Output current control in a boundary conduction mode buck converter
View Patent ↗A switching power converter has an input voltage source. An output load is coupled to the input voltage source. An inductive element is coupled to the load. A switch is coupled to the inductive element. A control circuit is coupled to the switch and the inductive element for activating and deactivating the switch, the control circuit activating and deactivating the switch based on a negative voltage drop across a resistive element of the control circuit.
1. A switching power converter comprising:
an input, voltage source;
an output load coupled to the input voltage source;
an inductive element coupled to the load;
a switch coupled to the inductive element;
a diode coupled to the inductive element and the input voltage source; and
a control circuit coupled to the switch and the inductive element for activating and deactivating the switch, the control circuit activating and deactivating the switch based on a negative voltage drop across a resistive element of the control circuit;
wherein the control circuit activates and then deactivates the switch once a current sense voltage across the resistive element exceeds a reference voltage adjusted by the negative voltage drop detected previously.
2. A switching power converter in accordance with claim 1 , wherein the control circuit comprises:
the resistive element having a first terminal coupled to the switch;
a sample and hold circuit having a first terminal coupled to a first terminal of the resistive element;
a summing node having a first input coupled to a second terminal of the sample and hold circuit and a second input coupled to a reference voltage;
a comparator having a first input coupled to the first terminal of the resistive element and a second input coupled to an output of the summing node;
a zero voltage detector circuit, having a first terminal coupled to the switch; and
a flip-flop having a reset input coupled to an output of the comparator, a set input coupled to a second terminal of the zero voltage detector; and an output coupled to the switch.
3. A switching power converter in accordance with claim 2 , wherein the control circuit further comprises a diode coupled across the switch.
4. A switching power converter in accordance with claim 1 , wherein the control circuit comprises:
the resistive element coupled to the switch;
a sample and hold circuit coupled to the resistive element;
a summing node coupled to the sample and hold circuit and to a reference voltage;
a comparator coupled to the resistive element and to an output of the summing node;
a zero voltage detector circuit, coupled to the switch; and
a flip flop coupled to the comparator, to the zero voltage detector, and to the switch.
5. A switching power converter in accordance with claim 4 , wherein the control circuit further comprises a diode coupled across the switch.
6. A switching power converter comprising:
an input voltage source;
an output load coupled to the input voltage source;
an inductive element coupled to the load;
a switch coupled to the inductive element; and
a control circuit coupled to the switch and the inductive element for activating and deactivating the switch, the control circuit activating the switch once a zero voltage condition is detected at the switch and deactivating the switch when a current sense signal in a resistive element of the control circuit exceeds a reference voltage, the control circuit further activating and deactivating the switch based on a negative voltage drop across the resistive element of the control circuit;
wherein the control circuit activates and then deactivates the switch once a current sense voltage across the resistive element exceeds a reference voltage adjusted by the negative voltage drop detected previously.
7. A switching power converter in accordance with claim 6 wherein the control circuit comprises:
the resistive element coupled to the switch;
a sample and hold circuit coupled to the resistive element;
a summing node coupled to the sample and hold circuit and to a reference voltage;
a comparator coupled to the resistive element and to an output of the summing node;
a zero voltage detector circuit coupled to the switch; and
a flip-flop coupled to the comparator, to the zero voltage detector, and to the switch.
8. A switching power converter in accordance with claim 7 , wherein the control circuit further comprises a diode coupled across the switch.
9. A power converter comprising:
an input voltage source;
an output load coupled to the input voltage source;
an inductive element coupled to the load;
a switch coupled to the inductive element;
a resistive element coupled to the switch;
a sample and hold circuit coupled to the resistive element; and
a zero voltage detector circuit coupled to the switch and to the sample and hold circuit;
wherein the zero voltage detector (ZVD) circuit comprises:
a differential capacitive element coupled to an input of the ZVD circuit; and
a pull-up element coupled to an output of the ZVD circuit.
10. The power converter of claim 9 , further comprising a body diode coupled across the switch.
11. The power converter of claim 9 , further comprising a capacitive element coupled in parallel to the output load.
12. The power converter of claim 9 , further comprising a diode coupled to the inductive element and the input voltage source.
13. The power converter of claim 9 , wherein the pull-up element is a resistor connected to a pull-up voltage source.
14. The power converter of claim 9 , further comprising a diode clamp for limiting voltage at the output of the ZVD circuit.
15. The power converter of claim 9 , wherein the zero voltage detector circuit further comprises a resistive element coupled in series with the differential capacitive element.