diode question

[makourain]

https://au.mouser.com/ProductDetail/511-STTH6002CW

^ the rectifier in question.
forgive my lack of knowledge but, as far as i know, you cant have diodes in parallel.
theyll pick a volunteer and only that 1 will work.

I've uploaded a schematic that i have to make a pcb layout for (later) but wanted to check with everyone that im not a complete idiot. it appears to call for 10 of these rectifiers in parallel (bottom right corner of schem)
what am i missing? D:

 

[Harald Kapp]

you cant have diodes in parallel.
theyll pick a volunteer and only that 1 will work.

The diodes will share the current among them. Assume one diode has a lower voltage drop than the others. Then more current will flow through this diode. The forward voltage will increase with current (datasheet, figure 2), thus forcing more current through th eother diodes and reducing current in the first diode.
The result will be an unequal current distribution among the diodes.

it appears to call for 10 of these rectifiers in parallel

It does indeed. The power dissipation is thus distributed among the diodes.

 

[Nanren888]

I always thought that the main effect would be forward voltage decreasing with temperature rise.
That is, as the diode taking more current gets hot, it takes more current.
Net result even more uneven sharing and potential destruction, one at a time.

Not done the math. Do not know which effect dominates or how the combined effect goes.

 

[Ylli]

Picture a perfect diode with a effective series resistor. While the junction voltage does drop with temperature, the voltage drop across those internal effective resistors increase with an increase in current. Similar (though not exactly) like the ballast resistors you need to add the the emitters of parallel transistors

 

[(*steve*)]

Those double diodes are on the same die and will track each other's temperature. Thus, they can be used in parallel.

 

[PETERDECO]

Hi Everyone. I know you're not "supposed" to parallel diodes but I've been doing it for years. I do it to reduce the temperature of the diode. I know they are equally sharing the forward current because they have the same voltage drop and they feel equally warm to touch. I also have been doing it with power mosfets with the same results.

 

[twister]

I converted my welder to dc. I used 6 full wave rectifiers. Everyone said it wouldn't work. Been several years, still working good.

 

[Tha fios agaibh]

Great question. I'd say you can have them in parallel provided they are on the same heat sink to keep their temp rise close.

An advantage would be that you can draw more current, but certainly not 10x the rating of one diode.
I would guess closer to 3 or 4x?

Seems to me, you'd be better off with one sufficiently rated diode, rather than 10 diodes in parallel.

 

[Nanren888]

Hi Everyone. I know you're not "supposed" to parallel diodes but I've been doing it for years. I do it to reduce the temperature of the diode. I know they are equally sharing the forward current because they have the same voltage drop and they feel equally warm to touch. I also have been doing it with power mosfets with the same results.

For MOSFETS, at least in the first approximation, parallel is ok as RDS(on) has a positive temperature coefficient.
I found https://assets.nexperia.com/documents/application-note/AN11599.pdf - for mosfets
.
For diodes with the negative coefficient, it will rely on the match being better and the temperature being close such as sharing a heatsink, as suggested by Tha flos agaibh.