JP2016059255A - Insulating synchronous rectification type dc/dc converter and synchronous rectification controller thereof, and power supply device, power supply adopter and electronic apparatus including the dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC/DC converter detecting abnormalities on a secondary side and capable of protecting a circuit if abnormalities occur.SOLUTION: A synchronous rectification controller 300 is disposed on the secondary side of an insulating synchronous rectification type DC/DC converter 200, and controls a synchronous rectification transistor M2. A primary side controller 202 is connected to an output side of a photocoupler 204 for feedback, and switches a switching transistor M1 in accordance with a feedback signal V. The synchronous rectification controller 300 includes a drive circuit 302 and an abnormality detection circuit 360, and is packaged in a single module. The drive circuit 302 switches the synchronous rectification transistor M2. The abnormality detection circuit 360 detects abnormalities of the DC/DC converter 200 on the secondary side. A fail (FAIL) terminal is connected so as to notify the occurrence of abnormalities to the outside.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a DC / DC converter.

  Various home appliances such as TVs 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 with commercial AC power, or a battery built into the device can be charged with commercial AC power. Such home appliances and electronic devices (hereinafter collectively referred to as electronic devices) incorporate a power supply device (AC / DC converter) that converts commercial AC voltage into AC / DC (AC / DC). Alternatively, an AC / DC converter may be built in a power adapter (AC adapter) external to the electronic device.

  FIG. 1 is a block diagram showing a basic configuration of an AC / DC converter 100r examined 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 the DC voltage _VIN .

The insulated DC / DC converter 200r receives a DC voltage _VIN at an input terminal P1, steps down the voltage, and connects a load (not shown) to the output terminal P2 with an output voltage _VOUT stabilized at a target value. ).

  The DC / DC converter 200r includes a primary 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, description thereof is omitted.

When the switching transistor M1 is switched, the input voltage _VIN is stepped down and an output voltage _VOUT is generated. The controller 202 stabilizes the output voltage _VOUT at the target value by adjusting the switching duty ratio of the switching transistor M1.

The output voltage _VOUT of the DC / DC converter 200r is divided by resistors R1 and R2. The shunt regulator 206 amplifies an error between the _divided voltage (voltage detection signal) V _S and a predetermined reference voltage V _REF (not shown), and _generates an error current I _ERR corresponding to the error on 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 input to the 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) V _FB at the FB terminal.

JP 2010-074959 A

  In the isolated DC / DC converter, abnormalities such as an overvoltage state, a temperature abnormality and an overcurrent state can occur not only on the primary side but also on the secondary side. No circuit protection function exists on the secondary side.

  The present invention has been made in view of these problems, and one of exemplary purposes of an embodiment thereof is to provide a DC / DC converter that can detect an abnormality on the secondary side and protect a circuit when the abnormality occurs. is there.

  An aspect of the present invention relates to a synchronous rectification controller that is disposed on the secondary side of an insulated synchronous rectification type DC / DC converter that supplies power to a load and controls a synchronous rectification transistor on the secondary side of the DC / DC converter. The insulated 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 the secondary winding of the transformer. A transistor, a feedback photocoupler, and a primary-side controller that is connected to the output side of the feedback photocoupler and switches the switching transistor in accordance with a feedback signal from the feedback photocoupler. The synchronous rectification controller includes a drive circuit for switching the synchronous rectification transistor, an abnormality detection circuit for detecting an abnormality on the secondary side of the DC / DC converter, and a fail terminal for notifying the occurrence of the abnormality to the outside. Packaged in a single module.

  According to this aspect, by providing the secondary side synchronous rectification controller with an abnormality detection function and taking out a fail signal indicating the result to the outside, circuit protection can be realized by cooperative operation with other ICs.

  A load may be connected to the fail terminal. In this case, the circuit can be protected by stopping the operation or reducing the current consumption in the load that has been notified of the occurrence of the abnormality.

The load may include a microcontroller and at least one circuit placed under the control of the microcontroller. A microcontroller may be connected to the fail terminal.
In this case, the microcontroller that has received the notification of the occurrence of the abnormality can protect the circuit by stopping the circuit under the control or reducing the current consumption.

A load switch capable of switching between cutoff and conduction may be provided on the supply path of the output voltage from the DC / DC converter to the load. The control terminal of the load switch may be connected to the fail terminal.
In this case, the load can be protected by turning off the load switch when an abnormality occurs.

The DC / DC converter may further include an error notification photocoupler whose output side is connected to the primary controller. The fail terminal of the synchronous rectification controller may be connected to the input side of the error notification photocoupler in order to notify the primary side controller of the occurrence of an abnormality.
In this case, the primary side controller that has received the notification of the occurrence of the abnormality can stop the switching transistor and reduce the power supplied to the secondary side of the transformer, thereby protecting the circuit.

A synchronous rectification controller according to an aspect amplifies an error of a photocoupler connection terminal connected to an input side of a feedback photocoupler, a voltage detection signal corresponding to an output voltage of a DC / DC converter, and a target voltage thereof, and generates an error. And an error amplifier that draws a corresponding current from the input side of the feedback photocoupler via the photocoupler connection terminal, and may be 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 rectifier controller instead of the 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 error amplifier and the drive circuit have independent power planes, and their ground planes may be independent.
As a result, the synchronous rectification transistor can be arranged on the high potential side (output terminal side) of the secondary winding of the transformer.

  An internal power supply voltage generated from the voltage of the photocoupler connection terminal may be supplied to the power plane of the error amplifier, and a secondary ground potential of the DC / DC converter may be supplied to the ground plane of the error amplifier.

  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 is configured to generate an external power supply voltage based on the potential of the line between the synchronous rectification transistor and the secondary winding using the auxiliary winding, and the ground plane of the drive circuit includes a line The external 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 drive circuit can be increased.

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

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

  Another aspect 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 One of the above-described synchronous rectification controllers that switches the capacitor, the photocoupler, and the synchronous rectification transistor, and supplies a current corresponding to an error between the output voltage of the output capacitor and the target level to the input side of the photocoupler, A primary-side controller that is connected to the output side of the photocoupler and drives the switching transistor in accordance with a feedback signal corresponding to the current generated by the synchronous rectification controller.

  Another aspect of the present invention relates to a power supply device (AC / DC converter). The power supply device includes 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 And the above-described DC / DC converter that supplies the voltage to a load.

  Another embodiment of the present invention relates to an electronic device. The electronic device includes a load, 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, The above-described DC / DC converter that steps down a DC input voltage and supplies it to a load.

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

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, an abnormality on the secondary side can be detected in an insulated synchronous rectification type DC / DC converter, and the circuit can be protected when an abnormality occurs.

It is a block diagram which shows the basic composition of the AC / DC converter which this inventor examined. 1 is a circuit diagram of an AC / DC converter according to a first embodiment. It is a circuit diagram which shows another structural example of a DC / DC converter provided with a synchronous rectification controller. It is a circuit diagram which shows another structural example of a DC / DC converter provided with a synchronous rectification controller. It is a circuit diagram which shows the specific structural example of a synchronous rectification controller. It is a circuit diagram of a DC / DC converter provided with the synchronous rectification controller which concerns on 2nd Embodiment. FIG. 7A is an operation waveform diagram of the DC / DC converter of FIG. 6 in the PFM mode, and FIG. 7B is an operation waveform diagram of the DC / DC converter of FIG. It is a circuit diagram of the AC / DC converter which concerns on 3rd Embodiment. It is a circuit diagram of the DC / DC converter which concerns on 4th Embodiment. It is a figure which shows an AC adapter provided with an AC / DC converter. FIGS. 11A and 11B are diagrams illustrating an electronic device including an AC / DC converter. It is a circuit diagram of a DC / DC converter provided with the synchronous rectification controller which concerns on a 1st modification. It is a circuit diagram of a DC / DC converter provided with the synchronous rectification controller which concerns on a 2nd modification.

  The present invention will be described below 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 repeated descriptions are omitted as appropriate. 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 the member A and the member B are electrically connected. The case where it is indirectly connected through another member that does not affect the state is also included.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through 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 insulating DC / DC converter 200.

  The insulation type DC / DC converter 200 includes a primary side controller 202, a photocoupler 204, a shunt regulator 206, an output circuit 210, and a synchronous rectification controller 300. The output circuit 210 has a flyback synchronous rectification type topology, and includes a transformer T1, a switching transistor M1 connected to the primary winding W1, a synchronous rectification transistor M2 connected to the secondary winding W2, and an output capacitor C1. Prepare. In the present embodiment, the synchronous rectification transistor M2 is inserted on the lower potential side (ground potential side) than the secondary winding W2 of the transformer T1.

The synchronous rectification controller 300 is disposed on the secondary side of the DC / DC converter 200 and switches the synchronous rectification transistor M2. The VD terminal, the drain voltage _{V D} of the synchronous rectification transistor M2 is input. The gate of the synchronous rectification transistor M2 is connected to the OUT terminal. The synchronous rectification transistor M2 may be built in the synchronous rectification controller 300. A voltage detection signal V _S corresponding to the output voltage V _OUT is input to the voltage detection (VO) terminal. The GND terminal is connected to the secondary ground line of the transformer T1.

  The synchronous rectification controller 300 includes a drive circuit 302 and an abnormality detection circuit 360, 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 threshold values 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 abnormality detection circuit 360 detects an abnormality on the secondary side of the DC / DC converter 200. Examples of the abnormality include an overvoltage state, a temperature abnormality state, and an overcurrent state, but are not particularly limited. Further, the method for detecting each abnormality is not limited. For example, the overvoltage state can be detected by monitoring the potential of the output line of the DC / DC converter 200 or an arbitrary node and comparing it with the threshold voltage. An abnormal temperature state can be detected using a thermistor or the like. The overcurrent state is detected by comparing the voltage across the synchronous rectification transistor M2 with a threshold voltage, or a sense resistor is inserted in series with the synchronous rectification transistor M2 to drop the voltage of the sense resistor. It can be detected by comparing with the threshold voltage.

  The synchronous rectification controller 300 is provided with a fail (FAIL) terminal for notifying the outside of the occurrence of an abnormality detected by the abnormality detection circuit 360. The FAIL terminal is of a so-called open drain (open collector) type, and the presence or absence of an abnormality may be notified according to whether the output transistor 362 connected to the FAIL terminal is on or off.

  The above is the configuration of the DC / DC converter 200. Next, the effect will be described.

  The synchronous rectification transistor M2 has a parasitic diode (body diode) between its back gate and drain. Therefore, if the synchronous rectification transistor M2 is simply turned off when an abnormality occurs, the DC / DC converter 200 continues to operate in the diode rectification method, and does not provide circuit protection. Therefore, the synchronous rectification controller 300 on the secondary side incorporates an abnormality detection function, and by providing a FAIL terminal so that the fail signal S2 indicating the result can be taken out from the synchronous rectification controller 300, a cooperative operation with other ICs is performed. Thus, circuit protection can be realized.

  In FIG. 2, the FAIL terminal is connected to the load 500 of the DC / DC converter 200. Thus, the circuit can be protected by stopping the operation or reducing the current consumption in the load 500 that has received the notification S2 of the occurrence of the abnormality.

  For example, the load 500 includes a microcontroller 502 and at least one circuit 504 that is placed under the control of the microcontroller 502. A microcontroller 502 is connected to the FAIL terminal. Upon receiving the abnormality notification S2, the microcontroller 502 can protect the circuit by stopping the circuit 504 under the control or reducing the current consumption.

  FIG. 3 is a circuit diagram illustrating another configuration example of the DC / DC converter 200 including the synchronous rectification controller 300. The DC / DC converter 200 includes an error notification photocoupler 208 in addition to the feedback photocoupler 204. The light emitting element on the input side of the error notification photocoupler 208 is connected to the FAIL terminal, and the light receiving element on the output side is connected to the fail terminal (FAIL) of the primary controller 202.

  The fail signal S2 output from the FAIL terminal of the synchronous rectification controller 300 is transmitted to the primary-side controller 202 via the error notification photocoupler 208. The primary-side controller 202 that has received the notification of the occurrence of an abnormality reduces the power supplied to the secondary side of the transformer T1 by stopping the switching transistor M1 or reducing the switching duty ratio of the switching transistor M1. Thus, the circuit can be protected.

FIG. 4 is a circuit diagram showing still another configuration example of the DC / DC converter 200 including the synchronous rectification controller 300. On the supply path of the output voltage _VOUT from the DC / DC converter 200 to the load 500, a load switch 108 capable of switching between cutoff and conduction is provided. For example, the load switch 108 may be inserted between the output terminal P2 and the load 500 as shown in FIG. 4, or may be provided between the resistor R1, the output line connection node, and the output terminal P2. The load switch 108 includes, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and its control terminal (gate) is connected to the FAIL terminal.

  The fail signal S2 output from the FAIL terminal of the synchronous rectification controller 300 is input to the control terminal of the load switch 108. The load switch 108 that has received the notification of the occurrence of abnormality is turned off, and the power supply from the DC / DC converter 200 to the load 500 is stopped. This can protect the circuit.

FIG. 5 is a circuit diagram illustrating a specific configuration example of the synchronous rectification controller 300.
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 side 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 such as a peak current mode, an average current mode, or a fixed off-time mode.

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

  Next, the synchronous rectification controller 300 will be described. The synchronous rectification controller 300 includes a synchronous rectification transistor M2. The 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. A drive circuit 302, an abnormality detection circuit 360, and a transistor 362 are integrated on the semiconductor chip SC2.

  The drive circuit 302 includes a UVLO circuit 320 and an internal regulator 322 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 at the VCC terminal becomes lower than the threshold value (3 V). The internal regulator 322 regulates the voltage at the VCC terminal and supplies it to other circuits.

  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 transitions to the off level (low level).

The blanking circuit 330 and the blanking circuit 342 are used to mask the set pulse from the set comparator 332 and the reset pulse from the reset comparator 334, respectively, during the period when the drain voltage V _D of the synchronous rectification transistor M2 varies due to noise. The Each blanking (masking) time can be set by resistors R11 and R12 externally attached 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 taking the logical sum of the reset pulse and the output of the blanking circuit 342.

  The FAIL terminal of the synchronous rectification controller 300 is connected to the load 500 as shown in FIG. 2, or to the error notification photocoupler 208 as shown in FIG.

The abnormality detection circuit 360 includes an OVP (Over Voltage Protection) comparator 364, a temperature protection comparator 366, an OR gate 368, a timer 370, and a flip-flop 372. A voltage detection signal V _S ′ corresponding to the output voltage V _OUT is input to the OVP terminal. V _S ′ is generated by dividing the output voltage _VOUT by a resistor pair (not shown). The OVP comparator 364 compares the voltage V _S ′ at the OVP terminal with a predetermined threshold value, and asserts its output when an overvoltage state is detected.

  A thermistor 220 having a negative temperature coefficient is connected to the NTC terminal. The thermistor 220 is disposed in the vicinity of a heating element such as the synchronous rectification transistor M2. The temperature protection comparator 366 compares the voltage generated at the thermistor 220 with a predetermined threshold, and asserts its output when an overvoltage condition is detected. The OR gate 368 generates a logical sum of the outputs of the OVP comparator 364 and the temperature protection comparator 366. The timer 370 gives a trigger to the flip-flop 372 when the time when the output of the OR gate 368 is asserted continues for a predetermined determination time or longer, that is, when any abnormal state continues for the determination time or longer. The output of the flip-flop 372 to which the trigger is applied transitions to a high level, and the transistor 362 is turned on.

  The configuration of the abnormality detection circuit 360 is not limited to that shown in FIG. 5, and may include only one of the OVP comparator 364 and the temperature protection comparator 366, or other abnormality detection means. Further, the type of protection is not limited to the timer latch type, and other methods such as an automatic return method may be used.

(Second Embodiment)
FIG. 6 is a circuit diagram of a DC / DC converter 200a including the synchronous rectification controller 300a according to the second embodiment.
The synchronous rectification controller 300a includes an error amplifier 310 and a photocoupler connection terminal (PC) terminal in addition to the synchronous rectification controller 300 of FIG. A cathode of a light emitting element (light emitting diode) on the input side of the photocoupler 204 is connected to the PC terminal.

The error amplifier 310 amplifies an error between the voltage detection signal V _S corresponding to the output voltage V _OUT of the DC / DC converter 200a and the target voltage V _REF , and _generates a current I _ERR corresponding to the error via the PC terminal. Pull in from the coupler 204 (sink). The error amplifier 310 has an output stage of an open collector or open drain type, and the collector (or drain) of the transistor 312 in the output stage is connected to the PC terminal. The differential amplifier 314 controls the base current or gate voltage of the transistor 312 according to the error between the voltage detection signal V _S and the reference voltage V _REF . In this 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 200a including the synchronous rectification controller 300a. Next, 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 of the light receiving element (photo transistor) on the output side of the photocoupler 204 also increases. At this time, the feedback voltage V _FB decreases, and therefore the duty ratio (ON time) of the switching transistor M1 decreases, and feedback is applied in the direction (decrease) in which the voltage detection signal V _S approaches the reference voltage V _REF . Conversely, when the voltage detection signal V _S becomes lower than the reference voltage V _{REF, the} current I _ERR drawn by the output transistor 412 decreases, and the current I _{FB of the} light receiving element also decreases. At this time, the feedback voltage V _FB increases, therefore the duty ratio of the switching transistor M1 increases, and feedback is applied in the direction in which the voltage detection signal V _S approaches the reference voltage V _REF (rise). In this way, the output voltage _VOUT of the DC / DC converter 200 is stabilized at the target level.

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

Specifically, in the DC / DC converter 200r of FIG. 1, when a commercially available shunt regulator 206 is used, the current consumption is about 700 μA, and the breakdown is 150 μA of 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 through the light emitting element and a resistor in parallel therewith, resulting in a loss.

On the other hand, the error amplifier 310 of FIG. 6 can reduce the operating current I _DD to about 50 μA even if the output current I _ERR is 150 μA, which is the same as that of the shunt regulator 206, and the DC The efficiency of DC / DC converter 200a can be improved particularly in a light load state.

Here, the power supply (VCC) terminal of the synchronous rectification controller 300a is connected to, for example, the output line of the DC / DC converter 200a, and the synchronous rectification controller 300a operates using the output voltage _VOUT as the 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 24V × 700 μA = 16.8 mW. Therefore, according to the DC / DC converter 200a in FIG. 6, the power consumption can be reduced by 10 mW or more.

In addition, according to the synchronous rectification controller 300a, the following effects can be obtained.
At light loads, the DC / DC converter 200a may be intermittently operated (also referred to as PFM mode) in order to increase efficiency. FIG. 7A is an operation waveform diagram of the DC / DC converter 200a of FIG. 6 in the PFM mode. FIG. 7B 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 period 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 a discharge current from the output capacitor C1, and is equal to the consumption current of the shunt regulator 206 or the error amplifier 310 at a light load. If the capacitance of the output capacitor C1 is 100 μF, the ripple ΔV = 100 mV, and T _ON ≈0, the switching cycle t ₁ of the DC / DC converter 200r in FIG. ₁ and the switching cycle t ₂ of the DC / DC converter 200a in FIG. 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 200a of FIG. 6, the switching frequency on the primary side at light load can be reduced to 1/3 or less as compared with the DC / DC converter 200r of FIG. As a result, the switching loss used for the controller 202 to charge / discharge the gate of the switching transistor M1 can be reduced to 1/3 or less.

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

(Third embodiment)
FIG. 8 is a circuit diagram of an AC / DC converter 100d according to the third embodiment. The synchronous rectification transistor M2 of the output circuit 210d is provided on the high potential side of the secondary winding W2 of the transformer T1.

  The synchronous rectification controller 300d includes a drive circuit 302d and an abnormality detection circuit 360. Although the basic configuration and operation of each are the same as those in FIG. 2, in the present embodiment, the drive circuit 302d and the abnormality detection circuit 360 have independent power planes and independent ground planes. The drive circuit 302d and the abnormality detection circuit 360 are integrated on separate semiconductor chips (dies) 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 302d and the abnormality detection circuit 360 are combined into a single chip. It may be integrated.

  The ground plane of the drive circuit 302d 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 external power supply voltage _VCC1 with reference to the source of the synchronous rectification transistor M2. The external power supply voltage _VCC1 is supplied to the power supply plane of the drive circuit 302d through the power supply terminal VCC of the synchronous rectification controller 300d.

On the other hand, the ground plane of the abnormality detection circuit 360 and the transistor 362 is connected to the secondary side ground via the GND2 terminal. Additional abnormal power plane of the detection circuit 360 and transistor 362, another internal power supply voltage _{V CC2} is supplied with the driving circuit 302d.

  According to this configuration, 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 drive circuit 302d, the ground plane of the abnormality detection circuit 360, and the power supply plane are made independent. Thus, even in an application in which the synchronous rectification transistor M2 is inserted on the high side, the fail signal S2 is output by the abnormality detection circuit 360 and the transistor 362 while the drive circuit 302d drives the synchronous rectification transistor M2 using the source voltage as a ground plane. Can be generated with reference to the ground potential on the secondary side of the transformer.

(Fourth embodiment)
FIG. 9 is a circuit diagram of a DC / DC converter 200e according to the fourth embodiment. The synchronous rectification controller 300e includes three semiconductor chips SC3, SC4, and SC5. The semiconductor chip SC3 is manufactured by a high withstand voltage process, includes a transistor M10 that is an FET having a predetermined bias voltage V _G applied to the gate, and clamps 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 302d of FIG. 8, and includes a pulse generator 304 and a driver 306 having the same configuration as that of FIG.

In the semiconductor chip SC5, in addition to the abnormality detection circuit 360 and the transistor 362, an error amplifier 310e, a UVLO circuit 350, and an internal regulator 352 are formed. The UVLO circuit 350 compares the voltage at the PC terminal (SH_OUT pin) with a predetermined threshold voltage (1.4 V), and stops the circuit on the semiconductor chip SC5 in the low voltage state. The internal regulator 352 supplies the internal power supply voltage _VCC2 obtained by stabilizing the voltage received from the PC terminal to the error amplifier 310e and the abnormality detection circuit 360. In the present embodiment, the diode D2 functions to clamp the voltage at the PC terminal with the Zener voltage Vz as the lower limit regardless of the state of the transistor 312, thereby reliably generating the internal power supply voltage _VCC2 of a predetermined level. Thus, stable operation in the semiconductor chip SC5 is guaranteed.

The above is the configuration of the synchronous rectification controller 300e according to the fourth embodiment.
According to the synchronous rectification controller 300e, 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 fourth embodiment, the driving circuit 302e, the ground plane of the error amplifier 310d, and the power plane are made independent. Thus, even in an application in which the synchronous rectification transistor M2 is inserted on the high side, the photocoupler 204 is transformed into the transformer 2 by the error amplifier 310e while the synchronous rectification transistor M2 is driven using the source voltage as the ground plane by the drive circuit 302e. The ground potential on the next side can be driven as a ground plane.

Next, the use of the DC / DC converter 200 will be described.
FIG. 10 is a diagram illustrating 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. Examples of the electronic device 810 include a notebook PC, a digital camera, a digital video camera, a mobile phone, and a mobile audio player.

FIGS. 11A and 11B are diagrams illustrating an electronic device 900 including the AC / DC converter 100. FIG. Although the electronic device 900 in FIGS. 11A and 11B is a display device, the type of the electronic device 900 is not particularly limited, and is a device including a power supply device such as an audio device, a refrigerator, a washing machine, or a vacuum cleaner. I just need it.
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 a load such as a microcomputer, a DSP (Digital Signal Processor), a power supply circuit, a lighting device, an analog circuit, or 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 will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. is there. Hereinafter, such modifications will be described.

(First modification)
FIG. 12 is a circuit diagram of a DC / DC converter 200b including the synchronous rectification controller 300b according to the first modification. The difference between FIG. 6 will be described. The first resistor R1 and the second resistor R2 are integrated on the same semiconductor chip as the error amplifier 310 and are built in the synchronous rectification controller 300b. The first resistor R1 and the second resistor R2 are provided in series between the VO terminal and the ground plane (ground line) of the semiconductor chip on which the error amplifier 310 is integrated.

  The first resistor R1 and the second resistor R2 are formed close to each other on the semiconductor chip so as to have a pair property, and they have the same device structure. As a result, the resistance values of the first resistor R1 and the second resistor R2 fluctuate in the same tendency with respect to process variations and temperature fluctuations, and their relative accuracy is increased.

  Preferably, the resistance value of at least one of the first resistor R1 and the second resistor R2 can be adjusted by trimming means such as laser trimming.

  The above is the configuration of the synchronous rectification controller 300b. According to the synchronous rectification controller 300b, the first resistor R1 and the second resistor R2 which are external chip components in FIG. 6 are not necessary, so that the cost can be reduced and the mounting area can be reduced.

Further, the DC / DC converter 200b of FIG. 12 has the following advantages. The output voltage _VOUT of the DC / DC converter 200b is stabilized at the following target voltage.
V _OUT = V _REF × (1 + R1 / R2)
When the first resistor R1 and the second resistor R2 are configured by chip components as shown in FIG. 6, when mass-producing an electronic device on which the DC / DC converter 200b is mounted, the resistance values of the first resistor R1 and the second resistor R2 (1 + R1 / R2) varies due to variations in the output voltage, and consequently, the output voltage _VOUT varies.

On the other hand, by integrating the first resistor R1 and the second resistor R2 in the semiconductor chip and ensuring their pairability, the specific accuracy can be improved. 1 + R1 / R2) is kept constant. Thereby, the stability of the output voltage V _OUT can be improved.

  In addition, by configuring at least one of the first resistor R1 and the second resistor R2 so that the resistance value can be adjusted, the value of R1 / R2 can be set to a target value with high accuracy before packaging the synchronous rectification controller 300. Can be approached.

(Second modification)
FIG. 13 is a circuit diagram of a DC / DC converter 200f including the synchronous rectification controller 300f according to the second modification. The synchronous rectification controller 300f is obtained by integrating a first resistor R1 and a second resistor R2 on the semiconductor chip SC5 of the synchronous rectification controller 300e of FIG. According to the synchronous rectification controller 300f of FIG. 13, the same effects as those of the first modification can be obtained.

(Third Modification)
In FIGS. 6, 9, 12, and 13, the output transistor 312 of the error amplifier 310 may be formed of a PNP bipolar transistor or a P-channel MOSFET. In this case, the inverting input terminal and the non-inverting input terminal of the differential amplifier 314 may be switched.

(Fourth modification)
Although the flyback converter has been described in the embodiment, the present invention can also be applied to a forward converter. In this case, a plurality of synchronous rectification transistors are disposed 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 in a single package. Or it can also respond to a forward converter by using a plurality of synchronous rectification controllers of Drawing 2 and Drawing 6. The converter may be a quasi-resonant type.

(5th 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 terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... AC / DC converter, 102 ... Filter, 104 ... Rectifier circuit, 106 ... Smoothing capacitor, 108 ... Load switch, 200 ... DC / DC converter, 202 ... Controller, 204 ... Photocoupler, 206 ... Shunt regulator, 210 ... Output Circuit, M1 ... Switching transistor, M2 ... Synchronous rectifier transistor, C1 ... Output capacitor, T1 ... Transformer, W1 ... Primary winding, W2 ... Secondary winding, R1 ... First resistor, R2 ... Second resistor, 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 ... Re Comparator, 336 ... AND gate, 338 ... OR gate, 340 ... flip-flop, 342 ... blanking circuit, 350 ... UVLO circuit, 352 ... internal regulator, 360 ... abnormality detection circuit, 362 ... transistor, 500 ... load, 502 ... micro Controller, 504 ... Circuit, 800 ... AC adapter, 802 ... Plug, 804 ... Housing, 806 ... Connector, 810, 900 ... Electronic equipment, 902 ... Plug, 904 ... Housing.

Claims (22)

A synchronous rectification controller that is disposed on a secondary side of an insulated synchronous rectification type DC / DC converter that supplies power to a load and controls a secondary side synchronous rectification transistor of the DC / DC converter;
The insulated synchronous rectification type DC / DC converter is
A transformer having a primary winding and a secondary winding;
A switching transistor connected to the primary winding of the transformer;
The synchronous rectification transistor connected to the secondary winding of the transformer;
A feedback photocoupler;
A primary side controller connected to the output side of the feedback photocoupler and switching the switching transistor in response to a feedback signal from the feedback photocoupler;
With
The synchronous rectification controller is
A drive circuit for switching the synchronous rectification transistor;
An abnormality detection circuit for detecting an abnormality on the secondary side of the DC / DC converter;
A fail terminal for notifying the outside of the occurrence of an abnormality,
With
A synchronous rectification controller packaged in a single module.   The synchronous rectification controller according to claim 1, wherein the load is connected to the fail terminal. The load is
A microcontroller,
At least one circuit placed under the control of the microcontroller;
Including
The synchronous rectification controller according to claim 2, wherein the microcontroller is connected to the fail terminal.   A load switch capable of switching between cutoff and conduction is provided on an output voltage supply path from the DC / DC converter to the load, and a control terminal of the load switch is connected to the fail terminal. The synchronous rectification controller according to claim 1. The DC / DC converter further includes an error notification photocoupler whose output side is connected to the primary side controller,
5. The fail terminal of the synchronous rectification controller is connected to an input side of the error notification photocoupler to notify the primary controller of the occurrence of the abnormality. The synchronous rectification controller in any one.   6. The synchronous rectification controller according to claim 1, wherein the abnormality detection circuit and the drive circuit have independent power supply planes and independent ground planes. 7. The synchronous rectification transistor is inserted on the high potential side of the secondary winding,
The transformer further includes an auxiliary winding provided on the secondary side thereof,
The DC / DC converter is configured to generate an external power supply voltage based on a potential of a line between the synchronous rectification transistor and the secondary winding using the auxiliary winding,
7. The synchronous rectification controller according to claim 6, wherein the potential of the line is supplied to the ground plane of the drive circuit, and the external power supply voltage is supplied to the power supply plane of the drive circuit. . A photocoupler connection terminal connected to the input side of the feedback photocoupler;
An error amplifier that amplifies an error between a voltage detection signal corresponding to the output voltage of the DC / DC converter and its target voltage, and draws a current corresponding to the error from the input side of the feedback photocoupler via the photocoupler connection terminal. When,
The synchronous rectification controller according to claim 1, further comprising: a single module.   9. The synchronous rectification controller according to claim 8, wherein a power plane and a ground plane of the error amplifier are common to the abnormality detection circuit.   The power supply plane common to the error amplifier and the abnormality detection circuit is supplied with an internal power supply voltage generated from the voltage of the photocoupler connection terminal, and the common ground plane of the error amplifier and the abnormality detection circuit is supplied to the power supply plane. 10. The synchronous rectification controller according to claim 9, wherein a ground potential on the secondary side of the DC / DC converter is supplied. The error amplifier is
A differential amplifier for amplifying an error between the voltage detection signal and the target voltage;
An output transistor in which an output signal of the differential amplifier is input to the base / gate, an emitter / source thereof is grounded, and a collector / drain thereof is connected to the photocoupler connection terminal;
The synchronous rectification controller according to claim 8, comprising: A voltage detection terminal for receiving an output voltage of the DC / DC converter;
A first resistor and a second resistor integrated in the same semiconductor chip as the error amplifier and provided in series between the voltage detection terminal and a ground plane;
The synchronous rectification controller according to claim 8, further comprising: The synchronous rectification transistor is inserted on the high potential side of the secondary winding,
The transformer further includes an auxiliary winding provided on the secondary side thereof,
The DC / DC converter is configured to generate an external power supply voltage based on a potential of a line between the synchronous rectification transistor and the secondary winding using the auxiliary winding,
The synchronous rectification controller according to claim 7, wherein the potential of the line is supplied to the ground plane of the drive circuit, and the external power supply voltage is supplied to the power supply plane of the drive circuit. .   The synchronous rectification controller according to claim 8, wherein the error amplifier and the driving circuit are integrated on separate semiconductor chips.   The synchronous rectification controller according to claim 6, further comprising the synchronous rectification transistor and packaged in a single module.   16. The synchronous rectification controller according to claim 1, wherein the abnormality detection circuit is configured to be capable of detecting at least one of an overvoltage state and an overheat state on the secondary side of the DC / DC converter. .   The synchronous rectification controller according to any one of claims 1 to 16, wherein the DC / DC converter is a flyback type.   The synchronous rectification controller according to any one of claims 1 to 16, wherein the DC / DC converter is a forward type. 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;
An output capacitor;
A photocoupler,
The synchronous rectification controller according to any one of claims 1 to 18, wherein the synchronous rectification transistor is switched, and a current corresponding to an error between an output voltage of the output capacitor and a target level thereof is supplied to an input side of the photocoupler. When,
A primary-side controller that is connected to the output side of the photocoupler and drives the switching transistor in response to a feedback signal corresponding to the current generated by the synchronous rectification controller;
An insulated synchronous rectification type DC / DC converter characterized by comprising: A filter for filtering commercial AC voltage;
A diode rectifier circuit for full-wave rectification of 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;
The DC / DC converter according to claim 19, wherein the DC input voltage is stepped down and supplied to a load.
A power supply apparatus comprising: Load,
A filter for filtering commercial AC voltage;
A diode rectifier circuit for full-wave rectification of 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;
The DC / DC converter according to claim 19, 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 rectification of 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;
The DC / DC converter according to claim 19, wherein the DC input voltage is stepped down to generate a DC output voltage.
A power adapter comprising:

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