Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

for LED drive = constent current or constent voltage which is batter ?

Status
Not open for further replies.
D

drbizzarow

Advanced Member level 1
Joined
May 24, 2006
Messages
414
Helped
25
Reputation
50
Reaction score
15
Trophy points
1,298
Activity points
3,662
hi guys !!

i need input from you, i am driving 3.2V-1watt supper bright 3 leds in serese
which make total load of 9.6 volt by 12VOLT-7AH battery.

i need your input which solution is batter to drive this load???

1: dirving load through lm317 as constent curent source.
2: driving load through lm2576 (switch regulator -adj type).

give your sugestion in term of heat desipation of these regulators and increase life of leds
 

Leds have to be driven using constant current, you will never get the current right using voltage regulation and even if you do the current will change with temperature.
Lm317 can probably do it with a consumption of about 1W (3.4v * 0.31A) but a switching regulator would make the battery last longer.

Alex
 
Leds can´t be voltage driven because the voltage on them is not a constant and they act like diodes, which means even a small voltage error can lead to a large current increase. You can use a voltage source and place a limitting resistor in series or you can current drive them.
 

thx both of you, it clears me alot.
 

Re: LED drive, constant current or constant voltage: Which is better?

about 1W (3.4v * 0.31A)
Click to expand...
You missed by 0.25W by using the wrong voltage. 12V - 9.6V = 2.4V and 2.4V * 0.3125A = 0.75W.

I'd use the LM317 since I've done it this way before, but be sure to calculate the tolerance of your resistor, otherwise you may have excess current.

For some really nice current driving options, look at: **broken link removed**.
 
Last edited:

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top