Intermittent switching power supply circuit

• US 20020089862A1
• Filed: 10/15/2001
• Published: 07/11/2002
• Est. Priority Date: 10/20/2000
• Status: Active Grant

• Current Assignee: SMK Corporation
• Original Assignee: SMK Corporation
• Inventors: Amei, Toshihiro
• Granted Patent: US 6,542,388 B2
• Time in Patent Office: Days
• US Class Current: 363/21.07
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H02M 3/3385 with automatic control of output voltage or current H02M3/33561 takes precedence

Abstract

An intermittent switching power supply circuit prevents excessive output power on a secondary side of a circuit. An intermittent oscillator is alternately switched on and off to maintain output voltage and/or current roughly constant, to An output power monitoring circuit monitors output power from a rectifying/smoothing circuit. A control circuit outputs a stop control signal to an control terminal of the intermittent oscillator when the output power monitoring circuit determines that the output voltage and/or current exceeds a reference value. The protection circuit and a photocoupler receiver element are connected in parallel with the control circuit. Where a circuit error occurs and the photocoupler receiver element fails to cycle the intermittent oscillator between active and inactive conditions for a predetermined time, the protection circuit provides a backup which outputs a stop control signal to stop oscillation of the intermittent oscillator element.

Claims

1. A intermittent switching power supply circuit, comprising:

a control terminal controlling an intermittent oscillator and producing an output power;

a rectifying-smoothing circuit smoothing said output power;

output power monitoring means for monitoring said output power and for sending a stop control to a photocoupler emitter element when said output power exceeds a reference power;

a photocoupler receiver element;

said photocoupler receiver element photocoupled to said photocoupler emitter element and controlling a control terminal of said intermittent oscillator when said output power exceeds said reference power;

protection circuit means for outputting a back-up stop control signal to said control terminal when said output power monitoring means determines that said output power exceeds a reference power;

said protection circuit means being connected in parallel with said photocoupler receiver element; and

said protection circuit means outputting said back-up stop control signal to said control terminal and stopping said intermittent oscillator when a failure occurs even when said photocoupler receiver element fails to control said intermittent oscillator, whereby said intermittent switching power supply circuit safely controls and stabilizes said output power.

2. An intermittent switching power supply circuit, according to claim 1, wherein:

said output power is at least one of an output voltage and an output current, whereby said intermittent switching power supply circuit is effective to stabilize said at least one of said output voltage and said output current.

3. An intermittent switching power supply circuit, according to claim 2, wherein:

said output monitoring circuit means includes at least a feed back winding, a rectifier diode, a lag network and a pair of voltage-divider resistors;

said feedback winding connecting at one end to a low-voltage terminal of a direct current power supply providing said output power;

said rectifier diode connecting said other end of said feedback winding;

said lag network including a first resistor and a first capacitor;

a series connection point between said first resistor and said first capacitor;

said lag network in series between an output side of said rectifier diode and said low-voltage terminal;

an intermediate tap between said pair of voltage-divider resistors; and

said pair of voltage-divider resistors connecting in parallel with said first capacitor between said low-voltage terminal and a base of said series connection point.

4. An intermittent switching power supply circuit, according to claim 3, further comprising:

a protection transistor in said protection circuit means;

said protection transistor connecting said control terminal of said intermittent oscillator and said low-voltage terminal;

a base of said protection transistor connecting said intermediate tap;

a discharge transistor connecting between said series connection point and said low-voltage terminal;

a second base on said discharge transistor; and

said photocoupler receiver element connecting between a base of said second base of said discharge transistor and said control terminal.

5. An intermittent switching power supply circuit, having an output voltage and an output current and controlling an oscillation interval of a primary winding of a transformer, comprising:

a rectifying-smoothing circuit;

said rectifying-smoothing circuit rectifying and smoothing said output voltage and said output current;

output power monitoring means for monitoring said output voltage and said output current from said rectifying-smoothing circuit;

said output power monitoring means operating a photocoupler emitter element and generating a stop output signal to a control terminal of an intermittent oscillator if either one of said output voltage and said output current exceeds a reference value;

said intermittent oscillator in series with said primary winding and a low-voltage terminal of an external direct current power supply;

a photocoupler receiver element photocoupled with said photocoupler emitter element effective to transmit said stop output signal to said control terminal;

said control terminal controlling said intermittent oscillator;

a protective circuit connecting parallel with said photocoupler receiver element to said control terminal; and

said protection circuit effective to output a backup stop control signal to said control terminal when said output monitoring determines that said one of said output voltage and said output current exceeds said reference value, whereby excessive output power is minimized and stabilized even during a circuit failure.

6. An intermittent switching power supply circuit, according to claim 5, further comprising:

a secondary winding on said transformer;

said output power monitoring means on a primary side winding of said transformer;

a feedback winding in said output power monitoring means;

said feedback winding having a first end connecting to said low-voltage terminal;

a rectifier diode in said output power monitoring means;

said rectifier diode connecting in series to a second end of said feedback winding;

a lag network in said output power monitoring means;

said lag network in series with said rectifier diode;

said lag network including at least a first resistor and a first capacitor;

said first resistor and said first capacitor in series with an output side of said rectifier diode;

a pair of voltage-divider resistors in said output power monitoring means;

at least an intermediate tap in series between said pair of voltage-divider resistors; and

said pair of voltage-divider resistors connecting in parallel with said first capacitor between said low-voltage terminal of said external direct current power supply and a series connection point between said first resistor and said first capacitor.

7. An intermittent switching power supply, according to claim 6, wherein:

said protection circuit includes a protection transistor;

said protection transistor connecting said control terminal and said low-voltage terminal of said external direct current power supply;

a base on said protection transistor; and

said base connecting at an intermediate tap between said pair of said voltage-divider resistors.

8. An intermittent switching power supply, according to claim 7, further comprising:

a discharge transistor;

a base on said discharge transistor;

said discharge transistor in series between said series connection point and said low voltage terminal; and

said photocoupler receiver element connecting said base of said discharge transistor and said control terminal of said intermittent oscillator, whereby said intermittent switching power supply circuit provides double control to said oscillation interval of said primary winding and stabilizing protection to said output voltage and said output current.

9. An intermittent switching power supply circuit, comprising:

a transformer including a secondary winding;

output monitoring circuit means for monitoring an output from an rectifying-smoothing circuit and a power output from said secondary winding and sending a stopping signal to said transformer when said output exceeds a reference output; and

protective circuit outputting means for sending a back-up stopping signal to said transformer when said output exceeds said reference output, whereby said protective circuit outputting means provides a safe and simple way to protect said intermittent switching power supply circuit from damage during element failure.

10. An intermittent switching power supply circuit, having an output voltage and output current and controlling an oscillation interval of a primary winding, comprising:

a rectifying-smoothing circuit;

output power monitoring means for monitoring said output voltage and said output current from said rectifying-smoothing circuit;

means for determining if said output exceeds a reference value;

said means for determining in said output monitoring means;

an intermittent oscillator in series with said primary winding;

a control terminal controlling said intermittent oscillator controlling said oscillation interval of said primary winding;

protection circuit means for controlling said control terminal when said output exceeds said reference value; and

said protection circuit means effective to output a stop control signal to said control terminal when said means for determining determines that said output power exceeds said reference power, whereby excessive output power is minimized and said output power is stabilized even during a circuit failure.

11. An intermittent switching power supply circuit, controlling a circuit oscillation interval of a primary winding and stabilizing at least one of an output voltage and an output current, comprising:

an intermittent oscillator controlling said circuit oscillation interval of said primary winding and said intermittent switching power supply circuit;

a control terminal on an intermittent oscillator for controlling said intermittent oscillator and for turning off said intermittent oscillator upon receipt of a control signal;

output monitoring means for monitoring said output voltage and said output current and providing said control signal to said control terminal if at least one of said output voltage and said output current exceeds a reference value; and

protective circuit means for providing a back up monitoring of said output voltage and said output current and providing a back up to said control signal if said at least one output voltage and current exceeds said reference value, whereby said protective circuit ensures protection of said intermittent switching power supply circuit and stability of said output voltage and said output current.

13. An intermittent switching power supply circuit as described in claim 12, wherein:

said output power monitoring circuit is disposed on a primary side of aid transformer;

said output power monitoring circuit includes a feedback winding connected at one end of said feed back winding to a low-voltage terminal of said external direct current power supply;

said output power monitoring circuit includes a rectifier diode connected said another end of said feedback winding;

said output power monitoring circuit includes a lag network;

said lag network including at least a first resistor and a first capacitor connected in series between an output side of said rectifier diode and said low-voltage terminal of said direct current power supply;

said output monitoring circuit includes a pair of voltage-divider resistors;

said pair of voltage-divider resistors connecting in parallel with said first capacitor between said low-voltage terminal and a series connection point;

said series connection point between said first resistor and said first capacitor;

said protection circuit including a protection transistor;

said protection transistor connecting said control terminal of said intermittent oscillator and said low-voltage terminal of said external direct current power supply;

a first base in said protection transistor;

said first base connecting to said intermediate tap of pair of said voltage-divider resistors;

a discharge transistor;

said discharge transistor connecting between said series connection point of said first resistor and said first capacitor and said low-voltage terminal of said external direct current power supply; and

said photocoupler receiver element connecting between a second base of said discharge transistor and said control terminal.

12. An intermittent switching power supply circuit, controls an oscillation interval of a primary winding and stabilizes an output voltage and an output current in a secondary winding comprising:

a transformer includes said primary and said secondary output winding;

an intermittent oscillator is connected in series between said primary winding and an external direct current power supply;

said intermittent oscillator providing said oscillation interval and ceasing said providing when a stop control signal is received at a control terminal;

a rectifying-smoothing circuit;

said rectifying-smoothing circuit rectifying and smoothing at least one of said output voltage and said output current from said secondary output winding;

an output monitoring circuit monitoring said output voltage and an output current from said rectifying-smoothing circuit and operating a photocoupler emitter element and outputting a limit signal if at least one of said output voltage and said output current exceeds a reference value;

a photocoupler receiver element photocoupled with said photocoupler emitter element;

said photocoupler receiver element outputting a stop control signal to said control terminal of said intermittent oscillator when said limit signal is received from said photocoupler emitter element;

an output power monitoring circuit monitoring output power from said rectifying-smoothing circuit;

a protective circuit outputting a control signal to said control terminal when said output monitoring circuit detects that at least one of said output voltage and said output current exceeds a reference value; and

said protective circuit connecting to said control terminal in parallel with said photocoupler receiver element, whereby said output voltage and said output current are stabilized and controlled effectively.

14. An intermittent power supply comprising:

an intermittent oscillator;

means responsive to at least one of an output current exceeding a predetermined output current and an output voltage exceeding a predetermined output voltage for stopping said intermittent oscillator, and restarting said intermittent oscillator when said output voltage and said output current are reduced below predetermined values, whereby said intermittent oscillator normally cycles on and off;

an integrator;

said integrator including a capacitor charged when said intermittent oscillator is turned off;

said integrator having a time constant exceeding a normal cycle time of intermittent operation of said intermittent oscillator;

a control element;

means for activating said control element when a charge in said capacitor exceeds a turn-on value; and

said control element including means for maintaining said intermittent oscillator in a quiescent condition when activated, whereby, in the absence of regular cycling of said intermittent oscillator, said intermittent oscillator remains quiescent.