Ultrafast diode

[epilot]

hello there,

what "ultrafast" word means for diodes?

today i had a TV for repair, i found a rectifier diode that was fried(shorted)
the number is "UF5407". could not to find one so i bought few 1N5407 rectifiers and replaced one with the original fried diode,
there was a problem, when i turned the TV on it returned to standby mode and yes i lost 1N5407(it was shorted too)
i tried to find any other problem but there was not any problem rather than the diode so i went to look at data sheet of 1N and UF 5407,
i noticed that UF5407 is an ultrafast rectifier diode while 1N5407 is a normal rectifier diode.

now i want to know what is an "ultrafast" rectifier diode really?

since i was not able to find UF5407 diode what is your suggestion for a replacement?

many thanks for any help.

 

[Hero999]

All diodes have a switching time, that is how long it takes to turn off or on when the current is reversed. Ultrafast diodes have a much shorter switching time than ordinary rectifiers, they are normally used in RF applications like TVs.

I recommend you look for the fastest diode you can find from your local supplier and see if it works.

 

[Nigel Goodwin]

hello there,

what "ultrafast" word means for diodes?

today i had a TV for repair, i found a rectifier diode that was fried(shorted)
the number is "UF5407". could not to find one so i bought few 1N5407 rectifiers and replaced one with the original fried diode,
there was a problem, when i turned the TV on it returned to standby mode and yes i lost 1N5407(it was shorted too)
i tried to find any other problem but there was not any problem rather than the diode so i went to look at data sheet of 1N and UF 5407,
i noticed that UF5407 is an ultrafast rectifier diode while 1N5407 is a normal rectifier diode.

What you need is a 'fast recovery' rectifier, normal rectifiers are too slow for line output or switch-mode use (and die VERY quickly!) - what specifically is the rectifier doing in the circuit?.

 

[epilot]

What you need is a 'fast recovery' rectifier, normal rectifiers are too slow for line output or switch-mode use (and die VERY quickly!) - what specifically is the rectifier doing in the circuit?.

i used 3 or 4 1N5407 and they was fried too, so that is why i lost them.

the diode sends a 150V to high voltage transformer,

can you suggest an alternative diode Nigel?

 

[Nigel Goodwin]

i used 3 or 4 1N5407 and they was fried too, so that is why i lost them.

the diode sends a 150V to high voltage transformer,

can you suggest an alternative diode Nigel?

OK, so it's the main HT rectifier, off the switch-mode transformer, 1N5407's are standard slow rectifiers, they will overheat and die in seconds!.

The fast diodes I stock at work are the RGP15J and the BY229, with the RGP15J being the one I use by far the most of.

 

[epilot]

OK, so it's the main HT rectifier, off the switch-mode transformer, 1N5407's are standard slow rectifiers, they will overheat and die in seconds!.

The fast diodes I stock at work are the RGP15J and the BY229, with the RGP15J being the one I use by far the most of.

ok thanks,

i could find some "BY298" & "GUF30J" and "BY399",
TV worked with GUF30J for 2min then i lost few components from power part:
a K2545 FET a 44608 IC and 2 resistors!

K2545 got very hot and then became shorted so i lost that IC and resistors too.

does anyone know this circuit for power part of Vestel TV's?

few days ago i tested the coil "l802" and it was cutted, as you can see there is no number for it in the scheme so i replaced it with a 27uH and then with a 100uH,
does anyone know if that is why i lost the fet and then the IC?

thanks

 

[raybo]

Maybe your problem is not the diode. To blow a 1n4007 that a trick. do you supose that your load to the diode is way to much. Shorted cap other loads?

 

[epilot]

Maybe your problem is not the diode. To blow a 1n4007 that a trick. do you supose that your load to the diode is way to much. Shorted cap other loads?

yes,
i removed that inductor and shorted its way,
now the diode and K2545 get less hot, but another problem is that the TV turns off after 5min and i have to wait for 2 or 3min and then when i turn it on it works and again... my idea is that there is any other thing that cause an overload yet, but i don't know what it is.

since a 20uH inductor is so important at overloading and warming of the stuff, so perhaps the problem is that:
i could not find a 0.22 ohm resistor(see the pic) for the source of K2545 and i used a 0.33 ohm instead,
does anyone know if it can cause the problem or not?
i think that resistor is important because i used a 1.5 ohm resistor too and the TV never worked?

P.s now i think i can understand the art of electronics design (lol)

 

[Nigel Goodwin]

yes,
i removed that inductor and shorted its way,
now the diode and K2545 get less hot, but another problem is that the TV turns off after 5min and i have to wait for 2 or 3min and then when i turn it on it works and again... my idea is that there is any other thing that cause an overload yet, but i don't know what it is.

since a 20uH inductor is so important at overloading and warming of the stuff, so perhaps the problem is that:
i could not find a 0.22 ohm resistor(see the pic) for the source of K2545 and i used a 0.33 ohm instead,
does anyone know if it can cause the problem or not?
i think that resistor is important because i used a 1.5 ohm resistor too and the TV never worked?

P.s now i think i can understand the art of electronics design (lol)

The 0.22 ohm resistor is the current limiting sensor, replacing it with a 0.33 will mean it current limits far earlier, so may well limit on bright scenes.

 

[ZIGGY_DAN]

keep going and at this rate you'll have no TV left! if you remove a damaged component then you must replace it with either the exact same component or a perfect like for like match, otherwise you will create other problems and eventualy have a completely screwed TV.

 

[Hero999]

It's perfectly fine to replace it with a similar componant with similar or better ratings.

 

[ZIGGY_DAN]

ok, you could replace it with a component with similar or better ratings, but not a component with worse ratings, or different operating characteristics.

like a 220Ω resistor replaced with a 330Ω resistor, this will affect circuit operation.

 

[Nigel Goodwin]

ok, you could replace it with a component with similar or better ratings, but not a component with worse ratings, or different operating characteristics.

like a 220Ω resistor replaced with a 330Ω resistor, this will affect circuit operation.

Not 'always' true, as long as you know EXACTLY what you are doing, and why, sometimes it's advantageous to replace with a different value. But this requires years of experience, and a good knowledge of how the circuit works!.

 

[epilot]

i solved the problem,
thanks for all helps.