DC-DC converter
View Patent ↗A DC-DC converter performing pulse frequency modulation (PFM) control with a fixed ON time, having a control circuit performing PFM control of the ON time for a switch, including an error amplifier amplifying the difference between an output voltage and a target voltage, a voltage controlled oscillator increasing and decreasing in frequency and outputting an error signal, and a one-shot circuit generating the ON time based on a trigger signal output from the VCO, where ON time is linked to an input voltage and/or an output voltage. The switching frequency decreases under light loads and current consumption is reduced, and the switching frequency is made to be approximately constant under heavy loads.
1. A DC-DC converter controlling direct current power comprising:
a switching element switching on and off an input direct current;
a control circuit periodically switching said switching element on for an ON time and off for an OFF time; and
a resistor dividing an output voltage of the DC-DC converter by a variable division ratio, the divided output voltage being fed back to the control circuit, wherein
the ON time is determined by a pulse width of a one-shot circuit, and
under both light and heavy load conditions, said control circuit applies a pulse frequency modulation (PFM) and controls the ON time, wherein
the PFM is applied by varying said OFF time in accordance with a pulse frequency modulation control, and
the ON time is controlled to increase when said pulse width is increased in accordance with one of a rise in the output voltage or a drop in the variable division ratio of the output voltage of said DC-DC converter.
2. The DC-DC converter according to claim 1 , wherein the control circuit includes
an error amplifier which amplifies a difference between the divided output voltage and the target voltage and outputs an error signal,
an oscillator generating a frequency that increases and decreases according to a value of the error signal, and
the one-shot circuit which generates the ON time based on a trigger by a signal being output by the oscillator.
3. The DC-DC converter according to claim 2 , wherein the one-shot circuit comprises:
a capacitor,
a current-supply circuit to supply a charging current to the capacitor, and a voltage decision circuit to determine whether a voltage of the capacitor is more than a decision voltage.
4. The DC-DC converter according to claim 3 , wherein the current-supply circuit supplies the charging current depending on the input voltage.
5. The DC-DC converter according to claim 3 , wherein the capacitor has a capacitance value that varies according to the output voltage or the target voltage.
6. The DC-DC converter according to claim 3 , wherein the voltage decision circuit uses a decision voltage corresponding to the output voltage or the target voltage.