Switching control device, insulated switching power supply device, and electrical apparatus

Abstract

A switching control device according to the present invention includes: a voltage detecting unit that detects the induced voltage generated at a connection node between a primary winding and a switching element or at an auxiliary winding of a transformer; a temperature correcting unit that subjects the detection result of the voltage detecting unit to temperature correction; and a logic unit that performs control to turn the switching element ON / OFF on the basis of the induced voltage which has been subjected to temperature correction by the temperature correcting unit. The temperature correcting unit includes either a first diode built into the switching control device or a first terminal connected to a second diode that is external to the switching control device.

Description

Switching control device, isolated switching power supply device, and electrical equipment

[0001] The invention disclosed in this specification relates to a switching control device, and an isolated switching power supply device and an electric device using the same.

[0002] 2. Description of the Related Art Conventionally, isolated switching power supplies that generate a desired output voltage from an input voltage while isolating a primary circuit system from a secondary circuit system have been used in various electrical devices.

[0003] JP 2015-76962 A

[0004] Generally, isolated switching power supplies are configured to use a photocoupler for output feedback control. However, conventional configurations using photocouplers have issues with reduced long-term reliability and increased costs due to the increased number of components.

[0005] Furthermore, an isolated switching power supply device has also been proposed that performs output feedback control based on a flyback voltage generated in a primary winding of a transformer or an induced voltage generated in an auxiliary winding of a transformer, without using a photocoupler (see, for example, Patent Document 1).

[0006] However, the flyback voltage generated in the primary winding of the transformer and the induced voltage generated in the auxiliary winding of the transformer each contain information about the forward voltage of the diode provided in the secondary circuit system. Because the forward voltage of the diode provided in the secondary circuit system changes with temperature, this amount of change may directly result in an error in the output voltage of the isolated switched-mode power supply.

[0007] The isolated switching power supply proposed in Patent Document 1 measures the period from when the primary current is turned off until the feedback voltage falls below a threshold voltage, and samples the feedback voltage based on the measurement result, thereby improving the accuracy of the output voltage. However, a configuration that samples the feedback voltage based on the measurement result results in a complex circuit configuration.

[0008] Therefore, it is desirable to improve the accuracy of the output voltage of an isolated switching power supply device using a method other than that disclosed in Patent Document 1.

[0009] A switching control device disclosed in this specification is configured to control a switching element connected to a primary winding of a transformer. The switching control device includes: a voltage detection unit configured to detect an induced voltage generated at a connection node between the primary winding and the switching element or at an auxiliary winding of the transformer; a temperature correction unit configured to temperature-correct a detection result from the voltage detection unit; and a logic unit configured to control the on / off of the switching element based on the induced voltage temperature-corrected by the temperature correction unit. The temperature correction unit has a first terminal configured to be connected to either a first diode built into the switching control device or a second diode externally attached to the switching control device.

[0010] The isolated switching power supply device disclosed in this specification includes the switching control device configured as described above, the transformer, and the switching element.

[0011] The electrical equipment disclosed in this specification includes an isolated switching power supply device having the above-described configuration.

[0012] According to the invention disclosed in this specification, it is possible to improve the accuracy of the output voltage of an isolated switching power supply device.

[0013] Fig. 1 is a diagram showing a comparative example of an isolated switching power supply apparatus. Fig. 2 is a diagram showing a first embodiment of an isolated switching power supply apparatus. Fig. 3 is a diagram showing temperature characteristics of output voltage. Fig. 4 is a diagram showing a second embodiment of an isolated switching power supply apparatus. Fig. 5 is an external view of a vehicle.

[0014] In this specification, a MOS (Metal Oxide Semiconductor) field effect transistor refers to a field effect transistor whose gate structure is composed of at least three layers: a layer made of a conductor or a semiconductor such as polysilicon with a low resistance value, an insulating layer, and a P-type, N-type, or intrinsic semiconductor layer. In other words, the gate structure of a MOS field effect transistor is not limited to a three-layer structure of a metal, an oxide, and a semiconductor.

[0015] 1 is a diagram showing a comparative example of an isolated switching power supply (i.e., a general configuration to be compared with the embodiments described later). The isolated switching power supply 100 of this comparative example has a transformer TR1, an output diode D1, an output capacitor C1, resistors RFB and RREF, and a semiconductor device 10.

[0016] The transformer TR1 includes a primary winding L1 and a secondary winding L2 that are electromagnetically coupled with each other and have opposite polarities. The number of turns of the primary winding L1 is N Ｐ and the number of turns of the secondary winding L2 is N Ｓ The primary winding L1 and the secondary winding L2 electrically insulate the primary circuit system from the secondary circuit system. An input voltage V is applied to a first end of the primary winding L1 and a terminal TVIN of the semiconductor device 10. ＩＮ A second end of the primary winding L1 is connected to a first end of a resistor RFB and a terminal TSW of the semiconductor device 201. A second end of the resistor RFB is connected to a terminal TFB of the semiconductor device 201. The resistor RFB has a resistance value R ＦＢ A first end of the secondary winding L2 is connected to the anode of the output diode D1. A cathode of the output diode D1 is connected to a first end of the output capacitor C1. The output diode D1 has a forward voltage V Ｆ１ The second end of the secondary winding L2 and the second end of the output capacitor C1 are connected to the ground potential of the secondary circuit system. The induced voltage generated in the secondary winding L2 is rectified by the output diode D1 and smoothed by the output capacitor C1 to produce an output voltage V ＯＵＴ The output voltage V ＯＵＴ is output from the connection node between the cathode of the output diode D1 and the first end of the output capacitor C1.

[0017] The semiconductor device 10 includes a switching element SW1 and a switching control device that controls the switching element SW1.

[0018] In this embodiment, the switching element SW1 is an N-channel MOS field effect transistor. The drain of the switching element SW1 is connected to the primary winding L1 via the terminal TSW. The source of the switching element SW1 is connected to the ground potential. In a modification of this embodiment, the switching element SW1 may be an element other than an N-channel MOS field effect transistor.

[0019] The switching control device includes a voltage detection unit, a slope circuit SLP1, a comparator COMP1, a control unit CNT1, a driver DRV1, a terminal TVIN, a terminal TFB, a terminal TSW, and a terminal TREF.

[0020] The voltage detection unit includes PNP transistors Q1 and Q2 and a current source IS1. The emitter of the PNP transistor Q1 is connected to the terminal TVIN. The emitter of the PNP transistor Q2 is connected to the terminal TFB. The bases of the PNP transistors Q1 and Q2 are connected to the collector of the PNP transistor Q1 and a first terminal of the current source IS1. The second terminal of the current source IS1 is connected to the ground potential.

[0021] The collector of the PNP transistor Q2 is connected to the non-inverting input terminal of the comparator COMP1 and the terminal TREF. A first end of an external resistor RREF is connected to the terminal TREF. A second end of the resistor RREF is connected to the ground potential. The resistor RREF has a resistance value R ＲＥＦ is the resistance.

[0022] The voltage detection unit detects an induced voltage generated at a connection node between the primary winding L1 and the switching element SW1 in the form of a feedback current IFB. A reference current IREF having a value substantially equal to the feedback current IFB is converted by a resistor RREF into a feedback voltage V ＦＢ The feedback voltage V ＦＢ is supplied to the non-inverting input terminal of the comparator COMP1.

[0023] The feedback current IFB can be expressed by the following equation (1), and the feedback voltage VFB can be expressed by the following equation (2).

[0024] The slope circuit SLP1 is connected to the internal reference voltage V ＩＮＴＲＥＦ Based on this, the internal reference voltage V ＩＮＴＲＥＦ The internal reference voltage V ＩＮＴＲＥＦ The slope voltage V is reset to ＳＬＰ The slope voltage V ＳＬＰ is supplied to the inverting input terminal of the comparator COMP1.

[0025] The comparator COMP1 detects the feedback voltage V ＦＢ and the slope voltage V ＳＬＰ The control unit CNT1 controls the driver DRV1 based on the output of the comparator COMP1. The driver DRV1 drives the switching element SW1. As a result, the feedback voltage VFB is equal to or higher than the internal reference voltage V ＩＮＴＲＥＦ Therefore, the output voltage V ＯＵＴ can be expressed by the following equation (3).

[0026] As is clear from the following equation (3), the isolated switching power supply device 100 of this comparative example has a forward voltage V of the output diode D1 that changes depending on the temperature. Ｆ１ is the output voltage V ＯＵＴ This has the problem of resulting in an error of

[0027] In view of the above considerations, a novel embodiment that can improve the accuracy of the output voltage of an isolated switching power supply device will be proposed below.

[0028] <Isolated Switching Power Supply (First Embodiment)> Figure 2 is a diagram showing a first embodiment of an isolated switching power supply. An isolated switching power supply 101 of this embodiment has a transformer TR1, an output diode D1, an output capacitor C1, resistors RFB, RREF, and RRVF, and a semiconductor device 11. In Figure 2, the same parts as in Figure 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0029] The semiconductor device 11 includes a switching element SW1 and a switching control device that controls the switching element SW1.

[0030] The switching control device includes a voltage detection unit, a temperature correction unit, a slope circuit SLP1, a comparator COMP1, a control unit CNT1, a driver DRV1, a terminal TVIN, a terminal TFB, a terminal TSW, and a terminal TREF.

[0031] The voltage detection unit includes PNP transistors Q1 and Q2 and a current source IS1, and detects an induced voltage generated at a connection node between the primary winding L1 and the switching element SW1 in the form of a feedback current IFB.

[0032] The temperature correction unit performs temperature correction on the detection result of the voltage detection unit and includes a current source IS2, a diode D2, an operational amplifier OP1, an N-channel MOS field effect transistor Q3, P-channel MOS field effect transistors Q4 and Q5, N-channel MOS field effect transistors Q6 and Q7, and a terminal TRVF.

[0033] A power supply voltage is applied to a first terminal of the current source IS2. A second terminal of the current source IS2 is connected to the non-inverting input terminal of the operational amplifier OP1 and the anode of the diode D2. The cathode of the diode D2 is connected to the ground potential. The diode D2 has a forward voltage V Ｆ２ The inverting input terminal of the operational amplifier OP1 is connected to the source of the N-channel MOS field effect transistor Q3 and the terminal TRVF. The terminal TRVF is connected to a first terminal of an external resistor RVF. The second terminal of the resistor RVF is connected to the ground potential. The resistor RVF has a resistance value R ＶＦ The output terminal of the operational amplifier OP1 is connected to the gate of an N-channel MOS field effect transistor Q3.

[0034] A first current mirror circuit formed by P-channel MOS field effect transistors Q4 and Q5 outputs a first mirror current corresponding to the drain current of N-channel MOS field effect transistor Q3.

[0035] A second current mirror circuit formed by N-channel MOS field effect transistors Q6 and Q7 outputs a second mirror current corresponding to the first mirror current. The second mirror current IVF is a current obtained by extracting a portion of the collector current of the PNP transistor Q2 from the output terminal of the second current mirror circuit. In this embodiment, the mirror ratio of the P-channel MOS field effect transistors Q4 and Q5 in the first current mirror circuit is 1, and the mirror ratio of the N-channel MOS field effect transistors Q6 and Q7 in the second current mirror circuit is also 1. Note that the mirror ratio of the P-channel MOS field effect transistors Q4 and Q5 may be other than 1, and the mirror ratio of the N-channel MOS field effect transistors Q6 and Q7 may also be other than 1. In the isolated switching power supply 101 of this embodiment, the current obtained after the second mirror current is extracted from the collector current of the PNP transistor Q2 serves as the reference voltage IREF.

[0036] The second mirror current IVF is the forward voltage V of the diode D2. Ｆ２ The resistance value R of resistor RVF ＶＦ Therefore, the output voltage V of the isolated switching power supply device 101 of this embodiment is ＯＵＴ can be expressed by the following equation (4): The second term on the right side of the following equation (4) is the forward voltage V of the output diode D1. Ｆ１ The third term on the right side of the following equation (4) is a correction term by the temperature correction unit.

[0037] The forward voltage V of the output diode D1 is set so that the error term is cancelled by the correction term. Ｆ１ Temperature characteristics and forward voltage V of diode D2 Ｆ２ The resistance value R of the resistor RFB is set so that the relationship of the following equation (5) holds between the temperature characteristics of ＦＢ and the resistance value R of resistor RVF ＶＦ In other words, the ratio of the resistance value R of the resistor RVF to ＶＦ is the resistance value R of the resistor RFB as shown in the following equation (6). ＦＢThe forward voltage V of the output diode D1 is preferably set in accordance with the winding ratio of the transformer TR1, the temperature characteristics of the diode D2, and the temperature characteristics of the output diode D1. Ｆ１ The temperature characteristic of the diode D2 is the forward voltage V Ｆ２ The diode D2 is designed so that the forward voltage V of the output diode D1 is cancelled by the temperature characteristic of Ｆ１ Temperature characteristics and forward voltage V of diode D2 Ｆ２ It is desirable that the temperature characteristics of the output diode D1 and the output diode D2 completely match. Ｆ１ Temperature characteristics and forward voltage V of diode D2 Ｆ２ There may be an error between the temperature characteristics of the

[0038] In this embodiment, the forward voltage V of the output diode D1 Ｆ１ Even if the output voltage V of the isolated switching power supply device 101 changes according to the temperature, the detection result of the voltage detection unit is corrected for temperature. ＯＵＴ More specifically, the accuracy of the forward voltage V of the output diode D1 can be improved. Ｆ１ The temperature characteristic of the diode D2 is the forward voltage V Ｆ２ are cancelled out by the temperature characteristics of the isolated switching power supply device 101, ＯＵＴ 3 shows the output voltage V of the isolated switching power supply device 100 of the comparative example. ＯＵＴ and the output voltage V of the isolated switching power supply device 101 of this embodiment. ＯＵＴ 101 and the temperature characteristic T101 of the output voltage V ＯＵＴ 3, the target value of the output voltage V ＯＵＴ High accuracy.

[0039] In this embodiment, the resistance value R of the resistor RVF ＶＦBy adjusting the resistor RVF, the temperature correction unit can perform appropriate temperature correction even when the turns ratio of the transformer TR1 is changed. If the turns ratio of the transformer TR1 is uniquely designed, the resistor RVF may be built into the semiconductor device 11.

[0040] <Isolated Switching Power Supply (Second Embodiment)> Figure 4 is a diagram showing a second embodiment of an isolated switching power supply. An isolated switching power supply 101 of this embodiment has a transformer TR1, an output diode D1, an output capacitor C1, resistors RFB, RREF, and RVF, a diode D3, and a semiconductor device 12. In Figure 4, the same parts as in Figure 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0041] The semiconductor device 12 includes a switching element SW1 and a switching control device that controls the switching element SW1.

[0042] The switching control device includes a voltage detection unit, a temperature correction unit, a slope circuit SLP1, a comparator COMP1, a control unit CNT1, a driver DRV1, a terminal TVIN, a terminal TFB, a terminal TSW, and a terminal TREF.

[0043] The voltage detection unit includes PNP transistors Q1 and Q2 and a current source IS1, and detects an induced voltage generated at a connection node between the primary winding L1 and the switching element SW1 in the form of a feedback current IFB.

[0044] The temperature correction unit performs temperature correction on the detection result of the voltage detection unit and includes a current source IS2, an operational amplifier OP1, an N-channel MOS field effect transistor Q3, P-channel MOS field effect transistors Q4 and Q5, N-channel MOS field effect transistors Q6 and Q7, a terminal TRVF, and a terminal TVF.

[0045] A power supply voltage is applied to a first terminal of the current source IS2. A second terminal of the current source IS2 is connected to the non-inverting input terminal of the operational amplifier OP1 and the terminal TVF. The anode of an external diode D3 is connected to the terminal TVF. The cathode of the diode D3 is connected to the ground potential. The diode D3, like the diode D2 in the first embodiment, has a forward voltage V Ｆ２ It is a diode.

[0046] The output voltage V of the isolated switching power supply device 102 of this embodiment ＯＵＴ is the output voltage V of the isolated switching power supply device 101 of the first embodiment. ＯＵＴ Similarly, it can be expressed by the above formula (4).

[0047] In this embodiment, the diode D3 is the same type of diode as the output diode D1, which allows the temperature characteristics of the diode D3 to be easily matched to the temperature characteristics of the output diode D1.

[0048] In the above equation (4), the forward voltage V of the output diode D1 is set so that the error term is cancelled by the correction term. Ｆ１ Temperature characteristics and forward voltage V of diode D2 Ｆ２ The resistance value R of the resistor RFB is set so that the relationship of the above formula (5) holds between the temperature characteristics of ＦＢ and the resistance value R of resistor RVF ＶＦ When the temperature characteristics of the diode D3 and the temperature characteristics of the output diode D1 are the same, the resistance value R of the resistor RVF is adjusted. ＶＦ is the resistance value R of the resistor RFB as shown in the following equation (7). ＦＢ and the winding ratio of the transformer TR1.

[0049] In this embodiment, the forward voltage V of the output diode D1 Ｆ１ Even if the output voltage V of the isolated switching power supply device 102 changes according to the temperature, the detection result of the voltage detection unit is corrected for temperature. ＯＵＴ More specifically, the accuracy of the forward voltage V of the output diode D1 can be improved. Ｆ１ The temperature characteristic of the diode D3 is the forward voltage VＦ２ are cancelled out by the temperature characteristics of the isolated switching power supply device 102. ＯＵＴ The accuracy can be improved.

[0050] In this embodiment, the resistance value R of the resistor RVF ＶＦ By adjusting the resistor RVF, the temperature correction unit can perform appropriate temperature correction even when the turns ratio of the transformer TR1 is changed. If the turns ratio of the transformer TR1 is uniquely designed, the resistor RVF may be built into the semiconductor device 12.

[0051] <Applications> The isolated switching power supply device 101 or 102 is used, for example, as a power supply for a gate driver device. The gate driver device is mounted in an electrical device together with, for example, an output transistor driven by the gate driver device and a load such as a motor connected in series to the output transistor. The electrical device is mounted, for example, in a vehicle X shown in FIG. 5 . Note that the application of the isolated switching power supply device 101 or 102 is not limited to being a power supply for a gate driver device. Furthermore, electrical devices equipped with the isolated switching power supply device 101 or 102 are not limited to use in the automotive field, but can be used in a variety of fields (automotive field, industrial machinery field, home appliance field, etc.).

[0052] <Others> In addition to the above-described embodiments, various modifications can be made to the configuration of the invention without departing from the spirit of the invention. The above-described embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0053] For example, in the above-described embodiment, the voltage detection unit is configured to detect an induced voltage generated at a connection node between the primary winding of the transformer and the switching element, but the voltage detection unit may also be configured to detect an induced voltage generated in an auxiliary winding of the transformer.

[0054] The switching control device (101, 102) described above is a switching control device configured to control a switching element (SW1) connected to a primary winding (L1) of a transformer (TR1), and includes: a voltage detection unit (Q1, Q2, IS1) configured to detect an induced voltage generated at a connection node between the primary winding and the switching element or at an auxiliary winding of the transformer; a temperature correction unit (IS2, OP1, Q3 to Q7) configured to temperature-correct the detection result of the voltage detection unit; and a logic unit (CNT1) configured to control the on / off of the switching element based on the induced voltage temperature-corrected by the temperature correction unit, and the temperature correction unit has a configuration (first configuration) that includes either a first diode (D2) built into the switching control device or a first terminal (TVF) configured to be connected to a second diode (D3) externally attached to the switching control device.

[0055] In the switching control device of the first configuration, even if the forward voltage of the diode provided in the secondary circuit system changes in accordance with temperature, the detection result of the voltage detection unit is temperature corrected, thereby improving the accuracy of the output voltage of the isolated switching power supply device.

[0056] In the switching control device of the first configuration, the temperature correction unit may be configured (second configuration) to have a second terminal (TRVF) configured to be connected to a first resistor (RVF) externally attached to the switching control device.

[0057] In the switching control device of the second configuration, by adjusting the resistance value of the first resistor, the temperature correction unit can perform appropriate temperature correction even when the winding ratio of the transformer is changed.

[0058] In the switching control device of the second configuration, the temperature correction unit may have the first diode, and the resistance value of the first resistor may be set according to the resistance value of a second resistor provided between the connection node or the auxiliary winding and the voltage detection unit, the turns ratio of the transformer, the temperature characteristics of the first diode, and the temperature characteristics of a third diode connected to the secondary winding of the transformer (third configuration).

[0059] The switching control device of the third configuration can cancel the error term included in the calculation formula for the output voltage of the isolated switching power supply device by using the correction term.

[0060] In the switching control device of the second configuration described above, the temperature correction unit may have the second terminal, and the resistance value of the first resistor may be set according to the resistance value of a second resistor provided between the connection node or the auxiliary winding and the voltage detection unit, and a turns ratio of the transformer (fourth configuration).

[0061] The switching control device of the fourth configuration described above can cancel, by a correction term, the error term included in the calculation formula for the output voltage of the isolated switching power supply device, by aligning the temperature characteristics of the second diode with the temperature characteristics of the third diode connected to the secondary winding of the transformer.

[0062] In the switching control device of any of the above first, second, or fourth configurations, the temperature correction unit may have the second terminal, and the second diode may be the same type of diode as a third diode (D1) connected to the secondary winding (L2) of the transformer (fifth configuration).

[0063] The switching control device having the fifth configuration can make the temperature characteristics of the second diode and the temperature characteristics of the third diode connected to the secondary winding of the transformer the same.

[0064] In the switching control device of any one of the first to fifth configurations, the temperature correction unit may be configured to extract a part of the current output from the voltage detection unit (sixth configuration).

[0065] The switching control device having the sixth configuration can achieve temperature compensation with a simple circuit configuration.

[0066] The isolated switching power supply device described above has a configuration (seventh configuration) that includes a switching control device having any one of the first to sixth configurations, the transformer, and the switching element.

[0067] The isolated switching power supply device having the seventh configuration can improve the accuracy of the output voltage.

[0068] The electrical equipment described above has a configuration (eighth configuration) that includes the isolated switching power supply device of the seventh configuration.

[0069] The electric device having the eighth configuration can improve the accuracy of the output voltage of the isolated switching power supply device.

[0070] 10, 11 Semiconductor device 100, 101 Isolated switching power supply C1 Output capacitor CNT1 Control unit COMP1 Comparator D1 Output diode D2, D3 Diodes DRV1 Driver IS1, IS2 Current source L1 Primary winding L2 Secondary winding OP1 Operational amplifier Q1, Q2 PNP transistor Q3, Q6, Q7 N-channel MOS field effect transistor Q4, Q5 P-channel MOS field effect transistor RFB, RREF, RVF Resistor SLP1 Slope circuit SW1 Switching element TFB, TREF, TSW, TVIN, TRVF, TVF Terminals TR1 Transformer X Vehicle

Claims

1. A switching control device configured to control a switching element connected to a primary winding of a transformer, a voltage detection unit configured to detect an induced voltage generated in a connection node between the primary winding and the switching element or in an auxiliary winding of the transformer; a temperature correction unit configured to perform temperature correction on a detection result of the voltage detection unit; a logic unit configured to control on / off of the switching element based on the induced voltage that has been temperature-corrected by the temperature correction unit; and having The switching control device, wherein the temperature correction unit has a first terminal configured to be connected to either a first diode built into the switching control device or a second diode externally attached to the switching control device.

2. The switching control device according to claim 1 , wherein the temperature correction unit has a second terminal configured to be connected to a first resistor external to the switching control device.

3. the temperature correction unit includes the first diode, 3. The switching control device according to claim 2, wherein a resistance value of the first resistor is set according to a resistance value of a second resistor provided between the connection node or the auxiliary winding and the voltage detection unit, a turns ratio of the transformer, temperature characteristics of the first diode, and temperature characteristics of a third diode connected to a secondary winding of the transformer.

4. the temperature correction unit has the second terminal, 3. The switching control device according to claim 2, wherein a resistance value of the first resistor is set according to a resistance value of a second resistor provided between the connection node or the auxiliary winding and the voltage detection unit, and a turns ratio of the transformer.

5. the temperature correction unit has the first terminal, 2. The switching control device according to claim 1, wherein the second diode is the same type of diode as a third diode connected to a secondary winding of the transformer.

6. The switching control device according to claim 1 , wherein the temperature correction unit is configured to extract a portion of the current output from the voltage detection unit.

7. A switching control device according to any one of claims 1 to 6, The transformer; and an isolated switching power supply device comprising the switching element.

8. An electric device comprising the isolated switching power supply device according to claim 7.