Simple Circuit for high power LED

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Discussion Overview

The discussion revolves around designing a simple circuit for powering a 3V high power LED with a maximum current of 0.8 amps, using battery voltages ranging from 4.5V to 9V. Participants explore various circuit configurations, components, and considerations for efficiency and heat management.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant suggests connecting a 9V battery to the LED in series with a resistor calculated as (9-3)/0.8 Ohm, and similarly for a 4.5V battery.
  • Another participant emphasizes the importance of using a resistor with a suitable power rating, recommending at least a 10 watt resistor due to significant heat generation.
  • There is a suggestion to use multiple LEDs in series to improve efficiency and reduce heat, or to consider a buck switching regulator for better efficiency.
  • One participant questions the inclusion of LM317 and L7805 voltage regulator ICs in a circuit found online, asking about their purpose and the role of capacitors.
  • Another participant explains that these ICs are used to maintain constant brightness of the LED as the battery voltage decreases.
  • A suggestion is made to use size-D or lantern batteries to support the current draw without excessive heat loss.

Areas of Agreement / Disagreement

Participants express varying opinions on the best approach to design the circuit, with no consensus on a single solution. Different methods for managing current and heat are discussed, indicating multiple competing views.

Contextual Notes

Participants mention the need for careful consideration of resistor ratings and the potential benefits of using voltage regulators in constant current configurations, but do not resolve the specifics of these implementations.

Who May Find This Useful

This discussion may be useful for hobbyists and engineers interested in LED circuit design, particularly those exploring power management and efficiency in high current applications.

selseg
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What simple circuit that I can design for a 3V high power LED with max current 0.8 amps , I think the component names would help me , I would like to power it on 4.5 to 9 V batteries .Preferably lower voltages. Thanks
 
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Connect the 9v battery to the led in series with a (9-3)/.8 Ohm resistor.

On a 4.5v battery use a (4.5-3)/.8 ohm resistor.
 
Antiphon said:
Connect the 9v battery to the led in series with a (9-3)/.8 Ohm resistor.

On a 4.5v battery use a (4.5-3)/.8 ohm resistor.

Just make sure the resistor has suitable power rating - in the above scenario, the resistor is dropping 6 volts at 0.8A, which is 4.8 watts. I'd use at least a 10 watt resistor in that case, and that is going to be a LOT of heat... it would need mounted on a pretty beefy heatsink. The LED will need mounted on a big heatsink too.

If the OP can do it, it would be better to have more LED's in series rather than burning all that power as heat, or if you want to get more advanced, a buck switching regulator will get you into the 90%+ efficiency range and make the battery last 3 times longer and massively reduce the heat output.
 
These are voltage regulator ICs that ensure the LED is constant brightness even as the battery voltage drops lower.
 
Last edited by a moderator:
You may want some size-D or lantern batteries for something that draws this much current. (3) size D alkalines have a nominal voltage of 4.5. That might get you there without wasting too much of your power as heat.
 
selseg said:
Thank you very much , I checked from the link below earlier on . Why do they include the LM317 in that circuit ? in another circuit i found online , they used l7805. Why do they include these ics and capacitor ?
http://www.instructables.com/id/Super-simple-high-power-LED-driver/?ALLSTEPS
They're using voltage regulator chips in a "constant current" configuration.
 

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