LD-2 : 6Amps pwm-less linear driver - info and FAQ thread

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LD-2 : 6Amps pwm-less linear driver - info and FAQ thread


Parasitic resistance of common drivers

Important note!

Driver comes with both solder jumpers unsoldered(driver's bottom side,1cell or 2 cell operation),so user must solder one of them (1S or 2S,never both at the same time) for proper operation. More under 2S (2x) Li-ion cell operation for “6V” LEDs" section.

Useful links:

LD-2 prototypes testing by djozz and HKJ(great reviews as usual,thanks guys):



Direct link to HKJ's page:


(Discontinued) LD-1 driver info thread:


LD-2 6 Amps PWM-less linear driver is successor of LD-1 driver(discontinued) , with few significant improvements and new features. The goal was to create even more powerful and flexible driver in the same 17mm size that will have all good features of LD-1, but with “DD”(direct drive) performance on the highest mode. New interesting features/upgrades are:

  • Dramatically reduced driver’s parasitic resistance ~3x lower than LD-1 and practically identical to DD drivers! Parasitic resistance of driver (together with other circuit resistances) determines max. current on high when driver is “out of regulation”. Most used LEDs in flashlights are CREE LEDs which have one of the highest LED forward voltage (Vf) in the industry. This means at high currents LED Vf is so high that linear, DD or buck regulators can’t provide desired current, so they behave as non-ideal switch with some resistance. Lower parasitic resistance means higher current under those conditions. LD-1 parasitic resistance is ~18mOhm,which is lower than 16 stacked 7135s(~20mOhm measured,confirmed by djozz), but not as low as DD drivers which usually have <10mOhm resistance(strongly depends on MOSFET type). LD-2 parasitic resistance is expected to be <6mOhm! (Update; 5.5-6mOhm measured and confirmed by djozz and HKJ). That’s so low that other parasitic resistances (springs,wires,battery type) have much bigger influence on max. current
  •         External temperature monitoring with remote NTC thermistor-this eliminates the need for “turbo or high timeout” which is commonly used method for preventing the flashlight from overheating, but it’s far from ideal; flashlight body temperature heavily depends on flashlight size and mass, used components (LED, battery, springs, wires etc.), and most importantly, ambient temperature. With external (body) temperature sensing, driver reduces power output only when it’s really needed-when body become hotter than threshold level

  • Multi-cell support(optional parts) – with only three extra components on bottom side, driver could be transformed into 2S(3S is also possible by changing one 0402 resistor) Li-ion driver -  driving 6V emitters is now possible! Low voltage protection works just as with single Li-ion battery, and parasitic drain of ~200uA in sleep mode is much lower than “Zener modded” drivers
  •          Resistor moonlight(optional parts) – moonlight on LD-2 will be optional; two extra components on bottom side are required for moonlight mode. Compared to LD-1, moonlight  mode on LD-2 is basically resistor-in-series with LED; the main advantage is that moonlight current can be lower and it can be easily set by user with different 0603 resistor.Another important advantage is that current drops as battery voltage drop - runtime is extended by several times(of course brightness drops also,but in "critical" situations,for ex. batteries are almost empty and you can't charge them because you are in the middle of nowhere,no electricity,etc... it's better to have even tiny amount of light than flashlight shutdown). Moonlight can be easily enabled/disabled in UI, without opening flashlight/soldering stars

  •         Completely redesigned  PCB with big  symmetrical through hole pads for 20AWG LED wires – wires can be very short and mounting driver is now easier than ever! Other smaller pads grouped around LED pads are for NTC external temp. sensor and e-switch connection

  •         Easier max. current set – current on LD-2 can be increased or decreased (4A-12A) with only one high resistance 0603 resistor change; with a lot of available resistor values, current can be “fine tuned” – much simpler and cheaper compared to shunt resistor change.


  •          Input voltage 2.8V-4.35V (1x cell solder jumper setting), 5.6V-8.7V(2x cell solder jumper setting)

  •         6 Amps(default) max. current (from 4A to 12Amps possible without main current sense resistor change)

  •          Off-time mode memory

  •          Place for decent size (up to 8mm bottom diameter) spring on spring side pcb

  •          PWM-less TRUE CONSTANT CURRENT on all modes(except moonlight)-no acoustical or EMI  noise on any mode

  •          Significantly longer run-times on lower modes compared to PWM-based(FET or AMCs) drivers-even >2x possible

  •          Stays in regulation on lower modes for longer periods of time compared to PWM-based(FET or AMCs) drivers

  •          64%-79% more overall efficiency in mid-low modes for XM-L2 LED compared to PWM based drivers(6Amp current, HKJ's test)

  • External temperature NTC sensor support for accurate over-temperature protection/stepdown(~72C threshold,driver decreases current to 1.2A and if temperature is still too high it further decreases current;when flashlight temp. become lower than threshold,driver increases current up to 1.2A)

  • Less than 6mOhm@3.7V parasitic resistance – 3 times lower than LD-1 and 16x 7135 drivers, direct drive performance on high!

  • Calibrated voltage reference and internal temp. indicator

  • ~40uA typ. parasitic current in sleep mode(65uA with ext. NTC sense resistor connected),~200uA for 2S configuration

  • Enough space for easy led wires soldering(20AWG recommended)

  • 4-layer high quality PCB for better heat distribution

  • 2-step low voltage protection(3V-restricted power; 2.8V-sleep)

  • Driver PCB over-temperature protection (~105C)

  • Modes: ~10mA-120mA-1200mA-6000mA ,standard half press to increase mode

  • Moonlight enable/disable via UIž

  • Tailcap switch and electronic side switch capable,independently or both at the same time with single firmware

  • Three  separated e-switch user interface types

  • 16.95(+-0.2mm)mm diameter


E-switch user interfaces