JPH082177B2 - Power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power supply device, and particularly to a circuit technique suitable for use in a power supply device known as a switching regulator system.

[Background technology]

Power supply devices for various electronic devices are used to obtain a stable power supply voltage with little voltage fluctuation. There are various circuit configurations for this power supply, but one side is "electronic technology".
(Published February 1, 1985, Publisher Nikkan Kogyo Co., Ltd., p3
It is shown as a separately excited forward type switching power supply in (0).

The above power supply device is included in a system called a switching regulator by those skilled in the art, and this system detects the level change of the output voltage obtained from the secondary coil of the main transformer and detects the level of the main transformer. The power supply of the primary coil is turned on and off to maintain the output voltage at a predetermined voltage level.

The current flowing through the primary side coil is a high current of about 1 A in most cases, but a bipolar power transistor is often used as a switching element for connecting and disconnecting the current.

Since the bipolar power transistor has a slow switching speed, the frequency signal for switching the transistor is also low frequency. Even if the base of the transistor becomes high impedance, it can be turned off within one cycle of the switching frequency because the switching frequency is low, and in particular, the base accumulated charge is discharged to protect the transistor. There was no need to provide a protection circuit.

The inventors of the present invention have studied that the current flowing through the primary coil is intermittently interrupted at a high speed. If a surface oxide film field effect transistor (power MOSFET) is used instead of the bipolar power transistor, the high-speed intermittent control of the current becomes possible, and an output voltage (power supply) obtained by rectifying the secondary side voltage can be obtained. It has been found that the voltage) can be further stabilized.

However, the gate charge C
The inventors of the present invention have revealed that if there is _GS and the power MOSFET is not discharged when the switching regulator is not operating or when the power MOSFET is off, the power MOSFET is easily destroyed during the next driving.

On the other hand, in the switching regulator, a so-called standby state in which the switching regulator is inoperative may be set in order to ensure system safety before and after normal operation and reduce current consumption.

The present inventors have found that if a protection circuit that discharges the gate accumulated charge C _GS is provided in synchronization with the switching to the standby state, the power MOSFET can be reliably protected with an extremely simple circuit configuration. The present invention has been proposed.

[Object of the Invention]

An object of the present invention is to control the current flowing through the primary coil of a switching regulator power supply device at high speed by using a power MOSFET and prevent the power MOSFET from being destroyed.

The above and other objects and novel features of the present invention are as follows.
It will be apparent from the description of this specification and the accompanying drawings.

[Outline of Invention]

The following is a brief description of the outline of the typical inventions among the inventions disclosed in the present application.

That is, the current I ₁ flowing through the primary coil L ₁₁ of the main transformer 4 with intermittently control a power MOSFET Q _13, and discharges the gate accumulated charge C _GS of the power MOSFET Q _13, performs breakdown prevention of power MOSFET Q ₁₃ By providing a protection circuit (transistor Q _P , switch S ₄ ), the object of the present invention is to perform high-speed switching control and protect the switching transistor.

[Embodiment 1] A first embodiment of a power supply device to which the present invention is applied will be described below with reference to FIGS. 1 and 2. 1 is a circuit diagram showing the circuit configuration of the power supply device (switching regulator), and FIG. 2 is a waveform diagram explaining the circuit operation of the power supply device.

The feature of this embodiment is that the current control of the primary side coil of the main transformer is performed by the power MOSFET and the power MOSF
The purpose of this is to prevent the destruction of the power MOSFET by providing a protection circuit that discharges the gate accumulated charge C _GS of ET.

A commercial power supply is supplied to the terminals T ₁ and T ₂ shown in FIG. S ₁ is a power switch, and when the switch is turned on as shown in the figure, the commercial power is supplied to the rectifier circuit 1 formed of a diode bridge.

A smoothing circuit 2 is composed of a coil L ₁ and a capacitor C _1, and obtains a DC-converted power supply voltage V _CC . The resistor R ₁ supplies the reduced power supply voltage V _CC2 to the control circuit 3, and the capacitor C ₂ stabilizes the power supply voltage V _CC2 .

Meanwhile, when supplied through all the current consumption of the control circuit 3 resistor R _1, the heating value of the resistor R ₁ becomes large, it must be the wattage of the resistor R ₁ to the atmospheric. This means that the resistance R ₁ becomes large, which is not preferable for mounting. Also,
It also contributes to the high cost and must be avoided.

Therefore, in the present embodiment, the following measures are taken.

That is, in the main transformer 4, L ₁₁ is a primary coil and L ₁₂ and L ₁₃ are secondary coils. Current I ₁ of the primary coil L ₁₁ is intended to be controlled intermittently by a control circuit 3, the output circuit 5 to be described later, the secondary coil L _12, L ₁₃
, Secondary voltages e ₁ and e ₂ are induced in response to the intermittent current I ₁ . The secondary voltage e ₂ is the output voltage V _O of this power supply device, but the secondary voltage e ₁ is the resistance R ₁
It is used to reduce the current flowing through the device and solves the above problems.

The voltage level of the secondary voltage e ₁ is set to a desired value according to the winding ratio of the primary coil L ₁₁ and the secondary coil L ₁₂ . When the secondary voltage e ₁ is induced, the output voltage rectified by the diode D ₁ is smoothed by the capacitor C ₂ and converted into a direct current.

The output voltage is supplied to the control circuit 3 and the output circuit 5 as the power supply V _CC2 . Therefore, the current flowing through the resistor R ₁ is
The amount can be reduced by the amount obtained by the secondary voltage e ₁ , and the above-mentioned problem is solved.

 Next, the control circuit 3 and the output circuit 5 will be described.

The protection circuit according to the present invention is composed of the transistor T and the inverter 14 in the control circuit 3.

A phototransistor Q ₁ is connected to the _first terminal and the second terminal to optically detect a change in the voltage level of the output voltage V _O. By this optical detection and the magnetic coupling of the main transformer 4, the primary side and the secondary side of this power supply device are separated.

When a voltage is generated in the phototransistor Q ₁ , the low input detection circuit 11 generates the reference voltage V ₁ . At the same time, the voltage V ₂ generated as a voltage drop across the resistor R ₂ is supplied to the PWM comparator 12. PWM comparator (Puls Width Modu
lation), "Pulse and Digital Circuit" (published February 20, 1974, publisher Ohm Co., Ltd., pp177
~ 180), basically comparing a sawtooth signal with a reference signal and generating a pulse signal of a time width in response to the time during which the sawtooth signal is high. It is a thing.

In this embodiment, the voltage V ₂ is used as the reference signal, and the sawtooth wave signal is supplied from the sawtooth wave signal generation circuit 13.

A resistor R ₃ and a capacitor C ₃ connected to the sawtooth wave signal generation circuit 13 via terminals 3 and 4 are for determining the peak value and time width of the sawtooth wave signal V ₃ . A sawtooth wave signal V ₃ as shown in FIG. 2 (A) is supplied to the PWM converter 12. The PWM converter 12 has a sawtooth wave signal V ₃
The voltage V ₂ is compared with the voltage V _{2 as} shown in FIG. 2 (A).
On the other hand, while the sawtooth wave signal V ₃ is at a high level, a pulse signal having a pulse width corresponding to the time width is generated. Since the voltage level of the voltage V ₂ slightly changes as shown in the drawing in response to the level change of the output voltage V _O of the power supply device, the time width of the pulse signal also slightly changes. In addition, PWM converter 1
2 is supplied with a Dead Band / Soft Start signal as an operation mode control signal for controlling the operation state via the terminal 5, and controls the driving of the PWM converter 12.

On the other hand, when the low input detection circuit 11 generates the reference voltage V ₁ , the switch S ₃ is turned on, and the power supply voltage V _CC2 is supplied to the transistor Q ₂ via the constant current circuit CS ₁ . Here it should be noted, the voltage which is a phase-inverted is supplied to the transistor Q _P by inverter 14, it is to turn off the transistor Q _P. That is, the transistor Q _P is turned off, along with the ground releasing the pin 7 is the midpoint of the transistors Q _3, Q ₄ is performed, the transistor Q ₂ is made operable by turning on the switch S3.

The transistor Q2 is turned on when the pulse signal P output from the PWM converter 12 is at a high level, and the transistor Q2 has a resistance.
The transistor Q ₄ is driven by the voltage drop of R ₄ . Further, when the pulse signal P is low, the constant current circuit CS ₁ transistor Q2 is turned off, and supplies the base current to the transistor Q ₃ via the switch S _3, drives the transistor Q _3. Therefore, the voltage level VP of the 7th terminal changes in a pulse shape by the above-mentioned operation of the transistors Q ₃ and Q ₄ . The transistor Q ₁₁ of the output circuit 5 is turned on when the voltage level V _P is high level, and the transistor Q ₁₂ is turned on when the voltage level V _P is low level. As a result, power
The gate voltage V _C of the MOSFET Q ₁₃ corresponds to the time when the sawtooth signal V ₃ is at a higher level than the voltage V _{2 as} shown in FIG. 2 (B). Then, the power MOSFET Q ₁₃ is turned on during the rising period of the gate voltage V _C , and the current I ₁ flows through the primary side coil during this period.

The voltage e ₂ is induced in the secondary coil L ₁₃ and the diode D
₂ , rectified by the capacitor D ₃ , and further smoothed by the coil L ₂ and the capacitor C ₄ to obtain the output voltage VO.

The resistors R ₅ and R ₆ are bleeder resistors, and the light emitting diode D
A bias voltage is supplied to 4 and a constant voltage element Q ₂₁ connected in series to this. The level change of the output voltage V _O, the light emitting diode is a light emitting amount of the change in D ₄ is detected by the photo transistor Q1 as described above, the control circuit 3, the output voltage V _O by the circuit operation of the output circuit 5 Stabilization takes place.

By the way, when the power supply unit is put in the standby state, the PWM converter 12 is controlled by the control signal supplied from the 5th terminal.
Is deactivated. The pulse signal P is not generated and the gate voltage V _C cannot be obtained. Then, the power MOSFET Q _{13 is} also deactivated, and the output voltage V _O gradually shifts to a low level by the capacitor C ₄ . Also, the voltage level of the power supply V _CC2 is gradually lowered by the capacitor C ₂ . As a result, the reference voltage V ₁
The voltage level of is also lowered, the switch S ₃ is turned off, and the transistor Q _P is turned on.

The base of transistor Q ₁₂ is now grounded by transistor Q _P , which turns on. Then, the electric charge C _GS accumulated in the gate of the power MOSFET Q ₁₃ is discharged to GND through the transistor Q ₁₂ . This discharging operation is performed while the power source V _CC2 is held by the capacitor C ₂ .

By the discharge of the charge C _GS, the control circuit 3 is next shifted to the normal operation state by the control signal from the fifth terminal, and when the voltage V _C is supplied to the gate of the power MOSFET Q ₁₃ ,
The power MOSFET Q ₁₃ is not destroyed and the protection operation is performed. Then, when the standby state is released by the control signal from the fifth terminal, the power supply device promptly resumes normal circuit operation.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG.

The parts that perform the same circuit operation as in the first embodiment are designated by the same reference numerals to avoid duplication of description.

The feature of this embodiment is that the charge C _{GS is}
It is configured to discharge the electric field.

That is, the switch S ₄ that works with the power switch S ₁
It is provided between the gate of power MOSFET Q ₁₃ and the GND line. Switch S ₄ is configured to turn off when power switch S ₁ is in the on state. Therefore, when the power is turned on, the output voltage V _O is stabilized, and when the power is turned off, the switch S ₄ is turned on to discharge the charge C _GS .

Since the discharging operation is performed regardless of whether the power source V _CC2 remains or not, the protection of the power MOSFET Q ₁₃ becomes even more reliable.

〔effect〕

(1) Power that provides a high-speed switching operation by providing a protection circuit that releases the non-operation of the power supply device and turns it on
By discharging the electric charge C _GS accumulated in the gate of the MOSFET, it is possible to obtain the effect of preventing the power MOSFET from being destroyed during the re-operation.

(2) In conjunction with the main switch of the power supply, the switch that turns off when the main switch operates in the on state and turns on when the main switch operates in the off state is the gate of the power MOSFET and the GND line. By providing it between the power supply circuit and the power supply circuit, an effect of discharging the charge C _GS accumulated in the gate of the power MOSFET when the power is turned off is obtained.

(3) Since the power supply to the control circuit is performed by using the secondary voltage of the main transformer, it is possible to reduce the current capacity of the resistor for voltage drop and improve the packaging density.

(4) The effect that the power consumption of the power supply device can be reduced is obtained by stopping the circuit operation of the control circuit by the control signal to enter the standby state.

Although the invention made by the present invention has been specifically described based on the embodiments above, it goes without saying that the present invention is not limited to the above embodiments and various modifications can be made without departing from the scope of the invention. Nor.

For example, the protection circuit composed of the transistor Q _A and the protection circuit composed of the switch S ₄ may be installed side by side,
Either one may be provided.

[Field of application]

In the above description, the case where the invention made by the present inventor is mainly applied to the power supply device which is the field of application which is the background has been described, but the present invention is not limited thereto and various types using power MOSFETs as output transistors are described. Can be widely used in the drive circuit of.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power supply device to which the present invention is applied, FIG. 2 is a waveform diagram explaining the circuit operation of the power supply device, and FIG. 3 is a second embodiment of the present invention. It is a circuit diagram of a power supply device. 3 ... control circuit, 4 ... main transformer, 5 ... output circuit,
11 …… Low input detection circuit, 12 …… PWM converter, 13 ……
Sawtooth wave signal generation circuit, V ₁ , V ₂ ... voltage, V ₃ ... sawtooth wave signal, V _P , V _C ... pulse signal, V _O ... output voltage, Q _{1 to} Q
₁₂ …… Transistor, Q ₁₃ …… Power MOSFET, Q _A …… Transistor that composes the protection circuit, S ₄ …… Switch that composes the protection circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 57-206944 (JP, A) JP 57-168524 (JP, A) JP 58-136137 (JP, A) JP 58- 48529 (JP, A) JP-A-61-40075 (JP, A)

Claims (2)

[Claims] 1. A transformer having a primary coil and a secondary coil, and a power MOSFET connected in series with the primary coil.
And a control circuit for switching the power MOSFET to interrupt and interrupt the current flowing through the primary coil, and an output mode is taken out from the secondary coil and an operation mode control for instructing a normal operation state or a standby state A control terminal to which a signal is input is provided, and the operation mode control signal input to the control terminal switches between a normal operation state and a standby state. In the normal operation state, the power MOSFET is turned on and off, and in the standby state, A power supply device configured to turn off a power MOSFET, wherein the control circuit includes a sawtooth wave generation circuit, a voltage corresponding to an output voltage induced in the secondary coil, and the sawtooth wave generation circuit. A PWM comparator for comparing the output sawtooth wave and a pulse comparator for controlling the on / off of the power MOSFET based on the output of the PWM comparator. Signal forming circuit for forming a power signal, and a first bipolar transistor and a power MOSFET for charging and turning on the gate of the power MOSFET according to a pulse signal from the signal forming circuit.
A gate drive circuit formed of a second bipolar transistor for discharging the electric charge of the gate of the power MOSFET and turning it off, and a protection circuit for discharging the gate accumulated electric charge of the power MOSFET to protect the power MOSFET when shifting to a standby state. A power supply device characterized by the above. 2. The protection circuit includes a switching element connected between the gate of the power MOSFET and a ground point,
The power supply device according to claim 1, wherein the switching element is configured to be turned on when the power switch is turned off and to be turned off when the power switch is turned on in conjunction with the power switch.