JP2013081283A - Signal transmission transformer for switching power supply and switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal transmission transformer for switching power supply device in which adjustment of the inductance and the degree of coupling is facilitated, and to provide a switching power supply device with high safety.SOLUTION: A signal transmission transformer 22 includes concentric coil patterns 52(3)-52(6) formed on a conductor layer 52 in a multilayer substrate 50 on which a switching power supply circuit is configured by mounting circuit elements. A pair of closure patterns 52(2), 52(7) are provided on the outside conductor layers 52 sandwiching the coil patterns 52(3)-52(6), and formed so as to close at least one turn of the innermost of the coil patterns 52(3)-52(6) and the inside region thereof. When a current flows through any one of the coil patterns 52(3)-52(6), a part of magnetic flux generated in the inside region of one turn of the innermost is closed by the closure patterns. The closure patterns 52(2), 52(7) are connected to a stable potential.

Description

  The present invention relates to a signal transmission transformer for a switching power supply using a coil pattern formed in a multilayer substrate in which circuit elements are mounted to constitute a switching power supply circuit, and a switching power supply apparatus.

  In the switching power supply device, in addition to the main transformer for power transmission, a signal transmission transformer for transmitting a driving pulse of a transistor element for switching and various AC signals is used. In recent years, due to the demand for high-density mounting of power supply circuits, transformers that have been miniaturized by omitting an insulating bobbin have been used.

  Conventionally, as this type of transformer, as disclosed in, for example, Patent Document 1, a plurality of coil patterns insulated from the outside are concentrically stacked in a multilayer substrate, and the innermost inner periphery of the coil pattern is formed inside. There is a printed coil transformer in which a magnetic core is inserted into an insertion hole that penetrates. In this printed coil transformer, the auxiliary coil with a low generated voltage is divided into two parts, arranged on the outer layer so as to sandwich the coil pattern other than the auxiliary coil, and one end thereof is grounded to the primary side. The auxiliary coil also serves as a shield layer that reduces electrostatic noise.

  Further, the switching power supply device disclosed in Patent Document 2 is provided with a sheet coil transformer formed by laminating a coil pattern insulated from the outside in a multilayer substrate on which circuit elements are mounted. An insulating sheet mixed with magnetic powder for increasing the inductance of a coil is used as an insulating sheet that insulates the gap. Since this sheet coil transformer can omit the mounting of the magnetic core, it is easy to assemble the switching power supply device and to secure a mounting space for other circuit elements.

  In addition, as disclosed in Patent Document 3, an insulated DC-DC converter using a signal transmission transformer, which includes a main transformer having input and output windings, a main switch element connected to the input windings, A PWM control circuit for driving the main switch element, a transformer winding drive type synchronous rectifier circuit connected to the output winding, and a single ended forward type with a smoothing circuit for smoothing the rectified voltage output by the synchronous rectifier circuit There is an insulated DC-DC converter. In this insulated DC-DC converter, a primary winding of a signal transmission transformer (drive transformer) is inserted in series at a connection point between a pulse output terminal of a PWM control circuit and a drive terminal of a main switch element, and also a secondary winding. The line is connected to the drive terminal of the drive switch element capable of short-circuiting the drive terminal of the commutation side synchronous rectifier element. With this configuration, when a drive pulse for turning on the main switch element is output from the PWM control circuit, the timing signal is transmitted to the drive switch element through the signal transmission transformer before the main switch element is turned on, and the drive switch element is turned on. By doing so, the commutation side synchronous rectifier element is turned off. With this operation, it is possible to avoid the problem that the main switching element, the rectifying side commutation side and the commutation side synchronous rectifying element are simultaneously turned on and a short circuit current flows.

JP-A-7-142269 JP-A-9-182432 JP 2000-262051 A

  However, in the magnetic device of Patent Document 1, the work of assembling the magnetic core to the multilayer substrate is complicated and time-consuming. The sheet coil transformer of Patent Document 2 must use a special multilayer substrate using an insulating sheet mixed with magnetic powder. Therefore, in any case, there is a problem that the cost becomes high.

  Moreover, the structure of patent document 1, 2 is a structure suitable for making the inductance of a coil and the coupling degree between each coil high. However, the signal transmission transformer used in the switching power supply device does not require high inductance and high coupling degree depending on the role in circuit operation and the type of signal to be transmitted, and it is often the case that a lower one is better. Therefore, the structures of the magnetic device and the sheet coil transformer disclosed in Patent Documents 1 and 2 have a narrow range in which the inductance and the degree of coupling can be adjusted, and are difficult to use as a signal transmission transformer.

  The structure of the signal transmission transformer used in the switching power supply device of Patent Document 3 includes a magnetic core, and it is described that it is desirable to reduce the number of turns in order to reduce inductance. Therefore, this signal transmission transformer also has a narrow adjustable range of inductance and degree of coupling, and adjustment for optimization is not easy.

  The present invention has been made in view of the above-described background art, and is a signal transmission transformer for a switching power supply device that is easy to adjust the inductance and the degree of coupling and is inexpensive, and highly safe switching using the signal transmission transformer. An object is to provide a power supply device.

  The present invention is formed by a plurality of concentric coil patterns formed on a conductor layer in a multilayer substrate in which circuit elements are mounted to constitute a switching power supply circuit, and an outer conductor layer sandwiching the plurality of coil patterns. At least one innermost turn of the coil pattern and a pair of closing patterns formed to close the inner region thereof, and when an electric current flows through the coil pattern, A part of the magnetic flux generated in the region is a signal transmission transformer for the switching power supply device that is absorbed by the closed pattern.

  The closed pattern may be an aggregate of a plurality of small patterns. The closed pattern is preferably connected to a stable potential. Moreover, the said closing pattern may be formed in the inner layer except the outermost layer in which a circuit element is mounted.

  Further, the present invention includes the above-described signal transmission transformer, connected in series to an input power source, and a main switching element that interrupts an input voltage at a predetermined switching cycle, and a pulse output terminal connected to a drive terminal of the main switching element, A main switching element control circuit that controls on / off of the main switching element by a rectangular-wave drive pulse output from the pulse output terminal, and the primary winding of the signal transmission transformer includes the main switching element control circuit Is inserted in series at a connection point between the pulse output terminal of the main switching element and the drive terminal of the main switching element, and the signal transmission transformer is configured such that the drive pulse is input to the primary winding side and the secondary winding A control circuit that generates a timing signal pulse at a different ground potential from the main switching element control circuit. Transmission, and the control circuit is a switching power supply device which performs synchronous control using the timing signal pulses.

  Further, according to the present invention, a main switching element that is connected in series to an input power supply, and that interrupts an input voltage at a predetermined switching period, and a pulse output terminal are connected to a drive terminal of the main switching element and output from the pulse output terminal A main switching element control circuit for controlling on / off of the main switching element by a rectangular-wave-like driving pulse, and an intermittent voltage connected in series with the main switching element and generated by the interruption of the main switching element is applied to both ends A main transformer having an input winding and an output winding for generating an AC voltage obtained by transforming the intermittent voltage; and one or two or more connected to the output winding and rectifying a voltage generated in the output winding A transformer winding driver having a synchronous rectification FET and each gate terminal using the output winding or other winding of the transformer. A synchronous rectifier circuit driven by a method, a smoothing circuit connected to the output of the synchronous rectifier circuit, smoothing the rectified voltage and outputting a DC output voltage, and each of the synchronous rectifier FETs, An auxiliary FET capable of short-circuiting / opening between source terminals, one or more DC power supplies that output a power supply voltage higher than the gate threshold voltage of the corresponding auxiliary FET, and the auxiliary FET corresponding to the DC power supply A pull-up resistor that is connected between the gate terminal and pulls up the gate-source terminal of the auxiliary FET to the power supply voltage, and is provided for each pull-up resistor, and the pull-up resistor is connected to the pull-up resistor A timing transistor element capable of short-circuiting / opening between the gate and source terminals of the auxiliary FET, and the signal transformer; Has two or more secondary windings, and the primary winding is inserted in series at a connection point between the pulse output terminal of the main switching element control circuit and the drive terminal of the main switching element, The corresponding secondary winding is connected to the drive terminal of the timing transistor element, and the timing transistor element is connected to the drive terminal when the drive pulse is input to the primary winding side of the signal transmission transformer. The timing signal pulse generated in the connected secondary winding is received and turned on / off, and the input capacitance between the gate and source of the auxiliary FET is passed through the pull-up resistor during the off period of the timing transistor element. The pull-up resistor is charged by the current from the DC power source flowing in, and the timing transistor element is turned off when the switch is turned off. The switching power supply device limits the charging current so that a voltage between a gate and a source terminal of the auxiliary FET exceeds the gate threshold voltage when it continues beyond a predetermined time longer than the etching period.

  The signal transmission transformer for a switching power supply device according to the present invention is formed in a multilayer substrate and can be configured at low cost without attaching a magnetic core. In addition to changing the coil pattern layout (number of turns, spiral shape, etc.), the thickness of the insulating member between the coil patterns and the thickness of the insulating member between the coil pattern and the closing pattern are adjusted as appropriate. Thus, the inductance and the degree of coupling between the coil patterns can be changed and adjusted in a wide range. In addition, since the multilayer substrate is manufactured with high dimensional accuracy using a mold and various devices controlled numerically, the optimized inductance and coupling degree can be realized without variation. The closed pattern prevents the magnetic flux passing through the innermost inner region of the coil pattern from leaking to the outside of the multilayer substrate, and prevents the external magnetic flux from interlinking with and interfering with the signal transmission transformer. Work as well. Further, by grounding the closed pattern to a stable potential, an effect as an electrostatic shield can be obtained.

  In the switching power supply device of the present invention, the primary winding of the signal transmission transformer is inserted in series at the connection point between the pulse output terminal of the main switching element control circuit and the drive terminal of the main switching element, Since it operates to output a timing signal with a very short pulse width, on / off timing control of the main switching element and the synchronous rectifying element can be easily performed by using a signal transmission transformer having the above structure. Can do. In addition, the rising or falling speed of the drive terminal voltage of the main switching element can be made steep by the balanced design of the inductance and the degree of coupling, so that the cross loss of the main switching element can be minimized.

1 is a block diagram showing a first embodiment of a switching power supply device of the present invention. It is a circuit diagram which shows the specific structure of the switching power supply device of 1st embodiment. It is sectional drawing (a) which shows the structure of the signal transmission transformer of 1st embodiment of this invention, and a schematic diagram (b) which shows the layout of a coil pattern. It is sectional drawing (a) which shows the structure of 2nd embodiment of a signal transmission transformer, and the schematic diagram (b) which shows the layout of a coil pattern. It is sectional drawing (a) which shows the structure of 3rd embodiment of a signal transmission transformer, and a schematic diagram (b) which shows the layout of a coil pattern. It is the circuit diagram (a), (b) explaining the modification of the switching power supply device of 1st embodiment.

  A signal transmission transformer for a switching power supply device and a switching power supply device according to a first embodiment of the present invention will be described below with reference to FIGS. As shown in the block diagram of FIG. 1, the switching power supply device 10 of the first embodiment includes a main switching element 12, a main switching element control circuit 14, a main transformer 16, a synchronous rectifier circuit 18, a smoothing circuit 20, and a signal transmission transformer 22. It has. The synchronous rectification circuit 18 and the smoothing circuit 20 described in blocks are represented by specific circuits as shown in FIG. Hereinafter, the configuration and operation of the switching power supply device 10 will be described with reference to the circuit diagram of FIG.

  The main switching element 12 is an N-channel MOS FET, and is connected in series to the input power supply 24, and the input voltage is intermittently switched at a predetermined switching period T. The main switching element control circuit 14 has a pulse output terminal 14a connected to the gate terminal 12g of the main switching element 12, and outputs a rectangular-wave-shaped drive pulse V14a from the pulse output terminal 14a to control on / off of the main switching element 12. To do.

  The main transformer 16 includes an input winding 16a, an output winding 16b, and an auxiliary winding 16c, and is closely coupled to each other. The input winding 16a is connected in series with the main switching element 12, and an intermittent voltage generated by turning on and off the main switching element 12 is applied to both ends. Then, a voltage approximately similar to the intermittent voltage applied to the input winding 16a is generated in the output winding 16b and the auxiliary winding 16c. Here, the dot attached | subjected to the transformer 16 of FIG. 2 has shown the polarity of each coil | winding.

  The synchronous rectification circuit 18 includes a rectification side FET 26 and a commutation side FET 28 which are two synchronous rectification FETs. The rectifying side FET 26 is an N-channel MOS type FET, the drain terminal is connected to one end of the output winding 16b without a dot, and the gate terminal is connected to one end of the output winding 16b with a dot through the driving capacitor 30. ing. A resistor 32 connected between the gate and source terminals of the rectifying side FET 26 is a discharge resistance of a gate input capacitance (not shown).

  The commutation side FET 28 is also an N-channel MOS type FET, the drain terminal is connected to one end of the output winding 16 b with the dot, and the source terminal is connected to the source terminal of the rectification side FET 26. The resistor 34 connected between the gate and source terminals of the commutation side FET 28 is a discharge resistance of a gate input capacitance (not shown). The gate terminal of the commutation-side FET 28 is connected to the cathode terminal of the drive Zener diode 35b via the drive capacitor 35a, the anode terminal of the drive Zener diode 35b is connected to one end of the auxiliary winding 16c without a dot, and the auxiliary winding One end of the line 16 c with a dot is connected to the source terminal of the commutation side FET 28.

  In the synchronous rectification circuit 18, the gate terminals of the rectification side and commutation side FETs 26 and 28 are driven by the transformer winding drive system using the output winding 16b and the auxiliary winding 16c, and the rectification side FET 26 is thus configured. The commutation-side FET 28 is turned on and off in a complementary manner to the main switching element 12 in the same phase as the main switching element 12, and the voltage generated in the output winding 16b can be properly rectified.

  Further, the synchronous rectification circuit 18 is provided with an abnormal oscillation prevention circuit 36 for avoiding a problem of abnormal oscillation described later. The abnormal oscillation prevention circuit 36 includes first and second auxiliary FETs 38 and 40 having their own drain and source terminals connected to each other so that the gate and source terminals of the rectifying side and commutation side FETs 26 and 28 can be short-circuited and opened. ing. The gate terminals of the first and second auxiliary FETs 38 and 40 are connected to each other and pulled up to a DC power supply 44 via a pull-up resistor 42. The DC power supply 44 is a simple voltage source that generates a DC power supply voltage using, for example, a voltage generated in the output winding 16b or the auxiliary winding 16c, and gates of the first and second auxiliary FETs 38 and 40. A power supply voltage higher than the threshold voltage is output. Further, there is provided a timing FET 46 having its own drain and source terminals connected so that the gate and source terminals of the first and second auxiliary FETs 38 and 40 can be short-circuited and opened. The timing FET 46 is a timing transistor element, and here, an N-channel MOS type FET is used. However, it can be replaced with a bipolar transistor.

  The gate terminal voltage V38g of the first and second auxiliary FETs 38 and 40 starts to rise when the timing FET 46 is turned off. The pull-up resistor 42 serves to limit the current for charging the gate input capacitance (not shown) of the first and second auxiliary FETs 38 and 40 by the DC power supply 44, and the rate of increase of the voltage V38g according to the time constant with the gate input capacitance. To decide. The resistance value of the pull-up resistor 42 is relatively high so that the voltage V38g reaches the gate threshold voltage after a time longer than the switching period T (for example, about 2 to 5 times the switching period T) has elapsed. It is set to a large value. Detailed operation of the abnormal oscillation prevention circuit 36 will be described later.

  The smoothing circuit 20 is a low-pass filter including a smoothing inductor 20a and a smoothing capacitor 20b. The smoothing circuit 20 smoothes the rectified voltage output from the synchronous rectifier circuit 18 to generate a DC output voltage, and supplies power to the subsequent load 48.

  The signal transmission transformer 22 includes a primary winding 22a and a secondary winding 22b. The dots in FIG. 2 indicate the polarity of each winding, and the primary winding 22a is inserted in series at the connection point between the pulse output terminal 14a of the main switching element control circuit 14 and the gate terminal 12g of the main switching element 12, One end of the dot is connected to the pulse output terminal 14a. In the secondary winding 22b, one end with dots is connected to the gate terminal of the timing FET 46 of the abnormal oscillation prevention circuit 36, and one end without dots is connected to the source terminal.

  As shown in FIG. 3, the signal transmission transformer 22 is provided in a multilayer substrate 50 on which the main switching element 12 and other circuit elements are mounted, and a primary winding 22a and a secondary winding 22b are formed on different conductor layers. The air core transformers are stacked and magnetically coupled to each other. Here, the number of turns of the primary and secondary windings 22a and 22b is the same, the inductance is set to 50 to 100 nH, and the degree of coupling is set to about 0.2 to 0.3. The detailed structure of the signal transmission transformer 22 will be described later in detail.

  Next, the operation of the switching power supply device 10 will be described. The switching power supply device 10 is a general single-ended forward type switching power supply device having a transformer winding drive type synchronous rectifier circuit provided that the abnormal oscillation prevention circuit 36 and the signal transmission transformer 22 are not provided. is there. Then, when the input power supply 24 is turned on to the switching power supply device 10 and the operation of stably supplying the output voltage and output current to the load 48 (hereinafter referred to as a steady operation) is performed, the abnormal oscillation prevention circuit 36 does not operate. Therefore, the power conversion operation during the steady operation is the same as the conventional one, and the description thereof is omitted here.

  The abnormal oscillation prevention circuit 36 and the signal transmission transformer 22 are circuits for avoiding the problem of abnormal oscillation that occurs when the input power supply 24 is stopped. Since the problem of abnormal oscillation cannot occur during normal operation, The function of the abnormal oscillation prevention circuit 36 is stopped. Specifically, the first and second auxiliary FETs 38 and 40 are held in the OFF state by the following operation.

  When the drive pulse V14a output from the main switching element control circuit 14 changes from a low level to a high level, a current for charging a gate input capacitance (not shown) of the main switching element 12 flows through the primary winding 22a. As a result, a predetermined signal is input to the primary winding 22 a side, and a timing signal output from the secondary winding 22 b is transmitted between the gate and source terminals of the timing FET 46. In the secondary winding 22b, since the terminal with dots becomes a high potential, the gate terminal voltage V46g instantaneously exceeds the gate threshold voltage, the timing FET 46 is turned on, and the gate input capacitances of the first and second auxiliary FETs are rapidly discharged. The gate terminal voltage V38g is reset.

  Thereafter, the gate terminal voltage V12g of the main switching element 12 rises toward the high level voltage of the drive pulse V14a. In the signal transmission transformer 22, since the inductance of the primary winding 22a is very small and the degree of coupling with the secondary winding 22b is not so high, the charging current of the gate input capacitance of the main switching element 12 is hardly limited, The gate terminal voltage V12g rises with a steep slope that is almost similar to the slope that the drive pulse V14a rises, and exceeds the gate threshold voltage, turning on the main switching element 12. Further, the gate terminal voltage V12g reaches the drive pulse voltage V14a within a short time, the timing signal output from the secondary winding 22b disappears, and the timing FET 46 turns off. Then, the gate input capacitances of the first and second auxiliary FETs 38 and 40 are opened, the charging current flows from the DC power supply 44 through the pull-up resistor 42, and the gate terminal voltage V38g starts to rise. The rising speed of the gate terminal voltage V38g is limited by the gate input capacitance and the time constant of the pull-up resistor 42, and increases very slowly.

  Thereafter, when the drive pulse V14a of the main switching element drive circuit 14 changes from the high level to the low level, a current for discharging the gate input capacitance of the main switching element 12 flows through the primary winding 22a. As a result, a predetermined signal is input to the primary winding 22 a side, and a timing signal output from the secondary winding 22 b is transmitted between the gate and source terminals of the timing FET 46. In the secondary winding 22b, since a terminal without a dot becomes a high potential, the gate terminal voltage V46g decreases in the negative direction. However, the timing FET 46 is already turned off before receiving the timing signal, and does not affect the rise of the gate terminal voltage V38g.

  After that, when the switching cycle T has elapsed since the drive pulse V14a first changed to the high level, the drive pulse V14a changes to the high level again, and the gate terminal voltage V38g is reset.

  The rising speed of the gate terminal voltage V38g is defined by the time constant of the pull-up resistor 42 and the like, and after the gate terminal voltage V38g is reset, a time longer than the switching period T (for example, about 2 to 5 times the switching period T). If the time does not elapse, the gate threshold voltage is not exceeded. Therefore, during the steady operation in which the above operation is repeated, the first and second auxiliary FETs 38 and 40 are held in the off state, and the abnormal oscillation prevention circuit 36 does not operate.

  Next, an operation when the drive pulse V14a of the main switching element drive circuit 14 is stopped, such as when the input power supply 24 is shut off while the switching power supply device 10 is in steady operation (hereinafter referred to as a power supply stop operation). ). First, the problem of abnormal oscillation that occurs when the abnormal oscillation prevention circuit 36 is not provided in the configuration of the switching power supply device 10 shown in FIG. 2 will be described.

  Consider a case where the driving pulse V14a is stopped during the steady operation of the switching power supply device 10 while the main switching element 12 is on, the rectifying side FET 26 is on, and the commutation side FET 28 is off. When the drive pulse V14a stops (turns to a low level and maintains a low level), the main switching element 12 turns from on to off, and the primary winding 16a is opened. Then, the release of the excitation energy accumulated in the main transformer 16 while the main switching element 12 is turned on starts to fly in the direction where one end without a dot becomes a high potential at both ends of the output winding 16b and the auxiliary winding 16c. Buck voltage is generated. By this flyback voltage, the rectification side FET 26 turns off and the commutation side FET 28 turns on. When the commutation side FET 28 is turned on, a current that releases the accumulated charge of the smoothing capacitor 20b flows through the path of the smoothing capacitor 20b, the commutation side FET 28, and the smoothing inductor 20a, and the excitation energy is accumulated in the smoothing inductor 20a.

  When the discharge of the excitation energy of the main transformer 16 is completed, the voltages of the output winding 16b and the auxiliary winding 16c are reduced, but the rectification side FET 26 and the commutation side FET 28 are kept on. Thereafter, the accumulated charge in the gate input capacitance of the commutation side FET 28 is gradually discharged by the resistor 34, and the commutation side FET 28 starts to turn off when the gate terminal voltage V28g drops to the gate threshold voltage. Then, the release of the excitation energy accumulated in the smoothing inductor 20a while the commutation-side FET 28 is turned on starts, and a flyback voltage is generated at both ends of the smoothing inductor 20a so that one end on the smoothing capacitor 20b side becomes a high potential. To do. Due to this flyback voltage, a voltage is generated at the ends of the output winding 16b and the auxiliary winding 16c in such a direction that one end with dots becomes a high potential, the rectifying side FET 26 is turned on, and the commutation side FET 28 is also completely turned on. Turn off. When the rectifying side FET 26 is turned on, a current that releases the accumulated charge of the smoothing capacitor 20a and the exciting energy of the smoothing inductor flows through the path of the smoothing capacitor 20b, the output winding 16b, the rectifying side FET 26, and the smoothing inductor 20a, and flows to the main transformer 16. Excitation energy is accumulated. This current is supplied from the input winding 16a, which is tightly coupled to the output winding 16b, to the input power supply 24 (or an input capacitor not shown), a drain-source diode (not shown) that is parasitic inside the main switching element 12, It also flows through the path.

  Thereafter, the accumulated charge in the gate input capacitance of the rectifying side FET 26 is gradually discharged by the resistor 32, and the rectifying side FET 26 starts to turn off when the gate terminal voltage V26g is lowered to the gate threshold voltage. Then, the release of the excitation energy accumulated in the main transformer 16 while the rectifying side FET 26 is turned on starts to fly back in a direction in which one end without a dot becomes a high potential at both ends of the output winding 16b and the auxiliary winding 16c. A voltage is generated, the commutation side FET 28 is turned on, and the rectification side FET 26 is also completely turned off. Thereafter, a self-excited abnormal oscillation occurs in which the rectifying side FET 26 and the commutation side FET 28 are turned on and off in a complementary manner.

  The period of abnormal oscillation is generally longer than the switching period T (for example, about 5 to 10 times the switching period T). Further, there is no circuit element that limits the magnitude of the current flowing through the main transformer 16 and the smoothing inductor 20a. Therefore, when an abnormal oscillation occurs, the current causes the main transformer 16 and the smoothing inductor 20a to be magnetically saturated, thereby generating a larger current, which causes excessive electrical stress on the rectifying side and commutation side FETs 26 and 28, resulting in damage. There is a risk.

  The switching power supply circuit 10 is provided with the abnormal oscillation prevention circuit 36 to avoid abnormal oscillation. If the drive pulse V14a stops during the steady operation of the switching power supply device 10, the timing signal is not output from the secondary winding 22b of the signal transmission transformer 22, so the timing FET 46 continues to be turned off, and the first and second auxiliary FETs 38, The gate voltage V38g of 40 continues to rise due to charging from the DC power supply 44 without being reset. The gate voltage V38g exceeds the gate threshold voltage when a time of about 2 to 5 times the switching cycle T (a time shorter than the abnormal oscillation cycle) has elapsed, and the first and second auxiliary FETs 38 and 40 are turned on. Is held as it is. The rectifying side and commutation side FETs 26 and 28 are fixed off because the gate and source terminals are short-circuited together. Therefore, the rectifying side and commutation side FETs 26 and 28 are surely fixed off regardless of the operation of the main transformer 16 and the smoothing inductor 20a, so that the above self-excited abnormal oscillation does not occur. .

  The abnormal oscillation prevention circuit 36 resets the gate voltage V38g using the timing signal when the drive pulse V14a changes to the high level, but uses the timing signal when the drive pulse V14a changes to the low level. Even if it changes to the structure to perform, the same effect can be acquired. When the latter configuration is selected, the polarity of the secondary winding 22b connected between the gate and source terminals of the timing FET 46 may be reversed. Therefore, when considering the component arrangement of each circuit element and the layout of the circuit pattern, the more convenient of the former and the latter can be selected.

  In order for the switching power supply device 10 to perform the above ideal operation, the characteristics of the signal transmission transformer 22 are important. During steady operation, the gate terminal voltage V12g of the main switching element 12 must be sharply increased to suppress cross loss at turn-on, so that the signal transmission transformer 22 preferably has a low inductance. On the other hand, during the steady operation, the timing FET 46 is turned on every switching period T to stop the function of the abnormal oscillation prevention circuit 36, so that a timing signal sufficient to turn on the timing FET 46 is generated in the secondary winding 22b. It is necessary to have a certain level of coupling.

  The signal transmission transformer 22 satisfies the above two conditions by setting the primary and secondary windings 22a and 22b to the same number of turns, setting each inductance to 50 to 100 nH, and coupling degree to about 0.2 to 0.3. . However, these numerical values are merely examples, and the high level voltage value of the drive pulse V14a, the gate input capacitance and gate threshold voltage of the main switching element 12, the gate input capacitance and gate threshold voltage of the timing FET 46, the switching period T, and the like. If they are different, the optimum values of the inductance and the degree of coupling of the signal transmission transformer 22 also differ. Therefore, it is desirable that the signal transmission transformer 22 has a structure in which the inductance and the degree of coupling can be easily adjusted and changed.

  As shown in FIG. 3, the structure of the signal transmission transformer 22 is formed in a multilayer substrate 50 on which circuit elements such as the switching elements 12 are mounted. The multilayer substrate 50 includes a conductor layer 52 made of copper or the like and an insulating layer 54 made of an insulating member such as resin or glass fiber, and seven insulating layers 54 (from the upper side of FIG. 3) between the eight conductor layers 52. This is a general printed circuit board laminated with 54 (1) to 54 (7)) alternately in order.

  The coil patterns 52 (3) and 52 (4) are formed on the third and fourth conductor layers 52 counted from the upper side in FIG. 3, and the coil patterns 52 (5 and 5 are formed on the fifth and sixth conductor layers 52. ), 52 (6) are formed, closed patterns 52 (2), 52 (7) are formed on the second and seventh conductor layers 52, and circuit elements are formed on the first and eighth conductor layers 52. Wiring patterns 52 (1) and 52 (8) for mounting and wiring are formed.

  The coil patterns 52 (3) and 52 (4) are planar coils formed in a spiral shape, and as shown in FIG. 3B, the ends of the innermost one turn are the insulating layers 54 (3 ) To form a primary winding 22a. In addition, the coil patterns 52 (3) and 52 (4) are also planar coils formed in a spiral shape, and as shown in FIG. They are integrally connected through the through hole provided in (5) to form the secondary winding 22b. The four coil patterns 52 (3) to 52 (6) have the same inner region shape of the innermost turn, the outer peripheral edge shape of the outermost turn is substantially equal, and are concentrically overlapped with each other. Has been placed.

  The closing patterns 52 (2) and 52 (7) are conductor patterns that close at least one innermost turn of the coil patterns 52 (3) and 52 (6) and an inner region thereof. It is sized to cover the inner area of the outer periphery. Accordingly, when a current flows through the coil patterns 52 (3) and 52 (4), which are the primary winding 22a, and a magnetic flux is generated that passes through the inner region of the innermost one turn, a part of the magnetic flux is partly closed. ), 52 (7) in the thickness direction and absorbed as eddy current loss.

  The wiring patterns 52 (1) and 52 (8) can be freely formed in a region overlapping with the closing patterns 52 (2) and 52 (7). The closed pattern 52 (2) is connected to the stable potential portion of the wiring pattern 52 (1) through a through hole (not shown) provided in the insulating layer 54 (1). Similarly, the closing pattern 52 (7) is also connected to the stable potential portion of the wiring pattern 52 (8) through a through hole (not shown) provided in the insulating layer 54 (7). The stable potential is a potential that is stable in terms of alternating current, and is, for example, the potential of the source terminal of the main switching element 12 in FIG. 2 or the potential of one end of the dot of the input winding 16a of the main transformer 16.

  The inductance of the signal transmission transformer 22 can be adjusted by the number of turns of the primary and secondary windings 22a and 22b. If the number of turns is reduced, the inductance is reduced. However, if the amount is too small, the degree of coupling between the two windings cannot be ensured. The signal transmission transformer 22 can easily adjust the inductance and the degree of coupling by changing parameters other than the number of turns.

  When the current flows through the coil patterns 52 (3) and 52 (4), the closing patterns 52 (2) and 52 (7) absorb a part of the magnetic flux generated in the inner region of the coil patterns 52 (3) and 52 (4). 5), 52 (6) works to reduce the amount of magnetic flux interlinking. That is, when the closed patterns 52 (2) and 52 (7) are present, the inductance is lowered and the degree of coupling is also lowered. The amount of magnetic flux absorbed by the closing patterns 52 (2) and 52 (7) can be adjusted by changing the thickness of the closing patterns 52 (2) and 52 (7). Further, the amount of magnetic flux passing through the inside of the insulating layer 54 (2) in the surface direction by changing the thickness of the insulating layer 54 (2) between the closing pattern 52 (2) and the coil pattern 52 (3). That is, the amount of magnetic flux that is not absorbed by the closing patterns 52 (2) and 52 (7) can be adjusted. The same applies to the thickness of the insulating layer 54 (6) between the closing pattern 52 (7) and the coil pattern 52 (6). Thus, by changing each of the above parameters, the inductance and the degree of coupling can be adjusted and changed over a wide range.

  There are other means for adjusting the inductance and the degree of coupling. For example, the thickness of the insulating layers 54 (3), 54 (4), 54 (5), 54 (6) can be changed, or one turn in the planar coil can be changed. A certain degree of adjustment is possible by changing the interval for each coil or increasing / decreasing the area of the innermost area of each coil pattern.

  As described above, the switching power supply device 10 according to the first embodiment is safe because the abnormal oscillation prevention circuit 36 operates when the power supply is stopped, so that problems due to abnormal oscillation can be reliably avoided. Furthermore, during steady operation, the signal transmission transformer 22 has a primary winding 22a inserted in series at the connection point between the pulse output terminal 14a of the main switching element control circuit 14 and the gate terminal 12g of the main switching element 12, and thus a very short pulse. An operation of transmitting the width timing signal to the secondary winding 22b is performed. Therefore, by optimizing the inductance and the degree of coupling of the signal transmission transformer 22, the rise of the gate terminal voltage V12g of the main switching element 12 can be made steep and the cross loss of the main switching element can be minimized.

  Further, since the signal transmission transformer 22 is formed inside the multilayer substrate 50 and does not require a magnetic core, the signal transmission transformer 22 can be configured at low cost. By arranging another circuit element at a position overlapping the signal transmission transformer 22, a switching power supply It can also contribute to downsizing of the device. In addition to changing the number of turns of the coil patterns 52 (3) to 52 (6), the thickness of the insulating layers 54 (3) to 54 (5) between the coil patterns, and the coil patterns 52 (3) and 52 By adjusting parameters such as the thickness of the insulating layers 54 (2) and 54 (6) between (6) and the closing patterns 52 (2) and 52 (7), the inductance and the degree of coupling can be changed over a wide range. Can be optimized. In addition, since the multilayer substrate 50 is manufactured with high dimensional accuracy using a mold and various devices controlled numerically, it is possible to realize optimized inductance and degree of coupling without variation. Therefore, it is very suitable for applications such as the signal transmission transformer 22 of the switching power supply device 10.

  The closing patterns 52 (2) and 52 (7) prevent the magnetic flux passing through the innermost inner region of the coil patterns 52 (3) to 52 (6) from leaking to the outside of the multilayer substrate 50. It acts as a magnetic shield that prevents extraneous magnetic flux from interlinking with and interfering with the signal transmission transformer 22. Furthermore, since the closed pattern is grounded to a stable potential, it also functions as an electrostatic shield.

  Next, a second embodiment of the signal transmission transformer of the present invention will be described with reference to FIG. The signal transmission transformer 58 of this embodiment includes primary and secondary windings 58a and 58b, and can be used in the same manner as the signal transmission transformer 22 of the switching power supply device 10.

  The multilayer substrate 60 includes a conductor layer 62 made of copper or the like and an insulating layer 64 made of an insulating member such as resin or glass fiber, and five insulating layers 64 (from the upper side in FIG. 4) between the six conductor layers 52. It is a general printed circuit board laminated with 64 (1) to 64 (5)) alternately sandwiched in order.

  The coil pattern 62 (3-1) as the primary winding 58a and the coil pattern 62 (3-2) as the secondary winding 58b are formed on the third conductor layer 62 counted from the upper side in FIG. Lead patterns 62 (4-1) and 62 (4-2) are formed on the conductor layer 62, and closed patterns 62 (2) and 62 (5) are formed on the second and fifth conductor layers 62. Further, wiring patterns 62 (1) and 62 (6) for mounting and wiring circuit elements are formed on the first and sixth conductor layers 62.

  The coil patterns 62 (3-1) and 62 (3-2) are planar coils formed in a spiral shape in parallel with each other as shown in FIG. Are connected to the extraction patterns 62 (4-1) and 62 (4-2) through through holes provided in the insulating layer 64 (3), and are extracted to the outside.

  The closing patterns 62 (2) and 62 (5) are conductor patterns that close at least one innermost turn of the coil patterns 62 (3-1) and 62 (3-2) and the inner region thereof. It is formed in a size that covers the inner region of the outermost peripheral edge. Accordingly, when a current flows through the coil pattern 62 (3-1), which is the primary winding 58a, and a magnetic flux is generated that passes through the inner region of the innermost one turn, a part of the magnetic flux becomes the closed pattern 62 (2), Passes 62 (5) in the thickness direction and is absorbed as eddy current loss.

  Thus, the signal transmission transformer 58 of the second embodiment differs from the signal transmission transformer 22 described above in that the primary and secondary windings 58a and 58b are configured by two conductor layers 62, and other configurations are the same. It is the same. The signal transmission transformer 58 can obtain the same effects as the signal transmission transformer 22 described above. In particular, the signal transmission transformer 22 includes four conductor layers 52 that constitute primary and secondary windings 22a and 22b. Compared to the above, there is an advantage that an inexpensive multilayer substrate having a small number of layers can be used.

  As shown in FIG. 5, the signal transmission transformer 66 according to the third embodiment of the present invention is configured on a multilayer substrate having a smaller number of layers. The signal transmission transformer 66 includes primary and secondary windings 66a and 66b, and can be used in the same manner as the signal transmission transformers 22 and 58 described above.

  The multilayer substrate 68 includes a conductor layer 70 made of copper or the like and an insulating layer 72 made of an insulating member such as resin or glass fiber, and three insulating layers 72 (from the upper side in FIG. 5) between the four conductor layers 70. It is a general printed circuit board in which 72 (1) to 72 (3)) are alternately sandwiched in order.

  A wiring pattern 70 (1) for mounting and wiring circuit elements is formed on the first conductor layer 70 counted from the upper side of FIG. 5, and a coil pattern 70 (primary winding 66 a) is formed on the third conductor layer 70. 3-1) and a coil pattern 70 (3-2) as the secondary winding 66 b are formed, and lead patterns 70 (4-1) and 70 (4-2) and a closing pattern are formed on the fourth conductor layer 70. 70 (4-3) and a wiring pattern (not shown) are formed.

  The coil patterns 70 (3-1) and 70 (3-2) are flat coils formed in a spiral shape in parallel with each other as shown in FIG. Are connected to the extraction patterns 70 (4-1) and 70 (4-2) through through holes provided in the insulating layer 72 (3), and are extracted to the outside. The closing pattern 70 (4-3) is a conductor pattern separated into one or two or more that closes at least one innermost turn of the coil patterns 70 (3-1) and 70 (3-2) and an inner region thereof. Yes, provided so as to avoid the drawing patterns 70 (4-1) and 70 (4-2).

  The signal transmission transformer 66 according to the third embodiment is different from the signal transmission transformer 22 in that the primary and secondary windings 66a and 66b are configured by two conductor layers 70. Further, the signal transmission transformer described above is provided in that one closing pattern 70 (4-3), lead-out patterns 70 (4-1), 70 (4-2), and a wiring pattern are provided on the same conductor layer 70. Different from 60. Other configurations are the same.

  The signal transmission transformer 66 can obtain the same effects as those of the signal transmission transformers 22 and 58. In particular, the signal transmission transformer 22 includes four conductor layers 52 and primary and secondary windings 22a and 22b. Compared to the configuration, there is an advantage that an inexpensive multilayer substrate having a significantly smaller number of layers can be used.

  The switching power supply device of the present invention is not limited to the above embodiment. The switching power supply 10 of FIG. 2 is a single-ended forward switching power supply having a transformer winding drive type synchronous rectifier circuit, but is also applicable to a switching power supply in which the inverter type is different from the single-ended forward type. can do. In the case of the single-ended forward type switching power supply device 10, since there are two synchronous rectifier elements (rectifier side and commutation side FETs 26 and 28), the abnormal oscillation prevention circuit 36 is provided for each synchronous rectifier element (auxiliary FET 38). 40) is provided. For example, when the inverter type is a flyback type, one auxiliary FET is sufficient because there is one synchronous rectifier element. In addition, when the inverter type is a bridge type and the output winding voltage of the main transformer is full-wave rectified, since there are four synchronous rectifier elements, four auxiliary FETs may be provided. In any case, similarly to the switching power supply 10, it is possible to easily and reliably avoid the problem of abnormal operation when the power supply is stopped.

  In the case of the switching power supply device 10 of FIG. 2, the timing signal output from the secondary winding 22b of the signal transmission transformer 22 is used for synchronous control for resetting the abnormal oscillation prevention circuit 36. Can be used for simple synchronous control. For example, like the isolated DC-DC converter described in Patent Document 3 of the background art, the turn-off timing of the commutation side FET driven by the transformer winding drive system is controlled, and the commutation side FET and the main switching are controlled. This timing signal can be used for synchronous control to prevent the elements from turning on simultaneously. Further, in a switching power supply device including a series switching element that connects and disconnects an active clamp capacitor in parallel with the primary winding of the main transformer, the turn-off or turn-off timing of the series switching element is controlled, and the series switching element and the main switching element are It is also possible to use this timing signal for synchronous control that prevents the switches from being turned on simultaneously. In any of the synchronous controls exemplified here, it is necessary to optimize the inductance and the degree of coupling of the signal transmission transformer. If the signal transmission transformer of the present invention is used, the optimization is easy, and variations during mass production are also extremely large. Can be kept small.

  In addition, as shown in FIGS. 6A and 6B, the timing signal can be selected by connecting a diode 74 in parallel with the primary winding 22a. For example, as shown in FIG. 6A, when the cathode of the diode 74 is connected in parallel with the main switching element 12 side, only the timing signal when the drive pulse V14a turns to the low level is output from the secondary winding 22b. The On the contrary, as shown in FIG. 6B, when the anode of the diode 74 is connected in parallel with the main switching element 12 side, only the timing signal when the drive pulse V14a turns to the high level is output. When the diode 74 is not connected, both timing signals when the drive pulse V14a changes to low level and when it changes to high level are output. Which timing signal is used is arbitrary and may be selected according to the purpose and circuit configuration of the control circuit that receives the timing signal. For example, considering the case of the switching power supply device 10 of FIG. 2, what is necessary for the operation of resetting the abnormal oscillation prevention circuit 36 is a timing signal when the drive pulse V14a changes to high level, and when it changes to low level. This timing signal is not used. In addition, it can be said that it is an unnecessary signal that may apply reverse voltage stress between the gate and source terminals of the timing FET 46. Therefore, as shown in FIG. 6B, it is possible to prevent the generation of unnecessary timing signals by connecting the anode of the diode 74 to the main switching element 12 side.

  The signal transmission transformer of the present invention is not limited to the above embodiment. The closing patterns of the signal transmission transformers 22, 58, 66 are all provided so as to cover the outermost turn of the coil pattern and the inner region thereof, but at least the innermost turn and the inner turn thereof. Anything that covers the inner region may be used. If the closing pattern is small, the magnetic flux leaks from the coil portion on the outer side, so that the shielding effect is slightly reduced, but there is no problem in changing and adjusting the inductance and coupling degree. If the closed pattern is separated into two or more small patterns across the lead pattern or other wiring patterns within the closed pattern area, all the small patterns are the same when using the closed pattern as an electrostatic shield. May be connected to different stable potentials, or may be connected to different stable potentials for each small pattern.

  Further, the coil pattern may be a spiral planar coil, and the winding shape is free, such as a circle, a rectangle, and an ellipse, and the number of turns, the pattern width, the pattern interval, etc. are not particularly limited. It is also possible to provide a multiple output type signal transmission transformer by providing a plurality of secondary windings.

DESCRIPTION OF SYMBOLS 10 Switching power supply device 12 Main switching element 14 Main switching element control circuit 14a Pulse output terminal 16 Main transformer 16a Input winding 16b Output winding 16c Auxiliary winding 18 Synchronous rectification circuit 20 Smoothing circuit 22, 58, 66 Signal transmission transformer 22a, 58a, 66a Primary winding 22b, 58b, 66b Secondary winding 26 Rectification side FET
28 Commutation side FET
36 Abnormal oscillation prevention circuit 38 First auxiliary FET
40 Second auxiliary FET
42 Pull-up resistor 44 DC power supply 46 Timing FET
50 multilayer substrate 52 conductor layers 52 (1), 52 (8) wiring patterns 52 (2), 52 (7) closing patterns 52 (3), 52 (4), 52 (5), 52 (6), coil patterns 54, 54 (1) to 54 (7) Insulating layer 60 Multilayer substrate 62 Conductor layers 62 (1), 62 (6) Wiring patterns 62 (2), 62 (5) Closing patterns 62 (3-1), 62 ( 3-2) Coil pattern 62 (4-1), 62 (4-2) Lead pattern 64, 64 (1) -64 (5) Insulating layer 68 Multilayer substrate 70 Conductive layer 70 (1) Wiring pattern 70 (2) , 70 (4-3) Closure patterns 70 (3-1), 70 (3-2) Coil patterns 70 (4-1), 70 (4-2) Lead patterns 72, 72 (1) to 72 (3) Insulation layer

Claims (6)

A plurality of concentric coil patterns formed on a conductor layer in a multilayer substrate on which circuit elements are mounted to constitute a switching power supply circuit;
Formed of an outer conductor layer sandwiching the plurality of coil patterns, and at least one innermost turn of the coil pattern and a pair of closing patterns formed to close the inner region thereof,
When the current flows through the coil pattern, a part of the magnetic flux generated in the inner region of the innermost turn is absorbed by the closed pattern.   2. The signal transmission transformer for a switching power supply device according to claim 1, wherein the closing pattern is a collection of a plurality of small patterns.   The signal transmission transformer for a switching power supply according to claim 1 or 2, wherein the closed pattern is connected to a stable potential.   3. The signal transmission transformer for a switching power supply according to claim 1, wherein the closed pattern is formed in an inner layer excluding an outermost layer on which the circuit element is mounted. A signal transmission transformer according to any one of claims 1 to 4,
A main switching element that is connected in series to the input power source and that intermittently switches the input voltage at a predetermined switching period;
A pulse output terminal connected to the drive terminal of the main switching element, and a main switching element control circuit for controlling on / off of the main switching element by a rectangular-wave drive pulse output from the pulse output terminal,
The primary winding of the signal transmission transformer is inserted in series at a connection point between the pulse output terminal of the main switching element control circuit and the drive terminal of the main switching element,
The signal transmission transformer generates a timing signal pulse in the secondary winding when the drive pulse is input to the primary winding, and transmits the timing signal pulse to a control circuit having a ground potential different from that of the main switching element control circuit. ,
The switching power supply device, wherein the control circuit performs synchronous control using the timing signal pulse. A signal transmission transformer according to any one of claims 1 to 4,
A main switching element that is connected in series to the input power source and that intermittently switches the input voltage at a predetermined switching period;
A main switching element control circuit, wherein a pulse output terminal is connected to the driving terminal of the main switching element, and the main switching element is controlled to be turned on and off by a rectangular-wave driving pulse output from the pulse output terminal;
A main transformer having an input winding connected in series to the main switching element, to which an intermittent voltage generated by the intermittent switching of the main switching element is applied, and an output winding generating an AC voltage obtained by transforming the intermittent voltage When,
One or two or more synchronous rectification FETs connected to the output winding and rectifying a voltage generated in the output winding are used, and each gate terminal uses the output winding or other windings of the transformer. A synchronous rectifier circuit driven by a transformer winding drive system;
A smoothing circuit connected to the output of the synchronous rectifier circuit and smoothing the rectified voltage to output a DC output voltage;
An auxiliary FET provided for each synchronous rectification FET and capable of short-circuiting / opening between the gate and source terminals,
A DC power supply that outputs a power supply voltage higher than a gate threshold voltage of the corresponding auxiliary FET;
A pull-up resistor connected between the DC power supply and the corresponding gate terminal of the auxiliary FET, and pulling up the gate-source terminal of the auxiliary FET to the power supply voltage;
A timing transistor element provided for each pull-up resistor and capable of short-circuiting / opening between the gate and source terminals of the auxiliary FET to which the pull-up resistor is connected;
The signal transmission transformer has one or more secondary windings, and the primary winding is in series with a connection point between the pulse output terminal of the main switching element control circuit and the drive terminal of the main switching element. And the corresponding secondary winding is connected to the drive terminal of the timing transistor element,
The timing transistor element is turned on / off in response to a timing signal pulse generated in the secondary winding when the drive pulse is input to the primary winding side of the signal transmission transformer,
During the off period of the timing transistor element, the input capacitance between the gate and source of the auxiliary FET is charged by the current from the DC power source flowing through the pull-up resistor,
The pull-up resistor is configured so that the voltage between the gate and source terminals of the auxiliary FET exceeds the gate threshold voltage when the timing transistor element is turned off for a predetermined time longer than the switching period. A switching power supply device that limits the charging current.

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