Pulse width modulation signal generator and switching mode power supply including the same

• US 6,972,971 B2
• Filed: 10/29/2003
• Issued: 12/06/2005
• Est. Priority Date: 10/29/2002
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: Jang, Kyung-Oun, Kim, Eung-Suen
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/698,056
• Publication Number:
  US 20040145924A1
• Time in Patent Office: 769 Days
• Field of Search: 363/49, 363/56.11, 363/21.01, 363/131, 363/21.1, 363/21.18
• US Class Current: 363/49
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A switching mode power supply includes a rectifier configured to convert AC power to a first DC power, an output unit configured to convert the first DC power to a second DC power under the control of a first switch, and a pulse width modulation generator coupled to control the first switch. The pulse width modulation generator has a regulator configured to regulate the first DC power. The regulated first DC power powers the pulse width modulation generator. The regulator includes a second switch coupled to control a transmitter so that when the second switch is in a first state the transmitter transmits the first DC power to a capacitor to charge the capacitor to thereby increase the regulated first DC power, and when the switch is in a second state the transmitter does not transmit the first DC power to the capacitor to thereby allow the charge in the capacitor to reduce and in turn the regulated first DC power to reduce.

Claims

1. A switching mode power supply comprising:

a rectifier configured to convert AC power to a first DC power;

an output unit configured to convert the first DC power to a second DC power under the control of a first switch; and

a pulse width modulation generator coupled to control the first switch, the pulse width modulation generator having a regulator configured to regulate the first DC power, the regulated first DC power powering the pulse width modulation generator, the regulator comprising a second switch coupled to control a transmitter so that when the second switch is in a first state the transmitter transmits the first DC power to a capacitor to charge the capacitor to thereby increase the regulated first DC power, and when the switch is in a second state the transmitter does not transmit the first DC power to the capacitor to thereby allow the charge in the capacitor to reduce and the regulated first DC power to decrease.

2. The switching mode power supply of claim 1 wherein the regulator further comprises a power supply voltage manager configured to bias the second switch so that during normal mode of operation the regulated first DC power is maintained at a substantially constant voltage level.

3. The switching mode power supply of claim 2 wherein the regulator further comprises a switch core coupled between the power supply voltage manager and the second switch so that during a power up mode the switch core biases the second switch in the first state until the regulated first DC power reaches a predetermined power level, and during the normal mode of operation the switch core couples an output of the power supply voltage manager to the second switch.

4. The switching mode power supply of claim 2 wherein the power supply voltage manager comprises a comparator configured to compare a first voltage derived from the regulated first DC power to a reference voltage and in response output a signal for biasing the second switch such that the regulated first DC power is maintained at the substantially constant voltage.

5. The switching mode power supply of claim 2 wherein the regulator is a switched-mode regulator.

6. An SMPS (switching mode power supply) comprising:

a power supply for converting AC power to DC power and outputting the DC power;

an output unit including a transformer having a primary coil one end of which is coupled to the power supply, the output unit outputting power transmitted to a secondary coil of the transformer from the power supply;

a switching driver including a first switch coupled to another end of the primary coil of the transformer, and a first capacitor coupled to store power derived from the DC power, the power stored in the first capacitor powering the switching driver, the switching driver generating a PWM (pulse width modulation) signal for driving the first switch;

a feedback circuit for feeding back to the switching driver an output signal provided by the output,

wherein the switching driver comprises;

a high-voltage regulator for supplying the DC power to the first capacitor when the level of the power stored in the first capacitor is less than a first level, and preventing the DC power from being supplied to the first capacitor when the level of the power stored in the first capacitor is greater than a second level;

a PWM generation unit for generating the PWM signal; and

a UVLO (under-voltage lockout)/bandgap unit for starting operation when the power in the first capacitor reaches a predetermined level, and controlling the operation of the PWM generation unit.

7. The SMPS of claim 6, wherein the high-voltage regulator comprises:

a JFET coupled to the power supply for lowering the level of the DC power; and

a second switch for controlling a current path between the JFET and the first capacitor in response to an enable signal generated by the UVLO/bandgap unit.

8. The SMPS of claims 6, further comprising:

an oscillator for generating a clock signal under the control of the UVLO/bandgap unit; and

a comparator for comparing the feedback signal with the clock signal, wherein the PWM generation unit controls the duty ratio of the PWM signal according to comparison results of the comparator.

9. The SMPS of claim 6, wherein the switching driver further comprises a protector coupled to inhibit the PWM generation unit from generating a PWM signal when one of a number of predetermined events occurs.

10. The SMPS of claim 9, wherein the switching driver further comprises a controller coupled to enable the PWM generation unit to generate the PWM signal a predetermined period of time after the PWM generation unit is inhibited from generating a PWM signal due to occurrence of one of the number of predetermined events.

11. The SMPS of claim 6, wherein the power supply comprises:

a full-wave bridge rectifier for receiving the AC power and rectifying the same; and

a second capacitor for smoothing the power rectified by the full-wave bridge rectifier.

12. The SMPS of claim 6, wherein the feedback circuit comprises:

an amplifier for amplifying the output signal provided by the output unit;

a photo coupler coupled to conduct current in response to the amplified signal provided by the amplifier; and

a second capacitor coupled to the photo coupler such that the current conduction in the photo coupler impacts the charge stored in the second capacitor.

13. An SMPS (switching mode power supply) comprising:

a transformer for receiving a DC power at one end of a primary coil, and outputting power through a secondary coil; and

a switching driver including a transistor coupled between another end of the primary coil and a reference voltage, for generating a PWM (pulse width modulation) signal for periodically turning on/off the transistor and operating the transformer by the on/off operation of the transistor,

wherein the switching driver comprises;

a capacitor coupled to store power derived from the DC power, the power stored in the first capacitor powering the switching driver;

a UVLO (under-voltage lockout)/bandgap unit for starting operation when the power in the capacitor reaches a predetermined level;

a high-voltage regulator including;

a switch configured to couple the power derived from the DC power to the capacitor when the power stored in the capacitor is less than a first level, and to decouple the power derived from the DC power from the capacitor when the power stored in the capacitor is greater than a second level; and

a switch core for controlling the switch according to an enable signal supplied by the UVLO/bandgap unit;

an oscillator for generating a clock signal under the control of the UVLO/bandgap unit; and

a PWM generation unit for generating a PWM signal according to the clock signal.

14. The SMPS of claim 13, further comprising a feedback circuit for providing a feedback signal to the switching driver in response to an output signal provided by the transformer, wherein

the PWM generation unit controls the duty ratio of the PWM signal according to the feedback signal.

15. The SMPS of claim 14, further comprising:

a protector coupled to inhibit the PWM generation unit from generating a PWM signal to thereby turn off the transistor when one of a number of predetermined events occurs; and

a controller coupled to periodically enable the PWM generation unit to generate a PWM signal after the PWM generation is inhibited from generation of a PWM signal in order to determine whether the one of a number of predetermined events still persists.

16. A PWM (pulse width modulation) signal generator including a transistor coupled between a primary coil of a transformer and a reference voltage, for supplying a PWM signal to a gate of the transistor to periodically turn on/off the transistor and thus operate the transformer, comprising:

a high-voltage regulator including a JFET coupled to lower a level of a DC power;

a capacitor coupled to store power corresponding to the lowered DC power,

a UVLO (under-voltage lockout)/bandgap unit for starting operation when the power in the capacitor reaches a predetermined level;

an oscillator for generating a clock signal under the control of the UVLO/bandgap unit; and

a PWM generation unit for generating the PWM signal according to the clock, wherein

the high-voltage regulator supplies the lowered DC power to the capacitor when the level of the power stored in the capacitor is less than a first level, and preventing the lowered DC power from being supplied to the capacitor when the level of the power stored in the capacitor is greater than a second level.

17. The PWM signal generator of claim 16, wherein the high-voltage regulator further comprises:

a power supply voltage manager for regulating the power stored in the capacitor;

a switch core for transmitting a control signal from the power supply manager to a switch under the control of the UVLO/bandgap unit, the

a switch being tuned on/off according to the control signal; and

a current transmitter for coupling the JFET to the capacitor when the switch is turned off, and decoupling the JFET from the capacitor when the switch is turned off.

18. The PWM signal generator of claim 16, comprising:

a source/sink unit for receiving a feedback signal derived from an output signal output by the transformer; and

a comparator for comparing an output of the source/sink unit with an output of the oscillator, wherein

the PWM generation unit controls the duty ratio of the PWM signal according to a comparison result of the comparator.

19. The PWM signal generator of claim 18, further comprising:

a protector coupled to inhibit the PWM generation unit from generating a PWM signal to thereby turn off the transistor when one of a number of predetermined events occurs; and

a controller coupled to periodically enable the PWM generation unit to generate a PWM signal after the PWM generation is inhibited from generation of a PWM signal in order to determine whether the one of a number of predetermined events still persists.