JP3613907B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a step-up switching power supply device of a switching regulator type using a reactor, a diode for a backflow element, and a switching element.
[0002]
[Prior art]
FIG. 3 shows an example of a conventional step-up switching power supply device. The device shown in FIG. 3 is for boosting the output voltage (12v) of the in-vehicle battery 1 to 48v, which is quadrupled, and outputting it from the output terminal Tout. As a basic component, the input terminal Tin And an output terminal Tout, a reactor 2 and a backflow prevention diode 3, and a chopping transistor 4 (npn type) connected between the anode side of the diode 3 and a ground terminal. .
[0003]
The transistor 4 receives a base signal from the AND circuit 5, and a pair of input terminals of the AND circuit 5 is supplied with outputs from the signal generator 6 and the comparison circuit 7. . In this case, the signal generator 6 outputs a drive pulse Pz (see FIG. 4A) for determining the ON timing of the transistor 4. Further, the comparison circuit 7 has a divided voltage Vd (proportional to the output voltage from the output terminal Tout) supplied through the high impedance voltage dividing circuit 8 and a reference voltage Vref (output) supplied from a reference voltage generating circuit (not shown). The output voltage level from the terminal Tout (voltage set to determine 48V) is compared, and a high level signal is output only during a period in which Vd ≦ Vref.
[0004]
Further, a known smoothing capacitor 9 is connected to the output terminal Tout side, and a smoothing capacitor 10 for suppressing pulsation of the input current is connected to the input terminal Tin side. R is a load connected between the output terminal Tout and the ground terminal.
[0005]
In the above configuration, the AND circuit 5 is only in a period in which the drive pulse Pz output from the signal generation circuit 6 is in a rising state and the output voltage level is less than 48 v (a period in which Vd ≦ Vref is satisfied). A high level signal is output from the transistor 4 to turn on the transistor 4. During the ON period of the transistor 4, a current flows from the battery 1 through the reactor 2 and the transistor 4. During the OFF period of the transistor 4, a current corresponding to the energy stored in the reactor 2 flows through the diode 3.
[0006]
In the state where the resistive load R is connected to the output terminal Tout, the transistor 4 is periodically turned on and off as shown in FIG. 4B, and the current flowing through the reactor 2 in response to this operation I1 varies as shown in FIG. 4 shows the waveform of the drive pulse Pz from the signal generator 6, the ON / OFF waveform of the transistor 4, the waveform of the current I1 flowing through the reactor 2, the waveform of the input current Iin from the battery 1, and the output flowing through the diode 3. The waveform of the current Iout (the waveform before smoothing by the capacitor 9) is shown.
[0007]
Here, when the inductance of the reactor 2 is L, the voltage between both ends thereof is V, and the time differential value of the current flowing through the reactor 2 is ΔI / Δt, the relationship V = L · ΔI / Δt is established. The slope of the current I1 during the on period is obtained at 12 v / L. Further, the gradient of the current I1 in the off period of the transistor 4 is (48v-12v) / L = 36v / L. Therefore, the slope of the current I1 when rising is 1/3 times the slope when falling.
[0008]
[Problems to be solved by the invention]
In the conventional configuration as described above, a smoothing capacitor 9 for smoothing the output current Iout is provided on the output side, and a smoothing capacitor 10 must also be connected on the input side. That is, in the configuration in which the capacitor 10 is not connected, a large noise is induced in the power supply line due to the large pulsation of the input current Iin, and therefore this noise may adversely affect other electronic circuit devices. Becomes higher. Therefore, in order to cope with such a situation, it is necessary to connect the capacitor 10 to the input side to suppress the pulsation of the input current Iin as shown in FIG.
[0009]
By the way, in order to sufficiently exhibit the function of suppressing the pulsation of the input current Iin as described above, it is necessary to use a capacitor having a large capacity as the smoothing capacitor 10. Since this is a relatively expensive and large component as a circuit component, this has been a problem that it becomes an obstacle to downsizing of the entire device and cost reduction.
[0010]
The present invention has been made in view of the above circumstances, and its purpose is to eliminate the need to use a large-capacitance capacitor in order to suppress pulsation of the input current, thereby reducing the size and cost of the entire apparatus. An object of the present invention is to provide a switching power supply device that achieves an effect such as realization.
[0011]
[Means for Solving the Problems]
In general, a switching regulator type power supply device that boosts the output voltage of a DC power supply using a reactor, a reverse-current element diode, and a chopping switching element, is connected to the reactor from the DC power supply during the ON period of the chopping switching element. In addition, the output voltage of the DC power supply is boosted by repeating the operation in which a current flows through the switching element and a current corresponding to the energy stored in the reactor flows through the reverse-current element diode during the OFF period of the switching element. Is.
[0012]
According to the configuration of the first aspect, the n chopping switching elements respectively corresponding to the n reactors connected in parallel are switched by the control means while being out of phase by 2π / n. In response to this, a boost ratio of n times is obtained. When such a switching operation is performed, since the increase / decrease timing of the current flowing through each reactor is shifted from each other, the combined current of the current flowing through these reactors, that is, the waveform of the input current from the DC power supply as a whole The waveform has less pulsation. As a result, the possibility of inducing large noise in the power supply line due to the pulsation of the input current is reduced, so that it is not necessary to provide a large-capacity smoothing capacitor as in the conventional configuration. Cost reduction can be realized.
[0013]
According to the configuration of the second aspect, the on-timing phase of the n chopping switching elements is controlled to be shifted by 2π / n by the driving pulse generated by the pulse generating means, and the output voltage is set to the set voltage. When this occurs, the chopping switching element is turned off by a signal generated by the voltage detection means. For this reason, the control of the ON period of the chopping switching element is accurately performed, and the control accuracy of the output voltage level is increased.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
In other words, this embodiment is intended for a switching power supply device for driving various circuit devices provided in an electric vehicle, and an example of boosting a power supply voltage from 12v to 48v (a boost ratio is 4 times). Example).
[0015]
In FIG. 1, one end side of a total of four reactors 12 a to 12 d is connected to an input terminal Tin connected to a plus side terminal of an in-vehicle battery 11 (rated output voltage 12 v) which is a DC power source. The other end sides of 12a to 12d are connected to the output terminal Tout through the backflow prevention diodes 13a to 13d, respectively. The collectors and emitters of npn transistors 14a to 14d serving as chopping switching elements are connected between the anode sides of the diodes 13a to 13d and the ground terminal. The negative terminal of the battery 11 is connected to the ground terminal.
[0016]
The transistors 14a to 14d receive base signals from the AND circuits 15a to 15d corresponding thereto. In the AND circuits 15a to 15d, outputs from the output terminals Qa to Qd of the signal generator 16 are respectively given to one input terminal, and outputs from the comparison circuit 17 are given to each other input terminal. It has become.
[0017]
The signal generator 16 corresponds to the pulse generating means referred to in the present invention, and drive pulses Pa to Pd (FIG. 2 (a) for determining the ON timing of the transistors 14a to 14d from the output terminals Qa to Qd. ), (D), (g), and (j)). In this case, the drive pulses Pa to Pd are in a state where their phases are shifted by π / 2 (90 °).
[0018]
The comparison circuit 17 constitutes the voltage detection means 19 in the present invention together with the voltage dividing circuit 18, and the divided voltage Vd (the output voltage from the output terminal Tout) given through the voltage dividing circuit 18 is used. Proportional) and a reference voltage Vref (voltage set to determine the output voltage level (= 48v) from the output terminal Tout) given from a reference voltage generation circuit (not shown), and Vd ≦ Vref A high level signal is output only for a certain period. The voltage dividing circuit 18 is configured by connecting a series circuit of resistors 18a and 18b between the output terminal Tout and the ground terminal, and its impedance is set sufficiently high.
[0019]
On the output terminal Tout side, a smoothing capacitor 20 for smoothing the output current through the diodes 13a to 13d is connected, and a load R is connected between the output terminal Tout and the ground terminal.
[0020]
According to the above configuration, the AND pulses 15a to 15d respectively corresponding to the transistors 14a to 14d are in a state in which the drive pulses Pa to Pd output from the signal generation circuit 16 have risen, and the output voltage level. A high level signal is output only during a period in which V is less than 48v (a period in which Vd ≦ Vref). In this case, since the phases of the drive pulses Pa to Pd are shifted by π / 2, the transistors 14a to 14d are shifted in phase by π / 2 as shown in FIG. Will be turned on.
[0021]
During the on period of each of the transistors 14a to 14d, current is supplied from the battery 11 to the reactors 12a to 12d, and during the off period of the transistors 14a to 14d, currents corresponding to the energy accumulated in the reactors 12a to 12d are respectively provided. It flows through the corresponding diodes 13a to 13d.
[0022]
In the state where the resistive load R is connected to the output terminal Tout, the transistors 14a to 14d are periodically turned on and off, and the currents Ia to Id flowing through the reactors 12a to 12d in response to this are shown in FIG. 2 (c), (f), (i), and fluctuate as shown in (l). 2 shows the waveforms of the driving pulses Pa to Pd from the signal generator 16, the on / off waveforms of the transistors 14a to 14d, the waveforms of the currents Ia to Id flowing through the reactors 12a to 12d, and the input current Iin from the battery 11. And the waveform of the total output current Iout flowing through the diodes 13a to 13d (the waveform before smoothing by the smoothing capacitor 20).
[0023]
Here, when the output voltage 12v of the battery 11 is boosted to 48v, as described in the description of the conventional configuration, the rising slopes of the currents Ia to Id during the on periods of the transistors 14a to 14d are the off-states of the transistors 14a to 14d. It turns out that it becomes 1/3 times of each falling gradient of the currents Ia to Id in the period.
[0024]
By the way, the input current Iin corresponds to the sum of the currents Ia to Id flowing through the reactors 12a to 12d, but the phase of each of the currents Ia to Id that repeats linear increase and decrease at the same rate as in the above configuration. Is shifted by π / 2, the waveform of the input current Iin (= Ia + Ib + Ic + Id) becomes a flat direct current as shown in FIG. As a result, there is no possibility that a large noise is induced in the power supply line due to the pulsation of the input current Iin.
[0025]
Therefore, it is not necessary to provide a large-capacity smoothing capacitor 10 (see FIG. 3) as in the conventional configuration in order to suppress fluctuations in the input current Iin. Therefore, it is possible to reduce the size and cost of the entire apparatus. In this embodiment, the number of circuit elements such as the transistors 14a to 14d is increased from the conventional configuration. For example, the transistors 14a to 14d themselves have a smaller capacity than the transistor 4 (see FIG. 3) having the conventional configuration. As a result, cost reduction can be realized in total.
[0026]
Further, the four kinds of drive pulses Pa to Pd output from the signal generator 16 are controlled so that the phases of the ON timing of the four transistors 14a to 14d are shifted by π / 2, and the output voltage is 48v or more. Then, the transistor 14a to 14d is controlled to be turned off by a signal (low level signal) output from the comparison circuit 17 in the voltage detection means 19, so that the ON period of the transistors 14a to 14d is controlled. Control can be executed accurately. As a result, there is an advantage when the control accuracy of the output voltage level is increased.
[0027]
Furthermore, even when the switching frequency of the transistors 14a to 14d is reduced, it is possible to obtain an output equivalent to the conventional one. When the switching frequency is lowered in this way, the generation of switching noise can be suppressed and There is an advantage that switching loss can be reduced. In addition, even if a failure occurs in any of the transistors 14a to 14d or the diodes 13a to 13d, the output level is maintained at a certain level or more, so a secondary effect that a fail-safe function can be obtained can be expected. become.
[0028]
The present invention is not limited to the above-described embodiment, and the following modifications or expansions are possible.
In the above embodiment, the example in which the step-up ratio is set to four times has been described. However, it can be arbitrarily set as long as it is an integer multiple. That is, when the step-up ratio is set to n times (n is an integer of 2 or more), n reactors, backflow element diodes, and n chopping switching elements may be provided. The chopping switching element is not limited to the bipolar transistor, and other semiconductor switching elements can be used.
[Brief description of the drawings]
FIG. 1 is an electric circuit configuration diagram showing an embodiment of the present invention. FIG. 2 is a timing chart showing waveforms of respective parts. FIG. 3 is an electric circuit configuration diagram showing a conventional example.
Timing chart showing the waveforms of each part [Explanation of symbols]
In the drawing, 11 is a vehicle-mounted battery (DC power supply), 12a to 12d are reactors, 13a to 13d are backflow blocking diodes, 14a to 14d are transistors (chopping switching elements), and 16 is a signal generator (pulse generating means). , 17 is a comparison circuit, 18 is a voltage dividing circuit, and 19 is a voltage detection means.

Claims (2)

In a switching regulator type power supply device that boosts the output voltage of a DC power supply using a reactor, a diode for backflow element and a switching element for chopping,
When the step-up ratio is set to n times (n is an integer of 2 or more), n reactors connected in parallel and n switching elements for chopping respectively corresponding to these reactors are provided.
A switching power supply device comprising a control means for switching the n chopping switching elements in a state of being shifted in phase by 2π / n. The control means includes
Pulse generating means for generating n types of drive pulses in a phase-shifted state by 2π / n for determining the on-timing of the n chopping switching elements;
2. The switching power supply device according to claim 1, further comprising: a voltage detection unit that generates a signal for turning off the chopping switching element when an output voltage becomes equal to or higher than a set voltage.

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