Voltage booster?

[bananasiong]

Hi,
I found this: drive a LED with a single AA battery, is this also called voltage booster circuit? I've googled, some voltage booster use 555 timer, some use handmade coil with center tapping, and some use capacitor to hold the output voltage so that it won't be lower than supply voltage.
Can this circuit last long if i use only a single rechargeable AA (rated 2500mAh)?

 

[audioguru]

I don't know what is the duty-cycle of the oscillator and don't know for what percentage of each half-cycle the inductor can power the LED. I don't know the efficiency of this circuit.

Assuming that the blue LED needs 3.6V then the voltage must be stepped up 3 times. Assuming that the average on-current of the LED is 30mA and with a 50:50 duty-cycle then the total average current is 15mA. Then a 2500mAh battery cell's charge would last for 2500/(15 x 3)= 55.6 hours. The peak current could be higher then the battery cell's charge would last only 55.6/2= 27.8 hours.

 

[hjames]

It would be nice if these circuits would be properly referenced - the caption font is the one that ednmag uses:

**broken link removed**

The author claims ~40mA current draw, for a ~4hr lifetime for a 1400mAH NiMH.

Whoops - typo'd that - should be 1600mAh

 

[audioguru]

The author claims ~40mA current draw, for a ~4hr lifetime for a 1400mAH NiMH.

Actually the author claims a 4 hours battery charge lifetime for a 1600mAh cell.
He can't calculate very well. A 1600mah cell will provide 40mA for about 40 hours.

 

[bananasiong]

Are the numbers in the circuit from the pins of 555 timer? Can the voltage be boosted without any oscillator i.e. 555 timer?

 

[audioguru]

The numbers on the schematic have nothing to do with a 555 IC. This circuit is a 2-transistor oscillator that boosts the voltage by using an inductor. A "charge-pump" circuit is different and uses an oscillator and capacitors to double or triple the supply voltage.

 

[bananasiong]

Can this circuit boost up to 5 volts to drive the microcontroller?
I've seen some booster with 555 timer, some with booster IC.

 

[mramos1]

Can this circuit boost up to 5 volts to drive the microcontroller?
I've seen some booster with 555 timer, some with booster IC.

Use two cells and run the microcontroller for a long time (without the 555).. Run it at low speed 30-50Khz.

Or if size is a problem get the small AG-13 cells. Use 2 of them and run a 12F683 for more than a week with two AG-13 cells driving a load.

What are you attempting? AudioGuru gave you the numbers for your question.

 

[bananasiong]

No, I just want to know how does it be boosted up. And any calculation can be done? For calculating the boosted voltage.

 

[audioguru]

The boosted voltage with an inductor can be 100V or more, but the current is reduced the same amount the voltage is boosted so that the power remains the same, minus losses. For LED drivers, the LED limits the boosted voltage.

 

[bananasiong]

Can I control or limit the boosted voltage to be 5 volts?

 

[Oznog]

The LED itself will limit the voltage, because it is primarily a current-output device. The LED's I/V relationship determines the voltage based on the current running through it.

 

[audioguru]

You can use a boost circuit then a zener diode to limit the voltage. The zener diode will waste a lot of power.

 

[RODALCO]

Look under google for Joule thief.
has been discussed in these forums too.

In it is a more simple cct which drains a standard battery down to about 0.4 volts.
That only consists of a double wound coil, transistor and resistor and works very well.

 

[RODALCO]

**broken link removed**

this is the link, with a good detailed describtion how to build it.

 

[Hero999]

When the current through an inductor is interrupted in theory an infinite voltage is produced for zero seconds, in pactice a resonant circuit it formed with the parasitic capacitance in the inductor, the maximum voltage is simply the Q multiplied by the applied voltage.

There are many other manufacturers around but MAXIM make step-up regulators with input voltages as low as 0.7V
**broken link removed**

 

[bananasiong]

Yes, maxim has many dc to dc step up converter, but many of them are QSOP package.
Does anyone have idea how to solder a QFN ic? That's too small, I have not idea..

 

[dknguyen]

I think you can use an oven maybe? Hot air? Either way it seems you require solder paste which is a pain in the ass.

I think I also heard somwhere to run the traces so that they extend beyond the edges of the chip, then you can just use a soldering iron.

 

[bananasiong]

But QFN seems to be 'Flat No Lead' type, need very strong soldering skill. If I use UV type PCB, do I need to remove the green film before soldering? Usually I don't remove it, but sometimes it cause the soldering iron to be dirty if u give too much heat.

 

[Hero999]

Yes, maxim has many dc to dc step up converter, but many of them are QSOP package.
Does anyone have idea how to solder a QFN ic? That's too small, I have not idea..

They do ready-made evaluation boards for some of the more popular ICs but they're expensive but worth it if you want to save the effort.