JP6651577B2 - Semiconductor device, DC / DC converter using the same, power supply device, power supply adapter, electronic device - Google Patents

Description

  The present invention relates to a DC / DC converter.

  Various home appliances such as televisions and refrigerators operate by receiving commercial AC power from the outside. Electronic devices such as laptop computers, mobile phone terminals, and tablet terminals can also be operated by commercial AC power, or can be charged with a battery built into the device by commercial AC power. A power supply device (AC / DC converter) for converting commercial AC voltage into AC / DC (AC / DC) is built in such home appliances and electronic devices (hereinafter collectively referred to as electronic devices). Alternatively, an AC / DC converter may be built in a power adapter (AC adapter) outside the electronic device.

  FIG. 1 is a block diagram showing a basic configuration of an AC / DC converter 100r studied by the present inventors. The AC / DC converter 100r mainly includes a filter 102, a rectifier circuit 104, a smoothing capacitor 106, and a DC / DC converter 200r.

Commercial AC voltage V _AC is input to the filter 102 through a fuse and an input capacitor (not shown). Filter 102 removes the commercial AC voltage _{V AC} noise. Rectifier circuit 104, a diode bridge circuit for full-wave rectifying the commercial AC voltage V _AC. The output voltage of the rectifier circuit 104 is smoothed by the smoothing capacitor 106 and converted to a DC voltage _VIN .

The isolated DC / DC converter 200r receives the DC voltage _VIN at the input terminal P1, reduces the voltage, and outputs the output voltage _VOUT stabilized at the target value to the load (not shown) connected to the output terminal P2. ).

  The DC / DC converter 200r includes a primary-side controller 202, a photocoupler 204, a shunt regulator 206, an output circuit 210, and other circuit components. The output circuit 210 includes a transformer T1, a diode D1, an output capacitor C1, and a switching transistor M1. Since the topology of the output circuit 210 is that of a general flyback converter, the description is omitted.

By the switching of the switching transistor M1, the input voltage _VIN is stepped down, and the output voltage _VOUT is generated. Then, the controller 202 stabilizes the output voltage V _OUT to a target value by adjusting the switching duty ratio of the switching transistor M1.

The output voltage V _OUT of the DC / DC converter 200r is divided by the resistors R1 and R2. Shunt regulator 206, amplifies an error divided voltage (voltage detection signal) _{V S} with a predetermined reference voltage _{V REF} (not shown), an error current _{I ERR} corresponding to the error, the input side of the photocoupler 204 (Sink) from the light emitting element (light emitting diode).

The output side of the light receiving element of the photocoupler 204 (phototransistor), the feedback current _{I FB} flows in accordance with the error current _{I ERR} on the secondary side. This feedback current I _FB is smoothed by a resistor and a capacitor, and is input to a feedback (FB) terminal of the controller 202. The controller 202 adjusts the duty ratio of the switching transistor M1 based on the voltage (feedback voltage) _VFB at the FB terminal.

Japanese Patent Application Laid-Open No. 2010-074959

The present inventor has studied the AC / DC converter 100r of FIG. 1 and has come to recognize the following problem. To the shunt regulator 206 of FIG. 1 is operated stably, it is necessary to use a state flowing a large cathode current I _K to some extent. Cathode current I _K is grasped and component contributing to the feedback, the sum of the fixed bias component (idle current). For example, many commercially available shunt regulators require an idle current of several hundred μA (eg, 700 μA), which is a factor that deteriorates the efficiency of the AC / DC converter 100r.

  The present invention has been made in view of such a problem, and one of exemplary purposes of one embodiment of the present invention is to provide a DC / DC converter with improved efficiency.

  One embodiment of the present invention relates to a synchronous rectification controller that is arranged on the secondary side of an isolated synchronous rectification type DC / DC converter and controls a secondary side synchronous rectification transistor of the DC / DC converter. The isolated synchronous rectification type DC / DC converter includes a transformer having a primary winding and a secondary winding, a switching transistor connected to the primary winding of the transformer, and a synchronous rectification connected to a secondary winding of the transformer. It includes a transistor, a photocoupler, and a primary-side controller that is connected to an output side of the photocoupler and that switches a switching transistor according to a feedback signal from the photocoupler. The synchronous rectification controller includes a drive circuit for switching the synchronous rectification transistor, a photocoupler connection terminal connected to the input side of the photocoupler, and an error between a voltage detection signal corresponding to the output voltage of the DC / DC converter and a target voltage thereof. And an error amplifier that amplifies and draws a current corresponding to the error from the input side of the photocoupler via the photocoupler connection terminal, and is packaged in a single module.

  In this embodiment, the current on the input side of the photocoupler is generated by an error amplifier built in the synchronous rectification controller instead of the conventional shunt regulator. As a result, the current consumption of the error amplifier can be significantly reduced as compared with the shunt regulator, and the efficiency can be improved.

The power planes of the error amplifier and the drive circuit may be independent, and the ground planes may be independent.
This makes it possible to cope with a topology in which the synchronous rectification transistor is arranged on the high potential side (output terminal side) of the secondary winding of the transformer.

  The power supply plane of the error amplifier may be supplied with an internal power supply voltage generated from the voltage of the photocoupler connection terminal, and the ground plane of the error amplifier may be supplied with a ground potential on the secondary side of the DC / DC converter.

  The synchronous rectification transistor is inserted on the high potential side of the secondary winding, and the transformer may further include an auxiliary winding provided on the secondary side. The DC / DC converter may be configured to use the auxiliary winding to generate a power supply voltage based on a potential of a line between the synchronous rectification transistor and the secondary winding. The potential of the line may be supplied to the ground plane of the drive circuit, and the power supply voltage may be supplied to the power supply plane of the drive circuit.

  The error amplifier and the drive circuit may be integrated on separate semiconductor chips. Thereby, the isolation between the error amplifier and the driving circuit can be improved.

  The synchronous rectification controller may be packaged in a single module further comprising a synchronous rectification transistor.

  The drive circuit may include a pulse generator that generates a pulse signal whose level changes based on at least a voltage between both ends of the synchronous rectification transistor, and a driver that switches the synchronous rectification transistor based on the pulse signal.

  When the voltage between both ends of the synchronous rectification transistor becomes lower than a predetermined negative first threshold voltage, the pulse generator sets the pulse signal to an on level, and (ii) the voltage between both ends of the synchronous rectification transistor becomes When the voltage becomes higher than a predetermined negative second threshold voltage higher than one threshold voltage, the pulse signal may be turned off.

  A pulse generator that compares a voltage between both ends of the synchronous rectification transistor with a first threshold voltage and compares a voltage between both ends of the synchronous rectification transistor with a second threshold voltage to generate a set pulse; It may include a reset comparator that generates a reset pulse, and a flip-flop whose output changes according to the set pulse and the reset pulse.

  The pulse generator may further include a blanking circuit for masking each of the set pulse and the reset pulse for a predetermined time.

  The DC / DC converter may be a flyback type or a forward type.

  Another embodiment of the present invention relates to a DC / DC converter. The DC / DC converter includes a transformer having a primary winding and a secondary winding, a switching transistor connected to the primary winding of the transformer, a synchronous rectification transistor connected to the secondary winding of the transformer, and an output. A capacitor, a photocoupler, and a synchronous rectifier controller for switching the synchronous rectification transistor, and supplying an output voltage of the output capacitor and a current corresponding to an error of the target level to the input side of the photocoupler, A primary controller connected to the output side of the photocoupler and driving a switching transistor in response to a feedback signal corresponding to a current generated by the synchronous rectification controller.

  Another embodiment of the present invention relates to a power supply device (AC / DC converter). The power supply device includes a filter for filtering a commercial AC voltage, a diode rectifier circuit for full-wave rectifying the output voltage of the filter, a smoothing capacitor for smoothing the output voltage of the diode rectifier circuit to generate a DC input voltage, and a DC input voltage. And the above-described DC / DC converter for lowering the voltage and supplying the load to the load.

  Another embodiment of the present invention relates to an electronic device. The electronic device includes a load, a filter for filtering a commercial AC voltage, a diode rectifier circuit for full-wave rectifying the output voltage of the filter, a smoothing capacitor for smoothing the output voltage of the diode rectifier circuit to generate a DC input voltage, And the above-described DC / DC converter for reducing the DC input voltage and supplying it to the load.

  Another embodiment of the present invention relates to an AC adapter. The AC adapter includes a filter for filtering a commercial AC voltage, a diode rectifier circuit for full-wave rectifying the output voltage of the filter, a smoothing capacitor for smoothing the output voltage of the diode rectifier circuit to generate a DC input voltage, and a DC input voltage. And a DC / DC converter for generating a DC output voltage.

  It should be noted that any combination of the above-described components, and any replacement of the components and expressions of the present invention between methods, apparatuses, systems, and the like are also effective as embodiments of the present invention.

  According to an aspect of the present invention, the efficiency of the isolated synchronous rectification type DC / DC converter can be improved.

FIG. 2 is a block diagram showing a basic configuration of an AC / DC converter studied by the present inventors. FIG. 2 is a circuit diagram of the AC / DC converter according to the first embodiment. FIG. 3A is an operation waveform diagram of the DC / DC converter of FIG. 2 in the PFM mode, and FIG. 3B is an operation waveform diagram of the DC / DC converter of FIG. 1 in the PFM mode. FIG. 3 is a circuit diagram illustrating a specific configuration example of the DC / DC converter of FIG. 2. FIG. 9 is a circuit diagram of an AC / DC converter according to a second embodiment. FIG. 6 is a circuit diagram illustrating a specific configuration example of the DC / DC converter of FIG. 5. FIG. 2 is a diagram illustrating an AC adapter including an AC / DC converter. FIGS. 8A and 8B are diagrams illustrating an electronic device including an AC / DC converter.

  Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and the repeated description will be omitted as appropriate. In addition, the embodiments do not limit the invention, but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this 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 that the member A and the member B are electrically connected. This includes the case where the connection is made indirectly via another member that does not affect the state.
Similarly, “the 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, This includes the case where the connection is made indirectly via another member that does not affect the connection state.

(First Embodiment)
FIG. 2 is a circuit diagram of the AC / DC converter 100 according to the first embodiment. The AC / DC converter 100 includes a filter 102, a rectifier circuit 104, and an isolated DC / DC converter 200.

  The isolated DC / DC converter 200 includes a primary-side controller 202, a photocoupler 204, an output circuit 210, and a synchronous rectification controller 300. The output circuit 210 has a topology of a flyback synchronous rectification type, and includes a transformer T1, a switching transistor M1 connected to a primary winding W1, a synchronous rectification transistor M2 connected to a secondary winding W2, and an output capacitor C1. Prepare. In the present embodiment, the synchronous rectification transistor M2 is inserted on a lower potential side (ground potential side) than the secondary winding W2 of the transformer T1.

The synchronous rectification controller 300 is arranged on the secondary side of the DC / DC converter 200, and switches the synchronous rectification transistor M2. The cathode of the light emitting element (light emitting diode) on the input side of the photo coupler 204 is connected to the photo coupler connection terminal (PC) terminal. The VD terminal, the drain voltage _{V D} of the synchronous rectification transistor M2 is input. The OUT terminal is connected to the gate of the synchronous rectification transistor M2. Note that the synchronous rectification transistor M2 may be built in the synchronous rectification controller 300. The VO terminal, the voltage detection signal _{V S} corresponding to the output voltage _{V OUT} is inputted. The GND terminal is connected to a ground line on the secondary side of the transformer T1.

  The synchronous rectification controller 300 includes a drive circuit 302 and an error amplifier 310, and is packaged in a single module. The drive circuit 302 switches the synchronous rectification transistor M2. More specifically, the drive circuit 302 includes a pulse generator 304 that generates the pulse signal S1, and a driver 306 that switches the synchronous rectification transistor M2 based on the pulse signal S1.

But are not limited to generating method is particularly configuration and pulse signal S1 of the pulse generator 304, for example, a pulse generator 304, the voltage across the at least synchronous rectification transistors M2, that is, the pulse signal S1 based on the drain-source voltage V _DS Generate. More specifically, the pulse generator 304 generates the pulse signal S1 based on the drain-source voltage _VDS and the two negative threshold voltages _VTH1 and _VTH2 . The two thresholds are determined so that V _TH1 <V _TH2 <0. For example, V _TH1 = −50 mV and V _TH2 = −10 mV. The pulse generator 304, the drain source voltage V _DS is lower than the first negative threshold V _TH1, the pulse signal S1, a level for instructing ON of the synchronous rectification transistor M2 (on-level, for example high level), Thereafter, the drain-source voltage V _DS is higher than V _TH2, the level instructing off of the synchronous rectification transistor M2 (off level, for example, low level).

The error amplifier 310 amplifies an error between the voltage detection signal V _S according to the output voltage V _OUT of the DC / DC converter 200 and the target voltage V _REF , and outputs a current I _ERR according to the error via a PC terminal. Pull in from the coupler 204 (sink). The error amplifier 310 has an open collector or open drain type output stage, and the collector (or drain) of the transistor 312 in the output stage is connected to the PC terminal. Differential amplifier 314, according to the error of the voltage detection signal _{V S} and the reference voltage _{V REF,} and controls the base current or gate voltage of the transistor 312. In the present embodiment, the diode D2 between the collector of the transistor 312 and the PC terminal is inserted for the purpose of circuit protection or voltage level shift, but may be omitted in another embodiment.

  The above is the configuration of the DC / DC converter 200 including the synchronous rectification controller 300. Subsequently, the operation will be described.

When the voltage detection signal V _S becomes higher than the reference voltage V _REF , the current I _ERR drawn by the output transistor 312 increases, and the current I _FB flowing through the photo transistor on the output side of the photocoupler 204 also increases. At this time the feedback voltage V _FB is reduced, thus the duty ratio of the switching transistor M1 (on-time) is reduced, is fed back to the direction (decrease) of the voltage detection signal V _S approaches the reference voltage V _REF according. Current _{I ERR} of the voltage detection signal _{V S} to the opposite becomes lower than the reference voltage _{V REF} pull output transistor 412 decreases, so does the current _{I FB} of the light receiving element. At this time the feedback voltage V _FB is increased, thus the duty ratio is increased in the switching transistor M1, is fed back to the direction (up) of the voltage detection signal V _S approaches the reference voltage V _REF according. Thus, output voltage _VOUT of DC / DC converter 200 is stabilized at its target level.

According to the DC / DC converter 200, the following effects can be obtained.
In the synchronous rectification controller 300, the current consumption of the error amplifier 310 can be significantly reduced as compared with the shunt regulator 206 of FIG. 1 by integrating the error amplifier 310 on the same semiconductor substrate as the drive circuit 302.

Specifically, when a commercially available shunt regulator 206 is used in the DC / DC converter 200r of FIG. 1, the current consumption is about 700 μA, of which 150 μA is the light emitting element on the input side of the photocoupler 204. It is assumed that the remaining 550 μA is the operating current I _DD of the shunt regulator 206. The operating current I _DD is supplied via the light emitting element and a resistor in parallel with the light emitting element, and causes a loss.

On the other hand, even if the output current I _ERR of the error amplifier 310 of FIG. 2 is 150 μA, which is the same as that of the shunt regulator 206, the operating current I _DD at that time can be reduced to about 50 μA, and DC The efficiency of the / DC converter 200, particularly in a light load state, can be improved.

Here, a power supply (VCC) terminal of the synchronous rectification controller 300 is connected to, for example, an output line of the DC / DC converter 200, and the synchronous rectification controller 300 operates using the output voltage _VOUT as a power supply voltage (for example, 24V). Then, the power consumption of the error amplifier 310 is 24 × 200 μA = 4.8 mW. On the other hand, the power consumption of the shunt regulator 206 in FIG. 1 under the same conditions is 24 V × 700 μA = 16.8 mW. Therefore, according to the DC / DC converter 200 in FIG. 2, the power consumption can be reduced by 10 mW or more.

In addition, according to the synchronous rectification controller 300, the following effects can be obtained.
At a light load, the DC / DC converter 200 may be operated intermittently (also referred to as PFM mode) in order to increase the efficiency. FIG. 3A is an operation waveform diagram of the DC / DC converter 200 in FIG. 2 in the PFM mode. FIG. 3B shows an operation waveform diagram of the DC / DC converter 200r of FIG. 1 for comparison.

In the PFM mode, the switching transistor M1 on the primary side is turned on for a certain time T _ON , and then turned off. When the output voltage _VOUT drops to a threshold value near the reference level, the switching transistor M1 is turned on again.

The OFF time T _OFF of the switching transistor M1 is given by the following equation using the capacitance C of the output capacitor C1, the ripple ΔV of the output voltage _VOUT , and the discharge current I from the output capacitor C1.
T _OFF = C · ΔV / I
The switching cycle t of the DC / DC converter is given by the following equation.
t = (T _ON + T _OFF ) = T _ON + C · ΔV / I

Here, I is the discharge current from the output capacitor C1, and is equal to the current consumption of the shunt regulator 206 or the error amplifier 310 at a light load. 100μF capacitance of the output capacitor C1 Now, if the ripple _{ΔV = 100mV, T ON ≒ 0} , the switching period _{t 1} of the DC / DC converter 200r in FIG. 1, the switching period _{t 2} of the DC / DC converter 200 in FIG. 2 Each is given below.
t ₁ ≒ 100 μA × 100 mV / 700 μA = 14.28 ms
t ₂ ≒ 100 μA × 100 mV / 200 μA = 50 ms

  That is, according to the DC / DC converter 200 of FIG. 2, the primary-side switching frequency at the time of light load can be reduced to 1/3 or less as compared with the DC / DC converter 200r of FIG. Thereby, the switching loss used by the controller 202 to charge and discharge the gate of the switching transistor M1 can be reduced to 1/3 or less.

  Further, by packaging the drive circuit 302 and the error amplifier 310, the design of the DC / DC converter 200 or the AC / DC converter 100 can be simplified.

  FIG. 4 is a circuit diagram showing a specific configuration example of the DC / DC converter of FIG. On the primary side of the transformer T1, a sense resistor Rs is provided in series with the switching transistor M1. The controller 202 monitors the primary current based on the voltage drop of the sense resistor Rs. The primary side current is used for current mode control or for overcurrent protection. The configuration of the controller 202 is not particularly limited, and may include a pulse modulator in a peak current mode, an average current mode, an off time fixed mode, or the like.

  A rectifier diode D3 and a smoothing capacitor C3 are connected to the auxiliary winding W3 of the transformer T1. The voltage generated at the smoothing capacitor C3 is used as a power supply voltage of the controller 202.

  Next, the synchronous rectification controller 300 will be described. The synchronous rectification controller 300 includes a synchronous rectification transistor M2. Synchronous rectification controller 300 includes two semiconductor chips (dies) SC1 and SC2. The semiconductor chip SC1 is manufactured by a high breakdown voltage process, and the synchronous rectification transistor M2 is integrated. The drive circuit 302 and the error amplifier 310 are integrated on the semiconductor chip SC2.

  The drive circuit 302 includes a UVLO circuit 320, an internal regulator 322, and a driver regulator 324 in addition to the pulse generator 304 and the driver 306. The UVLO (undervoltage lockout) circuit 320 stops the drive circuit 302 when the voltage of the VCC terminal becomes lower than the threshold value (3 V). The internal regulator 322 regulates the voltage of the VCC terminal and supplies it to other circuits. The driver regulator 324 regulates the voltage of the VCC terminal to generate the power supply voltage of the driver 306.

  The pulse generator 304 includes a blanking circuit 330, a set comparator 332, a reset comparator 334, an AND gate 336, an OR gate 338, a flip-flop 340, and a blanking circuit 342.

A high voltage clamp circuit (not shown) is inserted between the drain terminal of the synchronous rectification transistor M2 and the input terminals (−) of the set comparator 332 and the reset comparator 334. Set comparator 332 compares the drain-source voltage _{V DS} of the synchronous rectification transistor M2 and the first threshold voltage _V TH1 (= -50mV). When V _DS <V _{TH1 and} the output (set pulse) of the set comparator 332 is asserted (high level), the output (pulse signal) S1 of the flip-flop 340 transitions to the on level (high level).

The reset comparator 334 compares the drain-source voltage _{V DS} of the synchronous rectification transistor M2 and the second threshold voltage _V TH2 (= -10mV). When V _DS > V _{TH2 and} the output (reset pulse) of the reset comparator 334 is negated (low level), the flip-flop 340 is reset, and the output S1 changes to the off level (low level).

Each blanking circuit 330, a blanking circuit 342 is utilized to mask period, the set pulse from the set comparator 332, a reset pulse from the reset comparator 334 the drain voltage V _D of the synchronous rectification transistor M2 varies due to noise You. Each blanking (mask) time can be set by resistors R11 and R12 externally connected to the T_BLANK1 terminal and the T_BLANK2 terminal. The AND gate 336 masks the set pulse by taking the logical product of the set pulse and the output of the blanking circuit 330. Similarly, the OR gate 338 masks the reset pulse by ORing the reset pulse and the output of the blanking circuit 342.

(Second embodiment)
FIG. 5 is a circuit diagram of an AC / DC converter 100b according to the second embodiment. The configuration of the DC / DC converter 200b is different from that of FIG. Specifically, the synchronous rectification transistor M2 of the output circuit 210b is provided on the high potential side of the secondary winding W2 of the transformer T1.

  The synchronous rectification controller 300b includes a drive circuit 302b and an error amplifier 310b. Although the respective basic configurations and operations are the same as those in FIG. 2, in the present embodiment, the drive circuit 302b and the error amplifier 310b have independent power supply planes and independent ground planes. The drive circuit 302b and the error amplifier 310b are integrated on separate semiconductor chips (die) and packaged in a single module. When the process design rule allows two independent (isolated) power supply planes and two ground planes in the same die, the drive circuit 302b and the error amplifier 310b are integrated on a single chip. It may be.

  The ground plane of the drive circuit 302b is connected to the source of the synchronous rectification transistor M2 via the GND1 terminal. The VD terminal is connected to the drain of the synchronous rectification transistor M2.

The auxiliary winding W4, the diode D4, and the capacitor C4 of the transformer T1 generate the power supply voltage _VCC1 with reference to the source of the synchronous rectification transistor M2. The power supply voltage _VCC1 is supplied to the power supply plane of the drive circuit 302b via the power supply terminal VCC of the synchronous rectification controller 300b.

On the other hand, the ground plane of the error amplifier 310b is connected to the secondary-side ground via the GND2 terminal. The power supply plane of the error amplifier 310b is supplied with the PC terminal voltage V _PC or the internal power supply voltage V _CC2 generated based on the PC terminal voltage V _PC .

FIG. 6 is a circuit diagram showing a specific configuration example of the DC / DC converter of FIG. Synchronous rectification controller 300b includes three semiconductor chips SC3, SC4, and SC5. The semiconductor chip SC3 is produced in a high voltage process includes transistors M10 is a predetermined FET bias voltage V _G is applied to the gate, to clamp the drain voltage V _D of the synchronous rectification transistor M2. The drain voltage V _D ′ clamped by the transistor M10 is input to the set comparator 332 and the reset comparator 334. The semiconductor chip SC4 corresponds to the drive circuit 302b in FIG. 5, and includes a pulse generator 304 and a driver 306 having the same configuration as in FIG.

An error amplifier 310b, a UVLO circuit 350, and an internal regulator 352 are formed on the semiconductor chip SC5. The UVLO circuit 350 compares the voltage of the PC terminal (SH_OUT pin) with a predetermined threshold voltage (1.4 V), and stops the circuit on the semiconductor chip SC5 in a low voltage state. Further, the internal regulator 352 stabilizes the voltage of the PC terminal and supplies the internal power supply voltage _VCC2 to the error amplifier 310b.

The above is the configuration of the synchronous rectification controller 300b according to the second embodiment.
According to the synchronous rectification controller 300b, the current consumption on the secondary side can be reduced as in the first embodiment. Further, the switching loss on the primary side at the time of light load can be reduced.

  In the second embodiment, the ground plane and the power supply plane of the drive circuit 302b and the error amplifier 310b are made independent. Thus, even in an application in which the synchronous rectification transistor M2 is inserted on the high side, the drive circuit 302b drives the synchronous rectification transistor M2 as its ground voltage while using the error amplifier 310b to connect the photocoupler 204 to the transformer 2. The ground potential on the next side can be driven as a ground plane.

Next, the application of the DC / DC converter 200 will be described.
FIG. 7 is a diagram showing an AC adapter 800 including the 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 from the connector 806 to the electronic device 810. The electronic device 810 is exemplified by a notebook PC, a digital camera, a digital video camera, a mobile phone, a portable audio player, and the like.

FIGS. 8A and 8B are diagrams illustrating an electronic device 900 including the AC / DC converter 100. FIG. Although the electronic device 900 in FIGS. 8A and 8B is a display device, 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. I just need.
Plug 902, receives 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 applied to loads such as a microcomputer, a DSP (Digital Signal Processor), a power supply circuit, a lighting device, an analog circuit, and a digital circuit mounted in the same housing 904. Supplied.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and that such modifications are also within the scope of the present invention. is there. Hereinafter, such modifications will be described.

(First Modification)
In the embodiment, the flyback converter has been described, but the present invention is also applicable to a forward converter. In this case, a plurality of transistors for synchronous rectification are arranged on the secondary side of the transformer T1. In the synchronous rectification controller, a drive circuit 302 configured to switch a plurality of synchronous rectification transistors and an error amplifier 310 are modularized into a single package. Alternatively, a plurality of synchronous rectification controllers shown in FIGS. 2 and 5 can be used to support a forward converter. The converter may be of a quasi-resonant type.

(Second modification)
At least one of the switching transistor and the synchronous rectification transistor may be a bipolar transistor or an IGBT.

  Although the present invention has been described using specific words and phrases based on the embodiments, the embodiments are merely illustrative of the principles and applications of the present invention, and the embodiments are defined in the appended claims. Many modifications and changes in arrangement can be made without departing from the spirit of the present invention.

100: AC / DC converter, 102: Filter, 104: Rectifier circuit, 106: Smoothing capacitor, 200: DC / DC converter, 202: Controller, 204: Photocoupler, 206: Shunt regulator, 210: Output circuit, M1: Switching Transistor, M2: synchronous rectification transistor, C1: output capacitor, T1: transformer, W1: primary winding, W2: secondary winding, 300: synchronous rectification controller, 302: drive circuit, 304: pulse generator, 306 ... Driver 310, error amplifier 312 output transistor 314 differential amplifier 320 UVLO circuit 322 internal regulator 330 blanking circuit 332 set comparator 334 reset comparator 336 AND gate 338 … ORge G, 340 flip-flop, 342 blanking circuit, 350 UVLO circuit, 352 internal regulator, 800 AC adapter, 802 plug, 804 housing, 806 connector, 810,900 electronic equipment, 902 Plug, 904 ... housing.

Claims (16)

A semiconductor device for controlling a secondary side synchronous rectifier transistor of a DC / DC converter ,
A first chip including a drive circuit that outputs a drive signal that controls on and off of the synchronous rectification transistor ;
A first terminal for receiving the drive signal of the drive circuit;
A second terminal connected to the first chip and receiving an input voltage;
A second chip including an error amplifier;
A third terminal electrically connected to the error amplifier and receiving a first voltage;
A fourth terminal configured to receive a ground potential,
A reference voltage source for applying a reference voltage to the error amplifier and electrically connected to the fourth terminal;
A fifth terminal electrically connected to an output of the error amplifier ;
Have,
The error amplifier is configured to amplify an error between the first voltage and the reference voltage, and to draw a current corresponding to the error through the fourth terminal ,
The semiconductor device, wherein the first chip and the second chip are packaged in a single module .   2. The semiconductor device according to claim 1, further comprising a third chip including a transistor having a gate to which a predetermined bias voltage is applied.   3. The semiconductor device according to claim 1, wherein an internal power supply voltage generated from a voltage of the fifth terminal is supplied to a power supply plane of the error amplifier. 4. 4. The semiconductor device according to claim 3 , wherein the second chip further includes an internal regulator that stabilizes a voltage of the fifth terminal and generates the internal power supply voltage.   The semiconductor device according to claim 1, wherein the second chip further includes a low voltage lockout circuit that compares a voltage of the fifth terminal with a predetermined threshold voltage.   6. The semiconductor device according to claim 1, wherein a ground potential is supplied to a ground plane of the error amplifier. The error amplifier,
A differential amplifier for amplifying an error between the first voltage and the reference voltage;
An output transistor whose base or gate receives the output signal of the differential amplifier, whose emitter or source is grounded, and whose collector or drain is connected to the fifth terminal;
The semiconductor device according to claim 1, further comprising: The driving circuit includes:
A pulse generator that generates a pulse signal whose level transitions based on at least the voltage between both ends of the synchronous rectification transistor;
A driver for switching the synchronous rectification transistor based on the pulse signal;
The semiconductor device according to claim 1, further comprising:   The pulse generator sets (i) the pulse signal to an on level when a voltage between both ends of the synchronous rectification transistor becomes lower than a predetermined negative first threshold voltage, and (ii) a voltage between both ends of the synchronous rectification transistor. 9. The semiconductor device according to claim 8, wherein the pulse signal is turned off when a voltage becomes higher than a predetermined negative second threshold voltage higher than the first threshold voltage. The pulse generator,
A first comparator for comparing a voltage between both ends of the synchronous rectification transistor with the first threshold voltage;
A second comparator for comparing a voltage between both ends of the synchronous rectification transistor with the second threshold voltage;
The semiconductor device according to claim 9, comprising:   The semiconductor device according to claim 10, wherein the pulse generator further includes a blanking circuit that masks an output of the first comparator and an output of the second comparator for a predetermined time.   An isolated synchronous rectification type DC / DC converter comprising the semiconductor device according to claim 1.   The DC / DC converter according to claim 12, wherein the DC / DC converter is a flyback type. A filter for filtering commercial AC voltage,
A diode rectifier circuit for full-wave rectifying the output voltage of the filter;
A smoothing capacitor that smoothes an output voltage of the diode rectifier circuit and generates a DC input voltage;
14. The DC / DC converter according to claim 12, wherein the DC input voltage is stepped down and supplied to a load.
A power supply device comprising: Load and
A filter for filtering commercial AC voltage,
A diode rectifier circuit for full-wave rectifying the output voltage of the filter;
A smoothing capacitor that smoothes an output voltage of the diode rectifier circuit and generates a DC input voltage;
14. The DC / DC converter according to claim 12, wherein the DC input voltage is stepped down and supplied to the load.
An electronic device comprising: A filter for filtering commercial AC voltage,
A diode rectifier circuit for full-wave rectifying the output voltage of the filter;
A smoothing capacitor that smoothes an output voltage of the diode rectifier circuit and generates a DC input voltage;
14. The DC / DC converter according to claim 12, wherein the DC input voltage is reduced to generate a DC output voltage.
A power adapter comprising:

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