JPH04285464A - Power source circuit - Google Patents

Abstract

PURPOSE:To efficiently supply power to a controller so as to realize a DC/DC converter having a high conversion efficiency even in a range having a low output voltage. CONSTITUTION:Power for starting an operation in a converter CNV is supplied not directly from a power source E but to a controller CNT of the converter CNV through a switch SW. Thus, after the converter CNV starts operating, power is supplied from an auxiliary winding TA of a transformer T to the controller CNT, the supplied power is detected by a detector DET, the switch SW is opened, and power consumption at a circuit side for supplying power for starting the operation is reduced.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a power supply circuit that supplies power to a control circuit in a DC-DC converter, etc., and more specifically, the present invention relates to a power supply circuit that supplies power to a control circuit such as a DC-DC converter. The present invention relates to a power supply circuit that enables improvement of conversion efficiency of DC-DC converters and the like.

0002

2. Description of the Related Art A DC-DC converter is a device for converting input voltage (power) into a desired format, for example, another voltage, or for outputting the isolated voltage.

As a conventional example of such a DC-DC converter, a circuit configuration shown in FIG. 4 is generally known. In the figure, E is an external power supply, CNV is a converter circuit, I+ is its positive input terminal, I- is its negative input terminal, O+ is its positive output terminal, O- is its negative output terminal, R is a resistor, C is a capacitor, CNT is a control circuit, CV is its power input terminal, CE is its ground terminal, CT is its control output terminal, D is a diode, T is a transformer, and TP is its output winding. TD is its driving winding, TA is its auxiliary winding, TRS is a switching transistor, and REC is a rectifier circuit.

In this conventional connection configuration, a power source E is connected between the positive input terminal I+ and the negative input terminal I- of the converter circuit CNV, and the transformer T is driven between the input terminals I+ and I-. The winding TD and the switching transistor TRS are connected in series. The control output terminal CT of the control circuit CNT is connected to the base of the transistor TRS, and one end of the auxiliary winding TA of the transformer T is connected to the power input terminal CV of the control circuit CNT through a rectifying diode D.
The other end of the auxiliary winding TA and the ground terminal CE of the control circuit CNT are connected to the negative input terminal I-. Further, the power input terminal CV of the control circuit CNT is connected to the positive input terminal I+ through a resistor R, and to the negative input terminal I- through a capacitor C. The output winding TP of the transformer T is connected to the output terminals O+, O through the rectifier circuit REC.
– is connected to.

Next, the operation of the above-mentioned conventional example will be explained. The control circuit CNT controls the opening and closing of the switching transistor TRS using its control output CT, thereby converting the current supplied from the power source E to the drive winding TD of the transformer T into an intermittent or alternating current. The alternating current is induced into the output winding TP, rectified by the rectifier circuit REC, that is, converted into direct current, and output. At the same time, the alternating current is also induced in the auxiliary winding TA, rectified by the diode D, smoothed by the capacitor C, and supplied to the power input terminal CV as a power source for the control circuit CNT.

By the way, in the above operation, immediately after the power supply E is connected, the control circuit CNT is not operating, and therefore no output from the auxiliary winding TA can be obtained. Therefore, the auxiliary winding TA
Power is not supplied to the control circuit CNT from then on, and if this continues, it will not be able to operate thereafter, and the circuit operation will not start (will not start up) after all. For this reason, conventionally, the minimum current required to start the operation of the control circuit CNT was applied to the auxiliary winding T.
In order to be able to supply even when there is no output from A, the power supply E is directly supplied to the control circuit CNT via the resistor R.

[0007]

[Problems to be Solved by the Invention] However, in the conventional DC-DC converter described above, the control circuit C
A current constantly flows through the resistor R, which is necessary only for starting the operation of the NT, even after the start of the operation, resulting in a problem that unnecessary power consumption occurs all the time. Especially the output terminal O+,
In a region where the output power from O- is small, the above power consumption cannot be ignored and becomes a problem that deteriorates the conversion efficiency as a DC-DC converter.

The present invention has been made to solve the above problems, and its purpose is to provide a control circuit for the DC-DC converter with high conversion efficiency even in a region where the output power is small. It is an object of the present invention to provide a power supply circuit that can efficiently supply power to a user.

[0009]

[Means for Solving the Problems] In order to achieve the above object, in the power supply circuit of the present invention, a control circuit for a converter circuit that converts voltage or power supplied from an external power supply into a desired format and outputs the converted voltage or power is provided. a power supply circuit that supplies power to the control circuit from the external power supply via the switching means; comprising a second supply means for supplying power to the control circuit, and a detection means for detecting the presence or absence of power supply from the second supply means,
When the detection means detects the power supply from the second supply means, the output of the detection means operates the opening/closing means in the first supply means to stop the power supply from the first supply means. It is said that

0010

[Operation] In the power supply circuit of the present invention, power for starting the operation of the converter circuit is supplied not directly from an external power source but through the opening/closing means of the first supply means, so that the operation of the converter circuit is started and the power for starting the operation of the converter circuit is supplied to the converter circuit. When power supply starts from the first supply means, the opening/closing means is operated to stop the power supply from the first supply means. As a result, unnecessary power consumption after the converter circuit operates can be reduced to zero or significantly in a circuit for supplying the necessary power at the start of operation.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a first embodiment showing the basic configuration of the present invention. In the figure, SW is a switch, S1 and S2 are terminals of the switch, SC is a control terminal of the switch, and DET is a detection circuit.
I represents its input terminal, DR its reference terminal, and DO its output terminal. The other constituent parts are the same as those shown in FIG. 4 with the same symbols.

The circuit configuration in this embodiment includes a switch S
It is the same as the conventional example shown in FIG. 4 except for W, resistor R, and detection circuit DET. In this embodiment, S1 and S2 of the switch SW
The terminal side and the resistor R are connected in series to form the power input terminal CV of the control circuit CNT and the positive input terminal I of the converter circuit CNV.
Connect between +. On the other hand, in the detection circuit DET, the input terminal DI is connected to the power supply input terminal CV side of the control circuit CNT.
The output terminal DO is connected to the control terminal SC of the switch SW, the reference terminal DR thereof, and the negative input terminal I- of the converter circuit CNV, and the switch SW is connected to the detection circuit D
Opening/closing is controlled by ET. Further, as described above, the auxiliary winding TA of the transformer T is connected to the power input terminal CV of the control circuit CNT via the rectifying diode D. The resistor R and the switch SW constitute a first means for supplying power to the control circuit CNT, and the auxiliary winding TA of the transformer T constitutes a second means for supplying power to the control circuit CNT.

The operation and effect of the first embodiment configured as above will be described.

The detection circuit DET monitors the voltage supplied to the control circuit CNT via the input terminal DI and the reference terminal DR, and generates an output at the output terminal DO if this voltage is below a preset threshold. This output DO is connected to the control terminal SC of the switch SW, and as a result, the switch SW is closed, and current is supplied from the power source E to the control circuit CNT via the resistor R (first supply means). Converter CNV starts operating.

When converter CNV starts operating, current is supplied from auxiliary winding TA of transformer T (second supply means). Due to this current supply, the voltage supplied to the control circuit CNT increases, and when the voltage becomes equal to or higher than the threshold value of the detection circuit DET, the output of the output terminal DO of the detection circuit DET is stopped, and the switch SW is opened. The direct current supply from the power source E through the resistor R is stopped. Therefore,
Unnecessary power consumption in resistor R no longer occurs. Even if switch SW is opened, the current for operating control circuit CNT is then supplied from auxiliary winding TA of transformer T, so converter CNV can continue to operate.

To further explain the explanation, the resistor R is connected so that the voltage supplied to the control circuit CNT when the switch SW is closed and no current is supplied from the auxiliary winding TA is equal to or higher than the minimum voltage VST necessary for its operation. In addition, the threshold value of the detection circuit DET is selected to be equal to the converter circuit CNV.
The voltage is selected so that the voltage VOP applied to the control circuit CNT when the converter operates and current is supplied from the auxiliary winding TA is between the voltage VST before the converter starts operating.

Note that the resistor R in the above explanation can be modified in various ways, such as a constant current circuit, a Zener diode, or even a series regulator. It can be applied regardless. Furthermore, it goes without saying that the current supply from the auxiliary winding TA may be detected by other methods than voltage detection, such as current detection.

Next, a second embodiment showing a specific configuration of the present invention will be described.

FIG. 2 shows the circuit configuration diagram. In the figure, TR is an npn type transistor, DREV is a diode inserted as necessary, VRF is a reference voltage circuit for generating a reference voltage, RB is a resistor that is a component of the circuit, and ZD is a component of the same. It is a Zener diode. The other constituent parts are the same as those shown in FIG. 4 with the same symbols.

The circuit configuration of this embodiment is the same as that of the conventional example shown in FIG. 4, except for the transistor TR, diode DREV, and reference voltage circuit VRF. As for the transistor TR, its collector is connected to the positive input terminal I+ of the converter circuit CNV, and its emitter is connected to the power supply input terminal CV side of the control circuit CNT through the diode DREV. Regarding the reference voltage circuit VRF, a resistor RB and a Zener diode ZD are connected in series, and the resistor RB side is connected to the positive input terminal I+ side of the converter circuit CNV.
, I-, and the connection point between the resistor RB and the Zener diode ZD is connected to the base of the transistor TR. In this embodiment, the transistor TR constitutes the first means for supplying power to the control circuit CNT having an opening/closing means, and the transistor TR and the reference voltage circuit VR
F constitutes a detection means, and the auxiliary winding TA of the transformer T constitutes a second means for supplying power to the control circuit CNT.

The operation and effect of the second embodiment configured as above will be described.

The resistor RB and the Zener diode ZD of the reference voltage circuit VRF constitute a constant voltage circuit, and apply a constant Zener voltage VZD to the base of the transistor TR. Here, the Zener voltage VZ of the Zener diode ZD
D is the minimum voltage V required for the control circuit CNT to operate
is greater than the sum of voltage drops occurring in ST, transistor TR, and diode DREV, and converter circuit C
The value is selected to be greater than or equal to the sum of the voltage VST supplied to the control circuit CNT when NV is operating, and the voltage drops occurring in the transistor TR and diode DREV. In the following operation description, for the sake of simplicity, it is assumed that the voltage drop occurring in the transistor TR and the diode DREV is zero.

In this embodiment, before the converter circuit CNV starts operating, the transistor TR is connected to the power source E.
operates as an emitter follower using the power source as the power source, and outputs the Zener voltage VZD, that is, the power input terminal C of the control circuit CNT.
Supply to V. As a result, the control circuit CNT operates,
Converter circuit CNV starts operating. When the converter circuit CNV operates, the control circuit CN is connected from the auxiliary winding TA.
Since the voltage supplied to T increases, transistor TR
The base-emitter circuit of is reverse biased, so that transistor TR is turned off, and direct current supply from power supply E through transistor TR is stopped. diode DR
For EV, the above reverse bias is the base of the transistor TR.
It is inserted as necessary to prevent breakdown when the breakdown voltage between emitters is exceeded.

In the above, the resistor RB can have a high resistance since its load is an emitter follower circuit, that is, almost no current flows, and the power consumption can be reduced to a negligible value. Furthermore, since the transistor TR is turned off after the converter circuit CNV operates, there is no loss in the transistor TR, etc., and the only unnecessary power consumption is the power consumption of the resistor RB, which is negligible. In this way, in the second embodiment, the transistor T
R represents the switch SW and the detection circuit DE in the first embodiment.
It realizes both functions of T. The configuration shown in this example is
A major advantage is that the circuit for realizing both functions does not require a power source for its operation.

Next, a third embodiment of the present invention will be described.

FIG. 3 shows a circuit diagram thereof. This embodiment is an embodiment in which a field effect transistor is used in place of the transistor TR of the second embodiment. In the figure, FET is a field effect transistor, RB is a resistor, and ZD is a Zener diode. The other constituent parts are the same as those shown in FIG. 4 with the same symbols. The field effect transistor FET in this embodiment is a depletion type, that is, when the gate and source are reverse biased to a predetermined voltage, so-called pinch-off voltage VP, or higher, the drain and source transistors are reverse biased.
If the current does not flow between the sources, and if the current is less than that, use a type that allows current to flow.

The circuit configuration in this embodiment includes a field effect transistor FET, a resistor RB, and a Zener diode ZD.
This is the same as the conventional example shown in FIG. 4, except for. For the field effect transistor FET, the drain is connected to the converter circuit C
Connect to the positive input terminal I+ of NV, and connect the source to the control circuit C.
Connect to the NT power input terminal CV. Further, the resistor RB is connected between the gate and source of the field effect transistor FET, and the Zener diode ZD is connected between the gate of the field effect transistor FET and the ground terminal CE side of the control circuit with its cathode side as the gate side.

The operation and effect of the third embodiment configured as above will be described.

Initially, it is assumed that the Zener voltage VZD of the Zener diode ZD is 0 V, and the value of the resistor RB is infinite, that is, both elements are not inserted or connected. The gate of the field effect transistor FET is connected to the ground terminal CE of the control circuit CNT, and the pinch-off voltage VP (actually slightly lower voltage) is outputted to the source of the field effect transistor FET to control the control circuit. It is supplied to the circuit CNT.

[0031] As a result, control circuit CNT operates, and converter CNV starts operating. When the converter CNV operates, current is supplied from the auxiliary winding TA of the transformer T, the voltage supplied to the control circuit CNT increases, and the reverse bias between the gate and source of the field effect transistor FET increases by the increased voltage. However, if the value is selected to be equal to or higher than the pinch-off voltage VP, the field effect transistor FET is turned off, and the field effect transistor FET is turned off.
The direct current supply from the power supply E through is completely cut off.

In this embodiment as well, the resistor RB can have a high resistance, and the current can be supplied to the Zener diode ZD from the power supply side of the control circuit CNT. Therefore, the power consumption in the resistor RB can be reduced by the second It is possible to further reduce the amount than in the example. In the above, if a field effect transistor FET having a desired pinch-off voltage VP cannot be obtained, the substantial pinch-off voltage can be adjusted by the Zener diode ZD and the resistor RB. That is, by supplying current to the Zener diode ZD through the resistor RB, the gate voltage is changed to the Zener voltage V.
ZD can be increased, and the actual pinch-off voltage V
P can be increased by the Zener voltage VZD.

In the above description of each embodiment, the current is supplied to the control circuit CNT from the auxiliary winding TA of the transformer T after the operation of the converter circuit CNV. You can also insert a diode to prevent backflow if necessary. Further, although the converter normally has a feedback circuit for stabilizing the output voltage, it is omitted in each of the above embodiments. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with the gist thereof.

[0034]

As is clear from the above description, according to the power supply circuit of the present invention, the current for switching the operation of the converter circuit is supplied not directly from the power supply but through the switching means, and the current is supplied from the second supply. After the converter circuit operates until power is supplied from the means, the switching means is opened, so that the power consumption after the circuit that supplies power for starting the operation starts operating can be significantly reduced. This provides the advantage that power can be efficiently supplied to the control circuit of the converter circuit. In other words, a converter with high conversion efficiency can be constructed. The present invention is particularly effective in areas where the load is small because the power consumption of the control circuit-related portions greatly affects the conversion efficiency.

[0035] Furthermore, according to the second to fourth aspects of the present invention, the power consumption after the start of operation of the circuit that supplies power for starting the operation can be reduced to zero or significantly increased by a simple circuit. can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a first embodiment showing the basic configuration of the present invention.

FIG. 2 is a circuit configuration diagram of a second embodiment showing a specific configuration of the present invention.

FIG. 3 is a circuit configuration diagram of a third embodiment showing another specific configuration of the present invention.

[Fig. 4] Circuit configuration diagram for explaining conventional technology

[Explanation of symbols]

E...power supply, CNV...converter circuit, T...transformer, T
P...Output winding, TD...Drive winding, TA...Auxiliary winding, TR
S...switching transistor, REC...rectifier circuit,
CNT...control circuit, D...diode, R...resistance, C...capacitor, SW...switch, DET...detection circuit, VRF
...Reference voltage circuit, RB...Resistor, ZD...Zener diode, TR...Transistor, DREV...Diode, FE
T...Field effect transistor.

Claims (4)

[Claims] 1. A power supply circuit that supplies power to a control circuit of a converter circuit that converts voltage or power supplied from an external power supply into a desired format and outputs the converted voltage or power, the circuit comprising: a switching means from the external power supply; a first supply means for supplying power to said control circuit through said converter circuit; a second supply means for supplying power to said control circuit from output power obtained as a result of operation of said converter circuit; detection means for detecting the presence or absence of power supply from the second supply means, and when the detection means detects power supply from the second supply means, the opening/closing means in the first supply means is operated by the output of the detection means. A power supply circuit characterized in that the power supply from the first supply means is stopped. 2. The power supply circuit according to claim 1, wherein the first supply means includes a detection means, and comprises a reference voltage circuit and an emitter follower circuit whose power source is an external power supply and whose input is the output of the reference voltage circuit. A power supply circuit characterized in that the voltage supplied to the control circuit when power is supplied from the second supply means is set higher than the voltage supplied to the control circuit when power is supplied from the first supply means. . 3. The power supply circuit according to claim 1, wherein the first supply means includes a detection means, an external power supply is used as a voltage source, an input is connected to ground or a reference voltage of a reference voltage circuit, and the source is connected to an output. the voltage supplied to the control circuit when power is supplied from the second supply means is higher than the voltage supplied to the control circuit when power is supplied from the first supply means; A power supply circuit characterized by: 4. The power supply circuit according to claim 3, wherein power for the reference voltage circuit is supplied from the same system as a power supply for the control circuit.