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I'm looking for a proper power supply schematic which would fit my needs and would have all required protections (overcurrent, overvoltage, reverse current, etc) for use in car. I want to power Atmega 328p (3.3v@8MHz), PCM5102 and CSR64215 module with it. They all should be powered from 3.3V. Any suggestions?


So I've decided to use DC-DC switching regulator for the first stage and multiple LDO's at the end which will bring the voltage down to 3.3V and power rest of the circuit. For the first stage I chose BD9778F switching regulator with built-in power MOSFET which features wide input voltage range (7V-35V). For the end part I'll probably use AMS1117 LDO's. I already draw the schematic for the first power stage and would like to get some feedback from you if possible. Thank you!

BD9778F schematic

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  • \$\begingroup\$ Have you conducted any research ? \$\endgroup\$
    – Long Pham
    May 21, 2018 at 12:51
  • \$\begingroup\$ If you don't mind the efficiency, a linear regulator with some capacitors will do. \$\endgroup\$
    – Long Pham
    May 21, 2018 at 12:57
  • \$\begingroup\$ @LongPham I've tried to use LDO TPS7A4700 with inductor, few input/output capacitors and it burned my atmega and bluetooth right away when I was cranking the engine... \$\endgroup\$ May 21, 2018 at 13:19

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I would use the standard lM2576-5V switching regulator circuit and a lM1117-3.3 to bring that 5V down to 3.3v. I've had good luck with using this approach in cars in the past. You can use the schematics they have given in the schematics

http://www.ti.com/lit/ds/symlink/lm2576.pdf https://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/s2004/zz25/lm1117.pdf

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  • \$\begingroup\$ But isn't it true that it's not recommended to use switching regulators for audio applications like DAC? \$\endgroup\$ May 21, 2018 at 19:46
  • \$\begingroup\$ The switching regulator will be alot less noisy than the cars electrical system. And you are only bringing it down to 5v. The remaining regulation to get down to 3.3v is done by a linear regulator. Which provides a smooth dc voltage. \$\endgroup\$ May 22, 2018 at 0:28
  • \$\begingroup\$ Ok, the LDO part is clear enough for me. What is not clear for me is the front-end part of the circuit where the LDO and the rest of circuit including Atmega, Bluetooth an the DAC should be somehow protected from the harms in the car (overcurrent, overvoltage, reverse voltage and so on..) \$\endgroup\$ May 25, 2018 at 18:37
  • \$\begingroup\$ The LM2576 is able to handle > 24V. A diode should be placed in series with the input in order to prevent reverse voltage. Anything in a car environment should be fused (overcurrent). As far as some of the other SAE standards (ISO 7637, ISO 16750-2) an RC filter can be used on the input to filter out these pulses. \$\endgroup\$ May 29, 2018 at 16:11

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