DUAL CONTROL LOOP SWITCHING REGULATOR

• US 3,772,588 A
• Filed: 10/01/1971
• Issued: 11/13/1973
• Est. Priority Date: 10/01/1971
• Status: Expired due to Term

• Current Assignee: Robert J. Titus, William J. Kelly
• Original Assignee: Robert J. Titus, William J. Kelly
• Inventors: Kelly, William J., Titus, Robert J.
• Primary Examiner(s): Pellinen, A. D.
• Application Number:
  US05/185,590
• Time in Patent Office: 774 Days
• Field of Search: 307/297 321/2,19 323/1,17,20,22T,DIG.1
• US Class Current: 323/285
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A switching regulator having a conventional switching transistor and filter, and DC feedback loop which controls the duty cycle of the switching transistor in accordance with the output voltage. The regulator includes an additional AC feedback loop, the input to the feedback path being taken at a point in the forward path of the regulator which precedes the filter. In this way, the filter is not included in the second loop and this second loop can have a higher cross-over frequency than the DC loop so that the line ripple which would otherwise appear at the output can be suppressed.

Claims

1. A switching regulator comprising a source of unregulated voltage, output circuit means, current switching means, filter means, said current switching means being connected to extend current pulses from said unregulated voltage source through said filter means to develop a DC voltage across said output circuit means, means for controlling the periodic turning on and turning off of said current switching means at a rate which is substantially higher than the frequency of ripple components in said unregulated voltage source, DC feedback means for controlling the duty cycle of said current switching means in accordance with the changes in the DC voltage across said output circuit means, said DC feedback means comprising a conductor and an RC network connected between said output circuit means and said controlling means, and AC feedback means located between said current switching means and said DC feedback means for controlling the duty cycle of said current switching means in accordance with the voltage at a point intermediate said current switching means and said filter means said AC feedback means comprising an RC filter having a pair of resistors and a first capacitor connected in parallel to one of said pair of resistors, said AC feedback means further comprising a second capacitor connected to said controlling means.

2. A switching regulator in accordance with claim 1 wherein said duty cycle controlling means includes amplifying means for developing a voltage to control the duty cycle of said current switching means, said DC feedback means includes means for DC-coupling a voltage proportional to the voltage across said output circuit means to an input of said amplifying means, and said AC feedback means includes means for AC-coupling the voltage at said intermediate point to an input of said amplifying means, such that the voltage across said output circuit means is maintained constant independant of AC or DC changes in the voltage of said unregulated voltage source.

3. A switching regulator in accordance with claim 2 wherein said DC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies substantially below the resonant frequency of said filter means, said filter means is effective to suppress variations in the voltage across said output circuit means at frequencies above said resonant frequency, and said AC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies above which said DC feedback means and below which said filter means are ineffective to provide regulation.

4. A switching regulator in accordance with claim 3 wherein said duty cycle controlling means includes means for turning on said current switching means at predetermined intervals, and means for controlling the width of each current pulse extended by said current switching means through said filter means to said output circuit means in accordance with the control voltage developed by said amplifying means.

5. A switching regulator in accordance with claim 3 wherein said filter means includes capacitor means and inductor means connected in series, said DC feedback means being coupled to one end of said inductor means and said AC feedback means being coupled to the other end of said inductor means.

6. A switching regulator in accordance with claim 1 wherein said DC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies substantially below the resonant frequency of said filter means, said filter means is effective to suppress variations in the voltage across said output circuit means at frequencies above said resonant frequency, and said AC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies above which said DC feedback means and below which said filter means are ineffective to provide regulation.

7. A switching regulator in accordance with claim 6 wherein said filter means includes capacitor means and inductor means connected in series, said DC feedback means being coupled to one end of said inductor means and said AC feedback means being coupled to the other end of said inductor means.

8. A switching regulator in accordance with claim 1 wherein said filter means includes capacitor means and inductor means connected in series, said DC feedback means being coupled to one end of said inductor means and said AC feedback means being coupled to the other eNd of said inductor means.

9. A switching regulator comprising a source of unregulated voltage, output circuit means, current switching means for conducting current pulses from said unregulated voltage source to develop an unfiltered DC voltage, means for filtering said unfiltered DC voltage to develop a filtered DC voltage across said output circuit means, means for controlling the periodic turning on and turning off of said current switching means at a rate which is substantially higher than the frequency of ripple components in said unregulated voltage source, DC feedback means for controlling the duty cycle of said current switching means in accordance with changes in the filtered DC voltage across said output circuit means said DC feedback means comprising a conductor and an RC network connected between said output circuit means and said controlling means, and AC feedback means located between said current switching means and said DC feedback means for controlling the duty cycle of said current switching means in accordance with the unfiltered DC voltage developed by said current switching means said AC feedback means comprising an RC filter having a pair of resistors and a first capacitor connected in parallel to one of said pair of resistors, said AC feedback means further comprising a second capacitor connected to said controlling means.

10. A switching regulator in accordance with claim 9 wherein said duty cycle controlling means includes amplifying means for developing a voltage to control the duty cycle of said current switching means, said DC feedback means includes means for DC-coupling a voltage proportional to the filtered voltage across said output circuit means to an input of said amplifying means, and said AC feedback means includes means for AC-coupling the unfiltered DC voltage developed by said current switching means to an input of said amplifying means, such that the voltage across said output circuit means is maintained constant independent of AC or DC changes in the voltage of said unregulated voltage source.

11. A switching regulator in accordance with claim 10 wherein said DC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies substantially below the resonant frequency of said filter means, said filter means includes inductor means effective to suppress variations in the voltage across said output circuit means at frequencies above said resonant frequency, and said AC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies above which said DC feedback means and below which said filter means are ineffective to provide regulation.

12. A switching regulator in accordance with claim 11 wherein said filter means includes capacitor means connected in series with said inductor means, said DC feedback means being coupled to one end of said inductor means and said AC feedback means being coupled to the other end of said inductor means.

13. A switching regulator in accordance with claim 9 wherein said DC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies substantially below the resonant frequency of said filter means, said filter means includes inductor means effective to suppress variations in the voltage across said output circuit means at frequencies above said resonant frequency, and said AC feedback means is effective to provide servo control to regulate the voltage across said output circuit means at frequencies above which said DC feedback means and below which said filter means are ineffective to provide regulation.

14. A switching regulator in accordance with claim 13 wherein said filter means includes capacitor means connected in series with said inductor means, said DC feedback means being coupled to one end of said inductor means and said AC feedback means bEing coupled to the other end of said inductor means.

15. A switching regulator in accordance with claim 9 wherein said filter means includes capacitor means and inductor means connected in series, said DC feedback means being coupled to one end of said inductor means and said AC feedback means being coupled to the other end of said inductor means.