JPH1155947A - Power unit and air conditioner using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To materialize the security in voltage regulation with light load and the reduction of loss in a switching element, while maintaining the control effect on switching noise. SOLUTION: A switching element 5 is turned on and turned off by a predriver 17, and the instant of the OFF of the switching element 5, the power of the quantity corresponding to the load is transmitted from a main winding 2 to secondary windings 4a-4g with a transformer 1. After ON of the switching element 5, a feedback circuit 11 monitors the secondary voltage VR, and sets the OFF timing of the switching element 5. That is, at the time of heavy load, a microcomputer 19 selects the voltage VB of the base winding 3 and detects the timing of the secondary current IR becoming zero, and turns on the switching element 5. Moreover, at the time of light load, it selects the output of an off time fixing circuit 18, and turns on the switching circuit 5 after a certain time since the switching element 5 is turned off.

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 provided with a switching element and an air conditioner using the same, and more particularly to a power supply device which controls the switching element to stabilize a power supply voltage. The present invention relates to an air conditioner using the same.

[0002]

2. Description of the Related Art In order to obtain a DC voltage by rectifying and smoothing an AC power supply voltage, and to obtain a stable power supply voltage, a power supply device using a switching element has been conventionally known. This is to monitor a power supply voltage to be generated and output, and to control ON / OFF of a switching element so that the power supply voltage is stabilized. For example, when such a power supply device is used for a variable load device such as an air conditioner, even if the load fluctuates, the power supply voltage of the device can be stabilized by controlling the ON / OFF of the switching element. it can.

FIG. 11 is a circuit diagram showing an example of a conventional power supply device, wherein 1 is a switching transformer, 2 is a main winding, 3 'is a base winding, 4a to 4e are secondary windings, and 5 is a switching winding. An element, 6 is a capacitor, 7 is a resistor, 8 is a capacitor, 9 is a resistor, 10 is a diode, 11 is a feedback circuit, 12 is a pre-driver, and 13a and 13b are terminals.

In FIG. 1, a main winding 2 of a switching transformer 1 and a switching element 5 are connected in series between terminals 13a and 13b, and between a collector and an emitter of the switching element 5 (ie, the switching element 5). ), A noise suppression damper circuit comprising a resistor 7 and a capacitor 6 is connected thereto, and a noise suppression clamp circuit comprising a diode 10, a capacitor 8 and a resistor 9 in parallel with the main winding 2. Is connected. The damper circuit and the clamp circuit suppress the switching noise of the voltage waveform accompanying the turning on and off of the switching element 5. The damper circuit rounds the jump of the voltage waveform. It functions to cut the jump.

On the other hand, the switching transformer 1 is provided with a base winding 3 'together with a secondary winding for outputting each power supply voltage. One end of the base winding 3' has a diode and a resistor. The other end is connected to the base of the switching element 5 and the other end is connected to the emitter of the switching element 5. And this switching element 5
A pre-driver 12 composed of a transistor is provided between the base and the emitter of the driver, and the on / off of the pre-driver 12 is controlled by a feedback circuit 11.

FIGS. 12A and 12B are diagrams showing current, voltage waveforms and losses at various parts in FIG. 11, wherein FIG. 12A shows the collector current I _C of the switching element 5 and FIG. FIG. 5C shows the voltage V _CE between the collector and the emitter, FIG. 5C shows the loss P generated in the switching element 5, FIG. 5D shows the voltage V _B generated in the base winding 3 ′, and FIG. The secondary current I _R generated in the secondary winding 4e of the switching transformer 1 is shown.

Next, the operation of this conventional example will be described with reference to FIG.

An input DC voltage Vd is applied between the terminals 13a _and 13b, and when the switching element 5 is off, a voltage V _CE is applied between the collector _{and the} emitter of the switching element 5 and the collector current I _C Is zero, but when the induced voltage V _B of the base winding 3 ′ of the switching transformer 1 becomes a predetermined value or more, the switching element 5 is turned on, the collector-emitter voltage V _CE becomes zero, and the collector current I _C becomes lower. Flows.

Here, a period t ₁ in FIG. 12 is an enlarged view of the moment when the switching element 5 is turned on.
In this period t ₁ , the capacitor 6 of the damper circuit (also referred to as a snubber capacitor) during the off period of the switching element 5.
Is discharged instantaneously via the switching element 5 and the diode 10 of the clamp circuit is discharged.
Current flows through the capacitance of the (clamp diode), and the current flows through the switching element 5 in addition to the current (indicated by a broken line) flowing through the main winding 2 of the switching transformer 1. The current I _C becomes very large as shown. The damper circuit composed of the capacitor 6 and the resistor 7 is necessary for suppressing the switching noise in the switching element 5, and because of this, the damper circuit has
Such a large collector current I _C flows at the moment when the switching element 5 is turned on.

After that, the ON period t of the switching element 5
₂ increases the collector current I _C is substantially straight in, but the feedback circuit 11 is turned on to pre-driver 12, the switching element 5 is turned off. Period t in FIG.
_3, there is shown an enlarged period of the instantaneous turning off the switching element 5, the collector current I _C of the switching element 5 at the time t _3, therefore, the current flowing through the main winding 2 of the switching transformer 1 It suddenly changes to 0. Thus, a voltage is induced in the secondary winding of the base winding 3 'also switching transformer 1, including, by flowing the secondary current from these secondary windings in the next period t _4, the power to the secondary side Will be supplied. This secondary current decreases with supply to the load. On the secondary winding side, the secondary current is rectified and smoothed to generate a required power supply voltage.
FIG. 12E shows, as an example, the secondary current I _R on the secondary winding 4e side.

When this power supply device is used in an air conditioner, a power supply voltage for an indoor unit, for example, an indoor fan, is generated on the secondary winding 4a side, and the secondary windings 4b to 4d are generated.
Assuming that the power supply voltage for the inverter in the outdoor unit is generated and the power supply voltage for controlling the outdoor unit is generated on the secondary winding 4e side, the power supply voltage for control is, for example, 12
The feedback circuit 11 applies feedback to the primary side of the switching transformer 1 so as to be stabilized at V.

[0012] When the switching element 5 is turned off, the switching transformer 1, the voltage applied to the current flowing in the main winding 2 at that time (approximately equal to the collector current I _C of the switching element 5) in the main winding 2 Is distributed and supplied from the main winding 2 to each of the secondary windings 4a to 4d. This distribution is based on the respective secondary windings 4a-4
It is determined according to the magnitude of the load connected to d. Variations in the loads connected to the secondary windings 4a to 4d have almost the same tendency even though there is a difference between these values.

By the way, the load connected to the secondary winding 4a for generating the power supply voltage of the indoor unit occupies a large part of the total load, and therefore, this load fluctuation is larger than other loads. Therefore, the secondary winding 4a and the power supply voltage V _R
When the load on the secondary winding 4a side becomes large (that is, when the load becomes heavy), the electric power from the main winding 2 is supplied to the secondary winding 4a side. And more power is relatively distributed to the secondary winding 4d. For this reason, the winding voltage induced on the secondary winding 4d side drops, and the control voltage V _R obtained by rectifying and smoothing the winding voltage drops.

Therefore, the feedback circuit 11 detects the tendency of the control voltage V _R to decrease, and delays the timing of turning on the pre-driver 12 and thus the timing of turning off the switching element 5. Thus, a longer period t ₂ in FIG. 12, the amount of power supplied from the main winding 2 the secondary winding 4a~4e by increasing the current flowing through the main winding 2 when the switching element 5 is turned off increase.

Conversely, when the load on the secondary winding 4a side is reduced (ie, when the load is reduced), the power distributed to the secondary winding 4e side relatively increases, and the secondary winding 4e increases. 4d
Winding voltage induced in the side is increased, the control voltage V _R obtained this by rectifying and smoothing rises. Feedback circuit 11 detects the rise of the control voltage V _R,
The timing of turning off the switching element 5 is advanced.
Thus, the shorter the period t ₂ in FIG. 12, 4 a to 4 e secondary winding from the main winding 2 by reducing the current flowing through the main winding 2 when the switching element 5 is turned off
Reduce the amount of power supplied to the

On the other hand, the voltage V _B of the base winding 3 ′ of the switching transformer 1 turns on the pre-driver 12 (at this time, the switching element 5 turns off) and inverts the polarity to negative (then, the pre-driver 12 turns off). Even if the driver 12 is turned off,
The polarity does not reverse again), the switching element 5
When the power is supplied from the main winding 2 at the moment when the power supply is turned off (period t3), the power supply reverses in the negative direction, but starts to increase as the load current decreases. Then, when the voltage V _B reaches a predetermined positive level when the the secondary current I _R is zero, will be turned on takes base bias to the switching element 5. The feedback circuit 11 controls the off timing after the switching element 5 is turned on in accordance with the load on the secondary winding 4 side.

Therefore, the periods t ₁ , t ₂ , t ₃ ,
The total period of t ₄ T ₀ = a _{(t 1 + t 2 + t} 3 + t 4) as one cycle, the switching operation of the switching element 5 is to repeat this cycle, these periods t _2, t ₄ the secondary winding Since the period changes according to the load on the line 4a (hereinafter simply referred to as a load), the period T ₀ , and therefore the switching frequency f ₀ (= 1 / T ₀ ) of the switching element 5 also changes.
That is, when the load is large, the switching frequency f ₀ is low, and when the load is small, the switching frequency f ₀ is high.

In FIGS. 12A and 12E, the waveform I _C ′ of the collector current I _C shown by the broken line and the waveform I _R ′ of the secondary current I _R shown by the broken line in the period t ₂ are shown by solid lines. This is when the load is lighter than the load indicated by.

On the other hand, assuming that the inductance of the main winding 2 is L, the current I flowing through the main winding 2 immediately before the switching element 5 is turned off has a gradient of Vd / L, so that I = (Vd / L) × t ₂ . Assuming that the same current I flows through the main winding 2 with a constant load, when the input DC voltage Vd is low,
Period t ₂ is longer, when a high input DC voltage Vd, the period t ₃ becomes short. Here, since the period t ₂ and the period t ₄ are in a substantially proportional relationship, when the input DC voltage Vd is low, the switching frequency f _{0 of the} switching element 5
Becomes lower and the input DC voltage Vd is higher, the switching frequency f ₀ of the switching element 5 becomes higher.

As described above, the wider the fluctuation range of the load and the wider the fluctuation range of the input DC voltage Vd, the wider the fluctuation range of the frequency of the switching element 5.

Normally, when the input DC voltage Vd is minimum and the load is maximum, the switching frequency f
₀ is the minimum. Since the power at this time is very large, high-power noise is generated due to, for example, the windings of the switching transformer 1 oscillating. For this reason, the minimum switching frequency f _0min is limited to the human audible frequency limit. It is necessary to set so as not to fall below 20 kHz. Also, the maximum switching frequency f _0max of the switching element 5 is, during extreme _discussion , the period t
Assuming that ₂ and t ₄ are almost 0 (extremely light load state), the period is determined by T ₀ = t ₁ + t ₃ .

As described above, the required maximum switching frequency f _0max is determined from the fluctuation range of the input DC voltage Vd and the fluctuation range of the load, and the periods t ₁ and t ₃ must be designed accordingly.

[0023]

As described above, in the prior art, when the rate of change of the load is large, the switching frequency becomes high at a light load, but when operating at a high switching frequency, the following occurs. Problems arise.

First, as a first problem, if the load becomes too light, it may be necessary to drive at a switching frequency higher than the highest achievable switching frequency. In such a case, the switching frequency cannot be naturally increased to the frequency required for the load, and excessive power is supplied to the load. For this reason, the load can take in only a small load current corresponding to the supplied power, and the control voltage rises by that amount, making it impossible to secure regulation.

FIG. 13A shows a change in the switching frequency f ₀ with respect to the load current. As described above, the switching frequency f ₀ increases as the load decreases. Here, at the set maximum load, the switching frequency f _{0 is set} to the above 20 kHz.
z, the minimum load (for example, load =
0), the maximum switching frequency f _0max is determined.
As described above, when the load becomes lighter, the switching frequency f ₀ cannot follow the switching load, and the switching element 5 (FIG. 11) operates at a frequency lower than the switching frequency corresponding to the load. (That is, the period T ₀ (= t ₁ + t ₂ + t ₃ + t ₄ ) in FIG. 12 becomes longer than desired), and excessive power is supplied to the load. In FIG. 13, a load variation range including such a load region is expressed as “light load”, and a load region heavier than this is expressed as “heavy load”.

FIG. 13B shows the voltage regulation (ie, the switching frequency f ₀ ) shown in FIG.
In the case of FIG. 11, the output voltage on the secondary side indicates, for example, the control voltage on the side of the secondary winding 4a), and when there is a heavy load, there is no excess power. However, in the case of a light load in which the supply power is excessive, it indicates that the voltage regulation is increasing.

As described above, in the conventional power supply device shown in FIG. 11, it is difficult to ensure the regulation under a light load. In particular, in a home air conditioner, since the power supply of the electric equipment of the outdoor unit needs multiple outputs,
When the conventional power supply shown in FIG. 11 is used, the control voltage without feedback generally increases at light load, and even if feedback is applied, problems such as intermittent oscillation occur. there's a possibility that.

The second problem is that the switching loss increases.

The switching loss in the switching element 5 in FIG. 11 is, as shown in FIG. 12C, the transiently changing collector current I _C and the collector current IC during the period t ₁ when the switching element 5 is turned on. Emitter voltage V
_The on-loss P _on generated by the product of _CE and the product of the collector current I _C increasing and the collector-emitter voltage V _CE slightly generated during the period t ₂ during which the switching element 5 is on. The generated saturation loss P _sat , the transiently changing collector current I _C and the collector current IC during the period t ₃ at the moment when the switching element 5 is turned off.
Off loss P generated by the product of emitter voltage V _CE
There is _off .

By the way, at the time of light load, as shown by the broken line in FIG.
₂ is shorter, the collector current I _C during that period is smaller, and the value of the collector current at the moment when the switching element 5 is turned off is also smaller. Therefore, the saturation loss P _sat and the off loss P _off are smaller. Become.

On the other hand, in the period t ₁ at the moment when the switching element 5 is turned on, the discharge current from the capacitor 6 is added to the current from the main winding 2 of the switching transformer 1 due to the collector current I _{C and the} like of the switching element 5. be those with, this collector current I _C and the on loss P _on by the product of the transient changing the collector-emitter voltage V _CE is generated in the switching element 5, in this case, when the switching element 5 is turned off The charge amount Q stored in the capacitor 6 is expressed as Q = CV, where V is the voltage applied to the capacitor 6 when the switching element 5 is off, and C is the capacitance of the capacitor 6. Here, since the voltage V is proportional to the input DC voltage Vd, the discharge current when discharging the charge amount Q from the capacitor 6 is substantially constant regardless of the load. Accordingly, the ON loss P _on of the switching element 5 during the period t ₁ is substantially constant regardless of the load. Of course, if the input DC voltage Vd is high, the discharge current of the capacitor 6 also increases, and the on-loss _Pon also increases.

[0032] In this manner, the switching element 5, the switching operation thereof, but becomes substantially the constant on loss P _on occurs in the period t ₁ of the moment to its on, the switching frequency f ₀ becomes light load Becomes higher, the on-loss _Pon becomes effective. Then, even when the load becomes light, the on-loss P _on does not change, so that the ratio of the on-loss P _on to the input electric power increases.

In the self-excited switching power supply, when the input voltage increases, the on-period of the switching element (which is proportional to the current) is shortened, so that the switching frequency naturally increases and the loss further increases.

In order to solve the above problems, the following method has conventionally been adopted.

As one of the methods, there is a method in which a dummy resistor is inserted into each output, power is consumed by the dummy resistor at the time of the minimum load, and an apparent rate of load fluctuation is suppressed. According to this method, it is possible to ensure regulation, but even with a minimum load, unnecessary power in function continues to be consumed by the dummy resistor.

As another method, the maximum switching frequency can be increased by minimizing the periods t ₁ and t ₂ in FIG. According to this, the increased amount can be used for feedback of the regulation fluctuation, and even when the load fluctuation range is large, the excessive rise of the voltage on the secondary side can be suppressed.

However, according to this method, the periods t ₁ and t ₃
Is minimized, and d causes switching noise.
V / dt and dI / dt increase, and high-frequency noise increases. Further, by allowing the switching frequency f ₀ to a higher frequency, a harmonic noise component having a frequency n times higher than that is generated. Specifically, dV / dt, d
High-frequency noise due to the I / dt becomes large occurs in TV band and the FM band, the harmonic noise component n times the switching frequency f ₀ will be generated in the AM band.
Therefore, in order to prevent this, countermeasures such as a noise filter are required, which causes problems such as an increase in the number of components, an increase in cost, and an increase in component space.

Further, as another method, a method of reducing the capacity of the snubber capacitor 6 can be considered. However, the snubber capacitor 6 is provided to suppress noise. If the capacitance is reduced, the noise suppressing effect is reduced. That is, in the snubber capacitor 6, there is a trade-off relationship between the reduction of the on-loss P _on of the switching element 5 and the suppression of noise, and it is necessary to reduce the capacitance just to reduce the on-loss P _on. Can not.

An object of the present invention is to solve the above problem, to provide a power supply device capable of ensuring regulation at a light load and effectively reducing losses in a switching element, and an air conditioner using the same. Is to do.

[0040]

In order to achieve the above object, the present invention provides a first means for judging a light load and a heavy load, and a converter based on the judgment of the first means. Second means for fixing the off period of the switching element for turning on and off the output voltage of the circuit at a light load.

According to this, even under a light load, the operation cycle of the switching element becomes longer, the switching frequency becomes lower, and the number of ON times per unit time of the switching element becomes smaller. ON loss is reduced.

Further, according to the present invention, the converter circuit is switchable between a full-wave rectification operation and a voltage doubler rectification operation, and a first means for judging a light load state and a heavy load state; A second means for performing full-wave rectification operation of the converter circuit under light load and performing double voltage rectification operation under heavy load based on the determination of the means, wherein the output voltage of the converter circuit is turned on and off by a switching element. Turn off to supply the power supply voltage to the load.

According to this, when the load is light, the converter circuit performs the full-wave rectification operation, and the output voltage is applied to the capacitor of the damper circuit more than when the converter circuit performs the double voltage rectification operation under the heavy load. Voltage, the discharge current of the capacitor at the moment when the switching element is turned on becomes small, so that the collector current of the switching element at that moment becomes small, and the on-loss at the switching element is reduced. Also, when the output voltage of the converter circuit decreases, the time required for the collector current of the switching element to reach a value corresponding to the load increases, and as a result, the switching frequency of the switching element also decreases, and on average, the switching element On-loss is reduced.

Furthermore, the present invention combines the above, switches the converter circuit between full-wave rectification operation and voltage doubler rectification operation according to the load, and turns off the switching element for turning on and off the output voltage of the converter. The period is fixed at light load.

[0045]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of a power supply device according to the present invention and an air conditioner using the same, wherein 14 is an AC power supply, 15 is a converter circuit, 16 is a switching power supply circuit, and 17 is a pre-driver. , 18 are off-time fixing circuits, and 19 is a microcomputer (hereinafter referred to as a microcomputer). The same reference numerals are given to portions corresponding to those in FIG.

Referring to FIG.
Correspond to the parts shown in FIG.
And a converter circuit 15 for generating an input DC voltage Vd from the AC output of FIG. Here, the converter circuit 15 is configured as a voltage doubler rectifier circuit.
Assuming V, a DC voltage Vd of 280 V is output.

The most different point of the switching power supply circuit 16 from the circuit configuration shown in FIG. 11 is that an off time fixing circuit 18 is provided, and the on timing of the switching element 5 is changed according to the load state on the secondary side of the switching transformer 1. , in which to switch between the output of the output voltage V _B and the off-time fixing circuit 18 of the base winding 3. Such load condition is determined by the microcomputer 19, this determination, the pre-driver 17, the heavy load, and set in accordance with the output voltage V _B of the base winding 3, also in the light load, off-time fixing circuit 1
8 is set according to the output. Off timing of the switching element 5, the feedback circuit 11 when as in the prior art shown in FIG. 11, tends to increase from the specified voltage to the secondary winding 4e side of the output voltage V _R of the fixed Diseases It is set according to the output signal.

The pre-driver 17 sends information indicating the on-timing of the switching element 5 to the off-time fixing circuit 18, and the off-time fixing circuit 18 outputs a signal after a certain period of time after receiving this information, and outputs a signal. Send to When receiving the signal from the off-time fixing circuit 18, the pre-driver 17 turns on the switching element 5.

In FIG. 11, the switching element 5 is shown as a bipolar transistor.
In this embodiment, it is illustrated as an FET. However, it is clear that either may be used.

Further, in this embodiment, the base winding 3
Is opposite to the direction of the base winding 3 'in the conventional example shown in FIG. Therefore, the voltage V _B obtained by the Beth winding 3 has a waveform whose polarity is inverted from that of the voltage shown in FIG. However, in that case, the level is raised as a whole, and
The waveform is similar to the collector-emitter voltage V _CE shown in FIG. When the secondary current I _R becomes zero, the voltage V _B increases in a decreasing tendency, and by detecting the level at that time, it is possible to detect the time when the secondary current I _R becomes zero. it can. The pre-driver 17 detects the timing at which the secondary current I _R becomes 0 from the voltage V _B of the base winding 3 in this way.

Further, for noise suppression,
Snubber capacitor 6 provided in parallel with switching element 5
FIG. 11 shows only the circuit configuration similar to the circuit configuration shown in FIG.
A resistor 7, a capacitor 8, a resistor 9, and a diode 10 may be provided.

Further, when the first embodiment is used as a power supply for an air conditioner, the secondary windings 4a to 4e of the switching transformer 1 have the same power supply as that of the prior art shown in FIG. It is assumed that a voltage is generated. Also,
The secondary winding 4f generates a power supply voltage of another converter for making the power supply voltage of the inverter variable, and the secondary winding 4g is connected to the power supply of the inverter similarly to the secondary windings 4b to 4d. This is for generating a voltage (that is, a power supply voltage of the upper arm and a power supply voltage of the lower arm).

Further, the microcomputer 19 controls the start, stop, and drive of a compressor (not shown), an outdoor fan, an indoor fan, and the like, thereby controlling a load state (ie, a heavy load state or a light load state). Can be determined.

Next, a control operation of this embodiment when this embodiment is used as a power supply device of an air conditioner will be described with reference to a flowchart shown in FIG.

When the AC output is supplied from the AC power supply 14 when the power is turned on, the microcomputer 19 determines whether or not the indoor fan is turned on (step 100). This on
The microcomputer 19 itself performs the operation in response to a user's operation instruction. When the microcomputer 19 performs the ON control, the microcomputer 19 determines that the indoor fan is ON.

If the indoor fan is on, the microcomputer 1
9 determines a heavy load state (step 103), and notifies the pre-driver 17 of this determination result. Pre-driver 17
Is based on the result of this determination.
It is set to select the voltage V _B of the base winding 3 (step 105). When the microcomputer 19 determines that the indoor fan is not on (step 100), it then determines whether the compressor is on (step 1).
01). In this case, when the compressor is on, the microcomputer 19 determines that the load is heavy (step 103).
Similar to the above, the pre-driver 17 is set to select the voltage V _B of the base winding 3 (Step 10
5). As described above, when the voltage V _B of the base winding 3 is set to be selected, the pre-driver 17 outputs the secondary current I _R from this voltage V _B as described above.
The switching element 5 is turned on at this detection timing (step 106).

It is to be noted that the detection of whether or not the indoor fan is turned on in step 100 is performed in order to maintain a heavy load even when the indoor fan is operated to perform the blowing operation. Stopping the indoor fan to bring the compressor into the operating state includes, for example, a defrosting operation.

When both the indoor fan and the compressor are stopped (steps 100 and 101), the microcomputer 19 determines that the load is light (step 104), and notifies the pre-driver 17 of the determination result. The pre-driver 17 is set to select the detection output of the off-time fixing circuit 18 based on the determination result (step 105), and turns on the switching element 5 at the timing of the detection output (step 106).

FIG. 3A is a waveform diagram showing the collector current I _C and the secondary current I _R of the switching element 5 under heavy load in this embodiment.

The operation of this embodiment under a heavy load is to set the ON timing of the switching element 5 based on the voltage V _B of the base winding 3, so that the secondary current I _R
Becomes 0, the switching element 5 is turned on,
As shown in FIG. 3A, the same collector current I _C and secondary current I _R as in the conventional example shown in FIG. 11 are generated.

FIG. 3B is a waveform diagram showing the collector current I _C and the secondary current I _R of the switching element 5 at light load in this embodiment.

In FIG. 3B, the switching element 5
There turned on (period t _1), when the switching element 5 to flow only a short period of time t ₂ when the collector current I _C is corresponding to the load is turned off (period t _3), flows the secondary current I _R (period t ₄₎ .
In the conventional example shown in FIG. 11, when the secondary current I _R becomes 0, the switching element 5 is turned on. As a result, the next collector current I _C flows at the timing shown by the broken line.

In this embodiment, the microcomputer 1
9, the on-timing of the switching element 5 is selected so as to be set by the output of the off-time fixing circuit 18. The off-time fixing circuit 18, the pre-driver 17 turns off the switching element 5, and outputs therefrom signal after a predetermined time T _2, the pre-driver 17 at the timing of this signal turns on the switching element 2. The time T ₂ are, are set to the same light load predriver 17 on timing detection circuit longer than the time T ₁ of the 23-side switching element 5 when selecting until then switched from off to For example, it is assumed that the switching frequency f ₀ of the switching element 5 is approximately equal to the human audible frequency limit of about 20 kHz.

FIG. 4 is a characteristic diagram showing a change in the switching frequency f ₀ of the switching element 5 with respect to the load in this embodiment. Here, the normal mode is a mode in which the pre-driver 17 turns on the switching element 5 at a voltage V _B of the base winding 3, the off-time fixed mode, the switching element 5 at the output of the off-time fixed circuit 18 This is the mode to turn on.

In the heavy load state, as shown in FIG. 4 as the characteristics of the normal mode, the load decreases and
As in the case of the conventional example shown in FIG. 13A, the switching frequency f ₀ increases. Then, when the load is switched to a light load, in the conventional example, the switching frequency f ₀ further increases as shown by a dashed line,
In this embodiment, the switching frequency f ₀ switches from a high frequency to a relatively low frequency of around 20 kHz, as shown as the characteristic of the off-time fixed mode in FIG.
As the load decreases, it rises slightly.

As described above, when the switching frequency f ₀ at the time of light load is kept low, the power transmitted from the main winding 2 of the switching transformer 1 to the secondary windings 4a to 4g in FIG. The load on the secondary side is supplied with the power corresponding to the load, and the excess supply of the power is eliminated.

In FIG. 4, the characteristic curve of the fixed off-time mode is extended to a heavy load region.
This extension is for the case where the load is increased to a heavy load region with the pre-driver 17 selecting the output signal of the off-time fixing circuit 18.

FIG. 5 is a characteristic diagram showing a change in voltage regulation (secondary voltage) with respect to a load in this embodiment.

As described above, when an appropriate power supply corresponding to the load on the secondary side of the switching transformer 1 is performed at a light load, the load current corresponding to the load can be supplied to the load, and the power supply voltage for this load can be supplied. (Secondary voltage) can be kept constant, and as shown in FIG.
Voltage regulation can be ensured even at light load.

In FIG. 5, the characteristic curve of the fixed off-time mode is extended to a heavy load region.
This extension corresponds to the extension in the heavy load region in the fixed off-time mode in FIG.

[0071] Figure 4, as apparent the characteristic curve of the off-time fixed mode in FIG. 5 from the characteristics of the extension part up region of the heavy load, at a heavy load region, the switching frequency f ₀
Suddenly decreases, voltage regulation cannot be ensured, and finally, the operation becomes inoperable. Therefore, it is important to appropriately set the switching point between the fixed off-time mode and the normal mode (the boundary between the light load region and the heavy load region). If this boundary shifts to the lighter load side than the proper boundary, excess power supply occurs in the portion where the load in the heavy load region is small, and if it shifts to the heavy load side, the portion in the light load region where the load is large In addition, the switching frequency f ₀ is not sufficient, and the voltage regulation cannot be ensured.
According to experiments by the inventors, the maximum switching frequency f ₀ at the time of heavy load and 20kHz above, when the load current at this time was set to 1.2A, the boundary 0.3-0.4
A was found to be optimal.

In FIG. 5, the characteristic curve in the normal mode and the characteristic curve in the fixed off-time mode are shown separately, but this is because these characteristic curves are clearly shown. These characteristic curves are continuous at the boundary between the load region and the heavy load region.

In this embodiment, when the load is light, the switching element 5 is turned on at the timing of the output signal of the off-time fixing circuit 18, so that the switching frequency f ₀ is reduced as described above. The number of ON operations per unit time of the switching element 5 is greatly reduced as compared with the conventional example shown in FIG.
The on-loss P _on occurring at the moment when the switching element 5 is turned on (period t ₁ ) is greatly reduced. Therefore, even when the load becomes light, the loss in the switching element 5 is correspondingly reduced. Can be reduced.

When this embodiment is used as a power supply device of an air conditioner to perform the operation shown in FIG. 2, when the standby state in which the air conditioner is not operated is set to a light load state, this standby state is used. Power can be reduced.

In this air conditioner, this embodiment as a power supply device is installed on the outdoor unit side, and the heat generated by the switching element 5 is dissipated by a radiating mechanism provided with fins on the switching element 5. A configuration is adopted in which the heat is dissipated by ventilation of the outdoor fan to the heat radiation mechanism. By the way, when the air conditioner is in the waiting state, the outdoor fan is not rotating, and heat is radiated from the heat radiating mechanism by natural convection to cool the switching element 5. Conventionally, as described above, even in the standby state, the amount of heat generated by the switching element 5 is large because the ON loss P _on is large. For this reason, the heat radiation mechanism of the switching element 5 is also large-scale.

On the other hand, in this embodiment, since the ON loss P _on can be reduced, the amount of heat generated by the switching element 5 in the standby state of the air conditioner can be reduced. As the mechanism, the number of fins is reduced or the fins are downsized, so that the structure of the heat radiating mechanism can be simplified and downsized, and the cost and the component space can be reduced.

Further, the ON loss P of the switching element 5
_{When on} is reduced, the periods t ₁ and t ₃ during which the switching element 5 is turned on and off can be set larger. In this manner, dV / dt and dI / dt at the time of switching that reduce noise can be reduced, and noise can be reduced. As a result, unnecessary noise countermeasure parts can be reduced, and the cost can be reduced.

FIG. 6 is a circuit diagram showing a second embodiment of the power supply device according to the present invention, wherein 16 'is a switching power supply circuit, 20 is a rectifier circuit, 21 is a switching relay, and 22 is a converter circuit. The same reference numerals are given to the portions corresponding to 1 and the overlapping description will be omitted.

In the figure, a rectifier circuit 20 and a switching relay 21 constitute a converter circuit 22, which rectifies and smoothes an AC output from an AC power supply 14 and supplies it to a switching power supply 16 'as an input DC voltage Vd. In this converter circuit 22, the switching relay 21 is controlled to be turned on and off by the microcomputer 19.
Turns on to perform voltage doubler rectification operation, and at light load, the switching relay 21 turns off to perform full-wave rectification operation.

In the switching power supply circuit 16 ', the off-time fixing circuit 18 is removed from the switching power supply circuit 16 shown in FIG. 1, and the pre-driver 17 constantly switches the switching element from the voltage V _B of the base winding 3 of the switching transformer. 5 is configured to detect the ON timing.
Other configurations are the same as those of the switching power supply circuit 16 shown in FIG.

Next, a control operation of the second embodiment when used as a power supply device of an air conditioner will be described with reference to a flowchart shown in FIG.

When the AC output is supplied from the AC power supply 14 when the power is turned on, the microcomputer 19 determines whether or not the indoor fan is turned on (step 200). This ON is performed by the microcomputer 19 itself according to a user's operation instruction. When the ON control is performed, the microcomputer 19 determines that the indoor fan is ON.

If the indoor fan is on, the microcomputer 1
9 determines a heavy load state (step 203) and turns on the switching relay 21 (step 205). If the microcomputer 19 determines that the indoor fan is not on (step 200), it then determines whether the compressor is on (step 201). In this case, when the compressor is on, the microcomputer 19 determines that the load is heavy (step 203), and turns on the switching relay 21 (step 20).
5). Thus, when the switching relay 21 is turned on,
The converter circuit 22 performs double voltage rectification on the AC output of the AC power supply 14, and supplies the resulting DC voltage as an input DC voltage Vd to the switching power supply circuit 16 '.

The determination of the ON / OFF state of the indoor fan and the determination of the ON / OFF state of the compressor are based on the same reason as in the first embodiment.

When both the indoor fan and the compressor are stopped (steps 200 and 101), the microcomputer 19 determines that the load is light (step 204), and the switching relay 21 is turned off (step 204). As a result, the converter circuit 22 performs full-wave rectification on the AC output of the AC power supply 14, and supplies the resulting DC voltage to the switching power supply circuit 16 'as the input DC voltage Vd.

Here, assuming that the AC output of the AC power supply 14 is 100 V as an effective value, the input DC voltage Vd is 280 V when the converter circuit performs the voltage doubler rectification operation. 140V.
Therefore, in the switching power supply circuit 16 ', the input DC voltage Vd at the time of light load is 1/2 that at the time of heavy load.

FIG. 8A is a waveform diagram showing the collector current I _C and the secondary current I _R of the switching element 5 under heavy load in the second embodiment, and shows the first embodiment. This is the same as the waveform shown in FIG.

FIG. 8B is a waveform diagram showing the collector current I _C and the secondary current I _R of the switching element 5 at the time of light load in the second embodiment.

In FIG. 8B, the switching element 5
In There time instant to turn on t _1, but the collector current I _C is rapidly increased, because the charging voltage of the snubber capacitor 6 of the damper circuit, the input DC voltage Vd is 1/2 of the heavy load,
It is 1/2 that of a heavy load. Therefore, the switching element 5
The discharge current of the snubber capacitor 6 during the period t ₁ at the moment when the power supply is turned on becomes almost の of that at the time of heavy load, and the collector current I _C flowing during this period t ₁ is significantly reduced as compared with the case of heavy load. Further, the collector-emitter voltage V _{CE of} the switching element 5 is also substantially reduced by half because the input DC voltage Vd is reduced by half with respect to the heavy load.

As described above, the ON loss P of the switching element 5 represented by the product of the collector current I _C and the collector-emitter voltage V _CE during the period t ₁ under light load is obtained.
_On is greatly reduced as compared with a heavy load.

[0091] Further, in FIG. 8 (b), the input DC voltage Vd at light load equal to the time of heavy load, and it shows a collector current I _C when the load is equal in broken lines, which the above As is clear from comparison with the collector current I _C shown by the solid line, if the loads are equal, the switching element 5
Since the collector current I _{C at the} moment of turning off is the same, the on-period t ₂ of the switching element 5 is almost doubled by setting the input DC voltage Vd to の of that at the time of heavy load.

This means that the ratio of the time required at the moment when the switching element 5 is turned off by taking the ON period t ₂ sufficiently is sufficiently reduced, and the influence on the regulation is eliminated. Therefore, it becomes possible to transmit an appropriate amount of power according to the load at the time of light load to the secondary side of the switching transformer that is not fed back. As a result, on the secondary side, it is possible to supply only a necessary amount of current to the load, and it is possible to keep the power supply voltage constant, as shown in FIG.
Voltage regulation can be ensured.

In FIG. 9, the voltage doubler rectification mode refers to a mode in which the converter circuit 22 shown in FIG. 6 performs voltage doubler rectification operation. When the voltage doubler rectification mode is set at a light load, feedback of the switching transformer is applied. No excess power will be supplied on the secondary side,
As shown in FIG. 9, the regulation cannot be ensured like the extended portion in the light load region of the characteristic curve of the voltage doubler rectification mode. In FIG. 9, the full-wave rectification mode refers to a mode in which the converter circuit 22 in FIG. 6 performs full-wave rectification. When the full-wave rectification mode is set under heavy load, when the load is increased, the input DC voltage Vd is reduced. Insufficient power cannot be supplied to the load, and the power supply voltage for the load is greatly reduced.

Here, in FIG. 9, the characteristic curve in the voltage doubler rectification mode and the characteristic curve in the full-wave rectification mode are shown separately, but this is to clearly show these characteristic curves. These characteristic curves are continuous at the boundary between the light load region and the heavy load region.

In the second embodiment, the switching frequency f ₀ of the switching element 5 is lower in the full-wave rectification mode at light load than in the double voltage rectification mode. In this case, at light load, the period t _{3 at} the moment when the switching element 5 is turned off and the off-period t ₄ of the switching element 5 are sufficiently short, so that the switching frequency f ₀ is almost dominated by the period t _2. become. Therefore, as shown in FIG. 10, when the load is light, the switching frequency f ₀ is in the voltage doubler rectification mode (that is, the switching frequency f ₀ shown by a broken line obtained by extending the characteristic curve of the voltage doubler rectification mode to the light load region). ), The switching frequency f ₀ is almost halved.

When the switching frequency f ₀ is halved in this way, the number of times that the switching element 5 is turned on per unit time is also reduced, which also reduces the on-loss P _on of the switching element 5.

As described above, also in the second embodiment, the voltage regulation under a light load can be secured while the noise suppressing effect is maintained by holding the capacitance of the snubber capacitor 6 at a predetermined value, and the switching element , The ON loss P _on can be greatly reduced.

By combining the first and second embodiments described above, the converter circuit 2 can be operated under heavy load.
2 is the double voltage rectification mode, and the on timing of the switching element 5 is the timing at which the secondary current becomes 0. At light load, the converter circuit 22 is set to the full-wave rectification mode, and the on timing of the switching element 5 is set. May be set as the output timing of the off-time fixing circuit 18.

Although the above embodiments have been described using specific numerical values, these numerical values are merely examples, and the present invention is not limited to these numerical values.

[0100]

As described above, according to the power supply device of the present invention, the trade-off with noise suppression is eliminated by simply loading a simple circuit, and excessive power at light load is avoided. Voltage regulation can be ensured, and the loss of the switching element at light load can be significantly reduced.

Further, according to the power supply device of the present invention, the dV at the time of switching of the switching element which reduces noise is obtained.
Even if / dt and dI / dt are reduced, the loss of the switching element can be reduced.

Furthermore, according to the air conditioner of the present invention using such a power supply device, the power consumption of the switching element can be reduced and the amount of heat generated can be reduced even during a waiting period, so that the heat dissipation of the switching element can be reduced. The mechanism can be made simpler and smaller, so that the cost can be reduced and the space for parts can be reduced. According to the air conditioner of the present invention using such a power supply device, as described above, it is possible to reduce the noise generated by the on / off operation of the switching element while reducing the loss of the switching element. The number of countermeasures parts can be reduced, and the size and cost of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power supply device according to the present invention and an air conditioner using the same.

FIG. 2 is a flowchart showing a control operation of the embodiment shown in FIG.

FIG. 3 is a waveform diagram showing a collector current and a load current of the switching element under heavy load and light load in the embodiment shown in FIG. 1;

FIG. 4 is a characteristic diagram showing a switching frequency with respect to a load in the embodiment shown in FIG.

FIG. 5 is a characteristic diagram showing voltage regulation with respect to a load in the embodiment shown in FIG. 1;

FIG. 6 is a circuit diagram showing a power supply device according to a second embodiment of the present invention and an air conditioner using the same.

7 is a flowchart showing a control operation of the embodiment shown in FIG.

FIG. 8 is a waveform diagram showing a collector current and a load current of the switching element under heavy load and light load in the embodiment shown in FIG. 6;

FIG. 9 is a characteristic diagram showing voltage regulation with respect to a load in the embodiment shown in FIG. 6;

10 is a characteristic diagram showing a switching frequency with respect to a load in the embodiment shown in FIG.

FIG. 11 is a circuit diagram showing an example of a conventional power supply device and an air conditioner using the same.

FIG. 12 is a diagram showing current and voltage waveforms of respective parts in FIG. 11 and losses in switching elements.

FIG. 13 is a characteristic diagram showing switching frequency and voltage regulation with respect to a load in the conventional example shown in FIG. 11;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching transformer 2 Main winding 3 Base winding 4a-4g Secondary winding 5 Switching element 6 Noise removal capacitor 11 Feedback circuit 14 AC power supply 15 Converter circuit 16, 16 'Switching power supply circuit 17 Pre-driver 18 Off-time fixed Circuit 19 Microcomputer 20 Rectifier circuit 21 Switching relay 22 Converter circuit

Continuing on the front page (72) Inventor Makoto Ishii 800 Tomita, Ohira-machi, Ohira-machi, Shimotsuga-gun, Tochigi Prefecture Inside the Cooling Division, Hitachi, Ltd. Within the business division

Claims (4)

[Claims] 1. A power supply device for turning on and off an output voltage of a converter circuit by a switching element to generate a power supply voltage to be supplied to a load, comprising: first means for judging between a light load state and a heavy load state; A second means for fixing an off period of the switching element at a light load based on the determination of the first means. 2. A power supply device for turning on and off an output voltage of a converter circuit by a switching element to generate a power supply voltage to be supplied to a load, wherein the converter circuit can switch between a full-wave rectification operation and a voltage doubler rectification operation. A first means for determining a light load time and a heavy load time; and, based on the determination by the first means,
A second means for performing full-wave rectification operation under light load and performing voltage doubler rectification operation under heavy load. 3. A power supply device that turns on and off an output voltage of a converter circuit by a switching element to generate a power supply voltage to be supplied to a load, wherein the converter circuit can switch between a full-wave rectification operation and a voltage doubler rectification operation. A first means for determining between a light load and a heavy load, and a second means for fixing the off period of the switching element at a light load based on the determination of the first means. On the basis of the determination of the first means, the converter circuit is operated under a light load.
A power supply device comprising: a third means for performing full-wave rectification operation and performing voltage doubler rectification operation under heavy load. 4. An air conditioner to which the power supply voltage is supplied from the power supply device according to claim 1, 2, or 3 and which performs various operations with a refrigeration cycle, wherein the first means includes a refrigeration unit. An air characterized in that it is determined that a heavy load is present when at least one of the compressor and the indoor fan constituting the cycle is operating, and a light load is determined when the compressor and the indoor fan are stopped. Harmony machine.