Parallel Schottkey Diodes

[Longbow]

I see a lot of disparaging remarks about using rectifier diodes in parallel. This configuration is not always a sign of cost cutting or poor design. Naturally, discreet Si diodes in parallel will be unrepredictable in their operation. It is possible that Si rectifier diodes on the same substrate would behave better. However it is good to remember that Si diodes have a negative temp. coefficient. As the temperature rises, Vf will go down, which almost assures that only one diode will take the entire amount of current. Probably not worth the effort for power rectifiers.

Schottkey diodes on the other hand have a positive temperature coefficient. Parallel Schottkey diodes self-adjust their Vf with temperature variations to share the current equally. Parallel Schottkey's, especially on the same substrate or on the same heat sink is a workable arrangement and shouldn't be taken as a sign of poor design practice.

[budm]

Re: Parallel Schottkey Diodes

"Schottkey diodes on the other hand have a positive temperature coefficient."

Per NXP: also ST.
When the junction temperature of a Schottky rectifier rises, forward voltage VF is reduced
and this results in lower conduction state losses. To simulate losses for the secondary
side rectifier under elevated temperatures, a SPICE model at Tj = 85 °C was extracted for
NXP Semiconductors 40 V, 5 A IF(AV) MEGA Schottky rectifier PMEG4050ETP. The model
card is shown in Ref. 1 “Application Note AN11310 FlatPower Schottky rectifier in low
power adapter.”

Fulltext101:
The schottky diode is a majority carrier device making conductivity modulation
impossible. This makes the forward voltage more dependent on the forward
current than in equivalent PIN-diodes. The forward voltage of schottky diodes has
negative temperature dependency, meaning the forward voltage is dropping for
increasing temperatures. On the other hand, the reverse leakage current is
significantly increasing with increased temperature

May be SiC Schottky: