Ultrafast diode max current (smps)

juancho009

Joined Nov 2, 2016
6
hi, everyone

i want to know how many current can handle an ultrafast or Schottky diode if this is rectifying a square wave, or to be more exactly, if the diode is the output of an Switch mode power supply.

for example, i heard that the MUR815-840 (8Amp Ultrafast diodes) can rectify an continuous current of 16 Amp if they are working for the output of an smps

is this true?

Thanks!

GopherT

Joined Nov 23, 2012
8,012
What does the DATASHEET say?

DickCappels

Joined Aug 21, 2008
6,012
With most diodes the current rating reflects the manufacturer's best judgement for a trade-off between current handling and lifetime, and here junction temperature is the most important parameter. At currents under the maximum current rating of the device (8 amps in the case of the MUR815-840) you can go by the derating chart below, which is figure 13 from the datasheet. Note: Power is proportional to average current so in switching applications the current is averaged over an entire cycle.

If you want 16 amps continuous current with this diode, you will need more than one.

crutschow

Joined Mar 14, 2008
23,800
i heard that the MUR815-840 (8Amp Ultrafast diodes) can rectify an continuous current of 16 Amp if they are working for the output of an smps
Whomever you heard that from, is wrong.

Last edited:

juancho009

Joined Nov 2, 2016
6
If you want 16 amps continuous current with this diode, you will need more than one.
View attachment 116647
So, i must put these diodes like a Schottky barrier right?

i would like extract 10 Amps from this array

Last edited:

crutschow

Joined Mar 14, 2008
23,800
So, i must put these diodes like a Schottky barrier right?
View attachment 116655

i would like extract 10 Amps from this array

Better to use a single, higher current diode.
Schottky diodes have a negative temperature coefficient of forward voltage drop versus temperature and thus one diode of the two in parallel will tend to hog the current which can lead to failure of that diode.

juancho009

Joined Nov 2, 2016
6
Better to use a single
but in these array that i showed before i dont try to put these diodes in parallel (i understand finally only one diode make the work), i put these array for the rectifying of the current at the output of the high freq transformer (however i didn't be very exact in the image u.u)

this is more clearly hehe

Thanks to everyone!

Last edited:

crutschow

Joined Mar 14, 2008
23,800

juancho009

Joined Nov 2, 2016
6

juancho009

Joined Nov 2, 2016
6
The type of diodes used in most Atx psus are Double Common Cathode
hello
of course!, but what i want to know is, if i put two 8amp ultrafast diodes like this

i can get at least 10 amp?

Thanks to all!

Dodgydave

Joined Jun 22, 2012
8,592
You will only get the maximum rating for the diode 8A,or the transformer current, after that the diode will start to get hotter and may break down.

JUNELER

Joined Jul 13, 2015
183
Hi, i think you should removed the d3 and d4 since d1 and d2 is centered tap to gnd.
The positive output coming from d1 and d2 and the center tap is the gnd (negative).
Are you referring to a single type output , or your circuit look like a split type(dual) output.

schmitt trigger

Joined Jul 12, 2010
88
Like Crutschow mentions, it is better to use a single diode with the adequate current rating.
Schottky diodes are availble in currents up to 300 amps.

Paralleling diodes is always a challenge, for the negative temperature coefficient.

shortbus

Joined Sep 30, 2009
7,245
Like Crutschow mentions, it is better to use a single diode with the adequate current rating.
Schottky diodes are availble in currents up to 300 amps.

Paralleling diodes is always a challenge, for the negative temperature coefficient.
Does this include the ones that are doubled on a single 'die'? I have some that are dual diodes, some with common anode and some with common cathode. Thought they were to be used as a dual diode?

juancho009

Joined Nov 2, 2016
6
Like Crutschow mentions, it is better to use a single diode with the adequate current rating.
Schottky diodes are availble in currents up to 300 amps.

Paralleling diodes is always a challenge, for the negative temperature coefficient.
I said before that i dont want to use parallel diode, i want to know if i use a pair of diodes in common cathode (ultra fast or Schottky) and supossing that they support a max current of 8A, they can give a current (at least) of 10 amp

here's an example imagine that the diodes from the right dont exist

in that topology i can get 10amp from the diodes D1 and D2? (assuming that hey support a max current of 8 amp)