JP2002252974A - Switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power unit which allows to obtain the correct operation timing even if the input voltage fluctuates. SOLUTION: The switching power unit comprises a switching circuit 2 for converting a direct current input into an alternating current, an output rectifier circuit 5 and an output smoother circuit 6 for converting the alternating current into a direct current output, and a control circuit 7 for controlling the switching operation of the switching circuit 2. The control circuit 7 includes a first means for estimating the input voltage value of the direct current input, a second means for determining whether an inductor current flowing in an inductor 17 is in a continuous state or in a discontinuous state, based on the estimated input voltage value, and a third means for controlling the switching operation of the switching circuit 2 based on a first algorithm when it is determined to be in a continuous state, and for controlling the switching operation of the switching circuit 2 based on a second algorithm when it is determined to be in a discontinuous state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a switching power supply, and more particularly, to a switching power supply capable of obtaining correct operation timing.

[0002]

2. Description of the Related Art Heretofore, a so-called DC / DC converter has been known as a switching power supply device. In a typical DC / DC converter, a DC input is once converted into an AC using a switching circuit, then transformed (step-up or step-down) using a transformer, and further converted into a DC using an output circuit. This makes it possible to obtain a DC output having a voltage different from the input voltage.

Here, a choke input type smoothing circuit is sometimes used as an output circuit used in a DC / DC converter. When a choke input type smoothing circuit is used as the output circuit of the DC / DC converter, there are two operation modes, that is, an operation mode in a so-called “continuous state” and an operation mode in a “discontinuous state”. Here, the continuous state refers to a state in which a current always flows through an inductor included in the output circuit, and this state is established when the connected load is large (when the output current is large). On the other hand, the discontinuous state refers to a state in which a current is intermittently flowing through an inductor constituting an output circuit, and this state is established when the connected load is small (when the output current is small).

Generally, in this type of DC / DC converter, the operation of the switching circuit is controlled so that the output voltage becomes constant by monitoring the output voltage, the inductor current, and the like. The algorithm used must be changed depending on whether the output circuit is in a continuous state or a discontinuous state. That is, if the operation of the switching circuit is controlled in the discontinuous state by the same algorithm as in the continuous state, the output voltage rises and greatly deviates from a desired value. For this reason, conventionally, in a switching power supply device, it is determined whether an output circuit is in a continuous state or a discontinuous state, and based on the result, operation control is performed using a different algorithm between the continuous state and the discontinuous state. I was

As an example of such an algorithm switching, there is a switching power supply device disclosed in Japanese Patent Application Laid-Open No. 11-206119.

In the switching power supply described in the publication, it is determined whether the output circuit is in a continuous state or a discontinuous state. As a result, if it is determined that the output circuit is in a continuous state, the output voltage or the inductor is determined. The operation timing is determined by performing a predetermined operation based on the current or the like, and when it is determined that the state is discontinuous, the operation timing is determined by referring to a table provided in advance. .

Here, whether the output circuit is in a continuous state or a discontinuous state is determined by a value (current command value) calculated using an actually detected output voltage and a predetermined constant. This is done by comparing

[0008]

However, in the switching power supply described in the publication, the above constants are determined on the assumption that the input voltage always coincides with a predetermined voltage. Therefore, when the actual input voltage is different from the predetermined voltage, there is a problem that it is not correctly determined whether the state is the continuous state or the discontinuous state. As a result, the operation timing of the switching circuit is not correctly determined, and a desired output voltage may not be obtained.

Further, since the above table is also created on the assumption that the input voltage always matches the predetermined voltage, if the actual input voltage is different from the above voltage value, However, the correct operation timing of the switching circuit cannot always be obtained from such a table.

Although the above-mentioned problem does not occur when the actual input voltage is substantially equal to a predetermined voltage, the actual input voltage may fluctuate greatly depending on the power supply supplying the input voltage. When the fluctuation is large, it is difficult to obtain the correct operation timing of the switching circuit.

Therefore, an object of the present invention is to provide a switching power supply device that can obtain correct operation timing even when the input voltage fluctuates.

[0012]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
DC-AC conversion means for converting DC input into AC by switching operation, AC-DC conversion means having at least an inductor and converting the AC into DC output, and controlling the switching operation of the DC-AC conversion means. A control circuit, the control circuit estimating an input voltage value of the DC input, and an inductor current flowing through the inductor in a continuous state or a discontinuous state based on the estimated input voltage value. A second means for judging whether the inductor current is in a continuous state, and, if it is determined that the inductor current is in a continuous state, based on a first algorithm,
Controlling the switching operation of the AC conversion means, and controlling the switching operation of the DC-AC conversion means based on a second algorithm when it is determined that the inductor current is in a discontinuous state; And a switching power supply device.

According to the present invention, the input voltage value of the DC input is estimated, and based on the input voltage value, it is determined whether the inductor current flowing through the inductor is in a continuous state or a discontinuous state. It is possible to make a determination according to the input voltage value. Therefore, even when the input voltage value of the DC input fluctuates, the appropriate switching operation is performed, so that the output voltage value of the DC output can be stabilized at a desired value.

In a preferred embodiment of the present invention, the first means is based on at least an output voltage value of the DC output and at least one of the inductor current and a switching current flowing through the DC-AC conversion means. , The input voltage value of the DC input.

According to the preferred embodiment of the present invention, since the input voltage value of the DC input is estimated in consideration of not only the output voltage value of the DC output but also the inductor current or the switching current, accurate estimation is performed. It becomes possible.

In a further preferred aspect of the present invention, the control circuit further comprises fourth means for converting the estimated input voltage value to a threshold value,
Is determined by comparing the threshold value with a reference voltage value.

In a further preferred aspect of the present invention, the conversion by the fourth means is performed by referring to a table.

In a further preferred aspect of the present invention, the operation according to the second algorithm is performed using at least the threshold value and the estimated input voltage value without referring to a table. .

According to a further preferred embodiment of the present invention, even in a discontinuous state, the switching operation is performed by using the output voltage value of the DC output and the value to be calculated by the inductor current or the switching current. Is performed, an appropriate switching operation is performed even in the discontinuous state.

In a further preferred aspect of the present invention, the AC-DC converter includes a transformer for transforming the AC, an output rectifier circuit for rectifying an output of the transformer, and an output rectifier circuit including the inductor. An output smoothing circuit for smoothing the output.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
A preferred embodiment of the present invention will be described in detail.

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

As shown in FIG. 1, the switching power supply according to this embodiment includes a switching circuit 2 connected to a DC input power supply 1, an inductor 3 connected to one output of the switching circuit 2, and a switching circuit. Circuit 2
A main transformer 4 having a primary winding connected between the other output of the main transformer 4 and the inductor 3;
An output rectifier circuit 5 connected to the next winding;
, A control circuit 7 and a drive circuit 8. The output of the output smoothing circuit 6 is connected to a load 9.

The switching circuit 2 includes switch elements 11 and 12 connected in series between the DC input power supplies 1, and switch elements 1 and 12 similarly connected in series between the DC input power supplies 1.
3 and 14, the nodes of the switch elements 11 and 12 are connected to one end of the primary winding of the main transformer 4 via the inductor 3, and the switch elements 13 and 14
Is directly connected to the other end of the primary winding of the main transformer 4. As shown in FIG. 1, in this embodiment, n-channel MOSFETs are used as the switch elements 11 to 14.

The inductor 3 includes switching elements 11 to 14
Together with the parasitic capacitance of the resonance circuit. As a result, the switching elements 11 to 14 are turned on by ZVS.
(Zero Voltage Switching) is possible, so that switching loss is reduced and noise is suppressed.

The main transformer 4 is a transformer having a turn ratio between the primary winding and the secondary winding of 1: m, and has two secondary windings as shown in FIG. The midpoint between these two secondary windings is connected to the negative terminal of the load 9. Hereinafter, the voltage generated in the primary winding of the main transformer 4 is referred to as V1
Is defined.

The output rectifier circuit 5 is connected to the main transformer 4
At the end of the secondary winding, there are provided two diodes 15 and 16 each having an anode connected, and the cathodes of these two diodes are connected in common. Hereinafter, the common cathode connection point of these two diodes 15 and 16 is called a “rectification point”, and the voltage appearing here is defined as V2.

The output smoothing circuit 6 includes an inductor 17 connected between the rectification point and the positive terminal of the load 9 and a load 9.
, And a capacitor 18 connected between both ends of the capacitor. Hereinafter, the voltage appearing across the load 9 is referred to as “output voltage (V
o), and the current flowing through the load 9 is referred to as the “output current (I
o) ". Further, the current flowing through the inductor 17 is referred to as “inductor current IL”. As shown in FIG. 1, between the negative terminal of the load 9 and the main transformer 4,
A current detection circuit 19 for detecting the inductor current IL is provided.

The control circuit 7 samples the output voltage Vo /
A sample / hold circuit 21 for holding, a sample / hold circuit 22 for sampling / holding the inductor current IL detected by the current detection circuit 19, and an analog value held in the sample / hold circuits 21 and 22 are converted into digital values, respectively. A / D converters 24 and 25 for converting the data into an A / D converter, a calculation unit 27 for performing a predetermined calculation based on the digital output from the A / D converters 24 and 25, and switch elements 11 to 14, the phase control signal (gs1
1 to gs14). Sampling by the sample / hold circuits 21 and 22 is performed in response to a sampling signal S generated by the arithmetic unit 27.

FIG. 2 is a circuit diagram schematically showing an internal configuration of drive circuit 8.

As shown in FIG. 2, the drive circuit 8 includes four drivers 31 to 34. Drivers 31 to 3
4 are the corresponding phase control signals (gs11 to gs
14), the switching element 11 of the switching circuit 2
GS11 to GS14, which are amplified to a voltage and a current level capable of driving 〜14, are supplied to the gates of the corresponding switch elements 11 to 14, respectively.

FIG. 3 is an operation waveform diagram showing a basic operation of the switching power supply according to the present embodiment.

The basic operation of the switching power supply according to this embodiment is as follows. That is, GS11
And GS14 are at a high level, that is, while the switch elements 11 and 14 are both on, the DC input power supply 1 is connected to the primary winding of the main transformer 4.
Is applied in one direction, and a DC input power supply is applied to the primary winding of the main transformer 4 during a period when both GS12 and GS13 are at a high level, that is, a period when both the switching elements 12 and 13 are on. By applying the input voltage Vin from No. 1 in the reverse direction, the voltage V1 generated in the primary winding of the main transformer 4 has an AC waveform. The peak value of the AC waveform is multiplied by m in the secondary winding of the main transformer 4 and further rectified by the output rectifier circuit 5.

Here, GS11 and GS1 in FIG.
4 is high level, and GS12
The reason why the voltages V1 and V2 are not generated and the inductor current IL continues to decrease in the initial period of the period when both the GS13 and the GS13 are at the high level is that the energy regeneration of the inductor 17 is not completed.

As shown in FIG. 3, the voltage V2 at the rectification point
Is a pulse waveform having a predetermined width whose peak value is Vin × m, and its time average value is the output voltage Vo. Therefore, in order to control the value of the output voltage Vo, the phases of GS11 and GS14 and GS12 and G
What is necessary is just to control the phase of S13. Further, the waveform of the inductor current IL is a waveform obtained by superimposing the ripple current determined by the voltage waveform V2 at the rectification point and the inductance of the inductor 17 on the output current Io.

As shown in FIG. 3, the inductor current I
If the lower end of the L waveform is 0 A (amperes) or more, it means that current always flows through the inductor 17. That is, such a state is a continuous state. When the load 9 is sufficiently large, this continuous state is established. On the other hand, when the load 9 is small, since the output current Io decreases, the lower end of the waveform of the inductor current IL may be 0A.

FIG. 4 is a waveform diagram showing a state where the lower end of the waveform of inductor current IL is 0 A. As shown in FIG. 4, the value of the output current Io when the lower end of the waveform of the inductor current IL is 0 A is defined as Icp.

When the value of the output current Io further falls below Icp, the inductor current IL flows intermittently through the inductor 17. That is, a discontinuous state occurs.

FIG. 5 is a waveform diagram showing a case where inductor current IL is in a discontinuous state.

That is, when the value of the output current Io is Icp (FIG. 4) and when the output current Io is larger than this, the inductor current IL is in a continuous state (FIG. 3).
And if smaller than this, the inductor current IL
Becomes a discontinuous state (FIG. 5). Output current amount Ic defining the boundary between continuous state and discontinuous state of inductor current IL
p is called a discontinuity point (critical point).

Now, in order to maintain the output voltage Vo at a desired constant value, it is necessary to control the operation timing of the switching circuit 2. However, such control is performed when the inductor current IL is in a continuous state and when the inductor current IL is in a continuous state. Different control is required depending on the state. Hereinafter, the switching circuit 2
The method for controlling the operation timing of the operation will be described in detail.

FIG. 6 is a flowchart showing an algorithm for determining the operation timing of the switching circuit 2. The operation according to the algorithm is executed by software or hardware by referring to the table 30 provided in the operation unit 27.

First, when the arithmetic unit 27 generates the sampling signal S at a predetermined timing, in response to this,
Sampling by the sample / hold circuits 21 and 22 is performed. As described above, the sample / hold circuit 21 samples the output voltage Vo, and the sample / hold circuit 22 samples the inductor current IL detected by the current detection circuit 19. Note that the sampling signal S may be generated for each integral multiple of one cycle of the phase control signal generated by the phase control signal generation unit 28. The output voltage Vo and the inductor current IL, which are analog values held in the sample / hold circuits 21 and 22, respectively, are converted into digital signals by A / D converters 24 and 25, respectively, and supplied to the arithmetic unit 27.

In the arithmetic section 27 receiving the digital signal, first, the current command value ir is calculated based on the equation (1).
(N + 1) is calculated (step S1). Here, the current command value ir (n + 1) is the sampling point (n +
This is a control target value of the inductor current IL in 1).

[0045]

(Equation 1) Here, n is an arbitrary positive integer indicating a sampling point. Therefore, △ Vo (n-1) indicates the value of △ Vo calculated based on the detection value obtained at the sampling point (n-1). Note that Vref is a required output voltage value (reference voltage value), and K1 and K2 are circuit constants.

Thus, the current command value ir (n + 1)
Is calculated, the input voltage estimated value tpv (n) is calculated based on the equation (2) (step S2). Here, the estimated input voltage value tpv is the sampling point n−1
Is a value calculated based on the value detected in
sw / Vs (n). Where Tsw
Is ス イ ッ チ ン グ of the switching cycle, and Vs (n) is obtained by multiplying the input voltage Vin (n) by the number m of secondary windings of the transformer, and is m × Vin (n).

[0047]

(Equation 2) Here, K is a circuit constant, and ie (n-1) is an estimated current value. The estimated current value ie (n) is a value of the inductor current IL expected at the sampling point (n). In the equation (2), the estimated current value ie (n−n) calculated based on the detection value obtained at the sampling point (n−2).
1) and the input voltage estimated value tpv (n-1) calculated based on the detected value obtained at the sampling point (n-2), so that the estimated current value ie is obtained as in the initial state. (N
-1) or when the input voltage estimated value tpv (n-1) does not exist, the estimated current value ie (n-1) is 0 (zero), and the input voltage estimated value tpv (n-1) is a predetermined value. Is calculated as

Thus, the estimated input voltage tpv
When (n) is obtained, next, the threshold value Vd (n) is calculated based on the equation (3) (step S3).

[0049]

(Equation 3) In calculating the threshold value Vd (n), the table 30 in the arithmetic unit 27 is referred to. That is, the memory is read using the input voltage estimated value tpv (n) obtained in step S2 as an address, and table (tpv (n)), which is data stored therein, is used. The address of this table 30 (input voltage estimated value tpv
(N)) and the corresponding data (table (tpv
The relationship with (n))) is represented by a general formula as shown in formula (4).

[0050]

(Equation 4) Here, Lf is the inductance of the inductor 17.

After the threshold value Vd is obtained in this manner, the threshold value Vd (n) is compared with the reference voltage value Vref (step S4).

This comparison is performed to determine whether the inductor current IL is in a continuous state or a discontinuous state. If the threshold value Vd (n) is larger than the reference voltage value Vref, the state is a continuous state. And the threshold value Vd
If (n) is smaller than the reference voltage value Vref, it is determined that the state is a discontinuous state.

If it is determined that the threshold value Vd (n) is larger than the reference voltage value Vref (in a continuous state), then the estimated current value ie is determined based on the equation (5).
(N) is calculated (step S5).

[0054]

(Equation 5) Here, vir (n) is a command voltage value, that is, a control target value of the output voltage Vo at the sampling point (n). In the equation (5), the command voltage value vir (n−n) calculated based on the detection value obtained at the sampling point (n−2) is obtained.
Since 1) is used, the command voltage v
If ir (n-1) does not exist, it is calculated as 0 (zero).

When the estimated current value ie (n) is obtained in this manner, the command voltage value vi is then calculated based on equation (6).
r (n) is calculated (step S6).

[0056]

(Equation 6) Then, when the command voltage value vir (n) is obtained, next, the phase phase (n) is calculated based on the equation (7) (step S7).

[0057]

(Equation 7) The phase phase (n) is the phase of the phase control signals (gs11 and gs14) to be generated by the phase control signal generator 28 at the sampling point (n) and the phase control signal (g
s12 and gs13), and the phase control signal generator 28 receives the information and determines the phase control signal (gs).
11 and gs14) and the phase of the phase control signals (gs12 and gs13).

On the other hand, as a result of the judgment in step S4,
If it is determined that the threshold value Vd (n) is smaller than the reference voltage value Vref (discontinuous state), the threshold value Vd (n) obtained in step S3 is used as it is as the command voltage value vi.
r (n) (step S8), and then the estimated current value ie (n) is calculated based on equation (8) (step S8).
9).

[0059]

(Equation 8) Then, in the same manner as described above, the phase p
phase (n) is calculated (step S7), and the phase control signal (gs11) is calculated based on the phase (n).
To gs14) is generated.

As described above, when the inductor current IL is in the continuous state and in the discontinuous state, an appropriate phase phase (n) can be obtained. Here, whether the inductor current IL is in the continuous state or the discontinuous state is determined in step S4 by the threshold V
The comparison is performed between d (n) and the reference voltage value Vref, and the table 30 is used for calculating the threshold value Vd (n). As described above, the table 30
Is composed of data using the input voltage estimated value tpv (n) as an address. That is, in the present embodiment, the detected output voltage Vo and inductor current I
The threshold value Vd (n) is calculated based on the input voltage estimated value tpv (n) calculated based on L, and the threshold value Vd (n) is compared with the reference voltage value Vref. This determines whether the inductor current IL is in a continuous state or in a discontinuous state. Therefore, when the input voltage is different from a predetermined value, particularly when the input voltage is fluctuating, Also, the above determination can be accurately performed based on the input voltage estimated value tpv (n).

Further, in this embodiment, when it is determined that the inductor current IL is in a discontinuous state, the threshold Vd (n) obtained using the output voltage Vo and the inductor current IL is changed to the command voltage. Since the value vir (n) is set, even if the input voltage is different from the predetermined value, particularly, even if the input voltage is fluctuating, an appropriate phase phase is set in step S7.
(N) can be obtained.

As a result, in the switching power supply according to the present embodiment, even when the input voltage fluctuates, the correct operation timing of the switching circuit 2 can be obtained. The output voltage Vo can be stabilized at a desired value (Vref) both in a certain case and in a discontinuous state.

The present invention is not limited to the above embodiments, and various changes can be made within the scope of the invention described in the claims, and they are also included in the scope of the present invention. It goes without saying that it is a thing.

That is, the switching power supply device to which the present invention can be applied is not limited to the switching power supply device having the circuit configuration shown in FIG. 1, but can be applied to a switching power supply device having another circuit configuration. FIG. 7 shows an example of a switching power supply device having another circuit configuration. When the present invention is applied to a switching power supply having the circuit configuration shown in FIG.
The ON period of 0 may be determined based on ton. Of course, the present invention can be applied to a switching power supply device having a circuit configuration other than the above. According to the circuit configuration, control of the switching circuit is performed not only by the phase and the on period ton, but also by the duty, the off period, the frequency, May be performed using the above signal.

Further, in the switching power supply device according to the above embodiment, the sample / hold circuit 22 samples the value of the inductor current IL, and the calculation is performed by the calculation unit 27 based on the sampled value. Instead, the value of the input current and output current flowing through the switching circuit 2 or the value of the current (switching current) flowing through the switching elements 11 to 14 itself may be sampled, and the same calculation may be performed based on the sampled value.

The execution order of steps S8 and S9 shown in FIG. 6 may be reversed.

[0067]

As described above, according to the present invention,
It is possible to provide a switching power supply device that can obtain correct operation timing even when the input voltage fluctuates.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram schematically showing an internal configuration of a drive circuit 8.

FIG. 3 is an operation waveform diagram showing a basic operation of the switching power supply device according to a preferred embodiment of the present invention.

FIG. 4 is a waveform diagram showing a state where the lower end of the waveform of the inductor current IL is 0A.

FIG. 5 is a waveform diagram showing a case where the inductor current IL is in a discontinuous state.

FIG. 6 is a flowchart illustrating an algorithm for determining an operation timing of the switching circuit 2.

FIG. 7 is a circuit diagram showing an example of a switching power supply device having another circuit configuration.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 DC input power supply 2 switching circuit 3 inductor 4 main transformer 5 output rectifier circuit 6 output smoothing circuit 7 control circuit 8 drive circuit 9 load 10 to 14 switch element 15, 16 diode 17 inductor 18 capacitor 19 current detection circuit 21, 22 samples / Hold circuit 24, 25 A / D converter 27 Operation unit 28 Phase control signal generation unit 30 Table 31-34 Driver

Claims (6)

[Claims] A DC-AC converter for converting a DC input into an AC by a switching operation; an AC-DC converter having at least an inductor for converting the AC into a DC output; A control circuit for controlling a switching operation, the control circuit estimating an input voltage value of the DC input, and an inductor current flowing through the inductor based on the estimated input voltage value is in a continuous state. And a switching means of the DC-AC converter based on a first algorithm when it is determined that the inductor current is in a continuous state. And if it is determined that the inductor current is in a discontinuous state, the DC-AC conversion means is controlled based on a second algorithm. Third control of the switching operation
And a switching power supply device. 2. The method according to claim 1, wherein the first unit is configured to control the input of the DC input based on at least an output voltage value of the DC output and at least one of the inductor current and a switching current flowing through the DC-AC conversion unit. The switching power supply according to claim 1, wherein the voltage value is estimated. 3. The control circuit further comprises: fourth means for converting the estimated input voltage value into a threshold value, wherein the judgment by the second means determines that the threshold value and a reference voltage value 3. The switching power supply according to claim 1, wherein the switching power supply is performed by comparing the following. 4. The switching power supply according to claim 3, wherein the conversion by the fourth means is performed by referring to a table. 5. The method according to claim 3, wherein the calculation according to the second algorithm is performed using at least the threshold value and the estimated input voltage value without referring to a table. Or the switching power supply device according to 4. 6. An AC-DC converter, comprising: a transformer for transforming the AC; an output rectifier circuit for rectifying an output of the transformer; an output smoothing circuit including the inductor for smoothing an output of the output rectifier circuit. The switching power supply device according to any one of claims 1 to 5, further comprising: