JPH10285922A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the rectifying efficiency of a power unit which converts AC power into DC power by synchronously rectifying the AC power and supplies the DC power to a load at a high level without changing the basic circuit configuration of the unit. SOLUTION: A power unit is provided with a transformer 10, a switching means 12 which supplies AC power to the primaryside winding of the transformer 10 by intermittently supplying its DC power input by means of an incorporated switching element, a snubber circuit 14 which forms an annular resonance circuit together with the primary-side winding of the transformer 10 during the breaking period of the switching element, and a rectifying means 16 which incorporates a plurality of elements alternately conducted in accordance with the polarity of the voltage induced in the secondary-side winding of the transformer 10 and generates DC power by rectifying the AC power through the elements. The resonance period T of the resonance circuit is set to a value that meets the inequality of 2τ<=T<=4τ (where, represents the duration of the breaking period τ of the switching element).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for converting AC power into DC power by synchronous rectification and supplying the DC power to a load.

[0002]

2. Description of the Related Art A power supply device for supplying DC power to information equipment and communication equipment employs a switching regulator system for compensating for voltage fluctuations due to load fluctuations and supplying stable DC power. In recent years, in such a power supply device, the loss has been reduced by using a switching element such as a power transistor or an FET capable of increasing the switching speed and reducing the conduction loss.

FIG. 6 is a diagram showing a configuration of a conventional power supply device. In the figure, one end of a primary winding N1 of a transformer T is connected to the anode of the input power supply E, and the other end of the primary winding N1 of the transformer T is connected to the drain of the main switch Q1. The source of the main switch Q1 is connected to the cathode of the input power supply E, and the gate of the main switch Q1 is connected to the output of the control circuit 100.

[0004] One end of the secondary winding N2 of the transformer T has a gate of a rectifier-side synchronous rectifier (FET) Q2, a drain of a commutation-side synchronous rectifier (FET) Q3, and a choke coil L.
To one end. The other end of the secondary winding N2 of the transformer T is connected to the drain of the rectifier-side synchronous rectifier Q2 and the gate of the commutation-side synchronous rectifier Q3. The source of the rectifier side synchronous rectifier Q2 and the source of the commutation side synchronous rectifier Q3 are connected to one end of the load and the capacitor C2 and the control circuit 10.
0 is connected to one input. The other end of the choke coil L is connected to the other end of the load and the capacitor C2 and the control circuit 10.
0 is connected to the other input.

In the power supply device having such a configuration, when the main switch Q1 is turned on, electromagnetic energy is accumulated in the primary winding N1, and DC power supplied from the input power supply E is supplied to the secondary side. On the secondary side of the transformer T, when the main switch Q1 is ON, the rectifier-side synchronous rectifier Q2 is biased by the power supplied from the primary winding N1. When the rectifier-side synchronous rectifier Q2 is biased in this manner, a current flows to the load via the choke coil L on the secondary side of the transformer T. Further, the electromagnetic energy is stored in the choke coil L, and the capacitor C2 is charged.

On the other hand, when the main switch Q1 is turned off, the commutation side synchronous rectifier Q3 is biased on the secondary side of the transformer T. Thus, the commutation side synchronous rectifier Q3
Is biased, on the secondary side of the transformer T, the electromagnetic energy stored in the choke coil L is released via the commutation-side synchronous rectifier Q3, and a current flows to the load.
That is, on the secondary side of the transformer T, voltages having different polarities are induced alternately, and the rectification-side synchronous rectifier Q2 and the commutation-side synchronous rectifier Q3 are alternately turned on to perform rectification.

The control circuit 100 includes a main switch Q1
And a high-frequency pulse signal, and constantly monitors the voltage applied to the load. When the control circuit 100 recognizes that the DC voltage applied to the load has changed as a result of such monitoring, the control circuit 100 performs PWM control for adjusting the duty ratio of the pulse signal, thereby controlling the voltage. Compensate for fluctuations.

[0008]

However, in such a conventional example, a high-speed switching operation is performed to increase the switching loss, and the ON period of the main switch Q1 is increased or decreased by the PWM control. Since the electromotive force of the input power supply E fluctuates, the electromagnetic energy stored in the primary winding N1 is not constant.

Therefore, while the main switch Q1 is in the OFF state, the bias voltage to be applied to the commutation side synchronous rectifier Q3 is not maintained until the main switch Q1 is turned on, and the rectification efficiency is reduced. There was a problem. Therefore, an object of the present invention is to provide a power supply device capable of maintaining a high rectification efficiency without changing a basic circuit configuration.

[0010]

FIG. 1 is a block diagram showing the principle of the first aspect of the present invention. According to the first aspect of the present invention, the input of DC power is interrupted by a transformer and a built-in switching element, and switching means for supplying AC power to a primary winding of the transformer is provided.
And a snubber circuit 14 that forms an annular resonance circuit together with the primary winding of the transformer 10 during a period when the switching element built in the switching means 12 is cut off.
And a plurality of elements which alternately conduct according to the polarity of the voltage induced in the secondary winding of the transformer 10, and are supplied from the switching means 12 and transmitted by the transformer 10. A rectifier 16 for rectifying power through these elements to generate DC power, wherein a resonance cycle T of a resonance circuit formed by the snubber circuit 14 is determined by a switching element built in the switching means 12. 2τ for the length τ of the blocking period
It is characterized by being set to a value that satisfies the inequality of ≦ T ≦ 4τ.

FIG. 2 is a block diagram showing the principle of the second aspect of the present invention. The invention according to claim 2 is a transformer
And a switching element for interrupting the input of DC power, and the length of the period τ during which the switching element is interrupted.
Switching means 22 for supplying a desired level of AC power to the winding on the primary side of the transformer 20 by increasing or decreasing the voltage of the primary winding of the transformer 20 during a period in which the switching element built in the switching means 22 is cut off. A snubber circuit 24 that forms an annular resonance circuit with the winding of the transformer 20 and a plurality of elements that alternately conduct according to the polarity of the voltage induced in the secondary winding of the transformer 20. A rectifying unit 26 that rectifies AC power supplied from the switching unit 22 and transmitted by the transformer 20 through these elements to generate DC power.
A period during which the switching element incorporated in the switching means 22 is cut off, and the length of the period τ
On the other hand, there is provided a control means 28 for setting the resonance period T of the resonance circuit formed by the snubber circuit 24 to a value satisfying the inequality of 2τ ≦ T ≦ 4τ.

(Operation) In the power supply device according to the first aspect of the present invention, when the switching element built in the switching means 12 becomes conductive, DC power is supplied to the secondary side. On the other hand, when the switching element is shut off, the transformer 1
Since the electromagnetic energy stored in the primary winding of the transformer 10 is released, the current flowing through the primary side of the transformer 10 monotonously decreases.

In the period in which the switching element is cut off, a resonance circuit is formed on the primary side of the transformer 10 by the snubber circuit 14, so that the waveform of the voltage induced on the primary side and the secondary side of the transformer 10 is as described above. It becomes a sinusoidal wave that resonates in proportion to the current change rate and in synchronization with the resonance cycle T of the resonance circuit. That is, the waveform of such a voltage is
T / 2 is based on the time when the switching element is turned off.
It becomes a sine wave shape whose polarity is inverted every time.

Therefore, if an inequality of 2τ ≦ T is established between the length τ of the period during which the switching element is shut off and T, the polarity of the voltage induced in the secondary winding of the transformer 10 is It does not reverse until the element conducts. When the inequality T ≦ 4τ is satisfied between τ and T, a period in which the switching element is shut off is maintained until the polarity of the current flowing to the primary side of the transformer 10 is reversed. Magnetic saturation is avoided.

Therefore, when T is set to a value that satisfies the inequality of 2τ ≦ T ≦ 4τ, the voltage induced in the secondary winding of the transformer is surely inverted in synchronization with the switching element. The rectifying means 16 can rectify the AC voltage efficiently through the elements that are alternately turned on in response to the inversion of the voltage.

In the power supply device according to the second aspect of the present invention, when the switching element incorporated in the switching means 22 conducts, DC power is supplied to the secondary side. On the other hand, when the switching element is cut off, the electromagnetic energy accumulated in the primary winding of the transformer 20 is released, so that the current flowing through the primary side of the transformer 20 monotonously decreases.

In the period in which the switching element is cut off, a resonance circuit is formed on the primary side of the transformer 20 by the snubber circuit 24. Therefore, the waveform of the voltage induced on the primary side and the secondary side of the transformer 20 is as described above. It becomes a sinusoidal wave that resonates in proportion to the current change rate and in synchronization with the resonance cycle T of the resonance circuit. That is, the waveform of such a voltage is
T / 2 is based on the time when the switching element is turned off.
A sine wave whose polarity is inverted every time is shown.

The control means 28 adjusts the resonance period T to 2τ according to the increase or decrease of the length τ of the period during which the switching element is cut off.
It is set to a value that satisfies the inequality of ≦ T ≦ 4τ. Therefore, when the inequality of 2τ ≦ T holds, the polarity of the voltage induced in the secondary winding of the transformer 20 does not reverse until the switching element is turned on.

When the inequality T ≦ 4τ holds, the period during which the switching element is cut off is maintained until the polarity of the current flowing to the primary side of the transformer 20 is reversed. Saturation is avoided. Therefore, even if the level of the AC power is adjusted by increasing or decreasing τ, T is set to a value that satisfies the inequality of 2τ ≦ T ≦ 4τ. The AC voltage can be efficiently rectified through the elements that alternately conduct according to the inversion of the voltage induced in the winding.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 3 is a diagram showing a configuration of an embodiment corresponding to the first aspect of the present invention. In the figure, components having the same functions as those of the conventional example shown in FIG. 6 are denoted by the same reference numerals, and the description of the configuration is omitted here.

The difference between this embodiment and the conventional example shown in FIG. 6 is that the snubber circuit 20 is provided on the primary side of the transformer T.
This is the point where 0 has been added. The snubber circuit 200 includes two diodes (diodes Da1 and Da2) connected in the opposite direction to the polarity of the input power supply E, an inductance La connected in series between these diodes, the inductance La and the diode Da1. , And a capacitor C1 connected between the drain of the main switch Q1.

As for the correspondence between the principle block diagram shown in FIG. 1 and this embodiment, the transformer 10 corresponds to the transformer T, and the switching means 12 generates a pulse signal in the main switch Q1 and the control circuit 100. The snubber circuit 14 corresponds to the snubber circuit 200, and the rectifier 16 corresponds to the rectifier-side synchronous rectifier (FET) Q2, the commutation-side synchronous rectifier (FET) Q3, the choke coil L, and the capacitor C2.

FIG. 4 is a diagram showing operation waveforms of the embodiment according to the first aspect of the present invention. In the figure, T _ON indicates a period in which the main switch Q1 is in an ON state, and T _ON
OFF indicates a period of the OFF state. Hereinafter, FIGS. 3 and 4
The operation of the embodiment according to the first aspect will be described with reference to FIG.

On the primary side of the transformer T, the main switch Q1
Is turned on, DC power is supplied to the secondary side by the primary winding N1 and the primary side winding N1 is excited. In such a process, the capacitor C1 is once charged and then grounded via the main switch Q1. Therefore, the diode Da2
Is conducted, an annular circuit composed of the capacitor C1 and the inductance La is formed.

When the main switch Q1 is turned off, the surge voltage is absorbed by the primary winding N1, the capacitor C1, and the diode Da1. Further, the diode Da1 conducts, and LC oscillation is generated by the primary winding N1 and the capacitor C1, and the voltage V _{DS of the} main switch Q1 is changed.
Changes in a sine wave shape as shown in FIG. FIG. 4 shows a case where the half cycle of the sine wave coincides with the T _OFF period.

Furthermore, one in the primary winding N1, as shown in FIG. 4, flows alternating current I _L for the time t2 as one cycle from the time t0. Further, the waveform of the voltage V ₂ induced in the secondary side of the transformer T, the T _OFF period, as shown in FIG. 4, the drain of the main switch Q1 - voltage V _DS between the source
The signal has a phase opposite to that of the waveform.

Such a voltage V ₂ is applied as a bias voltage for the commutation-side synchronous rectifier Q3. Therefore, a period in which the waveform of the voltage V ₂ is less than 0 [V] (here,
This corresponds to a half cycle of LC oscillation. ) Is set longer than the T _OFF period (hereinafter, referred to as “condition 1”), so that the bias voltage is reliably applied to the commutation side synchronous rectifier Q3 until time t2.

In general, a resonance frequency f due to LC vibration is given by f = 1 / (2π (LC) ^1/2 ) (1). Therefore, assuming that the capacitance of the capacitor C1 and the inductance of the primary winding N1 are Ca and Lm, respectively, the period T of LC oscillation is T = 2π (LmCa) ^1/2 (2).

Here, for simplicity, it is assumed that Ca includes the coupling capacity with the secondary side of the transformer T. Here, if Lm is changed Ca was assumed to be constant, the waveform of the voltage V ₂ changes as shown in FIG. Therefore, in order to satisfy the above-mentioned “condition 1”, it is necessary to satisfy T / 2 ≧ T _OFF (3).

The transformer T is magnetically saturated when the direction of the current flowing through the primary winding N1 does not reverse during the T _OFF period. Therefore, in order not to saturate the transformer T, the period from the time t1 to the time when the voltage of the main switch Q1 becomes maximum (corresponding to a quarter cycle of the LC oscillation here) is shorter than the T _OFF period. (Hereafter,
Here, “condition 2” is set. )There is a need.

That is, in order to satisfy such “Condition 2”, it is necessary to satisfy T / 4 ≦ T _OFF (4). Here, by substituting equation (2) into equations (3) and (4), Ca ≧ (T _OFF / π) ² / Lm (5) Ca ≦ (2T _OFF / π) ² / Lm (6) is obtained.

From the expressions (5) and (6), "condition 1"
And the range of Ca that satisfies “Condition 2” is represented by (T _OFF / π) ² / Lm ≦ Ca ≦ (2T _OFF / π) ² / Lm (7) That is, when the capacitance of the capacitor C1 constituting the snubber circuit 200 satisfies Expression (7), the bias voltage is continuously supplied to the commutation side synchronous rectifier Q3 until the main switch Q1 is turned on without saturating the transformer T. be able to.

Therefore, the rectification can be performed efficiently by alternately conducting the rectifier-side synchronous rectifier Q2 and the commutation-side synchronous rectifier Q3. In the present embodiment, the present invention is applied to a single-stone forward converter. However, the present invention may be applied to a multi-stone converter or a boost converter, and any converter as long as it is a switching regulator type converter. It is also possible to apply to.

In the present embodiment, if a snubber circuit 200 having a configuration as shown in FIG. 3 is applied, and a resonance circuit including the primary winding N1 is formed when the main switch Q1 is in the OFF state, Any configuration of snubber circuit may be applied. FIG. 5 is a diagram showing the configuration of an embodiment according to the second aspect of the present invention. In the figure, components having the same functions as those of the embodiment shown in FIG. 3 are denoted by the same reference numerals, and the description of the configuration is omitted here.

The difference between the present embodiment and the embodiment shown in FIG. 3 is that the capacitor C1 is composed of a variable capacitance element, and the control circuit 1 is connected to the control terminal of the variable capacitance element.
The corresponding output of 00 is at the connected point. FIG.
In this embodiment, the transformer 20 corresponds to the transformer T, the switching means 22 corresponds to the main switch Q1 and the function of generating the pulse signal of the control circuit 100, and the snubber circuit 24 Corresponds to the snubber circuit 200, and the rectifying means 26 includes a rectifier-side synchronous rectifier (FET) Q2 and a commutation-side synchronous rectifier (FET) Q2.
3, corresponding to choke coil L and capacitor C2,
The control means 28 corresponds to a circuit for performing PWM control in the control circuit 100 and a circuit for controlling the capacitance of the capacitor C1.

The operation of the embodiment according to the second aspect of the present invention will be described below with reference to FIG. Control circuit 10
At 0, the DC voltage applied to the load is monitored as in the conventional example, and when it is recognized that the DC voltage has changed,
The duty ratio of the pulse signal is adjusted by the PWM control.

When the duty ratio of the pulse signal is adjusted in this manner, the control circuit 100 obtains the T _OFF period based on the adjusted duty ratio, and sets the capacitance of the capacitor C1 to satisfy the above equation (7). Change to a value. Therefore, according to the present embodiment, the voltage can be flexibly stabilized with respect to the fluctuation of the load, and the rectification efficiency is reliably maintained at a high level.

In the present embodiment, the case where the capacitance Ca of the capacitor C1 is changed has been described. However, the variable inductance element directly connected to the primary winding N1 is provided to change the inductance Lm, thereby optimizing the LC oscillation period. It is also possible to measure. Further, in the present embodiment, the length of the T _OFF period is adjusted by applying the PWM control, but the length of the T _OFF period may be adjusted by the PFM control.

[0039]

As described above, in the first aspect of the present invention, the voltage induced in the secondary winding of the transformer is synchronized with the intermittent switching of the switching element while avoiding magnetic saturation of the transformer. Therefore, the AC voltage can be efficiently rectified through the elements that are alternately turned on in response to the inversion of the voltage.

According to the second aspect of the present invention, even when the level of the AC power is adjusted by increasing or decreasing the length of the period during which the switching element is cut off, the AC power is controlled by the first aspect. The rectification can be performed efficiently as in the invention of the first aspect. Therefore, in the power supply device to which these inventions are applied, by providing the snubber circuit forming the resonance circuit during the period when the switching element is cut off, the efficiency of the synchronous rectification can be improved without changing the basic configuration of the existing circuit. It is definitely enhanced.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the invention according to claim 1;

FIG. 2 is a principle block diagram of the invention according to claim 2;

FIG. 3 is a diagram showing a configuration of an embodiment corresponding to the invention described in claim 1;

FIG. 4 is a diagram showing operation waveforms of the embodiment according to the first aspect of the present invention.

FIG. 5 is a diagram showing a configuration of an embodiment corresponding to the invention described in claim 2;

FIG. 6 is a diagram showing a configuration of a conventional power supply device.

[Explanation of symbols]

 10, 20, T transformer 12, 22 Switching means 14, 24, 200 Snubber circuit 16, 26 Rectification means 28 Control means E Input power supply N1 Primary winding Q1 Main switch Da1, Da2 Diode La Inductance C1 Capacitor 100 Control circuit N2 Two Secondary winding Q1 Rectifier synchronous rectifier (FET) Q2 Commutator synchronous rectifier (FET) L Choke coil C2 Capacitor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshikatsu Saito 1-17-3 Sakado, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Inside Fuji Denso Co., Ltd.

Claims (2)

[Claims] A switching means for intermittently inputting DC power by a transformer and a built-in switching element to supply AC power to a primary winding of the transformer; and a switching element built in the switching means. And a snubber circuit that forms an annular resonant circuit together with the primary winding of the transformer during a period in which the transformer is turned off, and a plurality of alternately conducting currents depending on the polarity of the voltage induced in the secondary winding of the transformer. Rectifying means for rectifying the AC power supplied from the switching means and transmitted by the transformer through these elements, to generate DC power, and comprising the snubber circuit. The resonance period T of the resonance circuit is 2τ ≦ T ≦ 4τ with respect to the length of the period τ during which the switching element built in the switching means is cut off. A power supply device set to a value satisfying the following inequality. 2. A transformer and a switching element for intermittently inputting DC power.
Switching means for supplying a desired level of AC power to the primary winding of the transformer by increasing or decreasing the length of the period τ during which the switching element is turned off; and a switching element built in the switching means being turned off. A snubber circuit that forms an annular resonance circuit together with the primary winding of the transformer during a period of time, and a plurality of elements that alternately conduct according to the polarity of the voltage induced in the secondary winding of the transformer. And a rectifier for rectifying AC power supplied from the switching means and transmitted by the transformer via these elements to generate DC power; and a switching element built in the switching means is turned off. Is detected, and for the length τ of the period,
A power supply device comprising: a control unit that sets a resonance period T of a resonance circuit formed by the snubber circuit to a value satisfying an inequality of 2τ ≦ T ≦ 4τ.