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Power Diode 1N5408 Burn

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1n5408 maximum power

Hi,

Recently i did a power supply. I'm using power diode 1N5408(they call it " STANDARD RECOVERY RECTIFIERS 50-1000 VOLTS 3.0 AMPERE") to design a rectifier and my transformer secondary is 12v-0-12v with 5Amp.

When i doing some testing the Load that i using is 12V/~2.9Amp is measured by multimeter. My problem is when i running the testing, the power supply rectifier is getting heat and hot. Not longer the diode 1n5408 is burn and explode. Finally the pcb is fire up :cry:. One thing i feel oddness is the output power supply FUSE 3A was not trip. Why?

According to the 1N5408 spec it able to carry up the power 1000Vx3A=3000W. For my case the total power drove 12Vx3A=36W is lest then 3000W, why the diode can burn? And the last, why the fuse wouldn't trip?

Please anyone can help to explain?...

Thank You.
 

Power Diode

i think you have misunderstood the specs... it has a maximum current rating of 3A and maximum voltage rating of 1000V but just because of that it doesnt mean it can undergo 3000W....

take a look at the thermal characteristics... it can undergo a maximum power dissipation of 6.25W...
 

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Depeding on mounting and load type, the current capacity could be lower than 3 A, e. g. 1.5 or 2A. Worst case is a capacitive load (large filter capacitor) and no copper areas soldered to the diode terminals. See the datasheet for details. I assume that you used a low frequency voltage source, e. g. a transformer.
 

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The voltage rating of 1000V is the Peak Inverse Voltage (PIV) i.e the maximum voltage it can block when reverse biased.
You also have to check whether the current rating is the average or the rms value.
The power rating is the on-state voltage drop (approx. 0.7V) X (forward current).
 

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Help,
Take a look at the data sheet: **broken link removed**
There are some key ratings:
. Tj Maximum Junction Temperature = 150 Deg C
. RthetaJA Thermal Resistance Junction to Ambient = 20 DegC/W.
To calculate the actual junction temperature, use
Tj = Tambient + P RthetaJA
Where P is the power dissipated by the junction. If this number exceeds 150 Deg C, then the device is overstressed.
Measuring the actual power can be tricky, since the forward voltage is a non-linear (logarithmic) function of current. However, you can come close by assuming the voltage is 0.8V.
.
As others have pointed out, the voltage rating does not enter into the picture (unless of course, you are exceeding it), since this rating is the reverse voltage rating, not the volward voltage rating.
I Hope this helps
Kral
 

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just ensure that the rectifier diode is mounted in such a way that the generated heat [Vf≈1.2V @ I≈3A, P=U*I≈3.6W] can be dissipated, that's all ..

rgds,
ianp
 

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Hi Dear All,

Thank for your kindly reply.

FvM:
There is no capacitor after the rectifier but after regulated output have a big cap 4700uF/50V. The incoming AC supply and the rectifier track on pcb is thick and full of copper-fill.
Our country is using 230VAC/50Hz. 50Hz is it too low frequency? Is it this is the root course?

kiprono:
I’m measured the current from the output power supply. In theoretical, Power-In = Power-Out. The power supply is linear type. Can we assume the current is measured at Output will equal to current Input (either transformer at secondary 12V-0V or after rectifier)?

IanP:
Vf is what voltage? How can we know the Vf is 1.2V?


Another question is why the FUSE no trip? In practical, the rectifier is consuming the high voltage and getting the heat before it burn. The current will slowly increasing am I rite? What I’m trying to say is.. Let say the full load output power is 12Vx3A=36W, after the load is increasing but the voltage is start dropping to 10V. So the current is start increasing to 3.6Amp already. So, in this situation the FUSE should trip am I rite?
Is it the true in theoretical? How bout practical?

Thank again…
 

Vf is what voltage? How can we know the Vf is 1.2V?
Click to expand...
it's the diode's forward voltage, and you can find it in it's data sheet ..

problem with fuses is that they can easily withstand I[rated] + roughly 20%[or more] and on top of that you have two types of fuses: slow-blow and fast-blow ..
just keep in mind that fuse is used as the last level of protection, basically protection against fires ..

another option is, if this diode is too hot, you can try to add another diode in parallel ..
it's not the best solution as diodes do not have identical Vf-s but it may help ..

for 3A load(s) you should really use 5-6A diode ..

rgds,
ianp
 

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It seems your transformer is a centre-tapped (12V-0-12V). Could you please upload the circuit schematic for proper response. It is possible for the input and output currents to be different.
 

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Thank Ianp,

Yes, you are rite. The datasheet shown Max Forward Voltage (Vf) is 1.2V @ 3A but some say 1V.

May i know what is Vf-s?

Please can you give some advice how to improve the design which can go more high Amp. Other than add another 4 diodes (so the total diode at rectifier is 8 diode's), what can i do?

Thank you.
 

May i know what is Vf-s?
Click to expand...
it's a shortcut:
1Vf and 1Vf => 2Vf-s

if this is CT (centre-tap) transformer the rectifier may have only two diodes, see attached picture ..

rgds,
ianp
 

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  • rectct_2042.gif
    rectct_2042.gif
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Hi,
I think your major problem is that large capacitor after the regulator without any cap after rectifier. The regulator will get reverse biased when the rectified output goes towards zero and the circuit may be malfunctioning. If it is not by design, your problem may go once you shift the cap to the rectifier output.

Regards,
Laktronics
 

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There are some unclear points left. You originally talked of a diode burned, later of four diodes involved in your circuit, also a regulator and a center-tapped transformer. I can imagine many different circuits that can be made from this parts, some hopefully operational. I don't like to add further guesses without knowing the true circuit.
 

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Help,
Another option is to use a Schottky diode. They have lower forward voltage. There are 2 disadvatages: They are usually only available in reverse voltages up to about 50V, although some low cuurrent Shottkys have higher voltage ratings. This should not be a problem in your application. Also, they have higher reverse leakage than a junction diode. Reverse leakage is usually not a problem in a power supply application. With the lower Vf, the dissipation will be lower that with the 1N5408. Take a look at the 1N5822 http://www.datasheetcatalog.org/datasheet/bytes/1N5820.pdf
Regards,
Kral
 

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Hi dear all,

Sorry for let you all waiting for so long. This few days i'm doing the testing and i already drawn out the circuit. This is my final design.
I had tried the expreriment again which is connect to heavy load. The result stil the same, the diode rectifier is very hot.
Sorry, i also confused when doing the testing on 1st time. I'm not using center-tap transformer, the AC In (H1) is connected to transformer secondary 12V-12V.

Please give some comment..

Thank you.
 

instead of 4 x 3A diodes use a 6A bridge mounted on a heat-sink ..
at this moment you have the power transistor sitting nicely on a heat-sink and 4 hard-working diodes cooled by nothing ..
D6 only deteriorates the voltage regulation, i‘d remove it from the circuit and connect the emitter of Q1 directly to R4 ..
also, i’d connect the fuse between H1 and D1<->D2 ..

cheers,
ianp
 

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What do you mean by transformer secondary 12V-12V?
A centre-tap is 12V-0-12V; the other is 12V-0; Can you tell us how many input and output terminals your transformer has?
 

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Hi Ianp,
Thank for your advice.
Bridge is much more expensive than diode. I plan to use 1N5554 (5A). But some of the datasheet show the Average DC Output Current 3A and some show Average Rectified current 5A.
https://pdf1.alldatasheet.com/datasheet-pdf/view/76086/MICROSEMI/1N5550.html
https://pdf1.alldatasheet.com/datasheet-pdf/view/145093/SENSITRON/1N5550.html
I abit confusing... What does it mean from datasheet? Do you have any recommend diode?

Hi kiprono,
Sorry, kiprono. I also confusing the transformer. On primary side have 2 wire's and the sencondary side have 2 wire only. I think should be 12V-0 as you mention.
Do you have any comment about the circuit?

Thank you.
 

The average current of 1N5554 is 5.0A; I don't see any problem with your circuit. However, the diodes are not supposed to get hot when there is no load. If they do, then check the circuit layout for possible short-circuits.
Otherwise 1N5554 is expected to give you better performance. Two diodes will be sufficient for the rectifier part.
 

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Silicon, Power Rectifier, General Purpose.
DC forward voltage(max V):1.2(1.3 for 1N5554) @DC forward current(pk A):9.0
DC reverse current(max µA):1.0 @ DC reverse voltage (V): 200, 600, 1000
Switching time (ns): 2000; IFSM= 100 A (pk); Io= 3.0 A (t=55°C.)
Operating Temperature range (°C.): -65 to +175.
Click to expand...

i would't trust data sheets that quote 1N555X diode as 5A diode ..
better find one that does not create confusion ..
for example, 6A1 ...
http://www.datasheetcatalog.org/datasheet/bytes/6A6.pdf

if this trasformer has only one secondary winding then there is no way it is CT ..

you need 4 diodes and i still think that a 6A rated bridge (that can be attached to a small heatsink) is cheaper than 4 x 6A diodes ..

rgds,
ianp
 

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