Double voltage from lithium battery
Double voltage from lithium battery
(OP)
I'm trying to create a very simple circuit where you have the following main components:
1x 3V lithium battery,
1x 3-positions switch (ON1-OFF-ON2),
1x fan (which can run from 1.5 up to 3V).
I want to create a circuit where my fan can have a high speed (ON1) at around 2.5V and a low speed at around 1.8V (ON2).
The problem is the low-speed position since if I'm using resistors divider to obtain these voltage values, as soon as my battery will starts to drain (even if it is a lithium battery, the voltage will go down at one point in time), my "low-speed" position at 1.8V will drop and if it reach 1.6V my fan will stop.
So I wanted to use a Zener diode of 1.8V (yes, they do exist!) for my low-speed. But my fan would need to be in parallel to this but it also needs to be in series with my resistor for the high-speed position...
Yes...I thought about using a resistor to lower my overall voltage to 2.5V right in the beginning but than my zener circuit would become unstable since I would not have a lot of voltage difference between my zener break-off voltage and my initial voltage...
Am I making simple things too complex?
What can I use instead of a zener then?
Thanks! :)
1x 3V lithium battery,
1x 3-positions switch (ON1-OFF-ON2),
1x fan (which can run from 1.5 up to 3V).
I want to create a circuit where my fan can have a high speed (ON1) at around 2.5V and a low speed at around 1.8V (ON2).
The problem is the low-speed position since if I'm using resistors divider to obtain these voltage values, as soon as my battery will starts to drain (even if it is a lithium battery, the voltage will go down at one point in time), my "low-speed" position at 1.8V will drop and if it reach 1.6V my fan will stop.
So I wanted to use a Zener diode of 1.8V (yes, they do exist!) for my low-speed. But my fan would need to be in parallel to this but it also needs to be in series with my resistor for the high-speed position...
Yes...I thought about using a resistor to lower my overall voltage to 2.5V right in the beginning but than my zener circuit would become unstable since I would not have a lot of voltage difference between my zener break-off voltage and my initial voltage...
Am I making simple things too complex?
What can I use instead of a zener then?
Thanks! :)





RE: Double voltage from lithium battery
On top of that, I don't think you understand the operation of a zener... while the zener will regulate a point to 1.8V, you'll be burning quite a bit in the resistor leading up to that point, particularly since the fan will need a good amount of current to run. Since the battery voltage is so low, your overhead is extremely small, making any form of current/voltage regulation with such simple components a challenge, at best.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Double voltage from lithium battery
Maxim makes a number of potential solutions in DC-DC switching regulators:
http
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RE: Double voltage from lithium battery
If you must use a lithium battery then the best solution is a pulse width modulation scheme to essentially turn your 3V on and off rapidly. Like 300 times a second so the average voltage is whatever value you want it to be.
Think 'variable speed drill'.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Double voltage from lithium battery
- The 3V lithium battery could possibly be replaced by 2x 1.5V BUT that would be even worse in terms of voltage stability since the alkaline batteries are very bad at that.
- The parallel/series suggestion is not applicable here...as I mentioned earlier, the fan needs at least 1.6V to run...below that, it simply stop.
- I'll go have a look at DC-DC regulator BUT for our needs, the use of a trigger logic signal (ON=1, OFF=0) is too complex for the simple needs of 2-speed fan. Unless this 1/0 signal can be connected directly connected to the power source (3V lithium) where a fraction of that voltage would be considered as 1 and a very-low voltage as 0. We cannot involve a more complex circuit involving a clock generator (ex. 555)or the like. I know this is not complex electronics, but everything is relative.
- I have seen some voltage regulator (ex.:MIC5320 from Micrel) but was wondering how to get a simple (1/0) signal since a switch would need to be used to toggle between Vout1 and Vout2 on the fan.
Thanks for the input though, it's really appreciated...makes the gears working...
RE: Double voltage from lithium battery
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Double voltage from lithium battery
RE: Double voltage from lithium battery
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Double voltage from lithium battery
RE: Double voltage from lithium battery
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If we learn from our mistakes I'm getting a great education!
RE: Double voltage from lithium battery
Power of the fan is about 0.25W and it's nominal current consumption is 0.08A.
Thanks for all your inputs!
RE: Double voltage from lithium battery
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RE: Double voltage from lithium battery
RE: Double voltage from lithium battery
You should be able to just pick a resistor that gives you an acceptable voltage drop. Say, a low battery voltage of 2.8V so subtract the minimum voltage of 1.6V = 1.2V drop required then divide by 0.08A = 15 ohms. Wattage is 1.2V x 0.08A = 0.096W so a 1/4 watt resistor should be good.
If you don't like this, then just use 2 small diodes in series to drop the voltage.
If you still don't like this then look to a small fixed PWM regulator and switch it on for the low speed.
RE: Double voltage from lithium battery