JP2003153529A - Switching power supply circuit - Google Patents

Switching power supply circuit

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Publication number
JP2003153529A
JP2003153529A JP2001348192A JP2001348192A JP2003153529A JP 2003153529 A JP2003153529 A JP 2003153529A JP 2001348192 A JP2001348192 A JP 2001348192A JP 2001348192 A JP2001348192 A JP 2001348192A JP 2003153529 A JP2003153529 A JP 2003153529A
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JP
Japan
Prior art keywords
circuit
transformer
power supply
output voltage
switching power
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP2001348192A
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Japanese (ja)
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JP3534400B2 (en
Inventor
Masaaki Ishihara
正明 石原
Original Assignee
Toshiba Corp
株式会社東芝
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Publication date
Application filed by Toshiba Corp, 株式会社東芝 filed Critical Toshiba Corp
Priority to JP2001348192A priority Critical patent/JP3534400B2/en
Publication of JP2003153529A publication Critical patent/JP2003153529A/en
Application granted granted Critical
Publication of JP3534400B2 publication Critical patent/JP3534400B2/en
Application status is Expired - Fee Related legal-status Critical
Anticipated expiration legal-status Critical

Links

Abstract

(57) [Problem] To provide a switching power supply circuit capable of reliably stopping even when an output voltage is reduced to a predetermined voltage due to a half short or the like. When a low voltage detection circuit detects that an output voltage applied to a load connected to a secondary side of a transformer has dropped to a predetermined voltage due to a half short circuit or the like, the secondary side of the transformer changes to a primary side. To shut off the switching power supply circuit.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit used for various electronic devices. 2. Description of the Related Art At present, small and highly efficient switching type power supply circuits are used in many electronic devices such as televisions. A switching power supply circuit rectifies an input AC power supply voltage, turns it on / off by a high-speed switching element, changes its on-time and on / off switching frequency, and keeps a DC voltage obtained as an output constant. Is controlled as follows. Among these switching power supply circuits, a ringing choke converter (hereinafter, RCC) type switching power supply circuit using a high-frequency inverter is known. This switching power supply circuit of the RCC system uses a transistor as a high-speed switching element connected to the primary side of a transformer, and has a feedback winding on the primary side of the transformer for monitoring a secondary voltage. ing. Using the pulse generated in the feedback winding, the transistor is automatically turned on / off regardless of an external pulse, and the magnetic energy stored in the coil of the transformer is released to the output side during the off period while the transistor is on. It is a self-excited power supply circuit. An RCC type switching power supply circuit using this type of feedback winding is disclosed in, for example, Japanese Patent Application Laid-Open No. 6-38520. Recently, as a switching power supply circuit of the RCC type, a transformer is connected via a photocoupler.
In many systems, the fluctuation state of the secondary voltage is directly fed back to the primary side of the transformer to perform on / off control. In the switching power supply circuit using the photocoupler, the switching power supply circuit using the feedback winding described above indirectly detects the secondary voltage from the voltage generated in the primary feedback winding. Since the secondary side voltage is directly detected and this voltage information is fed back to the primary side via the photocoupler, it is possible to control the output voltage with higher accuracy. In other words, a more stable output voltage can be obtained. From this, switching power supply circuits using this type of photocoupler, for example,
Used for power supply of TV flyback transformer. That is, since the stability of the power supply voltage of the flyback transformer in the television directly appears as the quality of the television image,
This is because a power supply circuit with a more stable secondary voltage is required. Recently, there has been an increasing number of RCC systems that perform a more efficient switching operation using a control circuit composed of an integrated circuit with more precise on / off control. The control circuit stabilizes the secondary voltage more accurately based on the information fed back from the secondary side,
Power detection is provided so as not to exceed the rating of the switching transistor. By the way, in this switching power supply circuit of the RCC system, various protection functions are provided, and overvoltage and overheat protection are often provided. For example, JP-A-5-30
No. 735 proposes a protection technique in which when a secondary-side output terminal is short-circuited, information on a secondary-side voltage is transmitted to the primary side via a photocoupler and the oscillation of the control circuit is stopped. I have. However, in the RCC type switching power supply circuit provided with the protection function described above, for example, if a part of the winding of the flyback transformer is short-circuited for some reason, In some cases, a half short circuit having a resistance value occurs, the load supply upper limit value is reached, the secondary side voltage is reduced to a certain level, a balanced state is maintained, and this state is maintained. In this case, since the output terminal on the secondary side has a certain resistance value and is not short-circuited, the above-mentioned protection technique cannot cope with it. Note that the load supply upper limit cannot be easily increased because it is determined by the rating of the component. SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply circuit capable of reliably stopping even when an output voltage drops to a predetermined voltage due to a half short circuit or the like. [0010] In order to achieve the above object, a switching power supply circuit according to the first aspect of the present invention, wherein a DC voltage is applied to one end via a switching element.
A transformer having a secondary winding and a secondary winding to which an output voltage is induced and to which a load is connected; a control circuit for controlling the operation of the switching element; and an output induced by the secondary winding of the transformer. A feedback circuit for detecting a voltage and a change with respect to a predetermined output voltage set in advance, and feeding back an error information signal based on the detected change to the control circuit. A protection circuit is provided which cuts off an error information signal fed back from the feedback circuit to the control circuit when the induced output voltage drops to the allowable minimum voltage. Further, in the switching power supply circuit according to the second aspect of the present invention, a primary winding to which a DC voltage is applied at one end via a first switching element, an output voltage are induced, and a load is connected. A transformer with a secondary winding;
A control circuit for controlling the operation of the switching element; detecting a change in an output voltage induced in a secondary winding of the transformer and a predetermined output voltage set in advance; and outputting an error information signal based on the detected change. A switching power supply circuit having a feedback circuit that feeds back to the control circuit, wherein a low voltage detection circuit that detects that the output voltage induced in the secondary winding of the transformer has dropped to a minimum allowable voltage and outputs a trigger; A protection circuit having a second switching element for interrupting an error information signal fed back from the feedback circuit to the control circuit in response to an output from the low voltage detection circuit. According to a third aspect of the present invention, in the switching power supply circuit according to the first aspect, the protection circuit blocks the error information signal until the voltage applied to the primary winding of the transformer is turned on again. Is held. According to a fourth aspect of the present invention, in the switching power supply circuit according to the first aspect, the feedback circuit includes a photocoupler, and controls a current passing through the photocoupler according to error information. According to a fifth aspect of the present invention, there is provided a switching power supply circuit according to the first aspect, wherein the load connected to the secondary winding of the transformer is a flyback transformer. In the switching power supply circuit according to the present invention, a primary winding to which a DC voltage is applied through one end of a first switching element, an output voltage are induced, and a load is connected. A transformer having a secondary winding, a control circuit for controlling the operation of the first switching element, and a photocoupler including a light emitting unit on the input side and a photoelectric conversion unit on the output side. An output voltage induced in the winding and a change with respect to a predetermined output voltage set in advance are detected, and a first feedback current according to an error information signal based on the detected change is caused to flow to a light emitting unit of the photocoupler. And a feedback circuit that feeds back a second feedback current generated in the photoelectric conversion unit of the photocoupler to the control circuit in accordance with the feedback current of 1 in the switching power supply circuit in parallel with the light emitting unit of the photocoupler. A second switching element connected to the transformer, and when the output voltage induced in the secondary winding of the transformer drops to the minimum allowable voltage, the second switching element is turned on to cut off the first feedback current. A protection circuit is provided. According to the present invention, it is possible to provide a switching power supply circuit that can be reliably stopped even when the output voltage drops to a predetermined voltage due to a half short circuit or the like. Embodiments of the present invention will be described below.
This will be described with reference to the drawings. The figure is a circuit diagram showing an RCC type switching power supply circuit. In this switching power supply circuit, the AC power supplied from the commercial AC power supply 1 is
The voltage is smoothed by the rectifying diode bridge 2 and the smoothing capacitor 3, and the voltage E <b> 1 is supplied to the subsequent switching power supply circuit as the DC voltage source 4. This switching power supply circuit includes a converter transformer 5, a switching transistor 6 as a switching element, and a control circuit 7 for controlling the operation of the switching transistor 6 so that the output voltage induced in the secondary winding 5c is constant. . The converter transformer 5 has a primary winding 5a and an auxiliary winding 5b on the primary side, and a secondary winding 5c on the secondary side. One end of the primary winding 5a is connected to the DC voltage source 4, and the other end is connected to the collector of the switching transistor 6. The emitter of the switching transistor 6 is grounded via a switching power supply detecting resistor 8. Further, a control signal from the control circuit 7 is applied to the base of the switching transistor 6. The voltage induced in the auxiliary winding 5b is rectified and smoothed by a diode 9 and a capacitor 10 for rectifying the auxiliary power to obtain an auxiliary voltage source E2 for the control circuit 7. The auxiliary voltage source E2 is also a power supply for feedback of the photocoupler 11, and is applied to the collector of the phototransistor constituting the photoelectric conversion unit 11a of the photocoupler 11. The control circuit 7 obtains power from the DC voltage source 4 via the starting resistor 12 when the commercial AC power supply 1 is turned on. The secondary winding 5c of the converter transformer 5 has:
Rectifier diode 13 for load power supply rectification, smoothing capacitor 1
4 and a load such as an output voltage rectifying / smoothing circuit and a flyback transformer. The voltage induced in the secondary winding 5c is subjected to rectification and smoothing, followed by a load as a DC voltage E3.
15 is applied. This switching power supply circuit comprises a transformer 5
Of the output voltage E3 from the predetermined voltage is detected on the secondary side, and an error information signal corresponding to the fluctuation amount is fed back to the control circuit 7 on the primary side of the transformer to stabilize the output voltage E3. For the feedback circuit. The feedback circuit includes an error amplifier 16 that detects a change in the output voltage E3 and outputs a signal corresponding to the change amount, resistors 17, 18, and a photocoupler 11. The resistor 18 is a light emitting unit 1 of the photocoupler 11.
This is a feedback current limiting resistor for adjusting the current flowing through 1b. Furthermore, in this switching power supply circuit, for example, if a part of the winding of the flyback transformer is short-circuited for some reason, it becomes a half short-circuit having a certain resistance value, reaches the load supply upper limit value, and May be kept in a balanced state while the output voltage is lowered to a certain level. The protection circuit 19 is provided to ensure that the present switching power supply circuit is turned off in such a situation. The protection circuit 19 includes the photocoupler 11
Of the switching transistor 20, which is connected in series with the light emitting unit 11b, and a low-voltage detecting circuit 2 which outputs a trigger to the base of the switching transistor 20 when detecting that the secondary voltage has dropped below the minimum allowable voltage.
1 Next, the operation of the switching power supply circuit will be described. The voltage E3 applied to the load 15 is determined by the error amplifier 16 and the resistor 17. During normal operation of the switch power supply circuit, the low-voltage detection circuit 21 of the protection circuit 19 does not operate, and the transistor 20 is off. Therefore, a secondary side feedback current corresponding to the fluctuation amount detected by the error amplifier 16 flows through the light emitting portion 11b of the photocoupler 11, and this error information signal is transmitted from the light emitting portion 11b of the photocoupler to the photoelectric conversion portion 11a. Conveyed as The error information signal is converted into a primary side feedback current by the photoelectric conversion unit 11 a and applied to the control circuit 7. The control circuit 7 controls the on / off of the transistor 6 based on the error information signal, corrects the fluctuation of the output voltage E3 from a predetermined voltage, and keeps the output voltage E3 constant. By the way, as described above, the load is not a complete short but a half short with a certain resistance value, the load supply upper limit is reached, and the output voltage on the secondary side is kept in a balanced state with a constant level. And may keep maintaining this state. In such a situation, when the output voltage E3 decreases when the load is half short-circuited and the low voltage detection circuit 21 detects that the voltage E3 has decreased to the minimum allowable voltage, a trigger is applied to the base of the transistor 20. Then, the transistor 20 is turned on (conducting).
When the transistor 20 is turned on, the photocoupler 11
The light emitting portion 11b is short-circuited and the secondary side feedback current does not flow, and the feedback from the secondary side to the primary side of the transformer 5 by the photocoupler 11 is cut off. When the primary-side feedback current is cut off and stopped, the control circuit 7 stops driving the switching transistor 6. As a result, the operation of the switching power supply circuit is reliably stopped. The low-voltage detection circuit 21 can be generally configured by conceivable resistance division. For example, after the switching power supply is stopped by a half short using a thyristor, the primary power supply of the transformer 5 is turned on again. It is preferable to have a latch function for maintaining this state until this state. According to the invention described in detail above, it is possible to provide a switching power supply circuit capable of reliably stopping even when the output voltage drops to a predetermined voltage due to a half short circuit or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a switching power supply circuit according to an embodiment of the present invention. [Description of Signs] 1 ... Commercial AC power supply 2 ... Diode bridge 3 ... Smoothing capacitor 4 ... DC voltage source 5 ... Converter transformer 5a ... Primary winding 5b ... Auxiliary winding 5c ... Secondary winding 6 ... Switching transistor 7 ... Control circuit 8 ... Switching current detection resistor 9 ... Diode 10 ... Capacitor 11 ... Photocoupler 11a ... Photoelectric converter 11b ... Light emitting unit 12 ... Start-up resistor 13 ... Rectifier diode 14 ... Smoothing capacitor 15 ... Load 16 ... Error amplifier 17 ... Resistance 18 Resistor 19 Protection Circuit 20 Switching Transistor 21 Low Voltage Detection Circuit

Claims (1)

1. A transformer having a primary winding to which a DC voltage is applied at one end via a switching element and a secondary winding to which an output voltage is induced and a load is connected. A control circuit for controlling the operation of the switching element, detecting a change in an output voltage induced in a secondary winding of the transformer and a predetermined output voltage, and generating an error information signal based on the detected change. A switching power supply circuit having a feedback circuit that feeds back to the control circuit, wherein when the output voltage induced in the secondary winding of the transformer drops to the minimum allowable voltage, the feedback circuit feeds back to the control circuit. A switching power supply circuit comprising a protection circuit for interrupting an error information signal. 2. A transformer having a primary winding on one end to which a DC voltage is applied via a first switching element and a secondary winding on which an output voltage is induced and a load is connected; A control circuit for controlling the operation of the element, an output voltage induced in the secondary winding of the transformer and a change with respect to a predetermined output voltage set in advance, and an error information signal based on the detected change detected by the control circuit; A switching power supply circuit having a feedback circuit for feedback to the transformer, detecting that the output voltage induced in the secondary winding of the transformer has dropped to the minimum allowable voltage, and outputting a trigger; and A protection circuit having a second switching element for blocking an error information signal fed back from the feedback circuit to the control circuit in response to an output from the low voltage detection circuit. Characteristic switching power supply circuit. 3. The switching power supply circuit according to claim 1, wherein the protection circuit keeps a state in which the error information signal is interrupted until the voltage applied to the primary winding of the transformer is turned on again. . 4. The switching power supply circuit according to claim 1, wherein the feedback circuit includes a photocoupler, and controls a current flowing through the photocoupler according to the error information signal. 5. The switching power supply circuit according to claim 1, wherein the load connected to the secondary winding of the transformer is a flyback transformer. 6. A transformer having a primary winding to which a DC voltage is applied at one end via a first switching element, and a secondary winding to which an output voltage is induced and a load is connected. A control circuit for controlling the operation of the switching element, and a photocoupler including a light-emitting part on the input side and a photoelectric conversion part on the output side, wherein the output voltage induced in the secondary winding of the transformer is set in advance. A change with respect to a predetermined output voltage is detected, and a first feedback current according to an error information signal based on the detected change is caused to flow to a light emitting unit of the photocoupler, and a photoelectric conversion unit of the photocoupler is controlled according to the first feedback current. A feedback circuit that feeds back a second feedback current generated to the control circuit to the control circuit, further comprising a second switching element connected in parallel with a light emitting unit of the photocoupler, A switching power supply circuit, comprising: a protection circuit for turning on a second switching element and interrupting a first feedback current when an output voltage induced in a secondary winding drops to an allowable minimum voltage.
JP2001348192A 2001-11-14 2001-11-14 Switching power supply circuit Expired - Fee Related JP3534400B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2001348192A JP3534400B2 (en) 2001-11-14 2001-11-14 Switching power supply circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2001348192A JP3534400B2 (en) 2001-11-14 2001-11-14 Switching power supply circuit

Publications (2)

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JP2003153529A true JP2003153529A (en) 2003-05-23
JP3534400B2 JP3534400B2 (en) 2004-06-07

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7525820B2 (en) 2006-04-12 2009-04-28 Rohm Co., Ltd. Inverter
US7558091B2 (en) 2006-12-14 2009-07-07 Sharp Kabushiki Kaisha Switching power supply apparatus
EP2164160A2 (en) 2008-09-11 2010-03-17 Funai Electric Co., Ltd. Voltage reduction detection circuit and switching power supply system
CN102298907A (en) * 2010-06-28 2011-12-28 罗姆股份有限公司 Load driving circuit, light-emitting device and display device using the same
US9277612B2 (en) 2013-10-07 2016-03-01 Rohm Co., Ltd. Switching converter, control circuit and control method thereof, and lighting device and electronic apparatus using the same
US9402287B2 (en) 2014-11-04 2016-07-26 Rohm Co., Ltd. Switching converter with light source dimming function
US9401649B2 (en) 2014-11-04 2016-07-26 Rohm Co., Ltd. Switching converter
US9723668B2 (en) 2015-06-05 2017-08-01 Rohm Co., Ltd. Switching converter and lighting device using the same
US9750113B2 (en) 2015-05-01 2017-08-29 Rohm Co., Ltd. Driving circuit of light source and control circuit thereof, driving method of light source, lighting apparatus, and electronic device
US9763295B2 (en) 2015-06-02 2017-09-12 Rohm Co., Ltd. Switching converter and lighting device using the same
KR20180017076A (en) 2015-06-08 2018-02-20 로무 가부시키가이샤 Switching converter and its control circuit, lighting device using same, electronic device
US10467967B2 (en) 2016-02-12 2019-11-05 Rohm Co., Ltd. Driving circuit of LED for liquid crystal backlight, control circuit thereof, and electronic device

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7525820B2 (en) 2006-04-12 2009-04-28 Rohm Co., Ltd. Inverter
US7778047B2 (en) 2006-04-12 2010-08-17 Rohm Co., Ltd. Inverter
US7558091B2 (en) 2006-12-14 2009-07-07 Sharp Kabushiki Kaisha Switching power supply apparatus
EP2164160A2 (en) 2008-09-11 2010-03-17 Funai Electric Co., Ltd. Voltage reduction detection circuit and switching power supply system
US8289740B2 (en) 2008-09-11 2012-10-16 Funai Electric Co., Ltd. Voltage reduction detection circuit and switching power supply system
CN102298907A (en) * 2010-06-28 2011-12-28 罗姆股份有限公司 Load driving circuit, light-emitting device and display device using the same
US8742691B2 (en) 2010-06-28 2014-06-03 Rohm Co., Ltd. Load driving circuit
CN102298907B (en) * 2010-06-28 2015-05-06 罗姆股份有限公司 Load driving circuit, light-emitting device and display device using the same
US9277612B2 (en) 2013-10-07 2016-03-01 Rohm Co., Ltd. Switching converter, control circuit and control method thereof, and lighting device and electronic apparatus using the same
US9402287B2 (en) 2014-11-04 2016-07-26 Rohm Co., Ltd. Switching converter with light source dimming function
US9401649B2 (en) 2014-11-04 2016-07-26 Rohm Co., Ltd. Switching converter
US9750113B2 (en) 2015-05-01 2017-08-29 Rohm Co., Ltd. Driving circuit of light source and control circuit thereof, driving method of light source, lighting apparatus, and electronic device
US9763295B2 (en) 2015-06-02 2017-09-12 Rohm Co., Ltd. Switching converter and lighting device using the same
US9723668B2 (en) 2015-06-05 2017-08-01 Rohm Co., Ltd. Switching converter and lighting device using the same
KR20180017076A (en) 2015-06-08 2018-02-20 로무 가부시키가이샤 Switching converter and its control circuit, lighting device using same, electronic device
US10348196B2 (en) 2015-06-08 2019-07-09 Rohm Co., Ltd. Switching converter
US10467967B2 (en) 2016-02-12 2019-11-05 Rohm Co., Ltd. Driving circuit of LED for liquid crystal backlight, control circuit thereof, and electronic device

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