JP6299377B2 - DC-DC converter and apparatus including the same - Google Patents

Description

  The present invention relates to a DC-DC converter and an apparatus including the same.

  2. Description of the Related Art Conventionally, a switching regulator that detects the magnitude of a coil current by detecting a voltage generated when the coil current flows through the on-resistance of a transistor is known (see, for example, Patent Document 1).

JP 2005-261102 A

  However, since the on-resistance of the transistor has a characteristic proportional to the temperature, in the above-described conventional technology, the current detection error may increase depending on the ambient temperature of the transistor.

  Therefore, an object of the present invention is to provide a DC-DC converter that can detect a current by reducing the influence of a temperature change.

One idea is that
A high-side transistor for step-down,
A low-side transistor for synchronous rectification,
A series circuit connected in parallel to the low-side transistor, in which a diode and a resistor are connected in series;
A detection circuit that detects a current flowing through the resistor during a dead time in which both the high-side transistor and the low-side transistor are off,
The voltage drop of the series circuit of the dead time, rather lower than the forward voltage of the parasitic diode of the low side transistor,
Drive that turns off the high-side transistor when the current flowing through the resistor exceeds a threshold during the dead time from when the high-side transistor switches from on to off until the low-side transistor switches from off to on A DC-DC converter comprising a circuit is provided .

  According to one aspect, the current can be detected while reducing the influence of temperature change.

Configuration diagram showing an example of a DC-DC converter Waveform diagram showing an example of the operation of the DC-DC converter The figure which shows an example of an apparatus provided with a DC-DC converter Diagram showing an example of power distribution Waveform diagram showing an example of operation simulation of a DC-DC converter

  FIG. 1 is a configuration diagram illustrating an example of the converter 100. Converter 100 is an example of a DC-DC converter including transistor 10, transistor 20, series circuit 30, inductor 40, capacitor 50, and control circuit 70. The converter 100 is, for example, a synchronous rectification step-down converter.

  Converter 100 may be a semiconductor device having a configuration formed by an integrated circuit, or may be a semiconductor device having a configuration formed by discrete components.

  The transistor 10 is an example of a step-down high-side transistor provided on the input node 81 side with respect to the input terminal of the inductor 40. The transistor 20 is an example of a low-side transistor for synchronous rectification provided on the ground 84 side with respect to the input terminal of the inductor 40. The input node 81 is an example of a conductive part to which a DC input voltage Vin is input.

  The transistor 10 is an example of an insulated gate transistor having a gate electrode to which a gate voltage Vg1 is applied, and is a switching element that is on / off controlled by the voltage level (high level or low level) of the gate voltage Vg1. Similarly, the transistor 20 is an example of an insulated gate transistor having a gate electrode to which the gate voltage Vg2 is applied, and is a switching element that is on / off controlled by the voltage level (high level or low level) of the gate voltage Vg2. .

  The transistors 10 and 20 are, for example, N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). Transistor 10 has a drain connected to input node 81 and a source connected to the drain of transistor 20 and the input end of inductor 40. The transistor 20 has a drain connected to the source of the transistor 10 and the input terminal of the inductor 40, and a source connected to the ground 84.

  The transistors 10 and 20 have a parasitic diode between the source and the drain. FIG. 1 shows a parasitic diode 21 of the transistor 20. The anode of the parasitic diode 21 is the source of the transistor 20, and the cathode of the parasitic diode 21 is the drain of the transistor 20.

  The series circuit 30 is an example of a series circuit that is connected in parallel to the parasitic diode 21 of the transistor 20 and in which a Schottky barrier diode 31 and a sense resistor 32 are connected in series. The series circuit 30 has a current path connected in parallel to the parasitic diode 21, and the Schottky barrier diode 31 and the sense resistor 32 are inserted in series in the current path.

  Schottky barrier diode 31 has a cathode connected to the cathode (drain of transistor 20) side of parasitic diode 21 and an anode connected to the anode (source of transistor 20) side of parasitic diode 21. In the illustrated case, the anode of the Schottky barrier diode 31 is connected to the anode (source of the transistor 20) side of the parasitic diode 21 via the sense resistor 32. The positions of the Schottky barrier diode 31 and the sense resistor 32 may be replaced with each other. The sense resistor 32 is an example of a resistance element.

  The other end of the inductor 40 is connected to the output node 82. The output node 82 is an example of a conductive part that outputs a DC output voltage Vout. Connected to the output node 82 is a load 60 to which the output voltage Vout is supplied. Capacitor 50 is connected to output node 82 so as to be inserted between output node 82 and ground 84, and smoothes output voltage Vout.

  The control circuit 70 is an example of a control unit that controls the step-down operation for generating the output voltage Vout having a voltage value lower than the input voltage Vin, and operates with the power supply voltage Vcc supplied from the power supply node 83. The control circuit 70 is, for example, a control IC (Integrated Circuit) having a drive circuit 71 and a detection circuit 72.

  The drive circuit 71 is a gate drive circuit that controls the gate voltage Vg1 to a voltage value that turns the transistor 10 on and off, and controls the gate voltage Vg2 to a voltage value that turns the transistor 20 on and off. The driver circuit 71 turns the transistor 20 on and off in synchronization with the on / off of the transistor 10 so that the transistor 20 is off when the transistor 10 is on and the transistor 20 is on when the transistor 10 is off.

  The detection circuit 72 is a current detection circuit that detects a sense current Ir flowing through the sense resistor 32 (that is, a current flowing through the series circuit 30) by detecting a sense voltage Vr generated across the sense resistor 32.

  FIG. 2 is a timing chart showing an example of operation waveforms of converter 100. Vg1 is the gate voltage of the transistor 10, Vg2 is the gate voltage of the transistor 20, Iout is the output current flowing through the output node 82 (in other words, the inductor 40), and I2 is the drain current flowing between the source and drain of the transistor 20. Ir represents a sense current flowing through the sense resistor 32, and Vr represents a sense voltage generated at both ends of the sense resistor 32.

  The drive circuit 71 turns on the transistor 10 by setting the gate voltage Vg1 to a high level, and turns off the transistor 10 by setting the gate voltage Vg1 to a low level. Similarly, the drive circuit 71 turns on the transistor 20 by setting the gate voltage Vg2 to high level, and turns off the transistor 20 by setting the gate voltage Vg2 to low level.

  The drive circuit 71 turns the transistors 10 and 20 on and off so that the dead time DT exists in order to prevent a through current from flowing into the transistors 10 and 20 when both the transistor 10 and the transistor 20 are turned on. The dead time DT is a period in which both the transistor 10 and the transistor 20 are off (in the case of FIG. 2, periods t2-t3, t4-t5, t6-t7, etc.).

  In the converter 100, the voltage drop Vx generated at both ends of the series circuit 30 due to the current flowing in the series circuit 30 during the dead time DT is set lower than the forward voltage Vf 1 of the parasitic diode 21 of the transistor 20. With this setting, the return current flowing during the dead time DT flows through the series circuit 30 without flowing through the parasitic diode 21.

  In the illustrated case, the voltage drop Vx is equal to the sum of the forward voltage Vf2 of the Schottky barrier diode 31 and the voltage drop of the sense resistor 32 (that is, the sense voltage Vr). For example, the forward voltage Vf2 of the Schottky barrier diode 31 is higher than the forward voltage Vf1 so that the voltage drop Vx of the series circuit 30 at the dead time DT is set lower than the forward voltage Vf1 of the parasitic diode 21. Is also good.

  The sense current Ir that flows during the dead time DT is equal to the output current Iout. Therefore, the detection circuit 72 can detect the magnitude of the output current Iout, for example, by detecting the current value Ir2 of the sense current Ir flowing during the dead time DT based on the voltage value Vr2 of the sense voltage Vr.

  In particular, the maximum current value Ir1 of the sense current Ir that flows during the dead time DT (for example, the period t2-t3) from the timing at which the transistor 10 switches from on to off until the timing at which the transistor 20 switches from off to on is equal to the output current Iout. It is equal to the maximum current value Iout1. Therefore, the detection circuit 72 detects, for example, the maximum current value Ir1 of the sense current Ir flowing during the dead time DT from the timing t2 to the timing t3 based on the maximum voltage value Vr1 (absolute value) of the sense voltage Vr. The maximum current value Iout1 of the output current Iout can be detected.

  As described above, the detection circuit 72 detects the sense current Ir flowing in the dead time DT which is extremely shorter than the ON time of the transistors 10 and 20 by using the sense resistor 32. Thereby, the loss of the sense resistor 32 can be suppressed, the influence on the temperature change can be reduced, and the output current Iout (in particular, the maximum current value of the output current Iout) can be detected. Moreover, since the loss of the sense resistor 32 can be suppressed, a decrease in the efficiency (ratio of output power to input power) of the DC-DC converter 100 can be suppressed.

  When the detection circuit 72 detects that the current value of the sense current Ir that flows during the dead time DT exceeds a predetermined threshold value Vth based on the sense voltage Vr, the drive circuit 71 detects only the transistor 10 or both the transistors 10 and 20. May be turned off. Thereby, it is possible to prevent an excessive output current Iout from flowing. In this case, the sense current Ir compared with the threshold value Vth may be a current that flows during a period from when the transistor 10 switches from on to off until the transistor 20 switches from off to on, or the transistor 20 switches from on to off. Current that flows during a period from when the transistor 10 is turned off to when it is turned on.

  The drive circuit 71 is based on the sense voltage Vr that the current value of the sense current Ir flowing during the dead time DT from when the transistor 10 is switched from on to off until the transistor 20 is switched from off to on exceeds a predetermined threshold value Vth. Thus, only the transistor 10 or both the transistors 10 and 20 may be turned off. Accordingly, it is possible to shorten the time from when the excessive output current Iout flows during the ON period of the transistor 10 until the excessive output current Iout is interrupted.

  FIG. 3 is a diagram illustrating an example of the notebook computer 200. The notebook computer 200 is an example of an information processing apparatus having a function for processing information. The notebook computer 200 operates with DC power supplied from the AC adapter 201 connected to the commercial power source 203. For example, the converter 100 is mounted on a mother board 202 in the notebook computer 200.

  FIG. 4 shows an example of power distribution on the motherboard 202. The AC adapter 201 is connected to the input terminal 211 of the motherboard 202 and can charge the battery 204 connected to the input terminal 212 of the motherboard 202 via the charging circuit 213. The DC power of the AC adapter 201 or the DC power of the battery 204 is supplied to the power supplies 216, 217, 218, and 219 via the diodes 214 and 215. The power source 216 supplies DC power to a CPU (Central Processing Unit) 226, and the power source 217 supplies DC power to a VGA (Video Graphics Accelerator) 227. The power source 218 supplies DC power to the power sources 220 to 224. The power source 220 supplies DC power to the VGA 227, the power source 221 supplies DC power to the PCH (Platform Controller Hub) 228, the power source 222 supplies DC power to the VRAM (Video Random Access Memory) 229, and the power source 223 and 224 supply DC power to a DIMM (Dual Inline Memory Module) 230. A power source 219 supplies DC power to an MMC (Multi Media Card) 231 and a power source 225, and the power source 225 supplies DC power to the PCH 228. The converter 100 of this embodiment can be applied to any of these power supplies.

  FIG. 5 shows an example of a simulation result when the converter 100 of the present embodiment is applied to the power supply 218 having an output voltage of 5 V / output current of 10 A. In FIG. 5, the input voltage Vin = 19V, the output voltage Vout = 5V, and the output current Iout = 10A. The model of the transistors 10 and 20 is irfru3711z (IR). The model of the Schottky barrier diode 31 is MBRB2545CT (ON Semiconductor). The model of the inductor 40 is 2.2 uH / DCR: 6.8 mΩ. The model of the capacitor 50 is 660 uF / ESR: 20 mΩ.

  As shown in FIG. 5, the current value of the sense current Ir flowing through the sense resistor 32 during the dead time is substantially equal to the peak of the output current Iout. Since the sense voltage Vr generated in the sense resistor 32 during this dead time changes in accordance with the current value of the sense current Ir, it can be used to determine the current limit.

  Further, when the efficiency of the converter 100 of the present embodiment is calculated, it is 94.7%. On the other hand, the converter when the sense resistor 32 is deleted and an alternative sense resistor is inserted between the inductor 40 and the output node 82 ( The efficiency of Comparative Example) is calculated to be 92.9%. Thus, according to the converter of this embodiment, the efficiency can be improved.

  As mentioned above, although DC-DC converter and an apparatus provided with it were described by embodiment, the present invention is not limited to the above-mentioned embodiment. Various modifications and improvements such as combinations and substitutions with some or all of the other embodiments are possible within the scope of the present invention.

  For example, the DC-DC converter is not limited to a synchronous rectification step-down converter, and may be a converter that can perform step-up or step-down switching (for example, an H-bridge type converter).

  In addition, the device including the DC-DC converter is not limited to the notebook personal computer, and may be another information processing device (for example, a server) or a device other than the information processing device (for example, a mobile phone or a smartphone). It may be.

Regarding the above embodiment, the following additional notes are disclosed.
(Appendix 1)
A high-side transistor for step-down,
A low-side transistor for synchronous rectification,
A series circuit connected in parallel to the low-side transistor, in which a diode and a resistor are connected in series;
A detection circuit that detects a current flowing through the resistor during a dead time in which both the high-side transistor and the low-side transistor are off,
The DC-DC converter, wherein a voltage drop of the series circuit in the dead time is lower than a forward voltage of a parasitic diode of the low-side transistor.
(Appendix 2)
The DC-DC converter according to appendix 1, wherein the dead time is a period from when the high-side transistor is switched from on to off until the low-side transistor is switched from off to on.
(Appendix 3)
The DC-DC converter according to appendix 1 or 2, further comprising a drive circuit that turns off the high-side transistor when the current exceeds a threshold value.
(Appendix 4)
The DC-DC converter according to any one of appendices 1 to 3, wherein the diode is a Schottky barrier diode.
(Appendix 5)
A load, and a DC-DC converter for supplying power to the load,
The DC-DC converter
A high-side transistor for step-down,
A low-side transistor for synchronous rectification,
A series circuit connected in parallel to the low-side transistor, in which a diode and a resistor are connected in series;
A detection circuit that detects a current flowing through the resistor during a dead time in which both the high-side transistor and the low-side transistor are off,
The apparatus, wherein a voltage drop of the series circuit in the dead time is lower than a forward voltage of a parasitic diode of the low-side transistor.

10, 20 Transistor 21 Parasitic diode 30 Series circuit 31 Schottky barrier diode 32 Sense resistor 40 Inductor 50 Capacitor 60 Load 70 Control circuit 71 Drive circuit 72 Detection circuit 81 Input node 82 Output node 83 Power supply node 84 Ground 100 Converter 200 Notebook computer 201 AC adapter 202 Motherboard 203 Commercial power supply 204 Battery

Claims (2)

A high-side transistor for step-down,
A low-side transistor for synchronous rectification,
A series circuit connected in parallel to the low-side transistor, in which a diode and a resistor are connected in series;
A detection circuit that detects a current flowing through the resistor during a dead time in which both the high-side transistor and the low-side transistor are off,
The voltage drop of the series circuit of the dead time, rather lower than the forward voltage of the parasitic diode of the low side transistor,
Drive that turns off the high-side transistor when the current flowing through the resistor exceeds a threshold during the dead time from when the high-side transistor switches from on to off until the low-side transistor switches from off to on A DC-DC converter comprising a circuit . A load, and a DC-DC converter for supplying power to the load,
The DC-DC converter
A high-side transistor for step-down,
A low-side transistor for synchronous rectification,
A series circuit connected in parallel to the low-side transistor, in which a diode and a resistor are connected in series;
A detection circuit that detects a current flowing through the resistor during a dead time in which both the high-side transistor and the low-side transistor are off,
The voltage drop of the series circuit of the dead time, rather lower than the forward voltage of the parasitic diode of the low side transistor,
Drive that turns off the high-side transistor when the current flowing through the resistor exceeds a threshold during the dead time from when the high-side transistor switches from on to off until the low-side transistor switches from off to on An apparatus comprising a circuit .

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