JP2000295846A - Inverter circuit and dc power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency by reducing waiting electric power at the time of a light load or no load. SOLUTION: In a fly-back inverter circuit, an LC snubber circuit 7 including a capacitor C3 and an inductance L1 connected in series is connected parallel to a switching element 5 of a control circuit 3 (IPD) connected in series to the primary windings Np of a fly-back transformer 1. The LC resonance cycle is set to twice to 20 times, desirably four times, larger than the minimum width of on range of the control circuit. To secure idling electric power required for the stable operation of the control circuit 3, wasteful energy by the driving with the minimum width of on range is regenerated at the primary side of the LC snubber circuit 7 so that inverter output by the drive with the on range minimum width can be lowered to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter circuit using a switch element known as an intelligent power device (hereinafter referred to as "IPD") as a control IC for a switching power supply for performing pulse width control (PWM), and a direct current (DC). Power supply.

[0002]

2. Description of the Related Art Conventionally, as an inverter circuit and a DC power supply device using an IPD, for example, there is one shown in FIG.

In FIG. 5, a flyback transformer 1
Has a primary winding Np, the secondary winding Ns and the auxiliary winding N _SUB, the primary winding Np and the voltage of the secondary winding Ns is winding as the polarity is reversed as black circles Is provided.

A rectifying / smoothing circuit 2, an IPD 3, and an auxiliary power supply circuit 6 are provided for the flyback transformer 1. That is, one end of the flyback transformer 1 is connected to the plus side of the input voltage V _IN , and the other end of the primary winding Np is connected to IP
Connect to D2. Note that Le is a leakage indantax equivalently shown. Secondary winding Ns of flyback transformer 1
Is connected to a rectifying diode D2 and a rectifying / smoothing circuit 2 of a smoothing capacitor C2, and supplies an output voltage Vo to a load.
Further, a bleeder resistor R2 for preventing an increase in the output voltage Vo at the time of light load or no load is connected.

The IPD 3 is a switching power supply control IC having a control terminal C, a drain terminal D, and a source terminal S, and has a PWM control circuit 4 and a power MOSFET.
A switching element 5 such as T is incorporated. The IPD 3 connects the switch element 5 in series with the primary winding Np of the flyback transformer 1, and switches the switch element 5 by the PWM control circuit 4.
, The flyback transformer 1 is switched and driven.

That is, when the switch element 5 is turned on, the primary winding N
s, a current is supplied to the secondary winding Ns to store energy, and the energy stored in the primary winding Ns when the switch element 5 is turned off.
And rectified by the rectifier diode D2, and then transferred to the smoothing capacitor C2. At this time, the PWM control circuit 4 controls the pulse width of the switch element 5 so that the output voltage Vo becomes a constant value.

Auxiliary power supply circuit 6 connected to auxiliary winding N _SUB
Generates and inputs a power supply for operation of the IPD 3 and a current source for control by rectification and smoothing by the diode D1 and the capacitor C1. The IPD 3 supplies an idling current to the control terminal C through the bias resistor R1 for stable operation. Further, by varying the variable resistor VR1, the control current for controlling the pulse width is varied, and the value of the output voltage Vo for stabilizing control is set.

The primary winding Ns of the flyback transformer 1
A CR snubber circuit 10 is provided in parallel with the above. The CR snubber circuit 10 is composed of a resistor R3, a capacitor C3, and a diode D3. It is absorbed by converting it into heat, thereby preventing an excessive spike voltage from being applied to the switching element 5 of the IPD 3.

[0009]

However, in such a conventional inverter circuit, the IPD 3 used for switching control uses a part of the inverter output for idling power for self-stabilizing operation. Therefore, the pulse width of the switch element 5 by the pulse width control is set inside the IPD so as not to be narrowed below the specified minimum pulse width.

FIG. 6A shows the control characteristics of the inverter output with respect to the control input of the IPD 3, in which the bleeder resistor R2 is not provided on the output side. With this control characteristic,
Even if the control input of the IPD 3 is changed from zero to the maximum drive value, the inverter output will be the control input i _{co with the} minimum ON width.
From the minimum power to the maximum power, the linearity of the control deteriorates near the minimum ON width, and the inverter output cannot be reduced to zero.

Therefore, the output side of the inverter circuit shown in FIG.
6B, the minimum power is consumed by the bleeder resistor R2 as indicated by the hatched portion in FIG.
6B is obtained by subtracting the power consumption of FIG. 3B from the inverter output of FIG.
The inverter output is reduced to zero by the control input _ico near the minimum ON width.

However, in order to obtain the control characteristic of the inverter output shown in FIG. 6C, by providing the bleeder resistor R2, the IPD3 in the inverter circuit and the DC power supply device is provided.
, The minimum power determined by the minimum ON width must be consumed, and there is a problem that standby power increases and efficiency deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide an inverter circuit and a DC power supply device which reduce standby power at light load or no load to increase efficiency. I do.

[0014]

In order to achieve this object, the present invention is configured as follows. The present invention provides a primary winding,
A flyback transformer having a secondary winding and an auxiliary winding and driven by switching, a rectifying and smoothing including a rectifying diode and a smoothing capacitor for rectifying and smoothing a switching output of a secondary winding after rectifying the switching output and supplying a DC output voltage to a load. A circuit, a switch element and a pulse width control circuit thereof. When the switch is turned on, a current flows through the primary winding to store energy, and when the switch is turned off, the energy stored in the primary winding is passed through the secondary winding to a smoothing capacitor. And a control circuit (IP
D) and an inverter circuit including an auxiliary power supply circuit for inputting a control current source and a DC auxiliary power supply generated from an output voltage of an auxiliary winding to a control circuit.

The present invention relates to such a so-called flyback type inverter circuit. The present invention relates to an LC having a predetermined LC resonance period in which a capacitor and an inductance are connected in series with a switch element of a control circuit connected in series to a primary winding. A snubber circuit is connected.

As described above, according to the present invention, since the snubber circuit of the LC resonance type is provided, when the control circuit (IPD) is operated with the minimum ON width so as to be able to operate with the idling power, the accumulation of the extra transformer. Energy is regenerated to the input side. For this reason, the load can be transferred by transferring the energy by the regenerative action of the LC resonance without using excess energy due to the operation of the minimum on-width to secure the idling power required by the control circuit at no load as heat by the bleeder resistance. Can be set to zero.

As a result, the control characteristics of the inverter become linear characteristics, and the power consumption inside the power supply at the time of no load or light load when the load is on standby can be reduced.

Here, the control circuit (IPD) has a minimum ON width such that the switch-on pulse width in the pulse width control of the switch element does not become narrower, and determines the LC resonance cycle of the LC snubber circuit by the minimum ON width of the control circuit. 2 to 2 times
Set to 0x.

As described above, by changing the LC resonance cycle of the LC snubber circuit within the range of 2 to 20 times the minimum ON width of the control circuit (IPD), the linearity of the control characteristic near the minimum ON width of the control circuit is obtained. Characteristics and power supply on the load side can be arbitrarily changed, and the degree of freedom of design according to the load is expanded.

Further, according to the present invention, the LC resonance cycle of the LC snubber circuit is preferably set to be equal to four times the minimum ON width of the control circuit. When the LC resonance cycle of the LC snubber circuit is set equal to four times the minimum ON width of the control circuit, the energy accumulated in the capacitor in the LC snubber circuit when the switch element is turned ON with the minimum ON width flows through the inductance. The current at that time is maximized by the LC series resonance, and the regenerative energy for the primary side can be maximized.

The LC snubber circuit absorbs the flyback energy of the primary winding by a capacitor when the switch is turned off, transfers the energy stored in the capacitor to the inductance when the switch is next turned on, and transfers the energy to the inductance at the next switch off timing. The stored energy is regenerated to the primary winding side.

Further, extra energy is regenerated by the regenerative action.
As a condition of the LC snubber circuit for returning to the next side, set the capacitance of the capacitor of the snubber circuit so that the voltage applied to the switch element when the switch is off does not exceed the specified withstand voltage of the switch element. The value of the inductance is set so that the current flowing through the switch element when the switch is turned off does not exceed a prescribed limit current of the switch element.

Further, the present invention provides a DC power supply device, comprising an inverter circuit circuit provided with the above-described LC snubber circuit, and a rectifying and smoothing circuit for inputting a DC voltage rectified and smoothed from an AC power supply to the inverter circuit. Is provided.

[0024]

FIG. 1 is a circuit diagram showing an embodiment of an inverter circuit according to the present invention. In Figure 1, an inverter circuit of the present invention has a flyback transformer 1, flyback transformer 1 has a primary winding Np, 2 winding Ns and the auxiliary winding N _SUB. The leakage inductance Le is equivalently shown in series with the primary winding Np. Also shows Lp, Ls, as L _SUB in the inductance of the primary winding Np, 2 winding Ns and the auxiliary winding N _SUB ().

The flyback transformer 1 is provided with a rectifying and smoothing circuit 2, an IPD 3 functioning as a control circuit, and an auxiliary power supply circuit 6. The rectifying and smoothing circuit 2 has a secondary winding N
After the rectification diode D2 rectifies the switching output of s, it is smoothed by the smoothing capacitor C2, and the output voltage Vo is supplied to the load.

The IPD 3 provided in series with the primary winding Np
It incorporates a PWM control circuit 4 and a switch element 5 such as a power MOSFET. As such IPD3, for example, MIPO223 manufactured by Matsushita Electronics Corporation can be used.

The pulse width control circuit 4 of the IPD 3 drives the switch element 5 on and off to output the output voltage Vo.
Is controlled to a constant value. When the switch element 5 is turned on, the primary winding N of the flyback transformer 1 is applied by the input voltage V _IN.
DC current flows through p and energy is stored. When the switch element 5 is turned off, the energy stored in the primary winding Np is rectified by the rectifier diode D2 through the secondary winding Ns, and then charged to the smoothing capacitor C2 and simultaneously supplied to the load.

The auxiliary power supply circuit 6 provided for the auxiliary winding N _SUB rectifies the switching output obtained by the switching drive of the flyback transformer 1 with the diode D1 and smoothes it with the capacitor C1.
, And a control current source for the pulse width control circuit 4 of the IPD 3 at the same time.

A bias resistor R1 is provided between the auxiliary power supply circuit 6 and the controller terminal C of the IPD, that is, the input of the PWM control circuit 4, and the idling current for stably operating the IPD when there is no load is provided by the bias resistor R1. I'm pouring. The variable resistor VR1 connected in parallel to the bias resistor R1 controls the input current to the IPD3. By changing VR1, the constant value of the output voltage Vo with respect to the load can be variably set within a predetermined range.

With respect to such a flyback type inverter circuit, in the present invention, the flyback transformer 1
Is newly provided with an LC snubber circuit 7 on the primary side. LC
The snubber circuit 7 includes a snubber capacitor C3, a snubber inductance L1, and diodes D3 and D4 for backflow prevention. That is, the primary winding N of the flyback transformer 1
A series resonant circuit of a snubber capacitor C3 and a snubber inductance L1 is connected in parallel with the switch element 5 of the IPD 3 connected in series to p.

Between the snubber capacitor C3 and the snubber inductance L1, a backflow preventing diode D4 for determining the direction of energy transfer is provided. Further, from between the snubber capacitor C3 and the backflow prevention diode D4, a backflow prevention diode D3 for regenerating energy to the primary side.
Is provided.

The LC snubber circuit 7 has a minimum on-width t _MIN of the IPD 3 when no load is supplied to the load.
When the switch element 5 is turned off in the operation state, unnecessary flyback energy generated by the switching operation of the flyback transformer 1 is absorbed by the snubber capacitor C3 and stored in the snubber capacitor C3 when the next switch element 5 is turned on. The energy is transferred to the snubber inductance L1, and the energy of the snubber inductance L1 is regenerated to the input side via the diodes D4 and D3 when the switch element 5 is turned off.

The minimum ON width t _MIN by the LC snubber circuit 7
In order to maximize the regeneration efficiency of the excess energy from the flyback transformer 1 during the no-load operation of the
The resonance cycle determined by four times the minimum ON width t _MIN of D3, the snubber capacitor C3 of the LC snubber circuit 7, and the snubber inductance L1 is made equal. That is, the resonance cycle t _LC of the LC snubber circuit 7 is

[0034]

(Equation 1)

Therefore, the minimum ON width t of the IPD 3 is
_{Between MIN}

[0036]

(Equation 2)

The value of the snubber capacitor C3 and the value of the snubber inductance L1 are set so that the following relationship is established.

Further, the capacitance value of the snubber capacitor C3 satisfying the condition of the expression (2) is determined by assuming that the withstand voltage of the switch element 5 provided in the IPD 3 when the switch element 5 is turned off is V _{D (MAX).} , Switch element 5 of LC snubber circuit 7
Is set so as not to exceed the IPD band voltage V _{D (MAX)} . That is

[0039]

(Equation 3)

The capacitance value of the snubber capacitor C3 is set so as to satisfy the following.

As for the value of snubber inductance L1, the current flowing when switch element 5 is turned on is IP
The value is set so as not to exceed the limit current _{ID (MAX)} of D3. That is

[0042]

(Equation 4)

The value of snubber inductance L1 is set so as to satisfy the following condition.

Further, in order to maximize the regenerative energy, the resonance period t _LC of the LC snubber circuit 7 given by the equation (1) is set to four times the minimum ON width t _MIN of the IPD 3 as shown in the above equation (2). It is equal, but twice to 20 the minimum oN width t _MIN of energy regeneration action IPD3 the LC resonance period TLC
By adjusting the regenerative energy by changing it in the range of 2t _{MIN to} 20t _MIN , the linearity of the control characteristic near the control energy corresponding to the minimum ON width of the inverter and the power supplied to the load can be arbitrarily set. Can be changed.

The conditions of the LC snubber circuit 7 according to the present invention are summarized as follows.

To maximize the regenerative energy, I
Four times the minimum on-width t _MIN of the PD is equal to the resonance period t _LC of L1 and C3. Further, the resonance period t _LC is arbitrarily set within a range of 2 to 20 times the minimum on-width t _MIN of the IPD as necessary.

The capacitance value of snubber capacitor C3 is set to a value equal to or not exceeding IPD band voltage V _{D (MAX)} when the inverter is off. The value of snubber inductance L1 is set to a value equal to or not exceeding IPD limit current _{ID (MAX)} when the inverter is off.

FIG. 2 is a circuit diagram of the inverter circuit of FIG.
FIG. 4 is an explanatory diagram showing characteristics of a control input and an inverter output with respect to PD3. First, FIG. 2A shows the characteristics in the case where the LC snubber circuit 7 is not provided in FIG. 1. When the IPD control input is equal to or less than the control input _ico which gives the minimum ON width, the inverter output has a constant value of the minimum power PMIN. The inverter output is linearly amplified in response to an increase from the control input _ico corresponding to the minimum ON width. In such an output characteristic of the inverter, even if the control input of the IPD 3 is narrowed, the inverter output decreases only to the minimum power P _MIN and cannot be reduced to zero.

Therefore, in the conventional circuit of FIG. 5, a bleeder resistor R2 is connected to the output side, and a current flows through the bleeder resistor R2 to be consumed as heat. Although as squeezable inverter output at the corresponding control input i _co zero, this energy inside the power supply in is wasted.

On the other hand, in the embodiment of the present invention shown in FIG. 1, an LC snubber circuit 7 is provided on the primary side of the flyback transformer 1 so as to be four times the minimum ON width t _MIN of the IPD 3 and the snubber capacitor C 3. By making the resonance periods t _LC by the snubber inductance L1 equal as shown in the equation (2), the characteristics of the regenerative power by the LC snubber circuit 7 shown by the hatched portion in FIG. 2B can be obtained.

Therefore, the overall output characteristic of the inverter circuit shown in FIG. 1 is a characteristic obtained by subtracting the characteristic of the regenerative power by the LC snubber circuit 7 from the characteristic shown in FIG. The inverter output can be reduced to zero by the control input _ico corresponding to the ON width, and the linearity is sufficiently improved as compared with FIG.

Next, referring to the time chart of FIG.
The energy regeneration action of the LC snubber circuit 7 provided in the inverter circuit will be described in detail.

FIG. 3 is a circuit diagram of the inverter circuit shown in FIG.
When the control input to the IPD 3 is in the operating state with the minimum ON width t _MIN , that is, the power MO that becomes the switch element 5 in the no-load state
SFET drain-source voltage V _DS , secondary winding Ns
Current I _LP, the voltage V _C3 of the snubber capacitor C3 through the,
A current I _L1 flowing from the snubber capacitor C3 to the snubber inductance L1, and a regenerative current flowing further to the primary side are shown.

First, in the initial state, the snubber capacitor C3 is not charged and the primary winding Np has a minimum ON width t _MIN indicated by the first ON of the switch element 5.
Minute current I _LP flows, the current I _LP When the switch element 5 is turned off returns to zero. At this first timing, the switch element 5 is turned on as shown in FIG.
The current I _LP flows through the inductance Lp of the next winding Np, and this current I _LP

[0055]

(Equation 5)

Is given by

At the timing of FIG. 3 in which the switch element 5 is turned on after being turned on with the minimum on width t _MIN , the extra energy generated due to the switch off causes the primary winding Np
Is absorbed by the snubber capacitor C3, and the voltage VC3 of the snubber capacitor C3 is charged and increases to a certain value.

At this timing, as in the equivalent circuit of FIG. 4, the snubber capacitor C3 is charged with the current I _LP of excess energy accompanying the switching off of the primary winding Np to absorb the energy. Snubber capacitor C3 at this time
The charging voltage VC3 of

[0059]

(Equation 6)

Is given by

Next, referring to FIG. 3, I is calculated based on the following minimum ON width t _MIN.
At the timing when the switch element 5 of the PD 3 is turned on, the energy absorbed by the snubber capacitor C3 as shown in the equivalent circuit of FIG. I _L1 flows according to the following equation.

[0062]

(Equation 7)

At this time, the current I _L1 is, as shown in the above equation (2), four times the minimum on-time t _MIN of the IPD 3 as L 1, C 3
Becomes maximum when the resonance period is equal to the resonance period t _LC .

Subsequently, at the timing when the switch element 5 is turned off, the exciting energy stored in the snubber inductance L1 is changed to the diodes D4 and D4 as shown in FIG.
It is regenerated through 3 to the input side. The regenerative power at this time is I
If the switching frequency by PD is f

[0065]

(Equation 8)

Is given by

Thereafter, the operation at the same timing (1) to (4) is repeated, and extra energy for switching of the flyback transformer as shown in FIG.
It is possible to obtain an output characteristic capable of reducing the inverter output to zero with a control input having a minimum ON width without providing a bleeder resistor on the output side.

Next, a DC power supply according to the present invention using the inverter circuit of FIG. 1 is provided with a rectifying / smoothing circuit for producing an input voltage V _IN input to the inverter circuit of FIG. 1 by rectifying / smoothing an AC power supply. Thus, it can be used as a so-called switching regulator power supply device.

The present invention is not limited to the above embodiment, but includes appropriate modifications without impairing the objects and advantages thereof. Further, the present invention is not limited by the numerical values according to the above embodiment.

[0070]

As described above, according to the present invention, in a so-called flyback type inverter circuit using a flyback transformer, an LC snubber circuit in which a capacitor and an inductance are connected in series is provided on the primary side thereof.
In an IPD as a control circuit used for switching drive of a flyback transformer, extra energy appearing in the inverter output is used during operation with a minimum on-width to secure the minimum power during idling, that is, during no-load operation.
By regenerating to the primary side by the snubber circuit, it is possible to reduce the inverter output to zero in the operation state of the minimum on-width at the time of no load, and to maintain the linearity of the inverter control characteristics.

Further, since the energy is regenerated to the input side without consuming unnecessary energy in the bleeder resistor as in the related art, the internal power consumption in the no-load state in the standby state on the load side can be reduced. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing output characteristics of the inverter of FIG. 1;

FIG. 3 is a time chart showing operation waveforms of each unit in FIG. 1;

FIG. 4 is an equivalent circuit diagram of an operation at each timing of FIG.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is an explanatory diagram showing inverter output characteristics of the conventional example of FIG. 5;

[Explanation of symbols]

1: flyback transformer 2: rectifying and smoothing circuit 3: IPD (control circuit) 4: PWM control circuit 5: switch element 6: auxiliary power supply circuit 7: LC snubber circuit Np: primary winding Ns: secondary winding N _SUB : Auxiliary winding D1, D2: Rectifying diode D3, D4: Backflow blocking diode C1, C2: Smoothing capacitor C3: Snubber capacitor L1: Snubber inductance L2: Leakage inductance Lp: Primary winding inductance Ls: Secondary winding inductance L _sub : auxiliary winding inductance R1: bias resistance (for idling current) VR1: variable resistance (for input current control)

Claims (6)

[Claims] A primary winding, a secondary winding, and an auxiliary winding;
A switching drive flyback transformer, a rectifying and smoothing circuit including a rectifying diode and a smoothing capacitor for rectifying and smoothing a switching output of the secondary winding and supplying a DC output voltage to a load, a switching element and a pulse width thereof. A control circuit, and when a switch is turned on, a current flows through the primary winding to store energy;
A control circuit for transferring the energy accumulated in the primary winding when the switch is turned off to the smoothing capacitor through a secondary winding, and controlling a pulse width of the switch element so that a DC output voltage is constant; An auxiliary power supply circuit that inputs a DC auxiliary power supply and a control current source generated from the output voltage to the control circuit,
In the inverter circuit having: a parallel connection of a switch element of the control circuit connected in series to the primary winding, and an LC snubber circuit having a predetermined LC resonance cycle in which a capacitor and an inductance are connected in series. Inverter circuit characterized. 2. The inverter circuit according to claim 1, wherein
The control circuit has a minimum ON width such that a switch-on pulse width in the pulse width control of the switch element does not further decrease, and sets an LC resonance cycle of the LC snubber circuit to:
An inverter circuit, wherein the minimum ON width of the control circuit is set to 2 to 20 times. 3. The inverter circuit according to claim 2, wherein
An inverter circuit, wherein an LC resonance cycle of the LC snubber circuit is preferably set to be equal to four times a minimum ON width of the control circuit. 4. The inverter circuit according to claim 1, wherein the snubber circuit absorbs flyback energy of the primary winding by a capacitor when the switch is off, and a capacitor when the switch is on next. The energy stored in the inductor is transferred to the inductance, and the energy stored in the inductance at the next switch-off timing is transferred to the above-mentioned 1.
An inverter circuit characterized by regeneration to the next winding side. 5. The inverter circuit according to claim 1, wherein the capacitance of the capacitor of the snubber circuit is set to a predetermined withstand voltage of the switch element when a voltage applied to the switch element when the switch is turned off. An inverter characterized in that the value of the inductance of the snubber circuit is set so that the current flowing through the switch element when the switch is turned off does not exceed a prescribed limit current of the switch element. circuit. 6. A DC power supply device comprising: the inverter circuit according to claim 1; and a rectifying / smoothing circuit for inputting a rectified / smoothed DC voltage from an AC power supply to the inverter circuit. .