D83-004 , Schottky Barrier Diode

Thread Starter

spike1947

Joined Feb 4, 2016
266
Hi
This is probably a stupid question to some of you , but here goes , I have some spare D83-004 : V 3N P , Schottky Barrier Diodes , and I am wondering how to use them to convert 12ac to 12v dc ! , to power 4x7w cob led downlighters ! .

cheers
Spike
 

LesJones

Joined Jan 8, 2017
2,948
You can connect 4 of those diodes in a bridge configuration. That will give about 15 volts peak unsmoothed DC output. If you add a capacitor to the output that will smooth the output. If the LEDs are just bare LEDs then you will need to add a constant current to regulate the current to each LED. If they are light fittings designed to run on 12 volts DC then you will need to add a 12 volt voltage regulator with a current rating of at least 2.5 amps.

Les.
 

Thread Starter

spike1947

Joined Feb 4, 2016
266
Hi
This is probably a stupid question to some of you , but here goes , I have some spare D83-004 : V 3N P , Schottky Barrier Diodes , and I am wondering how to use them to convert 12ac to 12v dc ! , to power 4x7w cob led downlighters ! .

cheers
Spike
You can connect 4 of those diodes in a bridge configuration. That will give about 15 volts peak unsmoothed DC output. If you add a capacitor to the output that will smooth the output. If the LEDs are just bare LEDs then you will need to add a constant current to regulate the current to each LED. If they are light fittings designed to run on 12 volts DC then you will need to add a 12 volt voltage regulator with a current rating of at least 2.5 amps.

Les.
Hi Les
These are the bulbs I am wanting to fit , in place of the G4 20W Halogen bulbs .

Cool White DC12V Lamp LED Light Spotlight Bulb G4 COB .
 

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Thread Starter

spike1947

Joined Feb 4, 2016
266
Hi
I have a transformer from 240 to 12v AC to power 4x20W, G4 Halogen Bulbs in the kitchen , now I would like to change these to 7w COB led's ,could I use a " LT 413 (PBL405 4.0A) BRIDGE RECTIFIER " to go from 12v AC to 12v DC , I have a few of these ? .

cheers
Spike
 

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LesJones

Joined Jan 8, 2017
2,948
Spike, I have looked at some of these G4 COB LEDs on ebay and many of them have what looks like a 4 pin DIL bridge rectifier on the back. Do the ones that use have have a bridge rectifier on the back ?

Les.
 

Thread Starter

spike1947

Joined Feb 4, 2016
266
Spike, I have looked at some of these G4 COB LEDs on ebay and many of them have what looks like a 4 pin DIL bridge rectifier on the back. Do the ones that use have have a bridge rectifier on the back ?

Les.
Hi Les
I had only used 1 12v ac , led to try with the 12v ac feed , but it blow the led , it did have a 4 pin chip on the back , but it was too damaged to read what it was , have seen some that have though MB10F , but they also say they are AC ! .
Cheers
Spike
 

LesJones

Joined Jan 8, 2017
2,948
It could be that the chip is an LED driver not a bridge rectifier. If it was an MB10F that is a bridge rectifier. It is also possible that there was nothing to limit the current and that if the transformer was lightly loaded it's output would have been more than 12 volts. Also the peak voltage of 12 volts RMS would be almost 17 volts. Even subtracting two diode forwards volts drop it would still be about 15.5 volts so the current through the LEDs would be very high near the waveform peak. I have some 10 watt COB LED panels that claim to be for 12 or 24 volts. They take a sensible current at 12 volts but if it gets up to 14 volts as it could do if they were used in a car then the current was much too high. You have to be careful about the claimed rating for items bought on ebay.

Les.
 

Thread Starter

spike1947

Joined Feb 4, 2016
266
It could be that the chip is an LED driver not a bridge rectifier. If it was an MB10F that is a bridge rectifier. It is also possible that there was nothing to limit the current and that if the transformer was lightly loaded it's output would have been more than 12 volts. Also the peak voltage of 12 volts RMS would be almost 17 volts. Even subtracting two diode forwards volts drop it would still be about 15.5 volts so the current through the LEDs would be very high near the waveform peak. I have some 10 watt COB LED panels that claim to be for 12 or 24 volts. They take a sensible current at 12 volts but if it gets up to 14 volts as it could do if they were used in a car then the current was much too high. You have to be careful about the claimed rating for items bought on ebay.

Les.
Hi
Tks for your reply ,what I don't understand though is , the ones online with the MB0F , still say that there output is 12v AC ! .
cheers

spike
 

LesJones

Joined Jan 8, 2017
2,948
I assume you are referring to the LEDs and mean input rather than output. If they are fitted with MB10F bridge rectifiers the should work with AC or DC. IF not they will only work with DC. I came across a thread on another forum asking about electronic transformers. I wondered if it might be you. Is the transformer you are using a normal transformer or an electronic one ? If it is electronic it could be another reason for your problems. Some have a minimum load requirement and the high switching frequency might cause problems with the normal diodes in the MB10F.

Les.
 

Thread Starter

spike1947

Joined Feb 4, 2016
266
I assume you are referring to the LEDs and mean input rather than output. If they are fitted with MB10F bridge rectifiers the should work with AC or DC. IF not they will only work with DC. I came across a thread on another forum asking about electronic transformers. I wondered if it might be you. Is the transformer you are using a normal transformer or an electronic one ? If it is electronic it could be another reason for your problems. Some have a minimum load requirement and the high switching frequency might cause problems with the normal diodes in the MB10F.

Les.
Hi Les
Tks for your reply Yes it was me asking about the electronic tranny , when you say it will only work on DC if a MB10F is not fitted , that puzzled me , the LED that had the MB10F fitted was advertised has DC ! .
Cheers
Spike
 

LesJones

Joined Jan 8, 2017
2,948
Many of the sellers on ebay don't know anything about the items they are selling. LEDs (The bare LED) work with DC (Direct current.) The polarity of the voltage is always the same. For example on an AA cell the case is always negative and the small cap is always positive. With AC (Alternating current.) the polarity reverses 100 times per second when the frequency is 50 hz (As in the UK and most of Europe.) or 120 times per second when the frequency is 60 hz (As in in the US) The bridge rectifier converts AC into DC. (Note the DC output of the rectifier is not smooth DC it will have ripple on it.) The bridge rectifier also means that the output will always the same polarity no matter which way a DC supply is connected to it's input. This saves the possibility of destroying the LED with the wrong polarity. Think of bayonet type car bulbs with two contacts. The polarity to the two contacts depends on the way it is inserted into the holder. As you can see from the two oscilloscope traces on the thread on electronic transformers the waveform is much more complex than the simple sine wave output of a normal transformer. The square wave part of the waveform was about 27 Khz so the polarity was reversing about 54000 tines per second. The diodes used in the MB10F bridge rectifier are not suitable for that frequency. I have never tried using normal diodes at such high frequencies so I don't know if they would fail in the way yours did. I think you should first test any new LED units using a current limited 12 volt DC supply. If you can it would be worth monitoring the current while adjusting the 12 volt supply between say 11 and 13 volts to see at what voltage they consume their rated wattage.

Les.
 
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Thread Starter

spike1947

Joined Feb 4, 2016
266
I assume you are referring to the LEDs and mean input rather than output. If they are fitted with MB10F bridge rectifiers the should work with AC or DC. IF not they will only work with DC. I came across a thread on another forum asking about electronic transformers. I wondered if it might be you. Is the transformer you are using a normal transformer or an electronic one ? If it is electronic it could be another reason for your problems. Some have a minimum load requirement and the high switching frequency might cause problems with the normal diodes in the MB10F.

Les.
Hi
This is a pic of the Transformer .
Cheers
Spike
 

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LesJones

Joined Jan 8, 2017
2,948
Did you make sure you had at least 35 watts of load on it before connecting the LED ? I think you should do the tests I suggested on the LED units to see if they are running at or over their wattage rating when fed with 12 volts DC and check how rapidly the power input increases with a small increase on the supposed rating on 12 volts.

Les.
 

Thread Starter

spike1947

Joined Feb 4, 2016
266
Did you make sure you had at least 35 watts of load on it before connecting the LED ? I think you should do the tests I suggested on the LED units to see if they are running at or over their wattage rating when fed with 12 volts DC and check how rapidly the power input increases with a small increase on the supposed rating on 12 volts.

Les.
Ok , will try what you suggest , tks for your time and help .
Spike
 
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