CN104350671B - Switch conversion power source device - Google Patents

Abstract

The present invention comprises: a buck converter disposed on a main current line (41) and having an inductor (L1), a FET (11), and a diode (D1); a driver circuit (30) for driving the FET (11); a drive voltage line (42) for transmitting the drive voltage applied to the driver circuit (30); a capacitor (C1) connected between the main current line (41) and the drive voltage line (42); a constant voltage circuit (20) for constantizing the input voltage based on the potential of the main current line (41) and supplying it to the drive voltage line (42); and a cathode load diode (D2) for transmitting an external control voltage higher than the voltage constantized by the constant voltage circuit (20) to the drive voltage line (42). Thus, a switching power supply device is provided that can reliably perform switching control of the switching elements at the start of operation even when the input power supply disconnection period is short, thereby obtaining the desired output voltage.

Description

switching power supply unit

technical field

The present invention relates to a switching power supply device, and more particularly to a switching power supply device including a bootstrap circuit.

Background technique

Conventionally, among switching power supply devices such as step-down converters, some devices include a bootstrap circuit. Patent Document 1 discloses a switching power supply device including a step-down converter. Since the switching element of the step-down converter is a switching element on the high-voltage side in the circuit, it is necessary to generate a control voltage based on a potential side higher than the ground level in order to control it, and a diode is provided for this purpose. and a bootstrap circuit with capacitors.

In Patent Document 2, two semiconductor switching elements connected in series at both ends of the DC power supply are alternately turned on/off by a control signal, thereby supplying power to a load connected to the midpoint of the two switching conversion elements. In the power circuit, a drive circuit using a bootstrap circuit is shown to supply power for driving a switching conversion element connected to a high voltage side of a DC power supply. When the low-side switching conversion element is turned on, the capacitor of the bootstrap circuit is charged from the auxiliary power supply through the diode.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 10-56776

Patent Document 2: Japanese Unexamined Patent Publication No. 2007-6207

Contents of the invention

The problem to be solved by the invention

However, in the circuit configuration of Patent Document 1, there is a problem that, since the input voltage directly charges the capacitor of the bootstrap circuit, when a large input voltage exceeding the withstand voltage of the FET driver circuit is input In this case, the step-down converter disclosed in Patent Document 1 cannot be applied. In addition, in the circuit of Patent Document 2, there is also a problem that since the capacitor of the bootstrap circuit is charged by turning on the switching element on the low-voltage side, when the bootstrap circuit is applied In a step-down converter with diode rectification, when the converter is temporarily stopped and then restarted, that is, it is started in a state where the capacitor or load on the output side is not exhausted but has a charge remaining In this case, the input voltage does not charge the capacitor of the bootstrap circuit, the bootstrap circuit does not function, and the switching element cannot be reliably driven.

Therefore, an object of the present invention is to provide a switching control of a switching element at the time of starting operation after the off-period, which can charge the capacitor of the bootstrap circuit even if the off-period of the input power supply is short. , so as to obtain the desired output voltage switching power supply device.

means to solve the problem

The switching power supply device according to the present invention is characterized by comprising: a main current line connecting the input terminal and the output terminal; a step-down converter provided on the main current line and having an inductor. , a switching element and a first diode; a driving circuit, which drives the switching element; a driving voltage line, which applies a driving voltage to the driving circuit; a capacitor, which is connected to the main current line and the driving voltage between the lines; a cathode load diode (bootstrap diode), which applies an external control voltage input from the outside to the driving voltage line; and a constant voltage circuit, which uses the potential of the main current line as a reference to make the slave The input terminal is converted to a constant voltage by the input voltage, and supplies a voltage lower than the external control voltage to the driving voltage line.

In this configuration, since the driving voltage based on the main current line is supplied to the driving circuit by the voltage charged in the capacitor of the bootstrap circuit, a voltage required for controlling the switching element can be obtained. When the potential of the driving voltage line is, for example, the ground potential at the time of initial start-up, the capacitor of the bootstrap circuit is charged by an external control voltage. At this time, since the voltage supplied by the constant voltage circuit is lower than the external control voltage, the capacitor of the bootstrap circuit is not charged by the constant voltage circuit.

In addition, even during steady operation, when the reference potential of the capacitor of the bootstrap circuit becomes the ground potential by the switching operation, the capacitor of the bootstrap circuit is charged under the external control voltage. Even at this time, since the voltage supplied by the constant voltage circuit is lower than the external control voltage, the capacitor is not charged by the constant voltage circuit. However, when the main current line becomes a stable potential, the capacitor is not charged by the constant voltage circuit even at this time because the capacitor is already charged by the external control voltage. Then, when the switching power supply device is temporarily stopped and the voltage between the output terminals is high (the voltage remains in the smoothing capacitor), the capacitor of the bootstrap circuit cannot be charged with the external control voltage, but the input terminal The voltage between the output terminals becomes higher than the voltage between the output terminals (because it is a step-down converter), so the capacitor of the bootstrap circuit can be charged by the constant voltage circuit with the main current line as the reference potential.

In this way, limited to the case where the voltage between the output terminals is high (the voltage remains in the smoothing capacitor) such as when the switching power supply device is restarted in a short period of time after a temporary stop, by the constant voltage with the main current line as the reference potential The capacitor of the bootstrap circuit is charged with the voltage constantized by the voltage circuit, and the driving voltage is applied to the driving circuit to enable restarting. Since the constant voltage circuit does not operate during stable operation, there is no resistance loss in the constant voltage circuit during stable operation, thereby achieving high efficiency.

Preferably, the constant voltage circuit includes: a transistor whose collector and base are connected to the input terminal, and whose emitter is connected to the driving voltage line; and a Zener diode whose anode is connected to the input terminal. The main current line is connected, and the cathode is connected to the base of the transistor.

In this configuration, the number of circuit components is small, and a stabilized constant voltage can be supplied to the driving voltage line.

Preferably, the switching power supply device includes a second diode provided between the input terminal and the constant voltage circuit to prevent reverse current from the constant voltage circuit.

In this structure, application of a reverse bias can be prevented, and damage to other elements can be prevented.

Preferably, the switching power supply device includes a fourth diode which is provided between the driving voltage line and the constant voltage circuit and prevents application of a reverse bias from the constant voltage circuit.

In this structure, application of a reverse bias can be prevented, and damage to other elements can be prevented.

Preferably, an LED is connected to the output side of the step-down converter.

In this configuration, even if the LED is turned on and off for a short time, the LED can be reliably turned on.

Invention effect

According to the present invention, it is possible to charge the capacitor of the bootstrap circuit to a predetermined driving voltage even when the switching power supply device is restarted for a short period of time after it is temporarily stopped. Therefore, switching control of the switching element of the step-down converter can be reliably performed at the start of the operation of the switching power supply device, and a desired output can be obtained.

Description of drawings

FIG. 1 is a circuit diagram of a switching power supply device according to Embodiment 1. As shown in FIG.

FIG. 2 is a circuit diagram of a switching power supply device according to Embodiment 2. FIG.

detailed description

(Embodiment 1)

FIG. 1 shows a circuit diagram of a switching power supply device according to Embodiment 1. As shown in FIG. The switching power supply device 101 according to this embodiment steps down the input voltage Vi input from the input terminals Pi(+) and Pi(-) by a step-down converter, and outputs the input voltage Vi from the output terminals Po(+) and Po( -) output the output voltage Vo. A DC voltage source E is connected to the input terminals Pi(+), Pi(-). A load that drives a constant current, such as an LED, is connected to the output terminals Po(+) and Po(-). In the following description, a line connecting the input terminal Pi(+) and the output terminal Po(+) is referred to as a main current line 41 .

The step-down converter of the switching power supply device 101 includes an n-type MOS-FET (hereinafter referred to as FET) 11 , an inductor L1 , and a diode D1 . FET11 corresponds to the switching element of the present invention, and diode D1 corresponds to the first diode of the present invention.

FET11 and inductor L1 are connected in series and provided on main current line 41 . More specifically, the drain of the FET11 is connected to the input terminal Pi(+), and the source is connected to the output terminal Po(+) via the inductor L1. The cathode of the diode D1 is connected to the connection point of the FET11 and the inductor L1, and the anode is connected to the ground connecting the input terminal Pi(-) and the output terminal Po(-).

The switching power supply device 101 includes a driver circuit 30 , a level shift circuit 31 , and a control circuit 32 . The driver circuit 30 corresponds to the driving circuit of the present invention.

The control circuit 32 detects the output current through, for example, a resistor (not shown) provided on the ground line, and outputs a drive signal for switching and switching the FET 11 to the level shift circuit 31 to obtain a given output Current Io. The control circuit 32 operates with an external control voltage Vcc input through an external power supply line 43 . In addition, a capacitor C2 serving as a decoupling capacitor or a smoothing capacitor is connected to the external power supply line 43 .

The level shift circuit 31 performs level shift of the drive signal output from the control circuit 32 and outputs it to the driver circuit 30 .

The driver circuit 30 controls switching of the FET 11 based on the drive signal level-shifted by the level shift circuit 31 . At this time, the driver circuit 30 raises the voltage level of the drive signal through the bootstrap circuit 10 and applies it to the gate of the FET 11 . The driving voltage is supplied from the bootstrap circuit 10 to the driver circuit 30 through the driving voltage line 42 .

The bootstrap circuit 10 has a capacitor C1 and a cathode load diode D2. The capacitor C1 is connected between the drive voltage line 42 and the main current line 41 . The cathode of the cathode load diode D2 is connected to the driving voltage line 42 , and the anode is connected to the external power supply line 43 .

Furthermore, the switching power supply device 101 includes a constant voltage circuit 20 that converts the input voltage Vi into a constant voltage Vb with reference to the potential of the main current line 41 and supplies it to the driving voltage line 42 . The constant voltage circuit 20 has a resistor R1, a transistor 12, and a Zener diode Dz. The base of the transistor 12 is connected to the input terminal Pi(+) via the resistor R1 , the collector is connected to the input terminal Pi(+), and the emitter is connected to the drive voltage line 42 . The Zener voltage of the Zener diode Dz is substantially equal to the constant voltage Vb, and the anode is connected to the main current line 41 , and the cathode is connected to the base of the transistor 12 .

In the present embodiment, the external control voltage Vcc is set higher than the Zener voltage (constant voltage Vb) of the Zener diode Dz of the constant voltage circuit 20 . Hereinafter, the operation of the switching power supply device 101 will be described by enumerating specific numerical values. The input voltage Vi is set to 80V, the output voltage Vo is set to 50V, the external control voltage Vcc is set to 15V, and the constant voltage Vb is set to 12V.

During the stable operation of the switching power supply unit 101, since the switching control of the FET 11 is performed, the potential of the cathode of the diode D1 on the main current line 41, which becomes the reference potential at which the capacitor C1 is charged, is changed by turning on the FET 11. change due to disconnection. For example, when the FET11 is turned on, the potential of the cathode of the diode D1 becomes Vin (80V), and when the FET11 is turned off, the potential of the cathode of the diode D1 becomes substantially the ground potential.

Therefore, when the FET 11 is turned off, the capacitor C1 is charged with the external control voltage Vcc of 15 V from the external power supply line 43 through the path A passing through the cathode load diode D2. The capacitor C1 is not charged by the constant voltage Vb of 12V generated by the constant voltage circuit 20 . In this manner, when the switching power supply device 101 is stably operating, the capacitor C1 is charged with a voltage from the external power supply line 43 , and the charged voltage is supplied to the driver circuit 30 as a driving voltage. Accordingly, the drive voltage is supplied to the driver circuit 30 , and the driver circuit 30 can apply the drive voltage between the gate and the source of the FET 11 , thereby reliably switching and controlling the FET 11 .

In addition, when the operation of the switching power supply device 101 is stopped and the off period is long enough, since the charge of the capacitor Co is discharged and the charge of the capacitor Co does not remain, the cathode potential of the diode D1 becomes approximately the ground potential. The line 43 is charged with the external control voltage Vcc of 15V to the capacitor C1 through the path A passing through the cathode load diode D2.

On the other hand, when the switching power supply device 101 is stopped and restarted during a short off-period, the capacitor Co may not be completely discharged but may remain in the capacitor Co. In particular, when the load has diode characteristics such as LEDs, since no current flows unless a voltage of a fixed value or higher is applied, the capacitor Co is less likely to be discharged. Therefore, for example, if the potential of the main current line 41 is set to 13V, the external power supply line 43 becomes substantially the same potential as the main current line 41 and the driving voltage line 42 . In this case, the cathode load diode D2 is non-conductive until the residual charge of the capacitor Co is eliminated, and the capacitor C1 is not charged by the external control voltage Vcc.

However, even when the potential of the main current line 41 is high in this way, the transistor 12 operates at a voltage corresponding to the Zener voltage (12 V of the constant voltage Vb) using the main current line 41 as a reference potential during the off period of the FET 11. Operates at high potential. Therefore, the transistor 12 of the constant voltage circuit 20 operates, and the constant voltage Vb of 12 V after the constant voltage of the input voltage Vi of 80 V is converted from the transistor 12 to charge the capacitor C1 with the constant voltage Vb of 12 V through the path B passing through the capacitor C1. .

As described above, even when the switching power supply device 101 is stopped and restarted after a short off period, the capacitor C1 of the bootstrap circuit 10 can be charged with a voltage by the constant voltage circuit 20 . Therefore, the driver circuit 30 can stably perform switching control of the FET 11 .

In addition, assuming a configuration in which the capacitor C1 is constantly charged with the constant voltage Vb obtained by the constant voltage circuit 20 , resistance loss occurs in the constant voltage circuit 20 . However, in the present embodiment, since the capacitor C1 is charged with the external control voltage Vcc higher than the voltage after constant voltage by the constant voltage circuit 20 during stable operation, the constant voltage circuit 20 does not operate. , so that the above-mentioned resistance loss can be reduced.

(Embodiment 2)

FIG. 2 shows a circuit diagram of a switching power supply device according to Embodiment 2. As shown in FIG. The basic circuit configuration of the switching power supply device 102 according to this embodiment is the same as that of the first embodiment. Hereinafter, differences from Embodiment 1 will be described.

Between the input terminal Pi(+) and the constant voltage circuit 20, a diode (second diode of the present invention) D3 and a resistor R2 are provided. The anode of the diode D3 is connected to the input terminal Pi(+), and the cathode is connected to the base of the transistor 12 via the resistor R2 and the resistor R1. In addition, the collector of the transistor 12 is connected to the resistor R2 via the resistor R3. A resistor R4 is connected in series to the cathode load diode D2 of the bootstrap circuit 10 . In addition, a diode (a third diode in the present invention) D4 is provided between the emitter of the transistor 12 and the drive voltage line 42 .

The purpose of the above-mentioned diode D3 is to prevent reverse bias from being applied to the constant voltage circuit 20 . For example, when the input voltage Vi drops sharply, the input terminal Pi(+) and the cathode of the diode D1 have the same potential due to the action of the body diode of the FET11, but when the charge remains in the capacitor C1, the reverse bias is applied to a constant voltage circuit. However, by providing the diode D3, it is possible to prevent the base and the emitter of the transistor 12 from being destroyed by the reverse bias voltage. In addition, resistors R2, R3, and R4 are elements for preventing overcurrent, and can prevent destruction of each element.

The diode D4 prevents a reverse bias voltage from being applied to the constant voltage circuit 20 . As described in Embodiment 1, since the external control voltage Vcc is set higher than the Zener voltage (constant voltage Vb) of the Zener diode Dz of the constant voltage circuit 20, a reverse bias voltage is applied to the base of the transistor 12 and the emitter. However, by providing the diode D4, it is possible to prevent the base and the emitter of the transistor 12 from being destroyed by the reverse bias voltage.

As mentioned above, the specific structure of the switching power supply device can be appropriately designed and changed. The actions and effects described in the above-mentioned embodiments are merely examples of the most suitable actions and effects produced by the present invention. The actions produced by the present invention And the effects are not limited to those described in the above-mentioned embodiment.

Symbol Description

10- Bootstrap circuit

11-FET (switching element)

12-transistor

20-Constant voltage circuit

30-driver circuit

31-level shift circuit

32-Control circuit

41-Main current wire

42-Drive voltage line

43-External power cord

101, 102-Switch conversion power supply device

C1-capacitor

D1-diode (1st diode)

D2 - cathode load diode

D3-diode (2nd diode)

D4-diode (3rd diode)

Dz-Zener diode

L1-inductor

Claims (5)

1. a kind of switch conversion power source device, possesses：

Principal current line, which is to making the input terminal of input voltage input and being attached the lead-out terminal of output voltage output；

Step-down controller, which is arranged on the principal current line, and has inducer, switch element and the 1st diode；

Drive circuit, which is driven to the switch element；

Drive voltage line, which applies driving voltage to the drive circuit；

Capacitor, which is connected between the principal current line and the drive voltage line；

Cathode-loaded diode, the External Control Voltage being transfused to from outside is applied by which to the drive voltage line；With

Constant voltage circuit, which makes the input voltage carry out constant pressure on the basis of the current potential of the principal current line, and will be than described The low voltage of External Control Voltage is supplied to the drive voltage line.

2. switch conversion power source device according to claim 1, wherein,

The constant voltage circuit has：

Transistor, the colelctor electrode and base stage of the transistor be connected with the input terminal, and emitter stage and the drive voltage line Connection；With

Zener diode, the anode of the Zener diode is connected with the principal current line, and negative electrode and the transistor base stage Connection.

3. switch conversion power source device according to claim 1 and 2, wherein,

The switch conversion power source device possesses：2nd diode, its be arranged at the input terminal and the constant voltage circuit it Between, and prevent reverse biased to be applied in the constant voltage circuit.

4. switch conversion power source device according to claim 1 and 2, wherein,

The switch conversion power source device possesses：3rd diode, which is arranged at the drive voltage line and the constant voltage circuit Between, and prevent reverse biased to be applied in the constant voltage circuit.

5. switch conversion power source device according to claim 1 and 2, wherein,

The step-down controller is connected with LED in outlet side.