FET Driver - 2S+ Momentary - 17mm / 20mm

FET Driver - 2S+ Momentary - 17mm / 20mm
FET Driver - 2S+ Momentary - 17mm / 20mm
Product Code: FET-2S+-MOM-LDO
Availability: Out Of Stock
Price: $13.99

Available Options


* LVP:

* Diameter:

* Firmware:

Turbo Timer:

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These 17mm & 20mm drivers are "direct-drive" drivers, flashed with firmware customized for this build with an ultra low resistance FET. This gives you near-direct-drive performance (limited mostly by your battery, LED, and connections) with the ability to still use lower power levels, set a turbo timer, among other functions. 

The difference between these drivers and the normal 17mm/20mm FET drivers is that they have been optimized for 2S+ cells and use of a momentary switch (power always connected to an external momentary switch; not a standard rear clicky switch).  With the additional of an LDO voltage regulator, the quiescent current is greatly reduced when compared to a zener mod solution.  This reduction is particularly important for momentary switch applications, where the power is always connected to the driver. 

For 1S cell input momentary use, you can use the normal line of 17mm/20mm/22mm FET drivers.   The 22mm FET driver already has an LDO option for 2S momentary use.

All drivers feature fast PWM and come with pre-soldered leads.  Unless the option is checked to remove the spring, all drivers also come with a copper braided spring pre-installed. 

Because each driver is hand built and tested, This driver may take up to 10 business days to build, test, and ship.

Standard Electronic Switch Firmware

  • Standard FET Electronic Switch.  This is for use with an external electronic switch, where the driver is always powered, not for use with a standard clicky switch where power is cut by the switch to change modes.  This option uses STAR momentary firmware, which allows you to start on either the lowest or highest mode from off with either a short tap or long press of the switch.  
    • One side of the switch is soldered to ground, the other to the pre-tinned switch pad on the driver (connected to pin 2).
  • Electronic Switch Custom Mode Levels.  Choose your own mode levels.  For this option, please enter the following information in your checkout comments:  
    • 1.  Number of light levels: 1-6 (plus moonlight if desired)
    • 2.  Approximate PWM levels of each mode:  Example: (1) 2% - (2) 15% - (3) 40% - (4) - 100%

Standard Electronic Switch Firmware Low Voltage Protection.  At around 6V/9V under load (depends on selection), the light will step down the power level.  At around 0.3V under the set point under load the light will shut off.  You can override any low voltage shut down by holding down the electronic switch button.  This system gives you ample warning and attempts to extend runtime before turning the light off.  

moppydrv Multi-Group Electronic Switch Firmware Option

This firmware allows the ultimate in user customizability, with 16 built-in mode groups, that the user can select via a series of button presses and a user programmable turbo timer that will automatically step the power down to 50% after the set time is hit (see below for instructions).  


Low voltage protection:  With 2S cells the light will begin to step down output at around 6V under load.  The light will not shut completely off, but will continue to run at a moonlight level.  

  • 3S cell drivers currently have no low voltage protection with moppydrv.  If you want low voltage rampdown with 3S cells on the input please choose one of the standard or custom firmware options.  

User Selectable Groups:



  1. 100% Only
  2. 5% - 100% | [100%]
  3. 30% - 100% | [100%]
  4. 70% - 100% | [100%]
  5. 50% - 10% | [100%]
  6. 75% - 20% | [100%]
  7. Moon - 30% - 100% | [100%]
  8. 100% - 30% - Moon | [Strobe]
  9. Moon - 20% - 70% - 100% | [100%]
  10. 100% - 70% - 20% - 0% | [Strobe]
  11. Moon - 5% - 15% - 50% - 70% - 100% | [100%]
  12. 100% - 70% - 50% - 15% - 5% - Moon | [Strobe]
  13. 100% | [Strobe]
  14. Strobe | [100%]
  15. 100% | [Blink1]
  16. 5% - 33% - 100% - Blink1 - Blink 3 - Beacon | [Strobe]

moppydrv ​Instructions



  • A short tap switches the light on to the previously used mode, or off if the light is already on.
  • press & hold while the light is on cycles through the modes in the selected mode group.  
    • press & hold while the light is off switches the light on in the first mode of the selected group.
  • double-click from either off or on puts the light into the special designated mode in that particular mode group.

To switch mode groups: rapidly tap the switch 8 times from either off or on.  The light will then enter the programming mode and begin to flash, reading out the battery charge state.  With the light in programming mode, tap the switch the same number of times as your desired mode group.  The light will blink and your mode group will be memorized. 


Example: To select mode group 3, tap the switch 8 times quickly to enter programming mode.  When the light enters programming mode and beings flashing, tap the switch three times.  The light will blink to recognize the mode group change.


To set the turbo timer: rapidly tap the switch 8 times.  The light will then enter the programming mode and begin to flash.  With the light in programming mode, tap the switch 20 times to enter the turbo timer set mode.  The light will then switch to 100% power.  When the light is at the desired temperature for the turbo step down, turn the light off.  The turbo timer will then be set.  The turbo timer steps the light down to 50% regardless of the mode group set.  To disable the turbo timer, simply set the time to under 4 seconds.  

Turbo Timer (n/a moppydrv FW)

A turbo timer may help reduce the chance of overheating.  Available Options:

  • No Timer
  • 30 Seconds
  • 60 Seconds
  • 90 Seconds
  • 120 Seconds
  • 180 Seconds

Spring Option

You can check this box if you don't want the copper braided spring installed or included with the driver.  This may be useful if you are planning on piggybacking this driver onto another driver, or if you have your own preferred spring you'd like to install yourself.  

2S+ Cell Low Voltage Protection 

You can choose between three options for low voltage protection with the 2S+ cell options:

  • No LVP:  Disable low voltage protection.
  • ~6V LVP:  The light will begin to ramp down power at around 6V under load.  The light will shut off at around 5.5V under load.  
  • ~9V LVP:  The light will begin to ramp down power at around 9V under load.  The light will shut off at around 8.25V under load. 
    • ~9V LVP currently does not work with moppydrv


1. What Is The Input Voltage Range?

  • 5.5V-16V (LDO)
  • This is a "direct drive" driver, meaning it doesn't step up or down voltage that the LED sees.  This driver can only be used with closely matched input and output voltages.  For example, 2 cells on the input and a single XHP50/XHP70/MT-G2 on the output (or multiple LEDs in parallel).  
  • If you do not match the number of cells with the correct LED configuraiton you will either blow the LEDs (voltage too high), or they simply will not turn on (voltage too low).

This driver was made possible and is heavily inspired by many members of the BLF flashlight community, especially comfychair (initial concept and development), Mattaus (PCB layout and development), JonnyC (firmware), DrJones (firmware), and wight (singe-sided PCB development and advice).  If you'd like to learn more about these drivers, and participate in further development, come visit our community at budgetlightforum.com 

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