JPS6225877A - Snubber circuit - Google Patents

Abstract

PURPOSE:To recover energy stored in a leakage inductance for a transformer efficiently by connecting a series circuit of a capacitor and a primary winding of the transformer in parallel with a switching element and connecting a rectifying circuit to a secondary winding of the transformer. CONSTITUTION:Voltage induced in a secondary winding for a transformer 4 by the ON-OFF of a switching transistor 3 is rectified and smoothed by diodes 5, 6, a choke coil 7 and a capacitor 8, and fed to load 9. A series circuit of a primary winding for the transformer 4 and a capacitor 11 is connected in parallel with the switching transistor 3. The charging and discharging energy of the capacitor 11 are fed back to the capacitor 8 on the main body side through rectifiers 12, 13.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a snubber circuit, and in particular suppresses spike-like overvoltage that occurs when a switching element turns off, protects the switching element from destruction, and suppresses the overvoltage. This invention relates to a snubber circuit that can efficiently recover generated energy.

[Summary of the invention]

The present invention suppresses spike voltages generated when switching elements turn off in DC-DC converters, switching regulators, etc. with low loss.
By connecting the primary winding and capacitor of the transformer in parallel to the switching element, and connecting a rectifier to the secondary winding, the energy charged and discharged in the capacitor is returned to the DC circuit of the converter main body. The aim is to reduce loss and improve the efficiency of the converter.

[Prior art]

Traditionally, in telephone offices, DC-DC converters are
It is used as +150V power supply for anode, +50V power supply for frequency meter registration, -21V power supply for transportation, etc. These power supply devices convert 48 V DC into AC using a parallel inverter with a conversion frequency of 400 Hz, control the voltage on the secondary side of the transformer, rectify it, and smooth it to convert it into the necessary DC voltage. In recent years, switching regulators have come into use due to the demand for smaller size, higher conversion efficiency, and less electrical noise. That is, DC-D
In a C conversion device, a switching element such as a transistor is used to first convert a DC voltage into a square wave AC voltage, the input and output are isolated using a transformer, and the voltage is stepped up or down to the required voltage value to convert the square wave AC voltage. A method of rectifying and smoothing to obtain DC voltage again is generally adopted.

In this method, by increasing the conversion frequency when converting DC voltage to AC voltage, the transformer and choke capacitor in the smoothing circuit can be made smaller and lighter. It is necessary to increase the switching speed and reduce switching loss. In DC-DC converters, when the switching speed is increased, a spike voltage is generated when the switching element turns off due to the leakage inductance of the transformer, which can destroy the switching element or cause noise generation. Become.

For this reason, a method has been proposed in which a snubber circuit consisting of a capacitor, a resistor, and a diode is connected in parallel to the switching element to suppress the spike voltage when the switching element is turned off.

FIG. 2 is a block diagram of a conventionally proposed snubber circuit.

As shown in FIG. 2, a circuit in which a capacitor 17 is connected in series to a parallel circuit of a diode 16 and a resistor 15 is connected in parallel to the switching element 14.

In this snubber circuit, when the switching element 14 is turned off, the energy stored in the transformer leakage inductance is transferred to the capacitor 17 through the diode 16. If the capacitor 17 has a capacity that can absorb this energy.

No spike voltage occurs. This energy is transferred to the capacitor 17 until the switching element 14 is turned on.
is retained. When the switching element 14 is turned on, this energy is consumed by the resistor 15.

[Problem that the invention seeks to solve]

In this way, in a conventional DC-DC converter connected to a snubber circuit, the energy stored in the leakage inductance of the transformer is consumed in the resistor 15 each time switching occurs, so as the number of switching increases, the resistor 15 increases.
consumption increases.

This causes a decrease in the efficiency of the DC-DC converter. Further, in this case, the resistor 15 is increased in size, and the resistor 15 is
There is a problem in that the space required to radiate heat increases.

An object of the present invention is to solve such conventional problems and provide a simple snubber circuit that suppresses the spike voltage generated when a switching element is turned off with low loss.

[Means for solving problems]

In order to achieve the above object, the snubber circuit of the present invention provides a conversion device that includes an input DC power source, a switching element that converts DC to AC, and means for rectifying and smoothing the converted AC and supplying it to a load. A series circuit of a primary winding of a transformer and a capacitor is connected in parallel to the switching element, and a rectifier circuit is connected to the secondary winding of the transformer, so that when the switching element is turned on and turned off, the The feature is that the charging and discharging energy of the capacitor is fed back to the DC circuit.

[For production]

In the present invention, by connecting a series circuit of a capacitor and the primary winding of a transformer to the switching element and connecting a rectifier circuit to the secondary winding of this transformer, the spike voltage accumulated in the leakage inductance of the transformer is reduced. Efficiently recover the energy generated.

【Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a DC-DC converter connected to a snubber circuit showing one embodiment of the present invention.

In Figure 1, 1 is a DC source, 2 is a clamp diode, 3 is a switching transistor, 4 is a transformer, and 5
is a rectifier diode, 6 is a freewheel diode, 7 is a choke coil, 8 is a capacitor, 9 is a load, 10 is a snubber transformer, 11 is a snubber capacitor, 12.1
3 is a snubber diode.

Now, when a positive signal is applied to the base of the switching transistor 3, the switching transistor 3 is turned on and the DC power supply (voltage E) is applied to the primary winding n11 of the transformer 4.
) is applied. Secondary winding n12 of transformer 4
A voltage nl·E/n1 is generated, and this voltage is rectified by the rectifier diode 5, smoothed by the choke coil 7 and the capacitor 8, and power is supplied to the load 9.

On the other hand, the tertiary winding n13 of the transformer 4 has n3・E/
Since a voltage of n 1 is generated, E + n 3 ・E / n 1 is applied as a reverse voltage to the clamp diode 2.0 Next, when a negative signal is applied to the base of the switching transistor 3, the switching transistor 3 turns off quickly. At this time, the energy stored in the leakage inductance of the transformer 4 is transferred to the capacitor 8 by the transformer 10 and diode 12 of the snubber circuit. After the switching transistor 3 is turned off, a voltage with a polarity opposite to the voltage when the switching transistor 3 is on is generated in each winding of the transformer 4 due to excitation energy. Therefore, the clamp diode 2 turns on, and the tertiary winding n1 of the transformer 4
The excitation energy is fed back to the DC power supply 1 while clamping the voltage of 3 to the power supply voltage E. The winding n11 has nl
・A voltage of E/n 3 is applied. Therefore, the snubber capacitor 11 is charged to E+n1·E/n3. In addition, the spring winding wire n11 of the transformer 4. n12
The number of turns of tn13.

respectively as "lt" 2 e n 3).

On the other hand, the rectifier diode 5 is turned off, the freewheel diode 6 is turned on, and when the excitation energy of the transformer 4, which causes the current in the choke coil 7 to flow continuously, disappears, the voltage of each winding of the transformer 4 becomes zero. Therefore, the voltage applied to the switching transistor 3 and the snubber capacitor 11 becomes the power supply voltage E, and when a positive signal is applied to the base of the switching transistor 3 again, the switching transistor 3 is turned on. At this time, the energy of the snubber capacitor 11 is transferred to the snubber transformer 10. It is transferred to the capacitor 8 by the snubber diode 13. As is clear from this result, compared to the conventional snubber circuit shown in Figure 2, the loss in the snubber circuit can be reduced because the charge stored in the capacitor does not have to be consumed by the resistor and is all charged in the capacitor 8. Then,
The efficiency of the DC-DC converter can be improved. For example, DC voltage 200V, output voltage 40V, conversion frequency 100KH
In the Z DC-DC converter, when the output current is 7A, the efficiency of the DC-DC converter is 90.7 with a conventional snubber circuit consisting of a resistor, capacitor, and diode.
%, whereas when the snubber circuit of the present invention was used in the same DC-DC converter, the efficiency was 92.0%, reducing the loss by about 4.4 W.

In this embodiment, the charging and discharging energy of the capacitor 11 in the snubber circuit is fed back to the capacitor 8 on the main body side via the rectifier 12. Anywhere is fine. For example, it may be fed back to both ends of the input DC power supply 1 in FIG. 1, or it may be fed back to the DC portion of the control circuit connected to the base of the switching element 3, although not shown. Further, in this embodiment, a case has been described in which the snubber circuit of the present invention is applied to a DC-DC converter, but it goes without saying that it can also be applied to other switching regulators, DC-AC converters, and the like.

〔Effect of the invention〕

As explained above, according to the present invention, there is no loss due to resistance in the snubber circuit, and the spike voltage generated when the switching element is turned off can be suppressed with low loss. It is possible to improve the efficiency of the DC conversion device, and as a result, there is an advantage that the conversion device can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a DC-DC converter connected to a snubber circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional snubber circuit. 1: DC power supply, 2: Clamp diode, 3 Niswitching transistor, 4 Nidorance, 5: Rectifier diode, 6: Freewheel diode, 7: Choke coil,
8: Capacitor, 9: Load, 10: Snubber transformer,
11: Capacitor for snubber, 12.13 Diode for Nisnano (Fig. 1, Fig. 2)

Claims (1)

[Claims] (1) In a conversion device that includes an input DC power source, a switching element that converts DC to AC, and a means for rectifying and smoothing the converted AC and supplying it to a load, the switching element is connected to the primary of a transformer. A series circuit of a winding and a capacitor is connected in parallel, and a rectifier circuit is connected to the secondary winding of the transformer, so that charging and discharging energy of the capacitor is fed back to the DC circuit when the switching element is turned on and turned off. A snubber circuit characterized by: