I've read through a lot of posts about sing linear regulators for VV mods, and some using Switching-regulators. I think there's much simpler solution; using a PWM circuit, something like this one:
DPRG: A Simple PWM Circuit Based on the 555 Timer
Most of the linear regulator circuits I've seen here don't use LDO regulators, but even so a linear regulator burns a lot of power (it burns off the voltage, so there is a 1:1 relationship between the current flowing through your atty and the current coming from your battery, if the battery is 7V and you're running at 4V, you're wasting almost half of your battery life).
The second solution I've seen is a switching-regulator module. This is a beautiful solution (particularly in the flyback configuration, since the output is totally independent from the input; you can get 6V from a 3.3v battery, or 3V from a 7.4V battery with the same circuit, for example). But switching regulators require bulky caps and inductors, and tend to be a little expensive.
For driving a carto, though, a PWM circuit would seem to be a great choice. It's much simpler than a switching regulator, and it doesn't waste battery power like a linear regulator. Also, the switch you use doesn't have to carry the whole current; the switch can provide the "+3-+18V" supply (which is very small), the "VMotor" supply can be permanently connected to the battery. (From the diagram above)
As an extra modification, this circuit might also provide a "touch-switch" feature. If you use a very low-power 555 (such as the TS555, available from DigiKey for under $1)
Digi-Key - 497-2299-5-ND (Manufacturer - TS555IN)
you could take pin 4; instead of connecting it to the supply voltage, take it to ground through a 10M resistor. Your finger (between pin 4 and the +5 supply) should be able to provide the 10 pA required (and since you would want to drive the carto shell at +5V, the outer shell of your e-cigg would be at the right potential).
But, even if you want to use a generic bipolar 555 from your junk box, the circuit ought to work well and be really small. The unusual thing about this circuit, of course, is that you would drive the outside of the carto with the + side of your battery, which isn't usually done but isn't really an issue either.
The on resistance of the MosFet is really small (.026 ohms!) and should work really well in this app.
The only disadvantage to a PWM circuit is that it can't boost the voltage; the battery voltage you have is the max it can supply (minus the loss through the transistor). So, you wouldn't use it in a single-battery configuration, it's only for a multi-batt setup.
I'll be working on this, but it will probably take a couple of weeks for me to get it all together, clumsy/busy/lazy as I am. If you try this out and it works for you, let me know! If you want to commercialize it, go for it! (I'd be happy to eval a couple of units <is_there_a_smirk_icon?> )
DPRG: A Simple PWM Circuit Based on the 555 Timer
Most of the linear regulator circuits I've seen here don't use LDO regulators, but even so a linear regulator burns a lot of power (it burns off the voltage, so there is a 1:1 relationship between the current flowing through your atty and the current coming from your battery, if the battery is 7V and you're running at 4V, you're wasting almost half of your battery life).
The second solution I've seen is a switching-regulator module. This is a beautiful solution (particularly in the flyback configuration, since the output is totally independent from the input; you can get 6V from a 3.3v battery, or 3V from a 7.4V battery with the same circuit, for example). But switching regulators require bulky caps and inductors, and tend to be a little expensive.
For driving a carto, though, a PWM circuit would seem to be a great choice. It's much simpler than a switching regulator, and it doesn't waste battery power like a linear regulator. Also, the switch you use doesn't have to carry the whole current; the switch can provide the "+3-+18V" supply (which is very small), the "VMotor" supply can be permanently connected to the battery. (From the diagram above)
As an extra modification, this circuit might also provide a "touch-switch" feature. If you use a very low-power 555 (such as the TS555, available from DigiKey for under $1)
Digi-Key - 497-2299-5-ND (Manufacturer - TS555IN)
you could take pin 4; instead of connecting it to the supply voltage, take it to ground through a 10M resistor. Your finger (between pin 4 and the +5 supply) should be able to provide the 10 pA required (and since you would want to drive the carto shell at +5V, the outer shell of your e-cigg would be at the right potential).
But, even if you want to use a generic bipolar 555 from your junk box, the circuit ought to work well and be really small. The unusual thing about this circuit, of course, is that you would drive the outside of the carto with the + side of your battery, which isn't usually done but isn't really an issue either.
The on resistance of the MosFet is really small (.026 ohms!) and should work really well in this app.
The only disadvantage to a PWM circuit is that it can't boost the voltage; the battery voltage you have is the max it can supply (minus the loss through the transistor). So, you wouldn't use it in a single-battery configuration, it's only for a multi-batt setup.
I'll be working on this, but it will probably take a couple of weeks for me to get it all together, clumsy/busy/lazy as I am. If you try this out and it works for you, let me know! If you want to commercialize it, go for it! (I'd be happy to eval a couple of units <is_there_a_smirk_icon?> )
