Led selection - hardware learning notes 3

The article is only for personal understanding , Learning record , You don't have to have any authority , Know .

These two days, the leader arranged the selection of light-emitting diodes , Record the learning experience .

Light emitting diodes should not be difficult for hardware engineers , Because of the frequent use of , I can't be more familiar .

about LED Pressure drop , Conducting current , Calculation of current limiting resistance , These parameters are no longer difficult .

For the drive circuit , Low current can be used directly I/O mouth , High current can be driven by triode .

There are two parameters for selection. We often follow our feelings , Record and remind yourself .

1. Pressure drop ;

About pressure drop , Data books always give such values .

Which one should I choose ？2.0V It's electric current 20MA Typical value at , I need it 10ma, What is the pressure drop ？

This picture may help us , But I haven't paid attention to it before .

 

2.LED Life curve

inquiry LED Manufacturer time , The answer is ： We LED In general, it can be used XXXXXh.

Is our usage general , What reference significance does this general value have for us , How much light can be used .

So we need LED Life curve , This data book generally does not reflect , Need to find the manufacturer , Sometimes the manufacturer will give us the life curve corresponding to current and service temperature , In this way, we can directly find .

The manufacturer sometimes gives 1000 A little time goes by , We need to estimate based on this data LED service life .

  Assume 1000 The light decay rate is ｎ％,    

50% Light attenuation formula ：t=1000*ln0.5/ln(1-ｎ％）   

30% Light attenuation formula ：t=1000*ln0.7/ln(1-ｎ％）

for instance ： Power indicator

Assume that the power supply is 5V,LED It's a red light , I need to turn on the current in 10MA, Then the pressure drop is 1.8V, The calculated current limiting resistance is ：（5-1.8）/10*10^(-3)=320Ω.

Suppose the manufacturer gives LED stay 10MA,25℃ when ,1000h Light decay is 2%, be L70( luminous attenuation 30%) The usage time is ：t=1000*ln0.7/ln(1-2％）=17657h.

Of course LED The service life of the lamp is not only related to the current, but also to the service temperature , The higher the temperature, the lower the service life , Therefore, the service life can only be roughly estimated .