Parallel operating system of DC-AC converters and controller IC therefor

A parallel operating system of operating in parallel a multiplicity (N) of dc-ac converters, each dc-ac converter comprising:

• a transformer having a primary winding and at least one secondary winding connected to a load;
• a semiconductor switch circuit for flowing current from a dc power supply to said primary winding in a first direction and a second direction alternately;
• a current detection circuit for detecting the current flowing through said load and generating a current detection signal;
• an oscillator block for generating a triangular wave signal and a clock signal synchronized with said triangular wave signal when connected to a frequency determination capacitor and a frequency determination resistor;
• and
• a PWM control circuit for providing said semiconductor switch circuit with a PWM-controlled switch drive signal upon receipt of said triangular wave signal, clock signal, and current detection signal, wherein said system is adapted to provide a startup signal for starting up said PWM control circuit to each group of dc-ac converters including at least one dc-ac converter.

A controller IC for controlling the ac power to be supplied to a load by driving a semiconductor switch circuit, said controller IC comprising:

• an oscillator block for generating a triangular wave signal and a clock signal synchronized with said triangular wave signal when connected to a frequency determination capacitor and a frequency determination resistor;
• a PWM control circuit for providing said semiconductor switch circuit with a PWM-controlled switch drive signal upon receipt of said triangular wave signal and clock signal and the current detection signal obtained by detecting the current flowing through said load;
• a first external terminal connected to said frequency determination capacitor and adapted to serve as an output terminal when said triangular wave signal is generated, but serve as an input terminal for receiving an external triangular wave signal when said triangular wave signal is not generated;
• a second external terminal connected to said frequency determination resistor;
• a third external terminal adapted to serve as an output terminal when said clock signal is generated, but serve as an input terminal when said clock signal is not generated;
• and
• a fourth external terminal adapted to serve as an input terminal of a startup signal for starting up said PWM control circuit, wherein
• said triangular wave signal is also outputted from said first external terminal and said clock signal is outputted from said third external terminal when said frequency determination capacitor is connected to said first external terminal and said frequency determination resistor is connected to said second external terminal;
• said triangular wave signal is externally inputted to said first external terminal and said clock signal is externally inputted to said third external terminal when said frequency determination resistor is not connected to said external terminal;
• and
• said PWM control circuit is started up for PWM-controlling said semiconductor switch circuit when startup signal is inputted into said fourth external terminal.

The controller IC according to 20 or 21, further comprising a sixth external terminal, wherein

• said triangular wave signal and said clock signal generated in said oscillator block have the same frequency;
• a synchronization signal is generated by stepping down said clock signal and said clock signal is outputted from said sixth terminal when said triangular wave signal is generated in said oscillator block;
• and
• said resultant clock signal is externally inputted to said sixth external terminal when said triangular wave signal is not generated in said oscillator block.