JPH0739152A - Power supply apparatus - Google Patents

Abstract

PURPOSE:To provide a power supply apparatus which is small and light weight, which reduces a switching noise and whose cost is favorable. CONSTITUTION:When semiconductor switches S1, S2 are switched alternately, a current flows alternately in a winding NP on the primary side of a transformer T as shown by arrows F1, F2, and a voltage corresponding to a turn ratio is induced in windings NS1, NS2, NS3 on the secondary side. Since the switching frequency fs of the semiconductor switches S1, S2 is set at a value which is different from the resonant frequency fr of series resonant circuits K1, K2, K3, the rectified output of individual diodes D1, D2, D3 displays an excellent constant current characteristic. The output current Im of every winding is expressed as Im=k.(Vm/Zr) when an output voltage is designated as Vm, a constant is designated as (k) and the characteristic impedance of the series resonant circuits is designated as Zr. By utilizing this relationship, it is possible to obtain an output which is matched to a load condition.

Description

Detailed Description of the Invention

[0001]

[Industrial applications] The present invention is applicable to load current and load voltage
Power supply for driving variable discharge lamps
More specifically, a power supply device that outputs a constant current
Regarding improvement.

[0002]

2. Description of the Related Art As a power supply device for outputting a DC constant current, there is a power supply device shown in FIG. In the figure, the voltage E _I is input to the non-inverting input side of the operational amplifier (hereinafter referred to as “OP amplifier”) A ₁ to which the power supply voltage V _CC is applied. The output side of the OP amplifier A ₁ is connected to the load R _L , and this load R _L is further connected to the ground via the current detection resistor R _S. Then, this current detection resistor R _S
The value of the load current I _L detected by is fed back to the inverting input side of the OP amplifier A ₁ . As a result, control is performed so that the load current _IL becomes constant.

The input voltage E _I and the load current I _L have the following relationship with the current detection resistor R _S. I _L = E _I / R _S …………………………………… (1) Let us consider the power loss. The power loss in this power supply device is the product of the load current I _L and the voltage difference V _CC -V _OUT between the power supply voltage V _CC and the output voltage V _OUT of the OP amplifier A ₁ . When the loss is a relatively small electric power of several watts, the power supply device as shown in FIG. 4 can be used without any trouble.

However, in the case of a metal halide discharge lamp having a load R _L of several hundreds of watts, the power supply voltage V _CC is set higher than a required value by 100 V or more in consideration of the change in the discharge start voltage. I need to put it. Therefore, the power loss reaches several hundred watts, which is not practical.

On the other hand, there is a power supply device using a chopper circuit as shown in FIG. In the figure, the power supply voltage V
_The terminal to which _CC is supplied is the semiconductor switch S of the chopper circuit.
Connected to _C. The output side of the OP amplifier A ₂ is the control input of this semiconductor switch S _C. The other terminal of the semiconductor switch S _C is connected to the cathode side of the diode D _C and the inductor L _C , respectively. The inductor L _C is further connected to the capacitor C _C and the load R _L. These are a semiconductor switch S _C , a diode D _C ,
A chopper circuit is formed by the inductor L _C and the capacitor C _C.

According to the power supply device of FIG. 5, the ON / OFF time ratio of the semiconductor switch S _C is controlled by the OP amplifier A ₂ , and a predetermined output current is obtained from the chopper circuit. Also in this case, the output current I _L is given by the above equation (1).

[0007]

[Problems to be Solved by the Invention] However, the above
With such conventional technology, although it is practically applicable,
Due to the large pressure and current, the switching of the chopper circuit
High chopper frequency for large size and small size
There is a limit to wave generation, and heat generation due to power loss and
In terms of size, where further improvement is desired.
It

[0008] The present invention focuses on these points,
Small size, light weight, low switching noise and low cost
It is an object of the present invention to provide a power supply device advantageous to
It is a thing.

[0009]

In order to achieve the above object, the power supply device of the present invention includes a primary side winding which is alternately energized by switching driving a switching means connected to a DC power supply at high frequency. , A transformer having a plurality of secondary side windings capable of obtaining a plurality of types of output voltages,
A series resonance circuit connected to the output side of each of the secondary windings and a rectification circuit connected to the output side of the series resonance circuit are provided, and the switching frequency of the switch means is set to the series resonance. It is characterized in that the value is different from the resonance frequency of the circuit.

[0010]

According to the present invention, the switching frequency on the primary side of the transformer is set to a value different from the resonant frequency on the secondary side, whereby the output of each winding destination on the secondary side has a constant current characteristic. Each output current value on the secondary side is determined by the characteristic impedance of the series resonant circuit and the output voltage of each winding, and therefore can be set according to the load. For this reason, it is possible to favorably deal with the case where the load voltage or the load current fluctuates even though the configuration is simple.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a power supply device according to the present invention will be described in detail below with reference to the accompanying drawings. <Structure of Embodiment> FIG. 1 shows the structure of a power supply device according to this embodiment. In the figure, DC power supply E
₁ is connected to the winding N _P on the primary side of the transformer T via a semiconductor switch S ₁ , and the DC power supply E ₂ is connected to the winding N _P via a semiconductor switch S ₂ . However, the polarities of the DC power supplies E ₁ and E ₂ and the connection terminals of the winding N _P are opposite to each other. Therefore, when the semiconductor switch S ₁ is turned on, a current flows through the winding N _P as shown by an arrow F ₁ , and when the semiconductor switch S ₂ is turned on, the winding N _P is turned on.
A current flows in the direction of arrow F ₂ .

Next, on the secondary side of the transformer T, three windings NS ₁ , NS ₂ and NS ₃ are provided. The relationship between the number of turns and the number of turns of the primary winding N _P is N _P > NS ₁ > NS ₂ > NS ₃ …………………… (2) is set.

A diode bridge D ₁ is connected to the winding NS ₁ via a series resonance circuit K _{1 including} an inductor L ₁ and a capacitor C ₁ . Similarly, the winding NS ₂ has
Series by the inductor L ₂ and capacitor C ₂ resonant circuit K ₂
A diode bridge D ₂ is connected to the winding NS ₃ , and a diode bridge D ₃ is connected to the winding NS ₃ via a series resonance circuit K _{3 including} an inductor L ₃ and a capacitor C ₃ .

The diode bridges D ₁ , D ₂ and D ₃ are connected inside the circuit so that so-called alternating current can be bridge rectified. These diode bridges D ₁ , D ₂ , D ₃
Are adapted to each and are connected to the series resonant circuit K _1, K _2, windings NS ₁ of the transformer T through the _{K 3, NS 2, NS 3} , whereby the resonance current output.
The output sides of the diode bridges D ₁ , D ₂ and D ₃ are commonly connected to the load R _L , and the negative side is grounded. A smoothing capacitor C ₄ is connected to the load R _L.

<Operation of the Embodiment> Next, the operation of the power supply device configured as described above will be described. First, the primary side of the transformer T will be described. Semiconductor switches S ₁ , S
_2, on the basis of the high-frequency switching pulse output from the control circuit, not shown, and performs high-frequency switching operation of ON / OFF alternately. For example, the duty ratio is about 5
0%, ON / with very little simultaneous OFF time
Repeated OFF.

In such an operating state, as is well known, the flyback voltage of the inductance of the winding N _P of the transformer T can be utilized, and the semiconductor switches S ₁ and S ₁ can be used.
_{The 2} comes to perform so-called zero volt switching operation. That is, switching operation without switching loss is possible, and power loss is reduced by the semiconductor switch S ₁ ,
It depends only on the ON resistance of S ₂ . Therefore, since heat generation is reduced, higher frequency switching becomes possible, and the transformer T, the semiconductor switches S ₁ and S ₂ , and the heat radiation mechanism (not shown) can be made smaller and lighter. Also,
The zero volt switching operation also reduces switching noise.

By the alternating switching of the semiconductor switches S ₁ and S ₂ as described above, the winding N on the primary side of the transformer T is
Current flows in _P alternately as indicated by arrows F ₁ and F ₂ .
Therefore, the secondary windings NS ₁ , NS ₂ , N of the transformer T are
A voltage corresponding to the turn ratio is induced in S ₃ .

Next, the secondary side of the transformer T will be described. In the present embodiment, when the switching frequencies of the semiconductor switches S ₁ and S ₂ are fs and the resonant frequencies of the series resonant circuits K ₁ , K ₂ and K ₃ on the secondary side of the transformer T are the same fr, The relationship of It is set so that fs> fr ………………………………………… (3). Preferably, the value of fs is set to a value near 1.5 fr. It has been experimentally confirmed that the rectified outputs of the diode bridges D ₁ , D ₂ , and D ₃ exhibit good constant-current characteristics with such a relationship. Even if fs <fr (preferably, the value of fr is set to a value near 1.5 fs), the same effect can be obtained.

The secondary side of the transformer T is equivalently shown in FIG. 2 on the premise of such a relationship. As shown in the figure, the output voltages of the windings NS ₁ , NS ₂ and NS ₃ are equivalently DC voltages V ₁ , V ₂ and V ₃ , and the windings NS ₁ and N ₃ are equivalent.
The current supplied to the load from S ₂ and NS ₃ is DC current I ₁ ,
I ₂ and I ₃ . The load voltage and the load current for the load R _L are indicated by V _O and I _O , respectively.

Here, the load current I _O and load voltage V _O supplied to the load R _L , and the output voltages V ₁ , V ₂ , V ₃ and output current I _{1 of the} windings NS ₁ , NS ₂ , NS ₃ , I ₂ , I ₃ will be considered as follows. It should be noted that V ₃ <V ₂ <from the relationship of the turn ratios of the windings NS ₁ , NS ₂ , NS ₃ described above.
It is V ₁ .

When V _O <V ₃ , each winding NS ₁ , N
Since current is supplied to the load R _L from S ₂ and NS ₃ , I _O = I ₁ + I ₂ + I ₃ …………………………………… (4).

When V ₃ <V _O <V ₂ , the windings NS ₁ and N
Since the current is supplied from S ₂ to the load R _L , I _O = I ₁ + I ₂ …………………………………… (5).

When V ₂ <V _O <V ₁ , the current is supplied from the winding NS ₁ to the load R _L. I _O = I ₁ …………………………………… (6).

When V ₁ <V _O , which winding N
Since no current is output from S ₁ , NS ₂ and NS ₃ , I _O = 0 …………………………………… (7).

By the way, the values of the inductors L ₁ , L ₂ and L ₃ of the series resonance circuits K ₁ , K ₂ and K ₃ are Lr, and the values of the capacitors C ₁ , C ₂ and C ₃ are Cr. Then,
The characteristic impedance Zr is: Zr = √ (Lr / Cr) …………………………………… (8). Output currents I ₁ , I of the windings NS ₁ , NS ₂ , NS _3
2 and I ₃ are inversely proportional to the characteristic impedance Zr, and output voltages V ₁ and V _{1 of} the windings NS ₁ , NS ₂ and NS ₃ are
It is obtained as a value proportional to V ₂ and V ₃ .

That is, assuming that the proportional constant is k, the output current Im (m = 1, 2, 3) is Im = k (Vm / Zr) ………………………………… (9). The circuit constants corresponding to the respective parameters are determined in accordance with the load conditions while considering such a relationship.

For example, in the case where the load R _L changes by several tens of volts between the voltage at the start and the time at which the load is stable like a metal halide discharge lamp, a plurality of resonance circuits are provided in this embodiment. The power supply becomes extremely effective. A concrete description is as follows.

At the start of discharge ... A large current is not required, but a high voltage is required. Therefore, as shown in the equation (6), the winding NS ₁ having a high output voltage corresponds to the windings NS ₂ and NS _3.
Is OFF).

Immediately after the start of discharge ... Although the load voltage is low, a large current is required. Therefore, as shown in the equation (4), the winding NS ₃ set to a particularly large current and the other winding N
All the output currents of S ₁ and NS ₂ are supplied to the load R _L.

Steady state after a lapse of a predetermined time: a state in which a rated current is supplied. Therefore, as shown in (5) above, the rated current is supplied by the windings NS ₁ and NS ₂ (the winding NS ₃ is OFF).

As described above, according to the present embodiment, since the plurality of windings are provided, the impedance conversion action of the transformer can be fully utilized even when the voltage and the current of the load largely change. . Further, due to the relationship between the turns ratios of the windings on the primary side and the secondary side of the transformer, the current change on the secondary side is reduced on the primary side, and the value of the current change of the semiconductor switch becomes small.

For example, the primary winding N _{P of the} secondary winding NS ₃
The winding ratio with respect to is set small as shown in the equation (2). On the other hand, in the state where a large current is required as shown in the equation (4), a large current flows through the winding NS ₃ . However, the current flowing through the primary winding N _P and the semiconductor switches S ₁ and S ₂ can be suppressed to a small value due to the relation of the winding ratio. Therefore, as the semiconductor switches S ₁ and S ₂ , it is possible to use a switch element having a relatively small capacity and generate less heat due to the current, so that the size and cost can be reduced.

Further, if the switching frequency of the semiconductor switches S ₁ and S ₂ on the primary side of the transformer T is changed, the value of the proportional constant k in the equation (9) is changed, so that Ir
Also changes. This can be used for fine adjustment of the output current Ir.

<Applied Operation> Next, referring to FIG.
A specific operation when this embodiment is used as a power source of a metal halide discharge lamp will be described. In Figure 3,
An example of the relationship between the load voltage V _O and the passage of time until a steady lighting state is reached when the load is a metal halide discharge lamp is shown. It is not shown from the start of discharge to the point P. At the start of discharge, a large current is not required but a high voltage is required. When the discharge is started, the voltage gradually decreases and the current increases conversely. At point P, the discharge voltage is about 40V and the current is about 10A. After passing the point P, the current may be about 7A.

Therefore, each of the windings NS ₁ , shown in FIG.
Output voltage V ₁ of the _{NS 2, NS 3, V 2} , V 3 and the current I _1,
I ₂ and I ₃ are set as follows. Winding NS ₁ : I ₁ = 1A, V ₁ = 260V Winding NS ₂ : I ₂ = 6A, V ₂ = 150V Winding NS ₃ : I ₃ = 3A, V ₃ = 40V

V ₁ = 260 V of the winding NS ₁ is a high voltage value required to start discharge. Further, I ₃ = 3A of the winding NS ₃ is a value of the auxiliary current required to increase the discharge firing voltage. With this setting, first, discharging is started at the output voltage V ₁ = 260V of the winding NS ₁ . Then, in the state of the formula (4) in which the load voltage V _O reaching the point P is lower than the output voltage of any winding,
The load current I _O is discharged at I ₁ + I ₂ + I ₃ = 10A. After passing the point P, the load voltage V _O becomes 40 V or more and exceeds the output voltage V ₃ = 40 V of the winding NS ₃ , so that the state of the equation (5) is established. Therefore, the load current I _O is discharged at I ₁ + I ₂ = 7A.

<Other Embodiments> The present invention is not limited to the above embodiments, and includes, for example, the following. (1) In the above-mentioned embodiment, the output side has three outputs having different current and voltage characteristics, but the number of stages of these outputs may be appropriately changed as necessary. (2) The above-mentioned metal halide discharge lamp is suitable as an application target of the present invention, but the present invention is not limited to this. However, it is particularly effective for loads in which the load voltage and load current fluctuate.

[0038]

As described above, according to the power supply device of the present invention, a plurality of windings are provided on the secondary side of the transformer and a series resonance circuit is provided, and the switching frequency on the primary side is set to the resonance of those resonance circuits. Since it is set to a value different from the frequency, it has a simple structure,
It is possible to supply a plurality of types of electric power having different voltages and currents, and it is possible to achieve size reduction, weight reduction, and cost reduction.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply device according to the present invention.

FIG. 2 is an explanatory diagram showing an operation of the embodiment.

FIG. 3 is a graph showing a discharge voltage characteristic of a metal halide discharge lamp which is a specific application example of the embodiment.

FIG. 4 is a circuit diagram showing a conventional basic power supply device.

FIG. 5 is a circuit diagram showing a conventional improved power supply device.

[Explanation of symbols]

C _{1 to} C ₃ ... Resonance capacitor, C ₄ ... Smoothing capacitor, D _{1 to} D ₃ ... Rectifying diode bridge, E ₁ , E ₂ ...
DC power supply, F ₁ , F ₂ ... Arrows indicating the direction of current flow, I
₁ ~I ₃ ... output current, I _O ... load current, K ₁ ~K ₃ ... series resonant circuit, L ₁ ~L ₃ ... resonance inductor, NP ₁ ~NP ₃ ...
Secondary windings, N _P ... primary winding, P ... characteristic change point,
R _L ... load, S _1, S ₂ ... semiconductor switch (switching means), T ... transformer, V ₁ ~V ₃ ... output voltage, V _O ... load voltage.

Claims (1)

[Claims] 1. A primary winding that is energized alternately by switching driving a switching means connected to a DC power supply at high frequency, and a plurality of secondary windings that obtain a plurality of types of output voltages. And a series resonance circuit connected to the output side of each of the secondary side windings, and a rectifier circuit connected to the output side of these series resonance circuits, the switching frequency of the switch means. Is a value different from the resonance frequency of the series resonance circuit.