12V output which will drive some Leds (0.5A). If the whole device will not be used (no Led driving), a months maybe, the uC will be in sleep mode draining as little power as possible.

A uC will be supplyed from a buck, but i need to start it from 42V battery directly and then switch to supply from a buck. It is because supplying a zener diode from 42V is too lossy, so i will have to disconnect a 42V supply after buck powers on.

I designed two different legs for driving buck also , one "light" for sleep mode and another "heavy" for Led driving.

Does anyone see some possible improvement, simplifying? Or do you see some problems in design?

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Have a look at the LM5164 100V in, 5uA at 40V Iq? Depending on the controller, you can either linear from 12V to 5V (low power) or use a small switcher (higher power). Note: most buck converters efficiency drops off when you start talking sub milliamp currents and 12V micro-watt BUCK is still not that common. Simon

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  • \$\begingroup\$ Thx for ideas, this low Iq converters must have a sophisticated internal control to reach this low drawing. They are hard/expensive to purchase in our local stores, so i decide to make it by myself. I have a free space in microcontroller, so it is posible to make pulse skipping etc.. Also I know the time when the load is connected, so I can prepare converter for loading. The LDO with 40V input is also pretty costy and decrease 40V to 5V cause losses they are not neglibigle. \$\endgroup\$ – Michal Podmanický Feb 18 at 13:49
  • \$\begingroup\$ you always LDO from the buck output if you can .... otherwise a LDO isn't required. \$\endgroup\$ – Simon Feb 21 at 2:18

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