Current detection circuit, switching power supply control device, light-emitting element driving device, and motor drive device

Abstract

To provide a current detecting circuit capable of detecting an average current for each switching period.SOLUTION: A current detection circuit (300) includes: a first comparator unit (COMP1) configured to compare a sense voltage according to a current flowing through a switching element when a switching element (Q1) is on with a threshold voltage; and a determination unit (C1, C2, CS1, CS2, Q4 to Q6, INV1, COMP2) configured to determine, on the basis of an output of the first comparator unit, whether or not a timing at which a magnitude relationship between the sense voltage and the threshold voltage is inverted after the switching element is turned on is before a predetermined time elapses after the switching element is turned on.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention disclosed in this specification relates to a current detection circuit, a switching power supply control device, a light-emitting element driving device, and a motor driving device. [Background technology]

[0002] Conventionally, as a technique for detecting the output current of a switching power supply device, there is a current detection method that uses a potential difference across a sense resistor provided in a stage subsequent to a capacitor that smoothes the output voltage of the switching power supply device (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-153621 A

[0004] [overview] The above current detection method cannot detect the average current for each switching period, and therefore cannot realize, for example, constant current control based on the average current for each switching period or overcurrent protection based on the average current for each switching period.

[0005] The current detection circuit disclosed in this specification includes a first comparison unit configured to compare a sense voltage corresponding to a current flowing through a switching element when the switching element is on with a threshold voltage, and a judgment unit configured to judge, based on the output of the first comparison unit, whether the timing at which the magnitude relationship between the sense voltage and the threshold voltage is reversed after the switching element is turned on is before a predetermined time has elapsed after the switching element is turned on.

[0006] The switching power supply control device disclosed in this specification includes a current detection circuit having the above-described configuration.

[0007] The light emitting element driving device disclosed in this specification includes a current detection circuit having the above-mentioned configuration.

[0008] The motor drive device disclosed in this specification includes a current detection circuit having the above-described configuration. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of a switching power supply device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the operation of the current detection circuit. [Diagram 3] FIG. 3 is a diagram illustrating an example of the operation of the current detection circuit. [Figure 4] FIG. 4 is a diagram illustrating an example of the operation of the current detection circuit. [Diagram 5] FIG. 5 is a diagram illustrating an example of the operation of the current detection circuit. [Figure 6] FIG. 6 is a diagram showing a configuration of a switching power supply device according to a modified example. [Figure 7] FIG. 7 is a diagram showing a schematic configuration example of a light emitting device. [Figure 8] FIG. 8 is a diagram illustrating an example of a schematic configuration of a motor device.

[0010] [Detailed Description] 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 having 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.

[0011] In this specification, a constant current means a current that is constant under ideal conditions, but in reality, it is a current that may fluctuate slightly due to temperature changes and the like.

[0012] <Switching power supply unit> 1 is a diagram showing the configuration of a switching power supply device according to an embodiment. The switching power supply device 100 includes a switching power supply control device 200 which is a semiconductor integrated circuit device, a P-channel MOS field effect transistor Q1 and an N-channel MOS field effect transistor Q2 which are switching elements, an inductor L1, and an output capacitor C0. In this embodiment, the switching elements are externally connected to the switching power supply control device 200, but may be built into the switching power supply control device 200. Also, in this embodiment, the switching elements are MOS field effect transistors, but may be elements other than MOS field effect transistors.

[0013] The P-channel MOS field effect transistor Q1 and the N-channel MOS field effect transistor Q2 are connected in series. The P-channel MOS field effect transistor Q1 is a high-side switch provided on the higher potential side of the N-channel MOS field effect transistor Q2. The N-channel MOS field effect transistor Q2 is a low-side switch provided on the lower potential side of the P-channel MOS field effect transistor Q1.

[0014] A power supply voltage VCC is applied to the source of a P-channel MOS field effect transistor Q1. A source of an N-channel MOS field effect transistor Q2 is connected to the ground potential. By switching the P-channel MOS field effect transistor Q1 and the N-channel MOS field effect transistor Q2, a pulse-shaped switch voltage is generated at the connection node between the P-channel MOS field effect transistor Q1 and the N-channel MOS field effect transistor Q2.

[0015] The inductor L1 and the output capacitor C0 smooth the switch voltage generated at the connection node between the P-channel MOS field effect transistor Q1 and the N-channel MOS field effect transistor Q2 to generate the output voltage VOUT.

[0016] The switching power supply control device 200 includes a control unit CNT1, drivers D1 and D2, and a current detection circuit 300.

[0017] The control unit CNT1 outputs control signals S1 and S2 based on a feedback voltage VFB. The feedback voltage VFB is a voltage based on the output voltage VOUT. The feedback voltage VFB may be the output voltage VOUT itself or a divided voltage of the output voltage VOUT. It is preferable that the control unit CNT1 performs control to provide a dead time during which both the control signals S1 and S2 are at a low level.

[0018] Furthermore, the control unit CNT1 can perform control using the output OUT2 of the comparator COMP2. For example, the control unit CNT1 can perform constant current control based on the average current flowing through the inductor L1 for each switching period, overcurrent protection based on the average current flowing through the inductor L1 for each switching period, etc. Here, the switching period refers to the switching period of the P-channel MOS field effect transistor Q1 and the N-channel MOS field effect transistor Q2.

[0019] The driver D1 supplies a gate drive signal obtained by amplifying the control signal S1 to the gate of the P-channel MOS field effect transistor Q1 to drive the P-channel MOS field effect transistor Q1. The driver D2 supplies a gate drive signal obtained by amplifying the control signal S2 to the gate of the N-channel MOS field effect transistor Q2 to drive the N-channel MOS field effect transistor Q2.

[0020] The current detection circuit 300 includes a switch SW1, a resistor R1, and a comparator COMP1. The current detection circuit 300 is supplied with a power supply voltage VCC.

[0021] The switch SW1 is provided between the drains of the P-channel MOS field effect transistor Q1 and the N-channel MOS field effect transistor Q2 and between the resistor R1 and the inverting input terminal of the comparator COMP1. When the control signal S1 is at a HIGH level, the switch SW1 is in an ON state. When the control signal S1 is at a LOW level, the switch SW1 is in an OFF state. The resistor R1 is a so-called pull-up resistor.

[0022] The sense voltage Vsns supplied to the inverting input terminal of the comparator COMP1 is a voltage according to the current flowing through the P-channel MOS field effect transistor Q1 when the P-channel MOS field effect transistor Q1 is on (= the current flowing through the inductor L1 when the P-channel MOS field effect transistor Q1 is on). More specifically, the sense voltage Vsns supplied to the inverting input terminal of the comparator COMP1 is a voltage according to the current flowing through the P-channel MOS field effect transistor Q1 when the P-channel MOS field effect transistor Q1 is on during the period when the switch SW1 is on, and is equal to the power supply voltage VCC during the period when the switch SW1 is off.

[0023] Moreover, the sense voltage Vsns is a voltage generated at the connection node between the P-channel MOS field effect transistor Q1 and the inductor L1. More specifically, the sense voltage Vsns is a voltage generated at the connection node between the P-channel MOS field effect transistor Q1 and the inductor L1 during the period when the switch SW1 is in the on state, and is equal to the power supply voltage VCC during the period when the switch SW1 is in the off state. In this embodiment, the sense voltage Vsns is generated by the on resistance of the P-channel MOS field effect transistor Q1. Therefore, it is not necessary to provide a sense resistor for generating the sense voltage Vsns, and power consumption in the sense resistor can be eliminated. This suppresses a decrease in efficiency of the switching power supply device.

[0024] The current detection circuit 300 further includes a P-channel MOS field effect transistor Q3 and a current source CS0. The P-channel MOS field effect transistor Q3 and the current source CS0 are an example of a voltage generating unit that generates a threshold voltage Vth. The threshold voltage Vth is supplied to a non-inverting input terminal of a comparator COMP1.

[0025] The power supply voltage VCC is applied to the source of the P-channel MOS field effect transistor Q3, and the gate of the P-channel MOS field effect transistor Q3 is connected to the ground potential, so that the P-channel MOS field effect transistor Q3 is turned on and acts as a resistive element.

[0026] The current source CS0 is provided between the drain of the P-channel MOS field effect transistor Q3 and the ground potential. The current source CS0 passes a set current (reference current IREF) through the P-channel MOS field effect transistor Q3. In this embodiment, the value of the set current (reference current IREF) is fixed to one value, but it may be changeable. For example, when the control unit CNT1 performs current mode control, the value of the set current (reference current IREF) may change according to an output signal of an error amplifier (not shown) according to an error between a feedback voltage based on the output voltage VOUT and a reference voltage.

[0027] The value (threshold value) of the voltage Vth is the product of the value of the set current (reference current IREF) and the value of the on-resistance of the P-channel MOS field effect transistor Q3.

[0028] In order to suppress power consumption in the voltage generating unit that generates the threshold voltage Vth, it is preferable that the on-resistance of the P-channel MOS field effect transistor Q3 is large. Therefore, it is preferable that the on-resistance of the P-channel MOS field effect transistor Q3 is larger than the on-resistance of the P-channel MOS field effect transistor Q1. For example, the P-channel MOS field effect transistor Q1 and the P-channel MOS field effect transistor Q3 may be MOS field effect transistors having different ratios of channel width to channel length. This makes it possible to easily set the on-resistance of the P-channel MOS field effect transistor Q1 and the on-resistance of the P-channel MOS field effect transistor Q3 to different values.

[0029] It is preferable that the P-channel MOS field effect transistor Q3 is formed so as to maintain a pair with the P-channel MOS field effect transistor Q1. If the P-channel MOS field effect transistors Q1 and Q3 are paired, it is possible to suppress the comparison result in the comparator COMP1 from being affected by temperature, etc.

[0030] The comparator COMP1 compares the sense voltage Vsns with the threshold voltage Vth. The output OUT1 of the comparator COMP1 goes to a HIGH level if the sense voltage Vsns is smaller than the threshold voltage Vth, and goes to a LOW level if the sense voltage Vsns is larger than the threshold voltage Vth.

[0031] The current detection circuit 300 further includes a P-channel MOS field effect transistor Q4, current sources CS1 and CS2, capacitors C1 and C2, and N-channel MOS field effect transistors Q5 and Q6. The P-channel MOS field effect transistor Q4, the current sources CS1 and CS2, the capacitors C1 and C2, and the N-channel MOS field effect transistors Q5 and Q6 are an example of a determination unit. The determination unit in this embodiment determines, based on the output of the comparator COMP1, whether the timing at which the magnitude relationship between the sense voltage Vsns and the threshold voltage Vth is inverted after the P-channel MOS field effect transistor Q1 is turned on is before a predetermined time has elapsed since the P-channel MOS field effect transistor Q1 is turned on.

[0032] The capacitor C1 is charged with the first constant current I1 by the P-channel MOS field effect transistor Q4 and the current source CS1 that outputs the first constant current I1 from when the P-channel MOS field effect transistor Q1 is turned on until the magnitude relationship between the sense voltage Vsns and the threshold voltage Vth is reversed. The value of the charging voltage V1 of the capacitor C1 at the timing when the magnitude relationship between the sense voltage Vsns and the threshold voltage Vth is reversed is held until the P-channel MOS field effect transistor Q1 is turned off.

[0033] The capacitor C2 is charged with the second constant current I2 by the current source CS2 that outputs the second constant current I2 after the magnitude relationship between the sense voltage Vsns and the threshold voltage Vth is inverted.

[0034] The N-channel MOS field effect transistor Q5 discharges the capacitor C1 during the period when the P-channel MOS field effect transistor Q1 is off.

[0035] The inverter INV1 and the N-channel MOS field effect transistor Q6 discharge the capacitor C2 during the period from when the P-channel MOS field effect transistor Q1 is turned on until the magnitude relationship between the sense voltage Vsns and the threshold voltage Vth is inverted and during the period when the P-channel MOS field effect transistor Q1 is off.

[0036] The current detection circuit 300 further includes a comparator COMP2. The comparator COMP2 compares the charging voltage V1 of the capacitor C1 with the charging voltage V2 of the capacitor C2. The output OUT2 of the comparator COMP2 becomes LOW level if the charging voltage V1 of the capacitor C1 is higher than the charging voltage V2 of the capacitor C1, and becomes HIGH level if the charging voltage V1 of the capacitor C1 is lower than the charging voltage V2 of the capacitor C1.

[0037] 2 to 5 are diagrams showing an example of the operation of the current detection circuit 300. In Fig. 2 to 5, from the top, a control signal S1, a control signal S2, a current IL flowing through an inductor L1, a sense voltage Vsns and a threshold voltage Vth, an output OUT1 of a comparator COMP1, a charging voltage V1 of a capacitor C1, a charging voltage V2 of a capacitor C2, and an output OUT2 of a comparator COMP2 are depicted. The charging voltage V2 of the capacitor C2 is depicted by a dashed line.

[0038] The average value of the current IL flowing through inductor L1 increases from Figure 2 to Figure 5. In other words, Figure 2 is the state in which the average value of the current IL flowing through inductor L1 is the smallest among the four states in Figures 2 to 5. Conversely, Figure 5 is the state in which the average value of the current IL flowing through inductor L1 is the largest among the four states in Figures 2 to 5.

[0039] For example, when the first constant current I1 and the second constant current I2 have the same value and the capacitance of the capacitor C1 and the capacitance of the capacitor C2 are the same, it is possible to confirm from the output OUT2 of the comparator COMP2 whether the current IL flowing through the inductor L1 has exceeded a predetermined value (a value corresponding to the threshold voltage Vth) at a timing earlier than half the period during which the N-channel MOS field effect transistor Q1 is on.

[0040] As shown in Figures 2 to 4, when no pulse appears at the output OUT2 of the comparator COMP2, the current IL flowing through the inductor L1 does not exceed the set value (the value corresponding to the threshold voltage Vth) earlier than half the period during which the N-channel MOS field effect transistor Q1 is on.

[0041] As shown in Figure 5, when a pulse appears at the output OUT2 of the comparator COMP2, the current IL flowing through the inductor L1 exceeds a set value (a value corresponding to the threshold voltage Vth) earlier than halfway through the period during which the N-channel MOS field-effect transistor Q1 is on.

[0042] There is a correlation between the instantaneous value of the current IL flowing through the inductor L1 when a predetermined time (e.g., half the period during which the P-channel MOS field effect transistor Q1 is on) has elapsed since the P-channel MOS field effect transistor Q1 is turned on, and the average value of the current IL flowing through the inductor L1 in a switching period. Therefore, the current detection circuit 300 can detect whether the average value of the current IL flowing through the inductor L1 in each switching period is greater than a set value.

[0043] For example, when a pulse appears in the output OUT2 of the comparator COMP2, the control unit CNT1 performs control to decrease the current IL flowing through the inductor L1, and conversely, when a pulse does not appear in the output OUT2 of the comparator COMP2, the control unit CNT1 performs control to increase the current IL flowing through the inductor L1, thereby enabling the average value of the current IL flowing through the inductor L1 per switching period to be kept close to a set value.

[0044] 6 is a diagram showing the configuration of a switching power supply device according to a modified example. Switching power supply device 101 differs from the above-described switching power supply device 100 in that it includes a sense resistor R0 and a resistor R2, and includes a switching power supply control device 201 instead of switching power supply control device 200.

[0045] The sense resistor R0 is connected in series to the inductor L1 and is provided in front of the output capacitor C0. The resistor R2 is a resistive element having a resistance value larger than that of the sense resistor R0 and having the same temperature characteristics as the sense resistor R0.

[0046] Switching power supply control device 201 differs from switching power supply control device 200 described above in that it includes current detection circuit 301 instead of current detection circuit 300.

[0047] The current detection circuit 301 differs from the current detection circuit 300 in that it includes an amplifier AMP1 instead of the switch SW and resistor R1, does not include a P-channel MOS field effect transistor Q3, and replaces the non-inverting input terminal and the inverting input terminal of the comparator COMP1. The amplifier AMP1 generates a sense voltage Vsns according to the potential difference across the sense resistor R0, and supplies the sense voltage Vsns to the non-inverting input terminal of the comparator COMP1. The resistor R2 described above is a resistive element that replaces the P-channel MOS field effect transistor Q3.

[0048] <Application Examples> Application examples of the current detection circuit are not limited to switching power supply devices. The current detection circuit having the above-described configuration may be mounted on, for example, a light-emitting element driving device, a motor driving device, and the like.

[0049] 7 is a diagram showing a schematic configuration example of a light emitting device. The light emitting device 400 includes a light emitting element driving device 401, an inductor 402, an N-channel MOS field effect transistor 403, an output capacitor 404, and a light emitting element 405. The light emitting element driving device 401 drives the light emitting element 405 by controlling the N-channel MOS field effect transistor 403. The light emitting element driving device 401 includes a current detection circuit 406.

[0050] 8 is a diagram showing a schematic configuration example of a motor device. Motor device 500 includes motor drive device 501, a three-phase inverter 502, and a three-phase motor 503. Motor drive device 501 drives three-phase motor 503 by controlling three-phase inverter 502. Motor drive device 501 includes a current detection circuit 504.

[0051] <Other> In addition to the above-described embodiment, various modifications can be made to the configuration of the invention without departing from the spirit of the invention. The above-described embodiment should be considered to be illustrative in all respects and not restrictive, and the technical scope of the present invention is indicated by the claims, not the description of the above-described embodiment, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0052] In the above-described embodiment, the sense voltage is a voltage corresponding to the current flowing through the high-side switching element, but it may be a voltage corresponding to the current flowing through the low-side switching element. Also, the low-side switching element may be, for example, a diode.

[0053] <Additional Notes> Regarding the present disclosure, specific configuration examples of which have been shown in the above-mentioned embodiments, additional notes will be provided.

[0054] A current detection circuit (300, 301, 406, 504) of the present disclosure has a configuration (first configuration) including a first comparison unit (COMP1) configured to compare a sense voltage corresponding to a current flowing through a switching element (Q1) when the switching element is on with a threshold voltage, and a judgment unit (C1, C2, CS1, CS2, Q4 to Q6, INV1, COMP2) configured to judge, based on the output of the first comparison unit, whether the timing at which the magnitude relationship between the sense voltage and the threshold voltage is reversed after the switching element is turned on is before a predetermined time has elapsed after the switching element is turned on.

[0055] The current detection circuit of the first configuration can detect an average current for each switching period. More specifically, the current detection circuit of the first configuration can detect whether the average current for each switching period is greater than a set value. Therefore, by using the current detection circuit of the first configuration, it is possible to realize, for example, constant current control based on the average current for each switching period, overcurrent protection based on the average current for each switching period, etc.

[0056] In the current detection circuit of the first configuration described above, the sense voltage may be a voltage generated at a connection node between the switching element and an inductor (L1) (second configuration).

[0057] In the current detection circuit of the above first or second configuration, the judgment unit may be configured (third configuration) to include a first charging unit (CS1, Q4, C1) configured to charge with a first constant current after the switching element is turned on until the magnitude relationship between the sense voltage and the threshold voltage is inverted, a second charging unit (CS2, C2) configured to charge with a second constant current after the magnitude relationship between the sense voltage and the threshold voltage is inverted, and a second comparison unit (COMP2) configured to compare the charging voltage of the first charging unit with the charging voltage of the second charging unit.

[0058] In the current detection circuit of the third configuration described above, the judgment unit may be configured (fourth configuration) to include a first discharge unit (Q5) configured to discharge the first charging unit during a period when the switching element is off, and a second discharge unit (Q6, INV1) configured to discharge the second charging unit during a period from when the switching element is turned on to when the magnitude relationship between the sense voltage and the threshold voltage is inverted and during a period when the switching element is off.

[0059] In the current detection circuit of any of the first to fourth configurations, the current detection circuit may be further provided with a voltage generating unit configured to generate the threshold voltage, the voltage generating unit being provided with a resistive element (Q3) having a resistance value larger than the on-resistance of the switching element, and a current source (CS0) configured to pass a set current through the resistive element (Q3).

[0060] In the current detection circuit of the fifth configuration, the switching element and the resistive element may be MOS field effect transistors having different ratios of channel width to channel length (sixth configuration).

[0061] A switching power supply control device (200, 201) of the present disclosure has a configuration (seventh configuration) including a current detection circuit having any of the first to sixth configurations described above.

[0062] A light emitting element driving device (401) of the present disclosure has a configuration (eighth configuration) including a current detection circuit having any one of the first to sixth configurations.

[0063] A motor driving device (501) of the present disclosure has a configuration (ninth configuration) including a current detection circuit having any of the first to sixth configurations. [Explanation of symbols]

[0064] 100, 101 Switching power supply 200, 201 Switching power supply control device 300, 301 Current detection circuit 400 Light Emitting Device 401 Light emitting element driving device 402 Inductor 403 N-channel MOS field effect transistor 404 Output Capacitor 405 Light emitting element 406 Current detection circuit 500 Motor Device 501 Motor drive unit 502 Three-phase inverter 503 Three-phase motor 504 Current detection circuit AMP1 Amplifier C0 Output Capacitor C1, C2 capacitors CNT1 control unit COMP1, COMP2 comparators CS0, CS1, CS2 current sources D1, D2 Driver INV1 Inverter L1 Inductor Q1, Q3, Q4 P-channel MOS field effect transistors Q2, Q5, Q6 N-channel MOS field effect transistors R0 Sense resistor R1, R2 resistance SW1 Switch

Claims

1. a first comparison unit configured to compare a sense voltage corresponding to a current flowing through the switching element when the switching element is on with a threshold voltage; a determination unit configured to determine, based on an output of the first comparison unit, whether or not a timing at which a magnitude relationship between the sense voltage and the threshold voltage is inverted after the switching element is turned on occurs until a predetermined time has elapsed after the switching element is turned on.

2. 2. The current detection circuit according to claim 1, wherein the sense voltage is a voltage generated at a connection node between the switching element and an inductor.

3. The determination unit is a first charging unit configured to charge with a first constant current from when the switching element is turned on until a magnitude relationship between the sense voltage and the threshold voltage is inverted; a second charging unit configured to charge with a second constant current after the magnitude relationship between the sense voltage and the threshold voltage is inverted; The current detection circuit according to claim 1 , further comprising: a second comparison unit configured to compare a charging voltage of the first charging unit with a charging voltage of the second charging unit.

4. The determination unit is a first discharge unit configured to discharge the first charge unit during a period when the switching element is off; 4. The current detection circuit according to claim 3, further comprising: a second discharging unit configured to discharge the second charging unit during a period from when the switching element is turned on until a magnitude relationship between the sense voltage and the threshold voltage is inverted and during a period when the switching element is off.

5. a voltage generating unit configured to generate the threshold voltage, The voltage generating unit is a resistor element having a resistance value greater than the on-resistance of the switching element; 2. The current sensing circuit of claim 1, further comprising: a current source configured to apply a set current to the resistive element.

6. 6. The current detection circuit according to claim 5, wherein the switching element and the resistive element are MOS field effect transistors having different ratios of channel width to channel length.

7. A switching power supply control device comprising the current detection circuit according to any one of claims 1 to 6.

8. A light emitting element driving device comprising the current detection circuit according to any one of claims 1 to 6.

9. A motor drive device comprising the current detection circuit according to any one of claims 1 to 6.

Images