JP4534657B2 - Self-excited step-down chopper regulator - Google Patents

Description

  The present invention relates to a self-excited chopper regulator, and more particularly to a self-excited step-down chopper regulator.

  Conventionally, so-called chopper regulators have been used to adjust the magnitude of the DC voltage. The self-excited chopper regulator performs DC power conversion / control, that is, step-down or step-up by turning on / off a switching element. This self-excited chopper regulator is a so-called ripple converter, which stabilizes the output voltage to a predetermined value by turning on / off the switch element in accordance with a decrease and an increase in the output voltage.

  However, the switching frequency of this switch element, that is, the oscillation frequency of self-excited oscillation, may fluctuate due to variations in circuit elements, the influence of wiring routing, and the like. However, there is a problem that desired stable output characteristics cannot be obtained due to the on / off operation.

  Japanese Patent Laid-Open No. 2003-70244 discloses a self-excited chopper regulator that provides a stable output characteristic by adjusting a desired oscillation frequency by providing a circuit that adjusts the on / off timing of a switching element. Yes.

  FIG. 6 is a block diagram illustrating a self-excited chopper regulator 10 in the conventional Japanese Patent Application Laid-Open No. 2003-70244.

  FIG. 7 is a specific circuit configuration diagram of a conventional self-excited chopper regulator 10.

  A conventional self-excited chopper regulator will be described with reference to FIG. A self-excited chopper regulator 10 is connected between a node N0 and a node N11, and includes a switch element 12 for switching on an input voltage applied to an input voltage terminal Vin electrically coupled to the node N0, and a switch Drive circuit 14 connected to element 12 for driving switch element 12, start circuit 16 connected to input voltage terminal Vin electrically connected to node N0 to start drive circuit 14, and output of switch element 12 Is connected between the output voltage terminal Vout electrically connected to the node N4 and the node N11 so that the switch element 12 is turned on. Connected between the DC reactor L1 for storing energy and the output of the switch element 12 and the node N1 on the ground side. Then, the current is recirculated by the electromagnetic energy of the DC reactor L1 when the switch element 12 is OFF, and the node N4 is connected to the return diode D1, and the output voltage of the DC reactor L1 is detected, and the drive circuit 14 is based on the detection result. A voltage detection circuit 20 that outputs a control signal to the control circuit, and a detection timing adjustment that is connected between the voltage detection circuit 20 and the drive circuit 14 and adjusts the timing of the control signal transmitted from the voltage detection circuit 20 to the drive circuit 14. A circuit 22.

  When the DC voltage Vi smoothed by the capacitor C1 is applied to the input voltage terminal Vin, the drive circuit 14 is activated by the activation circuit 16. When the drive circuit 14 is activated, the switch element 12 is turned on, and the output of the switch element 12 increases. Therefore, positive feedback is applied to the drive circuit 14 by the feedback circuit 18.

  At the same time, a current flows through the DC reactor L1, the amount of current increases linearly, the capacitor C3 is charged through the DC reactor L1, and the output voltage at the output voltage terminal Vout increases.

  When the switch element 12 is turned on, the voltage detection circuit 20 detects the output voltage of the output voltage terminal Vout, and detects that the output voltage exceeds a predetermined reference voltage via the detection timing adjustment circuit 22. A signal for turning off the drive circuit 14 is output. As a result, the switch element 12 is turned off.

  While the switch element 12 is off, the current is recirculated through the free-wheeling diode D1 by the electromagnetic energy stored in the DC reactor L1, and sent to the smoothing capacitor C3 and the load 24 connected to the output voltage terminal Vout.

  When the switch element 12 is off, the voltage detection circuit 20 detects the output voltage of the output voltage terminal Vout, and detects that the output voltage falls below a predetermined reference voltage, the detection timing adjustment circuit 22 To output a signal for turning on the drive circuit 14. Thereby, the switch element 12 is turned on again.

  Therefore, the voltage detection circuit 20 detects the voltage level of the output voltage terminal Vout and controls on / off of the switch element 12. Accordingly, the output voltage supplied to the output voltage terminal Vout is controlled to a desired voltage.

  With reference to FIG. 7, the connection relation of the circuit configuration of the conventional self-excited chopper regulator will be described. The switch element 12 includes a transistor TR4. Transistor TR4 has an emitter side connected to node N0, a collector side connected to node N11, and a base side connected to node N2. The drive circuit 14 includes a transistor TR3 and resistors R7 and R8. Transistor TR3 has an emitter side connected to node N1, and a collector side connected to node N2 via resistor R7. The base side is connected to the node N3. Resistor R8 is connected between nodes N0 and N2. The starting circuit 16 is configured by a resistor R9. Resistor R9 is connected between nodes N0 and N3. The feedback circuit 18 includes a capacitor C2 and a resistor R10. Capacitor C2 and resistor R10 are connected in series between nodes N11 and N3. The voltage detection circuit 20 includes resistors R5 and R6, a shunt regulator U1, and a capacitor C4. Resistor R5 is connected between nodes N4 and N8. Capacitor C4 is connected between nodes N7 and N8. Resistor R6 is connected between nodes N1 and N8. The shunt regulator U1 operates according to the voltage of the node N8, the cathode side is connected to the node N7, and the anode side is connected to the node N1. The detection timing adjustment circuit 22 includes transistors TR1 and TR2, resistors R2 to R4, and a variable resistor VR1. The transistor TR2 is a PNP bipolar transistor, the emitter side is connected to the node N4, the collector side is connected to the node N6 via the resistor R2, and the base side is connected to the node N5. Resistor R3 is connected between nodes N4 and N5. Resistor R4 is connected between nodes N5 and N7. The transistor TR1 is an NPN bipolar transistor, the emitter side is connected to the node N1, and the collector side is connected to the node N3. The base side is connected to node N6. Variable resistor VR1 is connected between nodes N6 and N1.

  The voltage at the output voltage terminal Vout is divided by the resistors R5 and R6 and supplied to the node N8. When the divided voltage becomes lower than the reference voltage of the shunt regulator U1, that is, the threshold voltage, the shunt regulator U1 is turned off.

  When the shunt regulator U1 is turned off, in the detection timing adjustment circuit 22, the base current flowing through the bias resistor R4 is cut off, so that the input transistor TR2 is turned off. When the input transistor TR2 is turned off, the output transistor TR1 is turned off because the base current flowing through the coupling resistor R2 is cut off, but there is a time delay until the base accumulated charge is discharged through the variable resistor VR1. . When the output transistor TR1 is turned off, in the drive circuit 14, the transistor TR3 is turned on because the base current flows through the resistor R9. When the transistor TR3 of the drive circuit 14 is turned on, the transistor TR4 of the switch element 12 is turned on because a base current flows through the resistor R7.

  Therefore, the capacitor C3 is charged through the DC reactor L1, and the output voltage to the output voltage terminal Vout increases.

  On the other hand, when the voltage at the output voltage terminal Vout increases, an operation process opposite to that described above occurs.

  Specifically, when the divided voltage supplied to the node N8 becomes higher than the detection voltage of the shunt regulator U1, that is, the reference voltage, the shunt regulator U1 is turned on.

  When the shunt regulator U1 is turned on, the voltage drop of the bias resistor R3 increases in the detection timing adjustment circuit 22, and the base current of the input transistor TR2 flows through the resistor R4, so that the input transistor TR2 is turned on. When the input transistor TR2 is turned on, the output transistor TR1 is also turned on.

  When the output transistor TR1 is turned on, the transistor TR3 of the drive circuit 14 is turned off. As a result, the transistor TR4 of the switch element 12 is also turned off, and the output voltage at the output voltage terminal Vout drops.

  In this way, the transistor TR4 of the switch element 12 repeats the switching operation at a constant frequency determined by the delay time of a series of feedback loops, and the output voltage of the output voltage terminal Vout is kept constant.

Since the switching frequency, that is, the oscillation frequency of the conventional self-excited chopper regulator 10 is correlated with the discharge time of the base accumulated charge of the output transistor TR1, the oscillation frequency is adjusted by adjusting the resistance value of the variable resistor VR1. Can do. Specifically, when the resistance value of the variable resistor VR1 is decreased, the discharge time of the base accumulated charge of the output transistor TR1 is shortened, so that the delay time is shortened and as a result, the oscillation frequency of the self-excited chopper regulator is increased. On the other hand, when the resistance value of the variable resistor VR1 is increased, the discharge time of the base accumulated charge of the output transistor TR1 becomes longer, so that the delay time becomes longer and consequently the oscillation frequency of the self-excited chopper regulator becomes lower.
JP 2003-70244 A

  On the other hand, in recent years, there has been a call for lower power consumption of devices, and the drive voltage of devices tends to be lower. Therefore, it is necessary to supply a stable voltage at a low voltage as the output voltage of the self-excited chopper regulator.

  However, the voltage detection circuit and the detection timing adjustment circuit in the configuration of FIGS. 6 and 7 described above are both configured to drive the output voltage supplied to the output voltage terminal Vout as the operating voltage. Accordingly, it is necessary to operate normally even when the set value of the output voltage is low. However, in actuality, there is a risk that normal operation will be hindered unless the output voltage is set to a certain level.

  Specifically, in order for the detection timing adjustment circuit 22 to operate normally, the sum of the base-emitter voltage VBE1 of the transistor TR1, the voltage VR2 across the resistor R2 and the collector-emitter voltage VCE2 of the transistor TR2, that is, VBE1 + VR2 + VCE2 It is necessary to secure the above voltage as an operating voltage.

  In order to operate the shunt regulator U1 normally, it is necessary to ensure the sum of the reference voltage VK, the voltage VR3 across the resistor R3 and the base-emitter voltage VBE2 of the transistor TR2, that is, a voltage equal to or higher than VK + VR3 + VBE2. There is.

  Therefore, for example, the shunt regulator U1 requires a higher operating voltage in order to operate normally at the reference voltage VK (= 1.24V), and normally when the output voltage at the output voltage terminal Vout is lower than that. It cannot be operated.

  The present invention has been made to solve the above-described problems, and even when the output voltage is low, the oscillation frequency is adjusted to a desired frequency and a stable output voltage can be supplied. An object is to provide a possible self-excited step-down chopper regulator.

A self-excited step-down chopper regulator according to the present invention includes a switch element that switches an input voltage, a drive circuit that drives the switch element, a voltage detection circuit that detects an output voltage and outputs a signal for controlling the drive circuit, and a voltage And a timing adjustment circuit that is provided between the detection circuit and the drive circuit and outputs a signal for controlling the drive circuit. The voltage detection circuit and the timing adjustment circuit operate upon receiving an input voltage. The timing adjustment circuit includes a first transistor that switches based on an output of the voltage detection circuit, and a second transistor that operates in response to switching of the first transistor. The first transistor has a base connected to the voltage detection circuit, a collector connected to the base of the second transistor, and an output voltage applied to the emitter. The second transistor has an emitter connected to the input side of the switch element, a base connected to the input side of the switch element via a bias resistor, and a collector connected to the drive circuit.

  In particular, the drive circuit includes a third transistor for driving the switch element that is driven at an adjustable timing in response to switching of the second transistor.

  In particular, the timing adjustment circuit includes adjustment means for adjusting the discharge time of the accumulated charge of the third transistor.

  Preferably, the voltage detection circuit includes a shunt regulator that operates in accordance with a voltage generated based on the output voltage. The shunt regulator is supplied with an input voltage via a bias resistor.

The voltage detection circuit and the timing adjustment circuit of the self-excited step-down chopper regulator according to the present invention operate upon receiving an input voltage. Therefore, even when the output voltage is a low voltage, the operational stability can be ensured in that a stable output voltage is supplied because the input voltage is the operating voltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a block configuration diagram of a self-excited step-down chopper regulator 1 according to an embodiment of the present invention.

  Referring to FIG. 1, self-excited step-down chopper regulator 1 according to the embodiment of the present invention has a voltage detection circuit 20 receiving an input voltage as compared with conventional self-excited chopper regulator 10 described in FIG. Further, the detection timing adjustment circuit 22 is replaced with the detection timing adjustment circuit 21, and the operation is performed in response to the input of the input voltage. The other points are the same as described with reference to FIGS.

  In the present invention, the case where the voltage detection circuit 20 and the detection timing adjustment circuit 21 operate using the input voltage as an operating voltage will be described.

  FIG. 2 is a specific circuit diagram of the self-excited step-down chopper regulator 1 described in FIG.

  Voltage detection circuit 20 includes resistors R5, R6, R11, a shunt regulator U1, and a capacitor C4. Since the connection relationship is the same as that described in FIG. 7, detailed description thereof will not be repeated. Resistor R11 is connected between nodes N0 and N7, which are electrically coupled to input voltage terminal Vin. Accordingly, the voltage detection circuit 20 drives the input voltage Vi as an operating voltage.

  The detection timing adjustment circuit 21 includes resistors R2 and R12 to R14, a variable resistor VR1, and transistors TR2 and TR5.

  Transistor TR5 has a collector side connected to node N5 and an emitter side connected to node N4 via resistor R12. The base side is connected to an output node N7 of an output signal from the voltage detection circuit 20. Variable resistor VR1 is connected between nodes N3 and N1. Transistor TR2 has an emitter side connected to node N0 and a collector side connected to node N3 via resistor R2. The base side is connected to the node N5 through the resistor R14. Resistor R13 is connected between nodes N0 and N5. Accordingly, the detection timing adjustment circuit 21 drives the input voltage Vi as an operating voltage.

  Drive circuit 14 includes a transistor TR3 and resistors R7 and R8. Since the connection relationship is the same as that shown in FIG. 7, detailed description thereof will not be repeated. Drive circuit 14 receives a signal from detection timing adjustment circuit 21 from node N3. Feedback circuit 18 includes a capacitor C2 and a resistor R10. Since the connection relationship is the same as that shown in FIG. 7, detailed description thereof will not be repeated. The detection timing adjustment circuit 21 does not function in the same manner as the transistor TR1 in the detection timing adjustment circuit 22 in FIG. 7, but the transistor TR3 in the drive circuit 14 performs the same function. Compared with the detection timing adjustment circuit 22, the detection timing adjustment circuit 21 is further provided with a transistor TR5. Thereby, the output signal of the voltage detection circuit 20 is logically inverted once. Therefore, in the detection timing adjustment circuit 21, the transistor TR1 is omitted by utilizing the fact that the transistors TR1 and TR3 are the same NPN bipolar transistor, and the transistor TR3 serves as the transistor TR1. At the same time, the number of logic inversions is made the same by reducing the logic inversions performed twice in the transistors TR1 and TR5 at a time. Since the transistor TR1 is omitted by the addition of the transistor TR5, the number of transistors is not changed as a circuit component.

  Next, the operation of self-excited step-down chopper regulator 1 according to the embodiment of the present invention will be described.

  When the power is turned on, the cathode side of the shunt regulator U1 becomes “H” level via the resistor R11. Accordingly, a base current flows through the transistor TR5 and the transistor TR5 is turned on. As the transistor TR5 is turned on, the base current of the transistor TR2 flows through the resistor R14, and the transistor TR2 is also turned on.

  When the transistor TR2 is turned on, a base current flows to the transistor TR3 via the resistor R2. Therefore, the transistor TR3 of the drive circuit 14 is turned on. When the transistor TR3 of the drive circuit 14 is turned on, the transistor TR4 of the switch element 12 is turned on, and the voltage level of the output voltage terminal Vout increases. Since the voltage detection circuit 20 is activated using the input voltage Vi as an operating voltage, the resistor R11 plays the role of the activation circuit, whereby the activation circuit provided in FIG. 7 is omitted. .

  When the divided value of the output voltage exceeds the reference voltage (threshold voltage) of the shunt regulator U1, the cathode side of the shunt regulator U1 becomes “L” level, and the transistor TR5 is turned off. As the transistor TR5 is turned off, the transistors TR2 and TR3 are turned off, the transistor TR4 of the switch element 12 is turned off, and the voltage level of the output voltage terminal Vout decreases.

  Further, when the divided value of the output voltage becomes lower than the reference voltage (threshold voltage) of the shunt regulator U1, the shunt regulator U1 is turned off. Accordingly, the cathode side of the shunt regulator becomes “H” level, and the transistor TR5 is turned on. As the transistor TR5 is turned on, the transistors TR2 and TR3 are turned on, the transistor TR4 of the switch element 12 is turned on, and the voltage level of the output voltage terminal Vout increases.

  In this way, the transistor TR4 of the switch element 12 repeats the switching operation at a constant frequency determined by the delay time of a series of feedback loops, and the output voltage of the output voltage terminal Vout is kept constant.

  Since the switching frequency, that is, the oscillation frequency of self-excited step-down chopper regulator 1 according to the embodiment of the present invention has a correlation with the discharge time of the base accumulated charge of transistor TR3, the oscillation frequency is adjusted by adjusting the resistance value of variable resistor VR1. Can be adjusted. Specifically, when the resistance value of the variable resistor VR1 is decreased, the discharge time of the base accumulated charge of the transistor TR3 is shortened, so that the delay time is shortened, and as a result, the oscillation frequency of the self-excited step-down chopper regulator is increased. On the other hand, when the resistance value of the variable resistor VR1 is increased, the discharge time of the base accumulated charge of the transistor TR3 becomes longer, so that the delay time becomes longer and consequently the oscillation frequency of the self-excited step-down chopper regulator becomes lower. This is the same as the conventional configuration.

  With the configuration of the self-excited step-down chopper regulator 1 according to the embodiment of the present invention, even when the reference voltage Vref (threshold voltage) of the shunt regulator is low, voltage detection is performed using the input voltage (>> output voltage). Since the circuit 20 and the detection timing adjustment circuit 21 can be driven, the circuit 20 and the detection timing adjustment circuit 21 can be operated normally, and can be controlled to a desired oscillation frequency.

  FIG. 3 is a diagram for explaining the load fluctuation characteristics when the output voltage is output using the shunt regulator of the reference voltage Vref (= 1.24 volts).

  As shown in FIG. 3, even in a low voltage output self-excited step-down chopper regulator, it is possible to continue to maintain a desired low voltage (1.24 V) even when the load characteristics fluctuate, that is, the load current changes. It has become.

  FIG. 4 is a diagram for explaining the fluctuation of the oscillation frequency when the resistance value of the variable resistor VR1 is adjusted.

  As shown in FIG. 4, a diagram is shown in which the oscillation frequency varies linearly by adjusting the resistance value of the variable resistor VR1. That is, it is possible to adjust to a desired oscillation frequency by adjusting the resistance value.

  In other words, the low voltage output self-excited step-down chopper regulator according to the embodiment of the present application can be controlled linearly, that is, normally, by using the input voltage as the operating voltage.

  FIG. 5 is a circuit configuration diagram of self-excited step-down chopper regulator 1 # when the switching element is replaced from a bipolar transistor to a MOS transistor.

  A self-excited step-down chopper regulator 1 # will be described with reference to FIG. Self-excited step-down chopper regulator 1 # differs from self-excited step-down chopper regulator 1 in that switch element 12 is replaced with switch element 12 # and drive circuit 14 is replaced with drive circuit 15. Further, the detection timing adjustment circuit 21 is replaced with a detection timing adjustment circuit 23. Since the other points are the same, detailed description thereof will not be repeated.

  Switch element 12 # includes a MOS transistor TR4 #. The detection timing adjustment circuit 23 is different in that the resistor R14 on the base side of the transistor TR2 is excluded. Since the other points are the same, detailed description thereof will not be repeated.

  Drive circuit 15 includes transistors TR3, TR6, TR7, resistors R12, R15, R16, and a capacitor C5.

  Transistor TR7 has a collector side connected to node N0 and an emitter side connected to node N2. The base side is connected to the node N0 through the resistor R15. Transistor TR6 has an emitter side connected to node N2 and a collector side connected to node N10. The base side is connected to the node N9. Transistor TR3 has an emitter side connected to node N1 and a collector side connected to node N9 via resistor R16. The base side is connected to the node N3. Resistor R12 is connected between nodes N1 and N10. Capacitor C5 is connected in parallel with resistor R12 between nodes N1 and N10.

  When the power is turned on, the cathode side of the shunt regulator U1 becomes “H” level via the resistor R11. Accordingly, a base current flows through the transistor TR5 and the transistor TR5 is turned on. As the transistor TR5 is turned on, the base current of the transistor TR2 flows through the resistor R13, and the transistor TR2 is also turned on.

  When the transistor TR2 is turned on, a base current flows to the transistor TR3 via the resistor R2. Therefore, the transistor TR3 of the drive circuit 15 is turned on. When the transistor TR3 of the drive circuit 15 is turned on, a base current flows through the transistors TR6 and TR7, and the transistors TR6 and TR7 are also turned on. As the transistors TR6 and TR7 are turned on, the transistor TR4 # of the switch element 12 # is turned on, and the voltage level of the output voltage terminal Vout increases.

  When the divided value of the output voltage exceeds the reference voltage (threshold voltage) of the shunt regulator U1, the cathode side of the shunt regulator U1 becomes “L” level and the transistor TR5 is turned off. As the transistor TR5 is turned off, the transistors TR2 and TR3 are turned off. Accordingly, the transistors TR6 and TR7 are also turned off, the transistor TR4 # of the switch element 12 # is turned off, and the voltage level of the output voltage terminal Vout is lowered.

  Further, when the divided value of the output voltage becomes lower than the reference voltage (threshold voltage) of the shunt regulator U1, the shunt regulator U1 is turned off. Accordingly, the cathode side of the shunt regulator becomes “H” level, and the transistor TR5 is turned on. As the transistor TR5 is turned on, the transistors TR2 and TR3 are turned on. Accordingly, the transistors TR6 and TR7 are also turned on, the transistor TR4 # of the switch element 12 # is turned on, and the voltage level of the output voltage terminal Vout is increased.

  With this configuration, it is possible to drive the voltage detection circuit 20 and the detection timing adjustment circuit 23 using the input voltage, so that the output voltage can be normally operated even at a voltage level equal to or lower than the reference voltage Vref of the shunt regulator. This is possible and can be controlled to a desired oscillation frequency.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a block configuration diagram of a self-excited step-down chopper regulator 1 according to an embodiment of the present invention. FIG. FIG. 2 is a specific circuit diagram of the self-excited step-down chopper regulator 1 described in FIG. 1. It is a figure explaining the load fluctuation characteristic at the time of outputting an output voltage using the shunt regulator of the reference voltage Vref. It is a figure explaining the fluctuation | variation of the oscillation frequency at the time of adjusting the resistance value of variable resistance VR1. FIG. 3 is a circuit configuration diagram of a self-excited step-down chopper regulator 1 # when a switch element is replaced from a bipolar transistor to a MOS transistor. It is a block block diagram explaining the conventional self-excited chopper regulator. It is a specific circuit block diagram of the conventional self-excited chopper regulator 10.

Explanation of symbols

  1, 1 #, 10 chopper regulator, 12, 12 # switch element, 14, 15 drive circuit, 16 start-up circuit, 18 feedback circuit, 20 voltage detection circuit, 21, 22, 23 detection timing adjustment circuit, 24 load.

Claims (4)

A switch element for switching the input voltage;
A drive circuit for driving the switch element;
A voltage detection circuit that detects the output voltage and outputs a signal for controlling the drive circuit;
A timing adjustment circuit that is provided between the voltage detection circuit and the drive circuit and adjusts the timing of outputting a signal for controlling the drive circuit;
The voltage detection circuit and the timing adjustment circuit operate by receiving the input voltage ,
The timing adjustment circuit includes:
A first transistor that switches based on an output of the voltage detection circuit;
A second transistor that operates in response to switching of the first transistor;
The first transistor has a base connected to the voltage detection circuit, a collector connected to the base of the second transistor, and the output voltage applied to the emitter.
In the second transistor, an emitter is connected to the input side of the switch element, a base is connected to the input side of the switch element via a bias resistor, and a collector is connected to the drive circuit. Chopper regulator. 2. The self-excited step-down chopper according to claim 1 , wherein the drive circuit includes a third transistor for driving the switch element that is driven at an adjustable timing in response to switching of the second transistor. regulator. 3. The self-excited step-down chopper regulator according to claim 2 , wherein the timing adjustment circuit includes adjustment means for adjusting a discharge time of the accumulated charge of the third transistor . The voltage detection circuit includes a shunt regulator that operates according to a voltage generated based on the output voltage,
The self-excited step-down chopper regulator according to claim 1, wherein the shunt regulator is supplied with the input voltage via a bias resistor .

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