5v Powered Charge Pump Battery Charger

Description: The circuit described will trickle charge a four-cell pack of AA or AAA NiMH batteries. It draws current from the +5V available from a USB connection and supplies approximately 70mA of current to the battery. This current level is sufficient to fully charge a pack of 2500mAh cells in approximately 36 hours. The circuit utilizes a single 74HC14 hex Schmitt trigger inverter in combination with a voltage doubler charge pump circuit.

The circuit operates by converting the 5V input from a USB power source into a suitable charging current for NiMH batteries. The 74HC14 hex Schmitt trigger inverter is essential for generating a square wave signal, which is then used to drive the charge pump circuit. This charge pump circuit effectively doubles the input voltage, providing the necessary voltage to ensure that the batteries receive adequate charging.

The trickle charging method is particularly beneficial for NiMH batteries as it prevents overcharging and prolongs battery life. The current output of approximately 70mA is calculated to allow for a safe and gradual charging process, ensuring that the 2500mAh battery pack can be charged without overheating or damaging the cells.

The circuit design must include the necessary filtering capacitors to smooth out the output voltage from the charge pump, ensuring stable operation. Additionally, protective components such as diodes may be required to prevent reverse current flow, which could damage the circuit or the batteries.

Overall, this charging circuit is an efficient solution for maintaining the charge of NiMH batteries, making it suitable for various applications where a reliable and safe charging method is required. Proper PCB layout and component selection will further enhance the performance and reliability of the circuit.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 inv erter in conjunction with a voltage doubler charge pump circuit.