WO2012070512A1

WO2012070512A1 - Insulated power source device and lighting device

Info

Publication number: WO2012070512A1
Application number: PCT/JP2011/076752
Authority: WO
Inventors: 稔加戸; 聡史有馬
Original assignee: ミツミ電機株式会社
Priority date: 2010-11-26
Filing date: 2011-11-21
Publication date: 2012-05-31
Also published as: JP2012115074A

Abstract

The problem addressed by the present invention is to cause an insulated power source device provided with an error amplifier at the secondary side to be able to reduce the time from starting up a power source voltage until a feedback voltage reaches a target value. The present invention has: a control circuit that generates and outputs a control signal of a switching element that controls the current that flows through the primary side of a power conversion means (transformer) in response to a feedback signal; a detection means that detects output voltage or output current; a feedback voltage generation circuit that generates feedback voltage in response to the detection signal from the detection means; and a signal transfer means that transfers the feedback signal generated by the feedback voltage generation circuit to the control circuit. The feedback voltage generation circuit is provided with: an error amplification circuit that outputs a voltage in response to the potential difference between the output signal and a predetermined baseline voltage; and a buffer amplifier that impedance converts and outputs the output of the error amplification circuit. An offset imparting means that imparts an offset to the output voltage of the buffer amp is provided between the output terminal of the buffer amp and an inverting input terminal.

Description

Insulated power supply and lighting device

The present invention relates to an insulation type power supply device provided with a voltage conversion transformer and a technology effective for use in a lighting device using the same.

The power supply device includes an insulated AC-DC converter that includes a voltage conversion transformer, converts the voltage of AC power, rectifies the AC induced on the secondary side, and converts it into a DC voltage of a desired potential. As an insulated AC-DC converter, for example, a switching power supply device is known which controls the power induced in the secondary winding by controlling the current flowing in the primary winding of the voltage conversion transformer. It has been.

By the way, in a switching power supply device, PWM (pulse width modulation) control is often employed in order to increase power efficiency. Even in an isolated AC-DC converter, a detection signal of a secondary side output is primary by a photocoupler. There has also been proposed an invention in which the primary side control circuit is fed back to the side control circuit and the switching element is turned on and off by PWM pulses to control the current flowing through the primary side coil (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-31142 JP-T-2004-527138

As disclosed in Patent Document 1, the detection signal of the secondary side output in the isolated AC-DC converter is obtained by subjecting the output voltage or the voltage obtained by converting the output current to current-voltage to resistance division, and the voltage and reference The voltage Vref is compared with an error amplifier, and a voltage (feedback voltage VFB) corresponding to the potential difference is output to drive the light-emitting element (photodiode) of the photocoupler and transmit it to the primary side control circuit via the photocoupler. Often configured.

By the way, in the output control loop of the isolated AC-DC converter, it is desirable to set a large time constant of the error amplifier in order to improve the stability of the loop. However, when the time constant of the error amplifier is increased, as shown in FIG. 7, when the power supply voltage Vcc of the secondary side circuit is raised at the time of startup, the change of the feedback voltage VFB becomes gradual, corresponding to the load. There is a problem that the delay time Td until the convergence value is reached becomes long, and the operation of the load becomes unstable during that time.

In particular, when it is desired to change the output voltage with an external PWM control signal, the cutoff frequency fc of the low-pass filter (smoothing choke coil and smoothing capacitor) connected to the secondary coil side to stabilize the output voltage is set. It is necessary to set higher than the frequency of the PWM control signal. However, since there is a relationship expressed by τ = 1 / 2πfc between the filter time constant τ and the cut-off frequency fc, the time constant decreases as the filter fc is increased. Therefore, it is necessary to set a large time constant for the error amplifier. As a result, there is a problem that when the power supply voltage Vcc is raised, the time until the feedback voltage VFB output from the error amplifier reaches the convergence value becomes long.

An object of the present invention is to provide an isolated power supply apparatus such as an AC-DC converter having an error amplifier on the secondary side that generates and outputs a feedback voltage corresponding to a potential difference between a voltage proportional to an output and a reference voltage. The purpose is to shorten the time from when the voltage is raised to when the feedback voltage reaches the target value, so that the control loop can be stabilized in a short time when the power is turned on.
Another object of the present invention is to start up a power supply while ensuring the stability of a feedback control loop in a steady state in an isolated power supply device configured to be able to change an output voltage with an external PWM control signal. Sometimes it is possible to shorten the time until the control loop stabilizes.

In order to achieve the above object, the present invention
Power conversion means for converting AC power input to the primary side and outputting it to the secondary side, rectification means provided on the secondary side of the power conversion means, and current / voltage rectified by the rectification means Among them, a filter for passing a current / voltage in a predetermined frequency band, a detection means for detecting an output current or output voltage supplied to a load through the filter, and a feedback voltage corresponding to a detection signal by the detection means are generated. A feedback voltage generation circuit that generates, a control circuit that generates and outputs a control signal for a switching element that controls a current that flows to the primary side of the power conversion unit according to the feedback signal, and a voltage generated by the feedback voltage generation circuit. And a signal transmission means for transmitting the feedback signal to the control circuit in response.
The feedback voltage generation circuit includes:
An error amplifying circuit for outputting a voltage corresponding to a potential difference between the detection signal and a predetermined reference voltage; and a buffer amplifier for converting the output of the error amplifying circuit by impedance conversion and inverting the output terminal of the buffer amplifier. An offset applying means for applying an offset higher than the input voltage by a predetermined potential to the output voltage of the buffer amplifier is connected between the input terminal and the input terminal.

According to the above means, the output voltage of the buffer amplifier becomes a voltage obtained by adding a predetermined offset to the output voltage of the error amplifier circuit in the previous stage, so that the feedback voltage reaches the target value after the power supply voltage is raised. The control loop can be stabilized in a short time when the power is turned on.

Here, desirably, the offset applying means is a two-terminal switching element that becomes conductive when a predetermined potential difference is exceeded, and is connected so that a conductive current flows from the output terminal of the buffer amplifier toward the inverting input terminal. The configuration.
By using a two-terminal switching element such as a diode as an offset providing means, an offset is added to the output of the buffer amplifier by adding only one element, and the time until the feedback voltage reaches the target value is increased. It can be shortened.

More preferably, the error amplifier circuit includes a differential amplifier, and a capacitive element is connected between the output terminal and the inverting input terminal of the differential amplifier.
By connecting a capacitive element between the output terminal and the inverting input terminal of the differential amplifier that constitutes the error amplifier circuit provided on the secondary side, the apparent capacitance value increases and the cutoff frequency is reduced. While functioning as a low-pass filter to stabilize the control loop, the lower cutoff frequency increases the time constant and delays the feedback voltage rise at power-up. The amount of change in the output voltage of the error amplifier circuit necessary for reaching the target voltage can be reduced and avoided by the action of the rectifying element provided between the terminals. That is, it is possible to shorten the time until the control loop is stabilized at the time of power activation while ensuring the stability of the feedback control loop in a steady state.

Further, the cutoff frequency of the filter is lower than the switching frequency of the control signal generated by the control circuit, and higher than the frequency of the output control pulse signal having control information in the duty ratio supplied from the outside. Set,
A correction circuit for correcting the detection signal based on the output control pulse signal having control information in a duty ratio is provided on the secondary side of the power conversion means,
The control circuit includes a pulse generation circuit that generates a PWM control pulse having a pulse width corresponding to a feedback signal, and a pulse limiting circuit that limits the PWM control pulse generated by the pulse generation circuit according to the output control pulse signal And comprising
The correction circuit is configured to have a function of canceling the change of the detection signal that changes when the output control pulse signal is input to the primary side circuit and the output is controlled by feedforward.
By providing the correction circuit, the output current or the output voltage can be controlled based on the output control pulse signal supplied from the outside, and the output voltage is set to a desired value by the supplied output control pulse signal. It is possible to avoid deviation.

Further preferably, the correction circuit includes a resistor connected in series between a constant potential terminal to which a predetermined constant potential is supplied and an input terminal to which the detection signal of the error amplifier circuit is input. And the output control pulse signal is applied to the control terminal of the transistor.
As a result, the correction circuit can be realized with a relatively simple circuit.

Preferably, the signal transmission means is a photocoupler including a light emitting element and a light receiving element, and the light emitting element is connected between an output terminal of the buffer amplifier and a ground potential point, and an output voltage of the buffer amplifier. A current corresponding to the current is passed through the light emitting element.
As a result, a current proportional to the output of the error amplifier circuit can be passed through the light emitting element with a relatively simple circuit, and an accurate feedback signal can be transmitted to the control circuit on the secondary side.

Also, an insulated power supply device having the above configuration, an LED lamp that is connected to the output terminal of the insulated power supply device and lights when the output current flows, and a control signal that generates the output control pulse signal An illuminating device is comprised with a production | generation means.
Thereby, while being able to control the brightness of an LED lamp with a PWM pulse, the LED illuminating device which can reach desired brightness rapidly at the time of power activation is realizable.

According to the present invention, in an isolated power supply device such as an AC-DC converter that includes an error amplifier on the secondary side that generates and outputs a feedback voltage corresponding to a potential difference between a voltage proportional to an output and a reference voltage. The time from when the voltage is raised to when the feedback voltage reaches the target value can be shortened so that the control loop can be stabilized in a short time when the power is turned on. In addition, in an insulated power supply device configured to be able to change the output voltage with an external PWM control signal, the control loop is stabilized at the time of power activation while ensuring the stability of the feedback control loop in a steady state. This has the effect of shortening the time until.

1 is a block configuration diagram showing a first embodiment of an AC-DC converter as an effective insulated power supply apparatus to which the present invention is applied. FIG. 2 is a timing chart showing changes in an enable signal, a reference voltage, a feedback voltage, and the like when the AC-DC converter of FIG. 1 is powered on. FIG. 2 is a circuit configuration diagram illustrating a specific configuration example of the AC-DC converter of FIG. 1. It is a block block diagram which shows 2nd Embodiment of the AC-DC converter as an insulation type power supply device effective by applying this invention. FIG. 5 is a circuit configuration diagram showing a specific configuration example of the AC-DC converter of FIG. 4. It is a circuit diagram which shows the other example of the method of applying the bias voltage to the light reception transistor of a photocoupler. 6 is a timing chart showing changes in an enable signal, a reference voltage, a feedback voltage, and the like at the time of starting a power supply of a conventional insulated AC-DC converter.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a block configuration diagram of a power supply device according to the first embodiment configured by an insulating AC-DC converter or the like.

The power supply device according to the present embodiment includes a power conversion unit 10 including a transformer that converts the AC input voltage Vin, a rectification unit 11 that rectifies the converted AC, and a predetermined frequency of the rectified voltage / current. A filter circuit 12 that passes the voltage / current of the band and supplies it to the load 30; a detection means 13 that detects a current flowing through the load 30; and a feedback voltage generation circuit 14 that generates a feedback signal corresponding to the detected current value. And an insulated signal transmission means 15 comprising a photocoupler or the like in which the input side and the output side are electrically isolated, and transmitting the feedback signal FB to the primary side, and a current to the primary side of the power conversion means 10 A switching means 16 comprising a self-extinguishing element such as a MOS transistor, and a pulse for controlling on / off of the switching means 16 in accordance with a signal transmitted by the signal transmission means 15. And a control circuit 17 which generates a signal.
The rectifying means 11 is composed of a diode, and the filter circuit 12 is a smoothing capacitor provided between a coil provided in series between the rectifying means 11 and an output terminal to which a load is connected, and a ground point. (See FIG. 3).

FIG. 3 shows a specific circuit configuration of the isolated AC-DC converter of FIG.
As shown in FIG. 3, the AC-DC converter of this embodiment includes a noise blocking filter 21 composed of a common mode coil and the like, a diode bridge circuit 22 that rectifies AC voltage (AC) and converts it into DC voltage, and As a transformer T1 having a smoothing capacitor C0, a primary winding Np, an auxiliary winding Nb, and a secondary winding Ns, and switch means 16 connected in series with the primary winding Np of the transformer T1 And a power supply control IC (semiconductor integrated circuit) as a primary side control circuit 17 for driving the switching element SW. The power conversion means 10 is composed of the diode bridge circuit 22 and the transformer T1.

The secondary side of the transformer T1 includes a rectifying diode D1 connected in series between the secondary winding Ns and the output terminal OUT1, and the cathode terminal of the diode D1 and the other of the secondary winding Ns. And a filter circuit 12 having a coil L1 connected in series with a rectifying diode D1 and a capacitor C1 connected between the terminals of the first and second terminals of the secondary winding by passing current intermittently through the primary winding Np. The alternating current induced in the side winding Ns is rectified, and the filter circuit 12 stabilizes the output voltage / current and outputs it from the output terminal OUT1.

In addition, a sense resistor Rs is connected between the output terminal OUT2 and the ground point as detection means 13 for detecting a current flowing through a load connected between the output terminals OUT1 and OUT2. The cut-off frequency of the filter circuit 12 is set lower than the switching frequency by the control circuit 17 so that the switching noise on the primary side is cut off and not transmitted to the output.

Further, on the secondary side of the transformer T1, the voltage Vd that has been subjected to current-voltage conversion by the sense resistor Rs is input to the inverting input terminal via the resistor R1, and the reference voltage Vref1 is input to the non-inverting input terminal to detect it. A standard for generating a reference voltage Vref1, which includes an error amplifier AMP1 that outputs a voltage corresponding to a current value, a buffer amplifier (voltage follower) AMP2 that receives the output of the error amplifier and generates a feedback signal VFB, a band gap reference circuit, and the like. A feedback voltage generation circuit 14 as a secondary side circuit including a voltage generation circuit VRG and the like is provided. In the present embodiment, the feedback voltage generation circuit 14 is configured as a semiconductor integrated circuit (secondary side IC).

Then, the signal generated by the feedback voltage generation circuit 14 is transmitted to the primary side by the photocoupler PC as the signal transmission means 15. Specifically, a light emitting side photodiode PD1 constituting the photocoupler PC is connected between the output terminal of the buffer amplifier AMP2 and the ground point, and a current corresponding to the output voltage of the buffer amplifier AMP2 is supplied to the photodiode PD1. A collector current proportional to the light emission amount is caused to flow through the phototransistor that has received the light, converted into a voltage by a resistor, and supplied to the error amplifier AMP3 of the primary side control circuit 17. Yes.

Also, a phase compensation capacitor Cf is provided between the output terminal and the inverting input terminal of the secondary side error amplifier AMP1, and the capacitor Cf and the resistor R1 constitute a low-pass filter. Then, the capacitance Cf has a value (1 + A) Cf that is substantially a gain multiple of the original capacitance value when viewed from the input side due to the mirror effect of the amplifier, and functions as a low-pass filter with a low cutoff frequency. The voltage Vd that changes according to the current can be smoothed. As a result, a DC voltage corresponding to the average voltage Vd is input to the inverting input terminal of the error amplifier AMP1.

The buffer amplifier (voltage follower) AMP2 is connected between the output terminal and the inverting input terminal so as to be in the forward direction from the output terminal toward the inverting input terminal, and becomes conductive when a predetermined potential difference is exceeded. A diode D2 is provided as a terminal switching element. By providing the diode D2, an offset is added to the output Va of the error amplifier AMP1, and the output of the buffer amplifier AMP2 becomes a voltage higher than Va by the forward threshold voltage Vf of the diode D2. The point where the diode D2 is provided is one of the points of the present invention. As the diode D2, a PN junction diode having a relatively large forward threshold voltage is more suitable than a shocky barrier having a small forward threshold voltage. This is because the number of diodes required to obtain a desired offset can be reduced. However, the means for adding an offset to the output of the error amplifier AMP1 is not limited to a diode, and may be, for example, a diode-connected MOS transistor in which a gate and a drain are coupled. Further, when the buffer amplifier AMP2 is configured by a current output amplifier, a desired offset can be added by simply changing the setting of the VI characteristic without adding a diode.

Further, the feedback voltage generation circuit 14 of the present embodiment is provided with a low voltage detection circuit UVLO for detecting whether the power supply voltage Vcc of the secondary side IC is lower than a predetermined potential, and from the low voltage detection circuit UVLO. The constant current sources of the amplifiers AMP1 and AMP2 in the secondary IC are controlled by the output enable signal EN so that the operation of these circuits is deactivated (the operation is turned off) at a low voltage. It is configured.
In the present embodiment, a resistor R2 and a capacitor C2 are connected between the error amplifier AMP1 and the subsequent buffer amplifier AMP2, and the transfer function as a secondary low-pass filter having two poles together with the error amplifier AMP1. By functioning, it is configured to effectively block high frequency band noise. However, the time constant as a filter including the error amplifier AMP1 increases as the cutoff frequency decreases.

Next, the power supply control IC 17 that receives a feedback signal from the secondary side via the photocoupler PC and turns the switching element SW on and off will be described.
The power supply control IC 17 is provided with an external terminal P1 to which the collector of the light receiving transistor Tr1 constituting the photocoupler PC is connected. The light receiving transistor Tr1 has its emitter terminal connected to the ground potential GND, and the external terminal P1 is a terminal to which the internal voltage Vreg generated inside the power supply control IC 17 is applied via the pull-up resistor Rp1. And is configured to apply a bias to the collector of the light receiving transistor Tr1. As a result, when the photodiode PD1 of the photocoupler PC is turned on while the Tr1 is biased by the internal voltage Vreg, a collector current flows through the Tr1, and the potential of the external terminal P1 decreases due to the voltage drop of the resistor Rp1. The internal circuit amplifies the control operation.

Further, in the power control IC 17, the voltage of the external terminal P1 is input to the inverting input terminal via the resistor R6, the reference voltage Vref2 is input to the non-inverting input terminal, and the voltage of the external terminal P1 and the reference voltage Vref2 An error amplifier AMP3 that outputs a voltage corresponding to the potential difference is provided. A combination of the error amplifier AMP3 and the photocoupler PC can be regarded as the signal transmission circuit 15.

The power supply control IC 17 receives a waveform generation circuit RAMP including a constant current source CC1, a capacitor C4, and a discharge MOS transistor SW2, an output of the error amplifier AMP3, and a waveform signal generated by the waveform generation circuit RAMP. A comparator (voltage comparison circuit) CMP1 for comparison is provided. In the waveform generation circuit RAMP, the output gradually rises when the capacitor C4 is charged by the current of the constant current source CC1, and when the switching element SW2 is turned on, the charge of the capacitor C4 is discharged at once and the output suddenly falls. By repeating the operation, a sawtooth waveform signal is generated. The comparator CMP1 functions as a PWM comparator that generates a PWM pulse having a pulse width corresponding to the output of the error amplifier AMP3.

Further, the power supply control IC 17 has an external terminal P3 to which one terminal of the auxiliary winding Nb provided in the transformer T1 (10) is connected, and an inverting input terminal connected to the external terminal P3 and a non-inverting input. A comparator CMP2 having a reference voltage Vref3 applied to its terminal, a one-shot pulse generation circuit OPG1 that detects a rising edge of the output of the comparator CMP2 and generates a pulse signal, a restart timer circuit RST, and an output of the circuit An OR gate G1 having the output of the shot pulse generation circuit OPG1 as an input, and an RS flip-flop FF1 in which the output of the OR gate G1 is input to the set terminal S and the output of the comparator CMP1 is input to the reset terminal R. ing.
An output Q of the RS flip-flop FF1 is output to the outside of the IC as an on / off control signal on / off of the switching element SW, and an inverted output / Q of the FF1 controls on / off of the discharge MOS transistor SW2 of the waveform generation circuit RAMP. A signal is supplied to the gate terminal of SW2.

In the AC-DC converter of this embodiment, the output of the comparator CMP2 changes to high level when the voltage induced in the auxiliary winding Nb becomes lower than the reference voltage Vref3, that is, when the current of the auxiliary winding decreases to some extent. Then, a one-shot pulse is generated by OPG1, and the flip-flop FF1 is set. Then, the control signal on / off changes to a high level, the switching element SW is turned on, a current flows through the primary side winding Np, and SW2 in the waveform generation circuit RAMP is turned off, so that the input of the comparator CMP1 is gradually increased. The flip-flop FF1 is reset when it becomes higher than the feedback signal FB. Then, the control signal on / off changes to the low level to turn off the switching element SW, and SW2 in the waveform generation circuit RAMP is turned on to discharge the capacitor and the waveform signal falls.

The period in which the current flows through the primary winding Np is controlled so that the feedback signal FB becomes constant by repeating the above operation, and the pulse width of the output current pulse is controlled. The on / off control of the current of the primary winding Np by the switching element SW is performed at a frequency sufficiently higher than the frequency of the input AC voltage AC.

In the secondary side IC (14) of the embodiment of FIG. 3, as shown in FIG. 2, when the power supply voltage Vcc rises to a certain potential, the reference voltage Vref1 rises and the enable signal EN output from the low voltage detection circuit UVLO. Rises from low level to high level. As a result, the error amplifier AMP1 and the buffer amplifier AMP2 are activated, and the output voltage Va of the error amplifier AMP1 and the output voltage VFB of the buffer amplifier AMP2 are gradually increased. At this time, when the diode D2 is not provided, as shown in FIG. 2E, the time Td until the output voltage VFB of the buffer amplifier AMP2 reaches the target voltage (convergence value) becomes long.

On the other hand, in the secondary side IC (14) of the embodiment of FIG. 3 provided with the diode D2, the output voltage VFB of the buffer amplifier AMP2 is Va + Vf obtained by adding an offset of Vf to the output voltage Va of the error amplifier AMP1. As shown in FIG. 2D, when the output voltage Va of the error amplifier AMP1 reaches Vt−Vf, the output voltage VFB of the buffer amplifier AMP2 reaches the target voltage (convergence value) as shown in FIG. Therefore, the required time Td is shortened. That is, it takes a short time until the control loop is stabilized after the power is turned on. Note that the voltage Vf corresponding to the clogging applied to the output of the buffer amplifier AMP2 appears as an error corresponding to one gain of the error amplifier with respect to the output, so that there is no significant problem in accuracy.

As described above, in the embodiment of FIG. 3, one diode D2 is provided between the output terminal and the inverting input terminal of the buffer amplifier AMP2. However, two or more diodes are provided in series. You may do it. Specifically, when the forward threshold voltage Vf of the diode is 0.7 V and the fluctuation range of the feedback voltage VFB in the steady state is to be set to a range such as 1 V to 5 V, for example, as shown in FIG. Diodes D2 are provided. If it is desired to set the fluctuation range of VFB to a range of 2V to 5V, for example, two diodes may be provided.

Next, a second embodiment of the present invention will be described.
FIG. 4 is a block diagram of the insulation type AC-DC converter according to the second embodiment. In the following embodiments, a power supply device that drives an LED as a load will be described and described. However, a power supply device to which the present embodiment can be applied is not limited to a case where the load is an LED. The AC-DC converter according to the present embodiment enables output voltage / current to be controlled by a PWM control signal supplied from the outside.

The AC-DC converter according to the present embodiment is similar to the AC-DC converter according to the first embodiment shown in FIG. 1 in that the power conversion means 10 including a transformer, the rectification means 11 that rectifies the converted alternating current, A filter circuit 12 that passes a voltage / current in a predetermined frequency band out of the rectified voltage / current and supplies the voltage / current to the load 30; a detection means 13 that detects a current flowing through the load 30; and a detected current value. A feedback voltage generation circuit 14 for generating a corresponding feedback signal FB, and an insulating signal transmission means 15 for transmitting the feedback signal FB to the primary side, which includes a photocoupler in which the input side and the output side are electrically insulated. Switch means 16 comprising a MOS transistor or the like for passing a current to the primary side of the power conversion means 10; and switch means according to the signal transmitted by the signal transmission means 15 And a control circuit 17 for generating a pulse signal for controlling on and off 6.

The filter circuit 12 is set such that the cutoff frequency is lower than the switching frequency of the switch means 16 by the primary side control circuit 17 and higher than the frequency of the external PWM control signal PWM supplied from the outside. Thus, a pulse current having the same frequency as that of the external PWM control signal PWM is output. In a system in which the load is an LED lamp, the external PWM control signal PWM is a signal for controlling dimming.
When the cutoff frequency of the filter circuit 12 is set to be lower than the frequency of the external PWM control signal PWM as described above, an absolute current corresponding to the duty ratio of the external PWM control signal PWM is output, and the DC adjustment is performed. Light control is possible. In the case of DC dimming control, the linearity of the brightness of the LED with respect to the average output current is deteriorated, but the PWM dimming control is performed by outputting the PWM-controlled pulse current as in the power supply device of this embodiment. Thus, the linearity of the brightness of the LED with respect to the average output current can be improved. In addition, in the DC dimming control, the emission color of the LED lamp also changes when the output current value changes. However, the change in the emission color can be reduced by applying the above embodiment that performs the PWM dimming control. Note that the time constant of the filter circuit 12 is reduced by increasing the cutoff frequency of the filter circuit 12 for PWM control of the output. Therefore, in order to improve the stability of the control loop, the time constant of the error amplifier AMP1 in the subsequent stage is set. It will be set larger.

Further, the power supply device according to the present invention outputs a feedback amount correction circuit 18 that corrects a feedback signal sent to the primary side by the feedback voltage generation circuit 14 in accordance with an external PWM control signal PWM supplied from the outside, and an output from the control circuit 17. And a mask circuit 19 for thinning out the pulses by masking the ON / OFF pulse signal. The mask circuit 19 is configured to change the thinning amount in accordance with the PWM control signal transmitted from the primary side.
Note that the external PWM control signal PWM supplied from the outside to the secondary circuit may be transmitted to the secondary side by a photocoupler that is separate from the photocoupler (signal transmission means) that transmits the feedback signal. Although it is good, the external PWM control signal PWM and the feedback signal generated by the feedback voltage generation circuit 14 are combined on the secondary side, and then transmitted to the primary side by one photocoupler, and the PWM control signal is extracted to the primary side A separation function may be provided.

FIG. 5 shows a specific circuit configuration of the AC-DC converter of the second embodiment shown in FIG. Hereinafter, differences from the AC-DC converter of the first embodiment shown in FIG. 3 will be mainly described.
In the power supply device according to the second embodiment, the control circuit 17 for driving the switching element SW is used as a primary power control IC (semiconductor integrated circuit) 23 together with a mask circuit 19 including OR gates G1 and G2 and a flip-flop FF1. It is configured.

Further, the secondary side IC 14 includes an error amplifier AMP1 and a buffer amplifier AMP2. Between the output terminal and the inverting input terminal of the buffer amplifier AMP2, as in the first embodiment, the output terminal is changed to the inverting input terminal. A diode D2 is provided so as to be in the forward direction. By providing the diode D2, the output of the buffer amplifier AMP2 is configured to be higher than the output Va of the error amplifier AMP1 by the forward threshold voltage Vf of the diode D2.
Thus, by providing the diode D2 between the output terminal and the inverting input terminal of the buffer amplifier AMP2 of the secondary IC (14), the present embodiment is similar to the embodiment of FIG. As shown in d), when the output voltage Va of the error amplifier AMP1 reaches Vt−Vf, the output voltage VFB of the buffer amplifier AMP2 reaches the target voltage Vt. The required time Td can be shortened.

In this embodiment, a feedback amount correction circuit 18 is provided, and the detection voltage Vd is relative to Vref1 according to the duty ratio or pulse width of the PWM control signal PWM generated by the external PWM pulse generation means PPG. The voltage Vd, which changes when the PWM control signal PWM is input to the primary circuit and the output is controlled by feedforward, can be compensated for.

In the present embodiment, the external PWM control signal PWM is supplied to the primary-side power supply control IC 17 to change the output current, thereby adjusting the brightness of the LED lamp connected as a load and undesirably occurring along with it. The detection voltage Vd is shifted by the feedback amount correction circuit 18 in accordance with the external PWM control signal PWM so as to cancel the change in the detection voltage Vd, and can be avoided by correcting the feedback signal FB. . That is, even if the duty ratio of the external PWM control signal PWM changes, the magnitude of the detection voltage Vd relative to the reference voltage Vref1 is not changed.

Specifically, the feedback amount correction circuit 18 includes a resistor R5 and an N-channel MOS transistor Q5 connected in series between the constant potential terminal to which the reference voltage Vref2 is supplied and the inverting input terminal of the error amplifier AMP1. And an external PWM control signal PWM is input to the gate terminal of Q5 for on / off operation. Note that the connection order of the resistor R5 and the transistor Q5 may be reversed.

The feedback amount correction circuit 18 of this embodiment acts to raise or lower the average potential of the voltage input to the inverting input terminal of the error amplifier AMP1 according to the duty ratio of the external PWM control signal PWM. That is, a filter circuit is configured by the resistor R5 in series with the transistor Q5 that is turned on / off by the external PWM control signal PWM and the capacitor Cf connected between the inverting input terminal and the output terminal of the error amplifier AMP1. This filter circuit averages the pulses of the external PWM control signal PWM to generate a potential proportional to the duty, and adds the detected voltage Vd, which is current-voltage converted by the sense resistor Rs, to the smoothed voltage to add the error amplifier AMP1. Is configured to input. Accordingly, the feedback amount correction circuit 18 in FIG. 5 operates so that the voltage at the (−) input terminal of the error amplifier AMP1 does not change even when the duty ratio of the external PWM control signal PWM changes.

Instead of configuring the feedback amount correction circuit 18 by the resistor R5 in series with the transistor Q5 connected to the (−) input terminal of the error amplifier AMP1, a reference voltage generation circuit that generates the reference voltage Vref1 is used as a variable voltage source. It is also possible to configure so that the reference voltage Vref1 input to the non-inverting input terminal of the error amplifier AMP1 is changed in proportion to the duty of the external PWM control signal PWM. However, in that case, the shift direction of the reference voltage Vref1 is opposite to the direction of the detection voltage Vd in the above embodiment.

Next, the difference between the primary side power supply control IC 23 and the embodiment of FIG. 3 will be described.
In the power supply control IC 23 of this embodiment, in addition to the photocoupler PC1 that transmits the feedback signal VFB from the secondary side IC 14 to the primary side power supply control IC 23, the external PWM control signal PWM is supplied to the primary side power supply control. A photocoupler PC2 for transmission to the IC 23 is provided, and an external terminal P2 to which the collector of the light receiving transistor Tr2 constituting the photocoupler PC2 is connected is provided.

The emitter terminal of the light receiving transistor Tr2 is connected to the ground potential GND, and the external terminal P2 is generated by the internal power supply circuit 20 provided in the power supply control IC 17 via the pull-up resistor Rp2. For example, it is connected to a terminal to which an internal voltage Vreg such as 5 V is applied, and is configured to apply a bias to the collector of the light receiving transistor Tr1. As a result, when the photodiode PD2 of the photocoupler PC2 is turned on while the Tr2 is biased by the internal voltage Vreg, the collector current flows through the Tr2, and the potential of the external terminal P2 decreases due to the voltage drop of the resistor Rp2, and the PWM The control signal PWM is restored and supplied to the mask circuit 19. Instead of the pull-up resistors Rp1 and Rp2, it may be configured to pull up with a constant current source.

Further, on the primary side of the power supply device of this embodiment, a rectifying diode D0 connected in series with the auxiliary winding Nb and a smoothing diode connected between the cathode terminal of the diode D0 and the ground potential point. The smoothed voltage is applied to the power supply voltage terminal VCC of the power supply control IC 17. At the same time, the voltage rectified by the diode bridge circuit 22 and applied to one terminal of the primary winding Np is supplied to the power supply voltage terminal VCC of the power supply control IC 23 via the resistor R0, and assists in starting the power supply. The power supply control IC 23 can be operated before a voltage is induced in the winding Nb. An internal power supply circuit 20 that generates the internal power supply voltage Vreg based on the voltage supplied to the power supply voltage terminal VCC is provided in the power supply control IC 23. The internal power supply circuit 20 is composed of, for example, a series regulator.

As described in Patent Document 2, a regulator composed of a rectifying diode and a smoothing capacitor connected to the auxiliary winding is provided outside the IC and supplied to the transistors Tr1 and Tr2 of the photocouplers PC1 and PC2. Although it is conceivable to configure such that it is biased, as described above, by supplying the internal voltage Vreg to the transistor Tr2 of the photocoupler PC2 and biasing it, the transistors Tr1 and Tr2 and the control IC are externally connected. It can be avoided that a relatively high voltage exceeding the withstand voltage is applied to the elements inside the IC via the terminals to destroy the elements inside the IC.

The light receiving transistors Tr1 and Tr2 are biased by applying Vreg to the collector via the pull-up resistors Rp1 and Rp2 as in this embodiment, and receiving Vreg as shown in FIG. Alternatively, a method may be adopted in which a resistor is connected between the emitter and the grounding point by directly applying to the collector of the transistor for grounding the collector.
However, when the light receiving transistor is connected to the collector ground and the voltage Vreg generated in the IC is applied to the collector, two external terminals, that is, a terminal for outputting Vreg and an input terminal for a signal from the secondary side. Must be provided in the IC for each photocoupler. On the other hand, by adopting a configuration in which Vreg is applied to the collectors of Tr1 and Tr2 via pull-up resistors Rp1 and Rp2 as in this embodiment, it is not necessary to increase the number of external terminals of the IC, and an increase in cost can be avoided. There is an advantage.
Although not shown in the drawings, the use of a variable resistor or a variable resistor circuit whose resistance value can be adjusted as the pull-up resistor Rp1 compensates for variations in received signal level caused by variations in characteristics of the photocoupler, and uses the photocoupler. Regardless of this, it is also possible to configure so that a highly accurate signal FB can be transmitted.

Further, in the power supply control IC 23 of this embodiment, a one-shot pulse generation circuit OPG2 that detects the rising of the external PWM control signal PWM restored by the photocoupler PC2 and generates a pulse signal, and an inverting input to the external terminal P3 A logic circuit that generates an on / off control signal on / off of the switching element SW in response to a signal from a one-shot pulse generation circuit OPG1 that detects a rising edge of the output of the comparator CMP2 connected to the terminal and generates a pulse signal LGC.

The logic circuit LGC includes an OR gate G1 that receives the outputs of the one-shot pulse generation circuits OPG1 and OPG2, and an OR gate G2 that receives the potential obtained by inverting the voltage of the external terminal P2 by the inverter INV and the output of the comparator CMP1. The output of the OR gate G1 is input to the set terminal S, and the output of the OR gate G2 is configured from the RS flip-flop FF1 input to the reset terminal R.
The RS flip-flop FF1 is a reset-priority flip-flop. The output Q of the FF1 is output to the outside of the IC as an on / off control signal on / off of the switching element SW, and the inverted output / Q of the FF1 is discharged from the waveform generation circuit RAMP. The signal is supplied to the gate terminal of SW2 as a signal for controlling on / off of the MOS transistor SW2.

The OR gates G2 and FF1 forcibly set the output Q of the RS flip-flop FF1 to the low level during the low level period of the external PWM control signal PWM input from the external terminal P2, and prohibit the output of the on / off control signal on / off. Functions as a mask circuit. At the timing when the external PWM control signal PWM changes to high level, a one-shot pulse is generated by OPG2, the RS flip-flop FF1 is set, and the mask is released.

Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment. For example, in the embodiments of FIGS. 3 and 5, the anode terminals of the photodiodes PD1 and PD2 constituting the photocoupler are connected to the output terminal of the buffer amplifier AMP2, and the output current of the buffer amplifier AMP2 is supplied to drive the lighting. However, the present invention is not limited to this, and an inverting amplifier circuit is provided after the buffer amplifier AMP2, and the cathode terminals of the photodiodes PD1 and PD2 are connected to the output terminal of the inverting amplifier circuit. Alternatively, a lighting drive may be performed by drawing a current from.

3 and 5 is configured as a current output type because the load is a current load, so that a sense resistor Rs is provided between the output terminal OUT2 and the ground point for output. In the voltage output type power supply device that controls the output voltage with a PWM signal, a voltage dividing circuit composed of a series resistor or the like is provided between the output terminal OUT1 and the ground point. Thus, the output voltage may be detected.

Furthermore, in the above embodiment, the switching element SW that allows current to flow intermittently through the primary winding of the transformer is an element (MOS transistor) that is separate from the power

supply control ICs

17 and 23. It may be incorporated into the

control ICs

17 and 23 and configured as one semiconductor integrated circuit. Further, the switching element SW is not limited to a MOS transistor and may be a bipolar transistor.

DESCRIPTION OF SYMBOLS 10 Power conversion means 11 Rectification means 12 Filter circuit 13 Detection means 14 Feedback voltage generation circuit 15 Signal transmission circuit 15a Signal synthesis circuit 15b Signal separation circuit 16 Switch means (switching element)
17 Control circuit (control IC)
18 Feedback amount correction circuit 19 Mask circuit 20 Internal power supply circuit 21 Filter 22 Diode bridge circuit (rectifier circuit)
23 IC for power control
AMP1 error amplifier AMP2 buffer amplifier AMP3 error amplifier D2 diode (offset applying means, two-terminal switching element)
PC, PC1, PC2 Photocoupler (signal transmission means)
CMP1, CMP2 Comparator OPG1, OPG2 One-shot pulse generation circuit RAMP Waveform signal generation circuit LGC Logic circuit

Claims

Power conversion means for converting AC power input to the primary side and outputting it to the secondary side, rectification means provided on the secondary side of the power conversion means, and current / voltage rectified by the rectification means Among them, a filter for passing a current / voltage in a predetermined frequency band, a detection means for detecting an output current or output voltage supplied to a load through the filter, and a feedback voltage corresponding to a detection signal by the detection means are generated. A feedback voltage generation circuit that generates, a control circuit that generates and outputs a control signal for a switching element that controls a current that flows to the primary side of the power conversion unit according to the feedback signal, and a voltage generated by the feedback voltage generation circuit. And a signal transmission means for transmitting the feedback signal to the control circuit in response.
The feedback voltage generation circuit includes:
An error amplifying circuit for outputting a voltage corresponding to a potential difference between the detection signal and a predetermined reference voltage; and a buffer amplifier for converting the output of the error amplifying circuit by impedance conversion and inverting the output terminal of the buffer amplifier. An insulated power supply apparatus, wherein an offset applying means for applying an offset higher than the input voltage by a predetermined potential to the output voltage of the buffer amplifier is connected between the input terminal and the input terminal.
The offset applying means is a two-terminal switching element that becomes conductive when a predetermined potential difference is exceeded, and is connected so that a conductive current flows from the output terminal of the buffer amplifier toward the inverting input terminal. The insulated power supply device according to claim 1.
3. The isolated power supply according to claim 1, wherein the error amplifier circuit includes a differential amplifier, and a capacitance element is connected between an output terminal and an inverting input terminal of the differential amplifier. apparatus.
The cutoff frequency of the filter is set to be lower than the switching frequency of the control signal generated by the control circuit and higher than the frequency of the output control pulse signal having control information in the duty ratio supplied from the outside. ,
A correction circuit for correcting the detection signal based on the output control pulse signal having control information in a duty ratio is provided on the secondary side of the power conversion means,
The control circuit includes a pulse generation circuit that generates a PWM control pulse having a pulse width corresponding to a feedback signal, and a pulse limiting circuit that limits the PWM control pulse generated by the pulse generation circuit according to the output control pulse signal And comprising
The correction circuit is configured to have a function of canceling a change in the detection signal that changes when an output control pulse signal is input to the primary side circuit and the output is controlled by feedforward. Item 4. The insulated power supply device according to Item 3.
The correction circuit includes a resistor and a transistor connected in series between a constant potential terminal to which a predetermined constant potential is supplied and an input terminal to which the detection signal of the error amplifier circuit is input. 5. The insulated power supply device according to claim 4, wherein the output control pulse signal is applied to a control terminal of the transistor.
The signal transmission means is a photocoupler composed of a light emitting element and a light receiving element,
The light emitting element is connected between an output terminal of the buffer amplifier and a ground potential point, and a current corresponding to the output voltage of the buffer amplifier is passed through the light emitting element. Item 6. The insulated power supply device according to Item 4 or 5.
The isolated power supply device according to any one of claims 4 to 6, an LED lamp that is connected to an output terminal of the insulated power supply device and that is turned on when the output current flows, and generates the output control pulse signal An illumination device comprising a control signal generating means, wherein the output control pulse signal is a dimming control pulse for controlling the brightness of the LED lamp.