JP6983024B2 - Insulated DC / DC converter, its primary controller, power adapter and electronics - Google Patents

Description

The present invention relates to an isolated DC / DC converter.

A flyback type DC / DC converter is used in various power supply circuits such as an AC / DC converter. FIG. 1 is a circuit diagram of a diode rectifying type flyback converter 200R.

The flyback converter 200R receives an input voltage V _{IN at its input terminal P1, generates a DC output voltage V OUT} stabilized at a predetermined target voltage, and is connected between the output terminal P2 and the ground terminal P3. Supply to load (not shown). A switching transistor M1 is connected to the primary winding W1 of the transformer T1, and a diode D1 is connected to the secondary winding W2. The output capacitor C1 is connected to the output terminal P2.

The feedback circuit (also referred to as a shunt regulator circuit) 206 drives the light emitting element of the photocoupler 204 with _{a current IERR} corresponding to an error _{between the output voltage V OUT} and its target voltage V _{OUT (REF). A feedback current IFB} corresponding to the error flows through the light receiving element of the photocoupler 204. The primary controller (Primary Controller) 202 feedback (FB) pin feedback signal _{V FB} is generated in response to the feedback current _{I FB.} The primary controller 202 generates a pulse signal having a duty ratio (or frequency) corresponding to _{the feedback signal VFB, and drives the switching transistor M1.}

Japanese Unexamined Patent Publication No. 2014-171290

FIG. 2 is a circuit diagram of the primary controller 500R examined by the present inventor. The primary controller 500R includes a pulse modulator 510, a driver 530, and a burst comparator 550. The FB pin of the primary controller 500R, the feedback signal _{V FB} is generated in response to the feedback current _{I FB.} Specifically, the feedback signal _VFB is expressed by the following equation.
V _FB = V _REF- R x I _FB

The current sense (CS) pin, a voltage drop proportional to the current I _S flowing through the primary winding W1 in the ON period of the switching transistor M1 (current detection signal) V _CS is input. Pulse modulator 510, PWM type or quasi-resonant: a (QR Quasi-Resonant) type, and generates a control pulse _{S 11} having a duty ratio corresponding to the feedback signal _{V FB} and the current detection signal _{V CS} (or frequency) .. The driver 530 drives the switching transistor M1 in response to a control pulse _{S 11.}

In a light load state, the DC / DC converter 200R operates in an intermittent mode in order to suppress a decrease in efficiency due to switching loss. A burst comparator 550 is provided for controlling the intermittent mode. A vibration component corresponding to the cutoff frequency of the feedback loop is superimposed on the feedback current I _FB , and this vibration component is also _{superimposed on the feedback signal V FB.} The burst comparator 550 compares the feedback signal V _FB with the threshold value V _BURST, and generates _{a burst pulse S BURST} according to the comparison result. The pulse modulator 510 generates the _{control pulse S 11 when the burst pulse S BURST} is at the first level. When the burst pulse S _BURST is at the second level, the control pulse S ₁₁ maintains the off level, and the switching of the switching transistor M1 is stopped.

FIG. 3 is an operation waveform diagram of the primary side controller 500R of FIG. 2 in a light load state. A ripple component corresponding to the cutoff frequency of the feedback loop is superimposed on the feedback signal _VFB. This feedback signal V _FB is sliced at the threshold value V _{BURST , and a burst pulse S BURST} having a level (high / low) corresponding to the magnitude relationship between _{V FB} and V _BUSRT is generated, which is intermittent for switching of the switching transistor M1. The operation is introduced. Have been simplified in FIG. 3, a fixed duty ratio, because actually the duty ratio of the switching of the switching transistor M1 is in response to the feedback signal V _FB, the feedback signal V _FB is lower than the threshold V _BURST area That is, by stopping the switching in the region where the duty ratio is small, the switching loss is reduced.

In recent years, DC / DC converters have been required to further reduce power consumption, and there are applications in which power reduction by the circuit configuration shown in FIG. 2 is insufficient.

The present invention has been made in view of the above problems, and one of the exemplary purposes of the embodiment is to provide a DC / DC converter with further reduced power consumption.

Aspects of the present invention relate to a primary controller for an isolated DC / DC converter. A DC / DC converter comprises a transformer having primary and secondary windings and a switching transistor connected to the primary winding of the transformer. The primary side controller compares the output detection signal indicating the output state of the DC / DC converter with the feedback signal generation circuit that inverts the polarity and multiplies the first gain to generate the feedback signal, and the feedback signal with the threshold value. It is equipped with a burst controller that generates a burst signal according to the comparison result, a pulse modulator that generates a control pulse having a duty ratio according to the feedback signal, and a driver that drives a switching transistor according to the control pulse. Switching of the switching transistor is intermittent according to the signal.

Another aspect of the invention relates to an isolated DC / DC converter. The DC / DC converter may include the above-mentioned primary controller.

Another aspect of the invention relates to an electronic device. Electronic equipment includes a filter that filters the load and commercial AC voltage, a diode rectifier circuit that full-wave rectifies the output voltage of the filter, and a smoothing capacitor that smoothes the output voltage of the diode rectifier circuit and generates a DC input voltage. The above-mentioned DC / DC converter that steps down the DC input voltage and supplies it to the load may be provided.

Another aspect of the invention relates to a power adapter. The power adapter consists of a filter that filters commercial AC voltage, a diode rectifier circuit that full-wave rectifies the output voltage of the filter, a smoothing capacitor that smoothes the output voltage of the diode rectifier circuit, and generates a DC input voltage, and a DC input voltage. The above-mentioned DC / DC converter may be provided, which steps down the voltage and generates a DC output voltage.

It should be noted that any combination of the above components or components or expressions of the present invention that are mutually replaced between methods, devices, systems, etc. are also effective as aspects of the present invention.

According to an aspect of the present invention, the power consumption of the DC / DC converter can be reduced.

It is a circuit diagram of a diode rectification type flyback converter. It is a circuit diagram of the primary side controller examined by the present inventor. FIG. 2 is an operation waveform diagram of the primary controller in FIG. 2 in a light load state. It is a circuit diagram of the DC / DC converter of the flyback system which concerns on embodiment. It is a figure explaining the operation of the primary side controller of FIG. _{6 (a) is a waveform diagram of the feedback signal VFB} of the DC / DC converter of FIG. 4 and related signals, and FIG. 6 (b) shows the feedback signal _{VFB of the DC / DC converter of FIG.} It is a waveform diagram of the signal related to it. 7 (a) is a diagram showing the relationship between the feedback signal and the feedback current in the primary controller of FIG. 4, and FIG. 7 (b) shows the relationship between the feedback signal and the feedback current in the primary controller of FIG. It is a figure. It is a circuit diagram which shows the structural example of the primary side controller which concerns on 1st Embodiment. It is a circuit diagram which shows the structural example of the primary side controller which concerns on 2nd Embodiment. It is a circuit diagram of an AC / DC converter including a DC / DC converter. It is a figure which shows the AC adapter which includes the AC / DC converter. 12 (a) and 12 (b) are diagrams showing an electronic device including an AC / DC converter.

(Overview)
The present disclosure relates to an isolated DC / DC converter. A DC / DC converter comprises a transformer having primary and secondary windings and a switching transistor connected to the primary winding of the transformer. The primary side controller compares the output detection signal indicating the output state of the DC / DC converter with the feedback signal generation circuit that inverts the polarity and multiplies the first gain to generate the feedback signal, and the feedback signal with the threshold value. It is equipped with a burst controller that generates a burst signal according to the comparison result, a pulse modulator that generates a control pulse having a duty ratio according to the feedback signal, and a driver that drives a switching transistor according to the control pulse. Switching of the switching transistor is intermittent according to the signal.

By inverting the polarity of the output detection signal and multiplying it by the first gain, the level of the feedback signal during the operation period (switching section) of the intermittent operation becomes high in the light load state, and the duty ratio of the control pulse increases. When a switching transistor is driven by a control pulse having a large duty ratio, a larger amount of energy is input, so that the increase range of the output voltage increases. As a result, the length of the stop section following the switching section is extended, and the number of switchings and thus the switching loss can be further reduced. This reduces the power consumption in the light load state.

The threshold value may be linked to the output detection signal. As a result, the threshold value can be linked to the output detection signal, and appropriate burst operation can be provided under various conditions.

The threshold value may be the output detection signal multiplied by the second gain and averaged.

The output detection signal may be a feedback current flowing through the feedback terminal. The feedback signal generation circuit may include a resistor provided in the path of the feedback current at which the potential at one end is fixed, and a non-inverting amplifier that amplifies the voltage of the feedback terminal and outputs the feedback signal.

The primary side controller may further include a threshold generation circuit that smoothes (averages) a signal obtained by multiplying the voltage drop of the resistor by a second constant and generates a threshold value.

The output detection signal may be a feedback current flowing through the feedback terminal. In the feedback signal generation circuit, the potential at one end is fixed, the resistance provided in the path of the feedback current, the first non-inverting amplifier that amplifies the voltage of the feedback terminal and outputs the feedback signal, and the voltage of the feedback terminal. It may include a second non-inverting amplifier to amplify. The primary controller may further include a threshold generation circuit that amplifies the output of the second non-inverting amplifier and smoothes (averages) it to generate a threshold.

The DC / DC converter includes a photocoupler including a light emitting element and a light receiving element, and a feedback circuit for driving the light emitting element of the photocoupler so that the detection voltage corresponding to the output voltage of the DC / DC converter approaches the target voltage. May be further provided.

The DC / DC converter may further include a current sense resistor provided on the path of the switching transistor. The primary controller may further include a current sense terminal that receives a voltage drop from the current sense resistor. The pulse modulator has a reset comparator that generates a reset signal that is asserted when the current detection signal corresponding to the voltage drop of the current sense resistor reaches the feedback signal, and an on-level and reset signal assertion that is asserted according to the assertion of the set signal. It may include a logic circuit that generates a control pulse that becomes an off-level according to the above.

The set signal may have a predetermined frequency. This enables PWM control.

The primary controller may be integrated into one semiconductor substrate.
"Integral integration" includes cases where all the components of a circuit are formed on a semiconductor substrate or cases where the main components of a circuit are integrated together, and some of them are used for adjusting circuit constants. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit element can be kept uniform.

(Embodiment)
Hereinafter, the present invention will be described with reference to the drawings based on the preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and duplicate description thereof will be omitted as appropriate. Further, the embodiment is not limited to the invention, but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

In the present specification, the "state in which the member A is connected to the member B" means that the member A and the member B are physically directly connected, or the member A and the member B are electrically connected. It also includes cases of being indirectly connected via other members that do not affect the state or impair the function.

Similarly, "a state in which the member C is provided between the member A and the member B" means that the member A and the member C, or the member B and the member C are directly connected, and also electrically. It also includes the case of being indirectly connected via other members that do not affect the connection state or impair the function.

FIG. 4 is a circuit diagram of the flyback type DC / DC converter 200 according to the embodiment. The DC / DC converter 200 receives an input voltage _{VIN at its input terminal P1, generates a DC output voltage V OUT} stabilized at a predetermined target voltage, and is connected between the output terminal P2 and the ground terminal P3. Supply to a load (not shown).

The transformer T1 has a primary winding W1 and a secondary winding W2. One end of the primary winding W1 is connected to the input terminal P1 and receives _{a DC input voltage VIN.} The drain of the switching transistor M1 is connected to the other end of the primary winding W1 of the transformer T1. _{A sense resistor RC S} for current detection is inserted between the source of the switching transistor M1 and the ground line.

A diode D1 and an output capacitor C1 are provided on the secondary side, and they rectify and smooth the current flowing through the secondary winding W2 of the transformer T1 to generate an _{output voltage V OUT.}

The photocoupler 204 includes a light emitting element and a light receiving element. The light emitting element is biased by _{resistors R 21} and R _22. The feedback circuit 240 drives the light emitting element of the photocoupler 204 so that _{the output voltage V OUT} of the DC / DC converter 200 approaches the target voltage V _{OUT (REF).} For example, the feedback circuit 240 receives the detected voltage V _{OUTS obtained by dividing the output voltage V OUT} by the resistors R ₁₁ and R _{12 at} its control input (SH_IN) pin, and responds to the error between the detected voltage V _OUTS and its target voltage V _REF. The light emitting element of the photocoupler 204 is driven by the current _IERR.

An auxiliary winding W3 is provided on the primary side of the transformer T1. The diode D2 and the capacitor C2 rectify and smooth the current flowing through the auxiliary winding W3 to generate a _{power supply voltage VCC on the primary side.} Supply voltage _{V CC} is supplied to the power supply of the primary controller 500 (VCC) terminal.

The primary controller 500 drives the switching transistor M1 based on the output detection signal corresponding to the output of the DC / DC converter 200. In the present embodiment, the output detection signal is the current I _FB flowing through the light receiving element of the photocoupler 204, and drives the switching transistor M1 based on the feedback current I _FB. Hereinafter, the configuration of the primary controller 500 will be specifically described.

The feedback (FB) terminal of the primary controller 500 is connected to the light receiving element of the photocoupler 204. The output (OUT) terminal of the primary controller 202 is connected to the gate of the switching transistor M1. _{The current detection signal VCS} is input to the current detection (CS) terminal.

The primary controller 500 includes a pulse modulator 510, a driver 530, a feedback signal generation circuit 540, and a burst controller 560. The feedback signal generating circuit 540, a feedback current _{I FB} flowing through the FB terminal and the first gain-multiplied to generate a feedback signal _{V FB.}

The burst controller 560 _{compares the feedback signal V FB} with the threshold value V _TH, and generates _{a burst signal S BURST} according to the comparison result.

The pulse modulator 510 generates _{a control pulse S 11} having a duty ratio according to _{the feedback signal VFB.} The driver 530 drives the switching transistor M1 in response to a control pulse _{S 11.} The switching of the switching transistor M1 is intermittent according to the _{burst signal S BURST.}

The above is the configuration of the primary controller 500. Next, the operation will be described.
FIG. 5 is a diagram illustrating the operation of the primary controller 500 of FIG. The feedback signal V _FB has a waveform obtained by multiplying the feedback current I _{FB by the first gain.} As a result, the voltage level _{of the feedback signal VFB} during the switching period increases, and the duty ratio of the _{control pulse S 11 increases. When the switching transistor M1 is driven by the control pulse S 11} having a large duty ratio, a larger amount of energy is input, so that the increase width of the _{output voltage V OUT increases.}

_{6 (a) is a waveform diagram of the feedback signal VFB} of the DC / DC converter 200 of FIG. 4 and related signals, and FIG. 6 (b) is the feedback signal V of the DC / DC converter 200R of FIG. _{It is a waveform diagram of FB} and the signal associated with it.

Comparing FIGS. 6 (a) and 6 (b), FIG. 6 (a) has a larger duty ratio of _{the control pulse S 11} and therefore a larger increase _{in the output voltage V OUT during the switching period.} As a result, the length of the suspension period is longer in FIG. 6A. When the length of the stop period is extended, the number of switchings of the switching transistor M1 decreases. As a result, the power consumption in a light load state can be reduced.

7 (a) is a diagram showing the relationship between the feedback signal and the feedback current in the primary side controller 500 of FIG. 4, and FIG. 7 (b) is a diagram showing the relationship between the feedback signal and the feedback current in the primary side controller 500R of FIG. It is a figure which shows.

In the configuration of FIG. 2, the reference voltage V _REF is fixed, and the only parameter that can be adjusted at the time of design is the resistance value of the resistor R. Therefore, as shown in FIG. 7B, only the slope of the _{feedback signal VFB can be changed.}

On the other hand, in the primary controller 500 of FIG. 4, the resistance value R and the first gain g ₁ can be set independently. Therefore, even if the reference voltage V _REF is constant, as shown in FIG. 7 (a), (i) _{the gradient of the feedback voltage V FB} , that is, the sensitivity to the duty ratio, and (ii) the fluctuation of the _{feedback voltage V FB.} It can be set independently of the range, that is, the fluctuation range of the duty ratio.

The present invention extends to various devices and circuits grasped as the block diagram and circuit diagram of FIG. 4 or derived from the above description, and is not limited to a specific configuration. Hereinafter, more specific configuration examples and examples will be described in order to help understanding the essence of the invention and circuit operation, and to clarify them, not to narrow the scope of the present invention.

FIG. 8 is a circuit diagram showing a configuration example of the primary controller 500A according to the first embodiment.
The feedback signal generation circuit 540A includes a resistor 542 and a non-inverting amplifier 544. The resistor 542 is provided between the FB pin and the reference voltage line 546. A voltage drop is generated in the resistor 542 according to the feedback current I _FB, and the voltage of the FB pin is given by _{V REF} −R × I _FB. R is the resistance value of the resistor 542. _{The voltage VA of the} FB pin is a voltage obtained by inverting the polarity _{of the feedback current I FB} , which is an output detection signal.
V _A = (V _REF- R x I _FB )
The non-inverting amplifier 544 non-inverting and amplifying _{the voltage VA of the} FB pin with a gain g ₁ to generate a _{feedback voltage V FB.}
V _FB = g ₁ x _VA
= G ₁ × (V _REF −g ₁ × R × I _FB )

The threshold value generation circuit 570A smoothes a signal obtained by _{multiplying the feedback signal VFB} by a second constant (× g ₂ ) to generate a _{threshold value VTH.} The configuration of the threshold value generation circuit 570A is not particularly limited, but it may be configured by a combination of an analog amplifier and a filter, or may be configured by using a peak hold circuit or the like.

Burst controller 560 generates a burst signal _{S BURST} indicating the comparison result comprises a voltage comparator for comparing the feedback signal _{V FB} and the threshold _{V TH.}

The pulse modulator 510 generates _{a control pulse S 11} having a duty ratio according to _{the feedback signal VFB.} Further, the pulse modulator 510 _{fixes the control pulse S 11} to the off level (low) when the burst signal S BUSRT is at a predetermined level (here, low).

The configuration of the pulse modulator 510 is not particularly limited, and known techniques can be used. The pulse modulator 510 of FIG. 8 is a current mode pulse width modulator. PWM comparator 512 compares the current detection signal _{V CS} and the feedback signal _{V FB,} and generates a reset signal _{S RESET} is asserted (high) when the _{V CS>} V _FB. The reset signal S _RESET and the burst signal S _BURST are input to the reset terminal of the flip-flop 518 via the OR gate 514. The control pulse S ₁₁ goes off-level in response to the assertion of the reset signal S _{RESET or the transition of the burst signal S BURST to the low level.}

_{The set signal S SET} and the burst signal S _BURST are input to the set terminal of the flip-flop 518 via the AND gate 516. The set signal S _SET is a pulse having a predetermined frequency and is generated by an oscillator (not shown). The AND gate 516, during the outage burst signal _{S BURST} is low, the set signal _{S SET} is masked off level of the control pulse _{S 11} is maintained.

FIG. 9 is a circuit diagram showing a configuration example of the primary side controller 500B according to the second embodiment.
The feedback signal generation circuit 540B includes an amplifier 548 in addition to a resistor 542 and a non-inverting amplifier 544. The amplifier 548 multiplies the voltage of the FB pin by the third gain (g ₃ ).

Threshold generator circuit 570B, the output voltage of the amplifier 548 and the second gain times (× _{g 2),} generates a threshold value _{V TH} is smoothed. For example, the threshold generation circuit 570B may include an average circuit 572 and an amplifier 574. The average circuit 572 and the amplifier 574 may be interchanged. By optimizing the gain of amplifier 548, amplifier 574 can be omitted.

The present invention has been described above based on the embodiments. It is understood by those skilled in the art that this embodiment is an example, and that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present invention. be. Hereinafter, such a modification will be described.

(First modification)
In the embodiment, a diode rectifying type flyback converter is taken as an example, but a synchronous rectifying type may be used. Further, the present invention is not limited to the flyback converter, and the present invention can be applied to the LLC converter.

(Second modification)
Although the PWM type primary controller 500 has been described in the embodiment, the present invention is not limited to this, and the present invention can also be applied to the pseudo-resonance (QR) method. In this case, the voltage generated in the auxiliary winding W3 may be compared with the threshold value, and the signal corresponding to the comparison result may be _{set as the set signal SSET in FIG.}

(Third modification example)
In the embodiment, the output of the photocoupler 204 is used as an output detection signal, but this is not the case. In applications where insulation between the primary side and the secondary side is not required, an error amplifier may be provided instead of the photocoupler 204 and the shunt regulator 206, and the output of the error amplifier may be used as an output detection signal. Alternatively, the signal generated in the auxiliary winding W3 of FIG. 4 may be used as an output detection signal. That is, the output detection signal may have a correlation with the output of the DC / DC converter 200.

(Use)
Subsequently, the use of the DC / DC converter 200 described in the embodiment will be described. The DC / DC converter 200 can be used for the AC / DC converter 100. FIG. 10 is a circuit diagram of an AC / DC converter 100 including a DC / DC converter 200.

The AC / DC converter 100 includes a filter 102, a rectifier circuit 104, a smoothing capacitor 106, and a DC / DC converter 200. The filter 102 removes noise from the _{AC voltage VAC.} The rectifier circuit 104 is a diode bridge circuit that full-wave rectifies the _{AC voltage VAC.} The smoothing capacitor 106 smoothes the full-wave rectified voltage to generate a _{DC voltage VIN.} The DC / DC converter 200 receives a DC voltage V _IN and generates an output voltage V _OUT.

FIG. 11 is a diagram showing an AC adapter 800 including an AC / DC converter 100. The AC adapter 800 includes a plug 802, a housing 804, and a connector 806. Plug 802 is subjected to a commercial AC voltage _{V AC} from the wall outlet (not shown). The AC / DC converter 100 is mounted in the housing 804. _{The DC output voltage V OUT} generated by the AC / DC converter 100 is supplied to the electronic device 810 from the connector 806. Examples of the electronic device 810 include a laptop computer, a digital camera, a digital video camera, a mobile phone, and a portable audio player.

12 (a) and 12 (b) are views showing an electronic device 900 including an AC / DC converter 100. The electronic device 900 shown in FIGS. 12A and 12B is a display device, but the type of the electronic device 900 is not particularly limited, and is a device having a built-in power supply device such as an audio device, a refrigerator, a washing machine, and a vacuum cleaner. All you need is.

Plug 902 is subjected to a commercial AC voltage _{V AC} from the wall outlet (not shown). The AC / DC converter 100 is mounted in the housing 904. _{The direct current output voltage V OUT} generated by the AC / DC converter 100 is used for loads such as microcomputers, DSPs (Digital Signal Processors), power supply circuits, lighting equipment, analog circuits, and digital circuits mounted in the same housing 904. Be supplied.

The present invention has been described using specific terms and phrases based on the embodiments, but the embodiments merely indicate the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangement changes are permitted within the scope of the above-mentioned idea of the present invention.

P1 ... Input terminal, P2 ... Output terminal, M1 ... Switching transistor, C1 ... Output capacitor, T1 ... Transformer, W1 ... Primary winding, W2 ... Secondary winding, D1 ... Diode, 100 ... AC / DC converter, 102 ... Filter, 104 ... Rectifier circuit, 106 ... Smoothing capacitor, 200 ... DC / DC converter, 202 ... Primary side controller, 204 ... Photocoupler, 500 ... Primary side controller, 510 ... Pulse modulator, 512 ... PWM comparator, 514 ... OR Gate, 516 ... AND gate, 518 ... Flip flop, 530 ... Driver, 550 ... Burst comparator, 540 ... Feedback signal generation circuit, 542 ... Resistance , 544 ... Non-inverting amplifier , 560 ... Burst controller, 570 ... Threshold generation circuit , 800 ... AC adapter, 802 ... plug, 804 ... housing, 806 ... connector, 810, 900 ... electronic device, 902 ... plug, 904 ... housing.

Claims (14)

It is the primary side controller of the isolated DC / DC converter.
The DC / DC converter is
With a transformer with primary and secondary windings,
A switching transistor connected to the primary winding of the transformer,
Equipped with
The primary controller is
A feedback signal generation circuit that inverts the polarity of the output detection signal indicating the output state of the DC / DC converter and multiplies it by the first gain to generate a feedback signal.
A burst controller that compares the feedback signal with the threshold value and generates a burst signal according to the comparison result.
A pulse modulator that generates a control pulse having a duty ratio corresponding to the feedback signal, and
A driver that drives the switching transistor in response to the control pulse,
The switching of the switching transistor is intermittently provided according to the burst signal.
The primary side controller characterized in that the value of the first gain is larger than 1. The primary controller according to claim 1, wherein the threshold value is generated based on the output detection signal. The primary controller according to claim 2, wherein the threshold value is obtained by multiplying the output detection signal by a second gain and averaging the output detection signal. It is the primary side controller of the isolated DC / DC converter.
The DC / DC converter is
With a transformer with primary and secondary windings,
A switching transistor connected to the primary winding of the transformer,
Equipped with
The primary controller is
A feedback signal generation circuit that inverts the polarity of the output detection signal indicating the output state of the DC / DC converter and multiplies it by the first gain to generate a feedback signal.
A burst controller that compares the feedback signal with the threshold value and generates a burst signal according to the comparison result.
A pulse modulator that generates a control pulse having a duty ratio corresponding to the feedback signal, and
A driver that drives the switching transistor in response to the control pulse,
The switching of the switching transistor is intermittently provided according to the burst signal.
The primary side controller, characterized in that the threshold value is obtained by multiplying the output detection signal by a second gain and averaging the output detection signal. The output detection signal is a feedback current flowing through the feedback terminal.
The feedback signal generation circuit is
The potential at one end is fixed, and the resistance provided in the feedback current path,
A non-inverting amplifier that amplifies the voltage at the other end of the resistor and outputs the feedback signal,
The primary controller according to any one of claims 1 to 4 , wherein the controller comprises. It is the primary side controller of the isolated DC / DC converter.
The DC / DC converter is
With a transformer with primary and secondary windings,
A switching transistor connected to the primary winding of the transformer,
Equipped with
The primary controller is
A feedback signal generation circuit that inverts the polarity of the output detection signal indicating the output state of the DC / DC converter and multiplies it by the first gain to generate a feedback signal.
A burst controller that compares the feedback signal with the threshold value and generates a burst signal according to the comparison result.
A pulse modulator that generates a control pulse having a duty ratio corresponding to the feedback signal, and
A driver that drives the switching transistor in response to the control pulse,
The switching of the switching transistor is intermittently provided according to the burst signal.
The output detection signal is a feedback current flowing through the feedback terminal.
The feedback signal generation circuit is
The potential at one end is fixed, and the resistance provided in the feedback current path,
A non-inverting amplifier that amplifies the voltage at the other end of the resistor and outputs the feedback signal,
A primary controller characterized by including. The primary controller according to claim 5 or 6 , further comprising a threshold value generation circuit that smoothes a signal obtained by multiplying the voltage drop of the resistor by a second constant and generates the threshold value. The DC / DC converter is
A photocoupler including a light emitting element and a light receiving element,
A feedback circuit that drives the light emitting element of the photocoupler so that the detection voltage corresponding to the output voltage of the DC / DC converter approaches the target voltage.
The primary controller according to any one of claims 1 to 7, further comprising. The DC / DC converter further comprises a current sense resistor provided on the path of the switching transistor.
The primary controller further comprises a current sense terminal that receives a voltage drop from the current sense resistor.
The pulse modulator is
A reset comparator that generates a reset signal that is asserted when the current detection signal corresponding to the voltage drop of the current sense resistor reaches the feedback signal.
A logic circuit that generates the control pulse that turns on level according to the assertion of the set signal and turns off level according to the assertion of the reset signal.
The primary controller according to any one of claims 1 to 8 , wherein the controller comprises. The primary controller according to claim 9 , wherein the set signal has a predetermined frequency. The primary controller according to any one of claims 1 to 10 , wherein the controller is integrally integrated on one semiconductor substrate. A DC / DC converter comprising the primary controller according to any one of claims 1 to 11. With load,
A diode rectifier circuit that full-wave rectifies commercial AC voltage,
A smoothing capacitor that smoothes the output voltage of the diode rectifier circuit and generates a DC input voltage,
The DC / DC converter according to claim 12 , wherein the DC input voltage is stepped down and supplied to the load.
An electronic device characterized by being equipped with. A diode rectifier circuit that full-wave rectifies commercial AC voltage,
A smoothing capacitor that smoothes the output voltage of the diode rectifier circuit and generates a DC input voltage,
The DC / DC converter according to claim 12 , wherein the DC input voltage is stepped down and supplied to the load.
A power adapter characterized by being equipped with.

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