Hello,
I'm using LUXEON Z high power LED for my application. I would like to have many LEDs (~1000) in series and parallel connections. Vf is 2.8V and If is 1.0A.

Can you please guide me how to protect LED strings? Resistors are needed? LED has inbuilt TVS diode.

How to select power supply? How many LED in series and how many strings allowed?

Thanks'
Arul

 

What do you have available as a power source?

 

LED has inbuilt TVS diode.

Do you have a part number? It would be unusual for LEDs to have TVS diodes. Maybe an anti-parallel diode for reverse breakdown protection. But a transient voltage suppressor?

How many LED in series and how many strings allowed?

What power supply voltage do you want to use? What is your definition of a "string"?

 

If you are starting from scratch regarding the supply, then just choose a safe DC voltage and wire the LEDs as needed.
I might choose a 48-volt constant current driver and place about 16 LEDs in series. (no resistors needed)
Then the main supply would have to produce the minimum voltage and current for all of the CC drivers.

If you want to power all 1000 LED from the same supply, then you must determine how many LEDs you want in a string before anybody could give you advice on the supply. There are just way too many combinations available.

The longer you make your strings the lower the current that will be needed, but a higher voltage as well, the shorter the strings the more current you will need but a lower voltage...but either way the same total wattage will be needed.

Example:

If you want 10 strings of 100 LEDs each you will need a supply of 280 volts plus overhead that can produce at least 10 amps.

 

2800W of LED light at lumens per Watt is 280,000 lumens. What are you lighting?

 

If you are starting from scratch regarding the supply, then just choose a safe DC voltage and wire the LEDs as needed.
I might choose a 48-volt constant current driver and place about 16 LEDs in series. (no resistors needed)
Then the main supply would have to produce the minimum voltage and current for all of the CC drivers.

If you want to power all 1000 LED from the same supply, then you must determine how many LEDs you want in a string before anybody could give you advice on the supply. There are just way too many combinations available.

The longer you make your strings the lower the current that will be needed, but a higher voltage as well, the shorter the strings the more current you will need but a lower voltage...but either way the same total wattage will be needed.

Example:

If you want 10 strings of 100 LEDs each you will need a supply of 280 volts plus overhead that can produce at least 10 amps.

Thank you for your reply. I'm planning to use MCPCB( Metal Core Printed Circuit Board) for placing all the LEDs and connect them.

How can I protect LEDs in case of anyone LED/string failure? This is always there in my mind. How can I say my circuit is good enough to power up all the LED?
Any calculations there to prove? Please help

Thanks

 

2800W of LED light at lumens per Watt is 280,000 lumens. What are you lighting?

Thanks. I'm heating some element with LED lighting.

 

Protecting the LEDs:
Normally protecting LEDs are a combination of thermal maintenance and derating.
I wouldn't worry about damage caused by LED failures as long as your supply/drivers are regulated as to not affect the other strings.

Making sure the system works:
After determining how you want to make the arrays regarding voltages and current and how you plan to power them, you need to ensure that you have more wattage available than you need, I would say at least 20% more. (the more the better)

After reading your last post I would have to say thermal management will be a huge challenge if you intend to heat something with LEDs.

 

Each series string should have a series resistor to allow for small variations in the forward voltage due to manufacturing tolerances.
For 1000 LEDs it will make sense to have series strings of 25 LEDs for each series resistor. that will mean a supply voltage between 60 and 100 volts, which will allow the use of a BUCK type switching regulator at an efficient operation mode.
But if your local mains voltage is 200 to 240 volts, then series strings of 50 LEDs might be more reasonable, for the power supply efficiency consideration.

 

Protecting the LEDs:
Normally protecting LEDs are a combination of thermal maintenance and derating.
I wouldn't worry about damage caused by LED failures as long as your supply/drivers are regulated as to not affect the other strings.

Making sure the system works:
After determining how you want to make the arrays regarding voltages and current and how you plan to power them, you need to ensure that you have more wattage available than you need, I would say at least 20% more. (the more the better)

After reading your last post I would have to say thermal management will be a huge challenge if you intend to heat something with LEDs.

Thank you for prompt response. Thermal management is been considered.

What LED driver can be used for this application? constant voltage or constant current?

 

Constant current should be used.

 

Each series string should have a series resistor to allow for small variations in the forward voltage due to manufacturing tolerances.
For 1000 LEDs it will make sense to have series strings of 25 LEDs for each series resistor. that will mean a supply voltage between 60 and 100 volts, which will allow the use of a BUCK type switching regulator at an efficient operation mode.
But if your local mains voltage is 200 to 240 volts, then series strings of 50 LEDs might be more reasonable, for the power supply efficiency consideration.

I was wondering how much voltage would have to be dropped across the series resistor to properly regulate a series string of 25 LEDs at a forward voltage of 2,8 each.

 

B

Constant current should be used.

But in the event of LED failure, the other strings also affected due to increasing in current. If voltage is constant then there shouldn't be issue in other strings. Is my understanding correct?

 

Constant current must be applied to each string, not a group of strings in parallel.

Applying CC to parallel LED strings would do exactly as you say.

If you want to parallel the strings on a single driver, then you must use constant voltage.

 

Thanks. I'm heating some element with LED lighting.

Why? Why not use a heating element?

 

Constant current must be applied to each string, not a group of strings in parallel.

Applying CC to parallel LED strings would do exactly as you say.

If you want to parallel the strings on a single driver, then you must use constant voltage.

My thinking was constant voltage set to provide the desired current , and a resistance to hold the current at about the desired level as the forward drop varied with temperature. This means that the forward voltage drop needs to be known.