JP2017085705A - Drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise generated from a drive circuit of a half bridge circuit.SOLUTION: A driving voltage transmission circuit 20 for transmitting a voltage for turning on and off a first switch Q2 and a second switch Q3 connected in series with the first switch Q2 comprises: a first drive circuit for turning on and off Q2; a second drive circuit for turning on and off Q3; a control circuit 34 for sending a signal to the first and second drive circuits; and a capacitor. The power supply of the first and second drive circuits are in common with the power supply of the control circuit. The high voltage side of the capacitor is connected to the power supply and the first drive circuit, and the low voltage side is connected between Q2 and Q3. When Q3 is in an on state, the capacitor is charged with electric power from the high voltage side. When Q3 is in an off state, Q2 is turned on and off by discharging the charge power. The driving voltage transmission circuit connects a resistor or an inductor in series with the capacitor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a drive circuit, and more particularly to reduction of noise generated from a drive circuit for driving a half bridge circuit.

  In recent years, LED elements have been rapidly replaced with conventional light sources due to improvements in luminous efficiency and lifetime. If the performance of the LED element is improved in the future, it is expected that LED light sources will be further adopted in the field of general-purpose lighting fixtures, and the demand for lighting power supply devices such as LED power supply devices will increase. By the way, in the lighting fixture using many LED elements, the structure restrictions by the shape of a lamp decreased compared with the lighting fixture using the conventional HID lamp, and it became possible to implement | achieve the lighting fixture of a free shape. Originally, the characteristic of LED elements is that the light output per unit is small, but the conventional HID lamp can be replaced with LED lamps by increasing the light output by combining many elements in series and parallel. Came to be done.

  The LED power supply system uses an insulation transformer that takes into account safety such as ground faults (referred to as an insulation transformer type), rectifies the commercial power supply without using an insulation transformer, and a half-bridge circuit (inverter There is a method (referred to as a half-bridge type) in which an LED is lit after being converted into a high frequency by a circuit) and again converted into direct current. Insulated transformer type LED power supply devices have the disadvantage that the transformer is heavy and expensive, and recently, half-bridge type LED power supply devices are increasingly used.

  In a half-bridge type LED power supply device, a half-bridge circuit configured as an intermediate circuit has FETs and other switching elements connected in series on the high potential side (high side side) and the ground side (low side side). . Then, high-frequency voltage generation is realized by alternately turning on and off the high-potential side and ground-side FETs. However, in order to stably turn on and off the high-side FET, boosting by power supply from an external power source is required.

  In Patent Document 1, in order to drive the high-potential side FET of the half-bridge circuit, the drive circuit is provided with a capacitor. When the ground-side FET is turned on, the capacitor is charged. A technique is disclosed in which boosting is possible by discharging electric power, and the FET on the high potential side is stably operated without using an external power supply or the like (or by reducing the capacity of the external power supply).

JP-A-2005-304210

  However, as in Patent Document 1, by using a capacitor to supply the operating voltage of the high-side FET, it is possible to discharge the power charged in the capacitor and smoothly drive the high-side FET. However, there has been a problem that the control circuit has caused a malfunction of unknown cause and cannot maintain a stable operation of the drive circuit. In general, such a malfunction of the control circuit is often caused by noise from a switching circuit (FET or the like) on the LED power supply side. Therefore, in order to realize a stable operation of the control circuit, the drive circuit or the control circuit is shielded and noise countermeasures are strengthened, but a stable operation of the control circuit cannot be maintained.

  The present inventors diligently studied the cause of malfunction of the control circuit in the drive circuit for driving the half-bridge circuit, and reached the present invention. According to the study by the present inventors, in order to make the circuit configuration compact, a drive circuit for driving the half bridge circuit and a drive power source for the control circuit for controlling the voltage from the drive circuit to the half bridge circuit are provided. It has been found that the control circuit malfunctions in the common case (when the wiring is common). As a matter of course, another power source (external power source or the like) may be provided in the control circuit in order to realize a stable operation. However, although the above-mentioned half-bridge type LED power supply device has been developed to make the circuit configuration compact, the use of a separate power supply may complicate the circuit configuration. There is still room for improvement.

  That is, the present invention has been made in view of the above-described problems of the prior art, and its purpose is a drive circuit in which a drive circuit for driving a half bridge circuit and a drive power supply for a control circuit are common (wiring is common). The present invention provides a drive circuit capable of preventing a malfunction of a control circuit and capable of stable operation, and an LED power supply device including a drive circuit capable of stable operation.

In order to solve the above-mentioned problem, a drive voltage transmission circuit according to the present invention includes:
A drive voltage transmission circuit for transmitting a drive voltage for on / off operation of a half bridge circuit having a first switch on a high potential side and a second switch on a ground side connected in series with the first switch,
The drive voltage transmission circuit sends a control signal to the first drive circuit for turning on / off the first switch, the second drive circuit for turning on / off the second switch, and the first drive circuit and the second drive circuit. A control circuit and a capacitor;
The first drive circuit, the second drive circuit, and the drive power of the control circuit are common,
The high potential side of the capacitor is connected to the drive power supply and the first drive circuit, and the low potential side is connected between the first switch and the second switch,
The capacitor is charged with power from the high potential side of the capacitor when the second switch is on, and the first switch is turned on and off by discharging the charged power when the second switch is off,
Further, the drive voltage transmission circuit is characterized in that a spike current generated from the capacitor is suppressed by connecting a resistor or an inductor in series with the capacitor.

The drive voltage transmission circuit includes a first voltage supply circuit that converts a supply voltage into drive voltages for the first drive circuit and the second drive circuit,
It is preferable to include a second voltage supply circuit that converts a voltage from the first voltage supply circuit into a drive voltage for the control circuit.

  The impedance of the resistor is preferably 10Ω to 500Ω.

  The inductance of the inductor is preferably 0.1 μH to 10 μH.

An LED power supply device having the drive voltage transmission circuit,
The drive voltage transmission circuit preferably causes the LED element to stably operate by turning on and off a half bridge circuit included in the LED power supply device.

  According to the present invention, in a drive circuit for driving a half-bridge circuit and a drive circuit in which a drive power supply of a control circuit for controlling the drive circuit is common (wiring is common), in series with a capacitor included in the drive circuit By connecting a resistor or inductor and suppressing the current flowing to the capacitor, it is possible to reduce the power noise generated by charging and discharging the capacitor from entering the control circuit, which is a common power source with the drive circuit. It was. As a result, stable operation of the control circuit included in the drive circuit according to the present configuration can be realized, and stable voltage supply to the LED element can be realized.

The schematic block diagram of the LED power supply device which concerns on this invention is shown. 1 is a schematic configuration diagram of a drive circuit and a conventional drive circuit in an LED power supply device according to the present invention. The voltage waveforms at points P1 and P2 in FIG. 1 in a conventional LED power supply device are shown. FIG. 2 shows voltage waveforms at points P1 and P2 in FIG. 1 in the LED power supply device according to the present invention. The internal logic schematic of the drive circuit with which the LED power supply device which concerns on this invention is provided is shown.

  Hereinafter, although the LED power supply device of this invention is demonstrated using drawing, it will not be limited to the following examples at all unless it exceeds the meaning of this invention.

  FIG. 1 shows a schematic diagram of an LED power supply device according to the present invention. The LED power supply apparatus 10 shown in the figure generates a DC voltage by boosting a voltage from a commercial power supply 12 for supplying a commercial AC voltage, a rectifier circuit 14 for rectifying the AC voltage, and the rectifier circuit 14. An active filter circuit 16 (power factor correction circuit), a half-bridge circuit 18 for generating a high-frequency AC voltage, a drive circuit 20 for turning the half-bridge circuit 18 on and off, and a high-frequency AC voltage as a DC voltage And a smoothing circuit 22 for supplying a direct current voltage to the LED element 24.

First, the rectifier circuit 14 will be described.
The rectifier circuit 14 includes a diode bridge DB1 and a smoothing capacitor C1. When an AC commercial voltage (such as AC 100 V or AC 200 V) is applied by the commercial voltage 12, the commercial voltage reaches the diode bridge DB1. The diode bridge DB1 is composed of a diode element or the like, but may be another semiconductor element as long as it can perform the same function. The voltage (also referred to as a pulsating voltage) that has been full-wave rectified by the diode bridge DB1 is smoothed to a rough DC voltage (an additional integration circuit is necessary to obtain a complete DC voltage) by the smoothing capacitor C1. .

  The smoothed voltage reaches the active filter circuit 16. The active filter circuit 16 includes an inductor L1, a power factor correction switch Q1 composed of an FET, a PFC circuit for instructing a switching operation of the power factor correction switch Q1, a diode D1, and a smoothing capacitor C2. Yes.

  The PFC circuit controls the power factor correction switch Q1 so that the power factor correction switch Q1 is repeatedly turned on and off. While the power factor correction switch Q1 is on, the pulsating voltage generated by the rectifier circuit 14 is applied to the inductor L1, and a current flows through the inductor L1. When the power factor correction switch Q1 is turned off, the current flowing through the inductor L1 charges the smoothing capacitor C2 (electrolytic capacitor) via the diode D1. As a result, the smoothing capacitor C2 is charged with the boosted voltage. The power factor of the LED power supply device 10 is improved by adjusting the timing at which the PFC circuit turns on and off the power factor correction switch Q1 through such a series of operations. Note that the cathode terminal of the smoothing capacitor C <b> 2 is connected to a ground wiring having a reference potential in the LED power supply device 10. The voltage generated by the active filter circuit 16 reaches the half bridge circuit 18 and also reaches the drive circuit 20.

Next, the operation of the half bridge circuit 18 will be described.
The half-bridge circuit 18 is a circuit in which a high-side switch Q2 and a low-side switch Q3 are electrically connected in series, and is electrically connected to both ends of the smoothing capacitor C2. The high-side switch Q2 and the low-side switch Q3 are composed of switching elements such as FETs. Further, the high-side switch Q2 and the low-side switch Q3 may be other switching elements as long as they can perform the same function as the FET. The high side switch Q2 is connected to the high voltage side (high side), and the low side switch Q3 is connected to the ground side (low side). According to the voltage signal from the drive circuit 20, the high-side switch Q2 and the low-side switch Q3 are alternately turned on and off according to the voltage signal from the drive circuit 20, so that a rectangular wave voltage is generated from the connection point b of the switches Q2 and Q3. Occur.

  Here, the drive circuit 20 for driving the half bridge circuit 18 will be described. The drive circuit 20 includes a drive circuit 32 that supplies a drive voltage to the half-bridge circuit 18, a control circuit 34 that controls the drive voltage from the drive circuit 32, and a drive that supplies a voltage for operating the drive circuit 32. A circuit voltage supply circuit 36 and a control circuit voltage supply circuit 38 that steps down the voltage from the drive circuit voltage supply circuit 36 and supplies a voltage for operating the control circuit 34 are provided.

  The drive circuit 20 operates by being supplied with the voltage smoothed by the smoothing capacitor C2 included in the active filter circuit 16. When the voltages required for driving the drive circuit 32 and the control circuit 34 are different from each other, the voltage from the smoothing capacitor C2 is stepped down to the required voltage and supplied. Specifically, the voltage from the smoothing capacitor C <b> 2 is stepped down to a necessary voltage by the drive circuit voltage supply circuit 36 and then supplied to the drive circuit 32. The drive circuit voltage supply circuit 36 is a switching DCDC converter. The stepped down voltage from the drive circuit voltage supply circuit 36 is also supplied to the control circuit voltage supply circuit 38, where the control circuit 34 further reduces the drive voltage to a necessary level and supplies it to the control circuit 36. The control circuit voltage supply circuit 38 is preferably a series type DCDC converter with less noise than the switching type.

  Thus, by making the power supply of the drive circuit 32 and the control circuit 34 common (wiring from the power supply is common), the LED power supply device (and the drive circuit 20) can be made compact. For example, by designing the above configuration and function as a dedicated IC, the LED power supply device can be made more compact.

Next, the drive circuit 32 will be described in detail.
FIG. 2A shows a schematic configuration diagram of the drive circuit 32 provided in the LED power supply device 10 according to the present invention. Vcc is supplied with a voltage from the smoothing capacitor C2 through the drive circuit voltage supply circuit 36, and COM is a ground wiring. A control signal from the control circuit 34 is input to IN which is an input terminal. LO and COM are connected to the low-side switch Q3 in FIG. Further, Vs is connected to a connection point b which is an intermediate point between the high-side switch Q2 and the low-side switch Q3 on the high potential side (high side) in FIG. 1, and HO is connected to the gate of the high-side switch Q2. It is connected. Further, as shown in FIG. 2A, a high-side switch Q2 is connected in series with a diode D6 for preventing backflow, a charging capacitor C7, and a resistor R3 as a characteristic configuration in the present invention. Has been.

FIG. 2B shows a schematic configuration diagram of a conventional drive circuit in a half-bridge type LED power supply device with respect to the operation of the drive circuit and the principle of noise generation . Here, a description will be given of the case where the conventional driving circuit shown in FIG. 2B (a circuit to which the resistor R3 is not connected) is incorporated as the driving circuit 32 of FIG. As the power source for the drive circuit 32 that drives the high-side switch Q2 on the high potential side, the power charged in the charging capacitor C7 is used. When the low-side switch Q3 is turned on, a spiked charging current flows through the charging capacitor C7. This spike current abruptly depresses the potential at the output P1 point of the drive circuit voltage supply circuit 36 (switching DCDC converter) to generate a spike-like voltage as shown in FIG. Since the spike-like voltage drop has a high frequency component, it passes through the control circuit voltage supply circuit 38 (series type DCDC converter) that generates a voltage necessary for the operation of the control circuit 34 through the floating capacitance between the input and output. Then, it appears at the point P2 with almost no attenuation. That is, the voltage point P2 input to the control circuit 34 becomes a spike-like voltage as shown in FIG. 3B, which causes the control circuit 34 to malfunction. In particular, when a microcomputer is used for the control circuit 34 and control is performed using an A / D converter, an unstable operation is caused.

  Therefore, in the present invention, the resistor R3 is connected in series with the charging capacitor C7 of the drive circuit 32 as shown in FIG. 2A, so that P1 with less noise (drop) as shown in FIG. A voltage waveform at a point can be obtained. This can be said to reduce the drop at the point P1 by reducing (suppressing) the spike current flowing into the charging capacitor C7 by connecting the resistor R3. The impedance of the resistor R3 is preferably 10Ω to 500Ω. The same effect can be obtained by connecting an inductor instead of connecting the resistor R3. The inductance of the inductor at this time is preferably 0.1 μH to 10 μH. Since the reduced spike voltage has a low frequency component, it does not pass through the stray capacitance between the input and output, but is attenuated by the resistor and output capacitance of the control circuit voltage supply circuit 38, as shown in FIG. 4B. It becomes a beautiful DC voltage. In addition, such a phenomenon has a very short operation time and is much shorter than the time that can be controlled to a constant voltage by the control function of the DCDC converter (the voltage supply circuit 36 for the drive circuit and the voltage supply circuit 38 for the control circuit). It cannot be set to a constant value by control.

The internal logic of the drive circuit showing an internal logic schematic diagram of a drive circuit 32 provided in the LED power device 10 according to the present invention in FIG. For high-side switch Q2, resistor R4, Schmitt trigger circuit ST, signal inversion circuit, pulse generator (PLUSE GEN), level shift circuit LVSh, voltage detection circuit (UV DETECT), pulse filter (PULSE FILTER), RS flip-flop Circuit RSFF. In addition, a resistor R4, a Schmitt trigger circuit ST, and a signal inversion circuit are provided for the low side switch Q3.

  When a control signal from the control circuit 34 is input to IN which is a control signal input terminal of the drive circuit 32, it is sent as a control signal to the signal inverting circuit via the Schmitt trigger circuit ST. The Schmitt trigger circuit ST and the resistor R4 are circuits for transferring a stable output level to the voltage detection circuit even when the control signal from IN fluctuates. A voltage detection circuit (UV DETECT) included in the signal inversion circuit detects the voltage level of the control signal from IN and performs a signal inversion function to HO or LO. As described above, when the LO output is on (when the low-side switch Q3 is on), the HO output is off, and at this time, the charging capacitor C7 is charged. Further, when the LO output is off (when the low-side switch Q3 is off), the HO output is on.

Next, the signal output operation to the high side switch Q2 will be described.
A pulse generator (PLUSE GEN) for generating a one-shot pulse generates a one-shot pulse signal at the rise and fall of the output of the signal inversion circuit. The level shift circuit LVSh is composed of a transistor Tr1 and a transistor Tr2, a resistor R5, and a resistor R6. The transistor Tr1 converts the one-shot pulse signal (signal due to the rise) from the pulse generator into the level of Vb, and the transistor Tr2 converts the one-shot pulse signal (signal due to the fall) from the pulse generator into the level of Vb. .

The output signal of the level shift circuit LVSh is input to the RS flip-flop circuit RSFF via the pulse filter (PULSE FILTER) and the voltage detection circuit (UV DETECT). For example, a one-shot pulse signal (signal due to rising) from the level shift circuit LVSh serves as a set input for RSFF, and a one-shot pulse signal (signal due to falling) from the level shift circuit LVSh serves as a reset input for RSFF. At this time, the pulse filter removes indefinite signals other than the prescribed control signal. The drive circuit 32 outputs the ON signal HO of the high side switch Q2 in accordance with the output signal of the RS flip-flop circuit RSFF. The voltage detection circuit (UV DETECT) monitors the voltage VB, and when the voltage VB drops, resets the RSFF. When the signal from the HO stops, the signal from the LO is output, and the on / off operation of the half bridge circuit 32 is performed.

  In this way, a voltage from the drive circuit 20 is received by a series of operations of the drive circuit 32, and a high-frequency current (high-frequency voltage) is generated by the on / off operation of the high-side switch Q2 and the low-side switch Q3 of the half bridge circuit 18. Generated. The generated high frequency current reaches the inductor L2.

  An LC series circuit of a small impedance inductor L2 and a small capacity insulating capacitor C3 is connected to the connection point b, and the other end of the capacitor C3 is connected to an input terminal on the high potential side of the smoothing circuit 22. A small-capacity insulating capacitor C4 is connected to the ground side of the low-side switch Q3, and the ground-side input terminal of the smoothing circuit 22 is connected to the other end of the insulating capacitor C4.

  The insulating capacitors C3 and C4 are connected to realize insulation between the input side (AC power supply 12 side) and the load side (LED element 24 side). The capacitances of the insulating capacitors C3 and C4 are such that when the insulation between the LED element 24 and the radiator is broken and the person contacts the radiator, the maximum value of the current that flows to the ground through the person does not affect the human body. The pF order is 1 mA or less, which is the current value. For example, it is preferable to use ceramic capacitors having the same pF-order capacitance as the insulating capacitors C3 and C4. The high-frequency voltage generated by the half bridge circuit 18 reaches the smoothing circuit 22 via the inductor L2 and the capacitor C3.

  A smoothing circuit 22 for converting a rectangular wave voltage (or high-frequency voltage) into a direct current is composed of a diode bridge DB2 and a smoothing capacitor C5. The diode bridge DB2 includes diodes D2 to D5 that are four rectifying elements. By these diodes D2 to D5, the current flowing through the inductor L2 is full-wave rectified, the smoothing capacitor C5 is charged, and a direct current that turns on the LED element 24 is generated. The diode bridge DB2 is configured using a high-speed diode having a sufficiently short reverse recovery time with respect to a high frequency.

  In such a configuration, when the high-side switch Q2 is turned on and the low-side switch Q3 is turned off in the half bridge circuit 18, a rectangular wave voltage is applied to the connection point b, and a pulse current is directed toward the inductor L2. is flowing. While the forward pulse current IS is limited by the inductor L2, the charge stored in the smoothing capacitor C2 flows in the order of C2, Q2, L2, C3, D2, C5, D5, C2, and the smoothing capacitor C5. Becomes a direct current for lighting the LED element 24.

  Next, when the high-side switch Q2 is turned off and the low-side switch Q3 is turned on, the pulse current IS flows through the charge stored in C3 and C4 in the reverse direction through the inductor L2. While the negative pulse current IS is limited by the inductor L2, it flows in the order of C3-> L2-> Q3-> C4-> D3-> C5-> D4-> C3, charges the smoothing capacitor C5, and also turns on the LED element 24 DC current is generated.

  Then, a control command from the control circuit 34 is sent to the drive circuit 32 so that an appropriate current flows through the LED element 24. A stable voltage is always applied to the control circuit 34 due to the influence of the resistor R3 described above (reduction in noise by suppressing the charging current to the capacitor C7), and the control circuit 34 itself can realize a stable operation. Therefore, the ON / OFF operation of the half bridge circuit 18 by the voltage from the drive circuit 32 is also stably performed, and the LED element 24 can be stably operated.

  As described above, in order to make the circuit configuration compact, the drive circuit for driving the half-bridge circuit and the drive power source for the control circuit for controlling the drive circuit are common (wiring is common). By connecting a resistor or inductor in series with the capacitor provided in the drive circuit, it is possible to suppress the current to the capacitor, and to reduce the noise generated by charging and discharging the capacitor from entering the control circuit, Stable operation of the control circuit and stable voltage supply to the LED element (maintaining stable operation of the LED power supply device) can be realized.

DESCRIPTION OF SYMBOLS 10 LED power supply device 12 Commercial power supply 14 Rectifier circuit 16 Active filter circuit 18 Half bridge circuit 20 Drive circuit 22 Smoothing circuit 24 LED element 32 Drive circuit 34 Control circuit 36 Drive circuit voltage supply circuit 38 Control circuit voltage supply circuit R1- R6 Resistors D1 to D6 Diodes C1, C2, C5 Smoothing capacitors C3, C4 Insulating capacitors C7 Charging capacitors Q1 Power factor improvement switch Q2 First switch Q3 Second switches L1 to L2 Inductor ST Schmitt trigger circuit LVSh Level shift circuit Tr1 ~ Tr2 transistor RSFF RS flip-flop circuit

Claims (5)

A drive voltage transmission circuit for transmitting a drive voltage for on / off operation of a half bridge circuit having a first switch on a high potential side and a second switch on a ground side connected in series with the first switch,
The drive voltage transmission circuit sends a control signal to the first drive circuit for turning on / off the first switch, the second drive circuit for turning on / off the second switch, and the first drive circuit and the second drive circuit. A control circuit and a capacitor;
The first drive circuit, the second drive circuit, and the drive power of the control circuit are common,
The high potential side of the capacitor is connected to the drive power supply and the first drive circuit, and the low potential side is connected between the first switch and the second switch,
The capacitor is charged with power from the high potential side of the capacitor when the second switch is on, and the first switch is turned on and off by discharging the charged power when the second switch is off,
Furthermore, the drive voltage transmission circuit is characterized in that a spike current generated from the capacitor is suppressed by connecting a resistor or an inductor in series with the capacitor. The drive voltage transmission circuit according to claim 1,
The drive voltage transmission circuit includes a first voltage supply circuit that converts a supply voltage into drive voltages for the first drive circuit and the second drive circuit,
A drive voltage transmission circuit comprising a second voltage supply circuit that converts a voltage from the first voltage supply circuit into a drive voltage for the control circuit. A drive voltage transmission circuit according to any one of claims 1 and 2,
The impedance of the resistor is 10Ω to 500Ω, and the driving voltage transmission circuit is characterized in that A drive voltage transmission circuit according to any one of claims 1 and 2,
The inductance of the inductor is 0.1 μH to 10 μH. An LED power supply device having the drive voltage transmission circuit according to any one of claims 1 to 4,
The drive voltage transmission circuit causes the LED element to stably operate by turning on and off a half-bridge circuit included in the LED power supply device.

Images