A small-sized DC power supply apparatus adapted for receiving input commercial AC voltages of different value includes an AC-to-DC converter 4 which converts an input commercial AC voltage to a first DC voltage. The first DC voltage is converted to a high-frequency voltage in an inverter 10 including IGBTs 10a-10d which are rendered conductive when a conduction control signal is applied thereto. A transformer 12 transforms the high-frequency voltage, which is, then, converted to a second DC voltage in a high-frequency-to-DC converter 16 for application to a load 22. The conduction control signal with a pause period disposed therein is generated in a controller 14. The conduction control signal occurs at a fixed period. The pause period disposed between the successive occurrences of the conduction control signal becomes longer as the input commercial AC voltage is higher.
An inventive inverter has a semiconductor switch circuit connected to the primary winding of a transformer. The semiconductor switch circuit is respectively controlled by PWM to supply a constant current to the load connected to a secondary winding of the transformer. The inverter is capable of deliberately regulating its ac power output to the load and lowering the lower limit of the output power through control of the intermittent operation, in which an error signal for carrying out the PWM control is reduced to zero during each off-duty period. In addition, the error signal for the PWM control is slowly decreased or increased in each shift from an off-duty period to on-duty period, and vise versa, by charging or discharging the capacitor in a feedback circuit, thereby allowing slow start or slow end of the respective on-off operations for the constant current control through the PWM.
An inventive inverter has a semiconductor switch circuit connected to the primary winding of a transformer. The semiconductor switch circuit is respectively controlled by PWM to supply a constant current to the load. connected to a secondary winding of the transformer. The inverter is capable of deliberately regulating its ac power output to the load and lowering the lower limit of the output power through control of the intermittent operation, in which an error signal for carrying out the PWM control is reduced to zero during each off-duty period. In addition, the error signal for the PWM control is slowly decreased or increased in each shift from an off-duty period to on-duty period, and vise versa, by charging or discharging the capacitor in a feedback circuit, thereby allowing slow start or slow end of the respective on-off operations for the constant current control through the PWM.
A transformer has a primary winding connected between a pair of d.c. input terminals via an on-off switch, and a secondary winding connected between a pair of d.c. output terminals via a rectifying and smoothing circuit. The output voltage applied from the rectifying and smoothing circuit to the load is held constant by switching the input voltage through feedback control. For intermittently operating the switch under light load, a sawtooth generator circuit is provided which provides a sawtooth voltage having a frequency less than that of the on-off operation of the switch. The sawtooth voltage is compared with a voltage indicative of the magnitude of a current flowing through the switch. The result of this comparison is utilized for modifying the delivery of switching pulses to the switch.
An inventive inverter has a semiconductor switch circuit connected to the primary winding of a transformer. The semiconductor switch circuit is respectively controlled by PWM to supply a constant current to the load connected to a secondary winding of the transformer. The inverter is capable of deliberately regulating its ac power output to the load and lowering the lower limit of the output power through control of the intermittent operation, in which an error signal for carrying out the PWM control is reduced to zero during each off-duty period. In addition, the error signal for the PWM control is slowly decreased or increased in each shift from an off-duty period to on-duty period, and vise versa, by charging or discharging the capacitor in a feedback circuit, thereby allowing slow start or slow end of the respective on-off operations for the constant current control through the PWM.
An inventive inverter has a semiconductor switch circuit connected to the primary winding of a transformer. The semiconductor switch circuit is respectively controlled by PWM to supply a constant current to the load connected to a secondary winding of the transformer. The inverter is capable of deliberately regulating its ac power output to the load and lowering the lower limit of the output power through control of the intermittent operation, in which an error signal for carrying out the PWM control is reduced to zero during each off-duty period. In addition, the error signal for the PWM control is slowly decreased of increased in each shift from an off-duty period to on-duty period, and vise versa, by charging or discharging the capacitor in a feedback circuit, thereby allowing slow start or slow end of the respective on-off operations for the constant current control through the PWM.
