DC-DC converter and method of controlling thereof
View Patent ↗A DC-DC converter can prevent intermittent failure of a PWM or driving signal (V M ) when a load becomes light and prevent generation of unusual noise from a transformer. The converter includes a transformer ( 2 ) having a primary winding ( 2 a ) and a secondary winding ( 2 b ), a semiconductor switching element ( 17 ) connected to the primary winding ( 2 a ), and a control unit controlling turning-ON and OFF periods of the switching element ( 17 ) so that an output voltage (V O ) matches a reference value (V REF ). By controlling the turning ON and OFF operation of the switching element ( 17 ), a DC voltage exactly equal to the reference value (V REF ) can be supplied to a load ( 5 ). The control unit includes an output voltage detecting and adjusting circuit ( 6 ) that outputs a command value (V C ) adjusted for the output voltage (V O ) and the reference value (V REF ), a triangular wave generating unit ( 7 ), and a comparator ( 15 ) that compares the command value (V C ) and the triangular wave (V T ) to generate the PWM signal (V M ) for driving the switching element ( 17 ) according to the result of the comparison. The triangular wave generating unit ( 7 ) varies the inclination of the triangular wave (V T ) in response to increase and decrease of the command value (V C ).
1. A DC-DC converter comprising:
a transformer having a primary winding for applying a DC voltage and a secondary winding for connecting to a load;
a semiconductor switching element connected to the primary winding; and
a control unit that controls turning ON and OFF periods of the switching element to match an output voltage of the secondary winding to a reference value,
wherein the switching element is turned ON and OFF to supply a DC voltage equal to the reference value for the load through the secondary wiring of the transformer,
wherein the control unit comprises:
an adjusting unit that outputs a command value adjusted for the output voltage of the secondary winding and the reference value;
a triangular wave generating unit that generates a triangular wave; and
a comparing unit that compares the command value and the triangular wave to generate a driving signal for the switching element based on the comparison,
wherein the triangular wave generating unit varies the inclination of the triangular wave in response to increase and decrease of the command value.
2. The DC-DC converter according to claim 1 , wherein the triangular wave generating unit comprises:
a capacitor for connecting to a charging and discharging power source; and
a unit that changes the voltage across the capacitor by flowing current whose amount depends on the magnitude of the command value, into the capacitor,
wherein the voltage across the capacitor is input to the comparing unit with the waveform of the voltage formed as the triangular wave.
3. The DC-DC converter according to claim 1 , wherein the triangular wave generating unit comprises:
a capacitor charged with a voltage depending on an amount of current flowing in the switching element; and
a unit that changes the voltage across the capacitor by flowing current, whose amount depends on the magnitude of the command value, into the capacitor,
wherein the voltage across the capacitor is input to the comparing unit with the waveform of the voltage formed as the triangular wave.
4. A method of controlling a DC-DC converter comprising a transformer having a primary winding for applying a DC voltage and a secondary winding for connecting to a load, a semiconductor switching element connected to the primary winding, and a control unit that controls turning ON and OFF periods of the switching element to match an output voltage of the secondary winding to a reference value, wherein the switching element is turned ON and OFF to supply a DC voltage equal to the reference value for the load through the secondary wiring of the transformer, the control unit comprising an adjusting unit, a triangular unit, and a comparing unit, the method comprising the steps of:
outputting a command value adjusted for the output voltage of the secondary winding and the reference value with the adjusting unit;
generating a triangular wave with the triangular wave generating unit;
comparing the command value and the triangular wave to generate a driving signal for the switching element based on the comparison with the comparing unit; and
varying the inclination of the triangular wave in response to increase and decrease of the command value with the triangular wave generating unit.