SWITCHING POWER SUPPLY CONTROLLER WITH SELECTIVE FEEDBACK SAMPLING AND WAVEFORM APPROXIMATION

• US 20100181980A1
• Filed: 01/06/2010
• Published: 07/22/2010
• Est. Priority Date: 01/21/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: RICHARDSON, KENNETH G.
• Granted Patent: US 8,633,682 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A switching power supply controller which includes at least one switching element, and controls a switching cycle during which the switching elements are switched on and off to regulate the power supply'"'"'s output voltage. The controller has a feedback signal which represents the output voltage, and a circuit node which conducts a current that is higher during a second portion of the switching cycle than it is during a first portion, such that the feedback signal varies with the current conducted by the node. To overcome feedback signal inaccuracies, a sampling circuit samples a signal which varies with the feedback signal only during the first portion of the switching cycle; the controller then regulates the output voltage in response to the sampled signal. The sampling circuit may be further arranged to produce an output which approximates the portion of the feedback signal waveform which is not sampled.

Claims

1. A switching power supply controller which is adapted to be connected to external components to produce a regulated output voltage at an output node, comprising:

at least one switching element, said controller arranged to control a switching cycle during which said switching elements are switched on and off to regulate the output voltage at said output node;

a feedback signal which represents the output voltage produced at said output node;

a circuit node which conducts a current that is higher during a second portion of said switching cycle than it is during a first portion of said switching cycle, said controller arranged such that said feedback signal varies with the current conducted by said circuit node; and

a sampling circuit arranged to sample a signal which varies with said feedback signal only during said first portion of said switching cycle, said controller arranged to regulate said output voltage in response to said sampled signal.

2. The controller of claim 1, wherein said controller is contained within an integrated circuit (IC) and said circuit node is an internal IC ground.

3. The controller of claim 1, wherein said at least one switching element comprises two switching elements, one of which is switched on during said first portion of said switching cycle and the other of which is switched on during said second portion of said switching cycle.

4. The controller of claim 1, wherein said at least one switching element comprises a first switching element connected between a supply voltage node and a switching node and a second switching element connected between said switching node and a circuit ground, said circuit node being said circuit ground, said controller arranged such that said first switching element is switched on during said first portion of said switching cycle and said second switching element is switched on during said second portion of said switching cycle.

5. The controller of claim 1, wherein said at least one switching element comprises a first switching element connected between a supply voltage node and a switching node and a second switching element connected between said switching node and a circuit ground, said circuit node being said supply voltage node, said controller arranged such that said second switching element is switched on during said first portion of said switching cycle and said first switching element is switched on during said second portion of said switching cycle.

6. The controller of claim 1, wherein said sampling circuit is a sample and hold (S/H) circuit.

7. The controller of claim 1, wherein said sampling circuit is a track and hold (T/H) circuit.

8. The controller of claim 7, wherein said T/H circuit tracks said signal which varies with said feedback signal throughout said first portion of said switching cycle, and holds the peak value of said tracked signal throughout said second portion of said switching cycle.

9. The controller of claim 1, wherein said sampling circuit comprises at least one sample and hold (S/H) circuit and one track and hold (T/H) circuit.

10. The controller of claim 1, wherein said sampling circuit is further arranged to produce an output which approximates the portion of said feedback signal'"'"'s waveform which is not sampled.

11. The controller of claim 10, wherein said feedback signal'"'"'s waveform is an upslope during the first portion of said switching cycle and a downslope during the second portion of said switching cycle, said sampling circuit comprising:

an input node connected to receive said feedback signal or a signal which varies with said feedback signal;

a sampling capacitor connected between a first node and a circuit common node;

a sampling switch connected between said input node and said first node;

a tracking capacitor connected between a second node and said circuit common node, said sampling circuit'"'"'s output produced at said second node;

a tracking switch connected between said input node and said second node;

a discharge switch connected between said first and second nodes; and

a resistance connected in series with said discharge switch between said first and second nodes;

said controller arranged such that, during the first portion of said switching cycle;

said sampling switch is closed for a time sufficient to cause said sampling capacitor to be charged to a voltage approximately equal to the voltage of the signal applied to said input node at the beginning of said upslope;

said tracking switch is closed so as to cause said tracking capacitor to be charged to a voltage approximately equal to the voltage of the signal applied to said input node at the peak of said upslope; and

said discharge switch is open;

and such that, during the second portion of said switching cycle;

said sampling switch is open;

said tracking switch is open; and

said discharge switch is closed, such that the voltage stored on said tracking capacitor is discharged through said resistance such that said sampling circuit'"'"'s output decays towards the voltage stored on said sampling capacitor.

12. The controller of claim 1, further comprising:

a reference voltage; and

an error amplifier arranged to produce an output which varies with the difference between first and second signals applied at respective inputs, a signal which varies with the output of said sampling circuit provided to said error amplifier'"'"'s first input and a signal which varies with said reference voltage provided to said error amplifier'"'"'s second input.

13. The controller of claim 12, further comprising a buffer amplifier connected between the output of said sampling circuit and said error amplifier'"'"'s first input.

14. The controller of claim 12, further comprising a second sampling circuit arranged to sample said reference voltage only during said first portion of said switching cycle, the output of said second sampling circuit provided to said error amplifier'"'"'s second input.

15. The controller of claim 14, further comprising first and second buffer amplifiers connected between the outputs of respective sampling circuits and said error amplifier'"'"'s first and second inputs, respectively.

16. The controller of claim 1, further comprising a resistive divider which is coupled to said output node and produces said feedback signal at an output.

17. The controller of claim 16, further comprising a capacitive network coupled to said resistive divider and arranged to provide high frequency compensation for said divider.

18. The controller of claim 1, wherein said controller and feedback signal form a feedback loop, further comprising a compensator circuit connected in the signal path between said feedback signal and said switching elements, said compensator circuit arranged to correct AC phase and gain characteristics of said feedback loop.

19. The controller of claim 1, further comprising:

a reference voltage; and

an error amplifier arranged to produce an output which varies with the difference between first and second signals applied at respective inputs, said feedback signal provided to said error amplifier'"'"'s first input and a signal which varies with said reference voltage provided to said error amplifier'"'"'s second input, said sampling circuit arranged to sample the output of said error amplifier.

20. The controller of claim 1, wherein said controller is configured to provide voltage mode control.

21. The controller of claim 1, wherein said controller is configured to provide current mode control.

22. A switching power supply controller which is adapted to be connected to external components to produce a regulated output voltage at an output node, comprising:

a first switching element connected between a supply voltage node and a switching node;

a second switching element connected between said switching node and a circuit ground node, said controller arranged such that said first switching element is switched on during a first portion of a switching cycle and said second switching element is switched on during a second portion of said switching cycle so as to regulate the output voltage at said output node, such that said circuit ground node conducts a current that is higher during said second portion of said switching cycle than it is during said first portion of said switching cycle;

a feedback signal which represents the output voltage produced at said output node, said controller arranged such that said feedback signal varies with the current conducted by said circuit ground node;

a sampling circuit arranged to sample a signal which varies with said feedback signal only during said first portion of said switching cycle;

a reference voltage; and

an error amplifier arranged to produce an output which varies with the difference between first and second signals applied at respective inputs, a signal which varies with the output of said sampling circuit provided to said error amplifier'"'"'s first input and a signal which varies with said reference voltage provided to said error amplifier'"'"'s second input, said controller arranged to regulate said output voltage in response to said sampled signal.

23. The controller of claim 22, wherein said sampling circuit is further arranged to produce an output which approximates the portion of said feedback signal waveform which is not sampled.

24. The controller of claim 22, wherein said controller is contained within an integrated circuit (IC) and said circuit node is an internal IC ground.

25. The controller of claim 22, further comprising a second sampling circuit arranged to sample said reference voltage only during said first portion of said switching cycle, the output of said second sampling circuit provided to said error amplifier'"'"'s second input.