# LED peak current

• PhysicsTest

#### PhysicsTest

TL;DR Summary
Does LED lamps have peak and nominal current?
I want to understand if LED's which are used in the vehicles have Peak and nominal current? This is to know the hardware design to support the LEDs with peak currents, if both peak and nominal currents are same we can design a single board else the hardware design shall also consider the peak current.

Peak current for LED is when it stops emitting light and emits smoke instead

LED driver keeps the current to be somewhat lower, so that the LED emits as much light as possible, yet survives.

berkeman, anorlunda and PhysicsTest
I want to understand if LED's which are used in the vehicles have Peak and nominal current?
The LED light output is a function of average current.
But the immediate efficiency of light production is reduced at higher temperatures.
Higher temperatures also age the device faster.

The fundamental aim of the design must therefore be, to keep the LED cool.

Circuit design must regulate light output by limiting the average LED current. There are several methods, in order of increasing efficiency …
1. Use a series resistor, close to the LED, which also heats the LED.
2. Use a series resistor, thermally isolated from the LED.
3. Switch the LED on/off, to average the current, which is noisy and strobes the light brightness.
4. Use a switching, constant current regulator with a series inductor.

hutchphd
Infrared LED datasheets often include a peak current that is much larger than the average forward current. This is so you can use the device at much higher intensities for various sensing purposes when the receiver can do its thing fast but needs more light than the average current can supply.

https://www.digikey.com/en/products/detail/stanley-electric-co/JGN1105H-TR/7606741
The nominal rating is 50mA and maximum rating is 120mA. If we can do accomplish our task in 0.1mS then 1.2A is the peak and we get over 10 times the brightness as the nominal current.

https://www.digikey.com/en/products/detail/kingbright/ACSC02-41CGKWA-F01/3084741
Nominal 10mA, max 30mA, peak 150mA. This one has a much smaller spread of current values but is a visible one. They are typically scanned so only one digit or even segment is on at once. You can get the nominal light output at much less than 100% duty cycle. These are designed with this in mind. That there is no graph in the datasheet that specifies the pulsed brightness values is odd.

https://www.digikey.com/en/products/detail/lumileds/L1SP-DRD0002800000/9805570
(White) Nominal 120mA, max 480mA, peak 500mA. Here is a lighting LED that has a very small max to peak difference. A strict reading of the datasheet shows that the duty cycle at 480mA is 100% and at 500mA it is 50%. This is suspicious.

These devices were selected based on being somewhere in the first page of that type of device in Digikey.

If a device doesn't include a peak value in the datasheet (I tried and failed to find an example) it is best not to design it for peak usage. It might work perfectly fine but you won't find that out until it fails embarrassingly (spectacularly in the case of a high power one).

Is there a specific application you are looking at? Why do you want to use the peak current?

BoB

The main reason is, i have asked a hardware person to design a hardware board to interface the LED lamps in motor cycle and i provided the nominal wattage (nominal current) ratings, but he was requesting for the peak wattages (peak currents) to take care in the hardware design. So, i wanted to understand does the LED lamp specifications include peak currents or not. I referred the website LED Lamps and downloaded the data sheets but it does not show any peak current.

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• GPS01_3611805_LEDriving_HLM.pdf
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So, i wanted to understand does the LED lamp specifications include peak currents or not.
I believe those lamps are direct replacements for the filament lamp. The LED lamps are rated to operate on 12 V, so they must include current regulation, and no extra PCB should be needed. Can you just plug them into the existing headlight socket ?

You can look at the specifications on eBay or another supplier.
https://www.ebay.com.au/itm/314073577919?

Here is a link to a mostly useless datasheet:
https://www.osram.com/appsj/pdc/pdf...PP_EUROPE_Europe_eCat&lid=EN&mpid=ZMP_4062794

It does state that:
Nominal Voltage: 12V
Test Voltage: 13.2V

Also note that the lifetime is rated for a minimum of 500 Hours.

Ordinary Lead-Acid batteries have a charging voltage of 14.4V, so the LED is likely designed to handle that. Of course for off-road use, the shock and vibration sometimes destroys internal connections in a battery; leaving it electrically disconnected.

Then, depending on the details of the charging circuitry, the voltage may be substantially higher than 14.4V.

Based only on the above, my recommendation would be to limit voltage to the lamp to 14.4V.

There is an alternative approach; design the control circuit for Constant Current to the LED. You can calculate the current from the datasheet by dividing the Wattage rating by the Voltage rating.

Cheers,
Tom

The main reason is, i have asked a hardware person to design a hardware board to interface the LED lamps in motor cycle and i provided the nominal wattage (nominal current) ratings, but he was requesting for the peak wattages (peak currents) to take care in the hardware design.
If it's a 'LED lamp' and not a 'LED' then that's a different beast. It'll contain a regulator and some more electronics to drive the LEDs, and all that has an 'inrush current' at startup, which you indeed need to account for in a design.

If it's not mentioned on the datasheet of the LED lamp (likely, won't) then - same class filament laps usually has even worse inrush current, so I think you can safely use those as a reference for the project.

There is an alternative approach; design the control circuit for Constant Current to the LED. You can calculate the current from the datasheet by dividing the Wattage rating by the Voltage rating.
Depending on the circuit included in the lamp assembly this may be difficult. If it is a switching current regulator then is is operating on small margins as there is only room for a limited amount of reactive components. A voltage regulator may be easier and let the lamp do its own thing.

@PhysicsTest What voltage does the motorcycle's electrical system run at?

BoB

It runs at 12V.

rbelli1
It runs at 12V.
Actually no. Pull out multimeter and measure actual voltages at various parts of motorcycle electrical system.

1. leaving RR, it's close to 15v
2. at battery at idle, it's most likely 14.5v @ idle and close to 15v @ 1/2-redline
3. at headlight socket, with good relay-harness, probably close to 14-14.5v.
4. at headlight socket, without relay-harness and all power going through dimmer-switch, 13.0-13.5v

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