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

LD-2

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):

https://budgetlightforum.com/t/-/33245

https://budgetlightforum.com/t/-/33324

Direct link to HKJ's page:

http://lygte-info.dk/review/DriverTest%20LD2%20UK.html

(Discontinued) LD-1 driver info thread:

https://budgetlightforum.com/t/-/29455


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.

Features/specification:

  • 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

UI_1

  • normal button switch press increases mode: sleep->(mode0)->mode1->mode2->mode3->sleep

  • double press decreases mode

  • long press from sleep->max mode

UI_2

  • normal switch press from sleep->last used mode

  • when on,normal press(<0.5sec)->driver goes to sleep

  • long switch press from sleep->lowest mode (moonlight if it’s activated)

  • when on,~>0.5sec switch press->mode up,release switch to stop;pressing switch again for >0.5sec->mode down

  • quick double press->current goes to max or min(toggle)

UI_3

  • double press increases mode

  • single press->driver shuts down

  • single press from sleep->last used mode

E-switch protection

If e-switch is pressed for more than 20sec(accidentally in pocket,bag etc.), driver shuts down.


How to set UI:

Turn the flashlight on and hold button switch pressed for more than 10sec(some blinks).This works in any mode and UI type.UI is changed to next one.Repeat to get UI you want.


Moonlight Enable/Disable:

Moonlight can be enabled/disabled by switching to low mode(120mA) and waiting for 2 minutes-short single blink appears;after that blink, user has 2 seconds to change mode or turn off the flashlight for moonlight Enable/Disable.

Moonlight is optional and requires two components on spring PCB side for operation.

Moonlight is not constant current regulated,so current will depend on voltage and led Vf.

User can change moonlight current by changing 0603 resistor on spring PCB side (default value is 154 Ohms,which gives ~10mA with typical white LED and fresh 1x Li-ion battery).

Equation is very simple: Rmoon=(Vbatt - Vled)/Imoon

Note: for 2S,3S and 4S configurations moonlight current will be 2,3 or 4 times higher if stock 154Ohm resistor is used! Upper equation is still valid,but because (Vbatt - Vled) is 2,3 or 4 times higher,current is also higher for the same factor.To keep moonlight current at ~10mA in case of 2S,3S and 4S configurations,moonlight resistor should have next values:

1S - R~150 Ohm

2S - R~300 Ohm

3S - R~450Ohm

4S - R~600Ohm

As it can be seen from equation,current depends on battery voltage,so it will drop as battery voltage drops.Typical Vled values for high power white LEDs at very low currents are 2.6-2.7V.


2S (2x) Li-ion cell operation for “6V” LEDs:

This is option and requires three components on spring PCB side for operation. Solder jumper for 1S operation (designated as 1 on PCB) must be deactivated (by removing solder) and solder jumper for 2S (designated as 2 on PCB) must be activated (by soldering).

Note: driver comes with both solder jumpers unsoldered,so user must solder one of them (1S or 2S,never both at the same time) for proper operation.

Warning!

Driver configured for 1x cell operation (solder jumper 1) should not be used with two cells!

Driver cannot protect itself from too high voltage,so it will burn if it’s connected to 2x cells in series in that case.

Added Op-amp chip doesn't have reverse polarity protection, so be careful when connecting batteries to driver modified for 2s operation!


3s and 4s Li-ion cell operation:


One resistor needs to be changed,and for 4s operation OPAMP chip needs to be replaced also,as in picture. Resistor should be 750kOhm for 2s operation(stock),375kOhm for 3s,and 250kOhm for 4s. OPAMP for 4s should be AD8641AKSZ(quiescent current ~200uA,pretty expensive ~3.5$).

If you don't have required values,two 750kOhm resistors can be stacked for 375kOhm,or three for 250kOhm(well it requires some skills and steady hand to stack 0402 resistors).

3s and 4s configurations could generate more(too much) heat in driver,it depends on LEDs,batteries and max. current,so it's always good idea to approximately calculate max. dissipation and ensure good cooling/thermal path before using LD-2.


Thermal considerations:

LD-2 is like LD-1 linear type of driver,and that means it must burn extra voltage from battery. Result is heat that’s generated mostly in MOSFET,and equation for generated heat in driver is:

Pheat=(Vbatt-Vled)*I

At low currents(low mode) dissipation is low because despite the big voltage difference Vbatt-Vled (~4.2V-2.8V=1.4V),generated heat is low because current is small.At high currents(high mode) current is large,but Vf of commonly used CREE XM-L2,XP-L,XP-G2 is very high at those currents and dissipation is usually very low(that’s generally not true with MT-G2or XHP70 or with multi-emitter setups!).

In typical 1xli-ion-1xLED setups dissipation is highest in medium (1.2A) mode because both current and voltage difference aren’t small.

So what amount of heat would be theoretically generated in driver while driving different LEDs at different currents? Values can be calculated from LEDs’ and battery U-I graphs (HKJ and djozz) using the upper equation. Values are “worst case scenario” because I used numbers for high drain batteries(HE2,VTC5),and any other voltage drop is neglected (springs, wires, contacts),so in reality,numbers should be lower,and they are completely different if you use 1-3C cells like NCRB,PD,BD,MH1,not to mention small 18350 cells for MT-G2 and XHP70 in 1x18650 hosts.

It is highly recommended to calculate dissipation levels by using mentioned graphs and equation on for mid and high mode if you aren’t sure about heat levels that would be generated in your setup.

XP-G2

XM-L2 XP-L

MT-G2

XHP70

3xXP-G2

3xXM-L2 3xXP-L

6A max.(default)

120mA

~0.2W

~0.2W

~0.4W

~0.4W

~0.2W

~0.2W

1.2A

~1.3W

~1.3W

~3W

~3W

~1.6W

~1.6W

6A

~0.2W(I2R)

~0.3W

~7.8W

~7.8W

~5.3W

~5.9W

9A max.

180mA

-

-

~0.6W

~0.6W

~0.3W

~0.3W

1.8A

-

-

~4W

~4W

~2.2W

~2.2W

9A

-

-

~7.2W

~7.2W

~4.5W

~5W

12A max.

240mA

-

-

-

-

-

~0.4W

2.4A

-

-

-

-

-

~2.7W

12A

-

-

-

-

-

~3W

Upper table shows theoretical numbers for max. driver dissipation with different LEDs and different current setups with fresh high drain batteries(HE2).It’s very hard to tell how close are those numbers to reality(some are suspiciously high,like 3xXP-G2 on 9A?),but I’m sure practical builds from BLF members will provide a better picture.

So the question that still remains is,how much heat LD-2 can handle?

I did a few basic thermal measurements to find an answer to that(further testing of better thermal upgrades under progress).

I measured thermal resistance (which determines max. allowed dissipation) for three cases:

1. Bare driver in air(not really used in practice,but it’s interesting for comparison),

2. Driver mounted in aluminum pill (old Convoy C8 pill),

3. Driver mounted in alu-pill+silicone cubes(~1W/mK,same C8 pill)

Results are following :

Thermal resistance[oC/W]

Max. continuous dissipation[W]

Bare driver

45

~1W

Driver+alu-pill

22

~2W

Driver+alu-pill+silicone cubes

16

~3W

TBA

TBA

Old Convoy C8 pill is pretty bad thermally,it has very thin contact ring and it’s relatively “empty”,but still improvements are very visible. In 3rd test(picture) I used silicone cubes only(~1W/mK) , to fill cavity,result is pretty good,but it would be much better if I used as much metal(copper,alu) as possible to fill cavity and use only thin thermal silicone sheet(0.5-1mm) between that added metal and driver(something like this would be my next test). Unlike cubes,silicone sheets are available with higher thermal conductivity,~3W/mK for low price and 7+W/mK for highest performance.

So even by using just basic thermal upgrade,driver can be used for most of setups with 1-3C rated batteries(PD,PF,BD,MH1,NCRB),and with some further upgrades,other more demanding setups should be also possible. Ultimate thermal upgrade would be custom pill that is very shallow so that top of the MOSFET case is practically in direct contact with “bottom” of the pill (+AS5,AA,etc.),but most of the pills could be upgraded with copper/alu piece that would mimic that(basic idea is fill the pill cavity with as much metal as possible,so that heat from MOSFET has shortest path to flashlight body).

Connection diagram:


·

LD-1 vs. LD-2 on high mode @turn-on(the same Convoy M1,first measured with LD-1,and then measured with upgraded LD-2,cell is fresh HE2):

When do we get to see a LD-2 sales thread?

Sounds fantastic! Good job guys

Nice work :beer:. When can we expect these drivers to be ready for sale?

Very soon.

So will RMM carry these?

where do we get them?

I can’t wait! Thank you for your hard work!!!

Off-time mode memory?
Can this be changed to on-time mode memory please?

Also you mention switching to low mode and waiting for 2 minutes a short single blink appears.
Can this blink be disabled?

I am interested when the sales thread starts… this looks very nice.

Depending on the price I will take 1 or 2 pcs for MT-G2 (2 cell configuration)…
P.S. Green silkscreen is boring imo, should be red instead :stuck_out_tongue:
Edit>After seeing conditions of the sale I am out unfortunately…

I like the programming pogo pin under the PCB. Great work on the driver!

Awesome work! Looking forward to the sales thread :D

Quick question: Are the Low and Medium modes set at 120mA and 1.2A? Or are they set at 2% and 20% of the maximum current?

I have some problems with bullets option,too much blank spaces in OP,and I can't fix that,but until then,here is updated LD-2 info in docx:

For those who can't read all the numbers about parasitic resistance,one simple picture:

Thanks

I had missed the LD-2 info thread.

I will be waiting for this :heart_eyes:

For sale: LD-2 (17mm 6Amps PWM-less linear driver) :party:

I now have a few projects planned. Things are starting to get a little exciting around here now! I’m going to dust off the soldering iron, clean off the work bench, in preparation for the 4 new drivers I’ll be receiving soon. Thanks led4power!!!

I’d like to see some of these in contest builds.