JP2607569B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a switching power supply device.

(Prior Art) Conventionally, switching power supply devices have been widely used as power supply means for various electronic devices. The switching power supply device adjusts the voltage by controlling the time ratio between ON and OFF of the switch, and adjusts the voltage including boosting and high voltage. As the above-mentioned switch, for example, a transistor or the like is used. The control of the time ratio between switching on and off in this transistor is performed, for example, by pulse width control in which the frequency is constant and the switching on time is variable, and the switching on time. Is constant and the frequency is variable.

As the above-mentioned switching power supply, for example, there is a switching power supply of a forward system. In this forward type switching power supply, for example, pulse width control is applied.

FIG. 5 is a diagram for explaining pulse width control of a conventional switching power supply device.

As shown in the figure, the switching operation frequency T ₁ is constant, when switching on (i.e. t _1, t _2, t ₃
..) Is controlled to control the voltage output to the secondary side. For example, when increasing the voltage to be outputted to the secondary side, a longer on-time as t _3, In the case of reducing the voltage is controlled to shorten the ON time as t _1.

By the way, factors that determine the efficiency of the switching power supply device configured as described above include conduction loss of the secondary-side rectifying diode, switching loss of the transistor, conduction loss, and copper loss and iron loss of the transformer.

Of these, the loss that changes depending on the switching frequency is mainly the switching loss of the transistor and the iron loss of the transformer. Transformer copper loss increases with increasing frequency due to the effect of AC resistance (skin effect and proximity effect), but can be considered substantially constant in a practical frequency range. Note that these losses occur when the duty factor of the transistor that is the switching element is constant.

Therefore, in the conventional forward-type switching power supply device, the loss at the time of switching of the transistor and the iron loss of the transformer are the efficiency determined by the constant switching frequency and the on time t ₁ (minimum) to t ₃ (maximum) of the transistor. there were. Therefore, there is a problem that the on-time of the transistor fluctuates in accordance with the fluctuation of the power consumed in the load, and thereby the efficiency fluctuates.

(Problems to be Solved by the Invention) As described above, in the conventional switching power supply,
The on-time of the transistor is changed in accordance with the fluctuation of the voltage supplied to the load, which affects the switching loss and the loss of the transformer, so that the efficiency of the power supply is changed.

An object of the present invention is to solve the conventional problem described above, and an object of the present invention is to provide a switching power supply device that can maintain high power supply efficiency even when the power supplied to a load fluctuates.

[Configuration of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a configuration in which input DC is switched to convert to a desired voltage, rectified and smoothed, and supplied to a load. A switching unit that stores a plurality of pieces of switching information obtained by combining a switching frequency and a switching operation on-time width; a voltage / current detection unit that detects an output voltage and an output current with respect to the load; The power of the load is calculated from the voltage value and the current value detected by the current detection means, and switching information of a combination of the switching frequency and the switching operation ON time width corresponding to the power is selected and read from the storage means. Means for switching based on switching information read from the storage means In which a control means for controlling the work.

(Operation) In the switching power supply device of the present invention, the current power consumption value of the load is obtained, and the combination of each value of the high-efficiency switching frequency and the switching operation ON width at this power consumption value is read out from the storage means. , The switching operation is controlled by the value of, so that even when the power consumed in the load fluctuates, high power efficiency can be maintained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram for explaining a configuration of a switching power supply device according to one embodiment of the present invention.

In the figure, 1 is a filter, 2 is a rectifier, 3 is a smoothing capacitor for storing a rectified voltage, 4 is a switching transistor, 5 is a snubber circuit that consumes energy stored in a transformer when the transistor 4 is off, Reference numeral 6 denotes a control circuit which controls the switching frequency of the transistor 4 and performs pulse width modulation control and detects power fluctuations in the load. Reference numeral 7 denotes a single-input / multi-output transformer RP.
Is a resistor connected to the emitter side of the transistor 4.

D11, D12, D21, D22, Dn1, and Dn2 are two
.. Cn are smoothing capacitors, L1, L2... Ln are coils for reducing the peak value of the current flowing through the transistor 4 and lowering the ripple voltage, and CF1, CF2. Smoothing capacitor, RF
1, RF2... RFn indicate resistances on the load side.

The above-described control circuit 6 includes a driver 8 that supplies a drive pulse to the base of the transistor 4, a pulse register 9 that holds the drive pulse, and a control signal and a high-power value in each power value accompanying a fluctuation in power supplied to a load described later. A ROM 10 in which data and a control program of a combination of a value of a switching frequency of the transistor 4 for efficiency and a value of a pulse width of an on-time of the transistor 4 are previously written, a RAM 11 serving as a work area, and a switching of the transistor 4. A microcomputer 12 for controlling the frequency and controlling the pulse width modulation of the switching-on time; a current / voltage register 13 for holding the current value and the voltage value output to the load as binary data; A / D converter 14 for converting current or voltage output to binary data into binary data, An input switching amplifier which can switch between input of the value of the emitter voltage generated by the resistor RP and the emitter current connected to the emitter of the converter 4 and the input of the voltage value at the load, amplify these and output to the AD converter 14. It consists of 15.

The above-described pulse register 9 has 8 bits, and bit 7 is an LSB. The driver 8 is connected to this LSB, and the pulse width that is the ON time of the transistor 4 is determined by the time when the LSB is "0". Therefore, when the microcomputer 12 turns on the transistor 4, "0" is written into this LSB, and when the transistor 4 is turned off, "1" is written into the LSB. The switching and amplification of each voltage in the input switching amplifier 15 by the control signal line a are performed by the microcomputer 12.

FIG. 2 is a diagram showing the relationship between the loss and the switching frequency, where PL is the core loss of the transformer, PS1 is the transistor loss at the minimum power consumption value, PS2 is the transistor loss at the maximum power consumption value, and A is PL B represents a loss curve obtained by combining Ps1 and Ps1, and B represents a loss curve obtained by combining P L and Ps2.

The core loss PL of the transformer shows a characteristic that it decreases as the frequency increases. The transistor losses PS1, PS2 and the frequency increase as the frequency increases.

And when the maximum power consumption value indicating characteristics of B, the switching frequency well the efficiency loss is small and set to f _1, and when the minimum power value indicating the characteristics of A, sets the switching frequency f ₂ Then, the loss is small and the efficiency is good. Then, the optimum value of the switching frequency (between f _{1 and} f ₂ ) at each power consumption value is obtained based on the line C connecting the intersections.

FIG. 3 shows a combination of the high-efficiency switching frequency and the pulse width of the switching-on time created based on the results of FIG. 2, and these values are stored in the ROM 10. The table of ROM10 is, for example, W is 40, 50, 60, 70W
Voltage of 4.8, 4.9, 5.0, 5.1, 5.2V
The switching period 1 / f and the pulse width P, which is the switching on time, Is remembered. The table of the ROM 10 is, for example, a period of 10 μS at 70 W, 8.5 μS at 60 W, 7 μS at 40 W, 40 W
Is set to 5.5 μS, so that the loss of the transformer and the loss of the transistor have the minimum characteristics.

Therefore, 1 / f of the table of ROM10 is 10, 8.5,
7, 5.5 (μS). Where P is 70W,
Assuming a pulse on width of 4μS at 5.0V, P at W70 is
4.2 (μS) at 4.8V, 4.1 (μS) at 4.9V, 4.0 at 5.0V
(ΜS), 3.9 (μS) at 5.1 V, 3.8 (μS) at 5.2 V.

For example, when W = 60, the P value is From the above formula, However, given that K is constant, P = 5.0 × 8.5 × 1 / K = 5.0 × 8.5 × 4/50 = 3.4 is obtained. Similarly, when W = 60, 4.8V, P = 3.6, and when 4.9V, P = 3.6
At 3.5 and 5.1 V, P = 3.3, at 5.2 V, P = 3.2 is obtained, and each P value at other W values is determined in the same manner.

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

In this circuit, when 100 V AC is applied, when the current passes through the filter 1 and is full-wave rectified by the rectifier 2, a charge corresponding to about 140 V is accumulated in the capacitor 3.

On the other hand, the operating voltage + V is applied to the control circuit 6, and the control circuit 6 gives an ON pulse to the base of the transistor 4 to turn on the transistor 4.

At this time, the charge of the capacitor 3 is A → B → C → D → E
It flows as a current in the direction of → F → G.

Also, respective outputs J, K, and L on the secondary side of the transformer 7
Generates a voltage of the ratio of primary: secondary winding, and diode D1
1, D21,..., Dn1, coils L1, L2,..., Ln, and reach loads RF1, RF2,. Here, the components of the ripple current are accumulated as charges in the capacitors C1, C2,... Cn, and output DC voltages, respectively.

When the transistor 4 is turned off, the exciting current B → C of the transformer 7 continues to flow as it is, and this energy and the energy stored in the leakage inductance are consumed by the snubber circuit 5.

At this time, the coils L1, L2... Ln of the respective secondary circuits of the transformer 7
.. Ln while the transistor 4 is on, the current flowing through the coils L1, L2... Ln continues flowing through the diodes D12, D22. ... Ripple current that reaches RFn is
Are stored as electric charges in the capacitors C1, C2,... Cn.

 Next, the operation of the control circuit 6 will be described.

First, an input switching amplifier by the microcomputer 12
To 15, an output voltage between a and b of +5 V is input, and an emitter voltage of the transistor 4 (hereinafter, referred to as an E voltage) is input. These values are input to the AD converter 14 and converted into digital data by the current / voltage register 13.
And read by the microcomputer 12,
Stored in RAM11. Then, the power consumption value at the current load is obtained from these values. That is, the current value of the transistor is obtained from the voltage E, and the output value of the secondary side of the transformer 7 is obtained by multiplying the current value by the turns ratio of the transformer 7. -B
The current power consumption of the load is obtained from the voltage value in between.

 Next, a description will be given with reference to the flowchart of FIG.

First, W stored in the RAM 11 is read, and a power value corresponding to the current power consumption value is read from a table of the ROM 10 (step 401). Thereafter, the voltage value between a and b is read, and the current voltage value is obtained by digital data by performing AD conversion (step 402). Then, the pulse width data P value in the table of the ROM 10 is obtained from the power value and the voltage value (step 403). For example, when W = 60W and the output voltage between a and b of + 5V is 4.8V,
P value = 3.6 μS is obtained from the ROM table. Thereafter, "FE" HEX data is written in the pulse register 9 to turn on the transistor 4 (step 404). Next, the current power value is calculated from the current value by the E voltage and the voltage value between a and b, and the RAM1 is calculated.
Store in table 1. The timing of calculating the power value and obtaining the E voltage is performed when the voltage becomes maximum within the time of the P value (step 405). This is transistor 4
At the maximum power, and to obtain an accurate power value. Then, the transistor 4 is turned off by writing "FF" HEX data in the pulse ranger 9 after the time of the P value (step 406). Thereafter, for example, when the obtained power value is 60 W and the voltage value is 4.8 V, the switching frequency value 1 / f = 8.5 μS corresponding to these values is stored in ROM1.
Read from table 0, remaining time 1 / f-P = 8.5μS-
The transistor 4 is turned off for 3.6 μS = 4.9 μS (step 407).

If there is a change in the power consumption of the load, the value of the switching frequency of the transistor 4 and the value of the pulse width, which is the ON time of the switching, are read from the table of the ROM 10 and controlled in the same manner as in the above-described operation.

In the table of ROM 10 described above, the power value is 40, 5
0, 60, 70 W and 10 W units are used, and the actual power value is rounded off and the W power value table is used. Voltage values are 4.8, 4.9,
5.0, 5.1, and 5.2 V, and the obtained voltage value between a and b is rounded off to be one of these voltage values.

Therefore, the microcomputer 12 determines the switching frequency at which the maximum efficiency of the power value is obtained by the output power, and the pulse-on width for constant voltage at that time,
1 / f and P can always be variably controlled.

Next, the relationship between the switching frequency and the loss for obtaining the maximum efficiency of the switching frequency and the pulse width will be described with reference to FIG.

For maximum efficiency it can be said that may be used out of the frequencies between the frequency f ₁ ~f ₂ in color in Figure 2.

In the loss curve B at the maximum power consumption, for example,
If 1 / f = period = 10 μS and frequency f ₁ = 100 kHz at 70 W, then the loss is: Further, in the loss curve A at the minimum power consumption, for example, at 40 W, the period is 5.5 μm.
If S, f ₂ = 182 kHz, the loss is For example f ₁
When the power of 40 W to 70 W is output in the state of the above, the loss becomes larger than the loss at the beginning. In addition, 40 at f ₂
When outputting ~ 70W, the loss becomes larger than the loss from the beginning. Therefore, the line C connecting the stakes is a value at which the maximum efficiency can be obtained.

Therefore, in this embodiment, even if the power consumed in the load fluctuates, the switching frequency is improved and the pulse width value of the on-time of the switching is varied to perform switching to control the current output to the load. Therefore, the efficiency of the power supply can be greatly improved as compared with the conventional switching power supply.

Further, since the efficiency is high, each component can be reduced in size, the temperature rise can be reduced, and the durability can be improved.

Note that the present invention can be applied not only to a switching power supply device of a forward system, but also to a DC-DC converter and a flyback system.

[Effect of the Invention] As described above, the switching power supply of the present invention obtains the current power consumption value of the load, and determines the combination of each value of the high-efficiency switching frequency and the switching operation ON width at this power consumption value. Since the switching operation is controlled based on these values read from the storage means, high power efficiency can be maintained even when the power consumed in the load fluctuates.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining the configuration of a switching power supply device according to one embodiment of the present invention, FIG. 2 is a diagram for explaining the relationship between loss and frequency, and FIG. 3 is a ROM table of FIG. FIG. 4 is a flowchart for explaining the operation of the control circuit of FIG. 1, and FIG. 5 is a diagram showing pulses for explaining pulse width modulation control in a conventional switching power supply device. is there. DESCRIPTION OF SYMBOLS 1 ... Filter 2 ... Rectifier 3 ... Smoothing capacitor 4 ... Transistor 5 ... Snubber circuit 6 ... Control circuit 7 ... Transformer 8 ... Driver 9 ... Pulse register 10 ... ROM, 11 ... RAM, 12 ... microcomputer, 13 ... power supply / voltage register, 14 ... AD converter, 15 ... input switching amplifier.

Claims (1)

(57) [Claims] 1. A switching power supply configured to switch an input direct current to convert to a desired voltage, rectify and smooth and supply the load to a load, wherein a switching frequency and a switching operation at which the load loss has a minimum characteristic. Storage means for storing a plurality of pieces of switching information in combination with an on-time width; voltage / current detection means for detecting an output voltage and an output current for the load; voltage and current detected by the voltage / current detection means Calculating the power consumption of the load from the value, selecting and reading switching information of the combination of the switching frequency and the switching operation ON time width at which the loss of the load with respect to the power consumption is the minimum from the storage means; A switching operation based on the switching information read from the storage means; A switching power supply, comprising: control means for controlling.