Switching Power Supply

Abstract

To provide a switching power supply device capable of correcting an error in an output voltage with high accuracy even with respect to an individual product.SOLUTION: An FET 6 is connected in series to primary winding 3 of a transformer 2. A current detection resistor 7 is connected in series between the FET 6 and a primary side ground. A diode 10 is connected in series to secondary winding 4. An output capacitor 11 is connected in parallel to a series circuit of the secondary winding 4 and the diode 10. A primary side feedback unit 9 generates a first feedback voltage corresponding to a secondary side output voltage of the transformer 2. A control unit 8 PWM-controls the FET 6 on the basis of a first control voltage obtained by amplifying a difference between the first feedback voltage and a first reference voltage, and a current value flowing to the current detection resistor 7. A secondary side feedback unit 12 generates a second control voltage on the basis of a second feedback voltage corresponding to the secondary side output voltage, and a second reference voltage. An isolated communication unit 13 transmits information on the second control voltage to the control unit 8. The control unit 8 receives information on the second control voltage to adjust the first reference voltage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a switching power supply device. [Background technology]

[0002] Patent Document 1 discloses a technique for correcting an error in the output voltage of a switching power supply device, which is a so-called flyback converter. This technique calculates the secondary current of a transformer and corrects a target voltage to cancel out the error in the output voltage caused by the secondary current. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6561612 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technique of Patent Document 1 has a problem in that correction is performed by calculation using fixed values, and therefore correction cannot be performed to accommodate variations in individual products.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching power supply device that can correct output voltage errors with high precision even for individual products. [Means for solving the problem]

[0006] According to the switching power supply device of claim 1, a switching element is connected in series with a primary winding of a transformer, a current detection resistor is connected in series between the switching element and a reference potential point, and a rectifying element is connected in series with a secondary winding. An output capacitor is connected in parallel with the series circuit of the secondary winding and the rectifying element. A primary-side feedback unit generates a first feedback voltage corresponding to the output voltage on the secondary side of the transformer. A control unit PWM-controls the switching element based on a first control voltage obtained by amplifying the difference between the first feedback voltage and a first reference voltage and the value of a current flowing through the current detection resistor.

[0007] The secondary-side feedback unit generates a second control voltage based on a second reference voltage and a second feedback voltage corresponding to the output voltage of the secondary side of the transformer. The isolated communication unit transmits information about the second control voltage to the control unit, and the control unit adjusts the first reference voltage by receiving the information about the second control voltage from the isolated communication unit.

[0008] With this configuration, the first reference voltage used for PWM control of the switching element is adjusted by the control unit acquiring information on the second control voltage generated based on the second reference voltage and the second feedback voltage corresponding to the output voltage on the secondary side of the transformer. Therefore, the output voltage can be corrected with high precision for each product, even if there are variations in the constants of the circuit elements, etc. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a switching power supply device according to a first embodiment. [Figure 2] Diagram showing the configuration of the primary side feedback section [Figure 3] Diagram showing the configuration of the secondary side feedback section [Figure 4] Diagram showing the configuration of the control unit [Figure 5] Diagram showing an example of the configuration of the insulated communication unit (part 1) [Figure 6] Diagram showing an example of the configuration of the insulated communication unit (part 2) [Figure 7] Startup control sequence diagram [Figure 8] This diagram shows the control sequence when the output voltage Vout exceeds a specific voltage range after startup. [Figure 9] A diagram showing the processing contents executed periodically in secondary side control [Figure 10] A diagram showing how the output voltage Vout changes with changes in the load current when the input voltage Vin is constant. [Figure 11] This diagram shows the change in output voltage Vout relative to the change in input voltage Vin when the load current is constant. [Figure 12] FIG. 10 is a diagram illustrating a configuration of a switching power supply device according to a second embodiment. [Figure 13] Diagram showing the configuration of the primary side feedback section [Figure 14] Timing chart showing the primary side control [Figure 15] FIG. 10 is a diagram showing a configuration in which a switching power supply device is applied to a gate drive IC according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] (First embodiment) As shown in Fig. 1, the switching power supply 1 of this embodiment is a so-called flyback converter that uses a transformer 2. The transformer 2 includes a primary winding 3, a secondary winding 4, and a tertiary winding 5. An input voltage Vin is applied to one end of the primary winding 3, and a series circuit of an N-channel MOSFET 6, which is an example of a switching element, and a current detection resistor 7 is connected between the other end and the primary ground. The primary ground corresponds to a reference potential point. The number of turns of the tertiary winding 5 may be the same as or different from that of the secondary winding 4.

[0011] A PWM signal generated by the control unit 8 is input to the gate of the FET 6 as a gate drive signal. The source of the FET 6 is connected to the input terminal of the control unit 8, and the terminal voltage of the current detection resistor 7 is input to the control unit 8. Both ends of the tertiary winding 5 are connected to the input terminals of the primary side feedback unit 9. The output terminal of the primary side feedback unit 9 is connected to the input terminal of the control unit 8.

[0012] A series circuit of a diode 10 and a capacitor 11, which are rectifying elements, is connected in parallel to the secondary winding 4. The common connection point of the diode 10 and the capacitor 11 is the output terminal of the switching power supply device 1, and a voltage Vout is output from this terminal. The common connection point of the secondary winding 4 and the capacitor 11 is connected to the secondary-side ground. The voltage Vout is input to a secondary-side feedback unit 12. An output signal of the secondary-side feedback unit 12 is input to an input terminal of the control unit 8 via an insulated communication unit 13.

[0013] 2, the primary-side feedback section 9 includes, for example, a series circuit of a diode 14 and a capacitor 15 connected in parallel to the tertiary winding 5, a resistor 16 connected in parallel to the capacitor 15, and a voltage divider circuit made up of resistors 17a and 17b. The common connection point of resistors 17a and 17b indicates a voltage obtained by dividing the terminal voltage of resistor 16, and this voltage becomes the first feedback voltage. Resistor 16 corresponds to a load resistor.

[0014] 3, the secondary-side feedback section 12 includes a voltage divider circuit 21 consisting of a series circuit of resistor elements 21a and 21b, which is connected between the output terminal Vout and the secondary-side ground. An RC filter circuit 24 consisting of a series circuit of a resistor element 22 and a capacitor 23 is connected between the common connection point of the resistor elements 21a and 21b and the ground. An input terminal of an A / D converter 25 is connected to an output terminal of the RC filter circuit 24, and an output terminal of the A / D converter 25 is connected to an input terminal of a subtractor 26.

[0015] Subtractor 26 subtracts second reference data, which is data equivalent to the second reference voltage, from the output data of A / D converter 25, and outputs the result to cumulative adder 27 in the next stage. Cumulative adder 27 cumulatively adds the data output from subtractor 26, and outputs the addition result to gain multiplication unit 28 in the next stage. Gain multiplication unit 28 multiplies the data output from cumulative adder 27 by a predetermined gain, and outputs the result as second control data, which is data equivalent to the second control voltage.

[0016] 4, in control unit 8, a first feedback voltage and a first reference voltage are input to error amplifier 31. The first reference voltage is generated by subtracting second control data from first reference data, which is set in advance according to the output voltage of switching power supply device 1, using subtractor 32, and then D / A converting the result of the subtraction using D / A converter 33.

[0017] The output voltage of the error amplifier 31 is input to the PWM control unit 34. The terminal voltage of the current detection resistor 7 is also input to the PWM control unit 34. The PWM control unit 34 compares the two voltages to generate a PWM signal, which is input to the next-stage switch control unit 35. The switch control unit 35 drives the gate of the FET 6 in accordance with the input PWM signal.

[0018] The insulated communication unit 13 may employ, for example, a capacitive isolation method in which a capacitor 38 is used to connect a transmitter 36 and a receiver 37 as shown in FIG. 5, or a magnetic isolation method in which a transformer 39 is placed between the transmitter 36 and the receiver 37 as shown in FIG. 6.

[0019] Next, the operation of this embodiment will be described. As shown in Fig. 7, when the input voltage rises from a stopped state to a certain level, the switching power supply device 1 starts switching with a soft start using primary-side control. Then, the output voltage starts to rise. When the output voltage exceeds the target voltage, the soft start ends and the device switches to normal operation using primary-side control.

[0020] With primary-side control alone, an error occurs in the output voltage, so secondary-side control is also used. By starting secondary-side control, the output voltage is adjusted so that the error with respect to the target voltage is eliminated. As shown in Figure 9, the "AD conversion," "calculation," "transmission," and "waiting time" phases are repeatedly executed during the secondary-side control cycle. AD conversion: The secondary feedback voltage, i.e. the output voltage, is divided and the filtered voltage is converted to AD. · Calculation: Calculate the second control data from the secondary side feedback data, which is the AD conversion result. Transmission: The insulated communication unit 13 transmits the second control data from the secondary side to the primary side. Waiting time: The waiting time until the next secondary control cycle begins.

[0021] The control period of the secondary-side control, which reflects the secondary-side feedback data, must be set slow enough so as not to affect the stability of the primary-side feedback control. Furthermore, if the control period is too slow, the reflection on the output voltage will be delayed, so this point must also be taken into consideration when setting an appropriate time. For example, if the crossover frequency of the primary-side control is 1 kHz, the secondary-side control period should be approximately 0.1 to 10 seconds. Furthermore, if there is sufficient time for obtaining output voltage data and for isolated communication, the calculation processing of the secondary-side feedback can be performed via isolated communication.

[0022] When the input voltage drops to a certain level, the switching power supply 1 stops switching. Also, if the input voltage does not drop but the output voltage exceeds a specific voltage range due to an overcurrent or a fault, the switching power supply 1 stops secondary-side control.

[0023] As shown in Figure 8, if the input voltage does not drop during operation after startup but the output voltage Vout exceeds a specific voltage range, the secondary-side control may be stopped. Furthermore, the secondary-side control may be stopped when a power supply protection function, such as overheat protection, overcurrent protection, or short-circuit protection, is activated. The secondary-side control may be stopped, for example, by preventing the primary-side feedback unit 9 or the secondary-side feedback unit 12 from updating the secondary-side feedback data. Furthermore, the primary-side feedback unit 9 may stop accepting secondary-side feedback data and reset the data to its initial value.

[0024] The measurement results shown in Figure 10 show a comparison between with and without secondary-side control, with the input voltage Vin set to 14V and the output voltage Vout set to 20V. It can be seen that the output voltage Vout is better able to follow changes in the load current when secondary-side control is implemented. Furthermore, the measurement results shown in Figure 11 show a comparison between with and without secondary-side control, with the input voltage Vin set to 14V and the load current Iout set to 60mA. It can also be seen that the output voltage is better able to follow changes in the input voltage when secondary-side control is implemented.

[0025] As described above, according to this embodiment, in the switching power supply device 1, the FET 6 is connected in series with the primary winding 3 of the transformer 2, the current detection resistor 7 is connected in series between the FET 6 and the primary-side ground, and the diode 10 is connected in series with the secondary winding 4. The output capacitor 11 is connected in parallel with the series circuit of the secondary winding 4 and the diode 10. The primary-side feedback unit 9 generates a first feedback voltage corresponding to the output voltage on the secondary side of the transformer 2. The control unit 8 PWM-controls the FET 6 based on the value of the current flowing through the current detection resistor 7 and on the first control voltage obtained by amplifying the difference between the first feedback voltage and the first reference voltage.

[0026] The secondary-side feedback unit 12 generates a second control voltage based on a second reference voltage and a second feedback voltage corresponding to the output voltage on the secondary side of the transformer 2. The insulating communication unit 13 transmits information about the second control voltage to the control unit 8, and the control unit 8 adjusts the first reference voltage by receiving the information about the second control voltage from the insulating communication unit 13.

[0027] With this configuration, the first reference voltage used for PWM control of the FET 6 is adjusted by the control unit 8 acquiring information on the second control voltage generated based on the second reference voltage and the second feedback voltage corresponding to the output voltage on the secondary side of the transformer 2. Therefore, the output voltage can be corrected with high precision in accordance with each product, even if there are variations in the constants of the circuit elements, etc.

[0028] In addition, the transformer 2 has a tertiary winding 5 on the primary side, and the primary side feedback unit 9 generates a first feedback voltage proportional to the secondary side output voltage detected via the tertiary winding 5, so that feedback information on the secondary side output voltage of the transformer 2 can be obtained more directly and stably.

[0029] (Second embodiment) 12, a switching power supply device 41 of the second embodiment uses a transformer 42 having only a primary winding 3 and a secondary winding 4, instead of the transformer 2. A primary-side feedback unit 43 is connected to the primary winding 3, and includes a control unit 44 instead of the control unit 8.

[0030] 13, the primary-side feedback unit 43 includes a voltage detection unit 45 that detects the terminal voltage of the primary winding 3, a gain multiplication unit 46 that multiplies the detected voltage by a feedback gain, and a sample-and-hold unit 47 that samples and holds the output signal of the gain multiplication unit 46. A sampling clock CKSH is input to the sample-and-hold unit 47 from the control unit 44. The output signal of the sample-and-hold unit 47 becomes the first feedback voltage.

[0031] Next, the operation of the second embodiment will be described. In the second embodiment, information about the voltage across the secondary winding 4, which is included in the flyback voltage generated when the FET 6 is turned off, is obtained to generate a primary-side feedback voltage. As shown in FIG. 14, when the gate voltage Vg reaches a high level, the FET 6 turns on, and the current Ip flowing through the primary winding 3 also flows through the current detection resistor 6. At this time, the voltage between the terminals Vin and Vsw of the primary winding 3 becomes 0V.

[0032] When the gate voltage Vg goes low and the FET 6 turns off, no current flows through the primary winding 3, and a flyback voltage is generated between the terminals Vin and Vsw of the primary winding 3, causing the voltage between the terminals to rise significantly. The control unit 44 outputs a sampling clock CKSH a fixed time after the falling edge of the gate voltage Vg. The sample-and-hold unit 47 samples the voltage between the terminals when the sampling clock CKSH goes high, and holds the sampled voltage when it goes low. The control unit 44 sets the sampling clock CKSH to low after a time Tsh has passed since the falling edge of the gate voltage Vg.

[0033] If the voltage sampled by the sample-and-hold unit 47 is Vsh, the voltage Vsh is expressed by the following equation. Vsh=G×(N1 / N2)×(Vout+Vf+Is×r) G: Feedback gain of the gain multiplication unit 46 N1: Number of turns of primary winding 3 N2: Number of turns of secondary winding 4 Vf: forward voltage of diode 10 Is: Current flowing through secondary winding 4 r: Resistance component in the output voltage path on the secondary side The voltage Vsh is input to the control unit 44 as a primary side feedback voltage.

[0034] As described above, according to the second embodiment, the primary-side feedback unit 43 generates the first feedback voltage from the flyback voltage generated after turning off the FET 6. Specifically, the terminal voltage of the primary winding 3 on which the flyback voltage is superimposed is multiplied by the feedback gain, and the result is sampled and held by the sample-and-hold unit 47 and output to the control unit 44. Therefore, the first feedback voltage can be generated without using the transformer 2 having the tertiary winding 5 as in the first embodiment.

[0035] (Third embodiment) 15, the third embodiment is achieved by applying the switching power supply device 1 of the first embodiment to a gate drive IC 50 for an IGBT 51. The IGBTs 51H and 51L are connected in series between a battery, which is a power supply, and a secondary ground, and their common connection point is connected to one end of a motor coil 52. The IGBT 51H is driven by a gate drive IC 50H, and the IGBT 51L is driven by a gate drive IC 50L, but their configurations are symmetrical, and the following description will focus on the gate drive IC 50H.

[0036] The output voltage Vout of the switching power supply 1 is supplied as a driving power supply to a gate driver 53 that drives the gate of the IGBT 51H. The output terminal of the gate driver 53 is connected to the gate of the IGBT 51H via a gate resistor 54. The gate driver 53 is controlled by a drive control unit 55 that is configured by a microcomputer or the like. A control input from the drive control unit 55 is input to the gate driver 53 via a drive command unit 56 and an isolated communication unit 57 of the gate drive IC 50H.

[0037] The gate driver 53 has functions for detecting abnormalities such as overcurrent in the IGBT 51H and obtaining temperature information using a temperature sensor. These abnormality detection and temperature information are input to the drive control unit 55 via the insulated communication unit 13A of the switching power supply 1. In this case, the insulated communication unit 13A has two communication channels. In this way, by sharing the insulated communication unit 13A between the switching power supply 1 and the gate driver 53-drive control unit 55, costs can be reduced.

[0038] (Other embodiments) The switching element is not limited to a MOSFET. The rectifying element is not limited to a diode, but may be a switching element such as an FET, and may perform synchronous rectification by switching at the timing of rectification. The reference potential is not limited to the ground potential. The application of switching power supplies is not limited to gate driver ICs. The specific values ​​of the input voltage, output voltage, load current, etc. are merely examples and may be set appropriately according to individual designs.

[0039] In addition to the inventions described in the claims, this case also includes the following inventions: [1] a transformer (2, 42) having a primary winding (3) and a secondary winding (4); a switching element (6) connected in series to the primary winding; a current detection resistor (7) connected in series between the switching element and a reference potential point; a rectifying element (10) connected in series with the secondary winding; an output capacitor (11) connected in parallel to a series circuit of the secondary winding and the rectifying element; a primary side feedback unit (9, 43) that generates a first feedback voltage according to an output voltage on the secondary side of the transformer; a control unit (8, 44) that PWM-controls the switching element based on a first control voltage obtained by amplifying the difference between the first feedback voltage and a first reference voltage and a current value flowing through the current detection resistor; a secondary-side feedback section (12) that generates a second control voltage based on a second feedback voltage corresponding to the secondary-side output voltage and a second reference voltage; an insulated communication unit (13) that transmits information about the second control voltage to a control unit, The control unit adjusts the first reference voltage by receiving information about the second control voltage from the insulating communication unit. [2] The transformer (2) has a tertiary winding (5) on the primary side, The switching power supply device according to [1], wherein the primary feedback section (12) generates a first feedback voltage proportional to a secondary output voltage detected via the tertiary winding. [3] The switching power supply device according to [2], wherein the primary feedback section includes a series circuit of a rectifying element (14) and a capacitor (15) connected in parallel to the tertiary winding. [4] The switching power supply device according to [3], further comprising a load resistor (16) and a voltage divider circuit (17) connected in parallel to the capacitor. [5] The switching power supply device according to any one of [1] to [4], wherein the primary side feedback unit (43) generates the first feedback voltage from a flyback voltage that is generated after the switching element is turned off. [6] The switching power supply device according to [5], wherein the primary side feedback unit extracts information about the voltage across the secondary winding from the flyback voltage, and outputs a first feedback voltage multiplied by a feedback gain to the control unit (44). [7] The secondary side feedback unit includes an A / D converter (25) that performs A / D conversion of the second feedback voltage; a subtractor (26) that subtracts data of a second reference voltage from the A / D converted second feedback data; an accumulator (27) that accumulates the results of the subtraction; The switching power supply device according to any one of [1] to [6], further comprising a multiplier (28) that multiplies the result of the cumulative addition by a control gain. [8] The secondary side feedback unit includes a voltage dividing circuit (21) that divides the second feedback voltage; The switching power supply device according to [7], further comprising a filter circuit (24) that low-pass filters the output voltage or the divided voltage. [9] The control unit receives first reference data indicating an initial value of the first reference voltage and the This is data corresponding to the second control voltage. a subtractor (32) that subtracts the second control data; The switching power supply device according to any one of [1] to [8], further comprising a D / A converter (33) that D / A converts the result of the subtraction and outputs the first reference voltage.

[0040] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure. [Explanation of symbols]

[0041] In the drawings, 1 indicates a switching power supply device, 2 indicates a transformer, 3 indicates a primary winding, 4 indicates a secondary winding, 5 indicates a tertiary winding, 6 indicates an N-channel MOSFET, 7 indicates a current detection resistor, 8 indicates a control unit, 9 indicates a primary side feedback unit, 10 indicates a diode, 11 indicates a capacitor, 12 indicates a secondary side feedback unit, and 13 indicates an insulated communication unit.

Claims

1. a transformer (2, 42) having a primary winding (3) and a secondary winding (4); a switching element (6) connected in series with the primary winding; a current detection resistor (7) connected in series between the switching element and a reference potential point; a rectifying element (10) connected in series with the secondary winding; an output capacitor (11) connected in parallel to a series circuit of the secondary winding and the rectifying element; a primary-side feedback unit (9, 43) that generates a first feedback voltage according to an output voltage on the secondary side of the transformer; a control unit (8, 44) that PWM-controls the switching element based on a first control voltage obtained by amplifying the difference between the first feedback voltage and a first reference voltage and on a current value flowing through the current detection resistor; a secondary-side feedback section (12) that generates a second control voltage based on a second feedback voltage corresponding to the secondary-side output voltage and a second reference voltage; an insulating communication unit (13) that transmits information about the second control voltage to a control unit, The control unit adjusts the first reference voltage by receiving information about the second control voltage from the insulating communication unit.

2. The transformer (2) has a tertiary winding (5) on the primary side, 2. The switching power supply device according to claim 1, wherein the primary feedback section generates a first feedback voltage proportional to the secondary output voltage detected via the tertiary winding.

3. 3. The switching power supply device according to claim 2, wherein the primary feedback section comprises a series circuit of a rectifying element (14) and a capacitor (15) connected in parallel to the tertiary winding.

4. 4. The switching power supply device according to claim 3, further comprising a load resistor (16) and a voltage dividing circuit (17) connected in parallel with the capacitor.

5. 2. The switching power supply device according to claim 1, wherein the primary side feedback section generates the first feedback voltage from a flyback voltage that is generated after the switching element is turned off.

6. 6. The switching power supply device according to claim 5, wherein the primary-side feedback unit extracts information about the voltage across the secondary winding from the flyback voltage, and outputs a first feedback voltage multiplied by a feedback gain to the control unit.

7. The secondary side feedback unit includes an A / D converter (25) that performs A / D conversion of the second feedback voltage; a subtractor (26) for subtracting data of a second reference voltage from the A / D converted second feedback data; an accumulator (27) for accumulating the results of the subtraction; 7. The switching power supply device according to claim 1, further comprising a multiplier (28) that multiplies the result of the cumulative addition by a control gain.

8. The secondary side feedback unit includes a voltage divider circuit (21) that divides the second feedback voltage; 8. The switching power supply device according to claim 7, further comprising a filter circuit (24) for low-pass filtering the output voltage or the divided voltage.

9. The control unit includes a subtractor (32) that subtracts first reference data indicating an initial value of the first reference voltage from second control data that is data corresponding to the second control voltage; 7. The switching power supply device according to claim 1, further comprising a D / A converter (33) that D / A converts the result of the subtraction and outputs the first reference voltage.

Images