component replacement help

[wejos]

Hi guys, happy new year!

I'm trying to swap a suspected bad component from an inverter board of lcd aoc monitor. Except the component is not yet available in our city, probably even country. SMD components are hard to find in our country. they have to be imported and I cannot engage in this transaction right now. The part number of the suspected bad component is SM240A. Datasheet says it is a 2.0 amp surface mount schottky barrier rectifier, with 20-100 volts. Please take note of the volts since the second component does not say 20-100 volts in the datasheet, only 20 volts. I am confused why the other one is saying "to one hundred volts" while the other one does not say anything about this rating. Is there a difference between them?

The available schottkly diode here is IN5820. Peak repetitive/recurring reverse voltage is the same. DC blocking voltage is the same also. RMS voltage match also. I checked but not like it really makes a lot of sense to me anyway. The only difference between the IN5820 and SM240A are IN5820 has rating of 3.0 amp and SM240A has 2.0 amp. Voltage looks the same but I cannot find anything saying 20-100 volts in the IN5820 datasheet, compared to SM240A where it was explicitly printed. The 100 volts there is peak voltage right?

Can I use this IN5820 as replacement for SM240A? May I be enlightened why you cannot do this if the answer is is no.

I have another available component of diode, the IN5822. Still 3.0 amp also but with higher voltage starting of 40. It is not saying 40-100 volts again in the datasheet. Can I use this for replacement also? Will appreciate it much if you can explain to my or teach me why you can use and why it's a no--no! If you can use these replacement diodes, what is the explanation and is it safe to use? Just short idea so I may know where to start reading about the subject matter.

Thanks a lot in advance...

 

[KeepItSimpleStupid]

SM240A 2 A, 40 V,

1N5822 is 3A 40 V; So B can likely substitute for A without knowing anything about the circuit.

The datasheets looked a little creepy. Take a look at this one: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CEgQFjAC&url=https://www.onsemi.com/pub/Collateral/1N4001-D.PDF&ei=CIXGUu_bAefgsAT5roKwDQ&usg=AFQjCNHjlGQqKlhLLPqSyOC3xK3kAVe2Yw&bvm=bv.58187178,d.cWc&cad=rja

The 1N400x series. Basically, the last digit is related to reverse voltage. They combine the data for all of the parts in the datasheet, so you have to be careful when reading the datasheet. The 1n400x sheet is probably clearer.

Reverse voltage is non destructive if it's current limited. A 3 A part is usually bigger than a 2 A part.

 

[wejos]

Hi KeepItSimpleStupid,

You are right about 40V of SM240A. Carefully reading the datasheet indeed says the diode is 40V. Thank you.

On the IN400x series that you asked me to look at, I have noticed this diode is in schottky. Can you still use this series even tho the original part was schottky? I am asking since I have no idea what would happen to it.

Just to be clear, is it correct to say the ampere part is okay as long the value you are replacing will not be lower than the original ampere of the part, e.g. original value 2 amp replaced with 1 amp is bad idea, only 2 amp up will do or 3 amp - 5 amp. More like the electrolytic capacitor rule?

THANKS A LOT MAN

 

[Willen]

Replacing a diode with less current value than original might short the diode easily again. But use any high current rated than necessary like 3A, 5A or lets say 20A. If your original broken diode is rated 2A then better to use little high value like 3A this time, whih will not burn easily again I think.

 

[KeepItSimpleStupid]

The 1n400x series is not Schottky. Look at the forward voltage drop.

Some broad categories:
Germanium (mostly obsolete) It was used is low power detectors.
Normal recovery (for low frequency applications like 50/60 Hz)
Fast recovery (For switching power supplies)
Variactor (variabe capacitance) diodes
Zener/Avalanche diodes (breakdown is controlled)
High voltage diodes (very high voltage drops)

Schottky has properties such as fast recovery, low voltage drop and low capacitance.

 

[wejos]

Thanks a lot guys, to both of you. KeepItSimpleStupid &Willen. I am very satisified with your answers to my question.

One last thing, I'm not really sure what you're trying to say about voltage drop KeepItSimpleStupid? Average Forward Voltage Drop of IN400x says .08V and no mention about voltage drop in SM240A datasheet which is a schottky diode. Is there supposed to be significant difference between the two?

THANK YOU AGAIN

 

[KeepItSimpleStupid]

Max instantaneous voltage drop: SM240a = 0.52 V https://www.digchip.com/datasheets/parts/datasheet/1059/SM240A-pdf.php in Absolute max ratings.

For the 1N4001 0.92 V page 2 of the datasheet referenced. There is also a graph with the current dependence.

Schottky diodes typically have a lower voltage drop.

 

[Willen]

Normally silicone diode like 1N4007 has from 0.6 to 0.9 forward voltage drop. I guessed schottky has little less voltage drop than silicone. Faster diode like Germenium has 0.2 to 0.5 forward voltage drop I measured.

If you are trying to learn voltage drop then it is simple. If you you just want to replace a diode on your device with another schottky diode then don't need to worry thinking about this 'voltage drop'. If your new diode is OK then it will give few hundred voltage drop. Just replace it.

 

[KeepItSimpleStupid]

Schottky is usually a faster diode too.

 

[Willen]

If I have 1A diode but I need 2A, Is there any way to increase power of a diode like parallel resistor? (parallel diode may be funny hehe)

 

[KeepItSimpleStupid]

NO!

 

[wejos]

Definitely going to read more about voltage drop later on.

I'm afraid that I might fall for paralleling diode since no one ever warned me

What could possibly happen if you arranged your diode like this?

GRATEFUL FOR YOUR HELP

 

[KeepItSimpleStupid]

Because the resistances are different, one diode takes more of the share. This is a typical problem with bipolar transistors in parallel. Resistors in the emitters kinda keep things sane, but the current gain has to to be similar.