Digital control method for improving heavy-to-light (step down) load transient response of switch mode power supplies
View Patent ↗A method for improving heavy-to-light load transient response in low-power switch-mode power supplies is described. It uses a negative voltage input power rail and a digital controller with an extended duty ratio control value to provide faster discharging current slew rate in the switched mode power supplies (SMPS) inductor.
1. A controller for a DC-DC power supply producing a positive DC output voltage, the controller producing switching signals during a heavy-to-light load transient response such that a negative input voltage is used by the DC-DC power supply; and
wherein the controller uses a duty cycle with a range that includes positive and negative values, positive duty cycle values indicating the portion of a cycle that a positive input voltage is provided rather than ground and negative duty cycle values indicating the portion of a cycle that the negative input voltage is provided rather than ground.
2. The controller of claim 1 , wherein the negative input voltage is switched into an external LC circuit of the DC-DC power supply to quickly adjust the positive DC output to the heavy-to-light load transient.
3. The controller of claim 1 , wherein the switching signals are sent to power switches to switch in a positive input voltage and ground during normal operation and to switch in the negative input voltage and ground during the heavy-to-light load transient response.
4. The controller of claim 1 , wherein a capacitor is charged to provide the negative input voltage.
5. The controller of claim 1 , wherein switching signals are used to control power switches to provide a positive input voltage, ground and the negative input voltage into an external LC circuit.
6. A DC-DC power supply that switches in a positive input voltage, ground and a negative input voltage into an LC circuit so as to produce a positive DC output voltage, the negative input voltage being used during a heavy-to-light load transient response.
7. The controller of claim 6 , wherein the negative input voltage is switched into an external LC circuit of the DC-DC power supply to quickly adjust the positive DC output to the heavy-to-light load transient.
8. The DC-DC power supply of claim 6 , including a controller to produce switching signals for power switches of the DC-DC power supply, the power switches switching in the positive input voltage input and ground during normal operation and the negative input voltage and ground during the heavy-to-light load transient response.
9. The DC-DC power supply of claim 6 , further comprising a capacitor to provide the negative input voltage.
10. The DC-DC power supply of claim 9 , wherein the positive input voltage is used to charge the capacitor to provide the negative input voltage.
11. A method for a DC-DC power supply comprising:
during normal operation, switching between a positive input voltage and ground so as to produce a positive DC output voltage; and
during a heavy-to-light load transient, switching between a negative input voltage and ground so as to adjust the positive DC output voltage; and
creating a duty cycle signal with a range that includes positive and negative values; and
wherein positive duty cycles values indicating the portion of a cycle that the positive input voltage is provided, rather than ground, and negative duty cycle values indicating the portion of a cycle that the negative input voltage is provided, rather than ground.
12. The method of claim 11 , wherein the positive input voltage, ground and negative input voltage are switched into a LC circuit.
13. The method of claim 11 , wherein switching signals are produced to select the positive input voltage, ground or negative input voltage.
14. The method of claim 11 , wherein a capacitor is used to produce the negative input voltage.