Compensating for cord resistance to maintain constant voltage at the end of a power converter cord
A cord correction circuit in a primary-side-controlled flyback converter compensates for the loss of output voltage caused by the resistance of the charger cord. In one embodiment, a correction voltage is subtracted from a feedback voltage received from a primary-side auxiliary inductor. A pre-amplifier then compares a reference voltage to the corrected feedback voltage. In another embodiment, the correction voltage is summed with the reference voltage, and the pre-amplifier compares the feedback voltage to the corrected reference voltage. The difference between the voltages on the input leads of the pre-amplifier is used to increase the output voltage to compensate for the voltage lost through the charger cord. The flyback converter also has a comparing circuit and a control loop that maintain the peak level of current flowing through the primary inductor of the converter. Adjusting the frequency and pulse width of an inductor switch signal controls the converter output current.
1. A method comprising:
(a) receiving a feedback signal indicative of an output voltage of a power converter, wherein the feedback signal has a voltage, wherein the power converter has a charger cord with a plug, wherein the charger cord has a resistance, and wherein a plug voltage is present on the charger cord at the plug;
(b) generating a cord correction signal, wherein the cord correction signal has a voltage;
(c) generating a corrected feedback signal by subtracting the voltage of the cord correction signal from the voltage of the feedback signal, wherein the corrected feedback signal has a voltage;
(d) comparing a reference voltage to the voltage of the corrected feedback signal;
(e) using the comparing in (d) to adjust the output voltage to compensate for a decrease in the plug voltage caused by the resistance of the charger cord, wherein an inductor switch control signal controls an inductor current flowing through an inductor, and wherein the inductor switch control signal has a pulse width; and
(f) adjusting the pulse width such that the plug voltage remains constant, wherein the generating in (c), the comparing in (d), the adjusting in (e) and the adjusting in (f) are performed by an integrated circuit that is packaged in an integrated circuit package.
2. The method of claim 1 , wherein the power converter outputs an output current and also operates in a constant output current mode, and wherein in the constant output current mode the output current remains constant as the output voltage varies.
3. The method of claim 1 , wherein the power converter is a switching converter.
4. The method of claim 1 , wherein the plug is connected to a cell phone.
5. The method of claim 1 , wherein the feedback signal is generated using a resistor divider.
6. The method of claim 1 , wherein the power converter has an inductor switch and an inductor, wherein the inductor current ramps up to a peak current while the inductor switch is turned on, and wherein the inductor switch is controlled by the inductor switch control signal, further comprising:
(g) controlling the peak current through the inductor by adjusting the pulse width of the inductor switch control signal.
7. The method of claim 1 , wherein the integrated circuit includes a cord correction circuit with a current mirror, and wherein the cord correction circuit generates the cord correction signal.
8. A method comprising:
(a) receiving a feedback signal indicative of an output voltage of a power converter, wherein the feedback signal has a voltage, wherein the power converter has a charger cord with a plug, wherein the charger cord has a resistance, and wherein a plug voltage is present on the charger cord at the plug;
(b) generating a cord correction signal, wherein the cord correction signal has a voltage;
(c) generating a corrected reference voltage by summing a reference voltage with the voltage of the cord correction signal;
(d) comparing the corrected reference voltage to the voltage of the feedback signal;
(e) using the comparing in (d) to adjust the output voltage to compensate for a decrease in the plug voltage caused by the resistance of the charger cord, wherein an inductor switch control signal controls an inductor current flowing through an inductor, and wherein the inductor switch control signal has a pulse width; and
(f) adjusting the pulse width such that the plug voltage remains constant, wherein the generating in (c), the comparing in (d), the adjusting in (e) and the adjusting in (f) are performed by an integrated circuit that is packaged in an integrated circuit package.
9. The method of claim 8 , wherein the power converter outputs an output current and also operates in a constant output current mode, and wherein in the constant output current mode the output current remains constant as the output voltage varies.
10. The method of claim 8 , wherein the power converter is a switching converter.
11. The method of claim 8 , wherein the plug is connected to a cell phone.
12. The method of claim 8 , wherein the feedback signal is generated using a resistor divider.
13. The method of claim 8 , wherein the power converter has an inductor switch and an inductor, wherein the inductor current ramps up to a peak current while the inductor switch is turned on, and wherein the inductor switch is controlled by the inductor switch control signal, further comprising:
(g) controlling the peak current through the inductor by adjusting the pulse width of the inductor switch control signal.
14. The method of claim 8 , wherein the integrated circuit includes a cord correction circuit with a current mirror, and wherein the cord correction circuit generates the cord correction signal.
15. A power converter, comprising:
an inductor, wherein the power converter is a switching converter and outputs an output voltage;
a resistor divider coupled to the inductor, wherein a feedback signal is generated using the resistor divider to divide the output voltage;
a charger cord with a plug, wherein the charger cord has a resistance, and wherein a plug voltage is present on the charger cord at the plug; and
an integrated circuit controller that is packaged in an integrated circuit package, wherein the integrated circuit controller receives the feedback signal and generates a cord correction signal, and wherein the integrated circuit controller adjusts the output voltage to compensate for a decrease in the plug voltage caused by the resistance of the charger cord.
16. The power converter of claim 15 , wherein the power converter outputs an output current and also operates in a constant output current mode, and wherein in the constant output current mode the output current remains constant as the output voltage varies.
17. The power converter of claim 15 , wherein the integrated circuit controller generates a corrected reference voltage by summing a voltage of the cord correction signal with a reference voltage, and wherein the integrated circuit controller compares the corrected reference voltage to a voltage of the feedback signal, and wherein the integrated circuit controller adjusts the output voltage using the comparison of the corrected reference voltage to the voltage of the feedback signal.
18. The power converter of claim 17 , wherein the power converter outputs an output current, and wherein the cord correction signal is dependent on the output current.
19. The power converter of claim 15 , wherein the integrated circuit controller generates a corrected feedback signal by subtracting a voltage of the cord correction signal from a voltage of the feedback signal, wherein the integrated circuit controller compares a reference voltage to a voltage of the corrected feedback signal, and wherein the integrated circuit controller adjusts the output voltage using the comparison of the reference voltage to the voltage of the corrected feedback signal.
20. The power converter of claim 19 , wherein the power converter outputs an output current, and wherein the cord correction signal is dependent on the output current.
21. The power converter of claim 15 , wherein the integrated circuit controller includes a cord correction circuit with a current mirror, and wherein the cord correction circuit generates the cord correction signal.