JP2012029362A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit which performs an adaptive switching control according to a difference between input voltage and output voltage by simple control method.SOLUTION: While the input voltage is considerably higher than the output voltage, in other words while an operation amount U is less than or equal to a predetermined value a, a power supply circuit enters into a step-down mode in which a second semiconductor switch element Q2 is always controlled off, and a first semiconductor switch Q1 is controlled on or off with a predetermined duty cycle. While the input voltage is considerably lower than the output voltage, in other words while an operation amount U is greater than or equal to a predetermined value b, the power supply circuit enters into a step-up mode in which the first semiconductor switch element Q1 is always controlled on, and the second semiconductor switch Q2 is controlled on or off with a predetermined duty cycle. While a potential difference between the input voltage and the output voltage is small, in other words while the operation amount U is larger than the value a and is smaller than the value b, the power supply circuit enters into a step-up/step-down mode in which the first and second semiconductor switch elements Q1 and Q2 are controlled on or off with an appropriate duty cycle, respectively.

Description

  The present invention relates to a power supply circuit that receives an AC voltage from a commercial power supply or the like and outputs a desired voltage or current to a load.

  Conventionally, various power supply circuits have been devised for converting an alternating current power source into a direct current and supplying a constant current to an LED. For example, the power supply circuit of Patent Document 1 converts the rectified voltage of an AC commercial power supply into a DC voltage using a non-insulated buck-boost converter, and performs switching control based on an output current value (load current value). A predetermined constant current is supplied to the load (LED module).

  The buck-boost converter can realize more efficient operation by using a two-stone buck-boost converter. The step-up / down converter shown in Patent Document 2 includes a high-side switch element and a low-side switch element, and these switch elements are on / off controlled. This step-up / step-down converter selects the step-down mode when the input voltage value is higher than the output current voltage value to be controlled, the step-up mode when it is lower, and the step-up / step-down mode when it is within a predetermined difference.

Special table 2008-537459 gazette JP 2003-111392 A

  However, in the power supply circuit using the step-up / step-down converter that switches the mode by detecting the input voltage value described above, unstable operation is likely to occur at the time of mode switching. In particular, when the input voltage constantly fluctuates like the rectified voltage of the AC power supply, or when the output capacity is small and the output voltage value is small, mode switching frequently occurs and stable operation is difficult. Further, it is necessary to determine the difference between the input voltage value and the output voltage value, and there is a problem that the control becomes complicated.

  Accordingly, an object of the present invention is to realize a power supply circuit capable of performing suitable switching control according to the difference between the input voltage and the output voltage by a simple control method.

  The present invention relates to a rectifier circuit connected to a commercial power source, a step-up / down converter including two semiconductor switch elements connected to a subsequent stage of the rectifier circuit, and connected to the subsequent stage of the step-up / down converter, both ends of which are output terminals Output capacitor, an output value detection unit for detecting an output value that is either an output voltage or an output current, and a switch control signal that switches between a plurality of modes based on the output value and applies to two semiconductor switch elements And a control unit that generates the power supply circuit. The control unit of the power supply circuit calculates an operation value based on a difference value between the target value and the output value, and sets a boost mode, a step-down mode, or a step-up / step-down mode according to the operation value.

  The control unit sets the boost mode when the operation value is equal to or greater than the first threshold value. The control unit sets the step-down mode when the operation value is equal to or less than the second threshold value. The control unit sets the step-up / step-down mode when the operation value is between the second threshold value and the first threshold value.

  This configuration shows a setting method for the boost mode, the step-up / step-down mode, and the step-down mode. Here, using the operation value that is a positive value based on the difference value, switching between the boost mode and the step-up / step-down mode is performed using the first threshold value, and switching between the step-down mode and the step-up / step-down mode is performed using the second threshold value. Thereby, the mode can be easily and smoothly switched only by the comparison result with respect to the threshold value using the numerical data.

  Further, the control unit of the power supply circuit according to the present invention defines the control in each mode by the on-duty for each semiconductor switch element. In the step-up / step-down mode, the control unit is configured such that the on-duty of the first semiconductor switch element is less than 1, the on-duty of the second semiconductor switch element is 0 or more, and the on-duty of the first semiconductor switch element is The on-duty of the second semiconductor switch element is set higher.

  In this configuration, the control content for each switch element in the step-up / step-down mode in the control unit is shown in more detail.

  The controller of the power supply circuit according to the present invention sets the on-duty according to the operation value in the step-up / step-down mode.

  This configuration also shows the specific contents of control for each switch element in the step-up / step-down mode in the control unit. With this configuration, more appropriate on-duty control is performed based on the difference value between the operation value, that is, the output value corresponding to the target value, in the step-up / step-down mode.

  In addition, the control unit of the power supply circuit according to the present invention controls the second semiconductor switch element to be on only during the period in which the first semiconductor switch element is on.

  This configuration also shows the specific contents of control for each switch element in the step-up / step-down mode in the control unit. With this configuration, the second semiconductor switch element is not turned on while the first semiconductor switch element is off. This improves efficiency.

  In the power supply circuit of the present invention, the output value is an output current value. The output current detector is connected in series between the output capacitor and the output terminal.

  In the power supply circuit of the present invention, the output value is an output voltage value. The output voltage detector is connected in parallel to the output capacitor.

  In these configurations, a more specific configuration of the power supply circuit is shown in the case where the output value used as the reference for mode switching of the switching control is an output current value and an output voltage value.

  According to the present invention, it is possible to prevent problems such as a sharp increase in ripple caused by sudden mode switching. Further, stable control can be performed even when the difference between the input voltage and the output voltage is small, or even when the magnitude relationship is frequently reversed. In addition, a configuration for detecting a dedicated input voltage is not required for mode switching, and the power supply circuit can be further downsized and control can be easily configured. Further, when the output value is an output current value, a configuration for detecting the output voltage for mode switching is not required, and the size can be further reduced.

It is a circuit diagram which shows schematic structure of the power supply circuit of this invention. FIG. 3 is a diagram for explaining a specific configuration and control of a control unit 10. It is a circuit operation explanatory view and a waveform diagram in the step-down mode. It is a circuit operation explanatory view in the boost mode, and a waveform diagram. It is circuit operation explanatory drawing at the time of buck-boost mode. It is a wave form diagram at the time of buck-boost mode. It is a figure which shows the relationship between the input voltage of the power supply circuit of this embodiment, an output voltage, and each mode.

  A non-insulated power supply circuit according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a schematic configuration of a power supply circuit according to the present embodiment.

  The power supply circuit of the present invention is a non-insulated switching power supply circuit having a step-up / step-down converter provided with two switch elements. The power supply circuit includes an input terminal Pin including a pair of input terminals connected to the commercial power supply 200.

  A diode bridge DB, which is a full-wave rectifier circuit, is connected to the input terminal Pin of the power supply circuit. An input capacitor Ci is connected in parallel at the subsequent stage of the diode bridge DB. The input capacitor Ci is a capacitor having a very small capacitance, and does not have a capacitance enough to smooth the full-wave rectification output from the diode bridge DB. Therefore, a pulse-wave input voltage is applied to the following step-up / down converter connected to the subsequent stage of the diode bridge DB.

  The buck-boost converter includes a choke coil L, a first semiconductor switch element Q1, a second semiconductor switch element Q2, a first diode element D1, and a second diode element D2.

  Specifically, a series circuit of the first semiconductor switch element Q1 and the first diode D1 is connected to a pair of input terminals of the buck-boost converter that is also an output terminal of the diode bridge DB. At this time, the drain of the first semiconductor switch element Q1 is connected to one input terminal (one output terminal of the diode bridge DB) as a step-up / down converter. The source of the first semiconductor switch element Q1 and the cathode of the first diode D1 are connected. The anode of the first diode D1 is connected to the other (ground line side) input terminal (one other terminal of the diode bridge DB) as the buck-boost converter.

  A series circuit of a choke coil L and a second semiconductor switch element Q2 is connected in parallel to the first diode D1. At this time, one end of the choke coil L is connected to the cathode of the first diode D1, and the other end of the choke coil L is connected to the drain of the second semiconductor switch element Q2. The source of the second semiconductor switch element Q2 is connected to the anode of the first diode D1.

  A series circuit of a second diode D2 and an output capacitor Co is connected in parallel to the second semiconductor switch element Q2. The anode of the second diode D2 is connected to the drain of the second semiconductor switch element Q2. Both ends of the output capacitor Co become output terminals Pout as a power supply circuit. A load 100 such as an LED module is connected between the pair of output terminals of the output terminal Pout.

  The power supply circuit includes a control unit 10 and a current detection unit 11. The current detection unit 11 is connected in series between any one of the output terminals constituting the output terminal Pout and one end of the output capacitor Co. Specifically, in the example of FIG. 1, the output terminal on the ground line side and the terminal of the output capacitor Co are connected in series. The current detection unit 11 has a circuit configuration that detects a known direct current, detects an output current value that is a current flowing through the load 100, and outputs the output current value to the control unit 10.

  The control unit 10 generates a switching control signal for individually turning on / off the first semiconductor switch element Q1 and the second semiconductor switch element Q2. At this time, the control unit 10 generates a switching control signal based on the detected output current value and the target current value.

  2 is a diagram for explaining a specific configuration and control of the control unit 10, FIG. 2A is a circuit block diagram, and FIG. 2B is a diagram for explaining a duty setting concept. As illustrated in FIG. 2A, the control unit 10 includes an adder 21, a phase compensator 22, a duty setting unit 23, and pulse generation units 241 and 242.

  The adder 21 subtracts the output current value Io of the current detector 11 from the target current value Iref and outputs a difference value e. The target current value Iref is a preset value, for example, a current value for causing the LED module that is the load 100 to emit light with a predetermined luminance.

  The phase compensator 32 calculates the operation value U based on the difference value e and outputs it. At this time, the phase compensator 30 increases the operation value U according to the difference value e during a period when the difference value e is positive, and operates according to the difference value e during a period when the difference value e is negative. Decrease U.

  Based on the operation value U, the duty setting unit 23 calculates the first duty D1 for the first semiconductor switching element Q1 and the first duty D1 from the correlation between the operation value U and the duty Duty as shown in FIG. And a second second duty D2 for the second semiconductor switch element. The duty setting unit 23 outputs the first duty D1 to the pulse generation unit 241. Further, the duty setting unit 23 outputs the second duty D2 to the pulse generation unit 242. The specific setting concept of the first and second duties D1 and D2 and the actual switching operation mode will be described later.

Based on the first duty D1, the pulse generator 241 generates a switching control signal V _GQ1 composed of binary potentials of high level and low level, and _{applies the} switching control signal V _GQ1 to the gate of the first semiconductor switch element Q1. Based on the second duty D2, the pulse generator 242 generates a switching control signal V _GQ2 composed of binary potentials of a high level and a low level, and applies it to the gate of the second semiconductor switch element Q2.

Thus based on the set switching control signal V _GQ1 switching control signal V _GQ2, first, by the second semiconductor switching elements Q1, Q2 for switching control, the output current becomes a desired target electric current value Thus, a controlled power supply circuit can be realized.

  At this time, the power supply circuit according to the present embodiment performs switching control by setting a period of “step-up / step-down mode” between the “boost mode” and the “step-down mode” as shown below. A specific method for setting the step-up mode, step-down mode, and step-up / step-down mode will be described below.

  The control unit 10 is a DSP, and as described above, the output current value Io detected by the current detection unit 11 is A / D converted to obtain a digital value, and the target current value Iref stored in the memory in advance is acquired. The difference value e is calculated by making a difference with the digital value.

  The control unit 10 calculates the operation value U from the difference value e as described above, and sets the first duty D1 and the second duty D2 as shown below based on the operation value U.

(I) Step-down mode control When the operation value U is equal to or smaller than “a” (the section on the side where U is lower than U = a in FIG. 2B), the control unit 10 (duty setting unit 23) The duty D2 is set to “0”. Further, the first duty D1 is set to a value that similarly increases monotonously according to the monotonic increase of the operation value U.

  In this period, the on-duty of the second semiconductor switch element Q2 is set to 0%. As a result, the second semiconductor switch element Q2 is continuously turned off. On the other hand, the on-duty of the first semiconductor switch element Q1 is a predetermined value corresponding to the potential difference between the output voltage and the input voltage. At this time, the larger the input voltage with respect to the output voltage, the smaller the on-duty becomes (closer to 0).

Such an operation mode is a step-down mode and has a state transition and a waveform as shown in FIG. FIGS. 3A and 3B are circuit operation explanatory diagrams in the step-down mode, and FIG. 3A shows a case where the first semiconductor switch element Q1 is on and the second semiconductor switch element Q2 is off. FIG. 3B shows a case where the first semiconductor switch element Q1 is off and the second semiconductor switch element Q2 is also off. FIG. 3C shows each waveform in the step-down mode. From the top, the voltage V _GQ1 of the switching control signal for the first semiconductor switch element Q1, and the voltage V of the switching control signal for the second semiconductor switch element Q2 are shown. _GQ2 , drain-source current I _{Q1 of} the first semiconductor switch element Q1, drain-source current I _Q2 of the second semiconductor switch element _Q2 , and current _IL of the choke coil _L are shown.

As shown in FIG. 3, in the step-down mode, the second semiconductor switch element Q2 is always off. Therefore, a charging current flows through the choke coil L according to the difference between the input voltage and the output voltage while the first semiconductor switch element Q1 is on. On the other hand, the current _IQ1 does not flow between the drain and source of the first semiconductor switch element Q1 while the first semiconductor switch element Q1 is off, and a discharge current flows from the choke coil L.

Choke coil variation of the relationship between current _{I L} of L with these on-period and off-period of the first semiconductor switching elements Q1, the input voltage Vin, the output voltage Vout, the ON period Ton, if the OFF period Toff ,
Vout = Vin * Ton / (Ton + Toff) − (1)
Thus, the output voltage is lower than the input voltage.

(Ii) Boosting Mode Control When the operation value U is “b” or more (the section on the side where U is higher than U = b in FIG. 2B), the control unit 10 (duty setting unit 23) The duty D1 is set to “1”. Further, the second duty D2 is set to a value that similarly increases monotonously in accordance with the monotonous increase of the operation value U.

During this period, the on-duty of the first semiconductor switch element Q1 is set to 1. As a result, the first semiconductor switch element Q1 is continuously turned on, and the input voltage is continuously supplied. On the other hand, the on-duty of the second semiconductor switch element Q2 is a predetermined value corresponding to the potential difference between the output voltage and the input voltage. At this time, the smaller the output voltage with respect to the input voltage, the larger the on-duty becomes (closer to a predetermined value _D2max close to 1).

Such an operation mode is a boost mode and has a state transition and a waveform as shown in FIG. FIGS. 4A and 4B are circuit operation explanatory diagrams in the boost mode. FIG. 4A shows a case where the first semiconductor switch element Q1 is on and the second semiconductor switch element Q2 is also on. FIG. 4B shows the case where the first semiconductor switch element Q1 is on and the second semiconductor switch element Q2 is off. Figure 4 shows the respective waveforms of the boost mode, the voltage V _GQ1 of the switching control signal from the _upper, the voltage of the switching control signal V _GQ2, drain-source current I _Q1 of the first semiconductor switching elements _Q1, the second semiconductor The drain-source current I _{Q2 of} the switch element Q2 and the current _IL of the choke coil _L are shown.

  As shown in FIG. 4, in the boost mode, the first semiconductor switch element Q1 is always on, and an input voltage is always applied to the buck-boost converter. When the second semiconductor switch element Q2 is on, a charging current flows through the choke coil L according to the input voltage. On the other hand, a discharge current flows from the choke coil L in accordance with the potential difference between the input voltage and the output voltage when the first semiconductor switch element Q1 is off.

Choke coil variation of the relationship between current _{I L} of L with these on-period and off-period of the second semiconductor switching element Q2, the input voltage Vin, the output voltage Vout, the ON period Ton, if the OFF period Toff ,
Vout = Vin * (Ton + Toff) / Toff− (2)
Thus, the output voltage is higher than the input voltage.

(Iii) Step-up / step-down mode control When the operation value U is “a” or more and less than “b” (the section between U = a and U = b in FIG. 2B), the control unit 10 (duty setting unit 23) ), Both the first duty D1 and the second duty D2 are set to values that monotonously increase in accordance with the monotonous increase of the operation value U. At this time, as shown in FIG. 2B, the first duty D1 is set to be always higher than the second duty D2.

  During this period, the on-duty of the first semiconductor switch element Q1 is set to be less than 1 and higher than the on-duty set in the above-described step-down mode. The on-duty of the second semiconductor switch element Q2 is set to be higher than 0 and lower than the on-duty set in the boost mode.

  Thus, both the first semiconductor switch element Q1 and the second semiconductor switch element Q2 have a period of an on state and an off state in one cycle.

  Specifically, the first semiconductor switch element Q1 and the second semiconductor switch element Q2 are on / off controlled so that the three types of states shown in FIG.

  FIG. 5 is an explanatory diagram of circuit operation in the step-up / step-down mode. FIG. 6 is a diagram showing each waveform in the switching state shown in FIG. 6A is a waveform diagram when acting as a step-down in the step-up / step-down mode, and FIG. 6B is a waveform diagram when acting as a step-up in the step-up / step-down mode.

FIG. 5A shows a case where both the first semiconductor switch element Q1 and the second semiconductor switch element Q2 are in the on state. In this state, a charging current flows through the choke coil L according to the input voltage. Thus, as shown in FIG. 6 (A), (B) , the current _{I L} of the choke coil L increases with time.

FIG. 5B shows a case where the first semiconductor switch element Q1 is in the on state and the second semiconductor switch element Q2 is in the off state. In this state, if the input voltage is higher than the output voltage, a charging current flows through the choke coil L according to the potential difference between the input voltage and the output voltage. Thus, as indicated by hatching of the cross line in FIG. 6 (A), the current I _L of the choke coil L increases with time.

On the other hand, if the input voltage is lower than the output voltage, in other words, if the output voltage is higher than the input voltage, a discharge current flows through the choke coil L according to the potential difference between the input voltage and the output voltage. Thus, as indicated by hatching of the cross line in FIG. 6 (B), the current I _L of the choke coil L decreases with time.

FIG. 5C shows a case where both the first semiconductor switch element Q1 and the second semiconductor switch element Q2 are in the off state. In this state, a discharge current flows through the choke coil L only in accordance with the output voltage. Thus, as shown in FIG. 6 (A), (B) , the current _{I L} of the choke coil L decreases with time.

  As described above, the first and second semiconductor switch elements Q1 and Q2 are repeatedly controlled so as to transit between the states as shown in FIGS. 5A, 5B, and 5C. In this case, the operation is performed by either step-up or step-down according to the magnitude relationship between the input voltage and the output voltage.

  As described above, by using the configuration and control processing of the present embodiment, the step-up / step-down mode is executed in a period in which the potential difference between the input voltage and the output voltage is small. As described above, in the step-up / step-down mode, the first and second semiconductor switch elements Q1 and Q2 are always on / off controlled in one cycle, and the second semiconductor switch element Q2 is always off-controlled. An intermediate on / off control is performed between the step-down mode in which the first semiconductor switch element Q1 is turned on and the step-up mode in which the first semiconductor switch element Q1 is almost always on.

  Thereby, in accordance with a change in the magnitude relationship between the input voltage and the output voltage, abrupt switching of the switching control between the modes having significantly different control contents does not occur. As a result, it is possible to prevent the occurrence of adverse effects due to the switching such as the occurrence of an unstable control state and a sudden increase in ripple.

  Further, as shown in FIG. 2B, during the step-up / step-down mode, each on-duty of the first and second semiconductor switch elements Q1, Q2 changes according to the potential difference between the input voltage and the output voltage. During the period close to the boost mode (the period when the input voltage is lower than the output voltage), the on-duty closer to the boost mode is set, and during the period close to the step-down mode (the period when the input voltage is higher than the output voltage) An on-duty close to the mode is set. This also suppresses a sudden change in the content of the switching control and can more effectively prevent the above-described adverse effects.

  Further, as described above, since the power supply circuit of the present embodiment has almost no smoothing effect on the input capacitor Ci, the input voltage to the step-up / step-down converter has a pulse wave shape as shown in FIG. In FIG. 7, Vpeak is a peak voltage value of the input voltage, and shows a case where a 60 Hz AC power supply is used. On the other hand, the output voltage outputs a DC voltage as shown in FIG. In this case, the change in the magnitude relationship between the input voltage and the output voltage always occurs four times within one cycle of the AC voltage from the commercial power supply. For this reason, the number of times the magnitude relationship between the input voltage and the output voltage is switched is significantly increased as compared with the conventional power supply circuit that converts the AC voltage into a DC voltage using a smoothing capacitor and inputs the DC voltage to the buck-boost converter. Therefore, it is more effective to use the step-up / step-down mode shown in this embodiment, and more stable control is possible.

Although not described in the above embodiments, the high-level period of the switching control signal V _GQ2 is set to appear only in the high level period of the switching control signal V _GQ1. That is, the second semiconductor switch element Q2 is set to be on-controlled only during the on-period of the first semiconductor switch element Q1. As a result, the current does not loop in the closed circuit including the choke coil L, the second semiconductor switching element Q2, and the first diode D1, and the efficiency can be improved.

  In the above description, the example in which the first duty D1 and the second duty D2 are changed based on the output current value has been described. However, the output voltage value may be used. In this case, an output voltage detector may be connected in parallel with the output capacitor Co.

  In the above description, the first duty D1 and the second duty D2 are set to have substantially the same rate of change, but they may be different.

10-control unit, 11-current detection unit, 100-load, 200-commercial power supply, 21-adder, 22-phase compensator, 23-duty setting unit, 241,242-pulse generation unit, Ci, Co-capacitor , D1, D2-diode, L-choke coil, Pin-input port, Pout-output port, Q1, Q2-semiconductor switching element

Claims (6)

A rectifier circuit connected to a commercial power source;
A step-up / down converter including two semiconductor switch elements connected to a subsequent stage of the rectifier circuit;
An output capacitor connected to the subsequent stage of the step-up / down converter and having both ends as output terminals;
An output value detector that detects an output value that is either an output voltage or an output current;
A control unit that generates a switch control signal to be given to the two semiconductor switch elements in a plurality of modes based on an output value,
The controller is
Calculate a positive operation value according to the difference value,
When the operation value is greater than or equal to the first threshold, set the boost mode,
When the operation value is less than or equal to the second threshold, set the step-down mode,
A power supply circuit that sets a step-up / step-down mode when the difference value is between the second threshold value and the first threshold value. The power supply circuit according to claim 1,
The control unit defines the control in each mode by the on-duty for each semiconductor switch element,
In the step-up / step-down mode, the on-duty of the first semiconductor switch element is less than 1, the on-duty of the second semiconductor switch element is 0 or more, and the on-duty of the first semiconductor switch element is the second The power supply circuit is set higher than the on-duty of the semiconductor switch element. The power supply circuit according to claim 2,
The control unit is a power supply circuit that sets the on-duty according to the operation value in the step-up / step-down mode. A power supply circuit according to any one of claims 1 to 3,
The control unit is a power supply circuit that controls the second semiconductor switch element to be ON only during a period in which the first semiconductor switch element is ON-controlled. A power supply circuit according to any one of claims 1 to 4,
The power supply circuit, wherein the output value is an output current value. A power supply circuit according to any one of claims 1 to 4,
The power supply circuit, wherein the output value is an output voltage value.

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