electronics-amplifier tutorial: Battery Charger

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Monday, April 6, 2009

Constant Current Battery Charger Circuit

Constant Current Battery Charger

Simple Power Supply and Charger Circuits
Figure 4 shows a simple power supply circuit. I have tested with KABO,
it works fine. For those who have a big capacity rechargeable battery,
the resistance value of R can be selected for approx. 10% output
charging current. DC in can be higher if your battery voltage higher than
8.4V, say. To ensure the output current is within the value calculated by
R, measure DC current before. The maximum supply for LM317 is ~35V.

A Simple Peak-detecting Nicad Charger
The circuit consists of two parts, a constant current generator using

a PNP power transistor (Q2), and a peak-detecting shutoff circuit

using a high-gain opamp (IC1). To start the charge cycle, switch

SW1 is momentarily closed, causing C1 to discharge. As IC1's

inverting input is now higher than its non-inverting input, its output

goes low, turning on Q1. This lights the red "charge" LED (D2) and

provides about 80mA through R6 and R7 to turn on Q2, which starts

charging the battery. Charge current flows through R8 on its way to

the battery. When the voltage across R8 exceeds about 0.6V, Q3

starts to turn on and robs current from the base of Q2. This regulates

the output current to an amount determined by the value of R8.

Constant Current Battery Charger Circuit

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