Power converters with adaptive output voltages
A switching power converter is provided that transitions between output voltage modes over a delay period using at least one of an adaptive resistor and an adaptive reference voltage circuit.
1. A switching power converter, comprising:
a voltage divider configured to produce a feedback voltage from an output voltage, the voltage divider including an adaptive resistor configured to produce an adaptive resistance for changing the feedback voltage, and a
a control circuit configured to control the adaptive resistor so that the adaptive resistance has a first value during a first output voltage mode for the switching power converter in which a cycling of a power switch is modulated so the output voltage is regulated to equal a first voltage and so that the adaptive resistance has a second value during a second output voltage mode for the switching power converter in which the cycling of the power switch is modulated so that the output voltage is regulated to equal a second voltage, wherein the first voltage and the second voltage are different, the second value being greater than the first value, and wherein the adaptive resistor is configured to increase its adaptive resistance over a delay period in a transition between the first value and the second value.
2. The switching power converter of claim 1 , wherein the adaptive resistor is further configured to continually decrease its adaptive resistance over the delay period in a transition between the second value and the first value.
3. The switching power converter of claim 1 , wherein the adaptive resistor is further configured so that the delay period has a duration between 1 millisecond and 20 milliseconds.
4. The switching power converter of claim 1 , further comprising:
a reference circuit configured to provide a reference voltage; and
an error amplifier having a first input terminal for receiving the feedback voltage and a second input terminal for receiving the reference voltage, the error amplifier being configured to compare the feedback voltage to the reference voltage to produce an error voltage, wherein the adaptive resistor is coupled between the first input terminal and ground.
5. The switching power converter of claim 4 , wherein the adaptive resistor comprises a transistor having a first terminal coupled through a first resistor to the first input terminal and a second terminal coupled to ground, and wherein a capacitor is coupled between a gate of the transistor and ground, and wherein the adaptive resistor is configured to continually charge the capacitor during the delay period.
6. The switching power converter of claim 5 , wherein the adaptive resistor further comprises an inverter configured to drive a first terminal of a second resistor having a second terminal coupled to the gate of the transistor.
7. The switching power converter of claim 5 , wherein the adaptive resistor further comprises a first current source configured to continually charge the transistor during the delay period.
8. The switching power converter of claim 4 , further comprising:
a power switch; and
a modulator configured to modulate a cycling of the power switch responsive to the error voltage.
9. The switching power converter of claim 1 , wherein the adaptive resistor comprises a pair of adaptive resistor coupled in parallel.
10. A method for a switching power converter, comprising:
in a first output voltage mode for the switching power converter in which a power switch is modulated so that an output voltage is regulated to equal a first voltage, dividing an output voltage for the first output voltage mode through a voltage divider including an adaptive resistance having a first value to produce a feedback voltage; and
during a transition from the first output voltage mode to a second output voltage mode in which the power switch is modulated so that the output voltage is regulated to equal a second voltage that is different from the first voltage, changing the adaptive resistance from the first value to a second value over a delay period.
11. The method of claim 10 , wherein the second value is less than the first value, and wherein changing the adaptive resistance over the delay period comprises continually decreasing the adaptive resistance over the delay period, and wherein an output voltage for the second output voltage mode is greater than the output voltage for the first output voltage mode.
12. The method of claim 11 , further comprising enumerating a device to be charged to determine if the device supports the output voltage for the second output voltage mode prior to transitioning from the first output voltage mode to the second output voltage mode.
13. The method of claim 11 , wherein continually decreasing the adaptive resistance over the delay period comprises charging a capacitor over the delay period and a driving a gate voltage of a transistor in a voltage divider using the charged capacitor over the delay period.
14. The method of claim 10 , further comprising:
during a transitioning from the second output voltage mode to the first output voltage mode; continually changing the adaptive resistance from the second value to the first value over the delay period.
15. The method of claim 10 , further comprising comparing the feedback voltage to a reference voltage to produce an error signal.
16. The method of claim 15 , further comprising: modulating a cycling of a power switch responsive to the error signal to regulate the output voltage.