Switching Buck Voltage Converter for Battery Charging

[CASSETTE DECK]

I have designed and built various designs of high efficiency switching step down, precision regulated, current limited voltage converters over the last 22 years. Most of these converter designs are self oscillating using discrete components. Foldback current limiting, adjustable under voltage lockout / threshold circuit are optional features of many of these circuit designs.

I prefer to use fixed component adjustments for reliability and stability.
Use top quality components well below their maximum ratings and encapsulate circuit using neutral cure silicon rubber to avoid maintenance but still make adjustment possible by changing fixed components, then re-sealing with neutral cure silicon rubber roof and gutter sealant.
Changing fixed components will be virtually impossible if epoxy resin encapsulation is used.

http://forums.phxaudiotape.com/showthread.php/6749-Voltage-Reduction?p=174019&viewfull=1#post174019
http://forums.phxaudiotape.com/showthread.php/1041-Bicycle-audio?p=104095&viewfull=1#post104095

 

[CASSETTE DECK]

Battery Charger SMPS for Cyclists + Other Applications

Schematic:



The circuit shown is designed to operate on negative earth systems.

The 6V 6W alternator shown in the schematic has an unusual waveform with a very high peak voltage. The output voltage of the voltage doubler circuit can exceed 40 volts at full speed.
The schottky or high speed diodes used should really have at least a 60 volt rating.
The power output is well above 6 watts at full speed.

Change 13V zener diode on the voltage error amplifier negative feedback circuit to 6.2V for 6V lead acid battery charging applications. Low voltage zener diodes have a much lower positive temperature coefficient.

Change 18V zener diode on the under voltage lockout / threshold circuit to 12V, 13V, 15V or 16V depending on type of solar panel or when a 13.8 volt DC input is used.

The current limit can be adjusted by changing the value of the low inductance 0.91 ohm resistor on the current sensing circuit. FOLDBACK current limiting is not normally required in this application.
A heatsink on the BDT94 or equivalent switching transistor is not normally required in this application.

100 turns of 1 amp wire on a 1 inch / 2.5 centimeter iron powder or air gapped ferrite toroid will provide sufficient inductance. The circuit is self oscillating using positive feedback.

The switching transistor could be changed to a mosfet with some modifications.
At the time I designed and built this circuit, the selection of mosfets available was fairly limited, but I had a large stock of PNP power transistors.

More schematics to add later.