I've been working on my first mod for a while, but needed a low voltage cutout. the batteries I have cut out at 2.5V each, and I wanted at least 3V each (running 2 in series). I wasn't satisfied with just using a zener diode for my low voltage protection, since I wanted to use a MOSFET switch, and wanted a low battery indication as well as cutout. Here is what I came up with. I have it configured for a 2 battery supply, but it can be configured for 1, 2, 3, or more batteries.
U1 - LTC1440, MAX921, or ISL21440
M1 & M2 - NTMS4177PRG or any suitable p-channel MOSFET
M3 - any small p-channel MOSFET
m4 - any small n-channel MOSFET
LED1 - LED for low battery indication
LED2 - LED for operation indication
MASTER SW - any master power switch you like
USER SW - any small button you like. It carries almost no current, so it can be small.
R1 - 2.49M
R2 - 511K
R3 - 15M
R4 & R5 - anything between 10K and 1M
R6 - 220 for the LED linked above
R7 - 1K or more for the LED linked above (it's really bright)
R8 represents the atomizer.
U1 senses battery voltage, and it's output goes positive if the voltage is good, and negative if it's bad. Positive voltage turns on M4, which turns on M2. Negative voltage turns on M3. However, no current will flow through M2 or M3 until M1 is turned on by pressing the USER SW. once M1 is on, power can flow through either M2 or M3 (but not both) turning on either the atomizer or the battery low LED. LTSpice simulated a cutoff of 6.12V, but in real life, it is 6.0. Closer tolerance resistors could probably help, but the comparator reference has a tolerance too. R3 at 15M gives me about 1V of hysteresis to prevent oscillation due to the battery voltage drop under load. The circuit draws <5uA.
For my mod (I'll post it eventually), I put an OKR-T/6 between M2 and R8. Any DC-DC converter could be placed here. To save space, I built most of it from surface mount components, but it's a challenge. It also looks funny in a mod, because I build it in pieces and heat shrink each one, so you open the mod and there's 4 or 5 heat shrink balls inside. If anyone likes making PCBs, this would probably be an easy one.
I look forward to hearing everyone's thoughts and suggestions for improvements.
U1 - LTC1440, MAX921, or ISL21440
M1 & M2 - NTMS4177PRG or any suitable p-channel MOSFET
M3 - any small p-channel MOSFET
m4 - any small n-channel MOSFET
LED1 - LED for low battery indication
LED2 - LED for operation indication
MASTER SW - any master power switch you like
USER SW - any small button you like. It carries almost no current, so it can be small.
R1 - 2.49M
R2 - 511K
R3 - 15M
R4 & R5 - anything between 10K and 1M
R6 - 220 for the LED linked above
R7 - 1K or more for the LED linked above (it's really bright)
R8 represents the atomizer.
U1 senses battery voltage, and it's output goes positive if the voltage is good, and negative if it's bad. Positive voltage turns on M4, which turns on M2. Negative voltage turns on M3. However, no current will flow through M2 or M3 until M1 is turned on by pressing the USER SW. once M1 is on, power can flow through either M2 or M3 (but not both) turning on either the atomizer or the battery low LED. LTSpice simulated a cutoff of 6.12V, but in real life, it is 6.0. Closer tolerance resistors could probably help, but the comparator reference has a tolerance too. R3 at 15M gives me about 1V of hysteresis to prevent oscillation due to the battery voltage drop under load. The circuit draws <5uA.
For my mod (I'll post it eventually), I put an OKR-T/6 between M2 and R8. Any DC-DC converter could be placed here. To save space, I built most of it from surface mount components, but it's a challenge. It also looks funny in a mod, because I build it in pieces and heat shrink each one, so you open the mod and there's 4 or 5 heat shrink balls inside. If anyone likes making PCBs, this would probably be an easy one.
I look forward to hearing everyone's thoughts and suggestions for improvements.
Last edited:
