Joule Thief Variations
— David Wagner 2007/07/16 09:04
CFL Salvage
This circuit is for making two joule thieves entirely by salvaging the parts from one CFL. The diode at the base of the transistor is there to limit the “on” time of the transistor if the base resistor value is too small (<1kΩ).
//
+-->|--+
| |
+------------------------------+-->|--+--||--+
| | |
| ======= |/ C |
+--UUU+UUU--+-/\/\/-+->|--+--| |
A2 | B1 200 | B|\|E |
| | +-------------+
| | |
| +--/\/\/-----------+
| | 10k |
+-----||-------------------------------+
|
Perhaps a better idea is to supplement the transistor's parasitic capacitance with a small capacitor, maybe 0.1μF.
//
+-->|--+
| |
+---------------------------+-->|--+--||--+
| | |
| +--||--+ |
| | | |
| ======= | |/ C |
+--UUU+UUU--+-/\/\/--+----| |
A2 | B1 200 | B|\|E |
| | +-------------+
| | |
| +--/\/\/-------------+
| | 10k |
+-----||----------------------------+
|
In this circuit, an SPDT is used to alternate between charging the cell from the panel and discharging it through the LED. It is necessary to compromise by using a single base resistor for both power sources. (But perhaps using two series LEDs to get similar boost ratios for charge and discharge will help.) The reverse current leakage through the solar cell when the LED is lit by the battery should be tiny.1)
However, I measured way too much reverse leakage, 50mA@1.2V through 20Ω.
//
+------------------------------------+-->|--+
| | |
| +--------------------------+-->S--+--||--+
| | | | |
| | ======= |/ C +--Z<--+
| +--UUU+UUU--+--/\/\/--+--| |
| | | B|\|E |
| | | +-------------+
| | | |
| | \ +--/\/\/-----------+
| | \ | |
o\ o--+----------||----------------------+
\ +0.45V| |
o | |
+---------------------------||-----------+
+1.2V|
More complete regulated power supply circuit
+------------/\/\/-------+
| |
| |/
+------------------------+-->S--+--/\/\/--+--/\/\/--+--|
| | | | |\|
| ======= |/ C +---||--+ | +--o
+--UUU+UUU--+-/\/\/-+--| | |
| | B|\|E | |
| | +--------+----+----->Z-----+
| | |
| +-------/\/\/------+
| | 100k |
| +--|<--------------+
| | |
+-----||-------------------------+--------------------o
+1V|
//
+-->|--+
| C1 |
+------------------------+-->S--+--||--+
| | D1 | |
| = = = = = R1 Q1|/ +--Z<--+
+-UUUU+UUUU--/\/\/--+--| Z1 |
T1 | | |\| |
| | +-------------+
| | D2 |
| +--|<--------------+
| | |
| +--/\/\/--+ _+--+
| R2 \ / |
| ----- |
| R3 |Q2 |
+-------------------/\/\/--+ |
| | |
+--||----------------------------+
|
+0.2V to +2.5V
+------------------------+--->S----+------------+
| | | |
| = = = = |/ C | |/
+--UUU+UUU--+-/\/\/-+--| +-||-+-/\/\/-+--|
| | B|\|E | | |\|
| | +----+----+-->Z---+ +
| | | | |
| +------/\/\/---+---||--+ +--o
| | 100k | >+2.5V
| +--|<----------+
| | |
+-----||---------------------+---------------o
>+0.2V |
Discussion