My system is working on breadboard so I decided to design PCB for it. I have stepper and relay. They are working on 24V so I am using 220 V AC to 24V DC switch mode adapter condrad.com.

I am using raspberry pi pico so I decided to use RP2040. My reference link is here page 13 raspberrypi. In breadboard , I am using 9V, raspberry pi pico's 5V and 3.3V. So I need to design this PCB for 9V, 5V and 3.3V. I need to use Micro USB for upload code.

1-) So my question is, How can I use micro usb and 9V. Can I use like this; I will plug micro usb for upload code then unplugged it. Then connect 24V to my PCB design for 9V, 5V and 3.3V. Is it work like this? If I design PCB's power like this, Is it work like what I want ?

2-) My another question is, which converter should I use for 24V to 9V on PCB design. Is it okay if I use 7809? Will it be a heat problem or something? I am asking because I didn't use or I didn't design PCB before. I am using batteries for 9V for now. Thank you.

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  • \$\begingroup\$ Regarding 2) then using switched step-down regulators is what's recommended. Depending on current and package used, 7809 might be possible, but it's terribly inefficient and produces lots of heat. How much current do you need to draw from the 9V? \$\endgroup\$
    – Lundin
    Commented Dec 14, 2021 at 13:28
  • \$\begingroup\$ @Lundin, I will use 9V for RFID. It requires 120mA. My 5V and 3.3V systems will draw about 500mA. I am using 9V's current right? So my all system needs 620mA I guess. \$\endgroup\$ Commented Dec 14, 2021 at 13:34
  • \$\begingroup\$ Do you get the 5V and 3.3V from the 9V or directly from 24V? \$\endgroup\$
    – Lundin
    Commented Dec 14, 2021 at 13:35
  • \$\begingroup\$ I am thinking of to get 5V and 3.3V from 9V. Which is the correct way ? 24V or 9V ? \$\endgroup\$ Commented Dec 14, 2021 at 13:36

1 Answer 1

  1. The normal USB standards don't allow 9V so I'm not sure what you are trying to do here. It would seem that you simply shouldn't mix up your 9V supply with the USB.

  2. Generally speaking, switch regulators is what is used by modern electronics. If you draw some 620mA from a 7809 supplied by 24V it will melt through the floor, even if you use TO220 with heat sink. However, using a LDO for powering the RF parts isn't a bad idea, since they give cleaner output.

    It sounds like you need to split this up with several different regulators. Maybe start with a switch regulator from 24V to 12V. Then from 12V, a low noise LDO for the 9V RF supply and two separate switch regulators from 12V down to 5V and 3.3V respectively.

  • \$\begingroup\$ thank you for quick answers. Thank you for suggestions. I will try to do that things. I will use this for 24 V to 12V link and then Can I use this for 9V and 5V link2 . \$\endgroup\$ Commented Dec 14, 2021 at 14:04
  • \$\begingroup\$ And then I need to use NCP117ST33 for 5V to 3.3V too I guess. \$\endgroup\$ Commented Dec 14, 2021 at 14:04
  • \$\begingroup\$ @Tryingtogetsome 20A??? I thought you said you only need <1A? \$\endgroup\$
    – Lundin
    Commented Dec 14, 2021 at 14:06
  • \$\begingroup\$ I need 1A right. Sorry for wrong link. I will check it out. For now, my system is working with 500mA (usb cable from computer). Here I found this aliexpress \$\endgroup\$ Commented Dec 14, 2021 at 14:07

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