Battery charging apparatus capable of completely charging secondary cell in safety

Battery charging apparatus connected between a power source and a secondary cell for supplying direct current (DC) power to the secondary cell, comprising:

• 1) power generation means for generating said DC power for charging;
• 2) switch means provided between said power generation means and said secondary cell for intermittently supplying said DC power from said power generation means;
• 3) voltage detection means provided between said switch means and said secondary cell for detecting a voltage of said secondary cell in order to check A remaining capacity of said secondary cell;
• 4) pulse generation means for generating a pulse voltage having a predetermined cycle and first and second voltage levels each having a predetermined period synchronized with a start of said supply of said DC power from said power generation means;
• and
• 5) control means for controlling said charging, by means of repeating a charging operation and an interrupting/detecting operation when said detected voltage of said secondary cell is less than a set value, wherein when said pulse voltage generated by said pulse generation means is at said first voltage level, said charging operation supplies said DC power by turning on said switch means, and when said pulse voltage is at said second voltage level, said interrupting/detecting operation is performed in which said supply of said DC power is interrupted and said detection means detects said voltage of said secondary cell, and by means of stopping pulse generating operation of said pulse generation means when said detected voltage of said secondary cell is more than said set value,
• wherein said control means comprises,
• a) a controller which samples said voltage of said secondary cell which is detected by said voltage detection means at a predetermined time interval, calculates a difference between a present sampling voltage and an immediately previous sampling voltage, and outputs a stop instruction signal for stopping said charging of said secondary cell when an absolute value of said voltage difference becomes less than a predetermined value,
• b) a first stage inverter for outputting a first inverted signal which is generated by inverting said stop instruction signal,
• c) an exclusive OR circuit providing an exclusive OR output of a first input and a second input, said first input being said pulse voltage outputted from said pulse generation means, and said second input being said inverted signal outputted from said first stage inverter,
• d) a resistor having a first end which is connected in series to an output terminal of said exclusive 0R circuit,
• e) a capacitor which is connected in series to a second end of said resistor and ground, and
• f) a second stage inverter for generating a second inverted signal which is generated by inverting a signal representing an output supplied from said exclusive OR circuit through said resistor and said capacitor, and for transmitting said second inverted signal to said pulse generation means.