JPS6237064A - Recovery circuit for snubber energy - Google Patents

Abstract

PURPOSE:To reduce loss in a snubber circuit by connecting a regenerative transformer on the primary side of a main transformer for a two-stone type DC-DC converter. CONSTITUTION:With a two-stone type ringing choke type DC-DC converter, series bodies of capacitors 9, 9a and diodes 10, 10a are connected in parallel a snubber circuits for switching elements 2, 2a for the converter, and the capacitor sides of each snubber circuit are connected to a power supply 1. The primary side of a regenerative transformer 12 for snubber energy is juxtaposed on the primary side of a main transformer 6 for the converter, and secondary and tertiary side windings for the regenerative transformer 12 are connected through diodes 13, 13a among nodes among the capacitors 9, 9a and the diodes 10, 10a and the power supply 1. Accordingly, the energy of the inductance of wirings is absorbed to the snubber capacitor 9, and the energy is recovered to the power supply 1 through the regenerative transformer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a circuit for reducing switching loss of a DC-DC converter using semiconductor switches.

[Prior art and its problems]

Conventionally, semiconductor switches have been designed to reduce the loss liability that occurs when the switch is turned off and to be able to turn off safely.
A snubber circuit using capacitors, resistors, diodes, etc. is added. The function of the snubber circuit 8 is to alleviate the surge voltage generated by the energy accumulated in the leakage inductance of wiring etc. when the switching element turns off, and also to take over some of the loss that would otherwise occur inside the element. be. As a result, the energy once absorbed by the snubber circuit, such as the energy of leakage inductance, was generally consumed by the resistor.

In recent years, with advances in semiconductor technology, the capacity of switching elements has increased, and switching losses occurring in unit switch sections have also tended to increase. Switching operations are also trending toward higher frequencies, which increases losses. In addition, there is a growing demand for devices to be smaller and lighter.

In addition to the development of elements with low switching loss, the development of techniques for recovering energy absorbed by snubber circuits is an important issue in order to make converter devices smaller, lighter, and more efficient.

FIG. 4 shows a circuit example of a ringing chime type DO-DC converter. In this circuit, two switching elements 2.2a are used to recover the energy accumulated in the leakage inductance of the transformer 6 to the power supply side 1, and a diode 3.2a is connected to the connection point between each element and the transformer. 3
It is connected to the power supply via a. In addition, transistors are used as switching elements, and the operation of each element is the same, so for simplicity, the leakage inductance is
Leakage inductance on the primary and secondary sides of the transformer is 11, l!
It is believed that there is a power supply in series with the switching element 2.2a.

This converter stores energy in a transformer 6 having an inductance by turning on the switching element 2.2a, and by turning off the switching element 2.2a, this energy is transferred to the smoothing capacitor 8 via the rectifier diode 7. The output voltage can be adjusted over a wide range by controlling the ON width of the switching element 2.2a.

Next, the surge voltage and loss that occur when the switching element 2.2a is turned off will be explained based on FIG. 5, which shows voltage and current waveforms for each operation mode. In mode 1, switching element 2.2a is turned on, power supply voltage E is applied to the primary side of transformer 6, and energy is stored in transformer 6. Mode 2 is a state in which the switching element 2.2a is turned off and current is cut off due to the characteristics of the switch. At this time, the energy stored in the leakage inductance of the transformer 6 is transferred to the power source via the diode 8a, that is, D
1-1@: Source-D Collected via route 2. Therefore, the voltage across the switching element 8 is 1t et = E + l'', and the power supply voltage and the leakage inductance in series with the switch decrease the current of the switch. A surge voltage generated by the rate dt is added to the applied voltage.During this period, a loss of the switching element occurs and increases in proportion to the switching frequency F.

Furthermore, in mode 3, similar to mode 2, the energy stored in the leakage inductance of the transformer is continuously recovered to the power supply. il
lE-Hv.

■0 is the voltage of capacitor 8) It continues for a time determined by . At time ts at the end of mode 8, the current on the primary side becomes completely zero. On the other hand, on the secondary side,
From the point in time in mode 2, the primary current starts to increase as the primary current decreases, and as mode 3 ends, the current is completely shifted, and in mode 4, the current is supplied to the smoothing capacitor.

As described above, a surge voltage is generated in the switching element 8 when shutting off, and depending on the value of l t 1a , the voltage may exceed an allowable voltage.

A snubber circuit is generally added for the purpose of reducing loss and surge voltage that occur when these switching elements 8.8a are shut off.

FIG. 6 shows an example of a snubber circuit using a capacitor 9, a diode 10, and a resistor 11. In this snubber circuit, the energy accumulated in the leakage inductance is absorbed by the snubber capacitor 9, and the maximum voltage of the switch is determined by . The pressure can be suppressed to below the breakdown voltage. However, in this snubber circuit, the absorbed energy is consumed by the resistor, so P=”0(E2+I?−’f
i) F=(10E cases 11!I) F(W)2
A loss of C22 occurs. As can be seen from this equation, in addition to the energy 2ltI possessed by the leakage inductance, the energy required to charge up to the power supply voltage is also included, resulting in a large amount of energy consumption. When the allowable withstand voltage of the element is low or in a circuit where the wiring inductance cannot be reduced, the value of the snubber capacitor becomes large, so the resistance loss increases,
It can be seen that there is a limit to increasing the switching frequency.

[Purpose of the invention]

An object of the present invention is to provide a snubber energy absorption circuit that can efficiently recover the energy consumed by the snubber circuit and form a highly efficient, compact, and lightweight C-DC converter.

[Key points of the invention]

This invention relates to a DC-DC converter device consisting of two switching elements and a transformer, in which a snubber circuit in which a diode and a capacitor are connected in series is connected to each of the switching elements with the capacitor on the power supply side, and one of the transformers is The next side is connected to the primary side of the regenerative transformer, and one end of the secondary winding and the eighth winding of this regenerative transformer are respectively connected to the connection point of the diode and capacitor of the snubber circuit, and the other 1J through the diode at the end! By connecting each to the L source side, surge voltage caused by energy accumulated in the wiring inductance is suppressed, and when the switching element is turned on, the energy accumulated in the snubber capacitor is transferred to the 1tti side using a regenerative transformer. It is designed so that it can be regenerated.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, which shows the above-mentioned two-stone ringing choke type DC-DO converter. In the figures, the same reference numerals as in FIGS. 4 and 6 indicate the same members.

As a snubber circuit for the switch, a capacitor 9.9a and a diode 10.10a connected in series are connected in parallel, and the capacitor side of each snubber circuit is connected to the power supply. Then, the primary side of the snubber energy recovery transformer is connected in parallel to the primary side of the main transformer 6 of the converter, and one end of the secondary and 8th windings of the recovery transformer 12 is connected in parallel to the primary side of the main transformer 6 of the converter. Connect to the connection point of the capacitor and diode of the snubber circuit, and connect the other end to the diode 1B, 18 &
It is connected to the power supply via.

FIG. 2 shows voltage and current waveforms for explaining the operation of this circuit. When the switching element 2 is turned off, the energy of the inductance of the wiring is absorbed by the snubber capacitor 9 similarly to the circuit shown in FIG. 6, and a voltage of yo=E+Il/fTj- is applied to the switching element 2.

At this time, the switching element 2 is in the off state and the diode 18 is E+'';; -(E+xt, /''@)='5-xt, /
l＞.

If so, this voltage becomes a reverse voltage, and the diode 13 is turned off.

Next, when the switching element 2 is turned on, the voltage of the secondary and tertiary windings of the regenerative transformer becomes er = -, so h A (E + IIX = A IIK <
0 Since the voltage expressed by the above equation becomes the forward voltage of the diode 18, the diode 8 immediately becomes conductive, and the energy stored in the snubber capacitor 9 is t! I
t source 1 → diode 18 → 8th winding of regenerative transformer 12 →
It is collected in the path of capacitor 9 to the tlt source.

In particular, Figure 3 is an equivalent representation of only the circuit of the regenerative section, and the sum of the leakage inductance of the regenerative transformer and the wiring inductance of the regenerative circuit! It is expressed as The voltage equation during regeneration is E-er = An Sl cdt +
l at At the start of regeneration, as shown in Fig. 1.2 and above, maC=bar51odt=B-1-fis#, io=
0, the voltage and current of the capacitor are expressed by the following equations.

vo=,g-er-)(er+IsJ)za+tic
= −J(er+itI)&ω, ω= ,H,
er = ゑ Therefore, if va = Q at the time of ωt = π, the capacitor voltage becomes zero and all the energy can be recovered.

Therefore, it is sufficient to set er=M>""r. 1JTa depends on the current at turn-off, and in the worst case, in order to enable regeneration even when there is no load, it is sufficient to select a turns ratio of nl<2, with 1=0.

As mentioned above, in 2 method D (3-DC converter,
By connecting a regenerative transformer to the primary side of the main transformer, the energy accumulated in the snubber circuit is recovered, reducing losses in the snubber circuit and realizing a highly efficient DC-DC converter. can do.

In the explanation so far, the ringing chiller type has been described as the DC-DC converter type, but the forward converter type can also be applied in exactly the same way if it is configured with a two-stone type. Furthermore, although a transistor is used as a switch element, it is a matter of course that the same principle can be applied to other switch elements.

〔Effect of the invention〕

According to this invention, in a DC-DC converter consisting of two switching elements and a transformer, a regenerative transformer is connected in parallel to the primary side of the transformer, and the secondary and eighth windings of the regenerative transformer are connected in parallel. By connecting one end to the connection point between the diode and capacitor of the snubber circuit, and connecting the other end to the LLC source side via the diode, it is possible to suppress the surge voltage caused by the energy accumulated in the wiring inductance, and When the switching element is turned on, the energy stored in the snubber capacitor can be regenerated to the power supply side through the regenerative transformer.

As a result, it is possible to reduce the loss within the snubber circuit and the loss of the switching element, and the DC-
The DC3 converter device can be made highly efficient, compact, and lightweight.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a voltage and current waveform diagram for explaining the invention in detail, Fig. 8 is an equivalent circuit diagram of the regeneration circuit of the invention, and Fig. 4 is the conventional D
A circuit diagram showing a C-DC converter device, FIG. 5 is a voltage and current waveform diagram for explaining the conventional device, and FIG. 6 is a conventional snubber circuit. 1... DC power supply, 2.2a... switching element,
8.8a17...Diode, 6...Transformer, 9.
9a...Capacitor, 10.10a...Snubber diode, 12...Regenerative transformer, l! ...Leakage inductance.
-7゜ｑPerson Patent Attorney, L Mouth Figure 1 Figure 4

Claims (1)

[Claims] 1) In a DC-DC converter device configured to obtain DC power by consisting of two switching elements, a transformer, and a rectifier circuit, a snubber circuit in which a diode and a capacitor are connected in series in parallel with each of the switching elements is connected to the capacitor. Connect it to the power supply side, and connect it to 1 of the transformer.
Connect the primary side of the regenerative transformer to the next side, connect one end of the secondary winding and the tertiary winding of this regenerative transformer to the connection point of the diode and capacitor of the snubber circuit, and connect the other end to the connection point of the diode and capacitor of the snubber circuit. A snubber energy recovery circuit connected to the power supply side through a diode.