JPS6232702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit comprising a full bridge DC-DC converter circuit suitable for large current output.

Conventionally, this type of power supply circuit is configured as shown in FIG. That is, the positive and negative power supplies are connected to input terminals 1 and 2, and a series connection circuit of transistors Q ₁ and Q ₂ , which are first and second switching elements that are turned on and off in a complementary manner by a control signal, and a similar switching element are used. A series connection circuit of transistors Q ₃ and Q ₄ is connected between the positive and negative power supplies. A capacitor _C1 is connected between input terminals 1 and 2 if necessary. Then, a series connection circuit between the capacitor C ₂ and the primary winding P of the power conversion transformer T is connected to the series connection point between the emitter of the transistor Q ₁ and the collector of the transistor Q ₂ , and the emitter of the transistor Q ₃ and the transistor Q ₄ . Connect between the series connection points with the collector. The bases of transistors Q ₁ to _{Q 4} are connected to gate terminals 5 to 8, respectively, and control pulses are alternately applied to gate terminals 5 and 8 and gate terminals 6 and 7. In response to the control pulse, the transistors Q ₁ and Q ₄ or the transistors Q ₂ and Q ₃ are alternately turned on, and the current flowing into the primary winding P of the transformer T is alternately reversed. That is, the DC power applied between the input terminals 1 and 2 is converted into AC power and output from the secondary winding S of the transformer T.
The middle point of the secondary winding S is connected to the negative output terminal 4,
Both ends of the secondary winding S are connected to the anodes of diodes D ₁ and D ₂ , respectively. Diode _D1 , _D2
The cathodes of the two are connected in common and connected to the positive output terminal 3 through the choke coil L. A capacitor _C3 is connected between output terminals 3 and 4. That is, the diodes D ₁ and D ₂ , the choke coil L, the capacitor C ₃ , and the like constitute an output circuit that rectifies the secondary winding output.

The conventional power supply circuit described above consists of transistors Q ₁ ~
In order to prevent biased magnetization of the transformer T caused by variations in the switching characteristics of _Q4 , a capacitor _C2 is connected in series with the primary winding P. Since it relies only on the excitation current, it is insufficient and has the drawback of lacking stability. Therefore, the switching element is likely to be destroyed. In addition, in order to realize a power supply circuit with a large current output that requires an output current of several hundred amperes, the diodes D ₁ and D ₂ and the choke coil L must have a large current capacity of several hundred amperes, and the There are major difficulties in selecting and manufacturing transformers and chiyoke coils. Also, even if two diodes are connected in parallel to halve the capacitance of each diode, the negative factor will not be halved due to the difference in diode characteristics, and more than half the current will flow through one diode. There are other difficulties.

A first object of the present invention is to solve the above-mentioned conventional drawbacks, and to prevent biased magnetization of the power conversion transformer due to differences in conduction time and loss between the two sets of switching elements, and therefore to prevent the switching elements from being easily destroyed. , to provide a stable power supply circuit. A second object of the present invention is to provide a power supply circuit that can halve the current flowing through the diodes, choke coils, etc. of the output rectifier circuit. Furthermore, a third object of the present invention is to connect the cathodes of all diodes of the output side rectifier circuit in common, thereby eliminating the need to insulate the heat sink from the diodes, and in some cases, connecting the heat sink itself to the positive output. An object of the present invention is to provide a power supply circuit that can be used as an electrode and is easy to implement.

The power supply circuit of the present invention includes a series connection circuit of first and second switching elements connected between the positive and negative sides of the power supply and turned on and off in a complementary manner by a control signal, and a series connection circuit of similar third and fourth switching elements. a circuit, a series connection of a capacitor and a primary winding of a power conversion transformer connected between a series connection point of the first and second switching elements and a series connection point of the third and fourth switching elements; circuit and
and an output circuit that rectifies a secondary winding output of the power conversion transformer, wherein the secondary winding of the power conversion transformer is composed of first and second secondary windings having the same number of turns. , four diodes whose respective anodes are connected to the beginning and end of the winding of the first and second secondary windings, whose cathodes are connected in common and connected to the positive output terminal; a first winding coil connected between the winding end of the first secondary winding; and a second winding coil connected between the negative output terminal and the winding start of the second secondary winding. , and a capacitor connected between the positive and negative output terminals.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a circuit diagram showing one embodiment of the present invention. In this embodiment, transistors Q ₁ ,
Q ₂ , Q ₃ , Q ₄ , capacitor C ₂ , primary winding P of power conversion transformer T, etc. are the same as in the conventional example shown in Fig. 1, and if necessary, a capacitor may be installed between input terminals 1 and 2. C ₁ is connected. However, the secondary winding of the power conversion transformer T is the first secondary winding S ₁ with the same number of turns.
and a second secondary winding _S2 . 1st winding
A diode is installed at the beginning (marked in the figure) and end of each winding S ₁ and second winding S ₂ .
The anodes of D ₁ ~ _{D 4} are connected, and the diodes D ₁ ~
The cathodes of _D4 are connected in common and connected to the positive output terminal 3. Negative output terminal 4 and the first secondary winding
A chiyoke coil _L1 is connected between the winding end of _S1 , and a chiyoke coil _L2 is connected between the negative output terminal 4 and the winding start of the second secondary winding _S2 . A capacitor _C3 is connected between output terminals 3 and 4. In this embodiment, as will be described later, the on-periods of transistors Q ₁ and Q ₄ and the transistor
Even if there is a difference in the on period of Q ₂ and Q ₃ , the transformer T
It is less likely to cause biased magnetization, enables stable operation, and has the effect of preventing destruction of switching elements (transistors). In addition, the current flowing through the diodes D ₁ to D ₄ and the chiyoke coils L ₁ and L ₂ is
This is half the current flowing through the diodes D ₁ and D ₂ of the conventional example shown in the figure. That is, there is an effect that a large current output can be obtained with a small capacitance diode or a choke coil. Diode for that
It is not necessary to select those having exactly the same characteristics of D ₁ to _{D 4} . Furthermore, since the cathodes of diodes D ₁ to _{D 4} are all connected in common, there is no need to insulate the diodes when installing a heat sink. For example, the case electrodes (usually the cathode side) of the four diodes can be directly It is possible to attach it to a heat sink. Further, in this case, the heat sink itself can be used as a positive output terminal, which facilitates mounting and provides a large cooling effect.

Next, the operation of this embodiment and the reason why magnetic bias does not occur will be explained. DC power applied between input terminals 1 and 2 is converted to AC power by alternately turning on and off transistors Q ₁ and Q ₄ and transistors Q ₂ and Q ₃ , and the secondary power of transformer T is converted to AC power. Output from windings S ₁ and S ₂ . The secondary output is rectified by diodes D ₁ to _{D 4} , smoothed by choke coils L ₁ , L ₂ and capacitor C ₃ , and output from output terminals 3 and 4 .

Now, assume that the conduction time of transistors Q ₂ and Q ₃ is t ₁ , and the conduction time of transistors Q ₁ and Q ₄ is t ₂ . Further, let T be the repetition period of these operations. Then, the voltage drop of transistors Q ₁ to Q ₄ , transformer T, diodes D ₁ to _{D 4} , and chiyoke coil
Ignoring the voltage drops of L ₁ , L ₂ etc. for convenience, the voltage of the secondary winding S ₁ of the transformer T is V _S1 , the voltage of the secondary winding S ₂ is V _S2 , and the voltage across the capacitor C ₃ is V ₀ Then, the DC current I _L flowing through the chiyoke coils L ₁ and L ₂ is
When the transistors Q _{2 and Q 3 are conductive, the alternating current components ΔI L1 and ΔI L2 of} 1 and I L2 are ΔI _L1 = (V _S1 − V _{0 )} t ₁ /L ₁ (1) Transistors Q ₂ , Q ₃ When transistors _{Q 1} and Q _{4 are conductive, ΔI L2 = (V S2 −V 0 ) t 2 / L 2 ...} ...(3) When transistors Q ₁ and Q ₄ are non-conductive, ΔI _L2 =V ₀ (T-t ₂ )/L ₂ ...(4). Note that in the above equation, the symbols L ₁ and L ₂ represent the inductance values of the chiyoke coils L ₁ and L ₂ . In steady operating conditions, equation (1) and
Since they are equal to equation (2), V _S1 =V ₀ T/t ₁ (5) and similarly, V _S2 = V ₀ T/t ₂ (6). Therefore, V _S1 t ₁ =V _S2 t ₂ (7). Since the number of turns of the secondary windings S ₁ and S ₂ are equal,
If the voltage applied to the primary winding of transformer T when transistors Q ₂ and Q ₃ are on is V _P1 , and the voltage applied to the primary winding of transformer T when transistors Q ₁ and Q ₄ are on is V _P2 , then , primary winding voltage V _P1 ,
A similar relationship holds true for V _P2 as well. That is, V _P1 t ₁ = V _P2 t ₂ ......(8) Now, if the voltage applied to the primary winding of the transformer T is a rectangular wave, the magnetic flux density of the transformer core is determined by the applied voltage and application time. is proportional to the product of Therefore, equation (8) means that the magnetic flux generated in the transformer core during the conduction period of transistors Q ₂ and Q ₃ is equal to the magnetic flux generated by excitation in the opposite direction during the conduction period of transistors Q ₁ and Q ₄ . However, this means that even if the conduction times t ₁ and t ₂ are not equal, no biased magnetization occurs. Therefore, there is an effect that biased magnetization does not occur due to differences in characteristics of the transistors Q ₁ to _{Q 4} or unequal lengths of control pulses. That is, there is no risk of instability due to saturation of the transformer core, which may destroy the transistors Q ₁ to Q ₄ and the like. The voltages V _P1 and V _P2 applied to the transformer primary windings described above are balanced with the sum of the power supply voltage and the voltage across the capacitor C ₂ . On the other hand, transistor
Let i ₂ be the current flowing into capacitor C ₂ while Q 1 and Q ₄ are conducting, and i ₁ be the current flowing out from capacitor C ₂ when transistors Q ₂ and Q ₃ are conducting, then i ₁ t ₁ = _{i 2} t ₂ ...(9). On the other hand, the above equations (7) and (8) are
It has nothing to do with the current value flowing through L ₁ and _{L 2. Therefore} , _the circuit shown in FIG. This means that the partial ratio changes freely within the range where the _load current) is constant, but it is 1/n ( _n is the primary winding and secondary winding S ₁ , It can be seen that the currents i ₁ and i ₂ (turning ratio with S ₂ ) ultimately take values determined by equation (9). That is, the conduction period
The difference between t ₁ and t ₂ appears as a difference between the inflow and outflow currents of the capacitor C ₂ , and this determines the load sharing. Since the voltage applied to the primary winding of the constant transformer T during each period satisfies the relationship of equation (8), no biased magnetization occurs.

In addition, in the above, the value of capacitor C ₂ is
Although it does not affect the operating principle of the present invention, if the value of capacitor C ₂ is too large, it will take time to reach stable operation, and when the input voltage or output current suddenly changes, the transistors Q ₁ to _{Q 4} may It can be a heavy burden. Conversely, if the capacitor _C2 is too small, the primary current of the transformer T approaches a sine wave, and the peak current increases, thereby increasing the load on the transistors _Q1 to _Q4 .

In addition, the current flowing through the chiyoke coils L ₁ and L ₂ is approximately half of the load current, and the current flowing through the diode
The current flowing through D ₁ and D ₂ is equal to the current flowing through the chiyoke coil L ₁ . The currents in the diodes D ₃ and D ₄ are equal to the current flowing in the choke coil L ₂ . Therefore, these elements have the advantage that the current capacity is only half that of conventional elements. For this purpose, it is not necessary to make the characteristics of the diodes D ₁ to _{D 4} the same.

Further, since the cathodes of the diodes D ₁ to _{D 4} are all connected in common, when attaching a heat sink, it can be attached directly to the electrodes of the diodes. In this case, it goes without saying that the heat sink can be used as an output terminal. Therefore, there is an effect that implementation becomes easy.

As described above, in the present invention, two secondary windings of the power conversion transformer are independently provided, and the output of each winding is rectified and the load current is supplied through a separate chiyoke coil. This has the effect that the product of the voltage applied to the primary winding of the power conversion transformer and the application time is equal in each period, so that biased magnetization of the power conversion transformer does not occur. Therefore, stable operation is possible and the switching element is not destroyed. Furthermore, since the load current is supplied from the two secondary winding outputs by separate choke coils, the current flowing through each choke coil is approximately half of the load current. The current flowing through each rectifier diode is also halved, so it is not necessary to make the diode characteristics particularly uniform, making it easy to select the elements. Also, since the cathodes of each diode are all connected in common,
It is possible to connect each diode directly to one heat sink, and it is also possible to use the heat sink as an output terminal. In other words, there is an effect that the selection of parts is easy and the mounting arrangement can be performed relatively easily.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional full bridge type power supply circuit, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 1, 2...input terminals, 3, 4...
Output terminals, 5 to 8... Gate terminals, C ₁ to _{C 3} ...
Capacitor, Q ₁ ~ Q ₄ ...Transistor, T...
Power conversion transformer, _D1 to _D4 ...Diode,
L, L ₁ , L ₂ ... Chiyoke coil, P ... Primary winding of the power conversion transformer, S, S ₁ , S ₂ ... Secondary winding of the power conversion transformer.

Claims (1)

[Claims] 1. A series connection circuit of first and second switching elements connected between the positive and negative power supplies and turned on and off in a complementary manner by a control signal, a series connection circuit of similar third and fourth switching elements, and the first and the series connection point of the second switching element and the third switching element.
and a series connection circuit of a primary winding of a power conversion transformer and a capacitor connected between the fourth switching element and a series connection point of the fourth switching element, and an output circuit that rectifies the secondary winding output of the power conversion transformer. In the power supply circuit, the secondary winding of the power conversion transformer is composed of first and second secondary windings having the same number of turns, and the winding start and winding of the first and second secondary windings are the same. four diodes connected to the positive output terminal with their respective anodes connected at the end and the cathodes connected in common; and four diodes connected between the negative output terminal and the end of the first secondary winding. a first chiyoke coil; a second chiyoke coil connected between the negative output terminal and the winding start of the second secondary winding;
A power supply circuit comprising a capacitor connected between positive and negative output terminals.