JP4172569B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synchronous rectification switching power supply device.
[0002]
[Prior art]
In the switching power supply device, a DC voltage supplied to a power conversion circuit is intermittently switched by a switching element, a switching output is supplied to an output rectifying / smoothing circuit, and rectified and smoothed to be converted into an arbitrary DC output voltage.
[0003]
In such a switching power supply device, a switching power supply device including a synchronous rectification circuit is known as means for reducing the loss of the output rectification smoothing circuit. The synchronous rectifier circuit is configured using a switch element having a lower voltage drop and less loss than a rectifier diode, typically a semiconductor element including a control electrode such as a field effect transistor or a bipolar transistor, as a rectifier element.
[0004]
In a switching power supply device equipped with a synchronous rectifier circuit, the synchronous rectifier circuit can be controlled by synchronizing on / off of the switching element on the input side that switches the supplied DC voltage and the synchronous rectifier element of the synchronous rectifier circuit. It is an extremely important factor in taking advantage of For example, in a forward-type switching power supply device, a flywheel current synchronous rectifier element is turned on during the OFF period of an input side switching element, and a flywheel current flows, but is synchronized before an input side switching element is turned off. If the input side switching element is turned on before the rectifying element is turned on or the synchronous rectifying element is turned off, a short-circuit current in the reverse direction flows through the synchronous rectifying element. This short circuit current causes noise and further increases the power loss of the switching power supply.
[0005]
Such a switching power supply device that suppresses the occurrence of noise and loss due to the shift in the on / off timing between the switching element and the synchronous rectifying element is disclosed in, for example, Japanese Patent Laid-Open No. 11-235029 by the present applicant. Proposed. The switching power supply device described in this publication includes a signal timing adjusting unit that delays the timing at which a control signal is input to the switch unit on the input side from the timing at which the control signal is input to the switch unit of the synchronous rectifier circuit. However, there is no disclosure of a specific circuit configuration.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a synchronous rectification type switching power supply apparatus that delays the on-timing of a switching element on the input side with a simple circuit configuration and suppresses a short-circuit current when the switching element is turned on.
[0007]
Another object of the present invention is to provide a synchronous rectification switching power supply apparatus that delays the on-timing of a synchronous rectifying element that is conducted during an off period of an input-side switching element and suppresses a short-circuit current when the switching element is turned off. That is.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, a switching power supply device according to the present invention includes a power conversion circuit, an output rectification smoothing circuit, and a control circuit.
[0009]
The power conversion circuit includes a switching element having a control electrode, and intermittently supplies an input DC voltage and supplies a switching output to the output rectifying and smoothing circuit.
[0010]
The output rectifying / smoothing circuit includes a synchronous rectifying element and an output smoothing capacitor, and rectifies and smoothes the switching output.
[0011]
The synchronous rectifier element includes a control electrode and is conductive during an off period of the switching element.
[0012]
The control circuit includes a drive pulse generation circuit, an on timing delay circuit, and an on block circuit.
[0013]
The drive pulse generation circuit generates a first drive pulse and a second drive pulse.
[0014]
The first drive pulse is supplied to the control electrode of the switching element through the on-timing delay circuit.
[0015]
The second driving pulse is supplied to the control electrode of the synchronous rectifying element through the on-blocking circuit.
[0016]
The on-timing delay circuit includes an inductance.
[0017]
The on-blocking circuit detects a voltage between the main electrodes of the synchronous rectifying element and blocks the conduction of the synchronous rectifying element until the detected voltage becomes a predetermined value or less.
[0018]
In the above-described switching power supply device, the power conversion circuit includes a switching element having a control electrode, and supplies the switching output to the output rectifying and smoothing circuit by intermittently inputting the input DC voltage. The output rectifying and smoothing circuit includes a synchronous rectifying element and an output smoothing capacitor, and rectifies and smoothes the switching output, so that an arbitrary DC voltage different from the input DC voltage can be output. .
[0019]
The synchronous rectifier element includes a control electrode and is conductive during an off period of the switching element.
[0020]
The control circuit includes a drive pulse generation circuit, an on timing delay circuit, and an on block circuit. The drive pulse generation circuit generates a first drive pulse and a second drive pulse. The first drive pulse is supplied to the control electrode of the switching element through the on-timing delay circuit. The second driving pulse is supplied to the control electrode of the synchronous rectifying element through the on-blocking circuit.
[0021]
Since the on-timing delay circuit includes an inductance, the rise of the first drive pulse is delayed by the inductance. For this reason, the switching element is turned on after the synchronous rectifying element is reliably turned off, and a short-circuit current when the switching element is turned on can be suppressed.
[0022]
The on-blocking circuit detects a voltage between the main electrodes of the synchronous rectifying element and blocks the conduction of the synchronous rectifying element until the detected voltage becomes a predetermined value or less. For this reason, the synchronous rectifier element is turned on after the switching element is reliably turned off and the voltage between the main electrodes of the synchronous rectifier element is equal to or lower than a predetermined value, thereby suppressing a short-circuit current when the switching element is turned off. it can.
[0023]
Other objects, configurations and advantages of the present invention will be described in more detail with reference to the accompanying drawings. However, the drawings are merely examples.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an electric circuit diagram showing an embodiment of a switching power supply device according to the present invention. The illustrated switching power supply device includes a transformer for power conversion, and shows an example of a flyback system. The illustrated switching power supply device includes a power conversion circuit 1, an output rectifying / smoothing circuit 3, and a control circuit 5.
[0025]
The power conversion circuit 1 includes a switching element 11 and a power conversion transformer 2. The power conversion transformer 2 includes an input winding 21 and an output winding 22. The input winding 21 is connected to the DC input terminal Tin via the main electrode of the switching element 11.
[0026]
An input capacitor 6 and a DC voltage source E are connected to the DC input terminal Tin. The DC voltage source E may be an internal element or an external element of the present invention, and may be any one of a battery, another DC voltage source, or a voltage obtained by converting an AC voltage into DC via a rectifying and smoothing circuit. But you can use it.
[0027]
The switching element 11 interrupts the DC input voltage Vin supplied through the input winding 21 and induces a voltage in the output winding 22. The induced voltage is supplied to the output rectifying / smoothing circuit 3 as a switching output. The switching element 11 only needs to be able to switch the supplied DC voltage Vin at a high frequency, and a semiconductor element having a control electrode such as a bipolar transistor or a field effect transistor is typically used. In this embodiment, an N-channel MOS field effect transistor is used.
[0028]
The output rectifying / smoothing circuit 3 includes a synchronous rectifying element 31, an output smoothing capacitor 33, and a diode 35. The main electrode of the synchronous rectifier 31 and the output smoothing capacitor 33 are connected in series and connected between the output windings 22 of the transformer 2, and both ends of the output smoothing capacitor 33 are connected to the output terminal Tout. The diode 35 is connected between the main electrodes of the synchronous rectifying element 31 with a polarity that is forward with respect to the voltage induced in the output winding 22 during the OFF period of the switching element 11. The synchronous rectifying element 31 is composed of a MOS field effect transistor and is conductive during the OFF period of the switching element 11. As the synchronous rectifying element 31, a semiconductor switching element having a control electrode such as a bipolar transistor can be suitably used. However, as in this embodiment, if it is composed of a MOS field effect transistor, the voltage drop during conduction is reduced. This is particularly suitable because the diode 35 can be eliminated by the built-in diode.
[0029]
The control circuit 5 includes a drive pulse generation circuit 51, an on timing delay circuit 55, and an on prevention circuit 56. The drive pulse generation circuit 51 includes a pulse generation circuit 510, a drive circuit 511, and an inversion drive circuit 512. The pulse generation circuit 510 receives various control signals such as an output voltage signal and a current signal via a signal line (not shown), and outputs a control pulse S0 for the switching element 11.
[0030]
The drive circuit 511 and the inversion drive circuit 512 are supplied with the control pulse S0 output from the pulse generation circuit 510, and generate a first drive pulse S1 and a second drive pulse S2 that are inverted from each other. The first and second drive pulses S1 and S2 drive the switching element 11 and the synchronous rectification element 31, respectively. The first drive pulse S1 is supplied to the control electrode of the switching element 11 through the on-timing delay circuit 55. The second drive pulse S <b> 2 is supplied to the control electrode of the synchronous rectification element 31 through the ON blocking circuit 56. The drive circuit 511 and the inversion drive circuit 512 may be configured by a signal conversion circuit including a pulse transformer or the like. For example, if a pulse transformer is used for the inverting drive circuit 512, the control circuit 5 and the output terminal Tout can be electrically insulated.
[0031]
The on-timing delay circuit 55 is configured by a parallel circuit of a coil element 551 and a diode 552 and is inserted between the drive circuit 511 and the control electrode of the switching element 11.
[0032]
The on-blocking circuit 56 includes resistors R1 and R2 and a transistor switch Tr. One end of each of the resistors R1 and R2 is connected to form a resistance voltage dividing circuit, and both ends thereof are connected to the main electrode of the synchronous rectifying element 31. The transistor switch Tr has a control electrode connected to the connection point of the resistors R1 and R2, a main electrode connected to the control input side of the synchronous rectifying element 31, and one of the main electrodes connected to the supply line of the second drive pulse S2. Connected.
[0033]
In the switching power supply described above, the switching element 11 intermittently causes the DC voltage Vin supplied through the input winding 21 to induce a voltage in the output winding 22. The induced voltage is supplied to the output rectifying / smoothing circuit 3 as a switching output.
[0034]
The diode 35 of the output rectifying / smoothing circuit 3 is connected between the main electrodes of the synchronous rectifying element 31 with a polarity that is forward with respect to the voltage induced in the output winding 22 during the OFF period of the switching element 11. The synchronous rectifying element 31 is conductive during the OFF period of the switching element 11. For this reason, the switching output supplied to the output rectifying and smoothing circuit 3 is stored in the transformer 2 as excitation energy during the ON period of the switching element 11, and via the synchronous rectifying element 31 and the diode 35 during the OFF period of the switching element 11. And is smoothed by the output smoothing capacitor 33. The output terminal Tout outputs the voltage of the output smoothing capacitor 33 as the DC output voltage Vout.
[0035]
On / off of the switching element 11 and the synchronous rectifying element 31 is controlled by a drive pulse supplied from the control circuit 5. Hereinafter, the on / off timing of the switching element 11 and the synchronous rectifying element 31 will be described with reference to FIG.
[0036]
FIG. 2 is a timing chart showing waveforms at various parts of the switching power supply device shown in FIG.
[0037]
First, the pulse generation circuit 510 outputs a control pulse S0 including a high level signal and a low level signal (FIG. 2 (a)).
[0038]
The drive circuit 511 and the inversion drive circuit 512 are supplied with the control pulse S0 output from the pulse generation circuit 510. The drive circuit 511 generates a first drive pulse S1 that is in phase with the control pulse S0 of the pulse generation circuit 510 in order to drive the switching element 11 (FIG. 2B).
[0039]
The inversion drive circuit 512 generates a second drive pulse S2 obtained by inverting the control pulse S0 of the pulse generation circuit 510 in order to drive the synchronous rectification element 31 (FIG. 2 (c)). The first drive pulse S1 is supplied to the control electrode of the switching element 11 through the on-timing delay circuit 55. The second drive pulse S <b> 2 is supplied to the control electrode of the synchronous rectification element 31 through the ON blocking circuit 56.
[0040]
With this configuration, control is performed so that the synchronous rectifying element 31 is turned off during the on period of the switching element 11 and the synchronous rectifying element 31 is turned on during the off period of the switching element 11.
[0041]
Now, when the control pulse S0 becomes a high level at time t1, the drive circuit 511 also generates a high-level first drive pulse S1 (FIG. 2B). The first drive pulse S1 is supplied to the control electrode of the switching element 11 through the on-timing delay circuit 55. The gate-source voltage Vgs11 of the switching element 11 rises slowly due to the inductance of the coil element 551 of the on-timing delay circuit 55 and reaches the threshold voltage VTH (FIG. 2 (d)). For this reason, the switching element 11 starts to turn on with a delay time of td1 (on), and is completely turned on with a turn-on delay time specific to the element.
[0042]
Meanwhile, at time t1, the inversion driving circuit 512 sets the second driving pulse S2 to a low level. The gate-source voltage Vgs31 of the synchronous rectifying element 31 quickly decreases, and the synchronous rectifying element 31 is completely turned off with a delay time td3 (off) that is only the element-specific turn-off delay time (FIG. 2 (e)). ).
[0043]
The turn-on delay time of the switching element 11 can be increased by increasing the inductance value of the on-timing delay circuit 55. Therefore, if the inductance value of the on-timing delay circuit 55 is set in consideration of the turn-off delay time of the synchronous rectifying element 31, a short-circuit current is generated due to the switching element 11 being turned on before the synchronous rectifying element 31 is turned on. Can be suppressed.
[0044]
Next, when the control pulse S0 becomes low level at time t2, the drive circuit 511 also generates the first drive pulse S1 having low level. The switching element 11 has a gate capacitance extracted through the diode 552 of the on-timing delay circuit 55. The gate-source voltage Vgs11 of the switching element 11 quickly decreases, and the switching element 11 is completely turned off with a delay time td1 (off) that is only the element-specific turn-off delay time (FIG. 2 (d)). .
[0045]
During this time, at time t2, the inversion drive circuit 512 sets the second drive pulse S2 to the high level. Immediately after time t2, the diode 35 has a high cathode-side potential and is in a reverse bias state. Therefore, the base-emitter voltage VBE of the transistor switch Tr is maintained at the threshold voltage by the divided voltage of the resistance voltage dividing circuit (FIG. 2 (5)), the transistor switch Tr is turned on, and the synchronous rectifier 31 Short the control input side. The synchronous rectifier 31 is prevented from being turned on by the on-blocking circuit 56 and the occurrence of a short-circuit current is suppressed even when the second drive pulse S2 is at a high level.
[0046]
Thereafter, when the switching element 11 is turned off and the potential on the cathode side of the diode 35 is lowered, the divided voltage of the resistance voltage dividing circuit is lowered and the base-emitter voltage VBE of the transistor switch Tr is lowered (FIG. 2). (5)), the transistor switch Tr is turned off. As a result, the gate-source voltage Vgs31 of the synchronous rectifying element 31 rises and reaches the threshold voltage VTH. The synchronous rectifier 31 starts to turn on with a delay time of td3 (on), and further becomes fully conductive with a turn-on delay time unique to the device (FIG. 2 (e)).
[0047]
As described above, the switching power supply device according to the present embodiment includes the above-described on-timing delay circuit 55 and the on-blocking circuit 56, thereby suppressing a short-circuit current when the switching element 11 is turned on and turned off.
[0048]
The on-timing delay circuit 55 only needs to include an inductance and can be realized with a simple circuit. If the inductance value is large, the delay time becomes long. For example, in a switching power supply device that operates at a switching frequency of several hundred KHz, several μH to hundred μH, or several hundred μH can be used. As the inductance, an inductance of a coil element or a line may be used.
[0049]
FIG. 3 is an electric circuit diagram showing another embodiment of the switching power supply device according to the present invention. The illustrated switching power supply device includes a transformer for power conversion, and shows an example configured by a forward method. The illustrated switching power supply device includes a power conversion circuit 1, an output rectifying / smoothing circuit 3, and a control circuit 5.
[0050]
The power conversion circuit 1 includes a switching element 11 and a power conversion transformer 2. The switching power supply apparatus according to the present embodiment is the same as the embodiment illustrated in FIG. 1 except that power is transmitted during the ON period of the switching element 11, and the description thereof is omitted.
[0051]
The output rectifying / smoothing circuit 3 includes a forward direction rectifying element 30, a synchronous rectifying element 31, a choke coil 32, an output smoothing capacitor 33, and a diode 35. The forward direction rectifying element 30 and the main electrode of the synchronous rectifying element 31 are connected in series and connected between the output windings 22 of the transformer 2. The choke coil 32 and the output smoothing capacitor 33 are connected in series, and are connected between the main electrodes of the synchronous rectifying element 31, and both ends of the output smoothing capacitor 33 are connected to the output terminal Tout.
[0052]
The forward direction rectifying element 30 is formed of a rectifying diode in the present embodiment, and is connected with a polarity that is forward with respect to the voltage induced in the output winding 22 during the ON period of the switching element 11, but includes a control electrode. Alternatively, a synchronous rectifier element may be used so that the switching element 11 is conductive during the ON period.
[0053]
The diode 35 is connected between the main electrodes of the synchronous rectifying element 31 with a polarity opposite to the voltage induced in the output winding 22 during the ON period of the switching element 11. The control circuit 5 has the same configuration as that of the embodiment shown in FIG.
[0054]
In the switching power supply described above, the switching element 11 intermittently causes the DC voltage Vin supplied through the input winding 21 to induce a voltage in the output winding 22. The induced voltage is supplied to the output rectifying / smoothing circuit 3 as a switching output.
[0055]
The output rectifying / smoothing circuit 3 conducts the forward direction rectifying element 30 with the voltage induced in the output winding 22 during the ON period of the switching element 11, stores energy in the choke coil 32, and charges the output smoothing capacitor 33. During the OFF period of the switching element 11, the output rectifying / smoothing circuit 3 releases the energy stored in the choke coil 32 through the synchronous rectifying element 31 and charges the output smoothing capacitor 33. Since both ends of the output smoothing capacitor 33 are connected to the output terminal Tout, the DC output voltage Vout is output to the output terminal Tout.
[0056]
On / off of the switching element 11 and the synchronous rectifying element 31 is controlled by a drive pulse supplied from the control circuit 5 as in the embodiment shown in FIG.
[0057]
When the switching element 11 is turned on, the synchronous rectification element 31 is controlled to be turned off by the second drive pulse S2 output from the inverting drive circuit 512. The on-timing delay circuit 55 delays the rise of the first drive pulse S1 output from the drive circuit 511 by the inductance of the coil element 551. For this reason, since the switching element 11 is turned on after the synchronous rectifying element 31 is completely turned off, the short-circuit current when the switching element 11 is turned on can be suppressed.
[0058]
When the switching element 11 is turned off, the switching element 11 is controlled to be turned off by the first drive pulse S1 output from the drive circuit 511. At this time, the second drive pulse S2 is output from the inverting drive circuit 512, but the on-blocking circuit 56 blocks the synchronous rectifying element 31 from being turned on. . The on-blocking circuit 56 turns on the synchronous rectifying element 31 after the voltage between the main electrodes of the synchronous rectifying element 31 drops to a predetermined voltage. For this reason, since the synchronous rectification element 31 is turned on after the switching element 11 is completely turned off, the short-circuit current when the switching element 11 is turned off can be suppressed.
[0059]
FIG. 4 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention. The illustrated embodiment shows an example in which a step-down chopper type switching power supply device is configured. The illustrated switching power supply device includes a power conversion circuit 1, an output rectifying / smoothing circuit 3, and a control circuit 5.
[0060]
The power conversion circuit 1 includes a switching element 11 and a switching element 12. The switching element 11 intermittently inputs the input DC voltage Vin and supplies a switching output to the output rectifying and smoothing circuit 3.
[0061]
The output rectifying / smoothing circuit 3 includes a synchronous rectifying element 31, a choke coil 32, an output smoothing capacitor 33, and a diode 35. The choke coil 32 and the output smoothing capacitor 33 are connected in series, and are connected to the DC input terminal Tin via the main electrode of the switching element 11. Both ends of the output smoothing capacitor 33 are connected to the output terminal Tout. The synchronous rectifying element 31 is conductive during the OFF period of the switching element 11. The main electrode of the synchronous rectifying element 31 is connected to both ends of a series circuit of the choke coil 32 and the output smoothing capacitor 33.
[0062]
The diode 35 is connected between the main electrodes of the synchronous rectifying element 31 with a polarity opposite to the voltage induced in the output winding 22 during the ON period of the switching element 11. The control circuit 5 has the same configuration as that of the embodiment shown in FIG.
[0063]
In the switching power supply device described above, the switching element 11 intermittently supplies the supplied DC input voltage Vin and supplies the switching output to the output rectifying and smoothing circuit 3.
[0064]
The output rectifying / smoothing circuit 3 excites the choke coil 32 during the ON period of the switching element 11, stores the excitation energy, and charges the output smoothing capacitor 33. The excitation energy stored in the choke coil 32 is released through the synchronous rectifying element 31 during the OFF period of the switching element 11 and charges the output smoothing capacitor 33. Since both ends of the output smoothing capacitor 33 are connected to the output terminal Tout, the DC output voltage Vout is output to the output terminal Tout.
[0065]
On / off of the switching element 11 and the synchronous rectifying element 31 is controlled by a drive pulse supplied from the control circuit 5 as in the embodiment shown in FIG.
[0066]
When the switching element 11 is turned on, the synchronous rectification element 31 is controlled to be turned off by the second drive pulse S2 output from the inverting drive circuit 512. The on-timing delay circuit 55 delays the rise of the first drive pulse S1 output from the drive circuit 511 by the inductance of the coil element 551, and drives the switching element 11 via the switching element 12. For this reason, since the switching element 11 is turned on after the synchronous rectifying element 31 is completely turned off, the short-circuit current when the switching element 11 is turned on can be suppressed.
[0067]
When the switching element 11 is turned off, the switching element 11 is controlled to be turned off by the first drive pulse S1 output from the drive circuit 511. At this time, the second drive pulse S2 is output from the inverting drive circuit 512, but the on-blocking circuit 56 blocks the synchronous rectifying element 31 from being turned on. . The on-blocking circuit 56 turns on the synchronous rectifying element 31 after the voltage between the main electrodes of the synchronous rectifying element 31 drops to a predetermined voltage. For this reason, since the synchronous rectification element 31 is turned on after the switching element 11 is completely turned off, the short-circuit current when the switching element 11 is turned off can be suppressed.
[0068]
FIG. 5 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention. The illustrated embodiment shows an example in which a step-up chopper type switching power supply device is configured. The illustrated switching power supply device includes a power conversion circuit 1, an output rectifying / smoothing circuit 3, and a control circuit 5.
[0069]
The power conversion circuit 1 includes a switching element 11 and a choke coil 13. The switching element 11 has a main electrode connected to the DC input terminal Tin via the choke coil 13, and supplies the switching output to the output rectifying and smoothing circuit 3 by intermittently inputting the input DC voltage Vin.
[0070]
The output rectifying / smoothing circuit 3 includes a synchronous rectifying element 31, an output smoothing capacitor 33, and a diode 35. The synchronous rectifying element 31 is driven via a transistor 8 for waveform inversion, with the driving voltage source 7 connected to the gate. The drive voltage source 7 includes a capacitor 71, diodes 72 and 73, a resistor 74, and the like. The synchronous rectifying element 31 and the output smoothing capacitor 33 are connected in series, and are connected to the DC input terminal Tin via the choke coil 13. Both ends of the output smoothing capacitor 33 are connected to the output terminal Tout.
[0071]
The synchronous rectifying element 31 is conductive during the OFF period of the switching element 11. The diode 35 is connected between the main electrodes of the synchronous rectifying element 31 with a polarity that is forward with respect to the current flowing through the choke coil 13.
[0072]
Unlike the embodiment shown in FIG. 1, the control circuit 5 does not include an inverting drive circuit, and includes a first drive pulse S1 in phase with the control pulse S0 output from the pulse generation circuit 51, and a second drive pulse S2. Are output from the drives 511 and 513, respectively. The waveform of the second drive pulse S2 is inverted by the transistor 8.
[0073]
In the switching power supply device described above, the switching element 11 intermittently supplies the DC input voltage Vin supplied via the choke coil 13 and supplies the switching output to the output rectifying and smoothing circuit 3.
[0074]
The power conversion circuit 1 excites the choke coil 32 during the ON period of the switching element 11 and stores excitation energy. The output rectifying / smoothing circuit 3 superimposes the excitation energy stored in the choke coil 32 on the DC input voltage Vin and discharges it through the synchronous rectifying element 31 during the OFF period of the switching element 11, and outputs the output smoothing capacitor 33. Charge. Since both ends of the output smoothing capacitor 33 are connected to the output terminal Tout, the DC output voltage Vout is output to the output terminal Tout.
[0075]
On / off of the switching element 11 and the synchronous rectifying element 31 is controlled by a drive pulse supplied from the control circuit 5 as in the embodiment shown in FIG.
[0076]
Also in the switching power supply device of this embodiment, by providing the on-timing delay circuit 55 and the on-blocking circuit 56, it is possible to suppress a short-circuit current when the switching element is turned on and off.
[0077]
6 to 8 are electric circuit diagrams showing a switching power supply device using another example of the on-blocking circuit. In the figure, the same reference numerals are given to the same components as those shown in FIG. 6 to 8 are modifications of FIG. 1, it is obvious that there are modifications based on the embodiment of FIGS. 3 to 5.
[0078]
The embodiment shown in FIG. 6 shows an example in which a field effect transistor is used for the transistor switch Tr. The connection relationship between the resistance voltage dividing circuit constituted by the resistors R1 and R2 and the synchronous rectifier 31 is the same as that of the embodiment shown in FIGS.
[0079]
The embodiment shown in FIG. 7 shows an example in which the temperature characteristic of VBE of the transistor switch Tr is compensated by using a Zener diode ZD. Zener diode ZD is inserted in series in a resistance voltage dividing circuit composed of resistors R1 and R2. The connection relationship with the synchronous rectifier 31 is the same as that of the embodiment shown in FIGS.
[0080]
The embodiment shown in FIG. 8 shows an example in which backflow prevention is achieved using a diode D. The diode D is connected in parallel with the resistance of the resistance voltage dividing circuit. The connection relationship with the synchronous rectifier 31 is the same as that of the embodiment shown in FIGS.
[0081]
The contents of the present invention have been described in detail with reference to the preferred embodiments. However, the present invention is not limited to these, and those skilled in the art will be able to use various techniques based on the basic technical idea and teachings. It is obvious that variations can be conceived.
[0082]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
(A) It is possible to provide a synchronous rectification switching power supply device that delays the on-timing of the switching element on the input side with a simple circuit configuration and suppresses a short-circuit current when the switching element is turned on.
(B) It is possible to provide a synchronous rectification type switching power supply apparatus in which the on-timing of the synchronous rectifying element that is conducted during the off period of the input-side switching element is delayed to suppress a short-circuit current when the switching element is turned off.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing an embodiment of a switching power supply device according to the present invention.
FIG. 2 is a timing chart showing waveforms at various parts of the switching power supply device shown in FIG. 1;
FIG. 3 is an electric circuit diagram showing another embodiment of the switching power supply device according to the present invention.
FIG. 4 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention.
FIG. 5 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention.
FIG. 6 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention.
FIG. 7 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention.
FIG. 8 is an electric circuit diagram showing still another embodiment of the switching power supply device according to the present invention.
[Explanation of symbols]
1 Power conversion circuit
11 Switching element
3 Output rectification smoothing circuit
31 Synchronous rectifier
33 Output smoothing capacitor
5 Control circuit
51 Drive pulse generation circuit
55 On-timing delay circuit
56 ON blocking circuit
S1 First drive pulse
S2 Second drive pulse

Claims (7)

A switching power supply device including a power conversion circuit, an output rectification smoothing circuit, and a control circuit,
The power conversion circuit includes a switching element provided with a control electrode, intermittently supplies an input DC voltage, and supplies a switching output to the output rectifying and smoothing circuit,
The output rectifying and smoothing circuit includes a synchronous rectifying element and an output smoothing capacitor, and rectifies and smoothes the switching output,
The synchronous rectifier element includes a control electrode, and is conducted during an off period of the switching element.
The control circuit includes a drive pulse generation circuit, an on-timing delay circuit, and an on-blocking circuit,
The drive pulse generation circuit generates a first drive pulse and a second drive pulse,
The first drive pulse is supplied to the control electrode of the switching element through the on-timing delay circuit,
The second drive pulse is supplied to the control electrode of the synchronous rectifier element through the on-blocking circuit,
The on timing delay circuit includes a parallel circuit of a coil element and the diode, delaying the rise of the first driving pulse,
The on-blocking circuit is a switching power supply device that detects a voltage between main electrodes of the synchronous rectifying element and blocks conduction of the synchronous rectifying element until a detected voltage becomes a predetermined value or less. The switching power supply device according to claim 1 ,
The on-blocking circuit includes a resistance voltage dividing circuit and a transistor switch,
The resistance voltage dividing circuit is connected between main electrodes of the synchronous rectifier element,
The transistor switch is a switching power supply device in which a control electrode is connected to a voltage dividing point of the resistance voltage dividing circuit and a main electrode is connected to a control input side of the synchronous rectifying element. A switching power supply device according to claim 2 ,
The switching power supply device, wherein the transistor switch is a field effect transistor. A switching power supply device according to any one of claims 1 to 3 ,
The power conversion circuit further includes a transformer, and the transformer includes an input winding and an output winding,
The input winding is connected in series with the main electrode of the switching element to induce a voltage on the output winding,
The output rectifying and smoothing circuit is a switching power supply device connected between both ends of the output winding. The switching power supply device according to claim 4 ,
The output rectifying and smoothing circuit includes a rectifier diode and a choke coil connected in series with the output smoothing capacitor,
The rectifier diode is conductive during the ON period of the switching element, stores energy in the choke coil and charges the output smoothing capacitor,
The choke coil is a switching power supply device that releases energy via the synchronous rectifying element during an off period of the switching element. A switching power supply device according to any one of claims 1 to 3 ,
The output rectifying / smoothing circuit further includes a choke coil, the choke coil and the output smoothing capacitor are connected in series, and further constitute a series circuit including a main electrode of the switching element, and the switching element Energy is stored in the choke coil during the on-period and the output smoothing capacitor is charged,
A step-down chopper type switching power supply apparatus that releases energy stored in the choke coil through the synchronous rectifier element during an off period of the switching element. A switching power supply device according to any one of claims 1 to 3 ,
The power conversion circuit further includes a choke coil, the choke coil is connected in series with the main electrode of the switching element, and stores energy during an ON period of the switching element,
The output rectifying and smoothing circuit rectifies and smoothes energy stored in the choke coil in an off period of the switching element by superimposing the input DC voltage.
Boost chopper type switching power supply.

Images