DC-DC converter using internal ripple with the DCM function
A DC-DC converter, having an input voltage and an output voltage, includes an inductor and a switch switching the input voltage to an input side of the inductor, where a feedback path controlling initiation of closing the switch includes capacitive coupling of the voltage at the input side of the inductor.
1. A DC-DC converter receiving an input voltage and generating an output voltage, comprising:
an inductor;
a switch switching the input voltage to a first side of the inductor;
a comparator controlling initiation of closing the switch; and,
the first side of the inductor capacitively coupled to a first input of the comparator;
a second switch switching the first side of the inductor to ground;
circuitry receiving a voltage at the first side of the inductor, receiving a state of the second switch, and controlling at least part of the signal path between the first side of the inductor and the first input of the comparator for providing a signal at a first strength to the first input of the comparator; and,
the circuitry configured to provide the signal at a second strength less than the first strength from the first side of the inductor to the first input of the comparator only when the circuitry determines that a discontinuous conduction mode (DCM) exists for the inductor;
further comprising:
a resistance comprising a series combination of a first resistor having a resistance much greater than a second resistor in the path between the first side of the inductor and the first input of the comparator;
a third switch in parallel with the first resistor; and,
the circuitry configured to cause the third switch to open when the circuitry determines that a DCM exists for the inductor.
2. The DC-DC converter of claim 1 , the circuitry further comprising:
a zero-crossing detector receiving the voltage at the first side of the inductor, the circuitry determining that a DCM exists for the inductor when the zero-crossing detector detects that the voltage at the first side of the inductor is positive during a period when the second switch is closed.
3. The DC-DC converter of claim 1 , further comprising:
a second switch switching the first side of the inductor to ground;
circuitry receiving the voltage at the first side of the inductor, and receiving a state of the second switch; and,
the circuitry configured to open the second switch when the circuitry determines that a DCM exists for the inductor.
4. The DC-DC converter of claim 3 , the circuitry further comprising:
a zero-crossing detector receiving the voltage at the first side of the inductor, the circuitry determining that a DCM exists for the inductor when the zero-crossing detector detects that the voltage at the first side of the inductor is not negative during a period when the second switch is closed.
5. The DC-DC converter of claim 1 , further comprising:
a differential difference amplifier having an output that is electrically coupled to the first input of the comparator;
the differential difference amplifier having a first input electrically coupled to the output voltage; and
the differential difference amplifier having a second input connected to a first reference voltage that is variable.
6. The DC-DC converter of claim 5 , the output of the differential difference amplifier offset by a bias voltage that is constant.
7. The DC-DC converter of claim 1 , further comprising:
a differential difference amplifier, having an output that is electrically coupled to the first input of the comparator; and,
the output of the differential difference amplifier offset by a bias voltage that is constant.
8. The DC-DC converter of claim 1 , further comprising:
switch control circuitry comprising a frequency locked loop to close the switch at a constant rate over a range of output currents.
9. The DC-DC converter of claim 8 , further comprising:
a voltage controlled current source, receiving the input voltage, and having an output current driving a capacitance to generate a ramp voltage signal;
a comparator, receiving the output voltage and the ramp voltage signal and generating a switch control signal;
a phase comparator comparing the phase of the switch control signal to the phase of a reference frequency signal;
the phase comparator driving a current source; and
current from the current source being added to current from the voltage controlled current source.
10. A DC-DC converter receiving an input voltage and generating an output voltage, comprising:
an inductor;
a switch switching the input voltage to a first side of the inductor;
a comparator controlling initiation of closing the switch; and,
the first side of the inductor capacitively coupled to a first input of the comparator;
a differential difference amplifier having an output that is electrically coupled to the first input of the comparator;
the differential difference amplifier having a first input electrically coupled to the output voltage;
the differential difference amplifier having a second input connected to a first reference voltage that is variable; and
reference adjust circuitry, having a first input electrically coupled to a fraction of the output voltage and a second input electrically coupled to a second reference voltage that is constant, the reference adjust circuitry integrating a difference between the fraction of the output voltage and the second reference voltage and adding the integrated difference to the second reference voltage to generate the first reference voltage.
11. The DC-DC converter of claim 10 , the reference adjust circuitry further comprising:
a threshold circuit, determining whether the magnitude of the difference between the fraction of the output voltage and second reference voltage is greater than a threshold, and,
the reference adjust circuitry integrating the difference between the fraction of the output voltage and the second reference voltage only when the difference exceeds the threshold.
12. A DC-DC converter receiving an input voltage and generating an output voltage, comprising:
an inductor;
a switch switching the input voltage to a first side of the inductor;
a comparator controlling initiation of closing the switch; and,
the first side of the inductor capacitively coupled to a first input of the comparator;
a feedback path comparing a fraction of the output voltage to a first reference voltage;
an amplifier receiving a fraction of the output voltage and a second reference voltage, and having an amplifier output that is the difference between the fraction of the output voltage and the second reference voltage;
a threshold circuit determining whether the magnitude of the output of the amplifier is greater than a threshold;
an integrator integrating the output of the amplifier only when the threshold circuit determines that the magnitude of the output of the amplifier is greater than the threshold; and,
an adder, adding an output of the integrator to the first reference voltage to adjust the first reference voltage.
13. The DC-DC converter of claim 12 , where the integrator is a digital integrator.