For higher currents, flashlight manufacturers use constant current drivers such as 5A, 6A, or 8A instead of stacking a huge number of AMC7135 chips. The constant current drivers used in these lights are still linear drivers from my understanding, but are they more efficient or less efficient than AMC7135s? Also, does anyone know what chips are used to regulate current in these high current drivers? I couldn’t find any info on the specific chips used.
Unless it’s buck or boost, linear is linear. Whatever difference in voltage there is between the battery and the LED’s forward voltage is getting burned off as heat somewhere. If that’s 0.5V at 3A, you’re making 1.5W of heat somewhere. If it’s 0.3V at 5A, it’s still making 1.5W of heat somewhere.
Ah, that makes sense. I wonder what is the advantages or disadvantages of using AMC7135s versus the drivers advertised as having high constant currents. It seems that the high constant current drivers have bigger but fewer regulators on them. Do the constant current drivers use different regulators for 1, 10, 35, 100 modes for example?
I know Hank now has a 9A constant current driver which you can request.
To get 9Amps you will need 26pcs. of 7135 instead of 1 mosfet in linear mode. But its nonsense to use hi power linear driver with 1 battery only . You didn’t get stabilization anyway , because at hi power batt voltage will drop very fast.
I put a shematic and explanation in the attiny 1 series thread somewhere.
An op Amp reads the voltage from a current sense resistor and adjust the voltage of the gate of a mosfet to get the desired current, the higher the gate voltage the lower the resistance of the FET and vice versa, basically a variable resistor.
A 7135 is the same thing, except all integrated in a single package, the current can’t be changed though and to dim the LED it’s just turned on and off (PWM).
PWM incurs losses because the LED is drived at a higher current when it’s on where it’s less efficient, also higher conduction losses in the circuit resistance due to higher RMS current, but multiple channels are used (e.g. 1+7 7135) and the total current is not very high so those effects are limited, this is much more significant in a 1+FET (direct drive) driver.
For high currents the Op-Amp/FET linear driver is a smaller solution.
It makes sense if you are trying to limit current. For example, to avoid damaging low forward voltage LEDs with a fully charged cell.
This is all important and accurate and somewhat contradicts my earlier post. PWM reduces efficiency and is a disadvantage of 7135-based drivers.
So how do the high constant current drivers work? And what regulators do they use if not 7135?
It’s just a MOSFET being operated in linear mode. It acts as a variable resistor which limits the current to the LED (s).