JP2005245165A - Drive circuit and switching power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the switching of a switching element with less loss. <P>SOLUTION: When a MOSFET 212 is turned off, a capacitor 252 is applied with voltage nearly equal to an input voltage Vin to be charged. When an H level control signal is input to a drive circuit 217 from a control circuit 216; a transistor 257 is turned on, and the voltage at both ends of the charged capacitor 252 is applied to a voltage-dividing circuit 222 via a resistor 259. The voltage applied to the voltage-dividing circuit 222 is divided by parallel circuits 271, 272, the voltage at both ends of the parallel circuit 271 are applied between the gate-sources of the MOSFET 212, and the MOSFET 212 is turned on. This drive circuit and the switching power unit can also be applied to a DC/DC converter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a drive circuit and a switching power supply, and more particularly to a drive circuit and a switching power supply that reduce power loss.

  FIG. 1 shows a circuit configuration of a typical step-down (down chopper type) DC / DC converter.

  The DC / DC converter 1 includes an input terminal 11, a switching element 12, a smoothing circuit 13, an output terminal 14, a constant voltage circuit 15, a control circuit 16, and a drive circuit 21.

  The switching element 12 is configured by, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The drain of the switching element 12 is connected to the input terminal 11, the gate of the switching element 12 is connected to the drive circuit 21, and the source of the switching element 12 is connected to the smoothing circuit 13. The switching element 12 is turned on or off in accordance with a drive signal output from the drive circuit 21, and a DC voltage Vin (hereinafter simply referred to as an input voltage Vin) input from the input terminal 11 is switched by the switching element 12. The signal is intermittently output to the smoothing circuit 13.

  The smoothing circuit 13 is a choke input type smoothing circuit, and includes a diode 31, a coil 32, and a capacitor 33. One end of the coil 32 is connected to the source of the switching element 12 and the cathode of the diode 31, and the other end of the coil 32 is connected to one end of the capacitor 33 and the output terminal 14. The anode of the diode 31 and the other end of the capacitor 33 are grounded. The intermittent voltage output from the switching element 12 is smoothed by the smoothing circuit 13, and the smoothed DC voltage Vout (hereinafter referred to as the output voltage Vout) is output from the output terminal 14 to the outside.

  The constant voltage circuit 15 converts the input voltage Vin input from the input terminal 11 into a predetermined DC voltage within the rated voltage of the control circuit 16 and the drive circuit 21, and supplies it to the control circuit 16 and the drive circuit 21. The control circuit 16 controls the drive circuit 21 by outputting to the drive circuit 21 control signals of two kinds of voltage levels, a high level (hereinafter referred to as H level) and a low level (hereinafter referred to as L level). .

  Therefore, the DC / DC converter 1 controls the duty ratio of the control signal output from the control circuit 16, thereby controlling the duty ratio of the switching element 12 and outputting a desired output voltage Vout.

  Various types of transistors can be used for the switching element 12. In particular, in order to reduce the size of a DC / DC converter, an n-channel MOSFET (Metal Oxide Semiconductor Field with low on-resistance and low power loss). It is desirable to use an effect transistor (MOS type field effect transistor).

  FIG. 2 shows a circuit configuration of the DC / DC converter 101 using the n-channel MOSFET disclosed in Patent Document 1. 2, the same parts as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The DC / DC converter 101 includes an input terminal 11, a MOSFET 111, a smoothing circuit 13, an output terminal 14, a constant voltage circuit 15, a control circuit 16, and a drive circuit 121.

  The MOSFET 111 is an n-channel MOSFET, the drain of the MOSFET 111 is connected to the input terminal 11, the gate of the MOSFET 111 is connected to the drive circuit 121, and the source of the MOSFET 111 is connected to the smoothing circuit 13 and the drive circuit 121.

  The drive circuit 121 includes a diode 151, a capacitor 152, a resistor 153, a transistor 154, a resistor 155, transistors 156 to 158, and a resistor 159. Transistors 154, 156, and 157 are NPN transistors, and transistor 158 is a PNP transistor.

  The anode of the diode 151 is connected to one end of the constant voltage circuit 15, the control circuit 16, and the resistor 153. The cathode of the diode 151 is connected to one end of the capacitor 152, one end of the resistor 155, and the collector of the transistor 157. One end of the capacitor 152, which is different from the one connected to the cathode of the diode 151, is connected to the source of the MOSFET 111 and the collector of the transistor 158.

  One end of the resistor 153 that is different from the one connected to the anode of the diode 151 is connected to the collector of the transistor 154 and the base of the transistor 156. The base of the transistor 154 is connected to the control circuit 16, and the emitter of the transistor 154 is grounded. One end of the resistor 155, which is different from the one connected to the cathode of the diode 151, is connected to the collector of the transistor 156, the base of the transistor 157, and the base of the transistor 158. The emitter of the transistor 156 is grounded. The emitter of the transistor 157 is connected to the emitter of the transistor 158 and one end of the resistor 159. One end of the resistor 159, which is different from the one connected to the emitter of the transistor 157, is connected to the gate of the MOSFET 111.

  Next, the operation of the DC / DC converter 101 will be described.

  First, when the input voltage is not inputted to the input terminal 11 and the transistors 154 and 156 to 158 and the MOSFET 111 are turned off, the input voltage Vin is inputted to the input terminal 11 and the control circuit 16 drives the drive circuit. When an L-level control signal is input to 121, a base current is supplied from the constant voltage circuit 15 to the base of the transistor 156 via the resistor 153 while the transistor 154 of the drive circuit 121 is turned off, and the transistor 156 Is turned on. When the transistor 156 is turned on, the collector potential of the transistor 156, the base of the transistor 157, and the base potential of the transistor 158 are substantially equal to the ground potential, and the transistor 158 is turned on while the transistor 157 remains off. .

  When the transistor 158 is turned on while the transistor 157 remains off, the voltage applied between the gate and the source of the MOSFET 111 remains substantially 0 V, and the MOSFET 111 remains off. Then, the output voltage of the constant voltage circuit 15 is applied to the capacitor 152 via the diode 151, the capacitor 152 is charged, and the voltage at both ends of the capacitor 152 becomes substantially equal to the output voltage of the constant voltage circuit 15. .

  Next, when an H level control signal is input from the control circuit 16 to the drive circuit 121, the transistor 154 of the drive circuit 121 is turned on, and the potentials of the collector of the transistor 154 and the base of the transistor 156 are substantially equal to the ground potential. Thus, the transistor 156 is turned off. When the transistor 156 is turned off, the base current is supplied from the constant voltage circuit 15 to the bases of the transistors 157 and 158 via the diode 151 and the resistor 155, the transistor 157 is turned on, and the transistor 158 is turned off.

  When the transistor 157 is turned on and the transistor 158 is turned off, a voltage approximately equal to the voltage across the charged capacitor 152, that is, a voltage approximately equal to the output voltage of the constant voltage circuit 15, is connected to the MOSFET 111 via the resistor 159. Is applied between the gate and the source, and the MOSFET 111 is turned on.

  Next, when an L-level control signal is input from the control circuit 16 to the drive circuit 121, as described above, the transistor 157 is turned off, the transistor 158 is turned on, and the voltage applied between the gate and source of the MOSFET 111. Becomes almost 0 V, and the MOSFET 111 is turned off.

  Thereafter, each time the output level of the control signal output from the control circuit 16 is switched, the above-described operation is repeated, and the MOSFET 111 is switched on or off.

  The rated voltage between the gate and the source of the n-channel MOSFET is typically ± 20 V or ± 30 V. In the DC / DC converter 101, when the input voltage Vin is within the rated voltage between the gate and the source of the MOSFET 111, The drive circuit 121 can be operated by directly inputting the input voltage Vin to the drive circuit 121 without going through the constant voltage circuit 15.

In this case, when the MOSFET 111 is turned off, the voltage across the charged capacitor 152 is approximately equal to the input voltage Vin. When the transistor 157 is turned on and the transistor 158 is turned off, a voltage substantially equal to the voltage across the capacitor 152, that is, a voltage substantially equal to the input voltage Vin is applied between the gate and source of the MOSFET 111. Is turned on.
Japanese Patent Application Laid-Open No. 02-244771

  However, in the invention described in Patent Document 1, when the input voltage Vin is higher than the rated voltage between the gate and the source of the MOSFET 111, the input voltage Vin is set within the rated voltage between the gate and the source of the MOSFET 111 by the constant voltage circuit 15. There is a problem that power must be converted into voltage and supplied to the drive circuit 121, and power loss occurs during voltage conversion by the constant voltage circuit 15.

  The present invention has been made in view of such a situation. When the input voltage is higher than the rated voltage of the switching element, the switching element can be switched with less loss.

  The drive circuit of the present invention is a drive circuit for driving a switching element that switches and outputs an input DC voltage, and when the switching element is turned off, a first capacitor charged by the input DC voltage and And a voltage dividing circuit for dividing the voltage of the charged first capacitor and applying the divided voltage to the switching element when the switching element is turned on.

  The switching element is composed of a semiconductor element such as a bipolar transistor, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and an IGBT (Insulated Gate Bipolar Transistor). For example, when the switching element is a MOSFET, the voltage divided by the voltage dividing circuit is applied between the gate and the source of the MOSFET.

  According to the driving circuit of the present invention, when the switching element is turned off, the first capacitor is charged by the input DC voltage, and when the switching element is turned on, the voltage of the charged capacitor is divided and divided. The applied voltage is applied to the switching element.

  Therefore, even if the input voltage of a power device such as a switching power supply in which the drive circuit is provided is higher than the rated voltage of the switching element, the input voltage is not converted by a constant voltage circuit or a voltage conversion circuit, and the drive circuit is not changed. The switching element can be switched at a voltage within the rated voltage of the switching element, and power loss due to voltage conversion can be reduced. In addition, the constant voltage circuit or voltage conversion circuit of the power equipment provided with the drive circuit can be deleted, or the capacity of the constant voltage circuit or voltage conversion circuit can be reduced, resulting in low loss, downsizing, and low power equipment. Cost reduction can be realized.

  In the driving circuit according to the present invention, the voltage dividing circuit includes a first parallel circuit in which the second capacitor and the first resistor are connected in parallel, and a third capacitor and the second resistor connected in parallel. When the switching element is turned on including the second parallel circuit, a voltage applied to both ends of the first parallel circuit, which is a divided voltage, can be applied to the switching element.

  Therefore, the drive circuit can be configured easily and inexpensively without using special parts.

  In the drive circuit of the present invention, the switching element can be configured by an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and the second capacitor can be configured by a parasitic capacitance of the n-channel MOSFET. .

  Therefore, the number of components of the drive circuit can be reduced, and the drive circuit can be reduced in size and cost.

  The switching power supply of the present invention includes a switching element that switches and outputs an input DC voltage, a capacitor that is charged by the input DC voltage when the switching element is turned off, and a charge that is charged when the switching element is turned on. A voltage dividing circuit for dividing the voltage of the capacitor and applying the divided voltage to the switching element; and a smoothing circuit for smoothing the DC voltage switched by the switching element.

  The switching element is composed of a semiconductor element such as a bipolar transistor, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and an IGBT (Insulated Gate Bipolar Transistor). For example, the voltage divided by the voltage dividing circuit is applied between the gate and the source of the MOSFET. The smoothing circuit is composed of, for example, a capacitor input type smoothing circuit constituted by a capacitor or the like, or a choke input type smoothing circuit constituted by a coil, a capacitor or the like.

  The voltage dividing means is constituted by, for example, two parallel circuits in which a capacitor and a resistor are connected in parallel. For example, when the switching element is a MOSFET, a voltage applied to one parallel circuit is applied between the gate and source of the MOSFET.

  According to the switching power supply of the present invention, the input DC voltage is switched and output by the switching element, and when the switching element is turned off, the capacitor is charged by the input DC voltage and the switching element is turned on. The voltage of the charged capacitor is divided, the divided voltage is applied to the switching element, and the DC voltage switched by the switching element is smoothed.

  Therefore, even if the input voltage of the switching power supply is higher than the rated voltage of the switching element, the input voltage is not converted by a constant voltage circuit or a voltage conversion circuit, and the switching element is operated at a voltage within the rated voltage of the switching element. Switching can be performed, and power loss due to voltage conversion can be reduced. In addition, the constant voltage circuit and voltage conversion circuit of the switching power supply can be eliminated, and the capacity of the constant voltage circuit and voltage conversion circuit can be reduced, realizing low loss, miniaturization, and cost reduction of the switching power supply. be able to.

  As described above, according to the drive circuit of the present invention, the switching element can be driven. Moreover, according to the drive circuit of the present invention, power loss can be further reduced.

  Further, according to the switching power supply of the present invention, the input DC voltage can be converted into a predetermined DC voltage. Moreover, according to the switching power supply of the present invention, power loss can be further reduced.

  FIG. 3 is a diagram showing a circuit configuration example of the DC / DC converter 201 to which the present invention is applied.

  The DC / DC converter 201 includes an input terminal 211, a MOSFET 212, a smoothing circuit 213, an output terminal 214, a constant voltage circuit 215, a control circuit 216, and a drive circuit 217.

  MOSFET 212 is an n-channel MOSFET. The drain of the MOSFET 212 is connected to the input terminal 211, and the source of the MOSFET 212 is connected to the smoothing circuit 213. Further, the gate and the source of the MOSFET 212 are connected to the drive circuit 217.

  The MOSFET 212 is turned on when a voltage higher than a threshold voltage (hereinafter referred to as an H level voltage) is applied between the gate and the source by the drive circuit 217, and the voltage applied between the gate and the source is less than the threshold voltage. Turned off when the voltage (hereinafter referred to as L level voltage) is reached. A DC voltage Vin input from the input terminal 211 (hereinafter simply referred to as input voltage Vin) is switched by the MOSFET 212 and intermittently output to the smoothing circuit 213.

  The smoothing circuit 213 is a choke input type smoothing circuit, and includes a diode 231, a coil 232, and a capacitor 233. One end of the coil 232 is connected to the source of the MOSFET 212 and the cathode of the diode 231, and the other end of the coil 232 is connected to one end of the capacitor 233 and the output terminal 214. The anode of the diode 231 and the other end of the capacitor 233 are grounded. The intermittent voltage output from the MOSFET 212 is smoothed by the smoothing circuit 213, and the smoothed DC voltage Vout (hereinafter referred to as the output voltage Vout) is output from the output terminal 214 to the outside.

  The constant voltage circuit 215 converts the input voltage Vin input from the input terminal 211 into a predetermined voltage within the rated voltage of the control circuit 216 and supplies the converted voltage to the control circuit 216. The control circuit 216 controls the drive circuit 217 by outputting to the drive circuit 217 control signals of two kinds of voltage levels, a high level (hereinafter referred to as H level) and a low level (hereinafter referred to as L level). .

  The drive circuit 217 applies an H level voltage between the gate and source of the MOSFET 212 when an H level control signal is input from the control circuit 216, as will be described later with reference to FIGS. The MOSFET 212 is turned on. Further, when an L level control signal is input from the control circuit 216, the drive circuit 217 applies an L level voltage between the gate and source of the MOSFET 212 to turn off the MOSFET 212.

  Therefore, the DC / DC converter 201 can control the duty ratio of the control signal output from the control circuit 216, thereby controlling the duty ratio of the MOSFET 212 and outputting the desired output voltage Vout.

  The drive circuit 217 includes a pre-drive circuit 221 and a voltage dividing circuit 222. As will be described later with reference to FIGS. 4 and 5, the pre-drive circuit 221 applies a voltage across the capacitor 252 to the voltage dividing circuit 222 when an H level control signal is input from the control circuit 216. The voltage dividing circuit 222 divides the voltage applied by the pre-drive circuit 221 and applies it between the gate and the source of the MOSFET 212 to turn on the MOSFET 212. Further, when an L level control signal is input from the control circuit 216, the voltage applied from the pre-drive circuit 221 to the voltage dividing circuit 222 is substantially 0 V, and between the gate and the source applied from the voltage dividing circuit 222 to the MOSFET 212. The voltage of V is also almost 0 V, and the MOSFET 212 is turned off.

  The pre-drive circuit 221 includes a diode 251, a capacitor 252, a resistor 253, a transistor 254, a resistor 255, transistors 256 to 258, and a resistor 259. Transistors 254, 256, and 257 are NPN transistors, and transistor 258 is a PNP transistor.

  The anode of the diode 251 is connected to the input terminal 211 and one end of the resistor 253. The cathode of the diode 251 is connected to one end of the capacitor 252, one end of the resistor 255, and the collector of the transistor 257. One end of the capacitor 252 that is different from the one connected to the cathode of the diode 251 is the cathode of the diode 273 of the voltage dividing circuit 222, one end of the capacitor 291 of the parallel circuit 272, and the resistor 292. Connected to one end. The capacitor 252 is charged with the input voltage Vin applied through the diode 251 when the MOSFET 212 is turned off. As described above, when the MOSFET 212 is turned on, the voltage across the capacitor 252 is applied to the voltage dividing circuit 222.

  The other end of the resistor 253 which is different from the one connected to the anode of the diode 251 is connected to the collector of the transistor 254 and the base of the transistor 256. The base of the transistor 254 is connected to the control circuit 216, and the emitter of the transistor 254 is grounded. One end of the resistor 255, which is different from the one connected to the cathode of the diode 251, is connected to the collector of the transistor 256, the base of the transistor 257, and the base of the transistor 258.

  The emitter of the transistor 257 is connected to the emitter of the transistor 258 and one end of the resistor 259. The collector of the transistor 258 is one end of the capacitor 281 and one end of the resistor 282 of the parallel circuit 271 of the voltage dividing circuit 222, and one end of the capacitor 291 of the parallel circuit 272 of the voltage dividing circuit 222, and one end to which the capacitor 252 is connected. One end of the resistor 292, one end different from the one end to which the capacitor 252 is connected, and the source of the MOSFET 212.

  As will be described later with reference to FIGS. 4 and 5, the transistor 254 and the transistors 256 to 258 are turned on or off by a control signal input from the control circuit 216 to the transistor 254, and are divided from the pre-drive circuit 221. The voltage applied to 222 is controlled.

  One end of the resistor 259, which is different from the one connected to the emitter of the transistor 257, is one end of the capacitor 281 of the parallel circuit 271 of the voltage dividing circuit 222 and is connected to the collector of the transistor 258. The other end different from the one end of the transistor 258 and the other end of the resistor 282 different from the one end to which the collector of the transistor 258 is connected are connected to the gate of the MOSFET 212.

  The voltage dividing circuit 222 includes a parallel circuit 271 in which a capacitor 281 and a resistor 282 are connected in parallel, a parallel circuit 272 in which a capacitor 291 and a resistor 292 are connected in parallel, and a diode 273. One end of the capacitor 281 is connected to one end of the resistor 282 and the gate of the MOSFET 212. The other end of the capacitor 281 is connected to the other end of the resistor 282, one end of the capacitor 291, and one end of the resistor 292. The other end of the capacitor 291 is connected to the other end of the resistor 292 and the cathode of the diode 273. The anode of the diode 273 is grounded.

  When the transistor 254 of the pre-drive circuit 221 is turned on, the voltage across the capacitor 252 is applied to the parallel circuits 271 and 272 of the voltage dividing circuit 222 via the resistor 259, and the applied voltage is applied to the parallel circuit 271. Voltage is divided by the ratio of the combined impedance of the capacitor 281 and the resistor 282 and the combined impedance of the capacitor 291 and the resistor 292 of the parallel circuit 272, and the voltage at both ends of the parallel circuit 271 (both ends of the capacitor 281 and the resistor 282) is applied to the MOSFET 212. Is done.

  Note that, instead of the capacitor 281 of the parallel circuit 271, a parasitic capacitance between the gate and the source of the MOSFET 212 may be used.

  Next, the operation of the DC / DC converter 201 will be described with reference to FIG. 4 and FIG.

  First, when the input voltage is not input to the input terminal 211 and the transistors 254 and 256 to 258 and the MOSFET 212 are turned off, the input voltage Vin is input to the input terminal 211 and the drive circuit is supplied from the control circuit 216. When an L-level control signal is input to 217, a base current is supplied from the input terminal 211 to the base of the transistor 256 via the resistor 253 while the transistor 254 of the pre-drive circuit 221 is turned off. Is turned on. When the transistor 256 is turned on, the potential of the collector of the transistor 256 and the potential of the bases of the transistors 257 and 258 are substantially equal to the ground potential, and the transistor 258 is turned on while the transistor 257 is turned off.

  When the transistor 258 is turned on while the transistor 257 is turned off, the capacitor 281 is not charged, and the voltage across the capacitor 281 remains substantially 0V. Therefore, the voltage applied between the gate and the source of the MOSFET 212 remains substantially 0 V, and the MOSFET 21 2 remains off. Then, a voltage substantially equal to the input voltage Vin is applied to the capacitor 252 via the diode 251, the capacitor 252 is charged, and the voltage across the capacitor 252 increases. At this time, the voltage across the capacitor 252 is equal to or lower than the input voltage Vin.

  Next, when an H level control signal is input from the control circuit 216 to the drive circuit 217, the transistor 254 of the pre-drive circuit 221 is turned on, and the potential of the collector of the transistor 254 and the base of the transistor 256 are substantially equal to the ground potential. And transistor 256 is turned off. When the transistor 256 is turned off, the base current is supplied from the input terminal 211 to the bases of the transistors 257 and 258 via the diode 251 and the resistor 255, the transistor 257 is turned on, and the transistor 258 is turned off.

  When the transistor 257 is turned on and the transistor 258 is turned off, a voltage substantially equal to the voltage across the charged capacitor 252 is applied to the parallel circuits 271 and 272 of the voltage dividing circuit 222 via the resistor 259. The voltage applied to the voltage dividing circuit 222 is divided according to the ratio of the impedance of the parallel circuit 271 (the combined impedance of the capacitor 281 and the resistor 282) and the impedance of the parallel circuit 272 (the combined impedance of the capacitor 291 and the resistor 292). The voltage across the compressed parallel circuit 271 is applied between the gate and source of the MOSFET 212, and the MOSFET 212 is turned on.

  The voltage applied to the voltage dividing circuit 222 is Vdivin, the impedance of the parallel circuit 271 is Z1, the impedance of the parallel circuit 272 is Z2, and the voltage across the parallel circuit 271, that is, the voltage applied between the gate and source of the MOSFET 212. The relationship of the voltage Vgs is expressed by the following equation (1).

  Vgs = Vdivin x Z1 ÷ (Z1 + Z2) (However, Vdivin ≤ Vin) (1)

  As expressed in Equation (1), the voltage Vgs applied between the gate and source of the MOSFET 212 is determined by the ratio of the impedance Z1 of the parallel circuit 271 and the impedance Z2 of the parallel circuit 272. Therefore, even when the input voltage Vin is larger than the rated voltage between the gate and the source of the MOSFET 212 and the voltage Vdivin applied to the voltage dividing circuit 222 exceeds the rated voltage, the impedance Z1 of the parallel circuit 271 and the impedance Z2 of the parallel circuit 272 By adjusting the ratio, the voltage Vgs applied between the gate and source of the MOSFET 212 can be within the rated voltage. That is, regardless of the magnitude of the input voltage Vin, the input voltage Vin is supplied to the drive circuit 217 as it is without converting the voltage by the constant voltage circuit 215 or the like, the drive circuit 217 is operated, and the MOSFET 212 is switched. Can do.

  Then, as indicated by an arrow 301 in FIG. 4, a charging current flows from the capacitor 252 to the capacitor 281 and the capacitor 291 of the voltage dividing circuit 222 through the transistor 257, the capacitor 281 and the capacitor 291 are charged, and the capacitor 281 , That is, the gate-source voltage Vgs of the MOSFET 212 transitions to a voltage not less than the gate-source threshold voltage and within the rated voltage. At this time, the diode 251 prevents the current flowing from the capacitor 252 from flowing into the input terminal 211 side.

  Thus, the constant voltage circuit 215 of the DC / DC converter 201 needs to supply power only to the control circuit 216, and supplies power to both the control circuit 16 and the drive circuit 121 of the DC / DC converter 101 of FIG. Compared with the constant voltage circuit 15, the capacity can be reduced, and power loss due to voltage conversion of the constant voltage circuit 215 can be reduced. As a result, the DC / DC converter 201 can improve the voltage conversion efficiency as compared with the DC / DC converter 101, and can be reduced in size and cost.

  Next, when an L-level control signal is input from the control circuit 216 to the drive circuit 217, the transistor 257 is turned off and the transistor 258 is turned on as described above. When the transistor 257 is turned off and the transistor 258 is turned on, the capacitor 281 of the voltage dividing circuit 222 is discharged through the resistor 259 and the transistor 258 as shown by an arrow 302 in FIG. The voltage, that is, the voltage Vgs between the gate and the source of the MOSFET 212 becomes almost 0 V, and the MOSFET 212 is turned off.

  Further, as indicated by an arrow 303 in FIG. 5, the capacitor 291 is discharged via the diode 273 and the smoothing circuit 213. Further, a voltage substantially equal to the input voltage Vin is applied to the capacitor 252 via the diode 251, and as indicated by an arrow 304 in FIG. 5, the diode 251, the capacitor 252, the parallel circuit 272, and the smoothing are input from the input terminal 211. A charging current flows through the circuit 213, and the capacitor 252 is charged again.

  Thereafter, each time the output level of the control signal output from the control circuit 216 is switched, the above-described operation is repeated, and the MOSFET 212 is switched on or off.

  When the input voltage Vin is within the rated voltage of the control circuit 216, the constant voltage circuit 215 is deleted from the DC / DC converter 201 as in the DC / DC converter 401 shown in FIG. It is also possible to input directly to the control circuit 216. As a result, the voltage conversion efficiency of the DC / DC converter can be further improved, and the DC / DC converter can be further reduced in size and cost.

  As described above, when the switching element is turned off, the first capacitor is charged by the input DC voltage, and when the switching element is turned on, the voltage of the charged first capacitor is divided to be divided. When the applied voltage is applied to the switching element, the switching element can be driven. In addition, power loss can be further reduced.

  In addition, when the input DC voltage is switched and output by the switching element and the switching element is turned off, the capacitor is charged by the input DC voltage, and when the switching element is turned on, the voltage of the charged capacitor is divided. When the divided voltage is applied to the switching element and the DC voltage switched by the switching element is smoothed, the input DC voltage may be converted into a predetermined DC voltage. it can. In addition, power loss can be further reduced.

It is a figure which shows the basic composition of the circuit of the conventional DC / DC converter. It is a figure which shows the structure of the circuit of the conventional DC / DC converter. It is a figure which shows the structural example of the circuit of the DC / DC converter to which this invention is applied. It is a figure explaining operation | movement of the DC / DC converter to which this invention is applied. It is a figure explaining operation | movement of the DC / DC converter to which this invention is applied. It is a figure which shows the structural example of the circuit of the DC / DC converter to which this invention is applied.

Explanation of symbols

1 DC / DC converter 12 Switching element 15 Constant voltage circuit 16 Control circuit 21 Drive circuit 101 DC / DC converter 111 MOSFET
121 Drive circuit 201 DC / DC converter 212 MOSFET
213 Smoothing circuit 215 Constant voltage circuit 216 Control circuit 217 Drive circuit 221 Pre-drive circuit 222 Voltage divider circuit 251 Diode 252 Capacitor 254, 256, 257, 258 Transistor 271, 272 Parallel circuit 281 Capacitor 282 Resistor 291 Capacitor 292 Resistor 401 DC / DC converter

Claims (4)

In a drive circuit that drives a switching element that switches and outputs an input DC voltage,
When turning off the switching element, a first capacitor charged by the input DC voltage;
And a voltage dividing circuit that divides a voltage of the charged first capacitor and applies the divided voltage to the switching element when the switching element is turned on. The voltage dividing circuit includes a first parallel circuit in which a second capacitor and a first resistor are connected in parallel, and a second parallel circuit in which a third capacitor and a second resistor are connected in parallel. ,
2. The drive circuit according to claim 1, wherein when the switching element is turned on, a voltage applied to both ends of the first parallel circuit, which is a divided voltage, is applied to the switching element. The switching element is composed of an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor),
The drive circuit according to claim 2, wherein the second capacitor is configured by a parasitic capacitance of the n-channel MOSFET. A switching element that switches and outputs the input DC voltage;
When turning off the switching element, a capacitor charged by the input DC voltage;
A voltage dividing circuit that divides the charged voltage of the capacitor and applies the divided voltage to the switching element when turning on the switching element;
A switching power supply comprising: a smoothing circuit that smoothes the DC voltage switched by the switching element.

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