JP2007288935A - Dc/dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient DC/DC converter in which conversion efficiency is improved and electric power is saved. <P>SOLUTION: When a gate control circuit 105 drives a p-chMOSFET 102 from an off state to an on state, an added lower side switch 201 for gate drive is switched on first to charge electric charge into an added output capacitor 202. When a voltage of the capacitor reaches a certain level, the added lower side switch 201 is switched off. By performing this control of switching on a lower side switch 104 for the gate drive, the electric charge charged in a gate-drain parasitic capacitance 102 is supplied from a regulator 203 to an output. Thereby, energy charged in the parasitic capacitance 102 is used effectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a DC / DC converter using a MOSFET as a switching element used in a power supply device of an electronic device such as a notebook personal computer.

  In a DC / DC converter used in a power supply device of a conventional electronic device such as a notebook personal computer, a charge is charged in the gate input parasitic capacitance of the MOSFET when the MOSFET being used is switched.

  FIG. 3 is a circuit diagram showing a conventional non-insulated step-down DC / DC converter.

  In FIG. 3, the power supply IC 106 drives the gate of the p-ch MOSFET 101 from the gate control circuit 105 using the gate drive upper switch 103 and the gate drive lower switch 104. The power supply IC 106 adjusts the on / off time ratio of the p-ch MOSFET 101 so that the output voltage becomes constant. The flywheel diode 108 is turned on to supply current to the output while the p-ch MOSFET 101 is off. Reference numeral 109 denotes a smoothing coil, and 110 denotes a smoothing capacitor, which smoothes a rectangular wave voltage output by turning on / off the p-ch MOSFET 101 and extracts a DC voltage.

  When the p-ch MOSFET 101 is driven from the off state to the on state, the charge charged in the gate-drain parasitic capacitance 102 of the p-ch MOSFET 101 is discharged by the gate drive lower switch 104, and the p-ch MOSFET 101 is driven. When switching from the on state to the off state, the gate-drain parasitic capacitance 102 is charged via the gate drive upper switch 103.

  In recent electronic devices such as notebook personal computers, a DC / DC converter having a larger maximum output current is required. In order to cope with this, it is necessary to use a p-ch MOSFET 101 having a lower on-resistance type. Generally, a MOSFET having a lower on-resistance has a gate-drain parasitic capacitance 102 and a gate-source parasitic capacitance. 107 tends to be large.

On the other hand, high conversion efficiency is required in a wide output current region from a light load region to a heavy load region in order to suppress standby power consumption of an electronic device and save energy. In order to improve the efficiency in the heavy load region, for example, a low on-resistance MOSFET is used as described above. In order to increase the conversion efficiency in the light / medium load region, for example, as in Patent Document 1, a technique for improving the speed of the switching operation and reducing the so-called switching loss has been used.
JP 2000-287440 A

  However, in the conventional configuration, when the p-ch MOSFET 102 is driven from the off state to the on state, the charge charged in the parasitic capacitance 102 between the gate and the drain is wasted through the switch 104 and the conversion efficiency is lowered. It had a problem of making it happen.

  In the power control MOSFET, the parasitic capacitance between the gate and the drain is larger than that of a normal one, and the ratio of this wasteful energy consumption is particularly remarkable when the DC / DC converter is operated at a very light load.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a high-efficiency DC / DC converter that improves conversion efficiency and saves power.

  In order to solve the above-described conventional problems, the high-efficiency DC / DC converter according to the present invention includes another additional gate drive switch, which performs MOSFET gate drive and external gate input parasitic capacitance. The charge taken out from the battery is reused as energy.

  With this configuration, the charge charged in the gate parasitic capacitance can be extracted as energy without waste.

  According to the high-efficiency DC / DC converter of the present invention, the conversion efficiency can be improved particularly during light load operation in which the gate drive power is the main conversion loss, and power saving can be achieved.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
1 is a circuit diagram of a high-efficiency DC / DC converter according to Embodiment 1 of the present invention.

  In FIG. 1, the same components as those of the conventional example shown in FIG. 3 differs from the conventional example in FIG. 3 in that an additional lower switch 201 for gate drive, an additional output capacitor 202, a regulator (three-terminal regulator, series regulator) 203 and a diode 204 are added to the circuit of FIG.

  In FIG. 1, a gate drive additional lower switch 201 is connected to the gate of the p-ch MOSFET 101 in parallel with the gate drive lower switch 104, and an additional output capacitor 202 and a regulator 203 supply power to the output. An output circuit is configured.

  The operation of the high-efficiency DC / DC converter configured as described above will be described below.

  When the gate control circuit 105 drives the p-ch MOSFET 101 from the off state to the on state, the gate drive additional lower switch 201 is first turned on, and the additional output capacitor 202 is charged. When the voltage reaches the optimum level, the gate drive additional lower switch 201 is turned off and the gate drive lower switch 104 is turned on. In this way, the electric charge charged in the gate-drain parasitic capacitance 102 is supplied from the regulator 203 to the output through the diode 204. The diode 204 prevents the output current from flowing back to the regulator 203.

  As a result, energy that has been wasted in the past can be extracted as output.

  In this embodiment, the regulator 203 is described as an example of the additional output circuit using a three-terminal regulator, but a switching regulator may be used.

  Further, the gate control circuit 105 may determine whether or not to turn on the additional lower switch for gate drive 201 for each switching cycle according to the load current or the voltage of the additional output capacitor 202. .

(Embodiment 2)
FIG. 2 is a block diagram of the high efficiency DC / DC converter according to the second embodiment of the present invention. 2, the same components as those in FIG. 1 of the first embodiment and FIG. 3 of the conventional example are denoted by the same reference numerals, and the description thereof is omitted.

  2, an n-ch MOSFET 301 constitutes a synchronous rectification step-down DC / DC converter with a synchronous rectification n-ch MOSFET 302 arranged in place of the flywheel diode 108 of FIGS.

  The gate drive additional lower switch 201 is connected to the gate of the n-ch MOSFET 101 in parallel with the gate drive lower switch 104, and power is supplied to the power supply Vcc (+ 5V) input of the power supply IC by the additional output capacitor 202 and the regulator 203. The additional output circuit for supplying

  The diode 303 prevents the output current from flowing backward from the power supply Vcc of the power supply IC to the regulator 203, like the diode 204 of the embodiment. The diode 304 and the capacitor 305 generate a voltage for turning on / off the n-ch MOSFET 301, and the details are omitted here.

  The operation of the high-efficiency DC / DC converter configured as described above will be described below.

  When the gate control circuit 105 drives the n-ch MOSFET 301 from the on state to the off state, the gate drive additional lower switch 201 is first turned on to charge the additional output capacitor 202 and the voltage of the additional output capacitor 202 When the gate drive additional lower switch 201 is turned off and the gate drive lower switch 104 is turned on, the gate-drain parasitic capacitance 102 and the gate-source parasitic capacitance 107 are controlled. The electric charge charged to the power supply IC 106 is supplied from the regulator 203 to the power supply IC 106 through the diode 303, and energy that has been consumed in the past can be taken out as an input power supply of the power supply IC.

  In this embodiment, the output of the regulator 203 is supplied as the power supply of the power supply IC 106, but it may be taken out to the output side as in FIG.

  The high-efficiency DC / DC converter according to the present invention can take out energy that has been wasted in the past and can be used effectively. Therefore, the DC / DC used in power supply devices for electronic devices such as notebook personal computers. Useful as a converter.

Circuit diagram of high-efficiency DC / DC converter in Embodiment 1 of the present invention Circuit diagram of high-efficiency DC / DC converter in Embodiment 2 of the present invention Circuit diagram of conventional DC / DC converter

Explanation of symbols

101 p-ch MOSFET
102 Gate-drain parasitic capacitance 103 Gate drive upper switch 104 Gate drive lower switch 105 Gate control circuit 106 Power supply IC
107 parasitic capacitance between gate and source 108 flywheel diode 109 smoothing coil 110 smoothing capacitor 201 additional lower switch for gate drive 202 additional output capacitor 203 regulator 204 diode 301 n-ch MOSFET
302 n-ch MOSFET for synchronous rectification
303 Diode 304 Diode 305 Capacitor

Claims (4)

MOSFET used as a switching element of a DC / DC converter;
A capacitor that moves and accumulates the charge of the parasitic capacitance between the gate and drain of the MOSFET; and
An additional gate drive switch for transferring charge to the capacitor;
A DC / DC converter comprising: a regulator that outputs a voltage obtained by converting the charge accumulated in the capacitor to an output side of the DC / DC converter. MOSFET used as a switching element of a DC / DC converter;
A capacitor that moves and accumulates the charge of the parasitic capacitance between the gate and drain of the MOSFET; and
An additional gate drive switch for transferring charge to the capacitor;
A power supply IC that controls the gate of the MOSFET to switch a DC voltage;
A DC / DC converter comprising: a regulator that converts the charge accumulated in the capacitor into a voltage and supplies it as drive power for the power supply IC. 3. The DC / DC converter according to claim 1, wherein the regulator is constituted by a three-terminal regulator. 3. The DC / DC according to claim 1, wherein the switching operation of the additional switch for gate drive is limited for each cycle of switching of the MOSFET based on a load current of the DC / DC converter. converter.

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