JPH0824424B2 - Switching Regulator Device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator device for supplying a regulated DC voltage to industrial or consumer equipment.

2. Description of the Related Art Conventionally, this type of switching regulator device has a configuration as shown in FIG. A conventional switching regulator device will be described with reference to FIG. 1,1 'are input terminals to which a commercial AC voltage is applied to both ends. An input smoothing circuit 3 rectifies and smoothes the commercial AC voltage applied to the input terminals 1 and 1'to a DC voltage. A switching circuit unit 4 turns on / off the DC voltage supplied from the input smoothing circuit 3 in accordance with the output of the PWM comparator circuit 12, and applies a pulse voltage to the primary winding 5 (a) of the transformer 5. Reference numeral 5 denotes a transformer. The pulse voltage applied to the primary winding 5 (a) is induced in the secondary winding 5 (b), and the induced positive pulse voltage is rectified by the diode 6, and the choke transformer 8 The voltage is smoothed by the capacitor 9 and converted into a DC voltage, and supplied to the load from the output terminals 2, 2 '. On the other hand, when the negative pulse voltage induced in the secondary winding 5 (b) turns off the diode 6, the energy stored in the choke transformer 8 is applied to the output via the diode 7. , And smoothed by the capacitor 9 and supplied to the output terminals 2, 2 '. The output voltages of the output terminals 2 and 2'are compared and amplified with the reference voltage 11 by the comparison circuit 10 and output to the PWM comparator circuit 12. The sawtooth wave voltage that oscillates at a constant frequency is applied to the PWM comparator circuit 12 from the oscillation circuit 13, and the on / off pulse waveform determined by the sawtooth wave voltage and the output of the comparison circuit 10 is output by the PWM comparator 12. It is output and applied to the switching circuit 4.

Regarding the operation of the PWM comparator circuit 12,
This will be described in detail with reference to the drawings. FIG. 4A shows the sawtooth wave voltage A of the oscillation circuit 13 applied to the PWM comparator circuit 12 and the output voltage B of the comparison circuit 10, and B3 shows the control value of the maximum output voltage. FIG. 4B shows a pulse waveform C of the PWM comparator circuit 12, which rises and falls at the cross points of the sawtooth voltage A and the output voltage B of the comparison circuit 10 at each level. When the output voltage of the output terminals 2 and 2'changes, the output voltage B of the comparison circuit 10 moves to B1 or B2 to change the duty ratio of the ON period D and the OFF period E of the pulse output C. The pulse waveform C is applied to the switching circuit 4, and the primary winding 5 (a) of the transformer 5
The duty ratio of the pulse voltage supplied to the
The duty ratio of the pulse voltage induced in (b) is changed, and the output voltage is changed in proportion to the duty ratio. By this series of operations, the output voltage at the output terminals 2 and 2'is kept constant from any fluctuation. The Zener diode 20 shown in FIG.
Is set, and the maximum duty ratio is determined by this.

Problems to be Solved by the Invention In such a conventional configuration, the stabilization of the output voltage due to the fluctuation of the input voltage, that is, the commercial AC voltage or the DC voltage is
Although it is performed by changing the output level of the comparator circuit 10, the comparator circuit 10 is generally designed to have a low feedback loop gain in order to prevent abnormal oscillation, and in particular, the high frequency gain is low. There is a delay in the response, the output voltage cannot be stabilized at a sufficient response speed, the output voltage undergoes a large transient fluctuation, and the rejection ratio of the commercial frequency ripple voltage contained in the DC voltage cannot be made sufficiently large. A similar response delay occurs for load responses such as output voltage, but the duty ratio is the maximum in these transient states (generally, the maximum duty ratio is limited to a fixed value).
There is a sufficient margin for the magnetic flux density so that the magnetic flux of the transformer 5 will not be saturated even when the input voltage reaches the maximum duty ratio that is limited even when the input voltage is maximum.
Therefore, there is a problem that the transformer 5 becomes large in size and expensive.

The present invention solves such a problem, and an object of the present invention is to improve the stability due to input voltage fluctuation and to provide a small-sized and low-priced switching regulator device.

Means for Solving the Problems In order to solve the above problems, the present invention provides a switching circuit to which a DC input voltage is supplied, a transformer to which the output of the switching circuit is supplied to a primary winding, and a transformer of this transformer. A rectifying / smoothing circuit connected to the secondary winding, a comparing circuit that detects the output voltage of the rectifying / smoothing circuit and compares and amplifies it with a reference voltage, and compares the output voltage of the comparing circuit with the output voltage of the oscillating circuit. PWM to generate on-off pulse waveform
A comparator circuit and a switch circuit for operating the switching circuit by the output of this PWM comparator circuit and discharging the capacitor in synchronization with the oscillation cycle of the oscillation circuit in the DC charging circuit of the resistor and the capacitor connected to the DC input voltage. And a second PWM comparator circuit that compares the charge / discharge voltage waveform of the capacitor with the output voltage of the comparison circuit to generate an ON-OFF pulse waveform.
The pulse waveform of the comparator and the pulse waveform of the second PWM comparator are logically AND-connected to operate the switching circuit.

Operation With this configuration, the response of the output voltage to the fluctuation of the input voltage is made fast, and the maximum duty ratio is changed in inverse proportion to the input voltage, so that the maximum magnetic flux density of the transformer in the transient response state It is possible to make the level constant with respect to the input voltage.

Embodiment 1 FIG. 1 is a block diagram of a switching regulator device according to an embodiment of the present invention, in which the same operation as that in FIG. 3 is denoted by the same reference numeral and its description is omitted. Reference numeral 14 in FIG. 1 is a second PWM comparator circuit, to which the output voltage of the comparison circuit 10 is applied, and to the other input is a resistor 15 connected across the DC voltage of the input smoothing circuit 3. The connection point of the DC circuit of the capacitor 16 is connected,
16 is connected to a switch circuit 17 that operates in synchronization with the oscillation frequency of the oscillation circuit 13. Further, the output of the second PWM comparator circuit 14 is connected to the output of the PWM comparator circuit 12, and their pulse waveforms are logically AND-connected, and the connection point is connected to the switching circuit 4.

The DC voltage of the input smoothing circuit 3 passes through the resistor 15
Although 16 is charged, the switch circuit 17 operates in synchronization with the oscillation frequency of the oscillation circuit 13 and is discharged, so that a so-called sawtooth voltage is applied to the input of the second comparator circuit 14. Further, the operations of the PWM comparator circuit 12 and the second comparator circuit 14 will be described in detail with reference to FIG. 2C shows a sawtooth wave voltage A of the oscillator circuit 13 applied to the PWM comparator circuit 12 and an output voltage B of the comparison circuit 10, and FIG. 2D shows an output pulse waveform C1 thereof.
Is shown. 2 (e) shows the second PWM comparator 1
Comparator circuit 10 and voltage F across capacitor 16 applied to 4
Of the output voltage B and (f) of FIG. FIG. 2 (g) shows the output pulse waveform C1 of the PWM comparator 12 and the output pulse waveform C2 of the second PWM comparator 14.
Is a pulse output C which is logically AND-connected and applied to the switching circuit 4. The voltage F across the capacitor 16 has a charging current determined by the DC voltage of the input smoothing circuit 3 and the resistor 15, and is discharged by the switch circuit 17, but the operation timing of the switch circuit 17 is similar to the output waveform of the oscillator circuit 13. It works in sync with.

In the normal operation range of the commercial AC voltage or the DC input voltage, the second PWM comparator 14 controls the voltage, that is, the voltage F across the capacitor 16 rises earlier than the sawtooth voltage A of the oscillator circuit 13. As described above, the series charging circuit including the resistor 15 and the capacitor 16 and the oscillation circuit 13
Is set.

With the above-described configuration, the charging current of the voltage F across the capacitor 16 changes with respect to the fluctuation of the commercial AC voltage applied to the input terminals 1, 1 '(DC voltage fluctuation of the input smoothing circuit 3). For this purpose, the process moves to F1 or F2 to change the duty ratio of the ON period D and the OFF period E of the pulse output C. Since the change of the duty ratio operates so as to make the output voltage of the output terminals 2 and 2'constant, the output voltage of the comparison circuit 10 is stable even if it hardly moves. Further, the maximum output voltage B3 of the comparison circuit 10 is set by the Zener diode 20, so the maximum value of the duty ratio is limited, but the maximum value of the duty ratio is also the commercial AC applied to the input terminals 1, 1 '. It will change in proportion to the fluctuation of the voltage. In addition, the commercial AC voltage or the DC input voltage drops and the voltage F across the capacitor 16 causes the oscillation circuit 13
Even if it rises later than the sawtooth voltage A of
Since the comparator 12 replaces the second PWM comparator 14 and changes the duty ratio so as to keep the output voltage constant and also controls the maximum value, the maximum duty ratio becomes unlimited as the commercial AC voltage decreases. Can be prevented from increasing,
The absolute value can be set freely.

EFFECTS OF THE INVENTION As described above, according to the present invention, the stabilization of the output voltage due to the fluctuation of the input voltage, that is, the commercial AC voltage or the DC voltage does not depend on the change of the output level of the comparison circuit, but the direct input voltage changes. Because it is controlled, the response is quick,
The transient fluctuation of the output voltage becomes extremely small. In addition, since the output voltage stability with respect to the input voltage can be sufficiently obtained without directly detecting and controlling the output voltage, it is possible to control the output voltage only on the primary side without feedback of the output voltage. is there. Moreover, the removal ratio of the commercial frequency ripple voltage included in the DC voltage is also reduced without using a special circuit. In addition, even if the duty ratio may expand to the maximum value in a transient state of load response such as output voltage, the maximum duty ratio varies inversely with the input voltage. Since the magnetic flux density is almost constant, it is not necessary to design the transformer in the worst case, the utilization factor of the transformer is increased, the size can be reduced, and the cost is advantageous.

In addition, even if the rise in the voltage across the capacitor slows down due to a sudden drop in commercial AC voltage or DC input voltage, and the duty ratio increases rapidly, the PWM comparator will
In order to control the duty instead of the PWM comparator of
It is possible to prevent the duty ratio from expanding more than necessary,
Since it is possible to prevent an excessive current from flowing through the transformer or the switching circuit section, an effect of improving reliability can be obtained.

[Brief description of drawings]

1 is a circuit configuration diagram showing a switching regulator device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing operation waveforms of the circuit configuration diagram of FIG. 1 of the present invention, and FIG. 3 is a conventional circuit configuration. FIG. 4 and FIG. 4 are explanatory diagrams showing operation waveforms of the conventional circuit configuration diagram of FIG. 3 ... Input smoothing circuit, 4 ... Switching circuit, 5 ...
Transformer, 6,7 ... Diode, 8 ... Choke transformer, 9,16 ... Capacitor, 10 ... Comparison circuit, 11 ... Reference voltage circuit, 12,14 ... PWM comparator circuit, 13 ... Oscillation circuit, 15 …… Resistance, 17 …… Switch circuit, 20 …… Zener diode.

Claims (1)

[Claims] 1. A switching circuit to which a DC input voltage is supplied, a transformer to which the output of the switching circuit is supplied to a primary winding, a rectifying / smoothing circuit connected to a secondary winding of the transformer, A comparator circuit that detects the output voltage of the rectifying and smoothing circuit and compares and amplifies it with a reference voltage, and a PWM comparator that creates an on-off pulse waveform by comparing the output voltage of the comparator circuit and the sawtooth voltage of the oscillation circuit, A switch circuit for discharging the capacitor in synchronization with a sawtooth voltage of the oscillation circuit in a series charging circuit of a resistor and a capacitor connected to the DC input voltage, a charge / discharge voltage of the capacitor, and an output voltage of the comparison circuit. And a second PWM comparator that produces an on-off pulse waveform by comparing the pulse waveforms of the PWM comparator and the second PWM comparator.
The pulse waveform of the comparator is logically AND-connected to operate the switching circuit, and the pulse waveform of the second PWM comparator is high in the range where the DC input voltage is high and the PWM waveform is low in the range where the DC input voltage is low.
A switching regulator device characterized in that a pulse waveform of a comparator is set so as to operate the switching circuit with priority.