Thanks for the correction. With that info, my head is a clearer:
What I think is the driver in Anduril S21E is the popular FET + n(7135) type driver, 7135 being a linear current regulator, n being the number used. The two components, FET and 7135 are combined to provide a wide range of output levels, n(7135) for efficient lower power modes, and extremely bright direct drive FET +/- PWM for Turbo.
This fits in with the 4 common types of flashlight drivers (to my limited technical understanding, helped by google search, anyone pls correct as needed): 1. Constant Current (by using multiple AMC7135ās?) 2. FET + n(7135): FET plus CC 3. Boost 4. Buck
Because a MOSFET can work on two regions: Ohmic (linear) or saturation (conmutation).
Convoy does not incorporate:
Thick PCBs with large copper areas for MOSFETs.
Dedicated heatsink fins for the driver.
Turbo time limitations due to internal driver heat.
If the MOSFET were operating in linear mode, these would be necessary. They are not, because the FET is not dissipating significant power.
The linkās driver is a PWM-modulated FET driver. It is neither a linear nor a constant-current regulator.
I have an MC-3 with an XHP70.3 HI R9050 5700K 2A, a 26800 7000mAh battery. I performed measurements to determine the efficiency in different modes because they donāt mention it in the flashlight description or the driver on their website.
No. The description is correct. The 519a LED uses a direct-switching FET driver (or a hybrid FET+PWM driver). If you see ā3V/5Aā or ā3V/6Aā in the description of a Convoy with a Nichia 519A, itās almost always a direct-switching FET driver, without active current regulation. That combination is chosen because the 519A handles well up to ~6 A, although its maximum efficiency is closer to 3.5ā4 A.
If you wanted to regulate the current precisely (for example, for stable performance or lower temperatures), you would need a constant-current buck or linear driver, which Convoy doesnāt typically factory-fit into that LED.
Your heat-based argument does sound convincing, but I still couldnāt quite iron out 2 apparent contradictions:
(1) ZeroAir has reviewed an S2+ with said driver, here. The runtimes on med/low modes are almost completely flat, which is characteristic of current-regulated drivers. A FET driver with constant duty cycle in every mode should see the output drop with battery voltage, over the course of the runtime; this is indeed what I observe in pure FET drivers or FET/7135 drivers in modes that engage the FET channel.
(2) The same review also features an oscilloscope test, which detects no PWM.
Would you explain to me how a non-current-regulated driver achieves the above?
I couldnāt quite answer this question because the term āconstant currentā seems to be ill-defined.
(1) The 3V 5A 12 group buck driver has green solder mask, not red as shown in the photo.
(2) The 3V 5A buck driver is known to draw less than 5A from the battery, since the battery voltage is higher than the LED needs; the driver in the review draws more than 5A.
(3) The review is dated May 2022, which IIRC is before the release of the buck driver.
Could you explain why you think the driver reviewed is a buck driver? If you would like to instead confirm that it is not a buck driver, then would you explain what the operating principle is?
Some things youāve said make sense on a first glance, but contradict what is observed/measured, so Iād like to understand exactly what is happening. Thank you very much.
I found this post written by @tactical_grizzly et al on this reddit page very good & helpful. I underlined the part that describes the oft seen FET + n(7135) driver. 7135 is only 0.35A, so when the current required is high, too many are needed (eg 6A would require 17 of them). In this case, the 7135 is replaced by a MOSFET acting as variable resistor (my understanding from multiple google search lol, pls correct as needed).
ā¦There are several different kinds of drivers listed below.
Direct Drive/FET. Direct Drive just connects the emitter directly to the battery. FET puts a mosfet in between them and rapidly turns on/off (pwm) in order to give you different levels. This is the cheapest type of driver, but is inefficient because LEDs burn off excess voltage, and there is no current regulation so output (brightness) will drop off over runtime along with the battery voltage.
Constant Current/Linear FET. Constant current drivers will regulate current using 7135 chips or a mosfet in an active current regulation circuit. Because they regulate current, the light has a nice flat output of same brightness until near end of battery life, instead of sagging over time like direct/fet. However since there is no power conversion involved, these drivers are also inefficient like fet drivers.
Some lights will combine the two, with current regulated output up to a certain level, but switch to a fet driver for higher levels. Finally there is:
** Buck/Boost** Buck converters convert power to lower voltages , while Boost converters convert to higher voltages. Hybrid Buck/Boost converters can do both. Drivers using them convert voltage to the ideal voltage for the LEDs, which makes them highly efficient, and they also control current, giving nice flat outputs as well. They are however more expensive / space required for high current outputā¦
This sounds like very good information, thank you very much! Only the following quoted claim regarding FET drivers requires correction; Iāll write it here because probably nobody on reddit would read it:
The FET driver, being a simulation of no driver at all, is close to 100% efficient because all of the power is delivered directly to the LED, without excess voltage losses (as with linear) or buck/boost conversion losses. FET drivers as as efficient as a driver can be.
Lights with FET drivers are generally inefficient as a system because LEDs are inefficient in the high power density regime, and FET drivers, being unregulated, often push an LED into this regime. Again, there is no excess voltage being burnt whatsoever.
All that aside, it seems that linear FET is the most plausible architecture. User @Isa2k does raise an interesting point of heat dissipation: if the FET is operating like a current limiting resistor, then with a Nichia 519A operating at 5A with Vf=3.32V, a full battery would require (4-3.32)(5)=3.4W to be burnt as heat, which an uncooled SMD component would have trouble handling. Note that I used 4.0V for full battery voltage due to voltage sag under 5A load.
I wonder if contact/resistance losses within the light can account for some of the voltage gap, which lessens the load on the current-limiting FET. I think this is plausible because I observe these drivers dropping out of regulation even when the battery voltage is far higher than the LEDās Vf at the corresponding current. Furthermore, disconnecting and forcefully grinding the tailcap often boosts turn-on output, which is suggestive of the contact resistance (possibly from oxidized aluminum) being a significant limitation.
I thought of an amateur method to test driver, donāt know if my reasoning is correct but posting in case this info is relevant to the discussion. Opple Lightmaster has flicker testing function that displays the actual waveform plus max brightness, min brightness, and average. My testing result with S21E with 519a FET around 1.5m from sensor:
Level 5: max 1500, min 360, average 750
Level 3: max 290, min 150, average 220
Does the difference in max brightness of the 2 levels mean there is current regulation as well (current/brightness is changed, IN ADDITION to PWM manipulation of modulation depth & freq)? Meaning this is a FET + CC driver?
Whoops, Iāve gotten off track from the main discussionāthe above comment was intended at the S2+ driver from the ZeroAir review.
Regarding the S21E driver, your test results are very interesting! The fact that there is PWM indicates that it is not a true constant-current driver, but the fact that the minimum is nonzero indicates itās not FET-only either. I think your hypothesis of a FET+CC hybrid is likely true.
To test whether there is current regulation, perform the same max/min/avg measurements on a high-ish mode with the battery at 4.2V, 3.9V, and 3.7V. If there is current regulation, there should be little/no difference in the regulated component (min) across these battery levels.
Iāve seen the argument that, since FET operates in max power/brightness region (and reduces brightness by PWM), it is less efficient than a regulated light that operates at lower brightness region without need for PWM. Implying lower brightness region is more efficient? This is the same as what youāre stating?
The bot excerpt you quoted from r/flashlight demonstrates that there is some confusion among the following concepts: driver efficiency, emitter efficiency, and system efficiency, which is the product of driver efficiency and emitter efficiency. In particular, the author of the bot mistook emitter/system efficiency for driver efficiency.
FET scores the highest in driver efficiency, but often scores low in emitter efficiency for the reason you described; for this reason, FET-driven lights are generally considered inefficient as a system. A linear driver has poor driver efficiency but high emitter efficiency; the resulting system efficiency may be higher or lower than that of a FET driver, depending on the specifics.
Buck/boost drivers offer an excellent compromise: the driver efficiency is better than linear, and the emitter efficiency is better than FET.
Beamshots of some of my most favorite Nichiaās. From 519a to B35AM then 219b, Duv progresses from dead neutral to legendary sw45k rosiness.
B35AM is in between and actually my most favorite of all Nichia LEDs - not too yellow-green, not too rosy. Beam color is warm and ācreamy.ā PERFECTION. I have the same B35AM in 3 different Convoy lights, M21B, H2 headlamp (very throwy), and latest, S21E.
My S21E with 519a 4500k is the FET Anduril version. Partly because I like Anduril, partly because IMO 519a looks most beautiful at highest (FET) output to my eyes (YMMV). Just donāt use high power battery with this light; I almost killed the LED with EVE 40PL battery.
All my Nichia 519a LEDs/lights, specifically 4500k + 5000k + 5700k, exhibit this behavior: Duv becomes more negative and beam color less greenish (for me, this means more beautiful) as I increase outputs (brightness).
This diagram from Nichia 519aās data sheet shows that behavior. It plots x, y points on the chromaticity curve for current vs CCT & Duv.
As current increaes, the points move leftward (higher CCT) and downward (more negative Duv).
I pulled the trigger on this latest tint-snob superstar: NTG50 4200k and first item on @ToyKeeper 's latest favorite lights list. Hopefully it will get to LA by Xmas for a self gift.
The shoot out with fellow tint snob LEDs (Nichia 219b sw4500k, 519a 5700k DD, Firefly FFL351A) should be fun and VERY interesting.
In case you havenāt noticed Convoy M21H does not have 519a 4500k (because itās no longer made). This happens to be my favorite CCT, so Iāve been looking. Below is the only quad 519a 4500k light that I could find commercially.
My D1K is green , this D4K is red. A coincidence.
Strings of street lights
Even flash-lights
Blink a bright red and green
For lesser cost thereās also Convoy S12 HERE, an interesting triple reflector design (vs TIR). This and Emisar D4K are the only multi-emiter lights remaining on market AFAIK.
Why my interest in 519a 4500k? Because my S21D with this LED has self-decapitated all the domes, so I need a replacement of this now out-of-production LED.
519a 4500k is an excellent neutral tint LED, Duv right at zero, 0.0000. If this is the beam color/tint you like (versus rosy Nichia 219b 4500k or Firefly 351A), this is the one IMHO.
End of an era - Nichia 219b 4500k bare LED is no longer available. Nichia stopped production per Simon. If you want the LED, you just have to buy them already installed on Convoy lights: M21H and S12.
I already have many 219b lights already but couldnāt resist ordering an S12, partly because of its interesting triple reflector design. I have found tint/Duv of 219b (or any LED for that matter?) highly dependent on the optic, so Iām giving this one a try.
Also added a supposedly very very powerful (high drain) Tenpower battery to the order, why not.
dainty tint-snob LEDs Christmas day.
