Diode question

[Ziddik]

heya all..

I am trying to build a 12V 5 amperes powersupply for a project and i bought four 6A4 MIC diodes which can deliver 6A current, but i can't use the diodes for this 12V transformer! why is that? Does it need more voltage in input to forward bias than 12V? I tried 1N4007 and it works fine, but it can't deliver more than 1A current, so it might't useful.. Pls help,

 

[ericgibbs]

heya all..

I am trying to build a 12V 5 amperes powersupply for a project and i bought four 6A4 MIC diodes which can deliver 6A current, but i can't use the diodes for this 12V transformer! why is that? Does it need more voltage in input to forward bias than 12V? I tried 1N4007 and it works fine, but it can't deliver more than 1A current, so it might't useful.. Pls help,

hi,
The datasheets says only 0.95V fwd drop, so they should work ok

 

[Ziddik]

hi,
The datasheets says only 0.95V fwd drop, so they should work ok

hi eric,

but is doesn't work! It was supposed to power a 7" LCD TV that requires only around 12V at 1300mA, and my 5 amperes transformer is centertapped thus i used only 2 diodes! After assembling, i powered the TV but i could't turn on! ( but works fine when use 1N4007 diodes), what should i do?

 

[Dragon Tamer]

If your tv only needs 1300mA why do you need a 6A diode? You only need one rated for 2A (you may even be able to get away with just 1.5A). Even though your transformer can deliver 5A, the load will only draw the current that it needs to run.

 

[ericgibbs]

hi eric,

but is doesn't work! It was supposed to power a 7" LCD TV that requires only around 12V at 1300mA, and my 5 amperes transformer is centertapped thus i used only 2 diodes! After assembling, i powered the TV but i could't turn on! ( but works fine when use 1N4007 diodes), what should i do?

Hi,
I would suggest you get a multi meter with a Diode Test option or an Analog meter set for Ohms resistance and measure the resistance of the diode in both directions, let us know the measurement

 

[MrAl]

Hello,


Does your transformer have 12vac on BOTH SIDES of the center tap, or just 6v on both sides? If it's only 6vac on both sides then you'll have to use four diodes and ignore the center tap.

 

[Reloadron]

I agree with MrAl. My thought is you have a 12 volt CT transformer as in 6 volts each side of CT. If you used two diodes you have a 6 volt supply. Use 4 diodes in a full wave bridge as suggested. That would be my guess.

Ron

 

[ericgibbs]

hi,
Its this comment which puzzles me... ( but works fine when use 1N4007 diodes).????

 

[Ziddik]

no, i measured both points using a DMM, it shows 12V on each output of the transformer, but only one thing which i can't understand is why it works fine when i use 1N4007? and why doesnt when use 6A4? ..its confusing me.. Btw Can i use the 1N4007? It doesn't get much hot when the tv is operating,..

 

[Ziddik]

Hi,
I would suggest you get a multi meter with a Diode Test option or an Analog meter set for Ohms resistance and measure the resistance of the diode in both directions, let us know the measurement

hi, the diodes are ok, i tested

 

[Ziddik]

any idea people?

 

[Reloadron]

hi,
Its this comment which puzzles me... ( but works fine when use 1N4007 diodes).????

My bad as I didn't catch that.

OK your transformer is exactly like the attached with 12 volts to each side of the CT. Using 2 diodes with a 12 - 0 - 12 transformer as attached you should be getting 12 VDC (filtering not drawn). It should not matter between 1N4000 series of the 6A4 diodes, The results should be the same in that you get about 12 VDC out.

<EDIT> Fixed image polarity, thanks Jim. </EDIT>

Ron

 

[JimB]

Ron
You may want to have a look at your attachment and review the +ve and -ve connections?
JimB

 

[Reloadron]

Ron
You may want to have a look at your attachment and review the +ve and -ve connections?
JimB

Thought it looked funny. Many thanks Jim. The image now has correct polarity designations.

Ron

 

[BrownOut]

hi, the diodes are ok, i tested

You were supposed to tell us the resistance of the diodes in both directions.

Originally Posted by ericgibbs »
Hi,
I would suggest you get a multi meter with a Diode Test option or an Analog meter set for Ohms resistance and measure the resistance of the diode in both directions, let us know the measurement

 

[JimB]

Thought it looked funny. Many thanks Jim.

Dont you just hate it when that happens?
You look at something and it is not right, and you just cant see what it is.
Been there, done that, numerous times.

JimB

 

[Ziddik]

You were supposed to tell us the resistance of the diodes in both directions.

hi dragon,the resistances are 542 ohms in forward bias, and "None" in reverse bias, any problems?

 

[ericgibbs]

hi dragon,the resistances are 542 ohms in forward bias, and "None" in reverse bias, any problems?

I would say those readings indicate a 'good' diode.??

I am assuming the 'none' means a very high resistance value.?

 

[Diver300]

hi dragon,the resistances are 542 ohms in forward bias, and "None" in reverse bias, any problems?

That seems fine.

What do you get with the 1N4007 diodes?

 

[MrAl]

Hi Zid,

When is the last time you had it working with the 1N4007 diodes?
I ask because now that i think about it, maybe you shouldnt be doing it this way anyway because the peak voltage is going to be a lot higher than 12v and things that run on a near perfect 12vdc often dont like to get banged with much higher peak voltage.
Also, where are the filter caps? Im a little surprised it worked at all with ANY diodes really.