Constant voltage output control method and constant voltage output control device for switching power supply circuit

• US 20040183507A1
• Filed: 03/04/2004
• Published: 09/23/2004
• Est. Priority Date: 03/18/2003
• Status: Active Grant

• Current Assignee: SMK Corporation
• Original Assignee: SMK Corporation
• Inventors: Amei, Toshihiro
• Granted Patent: US 7,027,313 B2
• Time in Patent Office: Days
• US Class Current: 323/222
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

The present invention provides a constant voltage output control method and a constant voltage output control device for a switching power supply circuit that allow accurate execution of a constant voltage control of an output voltage, even if there is variation in a utilized circuit element or an integrated circuit. A set voltage V_2aset is obtained based on equation (1),

V_2ASET=NP÷NS×V_2BSET  (1)

where, V_2bset represents an output voltage of a secondary output winding that is subject to the constant voltage control, Np represents a number of turns of a primary winding, and Ns represents a number of turns of the secondary output winding; and the set voltage V_2aset is compared with a flyback voltage V_2a of the primary winding.

Claims

1. A constant voltage output control method for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

a switching control circuit that executes ON/OFF control of the oscillating switching device; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control method executing a constant voltage control of an output voltage V_2b that is generated in the secondary output winding by changing an ON time T1 of the oscillating switching device of the switching power supply circuit, comprising the steps of;

deriving a set voltage V_2aset based on equation (1),

V_2aset=Np÷

Ns×

V_2bset 

 

(1)

where, V_2bset represents an output voltage of the secondary output winding that is subject to the constant voltage control, Np represents a number of turns of the primary winding, and Ns represents a number of turns of the secondary output winding;

comparing the set voltage V_2aset with a flyback voltage V_2a of the primary winding; and

executing at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2a is more than the set voltage V_2aset, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with a difference voltage dV between the set voltage V_2aset and the flyback voltage V_2a, and in the case that the flyback voltage V_2a is less than the set voltage V_2aset, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

2. A constant voltage output control method for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

a switching control circuit that executes ON/OFF control of the oscillating switching device; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control method executing a constant voltage control of an output voltage V_2o of the rectifying smoothing circuit by changing an ON time T1 of the oscillating switching device of the switching power supply circuit, comprising the steps of;

deriving a set voltage V_2aset′

based on equation (2),

V_2aset′

=V_2oset×

Np÷

Ns÷

(1−

T2×

k÷

Ls) 

 

(2)

where, V_2oset represents an output voltage of the rectifying smoothing circuit that is subject to the constant voltage control, Np represents a number of turns of the primary winding, Ns represents a number of turns of the secondary output winding, Ls represents an inductance of the secondary output winding, T2 represents an output time for which output is generated in the rectifying smoothing circuit within an oscillation time cycle Tc, and k represents a proportionality constant provided dividing a forward voltage drop of a diode of the rectifying smooth circuit by an output current;

comparing the set voltage V_2aset′

with a flyback voltage V_2a of the primary winding; and

executing at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2a is more than the set voltage V_2aset′

, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with a difference voltage dV between the set voltage V_2aset′ and

the flyback voltage V_2a, and in the case that the flyback voltage V_2a is less than the set voltage V_2aset′

, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

5. The constant voltage output control method for a switching power supply circuit according to claim 2 wherein

the output time T2 for which output is generated in the rectifying smoothing circuit during the oscillation time cycle Tc is detected based on a time from when flyback voltage is generated in the primary winding until when a first polarity reversal occurs.

6. The constant voltage output control method for a switching power supply circuit according to claim 2 wherein

the output time T2 for which output is generated in the rectifying smoothing circuit during the oscillation time cycle Tc is detected based on a time from when flyback voltage is generated in the auxiliary winding of the transformer until when a first polarity reversal occurs.

3. A constant voltage output control method for a switching power supply circuit having a transformer provided with a primary winding and an auxiliary winding on a primary side and a secondary output winding on a secondary side;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

a switching control circuit that executes ON/OFF control of the oscillating switching device; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control method executing a constant voltage control of an output voltage V_2b that is generated in the secondary output winding by changing an ON time T1 of the oscillating switching device of the switching power supply circuit, comprising the steps of;

deriving a set voltage V2cset based on equation (3),

V_2cset=Nt÷

Ns×

V_2bset 

 

(3)

where, V_2bset represents an output voltage of the secondary output winding that is subject to the constant voltage control, Nt represents a number of turns of the auxiliary winding, and Ns represents a number of turns of the secondary output winding;

comparing the set voltage V_2cset with a flyback voltage V_2c of the auxiliary winding; and

executing at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2c is more than the set voltage V_2cset, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with a difference voltage dV between the set voltage V_2cset, and the flyback voltage V_2c, and in the case that the flyback voltage V_2c is less than the set voltage V_2cset, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

4. A constant voltage output control method for a switching power supply circuit having a transformer provided with a primary winding and an auxiliary winding on a primary side and a secondary output winding on a secondary side;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

a switching control circuit that executes ON/OFF control of the oscillating switching device; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control method executing a constant voltage control of an output voltage V_2o that is generated in the rectifying smoothing circuit by changing an ON time T1 of the switching power supply circuit, comprising the steps of;

deriving a set voltage V_2cset′

based on equation (4),

V_2cset′

=V_2oset×

Nt÷

Ns÷

(1−

T2×

k÷

Ls) 

 

(4)

where, V_2oset represents an output voltage of the rectifying smoothing circuit that is subject to the constant voltage control, Nt represents a number of turns of the auxiliary winding, Ns represents a number of turns of the secondary output winding, Ls represents an inductance of the secondary output winding, T2 represents an output time for which output is generated in the rectifying smoothing circuit within an oscillation time cycle Tc, and k represents a proportionality constant provided dividing a forward voltage drop of a diode of the rectifying smooth circuit by an output current;

comparing the set voltage V_2cset′

with a flyback voltage V_2c of the auxiliary winding; and

executing at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2c is more than the set voltage V_2cset′

, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with a difference voltage dV between the set voltage V_2cset′ and

the flyback voltage V_2c, and in the case that the flyback voltage V_2c is less than the set voltage V_2cset′

, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

7. The constant voltage output control method for a switching power supply circuit according to claim 4 wherein

the output time T2 for which output is generated in the rectifying smoothing circuit during the oscillation time cycle Tc is detected based on a time from when flyback voltage is generated in the primary winding until when a first polarity reversal occurs.

8. The constant voltage output control method for a switching power supply circuit according to claim 4 wherein

the output time T2 for which output is generated in the rectifying smoothing circuit during the oscillation time cycle Tc is detected based on a time from when flyback voltage is generated in the auxiliary winding of the transformer until when a first polarity reversal occurs.

9. A constant voltage output control device for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

a primary side current detection portion that indicates a primary winding current Ip flowing in the primary winding based on a voltage drop V_ip of an Ip detection resistor, this Ip detection resistor having a resistance value r_ip and being connected in-series with the primary winding;

a switching control circuit that executes ON control of the oscillating switching device with a predetermined time cycle, and executes OFF control of the oscillating switching device when the primary winding current Ip reaches a maximum current Ip_max which is taken to occur when the voltage drop V_ip reaches a maximum voltage V_iMax that is the multiple of a maximum current Ip_max and the resistance value r_ip; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control device executing a constant voltage control of an output voltage V_2b that is generated in the secondary output winding by changing an ON time T1 of the oscillating switching device, comprising;

a voltage monitoring portion that detects a flyback voltage V_2a of the primary winding;

a difference voltage generation circuit which obtains a set voltage V_2aset based on equation (1),

V_2aset=Np÷

Ns×

V_2bset 

 

(1)

where, V_2bset represents an output voltage of the secondary output winding that is subject to the constant voltage control, Np represents a number of turns of the primary winding, and Ns represents a number of turns of the secondary output winding, and which outputs a difference voltage dV expressed by equation (5),

dV=V_2a−

V_2aset 

 

(5)

which is based on the set voltage V_2aset and the flyback voltage V_2a of the primary winding; and

an adder circuit that sets a correction voltage drop V_ip′

by adding the difference voltage dV to the voltage drop V_ip, wherein

the switching control circuit sets the correction voltage drop V_ip′

as the voltage drop V_ip that is compared with the maximum voltage V_iMax, and executes at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2a is more than the set voltage V_2aset, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV, and in the case that the flyback voltage V_2a is less than the set voltage V_2aset, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

11. The constant voltage output control device for a switching power supply circuit according to claim 9, further comprising

a maximum voltage V_imax′

is derived from equation (8)

V_iMax′

=V_iMax−

δ

t×

Vcc÷

Lp×

r_ip 

 

(8)

where, δ

t is a time difference between detection of the drop voltage V_ip, to which the difference voltage dV has been added, reaching the maximum voltage V_imax and stopping of ON control of the oscillating switching device, Vcc represents a power supply voltage of the direct current power supply, and Lp represents an inductance of the primary winding, and

the switching control circuit sets this maximum voltage V_imax′

as the maximum voltage V_imax that is compared with the correction voltage drop V_ip′

.

13. The constant voltage output control device for a switching power supply circuit according to claim 9, wherein

when the difference voltage dV output from the difference voltage generation circuit exceeds a permitted maximum difference voltage dV_LIM, the difference voltage dV is set to the permitted maximum difference voltage dV_LIM.

15. The constant voltage output control device for a switching power supply circuit according to claim 13, wherein

in the case that the voltage drop V_ip does not reach a minimum potential V_imin expressed by equation (7),

V_imin=V_imax−

dV_LIM 

 

(7)

ON control of the oscillating switching device is temporarily stopped.

16. The constant voltage output control device for a switching power supply circuit according to claim 13, further comprising

a maximum voltage V_imax′

is derived from equation (8),

V_iMax′

V_iMax−

δ

t×

Vcc÷

Lp×

r_ip 

 

(8)

where, δ

t is a time difference between detection of the drop voltage V_ip, to which the difference voltage dV has been added, reaching the maximum voltage V_imax and stopping of ON control of the oscillating switching device, Vcc represents a power supply voltage of the direct current power supply, and Lp represents an inductance of the primary winding, and

the switching control circuit sets this maximum voltage V_imax′

as the maximum voltage V_imax that is compared with the correction voltage drop V_ip′

.

10. A constant voltage output control device for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

a primary side current detection portion that indicates a primary winding current Ip flowing in the primary winding based on a voltage drop V_ip of an Ip detection resistor, this Ip detection resistor having a resistance value r_ip and being connected in-series with the primary winding;

a switching control circuit that executes ON control of the oscillating switching device with a predetermined time cycle, and executes OFF control of the oscillating switching device when the primary winding current Ip reaches a maximum current Ip_max which is taken to occur when the voltage drop V_ip reaches a maximum voltage V_imax that is the multiple of a maximum current Ip_max and the resistance value r_ip; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control device executing a constant voltage control of an output voltage V_2o of the rectifying smoothing circuit by changing an ON time T1 of the oscillating switching device, comprising;

a voltage monitoring portion that detects a flyback voltage V_2a of the primary winding;

an output time detection portion that detects an output time T2 for which output is generated in the rectifying smoothing circuit during an oscillation time cycle Tc;

a difference voltage generation circuit which obtains a set voltage V_2aset′

based on equation (2),

V_2aset′

=V_2oset×

Np÷

Ns÷

(1−

T2×

k÷

Ls) 

 

(2)

where, V_2oset represents an output voltage of the rectifying smoothing circuit that is subject to the constant voltage control, Np represents a number of turns of the primary winding, Ns represents a number of turns of the secondary output winding, Ls represents an inductance of the secondary output winding, T2 represents the output time for which output is generated in the rectifying smoothing circuit within the oscillation time cycle Tc, and k represents a proportionality constant provided dividing a forward voltage drop of a diode of the rectifying smooth circuit by an output current, and which outputs a difference voltage dV expressed by equation (6)

dV=V_2a−

V_2aset′

 

 

(6)

which is based on the set voltage V_2aset′ and

the flyback voltage V_2a of the primary winding; and

an adder circuit that sets a correction voltage drop V_ip′

by adding the difference voltage dV to the voltage drop V_ip, wherein

the switching control circuit sets the correction voltage drop V_ip′

as the voltage drop V_ip that is compared with the maximum voltage V_iMax, and executes at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2a is more than the set voltage V_2aset′

, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV, and in the case that the flyback voltage V_2a is less than the set voltage V_2aset′

, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

12. The constant voltage output control device for a switching power supply circuit according to claim 10, further comprising

a maximum voltage V_imax′

is derived from equation (8),

V_iMax′

=V_iMax−

δ

t×

Vcc÷

Lp×

r_ip 

 

(8)

where, δ

t is a time difference between detection of the drop voltage V_ip, to which the difference voltage dV has been added, reaching the maximum voltage V_imax and stopping of ON control of the oscillating switching device, Vcc represents a power supply voltage of the direct current power supply, and Lp represents an inductance of the primary winding, and

the switching control circuit sets this maximum voltage V_imax′

as the maximum voltage V_imax that is compared with the correction voltage drop V_ip′

.

14. The constant voltage output control device for a switching power supply circuit according to claim 10, wherein

when the difference voltage dV output from the difference voltage generation circuit exceeds a permitted maximum difference voltage dV_LIM, the difference voltage dV is set to the permitted maximum difference voltage dV_LIM.

21. The constant voltage output control device for a switching power supply circuit according to claim 10, further comprising:

a primary winding voltage monitoring circuit that monitors a voltage V_2a of the primary winding, and detects a time from when flyback voltage is generated in the primary winding until when a first polarity reversal occurs, wherein

the time from when flyback voltage is generated in the primary winding until when the first polarity reversal occurs is taken as the output time T2.

23. The constant voltage output control device for a switching power supply circuit according to claim 10, further comprising:

an auxiliary winding that is additionally provided at a primary side of the transformer; and

an auxiliary winding voltage monitoring circuit that monitors a voltage V_2c of the auxiliary winding, and detects a time from when flyback voltage is generated in the auxiliary winding until when a first polarity reversal occurs, wherein

the time from when flyback voltage is generated in the primary winding until when the first polarity reversal occurs is taken as the output time T2.

17. A constant voltage output control device for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

an oscillator circuit that generates a pulse control signal with a fixed time cycle Tc, a single cycle of the fixed time cycle Tc being formed by respective output periods of a first level and a second level continuous with the first level;

a switching control circuit that executes ON control of the oscillating switching device while the pulse control signal is the first level, and executes OFF control of the oscillating switching device while the pulse control signal is the second level; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control device executing a constant voltage control of an output voltage V_2b that is generated in the secondary output winding by changing an ON time T1 of the oscillating switching device, comprising;

a primary side current detection portion that indicates a primary winding current Ip flowing in the primary winding based on a voltage drop V_ip of an Ip detection resistor, this Ip detection resistor having a resistance value r_ip and being connected in-series with the primary winding;

a voltage monitoring portion that detects a flyback voltage V_2a of the primary winding;

a difference voltage generation circuit which obtains a set voltage V_2aset based on equation (1),

V_2aset=Np÷

Ns×

V_2bset 

 

(1)

where, V_2bset represents an output voltage of the secondary output winding that is subject to the constant voltage control, Np represents a number of turns of the primary winding, and Ns represents a number of turns of the secondary output winding, and which outputs a difference voltage dV expressed by equation (5),

dV=V_2a−

V_2aset 

 

(5)

which is based on the set voltage V_2aset and the flyback voltage 2a of the primary winding; and

a pulse width modulation circuit that executes pulse width modulation of a pulse width of the first level of the pulse control signal using the difference voltage dV, wherein

the switching control circuit executes at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2a is more than the set voltage V_2aset, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV, and in the case that the flyback voltage V_2a is less than the set voltage V_2aset, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

19. The constant voltage output control device for a switching power supply circuit according to claim 17, wherein

when the difference voltage dV output from the difference voltage generation circuit exceeds a permitted maximum difference voltage dV_LIM, the difference voltage dV is set to the permitted maximum difference voltage dV_LIM.

18. A constant voltage output control device for a switching power supply circuit having a transformer provided with a primary winding and a secondary output winding;

an oscillating switching device which is connected in-series with the primary winding to a direct current power supply that excites the primary winding;

an oscillator circuit that generates a pulse control signal with a fixed time cycle Tc, a single cycle of the fixed time cycle Tc being formed by respective output periods of a first level and a second level continuous with the first level;

a switching control circuit that executes ON control of the oscillating switching device while the pulse control signal is the first level, and executes OFF control of the oscillating switching device while the pulse control signal is the second level; and

a rectifying smoothing circuit that rectifies and smoothes an output of the secondary output winding;

this constant voltage output control device executing a constant voltage control of an output voltage V_2o of the rectifying smoothing circuit by changing an ON time T1 of the oscillating switching device, comprising;

a primary side current detection portion that indicates a primary winding current Ip flowing in the primary winding based on a voltage drop V_ip of an Ip detection resistor, this Ip detection resistor having a resistance value r_ip and being connected in-series with the primary winding;

a voltage monitoring portion that detects a flyback voltage V_2a of the primary winding;

an output time detection portion that detects an output time T2 for which output is generated in the rectifying smoothing circuit during an oscillation time cycle Tc;

a difference voltage generation circuit which obtains a set voltage V_2aset′

based on equation (2),

V_2aset′

=V_2oset×

Np÷

Ns÷

(1−

T2×

k÷

Ls) 

 

(2)

where, V_2oset represents an output voltage of the rectifying smoothing circuit that is subject to the constant voltage control, Np represents a number of turns of the primary winding, Ns represents a number of turns of the secondary output winding, Ls represents an inductance of the secondary output winding, T2 represents the output time for which output is generated in the rectifying smoothing circuit within the oscillation time cycle Tc, and k represents a proportionality constant provided dividing a forward voltage drop of a diode of the rectifying smooth circuit by an output current, and which outputs a difference voltage dV expressed by equation (6),

dV=V_2a−

V_2aset′

 

 

(6)

which is based on the set voltage V_2aset′ and

the flyback voltage 2a of the primary winding; and

a pulse width modulation circuit that executes pulse width modulation of a pulse width of the first level of the pulse control signal using the difference voltage dV, wherein

the switching control circuit executes at least one of a time shortening control and a time lengthening control such that, in the case that the flyback voltage V_2a is more than the set voltage V_2aset′

, the time shortening control is executed that shortens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV, and in the case that the flyback voltage V_2a is less than the set voltage V_2aset′

, the time lengthening control is executed that lengthens the ON time T1 of the oscillating switching device in accordance with the difference voltage dV.

20. The constant voltage output control device for a switching power supply circuit according to claim 18, wherein

when the difference voltage dV output from the difference voltage generation circuit exceeds a permitted maximum difference voltage dV_LIM, the difference voltage dV is set to the permitted maximum difference voltage dV_LIM.

22. The constant voltage output control device for a switching power supply circuit according to claim 18, further comprising:

a primary winding voltage monitoring circuit that monitors a voltage V_2a of the primary winding, and detects a time from when flyback voltage is generated in the primary winding until when a first polarity reversal occurs, wherein

the time from when flyback voltage is generated in the primary winding until when the first polarity reversal occurs is taken as the output time T2.

24. The constant voltage output control device for a switching power supply circuit according to claim 18, further comprising:

an auxiliary winding that is additionally provided at a primary side of the transformer; and

an auxiliary winding voltage monitoring circuit that monitors a voltage V_2c of the auxiliary winding, and detects a time from when flyback voltage is generated in the auxiliary winding until when a first polarity reversal occurs, wherein

the time from when flyback voltage is generated in the primary winding until when the first polarity reversal occurs is taken as the output time T2.