JPH04372575A - Switching regulator - Google Patents

Abstract

PURPOSE:To prevent generation of a wasteful power loss generated at a starting resistor by separating the resistor from a control IC after the IC is started. CONSTITUTION:When a control IC 5 is started and a MOSFET 4 is controlled ON, OFF at a predetermined time ratio, a pulse current flows to a primary winding 3P, an auxiliary winding voltage is generated in an auxiliary winding 3A, and a capacitor 6C is charged through a diode 6D. The auxiliary winding voltage is applied to a gate of a triac 14, which is in a continuity, and a base B of a transistor 12 is lowered to a substantially ground potential. As a result, a current flowing to a starting resistor 10 is interrupted. Accordingly, thereafter, a power source voltage VCC is supplied from a power source 6 to the IC 5 to perform a normal operation, and power loss of a starting resistor 10 becomes zero. As a consequence, a power conversion efficiency of a switching regulator can be improved, for example, by about 1 to 2% as compared with that of prior art.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is applicable to forward type or flyback type power supplies, which first convert AC power to DC power, perform PWM modulation control, and then convert it to constant voltage DC power and output it. The present invention relates to a separately excited switching regulator, and particularly to a switching regulator equipped with a circuit for reducing power loss in a starting resistor of a control IC that controls PWM modulation.

0002

[Prior Art] FIG. 3 is a connection diagram showing a conventional forward-type separately excited switching regulator.
On the output side of the diode bridge 1 that converts AC to DC, a smoothing capacitor 2 whose one end is grounded, a primary winding 3P of an isolation transformer 3, and a drain connected to the primary winding.
An insulated gate field effect transistor with a grounded source (
A closed circuit is formed with MOSFET) 4, and control IC 5
The signal 5S that controls the primary winding current by PWM modulation is MOS
By outputting to gate G of FET4, MO
The SFET is turned on and off at a predetermined time ratio, and a square wave pulse current flows through the closed circuit. In addition, the pulse current induced in the secondary winding having the same polarity as the primary winding with a magnitude based on the turns ratio is generated by the diodes Ds, Dp, the reactor L8,
A forward circuit 8 comprising a capacitor C8 converts the voltage into an averaged constant DC voltage and supplies it to an external load.

On the other hand, the input terminal 5A of the power supply voltage Vcc of the control IC 5 is connected to a power supply circuit 6 that converts the voltage of the auxiliary winding 3A of the isolation transformer 3 into direct current using a diode 6D and a capacitor 6C, and a diode bridge. A starting resistor 10, one end of which is connected to the output side of the control IC 5, is connected, and when the control IC 5 is started, a power supply voltage Vcc is supplied through the starting resistor 10, and after starting, a power supply voltage Vcc is supplied from both the starting resistor 10 and the power supply circuit 6. Power supply voltage Vcc is supplied. In addition, the forward circuit 8
The current flowing through is detected by the current detector 9 as a voltage drop across the detection resistor R9, and the detected value is compared with a reference value in the control IC, the error is amplified, and a control signal with a duty ratio corresponding to the difference from the reference value is generated. 5S is supplied to the gate of MOSFET4.

0004

[Problems to be Solved by the Invention] In the above-mentioned prior art, the starting resistor 10 is activated by the control IC 5 and the auxiliary winding 3
It becomes unnecessary when a voltage is steadily generated at A (when the switching regulator starts steady operation). However, in conventional devices, even when the switching regulator is in steady operation, the starting resistor 10 is connected to the control IC.
It is connected to the input terminal 5A of the power supply voltage and continues to supply a part of the power supply current to the control IC. Therefore, starting resistance 1
Since power loss occurs constantly at 0, and the value greatly exceeds the power loss generated in the power supply circuit 6 with low internal resistance, for example, a switching regulator with a constant output of about 100 W has a power conversion efficiency of 1 A problem arises in which the power decreases by about 2%. In particular, switching regulators can reduce the size of magnetic components such as isolation transformers, smoothing capacitors, etc. by increasing the switching frequency to, for example, 20 KHz or higher, and can regulate the output voltage by the switching operation of MOSFETs. This power supply device is characterized by its ability to reduce power loss, and an important issue is to prevent wasteful power consumption in the starting resistor and the resulting decrease in power conversion efficiency.

[0005] This invention aims to prevent wasteful power loss caused by the starting resistor by separating the starting resistor from the controlling IC after the controlling IC is started.

[0006]

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, a field effect transistor connected in series between a diode bridge and a primary winding of an isolation transformer is turned on and off. A control IC that rectifies the starting resistor connected between the input terminal of the power supply voltage and the output side of the diode bridge, and the auxiliary winding voltage of the isolation transformer and supplies the rectified power to the input terminal. The device including a circuit includes a cutoff circuit that detects generation of the auxiliary winding voltage after the control IC is started and disconnects the starting resistor from the input terminal of the power supply voltage.

The cutoff circuit also includes a transistor whose collector and emitter are connected in series between the starting resistor and the power supply voltage input terminal of the control IC, and a series resistor which is connected in parallel to the DC output side of the diode bridge. and a series circuit of a triac, the gate of the triac being connected to an auxiliary winding of an isolation transformer, and the base of the transistor being connected to an intermediate connection point of the series circuit.

Furthermore, the resistance value of the series resistor is made to be about 10 times or more higher than that of the starting resistor.

[0009]

[Operation] In the configuration of the present invention, after the control IC is started, the generation of the auxiliary winding voltage is detected and the starting resistance is changed to the control IC.
By providing a cutoff circuit that disconnects the power supply voltage from the input terminal of the switching regulator, the power loss that occurs in the starting resistor during steady operation of the switching regulator is eliminated. Compared to this, a function improved by about 1 to 2% can be obtained.

[0010] The cutoff circuit also includes a transistor whose collector and emitter are connected in series between the starting resistor and the power supply voltage input terminal side of the control IC, and a series resistor connected in parallel to the DC output side of the diode bridge. The gate of the triac is connected to the auxiliary winding of the isolation transformer, and the base of the transistor is connected to the intermediate connection point of the series circuit. The triac senses and becomes conductive,
Since the base current of the transistor is bypassed to the ground side, the transistor is turned off and the current flowing to the starting resistor is cut off. It is possible to obtain a cut-off circuit with a suitable configuration.

Furthermore, if the resistance value of the series resistor is made to be about 10 times or more higher than that of the starting resistor, the current flowing to the series resistor via the triac during steady operation of the switching regulator is suppressed, so that the breaking circuit This provides the ability to significantly reduce power loss.

0012

EXAMPLES The present invention will be explained below based on examples. FIG. 1 is a connection diagram showing a forward type separately excited switching regulator according to an embodiment of the present invention, and the same reference numerals are given to the same components as in the prior art.
Omit duplicate explanations. In the figure, the cutoff circuit 11 includes a series circuit of a series resistor 13 and a triac 14 connected in parallel to the DC output side of the diode bridge 1 whose one end is grounded, a starting resistor 10, and an input terminal 5A for the control IC power supply voltage. The base G of the transistor 12 is connected to the intermediate connection point m between the series resistor and the triac, and the collector C and emitter E are connected between the transistor 12 (npn transistor in the figure). The gate G of is connected to the non-ground terminal of the auxiliary winding 3A. Further, the resistance value of the series resistor 13 is set to a resistance value ten times or more higher than that of the starting resistor 10.

In the switching regulator equipped with the cutoff circuit 11 configured as described above, when the control IC 5 is not activated, the MOSFET 4 does not operate and the auxiliary winding voltage is also zero, so the triac 14 is in the off state. . Further, the capacitor 6C of the power supply circuit 6 is also in an uncharged state, and the emitter of the transistor 12 is also equivalently in a grounded state. Therefore, a forward voltage is applied between the base and emitter of the transistor via the series resistor 13, and a forward voltage due to the difference in potential drop between the resistors 10 and 13 is applied between the collector and the base. The transistor 12 becomes conductive, the capacitor 6C is charged by the emitter current controlled to a predetermined value by the starting resistor 10, the power supply voltage Vcc is applied to the power supply voltage input terminal 5A of the control IC, and the control IC 5 is started. .

When the control IC starts up and controls the MOSFET 4 to turn on and off at a predetermined time ratio, a pulse current flows through the primary winding, and an auxiliary winding voltage is generated in the auxiliary winding 3A, which is applied via the diode 6D. At the same time, the auxiliary winding voltage is applied to the gate of the triac 14, the triac becomes conductive, and the base of the transistor 12 drops to approximately ground potential. As a result, a reverse bias voltage is applied between the base and emitter of the transistor, the transistor 12 turns off, and the starting resistor 10
The current flowing through is cut off. Therefore, after that, the power supply voltage Vcc is supplied from the power supply circuit 6 to the control IC to perform steady operation, and the power loss of the starting resistor 10 becomes zero. Further, the power supply circuit 6 has a low internal resistance, and its power loss is significantly lower than that of the starting resistor. Furthermore, due to the conduction of the triac, the series resistor 13 always has a diode.
Although the output DC voltage of the bridge is applied, it can be suppressed to a small value by making the resistance value of the series resistor several tens of times that of the starting resistor 10. As a result, there is an advantage that the power conversion efficiency of the switching regulator can be improved, for example, by about 1 to 2% compared to the conventional one.

FIG. 2 is a connection diagram showing a flyback type separately excited switching regulator according to a different embodiment of the present invention.The difference from the above embodiment is that the isolation transformer 30 of the switching regulator is Its primary winding 30
P and the polarity of the secondary winding 30S are formed in opposite directions to each other,
When the MOSFET 4 is off, the energy stored in the isolation transformer 30 is released, and the primary winding current flows through the diode 31, and the secondary winding current is rectified by the rectifier circuit 31, and the average It is formed in a so-called flyback type that supplies constant voltage DC power to an external load.
By providing a cutoff circuit 11 consisting of a series resistor 13 and a triac 14, the auxiliary winding voltage is detected and the current flowing to the starting resistor is cut off, similarly to the previous embodiment, and the starting resistor is used during steady operation. The resulting power loss can be eliminated.

[0016]

[Effects of the Invention] As described above, the present invention is configured to provide a cutoff circuit that detects the generation of auxiliary winding voltage after the control IC is started and disconnects the starting resistor from the power supply voltage input terminal of the control IC. did. As a result, the power loss that occurs in the starting resistance during steady operation of switching regulators, which was a problem with conventional technology, has been eliminated, and the power conversion efficiency has been improved by about 1 to 2% compared to the conventional technology. A highly efficient switching regulator can be provided.

[0017] The cutoff circuit is also formed by a transistor whose collector and emitter are connected in series between the starting resistor and the power supply voltage input terminal side of the control IC, and a series resistor which is connected in parallel to the DC output side of the diode bridge. If the gate of the triac is connected to the auxiliary winding of the isolation transformer, and the base of the transistor is connected to the intermediate connection point of the series circuit, the auxiliary winding voltage can be reduced. The triac senses this and becomes conductive, bypassing the base current of the transistor to the ground.The function of turning off the transistor and cutting off the current flowing to the starting resistor is achieved by using a series resistor and two small capacitors. Since the switching regulator can be obtained using a small and simple-structured cut-off circuit made of semiconductor elements, it is possible to economically advantageously provide a switching regulator with high power conversion efficiency.

Furthermore, if the resistance value of the series resistor is made to be about 10 times higher than that of the starting resistor, the current flowing through the triac during steady operation of the switching regulator can be suppressed, so that a cutoff circuit with low power loss can be realized. A switching regulator can be provided.

[Brief explanation of the drawing]

[Fig. 1] A connection diagram showing a forward type separately excited switching regulator according to an embodiment of the present invention.

[Fig. 2] A connection diagram showing a flyback type separately excited switching regulator according to a different embodiment of the present invention.

[Figure 3] Connection diagram showing a conventional forward type separately excited switching regulator

[Explanation of symbols]

1 Diode bridge 2 Smoothing capacitor 3 Isolation transformer 3P Primary winding 3S Secondary winding 4 Insulated gate field effect transistor (MOSF
ET) 5 Control IC 6 Power supply circuit 6c Capacitor 8 Forward circuit 9 Current detector 10 Starting resistor 11 Cutoff circuit 12 Transistor 13 Series resistor 14 Triac 30 Isolation transformer 32 Rectifier circuit

Claims (3)

[Claims] 1. A control IC for controlling on/off a field effect transistor connected in series between a diode bridge and a primary winding of an isolation transformer, the control IC has a power supply voltage input terminal and a field effect transistor connected in series between the diode bridge and the primary winding of the isolation transformer. A power supply circuit comprising a starting resistor connected between an output side and a power supply circuit that rectifies the auxiliary winding voltage of the isolation transformer and supplies it to the input terminal, wherein the auxiliary winding voltage is rectified and supplied to the input terminal after the control IC is started. A switching regulator comprising a cutoff circuit that detects generation of line voltage and disconnects the starting resistor from the input terminal of the power supply voltage. Claim 2: The cutoff circuit includes a transistor whose collector and emitter are connected in series between the starting resistor and the power supply voltage input terminal side of the control IC, and a transistor whose collector and emitter are connected in series to the DC output side of the diode bridge. It comprises a series circuit of a resistor and a triac, the gate of the triac being connected to an auxiliary winding of an isolation transformer, and the base of the transistor being connected to an intermediate connection point of the series circuit. The switching regulator according to claim 1, wherein
Ta. 3. The switching regulator according to claim 2, wherein the resistance value of the series resistor is made to be about 10 times or more higher than that of the starting resistor.