JP2859611B2 - Switching regulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention absorbs noise generated from a commutating diode in a switching regulator or a rectifying diode in a switching regulator that controls an output voltage by a semiconductor switch. More particularly, the present invention relates to a switching regulator provided with a noise absorption circuit using a CR snubber circuit and a saturable reactor together. 2. Description of the Related Art A CR snubber circuit as shown in FIG. 5B is widely used as a means for absorbing noise generated from electricity, for example, noise based on a recovery current of a diode. In addition to the C snubber circuit, a saturable reactor is also effective as a noise absorbing unit. These C
It is considered that the means can be more effectively suppressed by using the R snubber circuit and the saturable reactor together. However, as shown in FIG. 5C, when a CR snubber circuit is connected in parallel to the diode D and a saturable reactor L is connected in series to these parallel circuits, the diode is turned on. When this happens, the charging current of the capacitor C in the CR snubber circuit as well as the forward current of the diode D flows through the saturable reactor L.
The energy stored in the saturable reactor L increases. For example, when the diode is used as a commutation diode in a switching regulator or a rectifying diode in a switching regulator that controls an output voltage by a semiconductor switch, the stored energy of the saturable reactor L is a loss, so Decrease efficiency. Therefore, when a CR snubber circuit and a saturable reactor are used together to improve the noise absorption effect, how to reduce the energy stored in the inductor becomes a major issue. SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and can effectively absorb noise based on a recovery current of a diode in a switching regulator, and can further reduce energy consumption. It is an object of the present invention to provide a switching regulator provided with a noise absorbing circuit that minimizes unnecessary accumulation of noise and can minimize a decrease in efficiency. A first switching regulator according to the present invention comprises a saturable reactor for absorbing a recovery current of the commutation diode in series with the commutation diode as a noise absorbing circuit. And a CR snubber circuit for absorbing a recovery current passing through the saturable reactor is connected in parallel to a series circuit of the commutating diode and the saturable reactor. A second switching regulator according to the present invention is a switching regulator for controlling an output voltage by a semiconductor switch for absorbing a recovery current of the rectifying diode in series with one end of the rectifying diode. A saturable reactor is connected, and a CR snubber circuit for absorbing a recovery current passing through the saturable reactor is connected in parallel to a series circuit of the rectifying diode and the saturable reactor. In such a noise absorbing circuit according to the present invention, the combined use of the saturable reactor and the CR snubber circuit only improves the noise absorbing effect as compared with the case where the saturable reactor and the CR snubber circuit are used alone. Instead, only the current flowing through the diode flows through the saturable reactor, and the charging current of the capacitor in the CR snubber circuit does not flow. Therefore, unnecessary energy is not accumulated in the saturable reactor. Therefore, there is an advantage that a side effect due to the stored energy of the saturable reactor, for example, a reduction in efficiency in the switching regulator can be suppressed to the same level as when the saturable reactor is used alone. FIG. 1 is a circuit diagram of a noise absorbing circuit according to an embodiment of the present invention. A saturable reactor L is connected in series with a diode D as a noise generating element. A CR snubber circuit, that is, a series circuit of a capacitor C and a resistor R is connected in parallel with the series circuit of the diode D and the saturable reactor L. The noise absorbing circuit of this embodiment is for absorbing a noise based on a recovery current of the diode D (a reverse current transiently flowing when the diode D transitions from the on state to the off state). . That is, a part of the recovery current of the diode D is absorbed by the saturable reactor L, and the recovery current component that has passed through the saturable reactor L flows into the CR snubber circuit and is absorbed. On the other hand, when the diode D is on, a current flows through the diode D through the saturable reactor L. Immediately after the diode D is turned on, CR
Although a current also flows through the snubber circuit, this current, that is, the charging current of the capacitor C does not flow through the saturable reactor L. That is, the energy stored in the saturable reactor L is only the current flowing through the diode D, and is smaller than that in the case of FIG. Therefore, when the diode D is a component of the switching regulator as described later, there is an effect that an increase in loss due to the saturable reactor L is suppressed. FIG. 2 shows an example in which the present invention is applied to a step-down chopper type switching regulator. As shown in the figure, a collector of a transistor 2 as a switching element is connected to an input DC power supply 1, and an emitter of the transistor 2 is connected to one end of an inductor 3. Inductor 3
Are connected to a smoothing capacitor 4 and a load 5. A commutation diode 6 is connected in parallel with the series circuit of the inductor 3 and the smoothing capacitor 4. The basic operation of the switching regulator of this type is well known. That is, a high-frequency switching pulse is applied to the base of the transistor 2 to turn the transistor 2 on and off. While the transistor 2 is in the ON state, power is supplied from the power supply 1 to the load 5 via the transistor 2 and the inductor 3.
When the transistor 2 is turned off, the energy stored in the inductor 3 is transferred to the load 5 and the commutating diode 6.
Is released via By repeating this operation, a stable DC power at a lower voltage than the power supply 1 is supplied to the load 5. In this embodiment, when the transistor 2 changes from the off state to the on state, a recovery current flows through the commutation diode 6, and this appears as noise on the output side (the load 5 side). To prevent this, a saturable reactor, a resistor R, and a capacitor C that constitute a noise absorbing circuit are provided. FIG. 3 is a waveform diagram of each part of the circuit of FIG. 2. V _CE is the collector-emitter voltage of the transistor 2, I _C is the collector current of the transistor 2, _ID is the power supply of the commutation diode 6, _VL indicates the waveform of the voltage between both ends of the noise absorbing saturable reactor L, respectively. Further, T _on and T _off indicate an on period and an off period of the transistor 2, respectively. When the transistor 2 is turned on, a recovery current tends to flow as indicated by broken lines in the waveforms I _D and I _C , but is absorbed by the saturable reactor L and the CR snubber circuit including the resistor R and the capacitor C. Is done. In this case, at both ends of the saturable reactor L pulse P ₁ of the positive polarity is generated. Meanwhile, the transistor 2 is for current starts to flow through the commutation diode 6 becomes off, at both ends of the saturable reactor L is pulse P ₂ having a negative polarity appears. Because the negative pulse P ₂ across the saturable reactor L is applied through the diode 6 to the emitter of the transistor 2, the rising waveform of the collector-emitter voltage V _CE of the transistor 2, corresponding to the negative pulse P ₂ pulse P ₃ of the positive polarity appears. This P ₃ occurs during the rise of V _CE , that is, during the transition period when the transistor 2 changes from the on state to the off state. During this period, the collector current I _C of the transistor 2 is not completely zero. The product of V _CE · I _C becomes the collector loss of transistor 2. Here, when a noise absorbing circuit having a configuration as shown in FIG. 5 is added to the commutation diode 6, energy for charging the capacitor C in the saturable reactor L is also accumulated as described above. The positive pulse P ₁ and the negative pulse P ₂ appearing in the voltage V _L across the saturable reactor L increase as shown by the oblique lines, and the positive pulse P ₃ appearing in the rising waveform of V _CE also increases. Therefore, the collector loss of the transistor 2 in the above period also increases. On the other hand, when a noise absorbing circuit based on the present invention is added to the commutation diode 6 as shown in FIG. 2, the voltage V across the saturable reactor L
_{Since the} positive pulse P ₁ and the negative pulse P ₂ appearing in _L are relatively small, and the positive pulse P ₃ appearing in the rising waveform of V _CE is also small, the collector loss of the transistor 2 is used and only the saturable reactor L is used for the noise absorbing element. Can be reduced to the same extent as when the FIG. 4 shows an embodiment in which the present invention is applied to a forward type switching regulator (also referred to as an on-on type). The output voltage of the input DC power supply 11 is converted to a high frequency by a high frequency inverter including a transistor 12 and a transformer 13, and then converted to a load 1 via a rectifying diode 14, an inductor 15 and a smoothing capacitor 16.
7 is supplied. Also, as in FIG.
A commutation diode 18 is connected in parallel to a series circuit including the capacitor and the smoothing capacitor 16. In the case of this embodiment, the rectifying diode 1
A noise absorbing circuit composed of a saturable reactor L and a CR snubber circuit having the same configuration as that of FIG. When the noise absorbing circuit is not added to the diodes 14 and 18 in FIG. 4 as shown in FIG. 5A (A), only the CR snubber circuit is added as shown in FIG. 5B. (B), when a CR snubber circuit and a saturable reactor L are added as shown in FIG. 5C (C), and as shown in FIG. 4 (FIG. 1). FIG. 6 shows the results of actually measuring the change in output noise with respect to the output voltage (current flowing into the load 17) for each of the cases (D) where the reactor L is added. From these results, it can be seen that the noise absorbing circuit of the switching regulator according to the present invention has a high noise absorbing effect. When the power supply efficiency was measured, it was 71.6% in the case of A and 69.4% in the case of B.
%, 67.1% for C and 69.4% for D according to the invention. In the present invention, it is preferable to use the commutation diode shown in each of the above-mentioned embodiments, in order to obtain the effect remarkably. As described above, according to the present invention, the noise based on the recovery current of the commutating diode in the switching regulator or the rectifying diode in the switching regulator in which the output voltage is controlled by the semiconductor switch is reduced by the CR snubber. Since the circuit and the saturable reactor can be effectively absorbed by the combined use of the circuit and unnecessary energy is not accumulated in the saturable reactor, the power supply efficiency of the switching regulator can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a noise absorbing circuit according to one embodiment of the present invention. FIG. 2 is a circuit diagram showing an embodiment in which the present invention is applied to a step-down chopper type switching regulator. FIG. 3 is a waveform chart for explaining the operation of the circuit of FIG. 2; FIG. 4 is a diagram showing an embodiment in which the present invention is applied to a forward switching regulator. FIGS. 5A to 5C are circuit diagrams (comparative examples) used for comparison with a noise absorbing circuit according to the present invention. FIG. 6 is a diagram showing a result of actually measuring a change in output noise with respect to an output current for the noise absorbing circuit according to the present invention and each circuit of FIG. 5; [Description of Signs] L: Saturable reactor R, C: Resistance and capacitor in CR snubber circuit D: Diode (noise generating element) 1, 11: Input DC power supply 2, 12 ... Transistor 3, 15 ... Inductor 4, 16 ... Smoothing capacitors 5, 17 ... Loads 6, 18 ... Commutation diodes 14 ... Rectifier diodes

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-55-147982 (JP, A) JP-A-55-133671 (JP, A) Jiko 47-19534 (JP, Y1) Shotaro Suzuki “SW regulator Key to Noise Resolution, Transistor Technology, March 1982, p. p. 13-14 (Fig. 3-10) MOTOROLA Inc. "Voltage Regulator Handbook", translated by Kazuo Kiyoshi, February 1, 1978, CQ Publishing Co., Ltd. (Figs. 12 and 13) "2nd Study of Switching Regulators, Problems of Switching Regulators and Their Countermeasures" Seminar July 1975 (Figure 16) (58) Fields surveyed (Int. Cl. ⁶ , DB name) H02M 3/00-3/44

Claims (1)

(57) [Claims] A series circuit in which a commutating diode and a saturable reactor are connected in series, and a CR connected in parallel to the series circuit.
A switching regulator comprising a noise absorbing circuit comprising a snubber circuit. 2. A rectifier diode and a series circuit including a saturable reactor connected in series to one end of the rectifier diode; and a noise absorbing circuit including a CR snubber circuit connected in parallel to the series circuit. Switching regulator characterized. 3. A switching regulator comprising the noise absorption circuit according to claim 1.