Circuit and method for increasing the stability of switch-mode power supplies
View Patent ↗An improved circuit and method for increasing the stability of switch-mode power supplies via frequency fold-back is disclosed. For example, a circuit for increasing the stability of a switch-mode power supply using the compensation signal to control the frequency of the oscillator is disclosed, which includes an operational amplifier that functions to scale the compensation signal. Thus, the switching frequency of the power supply involved is decreased as the load is reduced. This novel use of the compensation signal to control the switching frequency of a switch-mode power supply significantly increases the stability of the power supply as compared to prior switch-mode power supplies. Therefore, the switch-mode power supply may be used for those applications where relatively high stability is desired.
1. A frequency control circuit for a switch-mode power supply, comprising:
an oscillator device, an output of said oscillator device operable to set a frequency of said switch-mode power supply;
a storage device coupled to a switching rate input of said oscillator device;
a transistor device, an output of said transistor device coupled to said storage device, said transistor device operable to increase or decrease a level of a signal stored in said storage device, and responsive to said increase or decrease of said level of said signal, increase or decrease a switching rate of said oscillator device; and
an amplifier device, an input of said amplifier device operable to receive a signal indicating a load condition for said switch-mode power supply, and an output of said amplifier device coupled to an input of said transistor device.
2. The frequency control circuit of claim 1 , further comprising:
a diode device coupled to an emitter of said transistor device, said diode device operable to limit voltage at said output of said transistor device to a predetermined level.
3. The frequency control circuit of claim 1 , wherein said amplifier device is operable to scale said signal indicating a load condition for said switch-mode power supply and control said frequency of said oscillator device.
4. The frequency control circuit of claim 1 , wherein said signal indicating a load condition for said switch-mode power supply comprises a compensation signal from a feedback circuit associated with said switch-mode power supply.
5. The frequency control circuit of claim 1 , wherein said oscillator device comprises an oscillator device in a switch-mode power supply semiconductor chip.
6. The frequency control circuit of claim 1 , wherein said transistor device comprises a Field-Effect Transistor.
7. The frequency control circuit of claim 1 , wherein said storage device comprises a capacitor.
8. A frequency control circuit for a switch-mode power supply, comprising:
a voltage or current controlled oscillator for said switch-mode power supply;
means for receiving a first signal indicating a load condition for said switch-mode power supply;
means, coupled to said means for receiving, for generating a second signal indicating an increase or decrease in said load condition for said switch-mode power supply;
means, coupled to said means for generating, for storing said second signal indicating said increase or decrease in said load condition for said switch-mode power supply; and
means, coupled to said means for storing, for increasing or decreasing a switching rate of said voltage or current controlled oscillator responsive to said second signal.
9. The frequency control circuit of claim 8 , further comprising:
means for limiting a voltage to a predetermined level, said voltage being output from said means for generating and associated with said first signal indicating a load condition for said switch-mode power supply.
10. The frequency control circuit of claim 8 , wherein said means for generating comprises an amplifier device operable to scale said first signal indicating a load condition for said switch-mode power supply and control said frequency of said oscillator.
11. The frequency control circuit of claim 8 , wherein said first signal indicating a load condition for said switch-mode power supply comprises a compensation signal from a feedback circuit associated with said switch-mode power supply.
12. The frequency control circuit of claim 8 , wherein said voltage or current controlled oscillator comprises an oscillator device arranged in a switch-mode power supply semiconductor chip.
13. The frequency control circuit of claim 8 , further comprising a transistor device and a diode device operable to limit a voltage to a predetermined level, said voltage being output from said means for generating and associated with said first signal indicating a load condition for said switch-mode power supply.
14. The frequency control circuit of claim 8 , wherein said means for generating comprises an operational amplifier.
15. A method for frequency control in a switch-mode power supply, comprising the steps of:
receiving a first signal indicating a load condition for said switch-mode power supply;
generating a second signal indicating an increase or decrease in said load condition for said switch-mode power supply;
storing said second signal indicating said increase or decrease in said load condition for said switch-mode power supply;
coupling said stored second signal to an input of a voltage or current controlled oscillator device; and
increasing or decreasing a switching rate of said voltage or current controlled oscillator device responsive to said second signal.
16. The method of claim 15 , further comprising the steps of:
coupling a diode device to an output an amplifier device;
coupling said amplifier device to a frequency control input of said voltage or current controlled oscillator device; and
limiting a voltage at said output of said amplifier device to a predetermined level.
17. The method of claim 15 , further comprising the steps of:
scaling said first signal indicating a load condition for said switch-mode power supply; and
controlling a frequency of said voltage or current controlled oscillator device responsive to the scaling step.
18. The method of claim 15 , wherein said first signal indicating a load condition for said switch-mode power supply comprises a compensation signal from a feedback circuit associated with said switch-mode power supply.
19. The method of claim 15 , wherein said voltage or current controlled oscillator device comprises an oscillator device arranged in a switch-mode power supply semiconductor chip.
20. The method of claim 15 , wherein the generating step is performed by an operational amplifier.