Based on Texas Instruments documentation, this circuit is based on the BQ2000 a circuit used to power LEDs. The circuit can be used with lithium-ion batteries.
The output voltage depends on the zener diode. Zener in the range between 1.2 to 12 V rated to 1 W...
This shield with full-wave triggering was found in the Radio Electronics Experimenter magazine of 1989....
We obtained this circuit in a Maxim documentation from the 90s. The circuit is based on the...