JP4807142B2 - DC / DC converter - Google Patents

Description

  The present invention relates to a DC / DC converter, and more particularly to a DC / DC converter that performs current mode control.

As a control method of the DC / DC converter (switching power supply), there are voltage mode control and current mode control. In current mode control, line regulation is better than voltage mode control. Conventionally, a DC / DC converter that performs current mode control has been proposed (see, for example, Patent Document 1). This DC / DC converter is a forward type DC / DC converter having a transformer in which primary and secondary are insulated, and a primary switch is provided in a primary circuit, and an auxiliary winding is provided in the transformer. Is connected to a voltage detection circuit, and this voltage detection circuit is provided with an error amplifier. Then, peak current mode control is performed to detect the peak current of the primary circuit and determine the on period of switching, and by using the output of the error amplifier, positive feedback is applied to the reference voltage of the output voltage. Perform load current correction.
Japanese Patent Laid-Open No. 2003-244953

  When performing current mode control with a DC / DC converter, it is necessary to measure the reactor current. However, when the delay time of the current detection circuit is large compared to the control cycle, the control may become unstable because the correct current value at the time of control is not known. If control is performed without shortening the control cycle, it is possible to avoid instability of the control, but the longer the control cycle, the larger the peak current value, and the more the choke coil and smoothing capacitor used in the converter become. It becomes difficult to reduce the size of the converter by increasing the size.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to suppress unstable control even when the control cycle is shortened, and to reduce the size of the converter. It is to provide a DC / DC converter capable of

In order to achieve the above object, a first aspect of the present invention is a DC / DC converter that performs switching control of a switching element by current mode control. Then, a current detecting means for detecting the amount of current flowing through the coil, the input voltage, output voltage, current flowing through the coil, and calculates the current variation value from the duty and the current superposition characteristic of the coil of the switching element, the current A calculating means for outputting a current value fluctuation amount obtained by subtracting a detected current value from a fluctuation value, and adding the current value fluctuation amount output by the calculating means to the detected current value by the current detecting means, and adding the added value to the added value. A correction unit that outputs a correction value based on the detection current value as a current value for correcting the delay time, and a control unit that controls on and off of the switching element based on the current value output by the correction unit. ing. Here, the “current superposition characteristic” means an inductance value determined by a current value. Further, the “current fluctuation value” means a current value that changes during a delay time from when the current is detected by the current detection unit to when the current value signal is input to the control unit. Hereinafter, the same meaning is used in this specification.

  In current mode control, it is necessary to detect the amount of current flowing through the coil, but if current detection is delayed compared to the control cycle, control tends to become unstable. For example, when the carrier frequency is 100 kHz, the control may become unstable if the delay in current detection is several μsec or more. However, it is difficult to perform current detection without such a delay. In the present invention, current detection is not performed in a state where the delay is small, but the correct current value is detected when the control means performs switching control by correcting the detected current value detected by the current detection means by the correction means by the delay time. Can be used. Specifically, the calculation means calculates the current fluctuation value from the input voltage, the output voltage, the current value flowing through the coil, the duty of the switching element, and the current superposition characteristics. The correcting means corrects the detected current value based on the current fluctuation value. Then, the control unit performs on / off control of the switching element based on the corrected current value. Therefore, even if the control cycle is shortened, it is possible to prevent the control from becoming unstable, and it is possible to reduce the size of the converter.

Further, in the configuration in which the correction means outputs the correction value using the current fluctuation value as it is to the control means, the control means cannot continue control when the arithmetic means fails and the current fluctuation value cannot be obtained. However, in the present invention, the correction means outputs a correction value based on a value obtained by adding the current value fluctuation to the detected current value to the control means, so even if the calculation means fails and the current fluctuation value cannot be obtained, A correction value based on the detected current value is output to the control means, and control can be continued even when the arithmetic means is out of order.
According to a second aspect of the present invention, in the first aspect of the present invention, the calculation means stores a map or a calculation formula for calculating the current fluctuation value.

  According to the present invention, even if the control cycle is shortened, it is possible to prevent the control from becoming unstable, and it is possible to reduce the size of the converter.

Hereinafter, an embodiment in which the present invention is embodied in a step-down current mode control DC / DC converter will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the DC / DC converter 10 has two power switching elements Q1 and Q2 connected in series to a DC power source 11. N-channel MOSFETs are used for the switching elements Q1 and Q2, respectively. A coil (reactor) L1 and a capacitor C1 are connected in series between the connection point between the source of the switching element Q1 and the drain of the switching element Q2 and the negative terminal of the DC power supply 11. On the downstream side of the coil L1 (on the connection point side between the source of the switching element Q1 and the drain of the switching element Q2), a current detection resistor R1 constituting current detection means for detecting the amount of current flowing through the coil L1 is provided. One terminal of the capacitor C1 is provided with a positive output terminal 12a, and the other terminal is provided with a negative output terminal 12b. A load 15 is connected between the output terminals 12a and 12b.

  A control device 20 that performs switching control of the switching elements Q1 and Q2 by current mode control includes a current detection circuit 21 that constitutes a current detection unit, a calculation unit 22 that calculates a current fluctuation value, and a current value detected by the current detection unit. A correction means 23 for correcting the delay time and a control IC 24 as a control means for controlling on / off of the switching elements Q1, Q2 are provided.

The current detection circuit 21 detects a voltage across the current detection resistor R1 and outputs a current value signal SI.
The calculation means 22 calculates the current fluctuation from the input voltage Vin, the output voltage Vout, the current value signal SI corresponding to the current value flowing through the coil L1, the switching duty of the switching elements Q1 and Q2, and the current superposition characteristics of the coil L1. Calculate the value. The input voltage Vin is obtained by inputting a detection signal of a voltage detection sensor (not shown), and the output voltage Vout is obtained by inputting a detection signal of a voltage detection sensor (not shown) that detects the terminal voltage of the capacitor C1. The switching duty is confirmed by obtaining a duty signal from the control IC 24. The computing means 22 is constituted by a microcomputer, for example. The calculating means 22 stores a map or a calculation formula in a memory, and calculates the current fluctuation value using the map or the calculation formula.

  The correction unit 23 includes a D / A converter 25 that receives the output of the calculation unit 22 and converts it into an analog signal, and an error amplifier 26. The output terminal of the current detection circuit 21 is connected to the inverting input terminal of the error amplifier 26 via a resistor R2, and the output terminal of the D / A converter 25 is connected via a resistor R3. The reference voltage Vref is input to the non-inverting input terminal of the error amplifier 26. The output of the error amplifier 26 is input to the control IC 24. That is, the correction unit 23 outputs a correction value based on a value obtained by adding the current value variation to the detected current value to the control IC 24.

  The control IC 24 receives a voltage corresponding to the value of the current flowing through the coil L1, and outputs a PWM comparator (pulse width modulator) that outputs a control signal (duty signal) for on / off control of the switching elements Q1 and Q2. I have. The control signal output from the control IC 24 is input to the gates of the switching elements Q1 and Q2.

  Next, the operation of the DC / DC converter 10 configured as described above will be described. Based on a control signal output from the control IC 24, the switching elements Q1 and Q2 are on / off controlled so as to be alternately turned on at a predetermined on-duty.

  When the switching element Q1 is ON and the switching element Q2 is OFF, current flows from the DC power source 11 to the switching element Q1, the current detection resistor R1, the coil L1, and electromagnetic energy is stored in the coil L1 and the capacitor C1 is also charged. Done and electrostatic energy is stored. Next, when the switching element Q1 is turned off and the switching element Q2 is turned on, the electromagnetic energy of the coil L1 is released through the switching element Q2, and a current flows from the switching element Q2 toward the coil L1. During this period, the load 15 is continuously fed by the energy stored in the coil L1 and the capacitor C1.

  The control IC 24 sets the duty of the switching elements Q1, Q2 so that a predetermined current flows through the coil L1, and outputs a control signal. The amount of current flowing through the coil L1 is detected by the current detection resistor R1 and the current detection circuit 21. There is no problem if the detection signal of the current detection circuit 21 is input to the control IC 24 without delay. However, there is a delay before the detection signal of the current detection circuit 21 is input to the control IC 24. The amount of current flowing through the coil L1 changes with time, and the inductance (L value) changes depending on the value of the current flowing through the coil L1. As shown in FIG. 2, the inductance decreases as the direct current increases, and if the control is performed without taking the reduction amount into consideration, the control becomes unstable. Although FIG. 2 shows that the inductance changes linearly, it may change in a curved line depending on the conditions.

  In this embodiment, in the calculation means 22, the input voltage Vin, the output voltage Vout, the current value signal SI corresponding to the current value flowing through the coil L1, the switching duty of the switching elements Q1 and Q2, and the current superimposition characteristics. A current fluctuation value is calculated. That is, the current fluctuation value is calculated in consideration of the delay time until the current value detected by the current detection circuit 21 is input to the control IC 24. The calculation means 22 does not output the current fluctuation value as it is to the D / A converter 25 of the correction means 23, but the current fluctuation value obtained by subtracting the current value of the current value signal SI of the current detection circuit 21 from the current fluctuation value. Is output.

  The output signal of the arithmetic means 22 is converted into an analog signal by the D / A converter 25, added to the current value signal SI, and then input to the non-inverting input terminal of the error amplifier 26. Therefore, a signal corresponding to the current value whose delay time is corrected is input to the control IC 24. Then, the on-duty (switching duty) of the switching elements Q1, Q2 is set based on the correct current value that matches the control period (switching period), and a control signal is output to the switching elements Q1, Q2.

According to this embodiment, the following effects can be obtained.
(1) The DC / DC converter 10 performs switching control of the switching elements Q1, Q2 by current mode control. The DC / DC converter 10 includes a current detection resistor R1 for detecting the amount of current flowing through the coil L1 and a current detection circuit 21, an input voltage Vin, an output voltage Vout, a current value flowing through the coil L1, and the duty of the switching elements Q1 and Q2. And a calculating means 22 for calculating the current fluctuation value from the current superposition characteristics of the coil L1, and a correcting means 23 for correcting the detected current value by the delay time. Then, the control IC 24 that controls on / off of the switching elements Q1, Q2 sets the on / off time of the switching elements Q1, Q2, that is, the switching duty, based on the current value corrected by the correcting means 23. Therefore, by correcting the detected current value detected by the current detection means by the correction means 23 by the delay time, the correct current value can be used when the control IC 24 performs the switching control. Therefore, even if the control cycle is shortened, it is possible to suppress the control from becoming unstable, and a small-sized one can be used as the coil L1 and the capacitor C1 constituting the DC / DC converter 10, and the DC / DC converter 10 Miniaturization can be achieved.

  (2) The correction means 23 outputs to the control IC 24 a correction value based on a value obtained by adding the current value variation to the current value detected by the current detection resistor R1 and the current detection circuit 21. In the configuration in which the correction unit 23 outputs a correction value using the current fluctuation value as it is to the control IC 24, the control IC 24 cannot continue control when the calculation unit 22 fails and a current fluctuation value cannot be obtained. However, since the correction unit 23 outputs a correction value based on a value obtained by adding the current value variation to the detected current value to the control IC 24, even if the calculation unit 22 fails and a current variation value cannot be obtained, the detection current Since a correction value based on the value is output to the control IC 24, the control can be continued even when the computing means 22 is out of order.

The embodiment is not limited to the above, and may be embodied as follows, for example.
Not only the step-down DC / DC converter 10 but also a step-up DC / DC converter 30 as shown in FIG.

  Not limited to the configuration in which the two switching elements Q1 and Q2 are alternately turned on and off, for example, as shown in FIG. 4, a diode D may be provided instead of the switching element Q2. The diode D has an anode connected to the negative terminal side of the DC power supply 11 and a cathode connected to the switching element Q1. In this configuration, the configuration is simplified and the control is also simplified.

  The transistors constituting the switching elements Q1 and Q2 are not limited to MOSFETs, and other switching elements such as IGBTs (Insulated Gate Bipolar Transistors) may be used. When using an IGBT, an emitter is connected to a portion to which the source of the MOSFET is connected, and a collector is connected to a portion to which the drain is connected.

  The DC / DC converter 10 is not limited to a non-insulated converter, and may be applied to an insulated DC / DC converter in which an input side and an output side are insulated. Examples of the insulation type converter include a push-pull type converter and a one-stone forward type converter.

The power source of the DC / DC converter 10 is not limited to a battery but may be a direct current obtained by converting alternating current into direct current, that is, an output of an AC / DC inverter.
The following technical idea (invention) can be understood from the embodiment.

  -In invention of Claim 1 or Claim 2, the said DC / DC converter is a non-insulated type converter.

The circuit diagram of the DC / DC converter of one embodiment. The graph which shows the relationship between the magnitude | size of direct current, and an inductance. The circuit diagram of another embodiment. The circuit diagram of another embodiment.

Explanation of symbols

  L1 ... Coil, Q1, Q2 ... Switching element, Vin ... Input voltage, Vout ... Output voltage, 10, 30 ... DC / DC converter, 21 ... Current detection circuit constituting current detection means, 22 ... Calculation means, 23 ... Correction Means 24... Control IC as control means.

Claims (2)

A DC / DC converter that performs switching control of a switching element by current mode control,
Current detection means for detecting the amount of current flowing through the coil;
Calculates the current fluctuation value from the input voltage, output voltage, current value flowing through the coil, duty of the switching element, and current superimposition characteristics of the coil, and outputs the current fluctuation value obtained by subtracting the detected current value from the current fluctuation value and computing means for,
The current value fluctuation output by the computing means is added to the current value detected by the current detecting means, and a correction value based on the added value is output as a current value for correcting the detected current value by the delay time. Correction means;
DC / DC converter provided with the control means which carries out on-off control of the said switching element based on the electric current value output by the said correction means. 2. The DC / DC converter according to claim 1 , wherein a map or a calculation formula for calculating the current fluctuation value is stored in the calculation means .

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