Capacitor charging apparatus

A control circuit for a capacitor charging apparatus which comprises a transformer and an output capacitor which is charged with electric current that flows through a secondary coil of the transformer, and which charges the output capacitor by controlling the switching operation of a switching transistor provided on a path of a primary coil of the transformer, comprising:

• a voltage monitoring terminal connected to a tap provided to the secondary coil of the transformer;
• a switching control unit which receives a monitoring voltage that occurs at the voltage monitoring terminal, and which controls the switching operation of the switching transistor according to the monitoring voltage;
• and
• a protection circuit which monitors the impedance at the voltage monitoring terminal, and which stops the switching control operation of the switching control unit for the switching transistor in a case in which an abnormal state has been detected.

A control method for controlling a capacitor charging apparatus which comprises a transformer and an output capacitor which is charged with electric current that flows through a secondary coil of the transformer, and which charges the output capacitor by controlling the switching operation of a switching transistor provided on a path of a primary coil of the transformer, comprising an operation cycle which is repeatedly performed, comprising:

• detecting a primary current that flows through the primary coil of the transformer;
• setting the switching transistor to the ON state during a period before the primary current thus detected reaches a predetermined peak current value;
• setting an OFF period based upon a monitoring voltage that corresponds to the voltage at a tap provided to the secondary coil of the transformer;
• limiting the OFF period to a predetermined maximum OFF period or less;
• and
• setting the switching transistor to the OFF state during the OFF period thus set,
• and wherein the control method further includes comprises a protection operation in which, in a case in which the monitoring voltage continues to be smaller than a predetermined threshold value for a predetermined period, the switching control operation for the switching transistor is stopped.

A control method for controlling a capacitor charging apparatus which comprises a transformer and an output capacitor which is charged with electric current that flows through a secondary coil of the transformer, and which charges the output capacitor by controlling the switching operation of a switching transistor provided on a path of a primary coil of the transformer, comprising a cycle operation which is repeatedly performed, comprising:

• detecting a primary current that flows through the primary coil of the transformer;
• setting the switching transistor to the ON state during a period until the primary current thus detected reaches a predetermined peak current value;
• setting an OFF period based upon the voltage at a tap provided to the secondary coil of the transformer;
• limiting the OFF period to a predetermined maximum OFF period or less;
• and
• setting the switching transistor to the OFF state during the OFF period thus set, and wherein the control method further comprises an operation in which the impedance is monitored at the terminal to be connected to the tap, and the switching control operation for the switching transistor is stopped in a case in which an abnormal state has been detected.