Build led driver

Practically this circuit works stably in a reasonable power voltage range. But with more supply voltage, you dissipate more power with the transistor, so you get less efficiency. Your circuit is actually less efficient than just using a big power resistor. The power that would usually be consumed by the resistor is just shifted to the transistor and the extra circuitry takes some power too.

If you want mA, you need Using 5. If you want to improve your efficiency then you need to string LEDs in series minimise the voltage drop on the resistor or use a dedicated switching LED driver.

You have a point James. With simple resistor only if you double the power supply voltage you get double the current flowing through the led. For efficiency without argue it is better to use dedicated LED driver. Such circuit will work for laser diode, but you should adjust it for 1A current. You need to replace R2 with 0. Resistor will dissipate 0. As we discussed, this is not efficient driver especially if you use battery to power it.

Connect the base to the Emitter of the other transistor. The 3 pot versions have current limiting build in. You must be logged in to post a comment. Building simple constant current power LED driver admin Electronics. Amplifying Mobile Phone Signals. James French March 5, at Log in to Reply. The closest E12 value is 1,8 ohms, the output will be mA the resistor must be at least 1W in both calculations. I couldn't get my schematic drawing program to work, so here is a hand drawn.

The constant current source has a drop voltage of 3 V, so the supply voltage should always be 3 V higher than the LED voltage and can be up to 37V which is the maximum input voltage of the LM Example: You are going to connect two white Luxeon LEDs with 3,42 forward voltage each mostly mentioned as Vf in common datasheets. You can connect up to ten high power LEDs to this circuit.

The higher voltage you supply the LM with, the hotter it gets. I like how simple this is. Probably not that efficient as a lot of energy will be wasted on heating up the LM device but still a good job.

Reply 3 years ago. It won't waste heat if you use only the needed input voltage, not more. Excess voltage will be converted to heat. Too much heat in the LM means too much input voltage. Question 3 years ago on Step 3. Reply 6 years ago. In Europe they use a dot where a comma would go, and a comma where a dot would go. Just accept that and change it accordingly when you make your own plans.

Reply 4 years ago. Only in continental Europe, in the UK we use the dot to delineate a fractional part. It is very confusing when looking at continental european data. Switching is the way to go. If you get creative, the power loss in the driver circuit can be cut down to almost nothing. PTC fuses do not have a very accurate "trip" current. Typically they vary by a factor of 2 from the rated trip point. The only safe choice of PTC is a bit under-rated.

Connect in series with a PTC rated about mA. Driving voltage should be about 4. Question 11 months ago on Step Answer 10 months ago. First if your are driving 32 LEDS in series then you would need at least a 22 volt source considering 0.

In series the current would be the same at 20 ma. Adding in the drop for the current sense would increase the supply voltage. If you were to wire them in parallel then you would need to supply the ma. Some of the phone chargers are constant current devices so that may not work. Biggest problem I see is getting the low value correct current sense resistor to carry the current.

That's one of the best articles I read about constant current drivers. All solution I was finding through the web in one post. Thank you very much for the time and effort :. Tip 1 year ago. Good instructable but you seem to have the wrong impression of why LEDs need to be constant current. This continues with the LED getting hotter and hotter and conducting more and more power that even without "moving to a new environment" your LED will eventually fail and burn out regardless of how precisely you've set the voltage.

LEDs can never be driven by constant voltage unless you want them to die an early death. Question 1 year ago on Step 5. I would like to obtain a current source around mA. My Power Supply is 21V. Could you help me? I don't understand. Depuis un ans je suis dessus pour un avion Beechcraft Question 2 years ago. In the constant current led driver circuit you do state that in step 6, the input voltage varies from 3 volts right up to 60 volts. Is the input voltage dc or ac? I want to achieve it without opening the LED it without messing with the invite circuit.

What is a good approach to do this? Would an nchannel power mosfet do the trick? Thanks in advance! Question 3 years ago on Introduction. Question 3 years ago. Dan, thanks for this clear and simple explanation. I see only higher voltage values.