JP4611104B2 - Oscillation circuit and switching power supply using the same - Google Patents

Description

  The present invention relates to a switching power supply device, and more particularly to an oscillation circuit used for a power source of a portable device using a battery and a switching power supply device using the oscillation circuit.

  The conventional switching power supply device is configured as shown in FIG. In FIG. 4, 1 is an input power supply of the power supply apparatus, 2 is a smoothing capacitor of the input power supply 1, 3 is an output terminal of the power supply apparatus, 4 is a smoothing capacity of the output terminal 3, 6 and 7 are resistors, 8 is a triangular wave oscillation circuit, 9 is an error amplifying circuit configured by negatively inputting a reference voltage 10 and positively inputting a voltage between resistors 6 and 7, 16 is a switching element configured by, for example, an NMOS transistor, 17 is a choke coil, and 18 is a Schottky. It is a diode.

  FIG. 5 is a diagram showing an oscillation circuit in which the triangular wave oscillation circuit shown in FIG. 4 is replaced with a detailed circuit diagram. In the triangular wave oscillation circuit of FIG. 5, 1 is an input power supply, 35 is a capacitor, 36 is a switch, 37 and 38 are differential circuits composed of bipolar elements (for example, NPN transistors), I1, I2, I3 and I4 are Constant current sources VL and VH are reference voltages.

  6 (a) and 6 (b) are diagrams for explaining the operation of the triangular wave oscillation circuit in FIG. 5 and the PWM control circuit in FIG. 4. The switch 36 in FIG. 6 (a) is shown in FIG. This is the switch 36 described.

  The operation of the conventional switching power supply apparatus will be described below with reference to FIGS.

  In the prior art, for example, as described in Patent Document 1, in the switching power supply device shown in FIG. 5, the voltage generated in the capacitor 35 is set to the bias voltage as the voltage of the input power supply 1 before reaching the reference voltage VH. The switch 36 is turned off by charging with the constant current source I1, and when the reference voltage VH is reached, the differential circuit 37 operates to turn on the switch 36 and discharge with the constant current sources I1-I2 (<0). When the voltage reaches the reference voltage VL, the differential circuit 38 operates to turn off the switch 36 again and charge it with the constant current source I1.

As shown in FIG. 4, the output of the triangular wave oscillation circuit 8 is negatively input to the comparator 11, the voltage obtained by dividing the output voltage of the output terminal 3 of the switching power supply device by resistors 6 and 7 is positively input, and the reference voltage 10 is The output of the error amplifier circuit 9 that has been negatively input is positively input to the comparator 11, and the switching element 16 is driven by the output of the comparator 11 to obtain a desired voltage.
JP 59-147525 A Japanese Patent Publication No. 7-34650

  However, the conventional power supply system has a problem that when the input voltage is low, the triangular wave oscillation circuit constituted by bipolar elements does not operate and the switching power supply cannot be operated.

  The present invention is directed to solving the above-described problems of the prior art, and a ring oscillator circuit composed of a MOS transistor circuit that operates even at a low input voltage is used as a start-up oscillation circuit, and even when the input voltage is low. An object of the present invention is to provide an oscillation circuit that constitutes an operating switching power supply and a switching power supply using the oscillation circuit.

  In order to achieve the above object, an oscillation circuit according to the present invention is an oscillation circuit used in a switching power supply device, and is composed of an inverter circuit formed by cascading 2N (N: integer) pieces, and an input of the inverter circuit A first resistor having one end connected to the end, a PMOS transistor and an NMOS transistor having a gate connected to the output end of the inverter circuit, one end connected to the other end of the first resistor, and the other end to the output end of the inverter circuit , A second resistor connected between the drains of the PMOS transistor and the NMOS transistor, a third resistor having one end connected between the NMOS transistor and the second resistor, and a third resistor. One end connected to the other end, and the other end of the first resistor and a fourth resistor connected to the other end of the capacitor, and a plurality of inputs are connected to the output end of the inverter circuit. Connect the inverter group consisting of over data, characterized by the output of the inverter group and final output.

Further, the switching power supply device is a switching power supply device using the oscillation circuit according to claim 1, wherein the first oscillation circuit according to claim 1 constituted by a MOS transistor and a triangular wave oscillation constituted by a bipolar transistor. A second switch comprising a circuit, a switch for selectively switching connections between the first output terminal of the first oscillator circuit and the second output terminal of the second oscillator circuit, and an output of the switch And an output voltage generator for controlling the switching element to generate the output voltage of the switching power supply device, and switching the changeover switch based on the output voltage . When the output voltage is lower than the predetermined voltage , the first oscillation When the output voltage is higher than a predetermined voltage , the circuit is connected to the second oscillation circuit.

  According to the above configuration, in the switching power supply device that obtains the output voltage by switching the input power supply, the first oscillation circuit (ring oscillator circuit) configured by the MOS transistor circuit using the input voltage as the bias voltage, and the output voltage A first oscillation circuit having a second oscillation circuit (PWM control circuit) that performs pulse width control as a bias voltage, and that operates from a low input voltage by selecting a circuit drive signal of the switching power supply from one of the output voltages. By using this oscillation circuit, the output voltage is raised, and when the output voltage reaches a predetermined voltage, the oscillation is switched to the oscillation by the second oscillation circuit to obtain a switching power supply device that operates even at a low input voltage.

  According to the present invention, it is possible to configure a switching power supply device that operates even in the case of a low input voltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram showing a schematic configuration of a switching power supply apparatus according to an embodiment of the present invention. Here, components having the same functions corresponding to the components described in FIG. 4 showing the conventional example are denoted by the same reference numerals.

  In FIG. 1, 1 is an input power supply, 2 and 4 are smoothing capacitors, 3 is an output terminal, 5 is a ring oscillator circuit, 6 and 7 are resistors, 8 is a triangular wave oscillation circuit, 9 is an error amplification circuit, and 10 and 13 are reference. Reference numerals 11 and 14 denote comparators, 15 denotes an oscillation changeover switch, 16 denotes a switching element formed of, for example, an NMOS transistor, 17 denotes a choke coil, and 18 denotes a Schottky diode.

  FIG. 2 is a circuit diagram showing an oscillation circuit and a switching power supply device using the same in the present embodiment, in which the ring oscillator circuit shown in FIG. 1 is replaced with a detailed circuit diagram. In the ring oscillator circuit 5 shown in FIG. 2, 19, 29, 30, 31 are resistors, 20 is a capacitor, 21, 22, 23, 24, 25, 26, 32, 33, 34 are inverters, 27 is a PMOS transistor, 28 Is constituted by an NMOS transistor.

  In FIG. 2, A is a voltage between the resistors 30 and 31, B is a voltage output from an inverter group (inverters 32, 33, and 34) to which an output from the inverter 26 is input, and C is an oscillation changeover switch 15. This is the voltage of the drive signal for the selected switching element 16.

  FIG. 3 is a diagram for explaining the operation of the oscillation circuit of the present embodiment in FIG. 2 and the switching power supply apparatus using the oscillation circuit. A and B in FIG. 3 are A and B described in the explanation of FIG. Is the voltage.

  The operation of the oscillation circuit of the present embodiment configured as described above and the switching power supply apparatus using the oscillation circuit will be described below.

  First, immediately after the switching power supply device is activated, the ring oscillator circuit 5 constituted by a MOS transistor circuit operates. In the ring oscillator circuit 5, when the input level of an inverter circuit composed of 2N (N: integer) cascaded inverters is “H”, the output level of this inverter circuit is also “H”.

  Next, by inputting the output of the inverter circuit to the gate of the PMOS transistor 27 and the gate of the NMOS transistor 28, the voltage level between the resistor 29 and the drain of the NMOS transistor 28 becomes “L”. This voltage is input to the inverter circuit connected through resistors 30, 31, and 19. Therefore, although the input level of the inverter circuit goes to “L”, since the resistor 31 and the resistor 19 are connected to the output of the inverter circuit via the capacitor 20, the resistors 29, 30, 31, and 19 are connected. The input level of the inverter circuit goes to “L” with a delay due to the time constant determined by the capacitor 20.

  Thereafter, when the input level of the inverter circuit becomes “L”, the output level also becomes “L”. By inputting the output of the inverter circuit to the gate of the PMOS transistor 27 and the gate of the NMOS transistor 28, the voltage level between the resistor 29 and the drain of the NMOS transistor 28 becomes “H”. As described above, this voltage is input to the inverter circuit connected through the resistors 30, 31, and 19. Therefore, although the input level of the inverter circuit goes to “H”, since the resistor 31 and the resistor 19 are connected to the output of the inverter circuit via the capacitor 20, the resistors 29, 30, 31, 19 and the capacitor 20 are connected. The input level of the inverter circuit goes to “H” with a delay due to the time constant determined by

  By repeating this operation, the oscillation operation continues. By repeating this operation, the voltage of A operates as shown in FIG. 3, and B operates with a constant pulse width. Since this oscillation operates when the input power supply is higher than the VGS (gate-source voltage) of the MOS transistor, it operates even when the input power supply is at a low voltage.

  As shown in FIG. 3, when the output voltage of the output terminal 3 of the switching power supply device reaches a predetermined voltage, the oscillation changeover switch 15 that switches the output of the oscillation circuit outputs the drive signal of the switching element 16 to the output of the PWM control circuit 12. Since the operation after switching to is a known operation as described in Patent Document 2, for example, description thereof is omitted.

  As described above, with this circuit configuration, it is possible to configure a switching power supply device that operates even at a low input voltage.

  INDUSTRIAL APPLICABILITY The oscillation circuit according to the present invention and the switching power supply device using the oscillation circuit can constitute a switching power supply device that operates even when the input voltage is low, and are useful as a power supply device that is used for a power source of a portable device using a battery. It is.

The circuit diagram which shows the structure of the oscillation circuit in embodiment of this invention, and a power supply device using the same 1 is a circuit diagram illustrating a detailed configuration of an oscillation circuit and a power supply device using the oscillation circuit according to an embodiment of the present invention. Operation explanatory diagram of the oscillation circuit and the power supply device using the same in the embodiment of the present invention Circuit diagram showing schematic configuration of conventional switching power supply device A circuit diagram showing a detailed configuration of a triangular wave oscillation circuit used in a conventional switching power supply device The figure explaining operation | movement of the conventional switching power supply device

Explanation of symbols

1 Input power supply 2, 4 Smoothing capacitor 3 Output terminal 5 Ring oscillator circuit 6, 7 Resistor 8 Triangular wave oscillation circuit 9 Error amplification circuit 10, 13 Reference voltage 11, 14 Comparator 12 PWM control circuit 15 Oscillation changeover switch 16 Switching element 17 Choke Coil 18 Schottky diode 19, 29, 30, 31 Resistance 20, 35 Capacitance 21, 22, 23, 24, 25, 26, 32, 33, 34 Inverter 27 PMOS transistor 28 NMOS transistor 36 Switch 37, 38 Differential circuit

Claims (2)

An oscillation circuit used in a switching power supply device,
An inverter circuit composed of 2N (N: integer) cascaded inverters, a first resistor having one end connected to the input terminal of the inverter circuit, and a PMOS transistor and an NMOS having a gate connected to the output terminal of the inverter circuit A transistor, a capacitor having one end connected to the other end of the first resistor, a capacitor having the other end connected to the output end of the inverter circuit, and a second resistor connected between the drain of the PMOS transistor and the NMOS transistor; A third resistor having one end connected between the NMOS transistor and the second resistor, one end connected to the other end of the third resistor, and the other end of the first resistor and the capacitance A fourth resistor having one end connected to the other end, an inverter group comprising a plurality of inverters connected to the output end of the inverter circuit, Oscillation circuit and outputs of the final output. A switching power supply device using the oscillation circuit according to claim 1,
The first oscillation circuit according to claim 1 constituted by a MOS transistor;
A second oscillation circuit composed of a triangular wave oscillation circuit composed of bipolar transistors ;
A selector switch for selectively switching connection between the first output terminal of the first oscillation circuit and the second output terminal of the second oscillation circuit;
An output voltage generator that controls a switching element based on an output of the changeover switch and generates an output voltage of the switching power supply device ;
Switches the changeover switch on the basis of the output voltage, when the output voltage is lower than a predetermined voltage, before Symbol first oscillating circuit, when the output voltage is higher than the predetermined voltage, before Symbol second oscillation circuit A switching power supply characterized by being connected .

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