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I have been looking up dc-dc buck converter designs and have question regarding the diodes.

  1. It says "5A High current Schottky diode" is it common in buck converter design to parallel diodes and I would guess this is two 2.5A diodes?

  2. I understand that connecting them in parallel will share the load and result in a higher forward current but wont one diode try to carry a larger current due a potential for a lower forward voltage. Resulting in one diode overheating?

  3. I know to remedy this is to add a series resistor with the diode to have a equal current drop across each resistor resulting in a almost equal current share between each diode. However this will result in a overall higher power loss due to the parallel branch and due to the large current drop in the resistor. Wouldn't you just be better paying a little more for a single diode that can meet the current requirement for your buck converter?

Parallel diodes Image source

I would apprecitae your feedback.

Thanks,

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    \$\begingroup\$ Where did the data and pictures come from. Link please. \$\endgroup\$
    – Andy aka
    Commented Aug 13, 2020 at 19:39
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    \$\begingroup\$ They're fairly closely thermally coupled. I would not run them at the limit but maybe they are not doing so. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Aug 13, 2020 at 20:21

1 Answer 1

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Paralleling the two diodes reduces the forward drop and increases the efficiency, as well as doubling the power dissipation. The I-V curves are soft enough that they will carry roughly equal current. Although the forward drop does go down on heating, you'd need to get almost to thermal runaway conditions before that would result in a large imbalance.

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    \$\begingroup\$ So what your saying is if you were running at 4A across 2 2.5A diodes(total 5A), the current carried would roughly be equal. And only at close to 5A would you begin to get thermal runway? \$\endgroup\$
    – Newbie
    Commented Aug 13, 2020 at 22:34
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    \$\begingroup\$ Looks like the diodes are on the input. Not the output. The LM2596-ADJ is rated for 2.5A output only \$\endgroup\$
    – D.A.S.
    Commented Aug 13, 2020 at 23:16
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    \$\begingroup\$ Yet 7.5A Io pk so input current is shared if Diodes on input are in tandem. 6I mOhm Rs 0.3V @2A = 0.6 W so current sharing reduces temp rise on reverse protection diodes. \$\endgroup\$
    – D.A.S.
    Commented Aug 13, 2020 at 23:23
  • \$\begingroup\$ Todays technology allows for closely matched semiconductors, especially from the same lot. Large miss-matches is old-school stuff. \$\endgroup\$
    – user105652
    Commented Aug 14, 2020 at 4:26
  • \$\begingroup\$ I think the power dissipation issue may be a key driver in SMD designs. If you use a lot of 1W diodes it would be cheaper to use two than to add a 2W diode to inventory. \$\endgroup\$
    – KalleMP
    Commented May 20, 2023 at 10:34

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