Regarding this DC-DC converter datasheet the input specs are given as:

enter image description here

Mine is 12V to 5V DC and called MV 1205S. So my input voltage is regulated 12V DC.

I have couple of issues with this part:

  1. I want to obtain a reverse voltage protection for this converter input by using a 1N4148 because that is the only diode I have. I also have 1N5408 but it has 1.2V voltage drop.

    But do I really need that? Because the input specs mentions about reverse voltage protection as 0.3A max. What does that mean?

  2. Can I use 3.3uF at the input safely? It says 1uF or 3.3uF but there is an asterisk(*) so I'm not sure if it would have any complications.

  • \$\begingroup\$ 1. If the converter offers it, do you really need your own? 2. If you apply reverse voltage, the module will consume 300mA (most likely driving some protection circuitry). 3. You didn't show the part of the app note explaining the asterisk. This cap will see some ripple current and will dissipate power in it's ESR (hence the recommendation for a polyester film cap). If you stick with the recommended range and type you're likely safe. \$\endgroup\$ – Adam Lawrence Dec 6 '18 at 13:03
  • \$\begingroup\$ No I mean if it has reverse protection bulit-in for 12V input I dont need it. But it mentions 0.3A instead of max reverse voltage thats confusing. \$\endgroup\$ – cm64 Dec 6 '18 at 13:05
  • \$\begingroup\$ There is no explanation for asetrisk in datasheet docs-emea.rs-online.com/webdocs/13fb/0900766b813fbda6.pdf \$\endgroup\$ – cm64 Dec 6 '18 at 13:07
  • \$\begingroup\$ Yes I have film cap 3.3u \$\endgroup\$ – cm64 Dec 6 '18 at 13:07
  1. The device can have a reverse voltage applied but current must be limited to less than 0.3 amps. This is what it means.
  2. Adding 1 to 3.3 uF at the input will reduce input ripple current and I always do this and would probably go as high as 10 uF in some cases. Make the capacitor ceramic or film with a high self-resonant frequency. If necessary add a 10 nF for really high frequency EMI reduction.

Be aware that these are not really regulating converters - they will produce a regulated output based on the value of the input voltage but, if you change the input voltage then the output voltage also changes by about the same ratio.

  • \$\begingroup\$ Thanks for the answer. Do you mean 12V power supply with 1A rating will damage this IC if it is reverse applied to its inputs. I dont understand why thwy just dont add a diode inside the chip. \$\endgroup\$ – cm64 Dec 6 '18 at 16:00
  • \$\begingroup\$ Btw this question of mine didn't get any attention maybe you might have time for an input as well: electronics.stackexchange.com/questions/410722/… \$\endgroup\$ – cm64 Dec 6 '18 at 16:01
  • \$\begingroup\$ If they add a diode in series then the efficiency ratings are reduced and hardly any applications will require this feature. \$\endgroup\$ – Andy aka Dec 6 '18 at 17:03

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