I'm trying to use some part of this circuit dual power supply circuit:


Credits to embedded-lab.com.

enter image description here

I would like to use all SMD components (as I'm short on space).

  • I'm intending to substitute 1N5400 to 1N4001
  • AMS1117, resistors and the LED is no issue
  • 100 uF capacitors in 0805 I also have

However, I'm doubting about the electrolytical 22 uF capacitors. I ordered the SMD 0805, but I wonder if those can be substituted.

(for my project I need < 100 mA of 3.3V power and about 50-200 mA of 5V power).

  • \$\begingroup\$ What's the 1N5400 / 1N4001 for? \$\endgroup\$ – johnny_boy Mar 15 at 1:40
  • \$\begingroup\$ I can only find a datasheet for the LM1117. Assuming similar requirements, they recommend a 10 uF tantalum. Your reference design appears to use an aluminum electrolytic, so they didn't follow the recommendation. \$\endgroup\$ – Mattman944 Mar 15 at 1:43
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    \$\begingroup\$ @johnny_boy, presumably for supply polarity protection. \$\endgroup\$ – Jasen Mar 15 at 2:09
  • \$\begingroup\$ @Jasen I am almost sure it is. \$\endgroup\$ – Michel Keijzers Mar 15 at 2:14
  • \$\begingroup\$ @Mattman944 Not sure why, although I see many voltage regulators using electrolytic (for 22uF), and ceramic for smaller values. Maybe because tantalum's are reasonably expensive. \$\endgroup\$ – Michel Keijzers Mar 15 at 2:15

The output capacitor type mentioned is critical. The tantulum capacitor is specifically mentioned in the datasheet. Tantulum has higher ESR compared to ceramic, and will help in loop stability for the regulator. If you are switching to ceramic, there is a possibility of ringing and unstable output. I would choose I higher value of ceramic, indeed the same 100uF one used at the input. Higher value of the capacitor is good for stability.

enter image description here

Edit 2:

The drop out voltage is 1.3 V maximum. So, the input voltage for the 5 V regulator has to be at least 5 + 1.3 = 6.3 V. The diode drop if we consider, the input voltage from the DC jack has to be atleast 7 V. Either one should change the input DC jack vorlage range description or use a ideal diode (using PMOSFET for reverse voltage protection or a Schottky diode).

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  • \$\begingroup\$ Thanks for this answer ... would it be ok to use 47 uF tantalums? Because I have quite a bunch of them. \$\endgroup\$ – Michel Keijzers Mar 15 at 2:34
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    \$\begingroup\$ Yes, higher capacitance will help for the stability. \$\endgroup\$ – User323693 Mar 15 at 2:41
  • \$\begingroup\$ Thanks for the edit, I will check what I have already available to be used. \$\endgroup\$ – Michel Keijzers Mar 15 at 2:42
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    \$\begingroup\$ @MichelKeijzers You should unaccept my answer and accept this one if you still can. This one is right and mine is wrong. \$\endgroup\$ – johnny_boy Mar 15 at 15:26
  • \$\begingroup\$ @johnny_boy It's always possible to change an accepted answer afaik ... nice that you voluntarily offer to unaccept your answer, however, if your answer is wrong, shouldn't you delete it completely? Or remove/change parts which are wrong (if you want to keep comments for example). \$\endgroup\$ – Michel Keijzers Mar 15 at 16:16

Substitute them for what?

I'm sure that you can substitute them for ceramic capacitors if that's what you're asking. They'll have less ESR, and the datasheet for the AMS regulators doesn't say anything about needing a minimum ESR (for what it's worth, sometimes regulators with difficult-to-stabilize control loops may need capacitors with a minimum ESR, but this is certainly not one of those cases; the datasheet would tell you).

This answer is wrong; I didn't look at the datasheet closely enough. The accepted answer is right.

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  • \$\begingroup\$ Thanks ... I meant indeed a ceramic 0805 capacitors ... just a side question ... why would people not always use ceramic capacitors in this case, since they are much smaller than electrolytical capacitors (for both through hole and SMD) ? Only ESR reasons? \$\endgroup\$ – Michel Keijzers Mar 15 at 1:55
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    \$\begingroup\$ @MichelKeijzers There are advantages to both ceramic and electrolytic. See: electronics.stackexchange.com/questions/43161/… \$\endgroup\$ – user1850479 Mar 15 at 1:57
  • \$\begingroup\$ @user1850479 Thanks for that question reference. \$\endgroup\$ – Michel Keijzers Mar 15 at 2:12

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