JPS645985Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a switching power supply device used in communication equipment and the like.

[Conventional technology]

In general, switching power supplies have the advantages of being smaller, lighter, and more efficient than so-called dropper power supplies. However, on the other hand, there is a drawback that noise caused by the switching operation causes great harm to communication equipment. To counter this noise, the noise that is superimposed and infiltrated on the input AC line is usually absorbed by a chain yoke and a capacitor, and the noise generated by switching is absorbed by two capacitors whose middle point is grounded using the same yoke. Some measures have been taken.
(Published by Sanpo Publishing Co., Ltd., Electronic Science Blue Books "Switching Regulator").

However, even if the above measures are taken, noise leaks to the output side parts, wiring, outer box, etc. due to the stray capacitance of the transformer windings, electronic components, wiring, etc. used in the switching power supply, and the input side There is a problem in that a noise voltage is generated between the circuit and the output side circuit, and high frequency noise is leaked to the input commercial power supply.

[Problem that the invention attempts to solve]

This idea was made in view of the above circumstances.
To provide a switching power supply that prevents high-frequency noise from leaking into a commercial power supply.

[Means and actions for solving problems]

The present invention involves winding an auxiliary winding on the primary side of the transformer that is in antiphase to the main winding, connecting one end of the auxiliary winding to the input connection point of the main winding, and connecting the other end via a capacitor. It is connected to the negative side of the common connection point of the DC output terminals supplied to the load, and the voltage that generates noise is neutralized by the anti-phase voltage generated in the auxiliary winding.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

In the drawing, AC is an alternating current power source, and this alternating current power source
The AC is connected to the AC input terminal of the bridge rectifier circuit RECT ₁ via the input filters L ₁ , L ₂ and capacitors C ₁ , C ₂ , C ₃ . A low impedance smoothing capacitor C ₄ is connected between the DC output terminals of the rectifier circuit RECT ₁ with the polarity shown.

The capacitors C ₂ and C ₃ are connected in series, and their common connection point is connected to a negative bus BU ₁ connected to the negative side of the bridge rectifier RECT ₁ . The positive side of the bridge rectifier circuit RECT ₁ is connected to one end of the main winding tp of the transformer T ₁ . Main winding
The other end of tp is connected to the collector of transistor _TR1 , which serves as the main switching element. transistor
The base of TR ₁ is connected to the positive side of rectifier circuit RECT ₁ via a series circuit of resistors R ₁ and R ₂ . Also,
The emitter of transistor TR ₁ is a current detection resistor.
Connected to the negative bus BU ₁ through a parallel circuit of R ₃ and capacitor C ₅ .

TR ₂ is a transistor, this transistor TR ₂
The base of is connected to the emitter of transistor TR ₁ through a parallel circuit of resistor R ₄ and capacitor C ₆ ,
The collector is connected to the base of transistor _TR1 . Further, the emitter of the transistor _TR2 is connected to the negative bus line _BU1 . In addition to the main winding tp, the transformer _T1 is wound with a control winding td and an auxiliary winding tr that obtains a voltage in phase opposite to that of the main winding.

One end of the control winding td is connected to the negative bus BU ₁ , which is the input common potential point, and the other end is commonly connected to the resistors R ₁ and R ₂ through a parallel circuit of the rectifier RECT ₂ and capacitor C ₇ with the polarity shown. Connected to points. A series circuit of a rectifier RECT ₅ of the polarity shown and a capacitor C ₁₂ is connected between the control winding td. Also the main winding tp
A series circuit of a capacitor C ₁₃ and a resistor R ₉ is connected between them. One end of the first winding to of the output winding of the transformer T ₁ is connected to the load via the rectifier RECT ₃ and the choke L ₃
It is connected to the output terminal O ₁ to which the LD is connected, and the other end is directly connected to the output terminal O ₂ . Note that C ₈ and C ₉ are smoothing capacitors. One end of the auxiliary winding tr is connected to the main winding tp, and the other end is connected to a small capacitor
It is connected to the negative line BU ₂ , which is the output common potential point, which is connected to the output terminal O ₂ via C ₀ . The capacitance of the capacitor C ₀ is related to the amount of electromagnetic integration between input and output and the ratio of the number of turns between the main winding tp and the auxiliary winding tr.

OA is a differential amplifier, and the negative input terminal of this amplifier OA is a resistor R ₅ that divides the voltage between the output terminals O ₁ and O ₂ .
Connected to the common connection point of R ₆ . The positive input terminal of amplifier OA is connected to the common connection point of resistor _R7 and Zener diode Z. C ₁₁ is a capacitor.
The output terminal OU of the differential amplifier OA is connected to the cathode side of the light emitting diode LED of the photocoupler FC,
The anode side is a rectifier connected to one end of the winding t1.
Connected to the positive side of RECT ₄ . This positive side is connected to resistor _R7 and differential amplifier OA. winding t
The other end of 1 is connected to the negative line BU ₂ ,
Zener diode Z and one end of each capacitor _C11 are connected. _C10 is a capacitor. The collector of the phototransistor PHT of the photocoupler FC is connected to the common connection point of the rectifier RECT ₁₅ and the capacitor C ₁₂ , and the emitter is connected to the base of the transistor TR ₂ via a resistor R ₈ .

Next, the operation of the above embodiment will be described. The DC rectified by the bridge rectifier circuit RECT ₁ is smoothed by the capacitor C ₄ and then connected to the main winding tp and the transistor.
Supplied between TR ₁ . In addition, the direct current has a resistance R ₁ ,
The transistor TR ₁ is turned on because it is supplied to the base of the transistor TR ₁ via R ₂ . As a result of this turning on, the collector current of the transistor TR ₁ flows through the current detection resistor R ₃ to the negative terminal of the capacitor C ₄ . At this time, the transformer T ₁ is excited by the main winding tp. This excitation generates a voltage in the control winding td. This voltage is rectified by the rectifier RECT ₂ and supplied to the base of the transistor TR ₁ to amplify and saturate the base current. As the excitation current of the main winding tp increases, the current of the resistor R ₃ increases. When this current increase causes the voltage drop across resistor _R3 to reach the base-emitter operating voltage of transistor _TR2 , transistor _TR2 is turned on. When this transistor TR ₂ is turned on, the base and emitter of the transistor TR ₁ are short-circuited, and the transistor TR ₁
is off. When the transistor TR ₁ turns off, a voltage is induced in the first winding to of the secondary side of the transformer T ₁ . This voltage is rectified and smoothed by the rectifier RECT ₃ and output to the output terminal to which the load LD is connected.
Connected to O ₁ and O ₂ .

Note that when the transformer _T1 is de-energized, the voltage phase of the control winding td is reversed. Therefore, the transistor TR ₂ is turned off, current is again supplied to the base of the transistor TR ₁ , and the main winding tp is again excited. In this way, the excitation operation of the main winding tp is repeated by the switching operation of the transistor _TR1 , and a DC output appears at the output terminals _O1 and _O2 . Since this DC output varies depending on the load LD, it can be kept constant by the following operation of the error control circuit. The voltage divided by the resistors R ₅ and R ₆ is compared with the reference voltage of the Zener diode Z by the differential amplifier OA, and the error control current obtained from the comparison is supplied to the photocoupler FC to control the photocoupler FC. Ru. This photo coupler
The control current of the FC is passed through the resistor _R8 to the transistor
Supplied with TR ₂ base. When this control current increases, the bias voltage developed across resistor R ₄ and capacitor C ₄ is added to the voltage developed across resistor R ₃ by the current in the main winding tp, so that transistor TR ₂
is turned on. By turning on this transistor TR ₂ , transistor TR ₁ turns off at a small current, and
Reduce the excitation of transformer T ₁ . Therefore, the output voltage generated on the secondary side is reduced and the output voltage is adjusted.

Although a DC voltage is obtained at the output terminals O ₁ and O ₂ as described above, a high voltage is generated in the main winding tp by turning on and off the transistor TR ₁ . However, a voltage is generated in the auxiliary winding tr that is in opposite phase to the voltage generated in the main winding tp. This voltage is passed through the capacitor C ₀ to the negative line BU ₂ of the common connection point on the DC output side.
, so the input and output sides of transformer T ₁ are neutralized. As a result, the voltage between the input and output is generated by coupling with the output side electronic components, wiring, outer box CA, etc. through the stray capacitance of the transformer T ₁ windings, electronic components, wiring, etc. connected to the input side circuit. unwanted noise voltages are reduced or eliminated. In addition, since the common connection point of capacitors C ₂ and C ₃ is connected to the negative terminal of capacitor C ₄ , the input line is integrated with the rectifier circuit and becomes a common potential point on the input side, and the effect of the auxiliary winding tr is At the same time, it is possible to prevent noise from flowing to the input power line side.

[Effect of idea]

As described above, according to the present invention, it is possible to neutralize the high voltage generated in the main winding during the operation of the switching element, and eliminate the noise voltage generated between the input side circuit and the output side circuit. It is possible to eliminate the noise that flows into the

[Brief explanation of drawings]

The drawing is a circuit diagram showing an embodiment of the present invention. AC is an alternating current power supply, RECT ₁ is a bridge rectifier circuit,
RECT ₂ , RECT ₃ , RECT ₄ , RECT ₅ are rectifiers,
_T1 is a transformer, _TR1 and _TR2 are transistors, FC is a photocoupler, and OA is a differential amplifier.

Claims (1)

[Scope of utility model registration request] In a switching power supply device that converts alternating current into direct current and supplies it to the main winding of a transformer, inserts a main switching element in the direct current supply path of the main winding, and controls switching of the main switching element, the main winding and An auxiliary winding that obtains an antiphase voltage is wound around the transformer, one end of which is connected to the input common potential point of the main winding, and the other end of the auxiliary winding is connected to the output winding of the transformer. A switching power supply device that is connected via a capacitor to a common potential point on the output side of a rectifier circuit that supplies DC output to a load.