JPH06106019B2 - DC-DC converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a DC-DC converter used in a small electric device.

2. Description of the Related Art Conventionally, as this type of DC-DC converter, a series circuit of a DC power supply 1, a switching element 2, a reactor 3 and a capacitor 4 is formed as shown in FIG.
There is a configuration in which a load 7 is connected in parallel with. The diode 5 is connected in parallel between the DC power supply 1 and the switching element 2. The control circuit 6 detects the voltage across the capacitor 4, and turns on the switching element 2 when the voltage is a predetermined value a or less, and turns off the switching element 2 when the voltage is a predetermined value b or more.

4A, 4B and 4C show the waveforms of the current i _{L of the} reactor 3, the current i _{C of the} capacitor 4 and the output voltage V _O. In these waveform diagrams, O <t <t ₁ is the period when the switching element 2 is on.
T _ON , and t ₁ <t <t ₂ is the OFF period T _OFF . As shown in Fig. 4a, i _L is DC power supply 1 and output voltage V _{O at} T _ON.
The difference between the two increases with the current being supplied to the capacitor 4 and the load 7 while being applied to the reactor 3, and at T _OFF , the magnetic energy stored during the T _ON period is passed through the diode 5 to the capacitor 4 and the load. It decreases because it discharges to 7 parallel circuits. The i _C, as shown in FIG. 4 b, the AC component of the i _L (ripple) flows, V _O, as shown in FIG. 4 c, the integrated waveform of i _C.

Problems to be Solved by the Invention Such a conventional configuration has the following problems. That is, the control circuit 6 detects and turns on the switching element 2.
When the difference b-a between the voltage values a and b to be turned off, that is, the hysteresis voltage is small, the control circuit 6 is apt to malfunction due to noise, and if the hysteresis voltage is increased to prevent malfunction, the oscillation frequency decreases i _L Maximum value of i
_{L peak} becomes large, and the reactor 3 easily causes magnetic saturation. Since i _{L peak} matches the maximum value of the current flowing through the switching element 2,
You need to use a large ASO.

FIG. 5 is an operation waveform diagram when the hysteresis voltage is increased to prevent malfunction of the control circuit due to noise, a, b,
c shows i _L , i _C , and V _O , as in the case of FIG. FIG. 5 shows the operation when the hysteresis voltage is set to dc which is larger than that in FIG. In this case, the oscillation frequency 1 / (T _ON + T _OFF ) is reduced and the ripple current of i _L is increased as compared with FIG. On the other hand, since the direct current component of i _L is supplied to the load 7, it is equal to that in the case of FIG. 4, so that i _{L peak} increases and i _C also increases.

The operation waveforms shown in FIG. 4 are for the case where there is no delay in the operation of the switching element.
In many cases, a transistor is actually used, and in that case, the time delay from the on / off signal input from the control circuit 6 to the on / off of the transistor is considerably large.

Fig. 6 shows the operation waveforms when the oscillation frequency 1 / (T _ON + T _OFF ) and i _{L peak} are kept constant when the turn-off and turn-on time delays of switching element 2 are td ₁ and td ₂ , respectively. Indicates.

In this case, the hysteresis voltage is fe and the fourth
It becomes smaller than the case in the figure, and the problem of malfunction due to noise increases.

In view of the above problems, the present invention provides a DC-DC converter in which the hysteresis voltage is increased without lowering the oscillation frequency to prevent malfunction of the control circuit due to noise and improve circuit reliability.

Means for Solving the Problems In order to solve this problem, the DC-DC converter of the present invention includes a DC power supply, a switching element, a reactor, a resistor, and a capacitor connected in series, and the switching element includes the resistor and the capacitor. The ON / OFF control is performed by the control circuit that detects the voltage across the series circuit.

With this configuration, the rising and falling edges of the voltage waveform that can be detected by the control circuit can be made steep, so that a large hysteresis voltage can be obtained and malfunctions due to noise can be prevented.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a DC-DC converter according to an embodiment of the present invention has a DC power supply 11, a switching element 12, a reactor 13 and a load 17 connected in series. The diode 15 is connected in parallel with the DC power supply 11 and the switching element 12. A series circuit including a capacitor 14 and a resistor 18 is connected to the load 17 in parallel. The control circuit 16 detects the voltage V _O across the load 17 and turns on the switching element 12 when the voltage is a predetermined value g or less and turns off the switching element 12 when the voltage is a predetermined value h or more. Thus, it is connected between both ends of the load 17 and the switching element 12.

The operation will be described below. When the voltage across the series circuit of the capacitor 14 and the resistor 18, that is, the voltage V _O across the load 17 is less than or equal to g, the control circuit 16 turns on the switching element 12 to switch the DC power source 11 to the switching element 12 and the reactor. A current is supplied to a series circuit of a capacitor 14 and a resistor 18 and a load 17 via 13. When V _O becomes h or more, the control circuit 16 turns off the switching element 12, and the reactor is turned on during the on period.
The energy stored in 13 is transferred to the diode 15 and the reactor.
A current is supplied to a series circuit of a capacitor 14 and a resistor 18 and 17 through 13. FIG. 2 illustrates the on / off state of the switching element 12. The operation of the DC-DC converter of this embodiment will be described in detail with reference to FIG. I _{L in} the figure a is the current of the reactor 13, b in the figure b
I _C is the current of capacitor 14, and V _C in FIG.
Voltage, V _O is a waveform diagram of a detection voltage of the control circuit 16. The _ON period of the switching element 12 is T _ON , and the OFF period is T.
It is _OFF . In this embodiment, T _ON + T is set for the following reason.
_OFF is the same time as the conventional example. That is, the oscillation frequency of the switching element 12 is the same as the conventional one.

In this embodiment, since the resistor 18 is provided, the detection voltage V _O of the control circuit 16 is V _O = V _C + r × i _C , which is the waveform of V _O in FIG. 2C. Therefore, the hysteresis voltage of the control circuit 16 is set to a voltage at the time of switching the switching element 12, the voltage at the on time t ₁ and the voltage at the off time t ₂ to be g and h, respectively, and is set to be larger than the conventional hysteresis voltage set to a and b. The oscillation frequency can be kept constant, which is the same as before.

This hysteresis voltage has a relationship of h−g> b−a. Immediately, in this embodiment, the resistor 18 and the capacitor 14
Since the control circuit 16 detects the voltage at both ends of the serial circuit, the oscillation frequency can be kept constant and a large hysteresis voltage can be obtained.

In this embodiment, the load 17 is the resistor 18 and the capacitor 14
Although it is connected to both ends of the series circuit of, it may be connected to both ends of the capacitor 14. In this case, since the load current flows through the resistor 18, the voltage supplied to the load will be lower than in the case of the circuit shown in Fig. 1, but since a capacitor is directly connected across the load, the frequency The characteristic is that the impedance to Also capacitor 14
It goes without saying that a first load may be connected to both ends of the capacitor and a second load may be connected to both ends of the series circuit of the capacitor 14 and the resistor 18.

EFFECTS OF THE INVENTION As is clear from the above embodiments, the DC-DC converter of the present invention does not lower the oscillation frequency by detecting the voltage across the series circuit of the resistor and the capacitor and controlling the switching element. In addition, the hysteresis voltage can be increased to prevent malfunction due to noise, and reliability can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a DC-DC converter showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of the circuit of FIG. 1, and FIG.
The figure is a circuit diagram of a conventional DC-DC converter, and Fig. 4 is a conventional circuit diagram.
Operation waveform diagram of DC-DC converter, Fig. 5 shows conventional DC-DC
FIG. 6 is an operation waveform diagram when the hysteresis voltage is increased in the converter, and FIG. 6 is an operation waveform diagram when the hysteresis voltage is decreased because there is a time delay in turning on / off the switching element in the conventional DC-DC converter. 11 …… DC power supply, 12 …… Switching element, 13 …… Reactor, 14 …… Capacitor, 15 …… Diode, 16 ……
Control circuit, 18 ... resistor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Konan 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-50-67954 (JP, A) JP-A-57-34697 (JP, A)

Claims (1)

[Claims] 1. A control circuit for connecting a DC power supply, a switching element, a reactor, a resistor, and a capacitor in series, and connecting a diode in parallel to a series circuit of the switching element and the DC power supply to turn on / off the switching element. However, the control circuit is connected to both ends of the series circuit of the resistor and the capacitor, and has two thresholds, high and low, with respect to the voltage across the resistor, and the control circuit is connected between both ends of the resistor and the capacitor. Turn off the switching element when the voltage of is higher than the higher threshold,
A DC-DC converter that turns on the switching element when the voltage becomes lower than the lower threshold value.