JP2024036957A - Switching power supply device - Google Patents

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

The present invention relates to a switching power supply device.

Patent Document 1 discloses a technique for correcting an error in the output voltage of a switching power supply device that is a so-called flyback converter. In this technique, the secondary current of the transformer is calculated, and the target voltage is corrected in order to cancel out an error in the output voltage due to the secondary current.

Patent No. 6561612

However, in the technique of Patent Document 1, since correction is performed by calculation using fixed values, there is a problem that correction corresponding to variations in individual products cannot be performed.

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.

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

The secondary side feedback section generates a second control voltage based on a second feedback voltage corresponding to an output voltage on the secondary side of the transformer and a second reference voltage. The insulation communication unit transmits information regarding the second control voltage to the control unit, and the control unit adjusts the first reference voltage by receiving information about the second control voltage from the insulation communication unit.

With this configuration, the first reference voltage used for PWM control of the switching element can be changed by the control unit to the second feedback voltage and the second reference voltage according to the output voltage on the secondary side of the transformer. The adjustment is performed by acquiring information on the second control voltage generated based on the second control voltage. Therefore, the output voltage can be corrected with high precision even for products with variations in the constants, etc. of circuit elements.

This is a first embodiment and is a diagram showing the configuration of a switching power supply device. Diagram showing the configuration of the primary side feedback section Diagram showing the configuration of the secondary side feedback section Diagram showing the configuration of the control unit Diagram showing an example of the configuration of the insulated communication section (Part 1) Diagram showing an example of the configuration of the insulated communication section (Part 2) Diagram showing the control sequence at startup Diagram showing the control sequence when the output voltage Vout exceeds a specific voltage range after startup Diagram showing the contents of processing periodically executed in secondary side control A diagram showing changes in output voltage Vout with respect to changes in load current when input voltage Vin is kept constant. A diagram showing changes in output voltage Vout with respect to changes in input voltage Vin when the load current is constant. This is a second embodiment and is a diagram showing the configuration of a switching power supply device. Diagram showing the configuration of the primary side feedback section Timing chart showing details of primary side control This is a third embodiment, and is a diagram showing a configuration in which a switching power supply device is applied to a gate drive IC.

(First embodiment)
As shown in FIG. 1, the switching power supply device 1 of this embodiment is a so-called flyback converter using a transformer 2. As shown in FIG. 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 side ground. There is. The primary ground corresponds to a reference potential point. Note that the number of turns of the tertiary winding 5 may be the same as that of the secondary winding 4, or may be different.

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 section 8 , and the terminal voltage of the current detection resistor 7 is input to the control section 8 . Both ends of the tertiary winding 5 are connected to input terminals of the primary feedback section 9, respectively. An output terminal of the primary side feedback section 9 is connected to an input terminal of the control section 8.

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

As shown in FIG. 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 element 16 connected in parallel to the capacitor 15, and a resistor. A voltage dividing circuit consisting of elements 17a and 17b is provided. The common connection point of the resistance elements 17a and 17b shows a voltage obtained by dividing the terminal voltage of the resistance element 16, and this voltage becomes the first feedback voltage. Resistance element 16 corresponds to a load resistance.

As shown in FIG. 3, the secondary feedback unit 12 includes a voltage dividing circuit 21 that is connected between the output terminal Vout and the secondary ground and is made up of a series circuit of resistive elements 21a and 21b. An RC filter circuit 24 constituted by a series circuit of a resistive element 22 and a capacitor 23 is connected between the common connection point of the resistive elements 21a and 21b and the ground. An output terminal of the RC filter circuit 24 is connected to an input terminal of an A/D converter 25, and an output terminal of the A/D converter 25 is connected to an input terminal of a subtracter 26.

The subtracter 26 subtracts second reference data, which is data corresponding to the second reference voltage, from the output data of the A/D converter 25 and outputs the result to the cumulative adder 27 at the next stage. The cumulative adder 27 cumulatively adds the data output from the subtracter 26 and outputs the addition result to the gain multiplier 28 at the next stage. The gain multiplier 28 multiplies the data output from the cumulative adder 27 by a predetermined gain and outputs the result as second control data that is data corresponding to the second control voltage.

As shown in FIG. 4, in the control section 8, a first feedback voltage and a first reference voltage are input to the error amplifier 31. The first reference voltage is obtained by subtracting the second control data using a subtracter 32 from first reference data that is preset according to the output voltage of the switching power supply 1, and converting the subtraction result into a D/A converter 33. /A conversion.

The output voltage of the error amplifier 31 is input to the PWM control section 34. The terminal voltage of the current detection resistor 7 is also input to the PWM control section 34 . The PWM control section 34 compares both voltages to generate a PWM signal, and inputs it to the next stage switch control section 35. The switch control unit 35 drives the gate of the FET 6 according to the input PWM signal.

The insulated communication unit 13 uses, for example, a capacitive insulation method in which a capacitor 38 is used to connect a transmitter 36 and a receiver 37, as shown in FIG. A magnetic insulation method or the like in which a transformer 39 is interposed between the two is adopted.

Next, the operation of this embodiment will be explained. As shown in FIG. 7, when the input voltage rises to a certain extent from a stopped state, the switching power supply device 1 starts switching by soft start by primary side control. Then, the output voltage starts to rise. When the output voltage exceeds the target voltage, the soft start is ended and the primary side control of normal operation is started.

If only the primary side control is used, an error will occur in the output voltage, so a shift will be made to combined use with the secondary side control. By starting secondary side control, the output voltage is adjusted so that there is no error with respect to the target voltage. As shown in FIG. 9, in the secondary side control cycle, each phase of "AD conversion", "calculation", "transmission", and "waiting time" is repeatedly executed.
- AD conversion: divides the secondary side feedback voltage, that is, the output voltage, and performs AD conversion on the filtered voltage.
- Calculation: Calculate the second control data from the secondary side feedback data that 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: Waiting time until starting the next secondary control cycle.

The control cycle of the secondary side control that reflects the secondary side feedback data needs to be set to be slow enough not to affect the stability of the primary side feedback control. Furthermore, if the control cycle is too slow, the effect on the output voltage will be delayed, so it is necessary to take this 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 is about 0.1 to 10 seconds. Note that, if there is sufficient time for obtaining output voltage data and for isolated communication, calculation processing for secondary side feedback may be performed beyond the isolated communication.

When the input voltage drops to a certain voltage, the switching power supply device 1 stops switching. Also, if the input voltage has not decreased but the output voltage exceeds a specific voltage range due to overcurrent or failure, secondary side control is also stopped.

As shown in FIG. 8, in the operation after startup, although the input voltage has not decreased, if the output voltage Vout exceeds a specific voltage range, the secondary side control may be stopped. Further, the secondary side control may be stopped when power supply protection functions such as overheat protection, overcurrent protection, and short circuit protection start to operate. When stopping the secondary side control, the secondary side control is stopped by, for example, not updating the secondary side feedback data in the primary side feedback section 9 or the secondary side feedback section 12. Further, the primary side feedback unit 9 may stop accepting secondary side feedback data and reset the data to the initial value.

The actual measurement results shown in FIG. 10 show a comparison between the settings of input voltage Vin=14V and output voltage Vout=20V, with and without secondary side control. It can be seen that the followability of the output voltage Vout to changes in the load current is better when the secondary side control is implemented. Furthermore, the actual measurement results shown in FIG. 11 also show a comparison between the presence and absence of secondary side control under the settings of input voltage Vin=14V and load current Iout=60mA. It can also be seen that the followability of the output voltage to changes in the input voltage is better when the secondary side control is performed.

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

The secondary side feedback section 12 generates a second control voltage based on a second feedback voltage corresponding to the output voltage on the secondary side of the transformer 2 and a second reference voltage. The insulated communication unit 13 transmits information regarding the second control voltage to the control unit 8, and the control unit 8 receives information about the second control voltage from the insulated communication unit 13, thereby adjusting the first reference voltage.

With this configuration, the first reference voltage used for PWM control of the FET 6 can be changed by the control unit 8 to the second feedback voltage and the second reference voltage according to the output voltage on the secondary side of the transformer 2. The second control voltage is adjusted by obtaining information on the second control voltage generated based on the second control voltage. Therefore, the output voltage can be corrected with high precision even for products with variations in the constants, etc. of circuit elements.

Further, the transformer 2 has a tertiary winding 5 on the primary side, and the primary side feedback section 9 has a first feedback voltage proportional to the output voltage on the secondary side detected via the tertiary winding 5. Therefore, feedback information of the secondary output voltage of the transformer 2 can be obtained more directly and stably.

(Second embodiment)
Hereinafter, parts that are the same as those in the first embodiment are given the same reference numerals and explanations will be omitted, and different parts will be explained. As shown in FIG. 12, the 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. The primary side feedback section 43 is connected to the primary winding 3 and includes a control section 44 that replaces the control section 8 .

As shown in FIG. 13, the primary side feedback section 43 includes a voltage detection section 45 that detects the terminal voltage of the primary winding 3, a gain multiplication section 46 that multiplies the detected voltage by a feedback gain, and a gain multiplication section 46. A sample and hold section 47 is provided to sample and hold the output signal of. A sampling clock CKSH to the sample hold section 47 is input from the control section 44 . The output signal of the sample hold section 47 becomes the first feedback voltage.

Next, the operation of the second embodiment will be explained. In the second embodiment, information regarding 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 the primary side feedback voltage. As shown in FIG. 14, when the gate voltage Vg becomes high level, the FET 6 is turned on, and the current Ip flowing through the primary winding 3 also flows through the current detection resistor 6. Further, at this time, the voltage between the terminals Vin and Vsw of the primary winding 3 becomes 0V.

When the gate voltage Vg becomes low level and the FET 6 is turned 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, resulting in a large voltage between the terminals. Rise. The control unit 44 outputs the sampling clock CKSH after a certain period of time from the fall of the gate voltage Vg. The sample and hold unit 47 samples the inter-terminal voltage when the sampling clock CKSH becomes high level, and holds the sampled voltage when the sampling clock CKSH becomes low level. The control unit 44 sets the sampling clock CKSH to a low level after a time Tsh from the fall of the gate voltage Vg.

Assuming that the voltage sampled by the sample and hold section 47 is Vsh, the voltage Vsh is expressed by the following equation.
Vsh=G×(N1/N2)×(Vout+Vf+Is×r)
G: Feedback gain of gain multiplier 46 N1: Number of turns in primary winding 3 N2: Number of turns in secondary winding 4 Vf: Forward voltage of diode 10 Is: Current flowing in secondary winding 4 r: 2 The resistance component voltage Vsh in the next-side output voltage path is input to the control unit 44 as a primary-side feedback voltage.

As described above, according to the second embodiment, the primary side feedback section 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 a feedback gain, sampled and held by the sample and hold section 47, and outputted to the control section 44. Therefore, the first feedback voltage can be generated without using the transformer 2 including the tertiary winding 5 as in the first embodiment.

(Third embodiment)
A third embodiment shown in FIG. 15 is one in which the switching power supply device 1 of the first embodiment is applied to a gate drive IC 50 of an IGBT 51. The IGBTs 51H and 51L are connected in series with a battery as a power source and a secondary ground, and a common connection point between the two is connected to one end of the coil 52 of the motor. The IGBT 51H is driven by the gate drive IC 50H, and the IGBT 51L is driven by the gate drive IC 50L, but their configurations are symmetrical, and the gate drive IC 50H will be described below.

The output voltage Vout of the switching power supply device 1 is supplied as a driving power source 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 section 55 composed of a microcomputer or the like. Control input from the drive control unit 55 is input to the gate driver 53 via the drive command unit 56 and the insulation communication unit 57 of the gate drive IC 50H.

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

(Other embodiments)
The switching element is not limited to MOSFET.
The rectifying element is not limited to a diode, but may be a switching element such as an FET, or may perform synchronous rectification in which switching is performed at the timing of rectification.
The reference potential is not limited to the ground potential.
The application of the switching power supply device is not limited to gate drive ICs.
Specific numerical values such as input voltage, output voltage, and load current are merely examples, and may be appropriately set according to individual designs.

This case includes the following inventions in addition to the inventions described in the claims.
[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 the reference potential point;
a rectifier element (10) connected in series to 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 section (9, 43) that generates a first feedback voltage according to the output voltage on the secondary side of the transformer;
a control unit (8, 44) that performs PWM control of the switching element based on a first control voltage obtained by amplifying the difference between the first feedback voltage and the 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 and a second reference voltage according to the output voltage of the secondary side;
an insulated communication unit (13) that transmits information regarding the second control voltage to the control unit,
The control unit is a switching power supply device that adjusts the first reference voltage by receiving information about the second control voltage from the insulation 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 side feedback section (12) generates a first feedback voltage proportional to the secondary side output voltage detected via the tertiary winding.
[3]
The switching power supply device according to [2], wherein the primary side 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], comprising a load resistor (16) and a voltage dividing circuit (17) connected in parallel to the capacitor.
[5]
The switching power supply according to any one of [1] to [4], wherein the primary side feedback section (43) generates the first feedback voltage from a flyback voltage generated after turning off the switching element. Device.
[6]
The primary side feedback section extracts information regarding the voltage across the secondary winding from the flyback voltage, and outputs a first feedback voltage multiplied by a feedback gain to the control section (44) [5] switching power supply.
[7]
The secondary side feedback section includes an A/D converter (25) that A/D converts the second feedback voltage;
a subtracter (26) that subtracts second reference voltage data from the A/D converted second feedback data;
a cumulative adder (27) that cumulatively adds 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 feedback section 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 includes a subtracter (32) that subtracts first reference data indicating an initial value of the first reference voltage and 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.

Although the present disclosure has been described based on examples, it is understood that the present disclosure is not limited to the examples or structures. The present disclosure also includes various modifications and equivalent modifications. In addition, various combinations and configurations, as well as other combinations and configurations that include only one, more, or fewer elements, are within the scope and scope of the present disclosure.

In the drawing, 1 is a switching power supply, 2 is a transformer, 3 is a primary winding, 4 is a secondary winding, 5 is a tertiary winding, 6 is an N-channel MOSFET, 7 is a current detection resistor, and 8 is a control unit. , 9 is a primary side feedback section, 10 is a diode, 11 is a capacitor, 12 is a secondary side feedback section, and 13 is an isolated communication section.

Claims (9)

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 the reference potential point;
a rectifier element (10) connected in series to 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 section (9, 43) that generates a first feedback voltage according to the output voltage on the secondary side of the transformer;
a control unit (8, 44) that performs PWM control of the switching element based on a first control voltage obtained by amplifying the difference between the first feedback voltage and the 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 and a second reference voltage according to the output voltage of the secondary side;
an insulated communication unit (13) that transmits information regarding the second control voltage to the control unit,
The control unit is a switching power supply device that adjusts the first reference voltage by receiving information about the second control voltage from the insulation communication unit. The transformer (2) has a tertiary winding (5) on the primary side,
The switching power supply device according to claim 1, wherein the primary side feedback section (12) generates a first feedback voltage proportional to a secondary side output voltage detected via the tertiary winding. The switching power supply device according to claim 2, wherein the primary side feedback section includes a series circuit of a rectifying element (14) and a capacitor (15) connected in parallel to the tertiary winding. The switching power supply device according to claim 3, further comprising a load resistor (16) and a voltage dividing circuit (17) connected in parallel to the capacitor. The switching power supply device according to claim 1, wherein the primary side feedback section (43) generates the first feedback voltage from a flyback voltage generated after turning off the switching element. 6. The primary side feedback section extracts information regarding the voltage across the secondary winding from the flyback voltage, and outputs a first feedback voltage multiplied by a feedback gain to the control section (44). switching power supply. The secondary side feedback section includes an A/D converter (25) that A/D converts the second feedback voltage;
a subtracter (26) that subtracts second reference voltage data from the A/D converted second feedback data;
a cumulative adder (27) that cumulatively adds the results of the subtraction;
The switching power supply device according to any one of claims 1 to 6, further comprising a multiplier (28) that multiplies the result of the cumulative addition by a control gain. The secondary feedback section includes a voltage dividing circuit (21) that divides the second feedback voltage;
The switching power supply device according to claim 7, further comprising a filter circuit (24) that low-pass filters the output voltage or the divided voltage. The control unit includes a subtracter (32) that subtracts first reference data indicating an initial value of the first reference voltage and the second control data;
The switching power supply device according to any one of claims 1 to 6, further comprising a D/A converter (33) that D/A converts the result of the subtraction and outputs the first reference voltage.

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