5v Powered Charge Pump Battery Charger

The circuit below will trickle charge a four cell pack of AA or AAA NiMH batteries.  The circuit draws current from the +5v available a USB connection and pumps about 70ma of current into the battery. This should be enough current to fully charge a pack of 2500ma-hour cells in about 36 hours.  The circuit uses a single 74HC14 hex Schmitt trigger inverter in conjunction with a voltage doubler charge pump circuit.

Read More

LM3940 1A Low Dropout Regulator for 5V to 3.3V Conversion

LM3940 1A Low Dropout Regulator for 5V to 3.3V Conversion

General Description :
The LM3940 is a 1A low dropout regulator designed to provide 3.3V from a 5V supply.
The LM3940 is ideally suited for systems which contain both 5V and 3.3V logic, with prime power provided from a 5V bus.
Because the LM3940 is a true low dropout regulator, it can hold its 3.3V output in regulation with input voltages as low as 4.5V.
The T0-220 package of the LM3940 means that in most applications the full 1A of load current can be delivered without using an additional heatsink.
The surface mount TO-263 package uses minimum board space, and gives excellent power dissipation capability when soldered to a copper plane on the PC board.

Features
■ Output voltage specified over temperature
■ Excellent load regulation
■ Guaranteed 1A output current
■ Requires only one external component
■ Built-in protection against excess temperature
■ Short circuit protected
Applications
■ Laptop/Desktop Computers
■ Logic Systems

Typical Application

Connection Diagram

Read More