JP2015195677A - Switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent element destruction caused by an excessive inverse gate bias voltage during turning-off of a first switching element that is a normally-on type (D type), and to reduce a surge power loss between a drain and a source of a second switching element that is a normally-off type (E type).SOLUTION: A step-up converter 80 is configured to supply output of a snubber circuit 70 provided in a second switching element Q2 to a feed line HH of IC power supply to a control IC 40, switches a third switching element Q3 on the basis of an on-duty that is adjusted in accordance with an error between a voltage of the feed line HH and an IC reference voltage, and performs stabilization control on the voltage of the feed line. A snubber voltage determination circuit 90 determines whether a snubber output voltage outputted from the snubber circuit 70 exceeds a specific voltage and if exceeding the specific voltage, the step-up converter 80 increases the on-duty to the third switching element Q3.

Description

  In the present invention, the main switch means is constituted by cascade connection of two switching elements of normally-on type (D type) and normally-off type (E type), and the control IC responds to an increase / decrease in output voltage. A switching power supply device configured to reduce or increase the on-duty for a normally-off type (E-type) switching element, and absorbs high-frequency noise caused by the switching operation of the normally-off type (E-type) switching element. The present invention relates to a switching power supply device in which a regenerative snubber circuit is connected to a power supply line of a control IC. In this specification, in order to facilitate the distinction between “normally-on type” and “normally-off type”, the normally-on type is a depression type and the normally-off type is an enhancement type. ) "And" Normally off type (E type) ".

  FIG. 2 is a circuit diagram showing a configuration of a switching power supply device in the prior art. As shown in the figure, the primary side circuit 10 and the secondary side circuit 20 are transformer-coupled via a transformer T1. A first switching element Q1 of normally-on type (D type) and a second type of normally-off type (E type) which are further cascade-connected to the primary winding N1 of the transformer T1 connected to the positive terminal of the smoothing capacitor C1. A main switch circuit 30 composed of a series circuit of the switching element Q2 is connected. When the switching power supply is turned on, the smoothing capacitor C1 is charged through a diode bridge rectifier circuit (not shown), and a DC voltage is generated. The voltage of the power supply line HH for the IC power supply is supplied to the power input terminal (Vcc) of the control IC 40 from the voltage after the primary side rectification appearing in the smoothing capacitor C1 via the starting resistance element R1, and the control IC 40 is activated. Is done. The first switching element Q1 is of a depletion type (D type), and is a normally-on type FET (field effect transistor) that is conductive even when no gate voltage is applied before the power is turned on. For this reason, if the second switching element Q2 becomes conductive, a current flows through the primary winding N1 of the transformer T1, and a current also flows through the secondary winding N2 and the auxiliary winding N3. When the control IC 40 is activated, a switching control signal for PWM (pulse width modulation) control is sent from the pulse signal output terminal (Out) to switch the second switching element Q2 at a high frequency, and the primary winding of the transformer T1. A switching current is passed through the line N1. As a result, electric power is generated in the secondary winding N2 of the transformer T1 in an antiphase relationship, and the output voltage Vo rectified and smoothed by the rectifier diode D5 and the smoothing capacitor C6 is supplied to a load (not shown). At the same time, the current induced in the auxiliary winding N3 from the secondary winding N2 in the same phase is rectified by the rectifier diode D3 in the auxiliary power supply 60, smoothed by the smoothing capacitor C4, and then supplied to the power input terminal (Vcc) of the control IC 40. ). Immediately after this, the power supply voltage Vcc is supplied to the power supply input terminal of the control IC 40 by the auxiliary power supply 60 in place of the starting resistance element R1.

  A detection signal of the output voltage Vo detected by the output voltage detection circuit 50 connected between the DC output terminals T2p and T2n of the secondary side circuit 20 is input to the feedback terminal FB of the control IC 40. When the detected output voltage Vo exceeds the reference voltage, the control IC 40 decreases the on-duty of the PWM control switching signal output to the second switching element Q2, and the primary side circuit 10 to the secondary side circuit. The output voltage Vo is stabilized at a specified voltage by lowering the transmission power to 20. Conversely, when the output voltage Vo is lower than the reference voltage, the output voltage Vo is stabilized at a specified voltage by increasing the on-duty of the switching control signal for PWM control.

  High-frequency noise is generated when the second switching element Q2 is switched by the control of the control IC 40. This high-frequency noise is absorbed by the snubber circuit 70 including the rectifier diode D1 and the snubber capacitor C2, and passes through the backflow prevention diode D2. And is used for charging the smoothing capacitor C4 in the auxiliary power source 60.

JP 2009-76845 A JP 2006-352839 A

  In the conventional switching power supply device described above, the first switching element Q1 of normally-on type (D type) is a depletion type, and is composed of, for example, a GaN (gallium nitride) transistor. In such a case, the gate-source voltage at the time of OFF should be -5V. Incidentally, FIG. 3 reprints an example of the gate voltage / drain current characteristics described in the drawing (FIG. 5) of Patent Document 1 (Japanese Patent Laid-Open No. 2009-76845) for a normally-on type (D-type) GaN transistor. (See paragraph [0038]). This shows that the drain current can be turned off with a reverse gate bias of -5V. (Because the drain-source current Ids is 0 at -3.4 V, it is reliably kept off at -5 V).

  On the other hand, the normally-off type (E type) second switching element (power MOSFET) Q2 is an enhancement type, and the gate voltage to be applied is usually 10 V or more. For this reason, in many cases, the gate-source voltage when the first switching element (GaN) Q1 is off is set to −10V or less. However, if the gate-source voltage (absolute value) when the first switching element Q1 is turned off becomes too large, the gate voltage may become excessive and the first switching element Q1 may be destroyed. .

  Referring to the switching waveform (FIG. 3) in Patent Document 2 (Japanese Patent Laid-Open No. 2006-352839), the gate voltage of the second switching element Q2 is as high as 14 V, and the reverse gate when the first switching element Q1 is off. The bias voltage is about -15V. As a result, there is a problem that the surge power loss between the drain and source of the second switching element Q2 becomes large.

  The present invention was created in view of such circumstances, and prevents element destruction caused by an excessively large reverse gate bias voltage when the first switching element of the normally-on type (D type) is turned off. In addition, an object is to reduce the surge power loss between the drain and the source of the normally-off type (E type) second switching element.

  The present invention solves the above problems by taking the following measures.

The switching power supply device according to the present invention includes:
A first switching element whose main switch means is connected between a pair of DC input terminals via a primary winding of a transformer is a normally-on type (D type) and a second switching element which is a normally-off type (E type) Consists of a cascade connection of
The control IC that controls the switching of the second switching element is supplied with power for the IC from an auxiliary power supply unit that generates a DC voltage by the auxiliary winding of the transformer, and the second switching element is controlled according to the fluctuation of the output voltage. The output voltage is stabilized by varying the on-duty of the switching control signal for the element,
Between both ends of the second switching element, a snubber circuit that absorbs high-frequency noise due to the switching operation of the element and regenerates the generated voltage to the power supply line of the IC power supply from the auxiliary power supply unit to the control IC. In a switching power supply device having a configuration in which
The output voltage of the snubber circuit is boosted and regenerated in the power supply line of the IC power supply, the voltage of the power supply line of the IC power supply is detected, and the detected voltage of the power supply line of the IC power supply and the IC A step-up converter that controls the stabilization of the voltage of the power supply line of the IC power supply by the switching operation of the third switching element based on the on-duty adjusted according to the error from the reference voltage;
A snubber voltage determination circuit that monitors a snubber output voltage output from the snubber circuit and determines whether or not a specified voltage is exceeded;
The boost converter is configured to increase an on-duty for the third switching element in the boost converter when the snubber voltage determination circuit determines that the snubber output voltage exceeds a specified voltage. It is said.

  In order to transmit power with high power factor voltage conversion from the primary side circuit to the secondary side circuit via the transformer, normally-on type (D type) as the main switch means connected in series with the primary winding of the transformer ) And a normally-off type (E type) second switching element are connected in cascade. In addition, a snubber circuit is connected between both ends of the second switching element, and the voltage generated by the snubber circuit is regenerated to the power supply line of the IC power supply to the control IC, whereby high-frequency switching of the second switching element is performed. A high-efficiency switching power supply is realized by using high-frequency noise generated by operation as the voltage of the power supply line of the power supply for the control IC. Since the control IC decreases the on-duty of the switching control signal for the second switching element as the output voltage increases, the output voltage can be stabilized.

  In the switching power supply having such a configuration and function, in order to solve the problems of excessive reverse gate bias voltage when the first switching element is turned off and surge power loss of the second switching element, the present invention provides a snubber circuit and A feedback control system is constructed with the control IC. The feedback control system includes a boost converter and a snubber voltage determination circuit. The boost converter is connected between the snubber circuit and the power supply line of the IC power supply to the control IC, and is based on an on-duty adjusted according to an error between the voltage of the power supply line of the IC power supply and the IC reference voltage. Stabilization control of the voltage of the power supply line of the IC power supply is performed by the switching operation of the third switching element. Then, the snubber voltage determination circuit determines whether or not the snubber output voltage output from the snubber circuit exceeds the specified voltage. When it is determined that the snubber output voltage exceeds the specified voltage, the boost converter receives the determination result and The on-duty for the third switching element is increased. If the on-duty of the third switching element increases, the amount of discharge in the path of the third switching element from the output terminal of the snubber circuit increases, so that the snubber output voltage decreases and converges to the specified voltage. . As a result, the voltage at the common connection point between the first and second switching elements and the snubber circuit is also stabilized at a certain voltage level. If the voltage level of the common connection point is set to a low constant voltage, the reverse gate bias voltage when the first switching element which is normally on (D type) is turned off can be kept low. . Furthermore, controlling the voltage level of the common connection point to a constant voltage that is lower can suppress the voltage between the drain and the source of the normally-off type (E type) second switching element to be lower.

  Here, the error between the voltage of the IC power supply line and the IC reference voltage is not limited to the error between the IC power supply line voltage itself and the IC reference voltage. The error between the proportional voltage and the IC reference voltage is also included. In this case, the IC reference voltage is appropriately set according to a voltage proportional to the voltage of the power supply line of the IC power supply to be compared.

  Similarly, when the snubber output voltage exceeds the specified voltage is not limited to when the snubber output voltage itself exceeds the specified voltage, but also includes when the voltage proportional to the snubber output voltage exceeds the specified voltage. In this case, the specified voltage is appropriately set according to a voltage proportional to the snubber output voltage to be compared.

  According to the present invention, it is possible to prevent element breakdown due to excessive reverse gate bias voltage when the first switching element which is normally on (D type) is turned off, and is normally off (E type). The surge power loss between the drain and the source of the second switching element can be reduced.

The circuit diagram which shows the structure of the switching power supply device in the Example of this invention Circuit diagram showing configuration of conventional switching power supply device Example of gate voltage / drain current characteristics of normally-on (D-type) GaN transistor described in Patent Document 1

  The switching power supply device of the present invention having the above configuration has the following preferred modes.

  In the switching power supply having the above configuration, there is a configuration in which a detection voltage shift circuit is provided between the snubber voltage determination circuit and the boost converter. The detection voltage shift circuit is configured to jump upshift the voltage of the power supply line of the IC power supply detected by the boost converter when the snubber voltage determination circuit determines that the snubber output voltage exceeds the specified voltage. Yes. In the basic configuration of the switching power supply device according to the present invention, the boost converter is turned on with respect to the third switching element in the boost converter when the snubber voltage determination circuit determines that the snubber output voltage exceeds the specified voltage. It is configured to increase the duty. With respect to this basic control mode, this embodiment having the detection voltage shift circuit described above provides a higher-order adjustment.

  That is, when the snubber output voltage exceeds the specified voltage, the detection voltage shift circuit jumps up the voltage of the power supply line of the IC power supply detected by the boost converter. If the detected voltage of the power supply line of the IC power supply is upshifted at once, the boost converter dramatically increases the on-duty with respect to the third switching element, and the third switching element from the output terminal of the snubber circuit. In order to increase the amount of discharge in this path at once, the drop convergence toward the specified voltage of the snubber output voltage also responds at high speed.

  The snubber circuit is composed of a series circuit of a rectifier diode and a snubber capacitor connected between both ends of the second switching element, and the snubber voltage determination circuit determines the voltage across the snubber capacitor. In some embodiments, the voltage across the snubber capacitor is reduced by increasing the on-duty for the third switching element in the boost converter when it is determined that the specified voltage has been exceeded. This is a more specific description of the snubber circuit and the snubber voltage determination circuit, and simplifies the circuit configuration as much as possible.

  Embodiments of a switching power supply apparatus according to the present invention will be described below. FIG. 1 is a circuit diagram showing a configuration of a switching power supply apparatus according to an embodiment of the present invention. In FIG. 1, 10 is a primary side circuit, 20 is a secondary side circuit, T1p and T1n are DC input terminals in the primary side circuit 10, T2p and T2n are DC output terminals in the secondary side circuit 20, and T1 is a primary side circuit 10. , C1 is a smoothing capacitor, R1 is a starting resistance element, Q1 is a first switching element of a normally-on type (D type), and Q2 is a normally-off type (E type). Second switching element, 30 is a main switch circuit, 40 is a control IC, 50 is an output voltage detection circuit, 60 is an auxiliary power supply unit, 70 is a snubber circuit, 80 is a boost converter, 90 is a snubber voltage determination circuit, and 100 is This is a detection voltage shift circuit.

  In the primary circuit 10, a pair of DC input terminals T1p and T1n are connected to the output terminal of a full wave rectifier circuit (diode bridge) (not shown), but both terminals of the smoothing capacitor C1 are also connected to the DC input terminals T1p and T1n. ing. The main switch circuit 30 connected between the pair of DC input terminals T1p and T1n via the primary winding N1 of the transformer T1 is a normally-on type (D type) first switching element Q1 and a normally-off type (E type). ) Is the cascade connection of the second switching elements Q2. A series circuit of a rectifier diode D5 and a smoothing capacitor C6 is connected to the secondary winding N2 of the transformer T1, and DC output terminals T2p and T2n are connected to both ends of the smoothing capacitor C6. The output voltage detection circuit 50 connected between both ends of the smoothing capacitor C6 has its output terminal connected to the feedback terminal FB of the control IC 40. In this case, although a circuit that insulates the primary and secondary is not described, it is usual to use a photocoupler or the like to insulate the primary and secondary. An auxiliary power source 60 comprising a series circuit of a rectifier diode D3 and a smoothing capacitor C4 is connected between both ends of the auxiliary winding N3 of the transformer T1, and the positive terminal of the smoothing capacitor C4 is connected to the control IC via a power supply line HH for the IC power source. It is connected to 40 power input terminals (Vcc). The secondary winding N2 in the transformer T1 has a reverse polarity relationship with the primary winding N1, and the auxiliary winding N3 has a same polarity relationship with the secondary winding N2. The first switching element Q1 which is a normally-on type (D type) is formed of, for example, a GaN (gallium nitride) transistor. The normally-off type (E type) second switching element Q2 is formed of, for example, a silicon MOS-FET.

  The DC input terminal T1p on the positive electrode side is connected to the power supply line HH of the IC power supply via the starting resistance element R1. The control IC 40 has its pulse signal output terminal (Out) connected to the gate of the second switching element Q2. The second switching element Q2 is composed of an N channel type MOS transistor. By switching the second switching element Q2 at a high frequency by the control IC 40, AC power is transmitted from the primary side circuit 10 to the secondary side circuit 20 in the transformer T1, and further rectified and smoothed by the rectifier diode D5 and the smoothing capacitor C6. The obtained DC output voltage Vo is supplied from a DC output terminal T2p, T2n to a load (not shown). Then, the DC voltage induced by the secondary winding N2 to the auxiliary winding N3 and rectified and smoothed by the rectifier diode D3 and the smoothing capacitor C4 in the auxiliary power supply unit 60 is controlled through the power supply line HH of the IC power supply. The power is supplied to the power input terminal (Vcc) of the IC 40. The output voltage detection circuit 50 detects the output voltage Vo and outputs it to the feedback terminal FB of the control IC 40. The control IC 40 controls the second switching element Q2 according to the increase / decrease change of the obtained output voltage Vo. It is configured to change the on-duty to decrease / increase.

A snubber circuit 70 composed of a series circuit of a rectifier diode D1 and a snubber capacitor C2 is connected between both ends of the second switching element Q2. The positive terminal of the snubber capacitor C2, which is the output terminal of the snubber circuit 70, is connected to the power supply line HH to the control IC 40 via the boost converter 80. The step-up converter 80 includes an inductor (choke coil) L1, a third switching element Q3, a backflow prevention diode D2, a first reference voltage circuit 81 including a resistance element R5 and a Zener diode ZD1, and a resistance dividing circuit of resistance elements R3 and R4. The IC power supply voltage detection circuit 82, a first error amplifier 83 composed of an operational amplifier, a phase compensation circuit 84 composed of a capacitor C3 and a resistance element R2, and a control circuit 85. The third switching element Q3 is composed of an N channel type MOS transistor. A series circuit of the inductor L1 and the third switching element Q3 is connected between both ends of the snubber circuit 70, and the connection point of the inductor L1 and the third switching element Q3 is connected to the power supply line HH of the IC power supply via the backflow prevention diode D2. It is connected to the. A first reference voltage circuit 81 composed of a series circuit of a resistor element R5 and a Zener diode ZD1 is connected between the power supply line HH and the ground line LL of the IC power supply, and the connection point of the resistor element R5 and the Zener diode ZD1 is the first connection point. 1 is connected to a non-inverting input terminal (+) of an operational amplifier constituting one error amplifier 83. Further, an IC power supply voltage detection circuit 82 composed of a resistance dividing circuit of resistance elements R3 and R4 is connected between the power supply line HH of the IC power supply and the ground line LL, and the connection point of the resistance elements R3 and R4 is the first connection point. Are connected to the inverting input terminal (−) of the operational amplifier constituting the error amplifier 83. A phase compensation circuit 84 composed of a series circuit of a capacitor C3 and a resistance element R2 is connected between the output terminal and the inverting input terminal (−) of the operational amplifier constituting the first error amplifier 83. The first error amplifier 83 calculates an error voltage ΔV ₁ (= V _ref1) by taking an error between the reference voltage V _ref1 and the divided value k ₁ · V _HH of the detected voltage V _HH (= Vcc) of the IC power supply line. −k ₁ · V _HH ), and the signal is output to the control circuit 85. However, the resistance division ratio k ₁ is given by k ₁ = R4 / (R3 + R4). The control circuit 85 has a power supply line connected between the power supply line HH of the IC power supply and the ground line LL. The control circuit 85 has a third duty cycle with an on-duty according to the amplitude of the error voltage ΔV ₁ input from the first error amplifier 83. The switching element Q3 is subjected to switching control. That is, the voltage V _HH feed line HH of the power supply detected IC (= Vcc) divided value k ₁ · V _HH is lower than the reference voltage V _ref1, when the error voltage [Delta] V ₁ is negative and the third switching element A control signal for increasing the on-duty for Q3 is output. As a result, the energy stored in the inductor L1 is increased, the boosting level is increased to increase the voltage applied to the power supply line HH of the IC power supply, and the divided values k ₁ and V _HH of the voltage V _HH of the power supply line _HH are the reference. Raise it closer to the voltage. Contrary to the above, higher than the cutoff value k ₁ · V _HH reference voltage V _ref1 of the voltage V _HH of the detected power supply line HH, when the error voltage [Delta] V ₁ is plus on-duty for the third switching element Q3 A control signal for reducing the output is output. As a result, the energy stored in the inductor L1 is reduced, the boosting level is lowered, the applied voltage to the power supply line HH of the IC power supply is lowered, and the divided values k ₁ and V _HH of the voltage V _HH of the power supply line _HH are the reference. Lower to approach the voltage.

The voltage across the snubber capacitor C 2, that is, the snubber output voltage Vs that is the output voltage of the snubber circuit 70 is taken into the snubber voltage determination circuit 90. The snubber voltage determination circuit 90 includes resistance elements R6, R7, R8, R9, a capacitor C5, a Zener diode ZD2, and a second error amplifier 93 including an operational amplifier. A second reference voltage circuit 91 composed of a series circuit of a resistor element R6 and a Zener diode ZD2 is connected between both ends of the snubber circuit 70, and a connection point between the resistor element R6 and the Zener diode ZD2 constitutes a second error amplifier 93. It is connected to the non-inverting input terminal (+) of the operational amplifier. In addition, a snubber output voltage detection circuit 92 composed of a resistance dividing circuit of resistance elements R 7 and R 8 is connected between both ends of the snubber circuit 70, and a connection point of the resistance elements R 7 and R 8 is an operational amplifier constituting the second error amplifier 93. It is connected to the inverting input terminal (-). A phase compensation circuit 94 composed of a series circuit of a capacitor C5 and a resistor element R9 is connected between the output terminal and the inverting input terminal (−) of the operational amplifier constituting the second error amplifier 93. The second error amplifier 93 takes an error between the reference voltage V _ref2 and the detected value k ₂ · Vs of the detected snubber output voltage Vs, and outputs the error signal as a binary signal of “H” level and “L” level. It is supposed to be. However, the resistance division ratio k ₂ is given by k ₂ = R8 / (R7 + R8).

The output terminal of the snubber voltage determination circuit 90, that is, the output terminal of the second error amplifier 93 is connected to the resistance of the IC power supply voltage detection circuit 82 in the boost converter 80 via the detection voltage shift circuit 100 including the backflow prevention diode D4 and the resistance element R10. It is connected to the resistance dividing point of the elements R3 and R4. When the divided value k ₂ · Vs of the detected snubber output voltage Vs is lower than the reference voltage V _{ref2, the} snubber voltage determination circuit 90 outputs “H” level to inactivate the detection voltage shift circuit 100. Conversely, when the detected divided value k ₂ · Vs of the snubber output voltage Vs is higher than the reference voltage V _ref2 , the “L” level is output to activate the detection voltage shift circuit 100, and the first error in the boost converter 80 is detected. The resistor element R10 is connected in parallel to the resistor element R4 connected to the inverting input terminal (−) of the amplifier 83, and the voltage V _HH of the power supply line HH of the IC power supply applied to the inverting input terminal (−) is obtained. Make a dramatic upshift.

  Next, the operation of the switching power supply device configured as described above will be described.

(1) When the switching power supply is turned on, the smoothing capacitor C1 is charged. From the input voltage Vi after the primary side rectification appearing in the smoothing capacitor C1, the power input terminal (Vcc) of the control IC 40 through the starting resistance element R1. ) Is supplied with the voltage V _HH (= Vcc) of the power supply line HH of the IC power supply, and the control IC 40 is activated. The control IC 40 outputs a switching control signal (PWM control signal) from the pulse signal output terminal (Out) to the gate of the second switching element Q2, performs switching control of the second switching element Q2 at a high frequency, A switching current is passed through the primary winding N1 of T1. As a result, power is generated in the secondary winding N2 of the transformer T1 in an antiphase relationship, and the output voltage Vo generated by rectification and smoothing by the rectifier diode D5 and the smoothing capacitor C6 in the secondary side circuit 20 is supplied to a load (not shown). Supplied. At the same time, the current induced in the auxiliary winding N3 in the same phase relationship from the secondary winding N2 is rectified by the rectifier diode D3 in the auxiliary power supply 60, smoothed by the smoothing capacitor C4, and passed through the power supply line HH of the IC power supply. Then, power is supplied to the power input terminal (Vcc) of the control IC 40.

  (2) The detection signal of the output voltage Vo detected by the output voltage detection circuit 50 in the secondary side circuit 20 is input to the feedback terminal FB of the control IC 40. When the detected output voltage Vo exceeds the reference voltage, the control IC 40 decreases the on-duty of the switching control signal output from the pulse signal output terminal (Out) for the second switching element Q2, and the primary winding of the transformer T1. The output voltage Vo is lowered by reducing the magnetic energy stored in N1 and lowering the transmission power from the primary side circuit to the secondary side circuit. Conversely, when the output voltage Vo detected by the output voltage detection circuit 50 is lower than the reference voltage, the control IC 40 increases the output voltage Vo by increasing the on-duty of the switching control signal. In any case, the output voltage Vo of the secondary circuit 20 is stabilized at a specified voltage by feedback control from the output voltage detection circuit 50 to the control IC 40.

  (3) High frequency noise is generated when the second switching element Q2 is switched by the control of the control IC 40. This high frequency noise is absorbed by the snubber circuit 70 including the rectifier diode D1 and the snubber capacitor C2, and further the snubber circuit. 70 to the boost converter 80. In step-up converter 80, third switching element Q3 is subjected to switching control at a high frequency by a switching control signal from control circuit 85. In the ON period of the third switching element Q3, the current from the snubber circuit 70 flows through the path between the inductor L1 and the third switching element Q3, and magnetic energy is accumulated in the inductor L1. During the OFF period of the third switching element Q3, the current due to the magnetic energy released from the inductor L1 and the current from the snubber circuit 70 merge, and then power is supplied to the power supply line HH of the IC power supply via the backflow prevention diode D2. Is called. That is, the snubber output voltage Vs is boosted and then supplied to the power supply line HH of the IC power supply. The detailed operation of boost converter 80 is as follows.

In step-up converter 80, an IC power supply voltage detection circuit 82 composed of a resistance dividing circuit of resistance elements R3 and R4 detects a voltage V _HH (= Vcc) of power supply line HH of the IC power supply. The first error amplifier 83 includes a reference voltage V _ref1 generated by the first reference voltage circuit 81 including the resistor element R5 and the Zener diode ZD1, and a divided value k ₁ · V _{HH of the} detected voltage V _HH of the power supply line of the IC power supply. The error voltage ΔV ₁ (= V _ref1 −k ₁ · V _HH ) is taken and the signal is output to the control circuit 85. The control circuit 85 controls the on-duty for the third switching element Q3 according to the amplitude of the input error voltage ΔV ₁ . That is, when the divided value k ₁ · V _{HH of} the detected voltage V _HH of the power supply line of the IC power supply is lower than the reference voltage V _ref1 and the error voltage ΔV ₁ is positive, the control circuit 85 causes the third switching element Q3 to be positive. A control signal for increasing the on-duty with respect to is output. As a result, the energy stored in the inductor L1 is increased, the boosting level is increased, and the voltage applied to the power supply line HH of the IC power supply is increased. On the contrary, when the detected divided value k ₁ · V _HH of the power supply line V _HH of the IC power supply is higher than the reference voltage V _ref1 and the error voltage ΔV ₁ is negative, the control circuit 85 is turned on. A control signal for decreasing the duty is output. As a result, the energy stored in the inductor L1 is reduced, the boosting level is lowered, and the voltage applied to the power supply line HH of the IC power supply is lowered. In any case, the divided value k ₁ · V _HH of the voltage V _HH of the power supply line HH converges to the reference voltage V _ref1 by feedback control in the boost converter 80, and the power supply voltage Vcc of the control IC 40 is stabilized.

  (4) As described above, the output of the snubber circuit 70 is sent to the power supply line HH of the IC power supply to effectively use the switching noise component, while stabilizing the power supply voltage Vcc of the control IC 40, and the secondary side Control for stabilizing the output voltage Vo from the circuit 20 is also executed. In such a control operation, regarding the variation of the snubber output voltage Vs, which is the output voltage of the snubber circuit 70, the operation of feedback control by the snubber voltage determination circuit 90, the detection voltage shift circuit 100, the boost converter 80 and the control IC 40. This will be described below.

In the snubber voltage determination circuit 90, a snubber output voltage detection circuit 92 composed of a resistance dividing circuit of the resistance elements R 7 and R 8 detects a snubber output voltage Vs that is an output voltage of the snubber circuit 70. The second error amplifier 93 takes an error between the reference voltage V _ref2 by the second reference voltage circuit 91 composed of the resistor element R6 and the Zener diode ZD2 and the divided value k ₂ · Vs of the detected snubber output voltage Vs. Output as voltage ΔV ₂ (= V _ref2 −k ₂ · Vs). When the divided value k ₂ · Vs of the detected snubber output voltage Vs is lower than the reference voltage V _ref2 , the output terminal of the second error amplifier 93 is at the “H” level, so that the backflow prevention diode D4 is not conducted and is detected. The voltage shift circuit 100 remains inactive, and the configuration of the IC power supply voltage detection circuit 82 in the boost converter 80 is a resistance dividing circuit including only the resistance elements R3 and R4. The control operation at this time is as described above.

On the other hand, when the divided value k ₂ · Vs of the detected snubber output voltage Vs rises and becomes higher than the reference voltage V _ref2 , the output terminal of the second error amplifier 93 becomes “L” level and the backflow prevention diode D4. Is activated, the detection voltage shift circuit 100 is activated, and in the configuration of the IC power supply voltage detection circuit 82, the resistance element R10 is added to the resistance dividing points of the resistance elements R3 and R4. As a result, the potential of the inverting input terminal (−) of the first error amplifier 83, which is a resistance dividing point, decreases, and the output voltage of the first error amplifier 83 increases. Then, the control circuit 85 increases the on-duty for the third switching element Q3. The increase in the on-duty of the third switching element Q3 means that the amount of discharge in the path from the inductor L1 to the third switching element Q3 from the positive terminal of the snubber capacitor C2 in the snubber circuit 70 increases. As a result, the voltage across the snubber capacitor C2, that is, the snubber output voltage Vs is lowered, and the divided value k ₂ · Vs converges to the reference voltage V _ref2 .

When the reference voltage V _ref2 by the second reference voltage circuit 91 in the snubber voltage determination circuit 90 is set to 2.25 V, for example, and R7 = R8, the above-described snubber voltage determination circuit 90, detection voltage shift circuit 100, boost converter The snubber output voltage Vs, which is the output voltage of the snubber circuit 70, is suppressed to 4.5V or less by feedback control by the control circuit 80 and the control IC 40. If the forward voltage Vf of the rectifier diode D1 in the snubber circuit 70 is, for example, 0.5V, the drain-source voltage of the normally-off type (E type) second switching element Q2 is 5V, and the normally on type (D type). ), The reverse gate bias voltage of the first switching element Q1 can also be suppressed to -5V. As a result, it is possible to prevent element breakdown due to excessive reverse gate bias voltage when the first switching element Q1 is OFF, and to reduce surge power loss between the drain and source of the second switching element Q2. be able to.

In the above-described embodiment, the step-up converter 80 operates in accordance with an error between the divided value k ₁ · V _HH of the voltage V _HH (= Vcc) of the power supply line HH of the IC power supply and the IC reference voltage (reference voltage V _ref1 ). However, the present invention is not limited to this, and the voltage proportional to the voltage V _HH (= Vcc) of the power supply line HH of the IC power supply is not limited to this. The on-duty may be adjusted based on an error from the IC reference voltage. The on-duty may be adjusted based on an error between the voltage V _HH (= Vcc) of the power supply line HH of the IC power supply itself and the IC reference voltage. In the above case, the IC reference voltage is appropriately changed to achieve the purpose.

Similarly, the snubber voltage determination circuit 90 determines whether or not the divided value k ₂ · Vs of the snubber output voltage (voltage across the snubber capacitor C2) Vs exceeds the specified voltage (reference voltage V _ref2 ). The invention is not limited to this, and a determination may be made by comparing a voltage proportional to the snubber output voltage Vs with a specified voltage. Alternatively, the determination may be made by comparing the snubber output voltage Vs itself with the specified voltage. In the above case, the specified voltage is appropriately changed to achieve the purpose.

  The present invention comprises a first switching element whose main switch means is a normally-on type (D type) and a second switching element which is a normally-off type (E type) in cascade connection, and the switching of the second switching element. In a switching power supply device having a snubber circuit that absorbs high-frequency noise due to operation and regenerates to the power supply line of the control IC, due to an excessive reverse gate bias voltage when the first switching element that is normally on (D type) is off This is useful as a technique for preventing the element destruction and reducing the surge power loss between the drain and the source of the normally-off type (E type) second switching element.

10 Primary side circuit 20 Secondary side circuit 30 Main switch circuit 40 Control IC
DESCRIPTION OF SYMBOLS 50 Output voltage detection circuit 60 Auxiliary power supply part 70 Snubber circuit 80 Boost converter 81 1st reference voltage circuit 82 IC power supply voltage detection circuit 83 1st error amplifier 85 Control circuit 90 Snubber voltage determination circuit 91 2nd reference voltage circuit 92 Snubber output voltage detection circuit 93 Second error amplifier 100 Detection voltage shift circuit C2 Snubber capacitor Q1 Normally-on type (D-type) first switching element Q2 Normally-off type (E-type) second switching element Q3 Third Switching element T1p, T1n DC input terminal T2p, T2n DC output terminal T1 transformer ZD1, ZD2 Zener diode

Claims (3)

The main switch means connected between the pair of DC input terminals via the primary winding of the transformer is composed of a cascade connection of a first switching element that is normally on and a second switching element that is normally off.
The control IC that controls the switching of the second switching element is supplied with power for the IC from an auxiliary power supply unit that generates a DC voltage by the auxiliary winding of the transformer, and the second switching element is controlled according to the fluctuation of the output voltage. The output voltage is stabilized by varying the on-duty of the switching control signal for the element,
Between both ends of the second switching element, a snubber circuit that absorbs high-frequency noise due to the switching operation of the element and regenerates the generated voltage to the power supply line of the IC power supply from the auxiliary power supply unit to the control IC. In a switching power supply device having a configuration in which
The output voltage of the snubber circuit is boosted and regenerated in the power supply line of the IC power supply, the voltage of the power supply line of the IC power supply is detected, and the detected voltage of the power supply line of the IC power supply and the IC A step-up converter that controls the stabilization of the voltage of the power supply line of the IC power supply by the switching operation of the third switching element based on the on-duty adjusted according to the error from the reference voltage;
A snubber voltage determination circuit that monitors a snubber output voltage output from the snubber circuit and determines whether or not a specified voltage is exceeded;
The boost converter is configured to increase an on-duty with respect to the third switching element in the boost converter when the snubber voltage determination circuit determines that the snubber output voltage exceeds a specified voltage. .   The voltage of the power supply line of the IC power supply detected by the boost converter when the snubber voltage determination circuit determines that the snubber output voltage exceeds a specified voltage between the snubber voltage determination circuit and the boost converter. The switching power supply device according to claim 1, further comprising a detection voltage shift circuit that jumps up and down. The snubber circuit includes a series circuit of a rectifier diode and a snubber capacitor connected between both ends of the second switching element,
When the snubber voltage determination circuit determines that the voltage across the snubber capacitor has exceeded a specified voltage, the voltage across the snubber capacitor is decreased by increasing the on-duty for the third switching element in the boost converter. The switching power supply device according to claim 1, wherein the switching power supply device is configured to cause the switching power supply to be

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