Power Diode 1N5408 Burn

[sohail_akram]

ANY DIODE has 10 times ampare of normal rating, surge .

 

[dirana42]

hi,

to all....

i had similar problem wherin the transformer was getting heated , i found that while getting the bridge rectifier soldered in as shown in diagram of a 30 v dc powersullpy i had made mistake inlaying the diods in such away that current was getting path to flow and result was the heat.. i took some time to find out as rest of the components were not affected .. could similar be problem a practicle one ?


i am not from electonics field its my hobby so pl. dont mind if you feel it is absurd observation....

dirana42

 

[Help]

Hi Dear Fren,

For the latest experiment, i'd add a fuse between H1 and D1<->D2 as Ianp advice.
What i did on this experiment is:
Exp 1: check F1 & F2 which is fast burst up
- F1=3A Fuse and F2=3A Fuse
- Connect the Amp meter between Q1 and F2
- Slowly increase the output load
The result:
After increment the current to ~3.6A shown on meter. The F1 is start burning and last not longer the F1 will burst up. Before the F1 is bust up the F2 it seen like no burn and stay cool. This Exp 1 had tried 2 time's, the result is same.

Exp 2: check burst up current on F2
- F1=13A Fuse and F2=3A Fuse
- Connect the Amp meter between Q1 and F2
- Slowly increase the output load
The result:
After increment the current to ~5.4A shown on meter. The F2 is start burning and burst up when the current reach ~5.5A.

From this 2 experiment we can know very clear. Apply the fuse's at difference point have difference result and the peak current fuse can carry on.
F1(3A) apply at AC point. To burst up the fuse we just need ~3.6A.
F2(3A) apply at DC point. To burst up the fuse is ~5.5A.

That's why my initial design the diode 1n5408(3A) is burn and explode without connect the F1 and the F2 fuse was not burst.
But i still don't understand what's the reason the F2 have to goes up to 5.5A then wil burst? and it was 3A fuse.
2nd, Why the AC fuse and DC fuse have much more difference peak current to burst off?

Thank for sharing the experience and knowladge...

 

[FvM]

The results are as expectable to my opinion. F2 is basically loaded with the DC output current and acts as shown in fuse I-t-curves. You may consult datasheets for the specific fuse type used in your test. F2 is loaded by the DC current multiplied with a waveform factor (RMS/rectified mean value) depending on transformer impedance and filter capacitor, 1.5 - 1.6 is a typical value for a C-loaded full wave rectifier. While a fuse (resistive element) is always loaded with the RMS current, the effective diode load is somwhere between rectified mean value and RMS current.

 

[Help]

Hi,

F2 is basically loaded with the DC output current and acts as shown in fuse I-t-curves. You may consult datasheets for the specific fuse type used in your test.

Thank you FvM. The fuse I’m using is normal 3A fuse. I'm not sure which datasheet is attach for the fuse because it don't status the manufacturer but can we assume as standard 3A fuse? Bellow is shown the I-t curves that you mention? I attached the waveform from other datasheet.

F2 is loaded by the DC current multiplied with a waveform factor (RMS/rectified mean value) depending on transformer impedance and filter capacitor, 1.5 - 1.6 is a typical value for a C-loaded full wave rectifier.

Sorry, not so sure your explanation. Is it the F2 current 3A have to multiplied the RMS(1.414) value? What is the 1.5-1.6 number for? is voltage?

While a fuse (resistive element) is always loaded with the RMS current, the effective diode load is somewhere between rectified mean value and RMS current.

What will happen if effective the diode load value and RMS current? Is it will cause the DC fuse wouldn't burst off at 3A?


Thank you.

 

[FvM]

With C-load you get non-sinusoidal current form. It's RMS is much higher than the DC output current (or rectified mean value). 1.5 to 1.6 is an empirical value for the waveform factor. You can measure the actual current with an RMS capable meter or use an oscilloscope with a low ohmic shunt resistor and calculate the RMS value (modern DSOs will do that for you).

You can also perform a circuit simulation (the transformer windings resistance and stray inductance must be known to be exact). This would give the actual fuse and rectifier thermal load. But as discussed before, the rectifier datasheet has already data for current capacity with C-load, this should be sufficiant for most applications.