JP2780165B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter suitable for obtaining a high output voltage and a large output power.

[0002]

2. Description of the Related Art In recent years, as the applications of lamps that are lit by high voltage and high power have expanded, the development of DC-DC converters for stably illuminating such lamps has been urgently required. When an output voltage higher than the input voltage is to be obtained, in the conventional forward DC-DC converter, the ratio of the number of turns of the secondary winding to the primary winding of the switching transformer becomes high. Also, the secondary winding from which a high voltage can be obtained is
From the standpoint of withstand voltage, it cannot be wound together in a narrow position.

Accordingly, the secondary winding is distributed and wound over a wide area of the core, so that the magnetic coupling between the secondary winding and the primary winding is weakened. There is a technical problem due to the leakage inductance generated. For the later technical problem, the conventional forward formula D
This will be described with reference to FIG. 3 showing a circuit diagram of a C-DC converter.

[0004] In Figure 3, the primary winding L ₁ of the transformer T _1,
A switching transistor Q ₁ and a DC source E ₁ are connected in series, and a rectifying and smoothing circuit including a rectifying diode D ₁ , a flywheel diode D ₂ , a choke coil L ₃ and a smoothing capacitor C ₁ is connected to the secondary winding L _2. ing. In such a DC-DC converter, 20 turns the number of turns of the primary winding L _1, 200 turn secondary winding turns of L _2,
The case where the output voltage of 1400 V is obtained between the output terminals 1 and 2 when the voltage of the DC source E ₁ is 280 V will be described as an example.

[0005] The output voltage of the 1400V controls the Deyutei ratio of the transistor Q ₁ by the control circuit (1)
Obtained by the formula. In 1400 = 280 · (200/20) · T ON / (T ON + T OFF) (1) (1) formula, T _ON is the on-time of the transistor Q _1, T _OFF is the off time. Figure 5 is a voltage waveform diagram at the node A1 of the diode D ₂ and the coil L ₃ of the rectifying smoothing circuit, the rising portion of the instantaneous waveform transistor Q ₁ is turned on, i.e. waveform is accompanied by significant ringing.

Since the highest peak value V _R of the ringing portion may reach 2000 V, the diode D ₂ and the transformer T ₁ exceed the breakdown voltage limit and are likely to be damaged. FIG. 5 shows a case where the duty ratio is 50%. Due to such technical problems and the heat generated by the transformer due to the leakage magnetic flux, it has been difficult to obtain a high-voltage and large-power output with a forward DC-DC converter.

To obtain an output voltage higher than the input voltage, a flyback type DC-DC converter is often used. However, since the output is limited by the volume of the core, a gap is provided in the core to obtain a large output. A method of equivalently increasing the volume of the core is used. However, in this method, the amount of heat generated in the winding increases due to an increase in magnetic flux leaking from the gap, and a DC-DC converter that obtains a high voltage and a large output cannot be configured by a flyback method.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a forward type DC which can reduce the heat generation of a transformer and reduce the peak value of ringing to obtain a high voltage and high power output.
-To obtain a DC converter.

[0009]

SUMMARY OF THE INVENTION The inventor has 4 is an equivalent circuit diagram of FIG. 3 showing a conventional Fuowado type DC-DC converter, the stray capacitance parasitic to diode D ₂ C
When the capacitance value of _F C _F, the inductance value of Li Cage inductance L ₄ parasitic on the transformer T ₁ and the L _4, the peak value V _R of the ringing proportional to the value of (L ₄ / C _F) ^1/2 I focused on doing. Also, 2 for the primary winding
The present invention has been achieved by paying attention to the fact that the secondary winding can be wound in a well-coupled state with the primary winding by lowering the turn ratio of the secondary winding to lower the generated voltage of the secondary winding. .

According to the present invention, the primary windings of a plurality of switching transformers are connected in parallel to form a series circuit for driving the transformers with the primary windings connected in parallel, switching transistors, and a DC source. A rectifying / smoothing circuit is connected to each of the secondary windings, and the rectifying / smoothing circuits are connected to each other so that outputs thereof are obtained in series.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of a forward DC-DC converter according to the present invention. The same parts as those in FIG. 3 are denoted by the same reference numerals. The DC-DC converter of FIG. 1 has two switching transformers T ₂ and T ₃ , and the primary windings L ₂₁ and L ₃₁ are connected in parallel. The primary windings L ₂₁ and L ₃₁ connected in parallel are connected to the switching transistor Q ₁ ,
DC source are E ₁ and connected in series. Reference numeral 5 denotes a terminal to which a control circuit (not shown) is connected.

[0012] secondary winding L ₂₂ is the rectifier diode D ₃ of the transformer T _2, the flywheel diode D _4, a choke coil L _5, connected to the rectifying and smoothing circuit comprising a smoothing capacitor C _2. Further, the secondary winding L ₃₂ of the transformer T ₃ is connected to the rectifier diode D _5, the flywheel diode D _6, a choke coil L _6, a smoothing capacitor C ₃ rectifying and smoothing circuit.

The two rectifying / smoothing circuits are connected so that outputs can be obtained in series.
This is the output terminal of the converter. D configured in this way
In order to obtain the same output voltage as in FIG. 3 by C-DC converter, the number of turns of the secondary winding L ₂₂ and the secondary winding L ₃₂ is 2
It may be a half of the winding L _2. Thus, secondary winding L ₂₂
Turns ratio winding L _21, 1 of the secondary winding L ₃₂ winding L
Turns ratio _31, the primary winding L of the secondary winding L ₂ of FIG. 3
Since the turn ratio to ₁ can be made half, the generated voltage of the secondary winding decreases, and the consideration of the withstand voltage of the secondary winding may be eased. Since the secondary winding can be wound together in a narrow position, the magnetic coupling between the primary winding and the secondary winding can be strengthened.

The overall leakage inductance of the transformers T ₂ and T ₃ can be made much smaller than in the case of FIG. To obtain an output voltage of 1400V in the same manner as in FIG. 3, the output voltage of one of the rectifying and smoothing circuit is obtained by (2) by controlling the duty ratio of the transistor Q _1. 700 = 280 · (100/20) · T _ON / (T _ON + T _OFF ) (2) Then, an output voltage of 1400 V is obtained by connecting the outputs of the rectifying / smoothing circuit in series. However, the number of turns of the secondary winding L _22, L ₃₂ in formula (2) since the half of the secondary winding L ₂ of FIG. 3, a respective 100 turns.

[0015] Figure 2 is a voltage waveform diagram of a rectifier junction point A2 of the smoothing circuit of the flywheel diode D ₄ and choke coil L _5, the flywheel diode D _6, a connection point A3 of the choke coil L _6. Both waveform diagrams are the same,
The duty ratio shows a case of 50%. The inductance value corresponding to Lee Keiji inductance L ₄ in FIG. 4 becomes small, the highest peak value V of the ringing portion
_{R is} also very small. Of course, the heat generation of the transformer is also reduced.

In the embodiment, the one-stone type forward converter has been described, but the half-bridge type, the full-bridge type,
Further, it is clear that the present invention can be applied to an irregular forward converter in which switching transistors are connected to both ends of a switching transformer. Even if there are a plurality of switching transistors, all the switching transistors are forward type converters connected to drive a transformer by forming a series circuit with a DC source and primary windings of a plurality of transformers connected in parallel. Applicable to

[0017]

As described above, the forward type DC-DC converter of the present invention has a plurality of switching transformers, the primary windings of which are connected in parallel, the primary windings connected in parallel, and the switching. A series circuit is composed of a transistor and a DC source. Further, the output of the rectifying / smoothing circuit connected to the secondary winding is obtained in series. The turns ratio of the secondary winding to the primary winding of each transformer can be reduced, and the difference in the number of turns between the primary winding and the secondary winding can be reduced.

Even when a high voltage and high power output is obtained, the leakage inductance can be reduced and the peak value of the ringing portion of the voltage waveform in the rectifying and smoothing circuit can be reduced. Therefore, the breakdown of the flywheel diode and the transformer is less likely to occur, and the heat generated by the eddy current caused by the leakage magnetic flux is also reduced. These are indispensable effects for the configuration of the DC-DC converter that obtains high voltage and large power at the output, and greatly contribute to its practical use.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a forward DC-DC converter according to the present invention.

FIG. 2 is a voltage waveform diagram of FIG.

FIG. 3 is a circuit diagram of a conventional forward DC-DC converter.

FIG. 4 is an equivalent circuit diagram of FIG.

FIG. 5 is a voltage waveform diagram of FIG.

[Explanation of symbols]

T ₂ switching transformer T ₃ switching transformer L ₂₁ 1 primary winding L ₃₁ 1 winding Q ₁ switching transistor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-82213 (JP, A) JP-A-60-39367 (JP, A) JP-A-2-228257 (JP, A) JP-A-3-22813 60370 (JP, A) Japanese Utility Model 63-63094 (JP, U) Japanese Utility Model 63-29389 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02M 3/00-3 / 44

Claims (1)

(57) [Claims] A primary circuit of a plurality of switching transformers is connected in parallel, and a series circuit for driving the transformer by the primary winding, a switching transistor, and a DC source connected in parallel is formed. A forward type DC-DC converter, wherein a rectifying / smoothing circuit is connected to each of the secondary windings, and the rectifying / smoothing circuits are connected to each other so that outputs thereof are obtained in series.