Switching buck converter with floating regulator

• US 6,313,616 B1
• Filed: 09/21/2000
• Issued: 11/06/2001
• Est. Priority Date: 09/21/2000
• Status: Expired due to Fees

• Current Assignee: Home Touch Lighting Systems LLC
• Original Assignee: Home Touch Lighting Systems LLC
• Inventors: Heagey, Robert C., Deller, Robert W.
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US09/667,148
• Time in Patent Office: 411 Days
• Field of Search: 323/282, 363/89
• US Class Current: 323/282
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit
• CPC Class Codes: H02M 3/155 using semiconductor devices only

Abstract

A PWM switching power supply of the buck regulator type converts an unfiltered rectified d.c. input voltage into a regulated stepped down d.c. output voltage for use by load circuits. The power supply includes a PWM switching regulator which controls the duty cycle of an N-channel field effect transistor (FET) power switch which has its source connected to a Schottky flyback diode. The flyback diode is connected to an LC output filter which generates the stepped down output voltage. The PWM regulator includes a 555 timer operating in conjunction with an RC timing network in a modulated a stable mode. Timer 555 has an output lead electrically connected to the gate of the FET for switching the FET on/off in response to an output voltage modulating feedback input from a feedback path with the source of the FET serving as the “ground” for the PWM regulator. The feedback path includes a diode connected in series to a sampling capacitor which supplies a sampled output voltage feedback via a voltage divider and another diode to the 555 timer to allow the regulator circuit to fly with the FET power switch. When the FET is conductive, current flows through the LC output filter charging the capacitor and generating the stepped down d.c. output voltage. When the FET is non-conductive, the current loop is through the flyback diode. A smoothing filter is electrically connected to the FET power switch to smooth the unfiltered rectified d.c. input voltage.

Claims

1. A switching power supply for converting an unfiltered rectified direct current (d.c.) input voltage into a regulated d.c. output voltage, said switching power supply comprising:

(a) a smoothing filter for receiving said unfiltered rectified d.c. input voltage and generating a smoothed d.c. input voltage signal;

(b) a power switch operatively coupled to said smoothing filter and having a conductive state and a non-conductive state;

(c) a regulator operatively coupled to said power switch for driving said power switch at a pre-selected duty cycle to transform said smoothed d.c. input voltage signal into a pulsed d.c. input voltage signal in accordance with said pre-selected duty cycle, said regulator floating with said power switch instead of being connected to circuit ground;

(d) an output filter operatively coupled to said power switch for receiving said pulsed d.c. input voltage signal and generating a d.c. output voltage signal for use by at least one load, said pre-selected duty cycle being generally proportional to the ratio of said d.c. output voltage signal to said smoothed d.c. input voltage signal;

(e) a diode clamp operatively coupled between said power switch and said output filter for closing the current loop on said output filter when said power switch is in said non-conductive state; and

(f) a sampling circuit operatively coupled to said output filter for sampling said d.c. output voltage signal and feeding said sampled d.c. output voltage signal back to said regulator to regulate said d.c. output voltage signal.

2. The switching power supply of claim 1, wherein said sampling circuit comprises a first diode connected in series with a sampling capacitor for receiving said d.c. output voltage signal and generating said sampled d.c. output voltage signal.

3. The switching power supply of claim 1, wherein said smoothing filter comprises a choke inductor connected in series to a smoothing capacitor.

4. The switching power supply of claim 3, wherein said power switch comprises an N-channel field effect transistor (FET) having a source which serves as the ground of said regulator, a drain coupled to said smoothing capacitor and a gate coupled to said regulator, said regulator controlling the gate voltage of said FET.

5. The switching power supply of claim 4, wherein said output filter comprises an inductor connected in series to an output capacitor, said inductor receiving said pulsed d.c. input voltage signal, said output capacitor generating said d.c. output voltage signal.

6. The switching power supply of claim 4, wherein said diode clamp comprises a Schottky flyback diode connected in parallel with said output filter, said flyback diode having an anode and a cathode coupled between said source of said FET and said inductor of said output filter to define a fly back diode-switch-inductor node.

7. The switching power supply of claim 4, wherein said regulator comprises an a stable circuit having an output lead coupled to said gate of said FET and applying oscillatory voltage to said gate for transforming said smoothed d.c. input voltage signal applied to said drain of said FET into said pulsed d.c. input voltage signal in accordance with said pre-selected duty cycle, said regulator functioning as a pulse width modulation (PWM) regulator.

8. The switching power supply of claim 7, wherein said a stable circuit of said PWM regulator comprises a 555 timer, a resistor-capacitor (RC) network and a second diode, said 555 timer electrically coupled to said RC network and having threshold and trigger pins tied together and an out pin electrically coupled to said output lead of said a stable circuit, said 555 timer floating with said FET during operation.

9. The switching power supply of claim 8, wherein said RC network comprises a timing capacitor connected in series with a pair of series resistors, one of said pair of series resistors connected in parallel with said second diode.

10. The switching power supply of claim 9, wherein said PWM regulator further comprises a feedback voltage circuit for receiving said sampled d.c. output voltage signal from said sampling capicitor.

11. The switching power supply of claim 10, wherein said feedback circuit comprises a voltage divider, a feedback node, a third diode and a trigger/threshold node, said trigger/threshold node electrically coupled to said tied threshold and trigger pins of said 555 timer.

12. The switching power supply of claim 11, further comprising a power supply source.

13. The switching power supply of claim 12, wherein said power supply source comprises a capacitor connected in parallel to a Zener diode and a pair of series resistors electrically connected between said choke inductor and said Zener diode.

14. A switching power supply for converting a smoothed direct current (d.c.) input voltage into a regulated d.c. output voltage, said switching power supply comprising:

(a) a power switch having a conductive state and a non-conductive state;

(b) a regulator operatively coupled to said power switch for driving said power switch at a pre-selected duty cycle, said regulator floating with said power switch instead of being connected to circuit ground;

(c) an output filter operatively coupled to said power switch for generating a d.c. output voltage for use by at least one load, said pre-selected duty cycle being generally proportional to the ratio of said d.c. output voltage to said smoothed d.c. input voltage;

(d) a diode clamp operatively coupled between said power switch and said output filter for closing the current loop on said output filter when said power switch is in said non-conductive state; and

(e) a sampling circuit operatively coupled to said output filter for sampling said d.c. output voltage and feeding said sampled d.c. output voltage back to said regulator to regulate said d.c. output voltage.

15. The switching power supply of claim 14, wherein said sampling circuit comprises a first diode connected in series with a sampling capacitor for receiving said d.c. output voltage signal and generating said sampled d.c. output voltage.

16. The switching power supply of claim 14, wherein said power switch comprises an N-channel field effect transistor (FET) having a source which serves as the ground of said regulator, a drain and a gate coupled to said regulator, said regulator controlling the gate voltage of said FET.

17. The switching power supply of claim 16, wherein said diode clamp comprises a Schottky flyback diode connected in parallel with said output filter, said flyback diode having an anode and a cathode coupled between said source of said FET and said inductor of said output filter to define a flyback diode-switch-inductor node.

18. The switching power supply of claim 16, wherein said regulator comprises an a stable circuit having an output lead coupled to said gate of said FET and applying oscillatory voltage to said gate for transforming said smoothed d.c. input voltage into a pulsed d.c. input voltage in accordance with said pre-selected duty cycle, said regulator functioning as a pulse width modulation (PWM) regulator.

19. The switching power supply of claim 18, wherein said output filter comprises an inductor connected in series to an output capacitor, said inductor receiving said pulsed d.c. input voltage, said output capacitor generating said d.c. output voltage.

20. The switching power supply of claim 18, wherein said a stable circuit of said PWM regulator comprises a 555 timer, a resistor-capacitor (RC) network and a second diode, said 555 timer electrically coupled to said RC network and having threshold and trigger pins tied together and an out pin electrically coupled to said output lead of said a stable circuit, said 555 timer floating with said FET during operation.

21. The switching power supply of claim 18, wherein said PWM regulator further comprises a feedback voltage circuit for receiving said sampled d.c. output voltage from said sampling capacitor.

22. The switching power supply of claim 21, wherein said feedback voltage circuit comprises a voltage divider, a feedback node, a third diode and a trigger/threshold node, said trigger/threshold node electrically coupled to said tied threshold and trigger pins of said 555 timer.

23. The switching power supply of claim 22, further comprising a power supply source.