Switching mode power supply controller

• US 5,675,485 A
• Filed: 10/03/1995
• Issued: 10/07/1997
• Est. Priority Date: 12/22/1994
• Status: Expired due to Term

• Current Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Seong, Hwan-Ho
• Primary Examiner(s): Sterrett, Jeffrey L.
• Application Number:
  US08/538,808
• Time in Patent Office: 735 Days
• Field of Search: 363/21, 363/49, 363/95, 363/97, 363/131
• US Class Current: 363/97
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A controller for a switching mode power supply has connections for receiving direct operating potential, a voltage comparator for comparing a fraction of the direct operating potential to a first direct reference potential for developing a voltage comparator output signal, an oscillator for generating oscillations of a prescribed frequency, a pulse width modulator for supplying pulses at a rate determined by those oscillations and with a width controlled by the comparator output signal, and an under-voltage lock-out circuit producing a controlling signal to selectively disable the output pulse signal. The controller is included in a switching mode power supply receiving input power having a direct input potential. The switching mode power supply has a transformer for transforming an alternating voltage generated from the direct input potential; a rectifier for rectifying transformed alternating voltage to produce a direct output potential; a regulator sinking current responsive to the direct output potential from said rectifier being larger or smaller larger than a second direct reference potential; a photo-coupler conducting as input current the current sunk by the regulator, converting the current into an optical signal, and then converting said optical signal into an electric signal; and a switching controlling unit producing a controlling signal to control selective application of the direct input potential to the transformer in response to output current demanded by the photo-coupler. The switching controlling unit comprises a switching-mode-power-supply controller for performing the function of power supply, feedback and soft-start, in response to an operating voltage signal supplied thereto through external pins thereof; a resistor and capacitor converting the magnitude of the current supplied from the photo-coupler into the operating voltage signal; and a switching transistor cyclically tuned on and off in response to a pulse signal produced from the switching-mode-power-supply controller. The switching transistor selectively applies the direct input potential to the transformer for generating the alternating voltage that is transformed.

Claims

1. A controller for a switching mode power supply, said controller constructed as an integrated circuit with only three external connection pins, a first of said three external connection pins for receiving a reference ground potential, a second of said three external connection pins for receiving a direct potential used by said controller both as a direct operating potential and as an input control potential, and a third of said three external connection pins for supplying a pulsed output control potential, said integrated circuit receiving no electric power except via said three external connection pins and demanding a current flow between said first and second external connection pins of a prescribed substantially constant value at least when said direct potential is above a lower threshold voltage, said controller further comprising within said integrated circuit:

an oscillator powered by application of said direct operating potential for generating oscillations of a prescribed frequency;

a voltage comparator for comparing a fraction of said direct operating potential, as received by the controller via said second external connection pin, to a direct reference potential for developing a voltage comparator output signal;

a pulse width modulator for supplying an output pulse signal including pulses of a rate determined by said oscillations of a prescribed frequency generated by said oscillator and with a width controlled by said comparator output signal, the duty ratio of an output pulse being larger or smaller in amplitude depending on whether said fraction of said direct operating potential received by the controller via said second external connection pin is larger or smaller than said direct reference potential;

an under-voltage lock-out circuit producing a controlling signal, for disabling transmission of the output pulse signal of said pulse width modulator when the direct operating potential for the controller received via said second external connection pin has not risen above a higher threshold voltage since falling below said lower threshold voltage, and for enabling transmission of the output pulse signal of said pulse width modulator when the direct operating potential for the controller has risen above said higher threshold voltage since falling below said lower threshold voltage; and

an AND gate for selectively transmitting the output pulse signal of said pulse width modulator via said third external connection pin, in response to said controlling signal from said under-voltage lock-out circuit.

2. The controller according to claim 1 included in a switching mode power supply for receiving input power supplied at a direct input potential from a primary power supply, which said switching mode power supply further comprises:

a transformer having a primary winding and a secondary winding;

a switching transistor, having a control electrode connected for receiving the selectively transmitted output pulse signal of said pulse width modulator from said AND gate via said third external connection pin of said integrated circuit, and having a principal conduction path arranged for selectively applying said direct input potential across said primary winding in response to said selectively transmitted output pulse signal;

a first rectifier for supplying direct current output power responsive to alternating current power from said secondary winding, which direct current output power is supplied at a direct output potential;

a regulator for generating an error signal indicative of a departure of said direct output potential from a prescribed value; and

circuitry for generating said direct potential applied to said second external connection pin of said integrated circuit to be used by said controller both as a direct operating potential and as an input control potential, the voltage of said direct potential being established when input power is initially supplied from said primary power supply during a start-up time before said switching transistor begins applying said direct input potential across said primary winding in response to said selectively transmitted output pulse signal, and the voltage of said direct potential being adjusted in response to said error after said start-up time.

3. The switching mode power supply according to claim 2 in combination with said primary power supply for supplying a direct input potential, wherein said primary power supply is of a type for receiving alternating-current power having an alternating potential and includes a second rectifier for supplying said direct input potential to said switching mode power supply as a rectified response to said alternating potential of said alternating-current power received by said primary power supply.

4. The controller according to claim 1 included in a switching mode power supply for receiving input power supplied at a direct input potential from an output of a primary power supply, which said switching mode power supply further comprises:

a first capacitor and at least a first resistor in a series connection across the output of said primary power supply for receiving said direct input potential, said first capacitor having first and second plates respectively connected to the first external connection pin of said integrated circuit and to the second external connection pin of said integrated circuit, said first capacitor being charged via said series connection during said start-up time;

a transformer having a primary winding and a secondary winding;

a switching transistor, having a control electrode connected for receiving the selectively transmitted output pulse signal of said pulse width modulator from said AND gate, and having a principal conduction path arranged for selectively applying said direct input potential across said primary winding in response to said selectively transmitted output pulse signal;

a first rectifier for supplying direct current output power responsive to alternating current power from said secondary winding, which direct current output power is supplied at a direct output potential;

a regulator for generating an error signal indicative of a departure of said direct output potential from a prescribed value; and

a photo-coupler having an input circuit connected for receiving said error signal and having an output circuit connected in a shunt path across said first resistor.

5. The switching mode power supply according to claim 4 in combination with said primary power supply for supplying a direct input potential, wherein said primary power supply is of a type for receiving alternating-current power having an alternating potential and includes a second rectifier for supplying said direct input potential to said switching mode power supply as a rectified response to said alternating potential of said alternating-current power received by said primary power supply.

6. The switching mode power supply according to claim 4;

wherein said transformer has in addition to said primary and secondary windings a tertiary winding with first and second ends, the first end of said tertiary winding being connected to receive said ground reference potential;

wherein said series connection of said first capacitor and at least said first resistor further includes

a second resisistor;

wherein said first and said second resistors have respective first ends and have respective second ends, with the first end of said first resistor connected to the second plate of said capacitor, and with the second end of said first resistor and the first end of said second resistor having an interconnection therebetween;

wherein

a second rectifier connects from the second end of said tertiary winding to said interconnection between the second end of said first resistor and the first end of said second resistor; and

wherein

a second capacitor has a first plate connected to receive said ground reference potential and has a second plate connected to said interconnection between the second end of said first resistor and the first end of said second resistor.

7. The controller according to claim 1 included in a switching mode power supply for receiving input power supplied at a direct input potential from a primary power supply, which said switching mode power supply further comprises:

a primary power supply for supplying a direct potential from an output thereof;

a first capacitor and at least a first resistor in a series connection across the output of said primary power supply for receiving said direct potential, said connections for receiving direct operating potential for the controller being across said first capacitor, said first capacitor being charged via said series connection during said start-up time;

a transformer having a primary winding and a secondary winding;

a field effect transistor, having a gate electrode connected for receiving the selectively transmitted output pulse signal of said pulse width modulator from said AND gate, and having source and drain electrodes connected for selectively applying said direct input potential across said primary winding in response to said selectively transmitted output pulse signal;

a rectifier for supplying DC output power responsive to AC power from said secondary winding, which DC power is supplied at a direct output potential;

a regulator for generating an error signal indicative of a departure of said direct output potential from a prescribed value; and

a photo-coupler having an input circuit connected for receiving said error signal and having an output circuit connected in a shunt path across said first resistor.

8. The switching mode power supply according to claim 7;

wherein said transformer has in addition to said primary and secondary windings a tertiary winding with first and second ends, the first end of said tertiary winding being connected to receive said ground reference potential;

wherein said series connection of said first capacitor and at least said first resistor further includes

a second resisistor;

wherein said first and said second resistors have respective first ends and have respective second ends, with the first end of said first resistor connected to the second plate of said capacitor, and with the second end of said first resistor and the first end of said second resistor having an interconnection therebetween;

wherein

a second rectifier connects from the second end of said tertiary winding to said interconnection between the second end of said first resistor and the first end of said second resistor; and

wherein

a second capacitor has a first plate connected to receive said ground reference potential and has a second plate connected to said interconnection between the second end of said first resistor and the first end of said second resistor.

9. The switching mode power supply according to claim 7 in combination with said primary power supply for supplying a direct input potential, wherein said primary power supply is of a type for receiving alternating-current power having an alternating potential and includes a second rectifier for supplying said direct input potential to said switching mode power supply as a rectified response to said alternating potential of said alternating-current power received by said primary power supply.

10. The controller according to claim 1 included in a switching mode power supply for receiving input power supplied at a direct input potential from a primary power supply, which said switching mode power supply further comprises:

a transformer having a primary winding and a secondary winding;

a field effect transistor, having a gate electrode connected for receiving the selectively transmitted output pulse signal of said pulse width modulator from said AND gate, and having source and drain electrodes connected for selectively applying said direct input potential across said primary winding in response to said selectively transmitted output pulse signal;

a rectifier for supplying direct current output power responsive to alternating current power from said secondary winding, which direct current output power is supplied at a direct output potential;

a regulator for generating an error signal indicative of a departure of said direct output potential from a prescribed value; and

circuitry for generating said direct potential applied to said second external connection pin of said integrated circuit to be used by said controller both as a direct operating potential and as an input control potential, the voltage of said direct potential being established when input power is initially supplied from said primary power supply during a start-up time before said switching transistor begins applying said direct input potential across said primal winding in response to said selectively transmitted output pulse signal, and the voltage of said direct potential being adjusted in response to said error after said start-up time.

11. The switching mode power supply according to claim 10 in combination with said primary power supply for supplying a direct input potential, wherein said primary power supply is of a type for receiving alternating-current power having an alternating potential and includes a second rectifier for supplying said direct input potential to said switching mode power supply as a rectified response to said alternating potential of said alternating-current power received by said primary power supply.

12. A switching mode power supply for receiving input power having a direct input potential, said switching mode power supply comprising:

a transformer for transforming an alternating voltage generated from said direct input potential;

a rectifier for rectifying transformed alternating voltage from said transformer and producing a direct output potential;

a regulator, sinking a relatively larger current when the direct output potential from said rectifier is larger than a reference voltage, and sinking a relatively smaller current when the direct output potential from said rectifier is smaller than said reference voltage;

a photo-coupler conducting an input current thereinto in proportion to the magnitude of the current that said regulator sinks, converting the current into an optical signal, and then converting said optical signal into a photo-coupler output current;

a switching-mode-power-supply controller for performing the function of power supply, feedback and soft-start, to selectively supply pulse width modulated signal in response to an operating voltage signal supplied thereto through external pins thereof, the width of the pulses in said pulse width modulated signal being narrowed in response to decrease in said operating voltage signal and being widened in response to increase in said operating voltage signal, so long as said operating voltage signal is within a range of voltages of large enough values to provide sufficient power properly to operate elements within said switching-mode-power-supply controller;

a capacitor having first and second plates between which said operating voltage signal appears, connected to be charged by said photo-coupler output current;

a resistor connected for charging said capacitor toward said direct input potential during start-up for increasing said operating voltage signal to be within said range of voltages of large enough values to provide sufficient power properly to operate elements within said switching-mode power-supply controller; and

switching means cyclically turned on and off in response to a pulse signal produced from said switching-mode-power-supply controller, connected for supplying an alternating voltage to said transformer by selectively applying said direct input potential to said transformer.

13. The switching mode power supply according to claim 12, wherein said switching means includes a field effect transistor.

14. The switching mode power supply according to claim 12, wherein said regulator comprises:

a differential-input amplifier having an output terminal, having a non-inverting input terminal to which said direct ouput potential is applied, and having an inverting input terminal to which a reference voltage; and

a transistor having a base electrode to which the output terminal of said differential-input amplifier is connected, having an emitter electrode in common connection, and having a collector electrode through which said relatively larger current is sunk when the direct output potential from said rectifier is larger than said reference voltage, and through which said relatively smaller current is sunk when the direct output potential from said rectifier is smaller than said reference voltage.

15. A controller for a switching mode power supply, said controller constructed as an integrated circuit with only three external connection pins, a first of said three external connection pins for receiving a reference ground potential, a second of said three external connection pins for receiving a direct potential used by said controller both as a direct operating potential and as an input control potential, and a third of said three external connection pins for supplying a pulsed output control potential, said integrated circuit receiving no electric power except via said three external connection pins and demanding a current flow between said first and second external connection pins of a prescribed substantially constant value at least when said direct potential is above a lower threshold voltage, said controller further comprising within said integrated circuit:

an oscillator powered by application of said direct operating potential for generating oscillations;

a voltage comparator for comparing a fraction of said direct operating potential, as received by the controller via said second external connection pin, to a direct reference potential for developing a voltage comparator output signal;

a pulse width modulator for supplying an output pulse signal including pulses of a rate determined by said oscillations of a prescribed frequency generated by said oscillator and with a width controlled by said comparator output signal, the duty ratio of an output pulse being larger or smaller in amplitude depending on whether said fraction of said direct operating potential received by the controller via said second external connection pin is larger or smaller than said direct reference potential; and

an under-voltage lock-out circuit for forestalling application of output pulse signal from said pulse width modulator to said third external connection pin when the direct operating potential for the controller received via said second external connection pin has not risen above a higher threshold voltage since falling below said lower threshold voltage, and for causing application of output pulse signal from said pulse width modulator to said third external connection pin when the direct operating potential for the controller has risen above said higher threshold voltage since falling below said lower threshold voltage.

16. A switching mode power supply for receiving input power supplied at a direct input potential from an output of a primary power supply, which said switching mode power supply comprises:

a transformer having a primary winding and a secondary winding;

a switching transistor, having a control electrode connected for receiving a selectively supplied input pulse signal, and having a principal conduction path arranged for selectively applying said direct input potential across said primary winding in response to said input pulse signal received at its said contol electrode;

a first rectifier for supplying direct current output power responsive to alternating current power from said secondary winding, which direct current output power is supplied at a direct output potential;

a regulator for generating an error signal indicative of a departure of said direct output potential from a prescribed value; and

circuitry for generating said selectively supplied input pulse signal in response to said error signal, which said circuitry comprises;

an oscillator for generating oscillations;

a voltage comparator for comparing a fraction of a direct feedback signal potential to a direct reference potential for developing a voltage comparator output signal;

a pulse width modulator for supplying an output pulse signal including pulses of a rate determined by said oscillations generated by said oscillator and with a width controlled by said comparator output signal, the duty ratio of an output pulse being larger or smaller in amplitude depending on whether said fraction of said direct feedback signal potential is larger or smaller than said direct reference potential;

an AND gate responsive to a controlling signal for selectively supplying the output pulse signal of said pulse width modulator to the control electrode of said switching transistor as said input pulse signal selectively supplied thereto;

an under-voltage lock-out circuit for generating said controlling signal, for interrupting supply of the output pulse signal of said pulse width modulator to the control electrode of said switching transistor when said direct feedback signal potential has not risen above a higher threshold voltage since falling below a lower threshold voltage, and for enabling supply of the output pulse signal of said pulse width modulator to the control electrode of said switching transistor when said direct feedback signal potential has risen above said higher threshold voltage since falling below said lower threshold voltage;

a first capacitor having a first plate and a second plate between which said direct feedback signal potential is developed;

at least a first resistor in a series connection with said first capacitor across the output of said primary power supply for receiving said direct input potential, for charging said first capacitor to develop a direct feedback signal potential greater than zero when input power is initially from the output of said primary power supply; and

a photo-coupler having an input circuit connected for receiving said error signal and having an output circuit connected in a shunt path across said resistor, for regulating the charging and discharging of said first capacitor and thereby adjusting said direct feedback signal potential.

17. The switching mode power supply set forth in claim 16, wherein said oscillator is powered by said direct feedback signal potential being supplied thereto as a direct operating potential.

18. The switching mode power supply according to claim 16;

wherein said transformer has in addition to said primary and secondary windings a tertiary winding with first and second ends, the first end of said tertiary winding being connected to the first plate of said first capacitor;

wherein said series connection of said first capacitor and at least said first resistor further includes

a second resisistor;

wherein said first and said second resistors have respective first ends and have respective second ends, with the first end of said first resistor connected to the second plate of said capacitor, and with the second end of said first resistor and the first end of said second resistor having an interconnection therebetween;

wherein

a second rectifier connects from the second end of said tertiary winding to said interconnection between the second end of said first resistor and the first end of said second resistor; and

wherein

a second capacitor has a first plate connected to the first plate of said first capacitor and has a second plate connected to said interconnection between the second end of said first resistor and the first end of said second resistor.