JP7082902B2 - Load drive - Google Patents

Description

The present invention relates to a load drive device that drives a load.

As an LED drive device capable of improving the power factor and adjusting the output to the LED in a wide range, a two-converter type LED drive device has been conventionally known (see, for example, Patent Document 1).

In the two-converter type LED drive device, the power factor is improved by the converter in the front stage, and dimming is performed by the converter in the rear stage.

Japanese Unexamined Patent Publication No. 2017-08472

Since the two-converter type LED drive device has a configuration that requires two converters, it is difficult to reduce the cost.

Therefore, in order to reduce the cost, it is conceivable to configure the dimming while improving the power factor with one converter. However, in this configuration, when the dimming rate is low, there arises a problem that it is difficult to reduce the output current while suppressing the generation of harmonic components of the commercial AC power frequency (50 Hz or 60 Hz). The dimming rate is the ratio of the output at the time of dimming to the rated output of the light source. That is, the dimming rate means the degree of brightness of the light source when the brightness when the light source is lit at the rated output is 100%. For example, when the dimming rate is 10%, the brightness of the light source is 10% of the brightness when the rated output is lit.

In view of the above circumstances, it is an object of the present invention to provide a load drive device capable of improving the power factor and adjusting the output to the load in a wide range at low cost.

The load drive device disclosed in the present specification is a load drive device including a rectifier circuit for rectifying an AC voltage and a power factor improving circuit connected to the output side of the rectifier circuit, and the power factor is described. The improvement circuit includes a switching element and a switching control unit that controls the switching operation of the switching element, and the switching control unit adjusts the on-time of the switching element based on the first signal and the second signal. It is a configuration (first configuration) that determines whether or not to stop the switching operation based on the above.

In the load drive device having the first configuration, the frequency of the first signal may be higher than the frequency of the second signal (second configuration).

In the load drive device having the first or second configuration, when the first signal is a signal instructing to adjust the on-time to be larger than a predetermined value, the second signal stops the switching operation. When the first signal is a signal instructing that the on-time is adjusted to a predetermined value or less, the second signal stops the switching operation. It may be a configuration (third configuration) that is a signal instructing to provide a period.

In the load drive device having any of the first to third configurations, a smoothing unit for smoothing the first signal, a conversion unit for converting the current flowing through the load driven by the load drive device into a voltage, and the smoothing unit. The switching control unit includes an error amplifier that generates an error signal according to the difference between the output voltage of the unit and the output voltage of the conversion unit, and the switching control unit adjusts the on-time of the switching element based on the error signal. (Fourth configuration) may be used.

The load drive device having any of the first to fourth configurations includes a current detection unit that detects a current flowing through the switching element, and the switching control unit is said to have the second signal at a predetermined level. When the magnitude of the current flowing through the switching element detected by the current detection unit falls below the threshold value, the switching element is turned on, and if the second signal is at the predetermined level, the switching element is turned off. It may be configured to maintain and stop the switching operation (fifth configuration).

In the load drive device having the fifth configuration, the second signal is an output signal of an open drain circuit using a P channel transistor or an open collector circuit using a PNP transistor, and the output end of the current detection unit and the said. The connection point voltage with the output end of the open drain circuit or the open collector circuit may be input to the switching control unit (sixth configuration).

The load drive device having any of the first to sixth configurations may be configured to include the power factor improving circuit and include a SEPIC that performs voltage conversion with respect to the output voltage of the rectifier circuit (seventh configuration). ..

As a configuration (eighth configuration), the load drive device having any of the first to sixth configurations includes the power factor improving circuit and includes a flyback converter that performs voltage conversion with respect to the output voltage of the rectifier circuit. May be good.

Further, the lighting device disclosed in the present specification includes a load drive device having any one of the first to eighth configurations and a light emitting element driven by the load drive device (nineth configuration). ).

Further, the motor system disclosed in the present specification includes a load drive device having any of the first to eighth configurations and a motor driven by the load drive device (tenth configuration). Is.

According to the invention disclosed in the present specification, the output to the set load (for example, the dimming rate if the load is a light emitting element) is performed in order to perform constant current control beyond the adjustment range of the power factor improving circuit. By setting the output capacity of the power factor improvement circuit according to the above, the constant current control range can be expanded. Therefore, it is possible to provide a load drive device that can improve the power factor and can adjust the output to the load in a wide range at low cost.

The figure which shows one configuration example of a load drive device. The figure which shows the appearance example of a lighting device The figure which shows one configuration example of a switching control IC Timing chart showing operation examples of switching control ICs Diagram showing an open drain circuit Diagram showing a push-pull circuit Timing chart showing an example of dimming operation of a switching control IC The figure which shows the other configuration example of the load drive device.

FIG. 1 is a diagram showing a configuration example of a load drive device. The load drive device shown in FIG. 1 is a device that drives the load LD1 while improving the power factor, and mainly includes a diode bridge DB1, an input capacitor Cin, a transformer T1, a switching element Q1, and an output capacitor Cout. , A switching control IC (Integrated Circuit) 1 and an MCU (Micro Controller Unit) 2 are provided.

The diode bridge DB1 full-wave rectifies an AC voltage Vac such as a commercial AC power supply voltage. The input capacitor Cin smoothes the pulsating voltage output from the diode bridge DB1 to generate a DC voltage Vdc.

The transformer T1 includes a primary winding N1, a secondary winding N2, and an auxiliary winding N3.

A DC voltage Vdc is applied to one end of the primary winding N1. The switching element Q1 is an N-channel MOSFET, and the drain of the switching element Q1 is connected to the other end of the primary winding N1. The source of the switching element Q1 is grounded via the resistor R9. The resistor R9 is a resistor for detecting the current flowing through the switching element Q1. The source of the switching element Q1 is also connected to the fourth terminal of the switching control IC1 and one end of the capacitor C3. The other end of the capacitor C3 is grounded.

The source of the switching element Q1 is connected to the gate of the switching element Q1 via the resistor R8. The gate of the switching element Q1 is connected to the 7th terminal of the switching control IC1 via a parallel circuit composed of the diode D1 and the resistor R7 and the resistor R6.

One end of the resistor R12 and one end of the output capacitor Cout are connected to one end of the secondary winding N2 via a diode D4. The other end of the primary winding N1 is also connected to one end of the secondary winding N2 via the capacitor C1. Since the other end of the primary winding N1 and one end of the secondary winding N2 are connected via the capacitor C1 in this way, the load drive device shown in FIG. 1 includes a STEPIC (Single Ended Primary Inductor Converter). It becomes a configuration and efficiency can be improved. The other end of the secondary winding N2, the other end of the resistor R12, and the other end of the output capacitor Cout are grounded. One end of the load LD1 is connected to one end of the output capacitor Cout.

The input end of the regulator 3, the eighth terminal of the switching control IC1, and one end of the resistor R1 are connected to one end of the auxiliary winding N3 via the diode D3. The other end of the auxiliary winding N3 is grounded. One end of the resistor R10 is also connected to one end of the auxiliary winding N3.

The regulator 3 stabilizes the voltage applied to the input end and outputs the voltage from the output end. The output end of the regulator 3 is connected to one end of the capacitor C5 and the power supply terminal of the error amplifier A1. The other end of the capacitor C5 and the ground terminal of the error amplifier A1 are grounded.

The other end of the resistor R1 is connected to the first terminal of the switching control IC1 and one end of the resistor R2. The other end of the resistor R2 is grounded.

The other end of the resistor R10 is connected to the 5th terminal of the switching control IC1 and one end of the resistor R11. The other end of the resistor R11 is grounded via the diode D2. Further, the second signal SG2 output from the MCU 2 is supplied to the 5th terminal of the switching control IC 1.

One end of the resistor R5 and one end of the capacitor C4 are also connected to the input end of the regulator 3, the eighth terminal of the switching control IC 1, and one end of the resistor R1. The other end of the resistor R5 is connected to one end of the resistor R4, and the other end of the capacitor C4 is grounded. A DC voltage Vdc is applied to one end of the resistor R4.

The other end of the load LD1 and the inverting input terminal of the error amplifier A1 are connected to one end of the resistor R14. The other end of the resistor R14 is grounded. The resistance R14 is a resistance for detecting the current flowing through the load LD1.

The first signal SG1 output from the MCU 2 is smoothed by the resistor R15 and the capacitor C7, and then supplied to the non-inverting input terminal of the error amplifier A1.

The output terminal of the error amplifier A1 is connected to the second terminal of the switching control IC1 and one end of the capacitor C2. The other end of the capacitor C2 is grounded. Further, the output terminal of the error amplifier A1 is connected to the non-inverting input terminal of the error amplifier A1 via the capacitor C6 and the resistor R13.

The third terminal of the switching control IC1 is grounded via the resistor R3.

In the present embodiment, the load LD1 is a series of LEDs (Light Emitting Diodes), and the LEDs are dimmed by the first signal SG1 and the second signal SG2 output from the MCU2. Therefore, in the present embodiment, the load drive device is an LED drive device. The MCU2 determines the dimming rate of the LED based on the dimming signal sent from the external dimmer by wireless communication or wired communication, or the detection result of the illuminance sensor that detects the ambient brightness. The first signal SG1 and the second signal SG2 are generated according to the determined dimming rate.

FIG. 2 is a diagram showing an external example of a lighting device including the load drive device shown in FIG. 1 and the load LD1 which is a series of LEDs. The lighting device 10a is a bulb-shaped LED lamp, the lighting device 10b is a ring-shaped LED lamp, and the lighting device 10c is a straight tube type LED lamp. Further, the lighting device 10d is an LED ceiling light, and the lighting device 10e is an LED downlight. The lighting devices 10a to 10e are merely examples, and the lighting devices can be used in a wide variety of forms. For example, the lighting device may be a lighting device for a display device represented by an LED backlight of a liquid crystal television.

FIG. 3 is a diagram showing a configuration example of the switching control IC 1. FIG. 4 is a timing chart showing an operation example of the switching control IC1. The voltage Vzcd in FIG. 4 is a voltage applied to the 5th terminal of the switching control IC1.

In the configuration example shown in FIG. 3, the switching control IC 1 includes a hysteresis comparator 3, an error amplifier 4, a lamp voltage generation circuit 5, comparators 6 and 7, and a control logic circuit 8. The switching control IC 1 is driven by the voltage applied to the 8th terminal. Further, the switching control IC 1 generates a constant voltage such as the first to third reference voltages Vref1 to Vref3 from the voltage applied to the eighth terminal.

The hysteresis comparator 3 is a circuit that detects the zero cross of the current _IL flowing in the primary winding N1. When the voltage applied to the 5th terminal of the switching control IC1 is lower than the first reference voltage Vref1, the hysteresis comparator 3 switches the output signal from the high level to the low level, and then is applied to the 5th terminal of the switching control IC1. The output signal remains at low level until the voltage exceeds the voltage obtained by adding a positive predetermined value to the first reference voltage Vref1. The output signal of the hysteresis comparator 3 is supplied to the control logic circuit 8.

The error amplifier 4 is a circuit that monitors the output voltage of the load drive device. The error amplifier 4 outputs an offset signal according to the difference between the voltage applied to the first terminal of the switching control IC 1 and the second reference voltage Vref2.

The lamp voltage generation circuit 5 is a circuit that generates a lamp voltage Vramp having a slope determined by the resistance value of the resistor connected to the third terminal of the switching control IC1. The lamp voltage generation circuit 5 resets the lamp voltage Vram when a predetermined time elapses after the lamp voltage Vram exceeds the error output voltage Veo.

The switching control IC 1 generates an error output voltage Veo obtained by adding an offset signal of the error amplifier 4 to the voltage applied to the 5th terminal of the switching control IC 1.

The comparator 6 compares the error output voltage Veo and the lamp voltage Vramp, and outputs the comparison result to the control logic circuit 8.

The comparator 7 is a circuit that detects an overcurrent flowing through the switching element Q1. The comparator 7 compares the voltage applied to the 4th terminal of the switching control IC 1 with the third reference voltage Vref3, and outputs the comparison result to the control logic circuit 8.

The control logic circuit 8 generates a gate voltage Vg based on the output signal of the hysteresis comparator 3, the output signal of the comparator 6, and the output signal of the comparator 7. The gate voltage Vg is output from the 7th terminal of the switching control IC1.

As shown in FIG. 4, when the gate voltage Vg is switched from the low level to the high level, the drain-source voltage Vds of the switching element Q1 decreases and the switching element Q1 turns on (see timing t1 in FIG. 4). After that, the current IL flowing through the primary winding _N1 increases (see the period from timing t1 to timing t2 in FIG. 4).

Then, at the timing when the output signal of the comparator 6 is switched from the low level to the high level, that is, at the timing when the lamp voltage Vram exceeds the error output voltage Veo (timing t2 in FIG. 4), the control logic circuit 8 sets the gate voltage Vg. Switch from high level to low level. As a result, the switching element Q1 is turned off.

After that, the current IL flowing through the primary winding _N1 decreases (see the period from timing t2 to timing t3 in FIG. 4). Then, the timing at which the zero cross of the current _IL flowing in the primary winding N1 is detected by the hysteresis comparator 3, that is, the voltage applied to the 5th terminal of the switching control IC 1 falls below the first reference voltage Vref 1 of the hysteresis comparator 3. The control logic circuit 8 switches the gate voltage Vg from the low level to the high level after a predetermined time delay from the timing when the output signal is switched from the high level to the low level (timing t3 in FIG. 4). As a result, the switching element Q1 is turned on.

By the above operation, the control logic circuit 8 adjusts the on-time of the switching element Q1 based on the voltage applied to the second terminal of the switching control IC1. The voltage applied to the second terminal of the switching control IC 1 is the output signal (voltage signal) pressure of the error amplifier A1. The output signal of the error amplifier A1 is an error signal corresponding to the difference between the voltage obtained by smoothing the first signal SG1 with the resistor R15 and the capacitor C7 and the voltage obtained by converting the current flowing through the load LD1 with the resistor R14.

However, during the period when the overcurrent flowing through the switching element Q1 is detected by the comparator 7, that is, during the period when the output signal of the comparator 7 is at a high level, the control logic circuit 8 has a gate voltage Vg level as shown in FIG. The level of the gate voltage Vg is maintained at a low level without switching. As a result, the switching element Q1 is protected from overcurrent.

Further, in the present embodiment, when the second signal SG2 is set to a high level, the high level of the second signal SG2 is set so that the voltage applied to the fifth terminal of the switching control IC1 becomes larger than the first reference voltage Vref1. The value of is set. Therefore, during the period when the second signal SG2 is at a high level, the switching element Q1 does not turn on, so that the switching operation of the switching element Q1 is stopped.

In the period when the second signal SG2 is not at a high level, the terminal for outputting the second signal SG2 of the MCU 2 may be in a high pin- _pedance state so that the second signal SG2 does not interfere with the zero cross detection of the current IL. Therefore, in the present embodiment, the MCU 2 includes an open drain circuit using the P channel MOS transistor shown in FIG. 5, and outputs the second signal SG2 from the output end of the open drain circuit. An open collector circuit using a PNP bipolar transistor may be provided instead of the open drain circuit using the P channel MOS transistor shown in FIG.

The MCU 2 also includes the push-pull circuit shown in FIG. 6, and outputs the first signal SG1 from the output end of the push-pull circuit.

MCU2 makes the frequency of the first signal SG1 higher than the frequency of the second signal SG2. As a result, the second signal SG2 has a relatively low frequency, and it becomes easy to intermittently stop the switching operation of the switching element Q1. In the present embodiment, the frequency of the first signal SG1 is set to 20 kHz and the frequency of the second signal SG2 is set to 1 kHz, but this combination of frequencies is only an example and may be another frequency.

FIG. 7 is a timing chart showing an example of dimming operation of the switching control IC1. In FIG. 7, the waveform of the first signal SG1 is magnified 20 times in the direction of the time axis. Further, in FIG. 7, the percentage described in the upper part of the first signal SG1 is the on-duty of the first signal SG1, and the percentage described in the upper part of the second signal SG2 is the on-duty of the second signal SG2. be. The percentage shown at the top of the current bar _IL indicates the degree of magnitude of the current bar _IL when the current bar _IL at the rated output is 100%. The first signal SG1 is a PWM (Pulse Width Modulation) signal for setting an LED constant current whose on-duty is adjusted steplessly from 100% to 0%. The second signal SG2 is a PWM signal for adjusting the output capacity of the power factor improving circuit in advance in order to make the degree of the magnitude of the current bar IL correspond to the on-duty of the first signal _SG1 . The on-duty of the second signal SG2 may be adjusted steplessly or stepwise. There are two types of logic levels of the first signal SG1: high level (= voltage VH) and low level (= voltage VL). Similarly, there are two types of logic levels of the second signal SG2, a high level (= voltage VH) and a low level (= voltage VL).

When the MCU2 is a signal instructing that the first signal SG1 adjusts the on-time of the switching element Q1 to be larger than a predetermined value, the MCU2 does not provide a period for stopping the switching operation of the switching element Q1 from the second signal SG2. It is a signal to instruct. In the present embodiment, the first signal SG1 having an on-duty of greater than 60% is used as a signal instructing that the on-time of the switching element Q1 is adjusted to be larger than a predetermined value. Since the second signal SG2 having an on-duty of 0% does not have a period during which the second signal SG2 becomes at a high level, a signal indicating that a period for stopping the switching operation of the switching element Q1 is not provided. It becomes. In the present embodiment, whether or not the on-duty of the first signal SG1 is larger than 60% determines whether or not the signal indicates that the on-time of the switching element Q1 is adjusted to be larger than a predetermined value. This value of 60% is just an example, and may be another value. However, it is desirable to set the value larger than the dimming rate, which makes it difficult to reduce the output current while suppressing the generation of harmonic components of the commercial AC power frequency (50 Hz or 60 Hz).

When the on-duty of the first signal SG1 is larger than 60% and 100% or less, the output power W1 of the power factor improving circuit is substantially proportional to the on-duty of the first signal SG1.

On the other hand, when the MCU2 is a signal instructing that the first signal SG1 adjusts the on time of the switching element Q1 to a predetermined value or less, the MCU2 is provided with a period for stopping the switching operation of the switching element Q1 from the second signal SG2. It is a signal to instruct.

When the on-duty of the first signal SG1 is 60% or less, the output power W1 of the power factor improving circuit during the period when the second signal SG2 is not at a high level is automatically adjusted by the error amplifier A1.

However, since the switching operation of the switching element Q1 can be stopped by the high level period of the second signal SG2, the LED can be turned on with the brightness corresponding to the small dimming rate. As a result, the degree of the magnitude of the current bar IL _smoothed by the output capacitor Cout smoothing the output of the power factor improving circuit and supplied to the load LD1 (series of LEDs) follows the on-duty of the first signal SG1. Can be made to. That is, the power factor can be improved and the output current to the load LD1 can be adjusted in a wide range.

When the on-duty of the second signal SG2 is not 0%, the minimum adjustment width that can adjust the on-duty of the first signal SG1 and the minimum adjustment unit that can adjust the on-duty of the second signal SG2 are the same. There may be, and one may be larger than the other.

<4. Others>
In addition to the above embodiments, the configuration of the present invention can be modified in various ways without departing from the gist of the invention. That is, it should be considered that the embodiments are exemplary in all respects and are not restrictive, and the technical scope of the invention is not the description of the embodiments but the claims. It is shown and should be understood to include all modifications that fall within the meaning and scope of the claims.

For example, in the above-described embodiment, the LED is used as the light emitting element, but another light emitting element such as an organic EL (Electro Luminescence) may be used instead of the LED.

For example, in the above-described embodiment, the load drive device adjusts the light emitting element, but the light emitting element may be adjusted in place of the dimming of the light emitting element or in addition to the dimming of the light emitting element. The toning of the light emitting element can be realized by independently adjusting each of a plurality of light emitting elements having different light emitting colors.

For example, in the above-described embodiment, the load of the load drive device is the light emitting element, but the load of the light emitting element is not limited to the light emitting element, and may be, for example, a motor or the like. A motor system including a motor and a load drive device for driving the motor is used in various devices, devices, equipment, and the like.

For example, in the above-described embodiment, the MCU2 that generates the first signal SG1 and the second signal SG2 is included in the load drive circuit, but the circuit that generates the first signal SG1 and the second signal SG2 is outside the load drive circuit. The load drive circuit may be configured to receive the first signal SG1 and the second signal SG2.

For example, in the above-described embodiment, the load drive device is configured to include a SEPIC, but by replacing the capacitor C1 of the load drive device shown in FIG. 1 with the snubber circuit S1 as shown in FIG. 8, the flyback converter can be obtained. It may be changed to the provided configuration. The specific configuration of the snubber circuit S1 is not limited to the example shown in FIG. 8, and may be another configuration.

Further, the load drive device may be provided with a photocoupler so that the load drive device includes a back converter and a back boost converter.

1 Switching control IC
2 MCU
10a-10e Lighting equipment Cin input capacitor Cout output capacitor DB1 diode bridge Q1 switching element T1 transformer

Claims (9)

A load drive device including a rectifier circuit that rectifies an AC voltage and a power factor improving circuit connected to the output side of the rectifier circuit.
The power factor improving circuit includes a switching element and a switching control unit that controls the switching operation of the switching element.
The switching control unit adjusts the on-time of the switching element based on the first signal, and determines whether or not to stop the switching operation based on the second signal .
When the first signal is a signal instructing to adjust the on-time to be larger than a predetermined value, the second signal is a signal instructing not to provide a period for stopping the switching operation.
When the first signal is a signal instructing to adjust the on-time to a predetermined value or less, the second signal is a signal instructing to provide a period for stopping the switching operation, which is a load drive. Device. The load drive device according to claim 1, wherein the frequency of the first signal is higher than the frequency of the second signal. A smoothing portion that smoothes the first signal,
A conversion unit that converts the current flowing through the load driven by the load drive device into a voltage, and
An error amplifier that generates an error signal according to the difference between the output voltage of the smoothing section and the output voltage of the converting section is provided.
The load drive device according to claim 1 or 2 , wherein the switching control unit adjusts the on-time of the switching element based on the error signal. A current detection unit that detects the current flowing through the switching element is provided.
If the second signal is not at a predetermined level, the switching control unit turns on the switching element when the magnitude of the current flowing through the switching element detected by the current detection unit falls below the threshold value. The load drive device according to any one of claims 1 to 3 , wherein if the second signal is at the predetermined level, the switching element is kept in an off state to stop the switching operation. The second signal is an output signal of an open drain circuit using a P channel transistor or an open collector circuit using a PNP transistor.
The load drive device according to claim 4 , wherein the connection point voltage between the output end of the current detection unit and the output end of the open drain circuit or the open collector circuit is input to the switching control unit. The load drive device according to any one of claims 1 to 5 , further comprising a SEPIC that includes the power factor improving circuit and performs voltage conversion with respect to the output voltage of the rectifier circuit. The load drive device according to any one of claims 1 to 5 , further comprising a flyback converter that includes the power factor improving circuit and performs voltage conversion with respect to the output voltage of the rectifier circuit. The load drive device according to any one of claims 1 to 7 .
A lighting device including a light emitting element driven by the load drive device. The load drive device according to any one of claims 1 to 7 .
A motor system comprising a motor driven by the load drive device.

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