JP2009284667A - Power supply device, its control method, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply device that also suppresses costs for achieving the power supply device without using a special element, its control method, and a semiconductor device for control that has a simple circuit configuration and a smaller number of connection terminals with the outside. <P>SOLUTION: The power supply device is configured such that a secondary-side circuit performs rectification of an output voltage by using a secondary-side switching element of the synchronous rectification method. Timing to turn on or off the secondary-side switching element is detected on the basis of a signal appearing in an auxiliary winding provided in the secondary-side circuit or a signal appearing in a tap of a secondary winding. A drive signal for controlling an operation of the secondary-side switching element is generated on the basis of the detected timing so as to control the operation of the secondary-side switching element by the drive signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an insulating power supply device, and in particular, a power supply device in which a secondary side circuit rectifies an output voltage by a synchronous rectification method, such as an AC-DC converter, a method for controlling the switching, and a control device for the same The present invention relates to a semiconductor device (IC).

  In power supply devices such as flyback AC-DC converters, Schottky diodes are widely used for rectification of the output voltage of the secondary circuit.

  However, this diode causes a conduction loss due to the forward voltage drop Vf it has, resulting in a reduction in power conversion efficiency of the AC-DC converter. In order to avoid this reduction in conversion efficiency, instead of a diode, a MOSFET or other control switching element having a forward voltage drop and a low on-time resistance is used, and this is driven by an appropriate control method to simulate the operation of the diode. Therefore, a circuit system called synchronous rectification has been used.

  However, if the diode rectification is used, a complicated control circuit is not necessary. However, in order to control by the synchronous rectification method, it is necessary to adopt a dedicated drive circuit method. This is because when the drive signals of the primary side control switching element and the secondary side control switching element are superimposed at the same time and turned on at the same time, a “short circuit phenomenon” may occur in the secondary side circuit and the circuit may be destroyed. This is because a large current flows. The control IC for controlling to avoid this has become complicated, and the number of terminals for connecting it to the outside tends to increase.

  On the other hand, as a first example of the prior art, Patent Document 1 discloses a technique for realizing an integrated synchronous rectifier package. In the same document, an IC for controlling the secondary side synchronous rectifier circuit includes two terminals for detecting a voltage between the drain and the source of the secondary side control switching element (controlled switching element), and a drive terminal for the control switching element. VGate, power supply terminal Vcc, and ground terminal GND have a total of five terminals.

  As a second example of the prior art, Patent Document 2 discloses that in the synchronous rectification ACDC converter, the off-timing of the secondary side control switching element is performed by digital control. In the present disclosure, the control IC connects a detection terminal for detecting the timing for turning on the secondary side control switching element, a drive terminal for the control switching element, and a resistor for setting a switching cycle of synchronous rectification in advance. Terminal, a ground terminal, and five power supply terminals not shown in the present disclosure.

  Further, as a third example of the prior art, in Patent Document 3, a drive signal for the primary side switching element is transmitted to the secondary side control IC to control the secondary side control switching element. Is disclosed. In the same document, in the case of the simplest circuit configuration example (FIG. 1 of Patent Document 3), the control IC has a drive signal detection terminal for the primary side switching element and a drive terminal for the secondary side control switching element. In addition, it is necessary to have four terminals, that is, a ground terminal and a power supply terminal that is not explicitly shown in the disclosed example.

  As a fourth example of the prior art, Patent Document 4 shows an example of controlling the drive timing of the secondary side control switching element from the auxiliary winding of the transformer in a flyback type. However, in this example, the turn-on timing of the secondary side control switching element is certainly generated from the auxiliary winding signal. However, at the turn-off timing, a charging current is supplied to a capacitor called a timing capacitor, and the voltage is predetermined. The method of turning off when the threshold value is exceeded is adopted.

  As fifth and sixth examples of the prior art, Patent Documents 5 and 6 also show examples of controlling the drive timing of the secondary side control switching element from the auxiliary winding of the transformer in the flyback type. However, in this example as well, in determining the off timing, a current transformer is used to detect the current value of the secondary circuit, and this component contributes to the economic cost of the entire flyback AC-DC converter. The ratio is not small.

JP 2005-143287 A U.S. Pat. No. 6418039 US Pat. No. 7,345,896 JP 2005-151768 A JP 2005-525069 gazette JP-T-2004-514390

  In the above-mentioned Patent Documents 1 and 2, there is a problem that the number of connection terminals to the outside increases because the circuit configuration of the control IC of the flyback AC-DC converter is complicated.

  Moreover, in patent document 3, since it was necessary to use a special coupling element, there existed a problem that the cost which comprises a power supply circuit rose. In order to realize the disclosed example of Patent Document 3, a coupling element for transmitting the drive signal of the switching element on the primary side to the secondary side in a non-insulating manner is necessary. As the coupling element, a pulse transformer or a photocoupler shown in the disclosure example of the same document is generally used. The ratio of the economic cost to the whole flyback AC-DC converter of these coupling elements is not small.

  In Patent Document 4, the off timing is generated from a detection voltage based on the amount of charge to the timing capacitor. For this reason, there is a problem that it is difficult to avoid the “short-circuit phenomenon” while maintaining high efficiency.

  In Patent Documents 5 and 6, a component called a current transformer is used to determine the off timing. For this reason, there existed a problem that the expense which comprises an AC-DC converter will become high.

  An object of the present invention is to solve the above-mentioned problems of the prior art, to use a power supply device that does not use a special element and can reduce the cost for the realization, a control method thereof, and a circuit configuration that is simple and external. An object of the present invention is to provide a control semiconductor device with a small number of connection terminals.

To achieve the above object, the present invention provides a semiconductor device for controlling the operation of a power supply device in which a secondary side circuit rectifies an output voltage by using a synchronous rectification type secondary side switching element,
Rise and rise of a signal appearing in the auxiliary winding or a signal appearing in the tap of the secondary winding based on a signal appearing in the auxiliary winding of the secondary circuit or a signal appearing in the tap of the secondary winding Provided is a semiconductor device comprising a switching control circuit that detects a downstream timing and generates a drive signal for controlling the operation of the secondary side switching element based on the detected timing. is there.

  Here, the switching control circuit detects that the voltage of the signal appearing in the auxiliary winding or the signal appearing in the tap of the secondary winding exceeds the first reference voltage, and the secondary-side switching element Detecting that the voltage of a signal appearing in the auxiliary winding or a signal appearing in the tap of the secondary winding is lower than a second reference voltage; It is preferable to include an off detection circuit that detects a timing at which the secondary side switching element should be turned off.

  The ON detection circuit includes: a first comparator that compares a voltage of a signal appearing in the auxiliary winding or a signal appearing in a tap of a secondary winding with the first reference voltage; and A first delay circuit that delays the output signal of the comparator so that the on-period falling of the primary-side switching element of the primary-side circuit and the rising of the on-period of the secondary-side switching element do not overlap. It is preferable.

  Similarly, the off detection circuit includes a second comparator that compares a voltage of a signal appearing in the auxiliary winding or a signal appearing in a tap of a secondary winding with the second reference voltage, and the power supply device. A second delay circuit that delays the output signal of the comparator so that the rise of the on-period of the primary-side switching element of the primary-side circuit and the fall of the on-period of the secondary-side switching element do not overlap. It is preferable to provide.

  The off detection circuit preferably includes a differentiation circuit that differentiates a signal appearing in the auxiliary winding or a signal appearing in the tap of the secondary winding and supplying the differentiated signal to the second comparator.

  Alternatively, the switching control circuit calculates an oscillation frequency of the power supply device by measuring a cycle of timing to be turned on and off based on at least one of the output signals of the first and second comparators, It is preferable that a frequency detection circuit for adjusting a delay time by the first and second delay circuits or a reference voltage of the on detection circuit or the off detection circuit according to an oscillation frequency is provided.

Further, the present invention is a power supply device in which the secondary side circuit rectifies the output voltage using a synchronous rectification type secondary side switching element,
An operation of the secondary side switching element is controlled by a drive signal supplied from any of the semiconductor devices described above.

Furthermore, the present invention is a method for controlling the operation of a flyback type power supply device in which the secondary side circuit rectifies the output voltage using a synchronous rectification type secondary switching element,
Based on a signal appearing in the auxiliary winding of the secondary side circuit or a signal appearing in the tap of the secondary winding, the timing at which the secondary side switching element should be turned on and off is detected,
Based on the detected timing, a drive signal for controlling the operation of the secondary side switching element is generated,
There is provided a control method characterized in that the operation of the secondary side switching element is controlled by the drive signal.

  According to the present invention, the timing at which the switching element of the secondary side circuit should be turned on and off is detected based on the signal appearing at the auxiliary winding of the secondary side circuit of the transformer or the tap of the secondary side winding. Since the drive signal is generated, the control IC of the secondary circuit that realizes this is a simple circuit consisting of four terminals: a power supply terminal, a ground terminal, a switching element drive terminal, and a switching element on / off timing detection terminal. It can be realized with a configuration.

  Further, according to the present invention, it is possible to detect the ON / OFF timing of the switching element of the secondary side circuit without adding a special circuit element such as a pulse transformer or a photocoupler. The device can be manufactured economically.

  Hereinafter, a power supply device, a control method thereof, and a semiconductor device for control will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a schematic diagram of a first embodiment showing a configuration of a power supply device of the present invention. A power supply device 10 shown in the figure is a flyback type AC-DC converter, and includes a primary side circuit 12 shown on the left side and a secondary side circuit 14 shown on the right side in FIG. The secondary side circuit 14 rectifies the output voltage by turning on and off the synchronous rectification switching element Tr2 instead of the normally used rectifier diode.

  The power supply device 10 includes a transformer 16. The transformer 16 includes a primary winding (inductor) L1 included in the primary side circuit 12, a secondary winding (inductor) L2 included in the secondary side circuit 14, and an auxiliary winding similarly included in the secondary side circuit 14. (Inductor) L2aux is included. As will be apparent to those skilled in the art, each circuit element connected to the primary winding L1 must be electrically isolated from the secondary winding L2.

  The power supply apparatus 10 receives electric power energy (AC power supply) applied between the Vin terminal of the primary side circuit 12 and the Primary Return terminal. Then, through the control described later, the Vout terminal and the ground terminal are used as the output voltage (DC power supply) between the Vout terminal and the ground terminal of the secondary side circuit 14 regardless of the magnitude of the load connected thereto. Is controlled so as to have a desired constant voltage value.

  A switching element Tr1 for switching the primary current is connected to the non-dot side terminal of the primary winding L1. The switching element Tr1 is switched by the primary side switching control circuit 18 and controls the current flowing through the primary winding L1 with the required on time and off time. A transistor called a MOS (Metal Oxide Semiconductor) is desirable as the switching element.

  As will be apparent to those skilled in the art, the switching element Tr1 may be a bipolar transistor or other switching element. The switching control circuit 18 that controls the switching element is desirably a control circuit for a pseudo resonance mode. In this case, as shown in FIG. 1, a resonance capacitor C1 is connected in parallel with the switching element Tr1.

  The switching control circuit 18 may be a general PWM (pulse width modulation) control device as long as it controls the power supply device 10 in discontinuous mode control or critical mode control. Control of the switching element by the switching control circuit 18 is performed by a known method.

  In the secondary side circuit 14, a switching element Tr2 for synchronous rectification different from the primary side circuit 12 is connected to the dot side terminal of the secondary winding L2. The winding direction of the secondary winding L2 is opposite to that of the primary winding L1 because the power supply device 10 is a flyback type. The switching element Tr2 has a body diode BdyDi generally connected in parallel with the source-drain current path. A drive signal is applied to the gate terminal of the switching element Tr2 from the switching control circuit 20 on the secondary side, and its on and off are controlled.

  Here, the semiconductor device (IC) of the present invention includes the secondary-side switching control circuit 20 and controls the operation (ON, OFF) of the secondary-side control switching element Tr2.

  The power supply device 10 has a capacitor C2 between the non-dot side terminal of the secondary winding L2 and the ground terminal, and has a ripple removing capacitor C3 between the Vout terminal and the ground terminal. In order to provide feedback to the primary side switching control circuit 18 so as to stabilize the output voltage, a three-terminal shunt regulator Shunt Reg. And a photocoupler Photo Coupler is used. The light emitting diode 22 of the photocoupler Photo Coupler is connected to both ends of R2 among the series-connected divided resistors R1 and R2 that generate a voltage corresponding to the output voltage level at the Vout terminal.

  Three-terminal shunt regulator Shunt Reg. Are connected between the resistor R2 and the ground. Three-terminal shunt regulator Shunt Reg. Is a reference potential that is the contact potential of resistors R3 and R4 connected in series between the Vout terminal and the ground terminal, and a three-terminal shunt regulator Shunt Reg. It works to keep the cathode terminal of a constant value. With the above configuration, it is possible to avoid that the output voltage of the Vout terminal, which is generally a voltage higher than the withstand voltage of the light emitting diode 22, is applied directly to both ends of the light emitting diode 22.

  Note that a three-terminal shunt regulator Shunt Reg. The capacitor C4 and the resistor R5 connected in series between the cathode terminal of the resistor R3 and the resistor R4 are connected to the contacts of the resistors R3 and R4 because the output voltage of the Vout terminal includes ripples. Used to stabilize the potential.

  The photocoupler Photo Coupler is provided with a phototransistor 24 so as to face the light emitting diode 22 and receives light emitted from the light emitting diode 22 whose light amount changes according to the output voltage of the Vout terminal. The impedance of the current path of the phototransistor 24 changes according to the amount of light emission. Thus, a feedback signal is generated according to the level of the output voltage at the Vout terminal, and this is further fed back to the primary side switching control circuit 18 by a known connection method.

  The light emitting diode 22 of the photocoupler Photo Coupler belongs to the secondary side circuit 14, while the phototransistor 24 belongs to the primary side circuit 12 and is electrically insulated from each other.

  In the present embodiment, the auxiliary winding L2aux of the secondary side circuit 14 includes a signal for causing the secondary side switching control circuit 20 to detect the timing when the switching element Tr2 should be turned on and off, and the secondary side circuit 14 A power supply voltage for the switching control circuit 20 is supplied. The auxiliary winding L2aux is in the same direction as the secondary winding L2, that is, the winding direction opposite to the primary winding L1. A resistor R7 is connected between the non-dot side terminal of the auxiliary winding L2aux and the signal detection terminal DET of the secondary side switching control circuit 20.

  Further, a diode Di2 and a resistor R2 are connected in series between the non-dot side terminal of the auxiliary winding L2aux and the power supply voltage terminal Vcc of the secondary side switching control circuit 20, and a positive voltage is supplied to the Vcc terminal. The

  It should be noted that even if the transmission of power energy from the primary side circuit 12 to the secondary side circuit 14 is temporarily interrupted, the Vcc terminal is set so that the secondary side switching control circuit 20 operates normally for a certain period. The capacitor C5 is connected between the ground terminal. As a result, the Vcc terminal is kept at a voltage higher than the voltage required for the secondary side switching control circuit 20 to operate.

  Next, the operation of the power supply apparatus 10 shown in FIG. 1 will be described according to the method for controlling the power supply apparatus of the present invention.

  3A to 3E are timing charts showing the operation of the power supply device shown in FIG. Since the power supply device 10 is described for the flyback system, first, the primary side switching element Tr1 is turned on, the drain current increases, the transformer is excited, and current energy is stored in the transformer (FIG. 3). (B)). Since the primary side switching element Tr1 is on, its drain voltage Vds changes around 0V (FIG. 3A). At this time, since the transformer winding direction is the opposite direction, no current flows through the switching element Tr2 on the secondary side.

  When the ON period of the switching element Tr1 on the primary side ends and the accumulation of current energy in the transformer ends, the current flows out from the secondary winding L2. The current value reaches its maximum at the start of flow and decreases with the release of energy (FIG. 3 (d)). In this current path, since there is the secondary side switching element Tr2 and the body diode BdyDi incorporated in parallel therewith, the current first flows through the body diode BdyDi.

  In this state, the forward voltage drop of the body diode BdyDi and the loss due to the internal resistance occur, so it is necessary to turn on the gate of the secondary side switching element Tr2 as early as possible from the start of the current flow. It is.

  For this purpose, the auxiliary winding L2aux is used. The DET terminal of the switching control circuit 20 on the secondary side is connected to this via a resistor R7. The voltage change in this portion becomes a high level while a current flows through the secondary winding L2, and the secondary winding. When the current of the line L2 finishes flowing, that is, when the energy emission from the secondary winding L2 ends, the level becomes low (FIG. 3C). Therefore, the secondary-side switching control circuit 20 detects the signal at the DET terminal and generates a drive signal for the gate of the secondary-side switching element Tr2 (FIG. 3 (e)).

  FIG. 2 is a block diagram showing the configuration of the secondary side switching control circuit. The switching control circuit 20 on the secondary side includes an ON detection circuit 26 and an OFF detection circuit 28 connected to the DET terminal, an RS flip-flop 30 in which respective output signals are input to the set terminal S and the reset terminal R, The output is connected, and a driver 32 that outputs a drive signal for the gate of the secondary side switching element Tr2 from the DRV terminal, and a built-in voltage regulator 34 that is connected to the Vcc terminal and generates a voltage used in the control circuit 20 are provided. And is composed of.

  The built-in voltage regulator 34 includes a power supply voltage (including a power supply voltage of the driver 32 that drives the control switching element of the secondary side circuit 14) used in the secondary side switching control circuit 20 and a reference voltage Von, ref. And Voff, ref are used to generate. The delay time from when the ON detection circuit 26 and the OFF detection circuit 28 connected to the DET terminal detect the ON timing and the OFF timing, respectively, until the ON signal and the OFF signal are output to the terminal DRV is generally from 50 nsec. Although it is 1000 nsec, Preferably it is 100 nsec to 200 nsec.

  The on detection circuit 26 includes a comparator 36 with hysteresis and a delay circuit 38. The comparator 36 detects that the voltage of the signal input to the DET terminal has exceeded the reference voltages Von and ref, and detects the ON timing of the switching element Tr2. The delay circuit 38 is provided after the comparator 36, and delays the output signal of the comparator 36 (that is, the rising edge of the signal output from the terminal DRV) by a delay time Delay1 (see FIG. 3E). The fall of the on-period of the switching element Tr1 on the secondary side and the rise of the on-period of the switching element Tr2 on the secondary side overlap, resulting in a so-called Reverse Conduction (reverse conduction) state. Avoid that happening. A delay time Delay 1 shown in FIG. 3E is provided to avoid this superposition.

  When the rising edge of the signal shown in FIG. 3C is detected by the on detection circuit 26, the subsequent stage RS flip-flop 30 is set by the output signal of the on detection circuit 26, and its output is driven by the driver 32. The output signal of the terminal DRV becomes high level, and the secondary side switching element Tr2 is turned on.

  On the other hand, the off detection circuit 28 includes a comparator 40 with hysteresis and a delay circuit 42. The comparator 40 detects that the voltage of the signal from the DET terminal is lower than the reference voltages Voff and ref, and detects the off timing of the switching element Tr2. The delay circuit 42 is provided in the subsequent stage of the comparator 40, and the output signal of the comparator 40 (that is, the falling edge of the signal output from the terminal DRV) is used as the delay time Delay2 (FIG. (See (e)), the last falling of the on-period of the switching element Tr2 on the secondary side does not overlap with the rising of the on-period of the switching element Tr1 on the primary side, and The off timing is adjusted so as to ensure an on period during which energy is sufficiently discharged. This means that a period of dead time Dead Time and delay time Delay2 shown in FIG. 3 (e) is provided. Providing the dead time Dead Time is particularly essential in order to avoid the “short circuit phenomenon” of the secondary circuit 14.

  When the fall of the signal shown in FIG. 3C is detected by the off detection circuit 28, the RS flip-flop 30 is reset by the output signal of the off detection circuit 28, and the output is driven by the driver 32, and the terminal The DRV output signal becomes low level, and the secondary side switching element Tr2 is turned off.

  For example, the power supply device 10 of the above embodiment enables secondary side control of a flyback type power supply device in which the secondary side circuit 14 is controlled by a synchronous rectification method. The secondary output rectification is performed by using the switching element Tr2 having a low on-resistance instead of the diode that generates a loss due to the forward voltage, so that a power supply device that minimizes the loss is configured. be able to.

  In the embodiment shown in FIG. 2, in the circuit configuration of the secondary side switching control semiconductor device (secondary side switching control circuit 20), the reference voltages Von, ref and Voff, ref are the secondary side switching. The change can be easily made regardless of the circuit configuration outside the control semiconductor device. In addition, it is easy to change and adjust the drive voltage of the secondary side switching element Tr2 supplied to the driver 32 that drives the secondary side control switching element Tr2 according to the transistor characteristics of the secondary side control switching element Tr2. .

  FIG. 4 is a schematic diagram of the second embodiment showing the configuration of the power supply device of the present invention. In the power supply device shown in the figure, the power supply terminal Vcc of the secondary side switching control circuit 20 is connected to the non-dot side terminal of the secondary winding L2 through a diode Di2 and a resistor R6 connected in series. Receive power supply from It is also possible to use the secondary side switching control circuit 20 in the power supply device having such a configuration.

  FIG. 5 and FIG. 6 show modifications of the first and second embodiments as the third and fourth embodiments. In these examples, taps are taken out from the middle of the secondary winding L2 instead of the secondary auxiliary winding (L2aux in FIGS. 1 and 4) of the transformer 16 of the example shown in FIGS. 1 and 2, respectively. Here, the power supply terminal Vcc of the secondary side switching control circuit 20 and the detection terminal DET are connected via a diode Di2 and resistors R6 and R7. Even with this configuration, the power supply operations described in the first and second embodiments are essentially unchanged.

  The semiconductor device for secondary side switching control of the flyback type power supply device and its control method according to the present invention are suitable for so-called discontinuous mode power supply and critical mode power supply, as those skilled in the art can easily understand. It is. That is, since the voltage appearing in the secondary side auxiliary winding L2aux is directly detected to control the secondary side control switching element Tr2, the efficiency is not reduced even if the frequency of the primary side switching control changes. In addition, the on-timing and off-timing can be determined without causing a short circuit phenomenon.

  Next, FIG. 7 is a schematic diagram of the fifth embodiment showing the configuration of the power supply device of the present invention. The power supply device shown in FIG. 3 is a three-terminal shunt regulator shown in FIG. Is incorporated in the secondary-side switching control circuit 21. In this case, the switching control circuit 21 includes a three-terminal shunt regulator Shunt Reg. By sharing the ground terminal (anode terminal) excluding the two terminals of the cathode terminal CATH and the reference voltage detection terminal REF with the ground terminal of the original control semiconductor device, it is possible to configure 6 terminals. Even if the switching control circuit 21 on the secondary side has six terminals in this manner, it is within the scope of this patent.

  FIG. 8 is a block diagram showing a configuration of a modified example of the secondary side switching control circuit (secondary side switching control semiconductor device) of FIG. A difference from the off detection circuit 28 of FIG. 2 is that in the off detection circuit 44 of FIG. 8, a signal from the DET terminal is input to the differentiation circuit 46, and the differentiated waveform enters the comparator 40 and the reference voltage Voff, Compared with ref, when it exceeds the reference voltages Voff, ref, it is detected that it is the off timing of the secondary control switching element Tr2.

  FIG. 9 is a block diagram showing a configuration of another modification of the secondary side switching control circuit of FIG. The difference from the secondary side switching control circuit 20 of FIG. 2 is that a frequency detection circuit 48 is further provided. The frequency detection circuit 48 measures the on-timing or off-timing period based on at least one of the output signals of the comparator 36 of the on-detection circuit 26 and the comparator 40 of the off-detection circuit 28 to oscillate the AC-DC converter. The delay time Delay1 shown in FIG. 3 is calculated so that the frequency is calculated and the fluctuation of the voltage waveform at the DET terminal is estimated from the change in the oscillation frequency due to the load fluctuation, so that the drive can be performed at an appropriate timing even if the oscillation frequency fluctuates. Alternatively, it is possible to realize a function of adjusting (changing) Delay2. Further, the delay time Delay1 or Delay2 can be adjusted (changed) by adjusting the reference voltages Von, ref, Voff, and ref in FIG. According to this embodiment, it is possible to generate the drive waveform of the secondary side control switching element Tr2 for increasing the conversion efficiency of the AC-DC converter even if there is a load fluctuation.

  In the present invention, the secondary side circuit may be a flyback type power supply device that rectifies the output voltage using a synchronous rectification type switching element, and the specific circuit configuration is not limited to the illustrated example. . Further, the semiconductor device of the present invention only needs to include a secondary-side switching control circuit, and its specific circuit configuration is not limited to that of the illustrated example, but the number of terminals can be configured with a minimum of four terminals. Is.

The present invention is basically as described above.
Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and it is needless to say that various improvements and modifications may be made without departing from the gist of the present invention.
In the above embodiment, the semiconductor device that controls the operation of the flyback power supply device has been described. However, the present invention is not limited to this, and the present invention is also applicable to a semiconductor device that controls the operation of the forward power supply device. Is done.

It is the schematic of 1st Embodiment showing the structure of the power supply device of this invention. FIG. 2 is a schematic diagram illustrating a configuration of a secondary side switching control circuit illustrated in FIG. 1. (A)-(e) is a timing chart showing operation | movement of the power supply device shown in FIG. It is the schematic of 2nd Embodiment showing the structure of the power supply device of this invention. It is the schematic of 3rd Embodiment showing the structure of the power supply device of this invention. It is the schematic of 4th Embodiment showing the structure of the power supply device of this invention. It is the schematic of 5th Embodiment showing the structure of the power supply device of this invention. It is a block diagram showing the modification of the switching control circuit of a secondary side. It is another block diagram showing the modification of the switching control circuit of a secondary side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Power supply device 12 Primary side circuit 14 Secondary side circuit 16 Transformer 18 Primary side switching control circuit 20, 21 Secondary side switching control circuit 22 Light emitting diode 24 Phototransistor 26 On detection circuit 28, 44 Off detection circuit 30 RS flip-flop 32 Driver 34 Built-in voltage regulator 36, 40 Comparator 38, 42 Delay circuit 46 Differentiation circuit 48 Frequency detection circuit L1 Primary winding L2 Secondary winding L2aux Auxiliary winding Tr1 Primary side switching element Tr2 Secondary side Switching element BdyDi body diode Shunt Reg. 3-terminal shunt regulator Photo Coupler Photocoupler R1 to R7 Resistor C1 to C5 Capacitor Von, ref, Voff, ref Reference voltage Delay1, Delay2 Delay time Dead Time Dead time

Claims (8)

A semiconductor device for controlling an operation of a power supply device in which a secondary side circuit rectifies an output voltage using a synchronous rectification type secondary switching element,
Rise and rise of a signal appearing in the auxiliary winding or a signal appearing in the tap of the secondary winding based on a signal appearing in the auxiliary winding of the secondary circuit or a signal appearing in the tap of the secondary winding A semiconductor device comprising: a switching control circuit that detects a downstream timing and generates a drive signal for controlling the operation of the secondary side switching element based on the detected timing.   The switching control circuit detects that the voltage of the signal appearing at the auxiliary winding or the signal appearing at the tap of the secondary winding exceeds the first reference voltage, and turns on the secondary switching element. An on-detection circuit for detecting a timing to be detected, a signal that appears in the auxiliary winding, or a signal that appears in the tap of the secondary winding is detected to be lower than a second reference voltage; The semiconductor device according to claim 1, further comprising an off detection circuit that detects a timing at which the switching element is to be turned off.   The ON detection circuit includes a first comparator that compares a voltage of a signal appearing in the auxiliary winding or a signal appearing in a tap of a secondary winding with the first reference voltage, and a primary of the power supply device. A first delay circuit that delays the output signal of the comparator so that the on period falling of the primary side switching element of the side circuit and the rising of the on period of the secondary side switching element do not overlap. The semiconductor device according to claim 2.   The off detection circuit includes: a second comparator that compares a voltage of a signal appearing in the auxiliary winding or a signal appearing in a tap of a secondary winding with the second reference voltage; and a primary of the power supply device A second delay circuit that delays the output signal of the comparator so that the rise of the ON period of the primary side switching element of the side circuit and the fall of the ON period of the secondary side switching element do not overlap. The semiconductor device according to claim 2, wherein:   The off-detection circuit includes a differentiation circuit that differentiates a signal appearing in the auxiliary winding or a signal appearing in a tap of the secondary winding and supplying the differentiated signal to the second comparator. 5. The semiconductor device according to 4.   The switching control circuit calculates an oscillation frequency of the power supply device by measuring a cycle of timing to be turned on and off based on at least one of the output signals of the first and second comparators, and the oscillation frequency 5. A frequency detection circuit for adjusting a delay time by the first and second delay circuits or a reference voltage of the on detection circuit or the off detection circuit according to A semiconductor device according to claim 1. A power supply device in which a secondary side circuit rectifies an output voltage by using a secondary side switching element of a synchronous rectification type;
The operation of the secondary side switching element is controlled by a drive signal supplied from the semiconductor device according to claim 1. A method for controlling an operation of a power supply device in which a secondary side circuit rectifies an output voltage by using a secondary side switching element of a synchronous rectification method,
Based on a signal appearing in the auxiliary winding of the secondary side circuit or a signal appearing in the tap of the secondary winding, the timing at which the secondary side switching element should be turned on and off is detected,
Based on the detected timing, a drive signal for controlling the operation of the secondary side switching element is generated,
A control method comprising controlling an operation of the secondary side switching element by the drive signal.

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