JPS5980164A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To prevent a secondary failure from occurring when a large power transistor and a power diode fail by providing an overcurrent detecting resistor at the secondary side of a current transformer and applying the output to an overcurrent detecting and conduction breaking circuit. CONSTITUTION:Overcurrent detecting resistors R1, R2 are respectively inserted into the secondary side of a current transformer CT. A voltage which is produced by a current flowed through the resistors R1, R2 is introduced to a controller C/C through connecting lines 105, 106 which respectively include diodes. The overcurrent detecting and conduction breaking circuit EDT in the controller C/C detects threshold voltage when the voltage produced at the resistors R1, R2 exceeds the specific threshold voltage, and immediately interrupts the supply of the conduction control signal to transistors Q3, Q4 thereafter.

Description

[Detailed description of the invention] The present invention relates to a DC-DC converter.

Generally, a DC-DC converter is used to convert DC power with a specific voltage into DC power with a voltage required by a load.

The following type is often used as a type of C-, DC converter.

In other words, a conduction drive signal having a specific time width is applied to two high-power transistors to make them conductive alternately, and this causes an alternating current to flow through the primary side of the main transformer, and transforms the transformed secondary side. DC power is generated by rectifying and submerging the power to produce the desired voltage.

The conduction and drive signals are determined by the conduction control signal (the output of the conduction driving transistor that is pivoted and the conduction current of the high power transistor flowing through the primary side of the current transformer and appearing at the secondary hook). In addition, to control the IB force tc pressure, the output voltage is compared with a desired reference voltage and voltage, and the conduction control signal is adjusted according to this difference. control the time width.

Now, in such a C-DC converter, generally when the high power transistor turns on/off the current flowing to the primary side of the main transformer,
In order to completely prevent a reverse polarity voltage from being applied to the high power transistor due to the energy stored in the inductance (leakage inductance) of the transformer, and also to return a part of this energy to the input side, This is how C-
, these two human rights in DC converters.

The blade diode and the two high power transistors mentioned above are considered to be the components most likely to cause failure.

However, in the conventional DC-DC converter of this type, as will be described later, either one of the two high-power transistors and two high-power diodes may cause a short circuit due to a fault. When purchasing a circuit, it is inevitable that an overcurrent will flow through the non-faulty high-power transistor and destroy it.As a result, the input power supply will be short-circuited, and an abnormally large current will flow, causing the wiring on the printed circuit board to be damaged. Secondary failures may occur, such as burnout or damage to the input power supply.

In order to prevent such secondary failures, conventionally, vC-D C
Although a fuse is inserted on the input side of the converter for one cycle of operation, even the insertion of this fuse cannot prevent the above-mentioned high-power transistor from being destroyed.

C
- To provide a DC converter.

The DC-DC converter of the present invention has a conduction current generated on the secondary side of the feedback transformer due to the output from the conduction driving transistor driven by the conduction control signal and its own conduction current flowing to the primary side of the feedback transformer. The feedback output and the second high-power switching transistors are periodically and alternately brought into conduction during the winning state, thereby exciting the primary side of the main transformer with alternating current. The main transformer has two power storage diodes for feeding back part of the energy stored in the inductance of the main transformer to the input power supply side and completely preventing reverse voltage from being applied to the high power switching transistor. and a DC-DC converter which performs full rectification and five waves on the secondary side of the main transformer to obtain a DC output, the primary side of the feedback transformer for the @1 high power switching transistor and the 20th It has a configuration such that when a conducting current for the large power switching transistor flows simultaneously with the primary side of the large power switching transistor, the feedback outputs are canceled, and the feedback outputs are canceled during excitation in the normal state. The feedback transformer is connected so that when one of the two diodes is short-circuited, abnormal current information is generated on its secondary side, and when the abnormal current information exceeds a specific threshold value. an overcurrent production conduction cutoff means that detects this and cuts off the output of the continuity control signal, and detects when the voltage of the DC output becomes lower than a specific threshold value and controls the continuity control. It includes a pressure detection conduction cutoff means and a gold plate for cutting off the output of the signal.

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

First, a conventional example will be explained for the ratio axis.

Figure 1 is a circuit diagram showing a conventional example.

This DC-DC converter supplies a conduction control signal (square wave pulse) from the control unit C/C' to the conduction drive transistor Q3' via the connection line 100'.

When a conopulse is applied to transistor Q3', from the supply voltage +Vcc' to resistor r, / and diode d5
'k, the pulse transformer 12' is driven, and as a result, the two pulse transformers T2'
High power switching transistor Q connected to the next side
1' is a moderate amount of 4 pieces of stool. This current of Q1' drives the current transformer CT'i, and the secondary output of CT' passes through the pulse transformer T2/full valve and is positively fed back to the input side of the high power switching transistor Q1/.As a result, the transistor Q 1 / becomes more strongly conductive, and due to the positive feedback effect of the current, transistor Q 1 / becomes very quickly (JN state (saturated conduction state)).

Next, the control unit C/C' stops applying the conduction control signal (square wave pulse) to the transistor Q3', and
In order to turn off the transistor Q4' for a short period of time, the transistor Q4' for interrogation control I is made conductive via the connection line 101'.

In this way, the heavy snow/power switching transistor Q1' can be controlled to be in the ON or N state for a specific time period.

Now, after a necessary time has passed since the transistor Ql' becomes OF, l'', the control unit C/C' next connects the connecting line 102''.
A conduction control signal with a phase delay of 180° is supplied to the other conduction driving transistor Q5' through the conduction drive transistor Q5'. This controls the other large gravity switching transistor Q2'Th through the dipulse transformer T3'' and turns it on in exactly the same process as transistor Q1'. After turning ON, a pulse is supplied to the transistor Q 6 / for the other conduction '1.Iλlh fill ' jt11. do.

By repeating the above operation, alternating current is supplied to the primary side of the main transformer TI', the transformed secondary side is full-wave rectified using the rectifying diodes D3' and D4', and this is connected to the choke coil. C) 1' and capacitor C4' A smoothed DC output is obtained by filtering with a different filter circuit.

The output voltage is led to the control unit C/C' through the connection line 104', where it is compared with the reference voltage, and depending on the difference,
Transistors Ql' and Q2"jz as described above
The output voltage is stabilized by controlling the ON time width.

Now, power diodes DI' and D2' are used for reverse voltage and pressure protection in this DC-DC converter, and these operate as follows.

-ff, there is a shallow inductance in the transformer T1', so if the current flowing in T1' is abruptly cut off by setting all the transistors Q1' or Q2/ to (JFF), a strong take-up force will be generated. is generated, and therefore the potential of P′ is, depending on the direction of the interrupted current,
Driven to a potential higher than the high side of the input supply voltage or lower than the low side of the input supply voltage. If this is left as is, a reverse voltage higher than the reverse withstand voltage will be applied to the high-power switching transistor Q1'''! or Q2', and there is a risk of destroying these transistors.
), in order to prevent this and to return the energy stored in this inductance to the power supply side to minimize power loss, power diodes D1' and D2' are connected to the power supply as shown in Figure 2. Reverse pole 1 is mainly inserted in series.

Now, when the L)C-[)C connector (-) is in operation, for example, if the diode D1' fails and shorts (-), the transistor Q2' is turned on and the input power is turned off. The load connects the transistor Q2' and turns it on, destroying the transistor Q2/ in an instant.The input power supply is therefore short-circuited, causing damage to the power supply and causing a large current. Failures such as burning out the printed circuit board wiring may occur.

To avoid this, conventionally all input power supplies are connected via fuses. Of course, even if connected to the input power supply via a fuse in this way, the transistor Q 2 /
It is almost impossible to save from destruction.

In the above example, we explained the short circuit of the power diode IJ1', but as is clear from Fig. 1, the power diode IJ1' is considered to be the circuit element with the highest probability of failure in the DC-DC converter circuit. '])1', D2' and high power switching transistors Ql', C2
If a short circuit occurs in any one of them, it will inevitably lead to destruction of the high power switching transistor as described above, resulting in a short circuit of the input power supply.

According to the present invention, in such a case, the influence on the Taichi electric rj side is minimized, and the destruction of the transistor as described above is prevented, thereby reducing the input side glue.

- Since the step can be omitted, all C-IJc converters can be provided.

Next, one embodiment of the present invention will be described in detail.

FIG. 2 is a circuit diagram showing one embodiment of the present invention.

In this embodiment, a control Is including an overcurrent detection conduction:a cutoff circuit El)T and an undervoltage detection conduction cutoff circuit UJJT is used.
C/C, switching transistor for deep sleep Ql.

C2, conduction driving transistor Q3. Q, 5. Conduction stop control transistor Q4. Q6. Series resistance rs1゜rs
2. Series diode d51. d32. Overcurrent detection resistor R, 1, R, 2, protective power diode I) 1. L)
2. Rectifier power diode I)3. D4. Main transformer TI, pulse transformer T2. T3゜Current transformer CT, capacitor CI.

C2, C3, C4, and a choke coil C)I.

Now, the operation of this embodiment in the royal palace state is almost the same as that described for the 11th J circuit.

That is, the control unit C/C sends a conduction control signal (rectangular wave pulse) through the connection line 100 to the full conduction driving transistor Q3.
supply to. When this pulse is applied to the transistor Q3[11, the pulse transformer T2 is driven from the supply voltage +VCC through the series resistor Fcrs1 and the series diode d51, and as a result, this transformer T2
The high-power switching transistor Q1 connected to the secondary side of is driven to a 2N conduction state. However, with this drive alone, the transistor Q1 only becomes conductive to a certain degree, but it is completely turned off.
It will not be in N state.

Now, when the transistor Ql becomes conductive as described above, this is it! The current 1 flows as the primary current of the current transformer CT, drives the transformer CT-i and produces an output on its secondary side, but this output is transmitted to the input side of the transistor Q1 via the pulse transformer T2Th. As a result, the transistor Ql [1 drive #J for the transistor Ql] becomes even stronger. As a result, the conduction current of transistor Q1 increases rapidly, and as a result of this positive feedback, transistor Q1 rapidly becomes
It becomes N state.

Next, the control unit C/C applies the conduction control signal to the transistor Q3, and then applies the conduction control signal to the transistor Q3.
4 through the connection line 101 for a short period of time to bring it into the '1 (JN) state, the barrel conduction drive for the transistors Q1 & C is canceled and all of them are turned off.

Thus, the high-power switching transistor Q1 is controlled in a specific manner by controlling the conduction control signal supplied from the control unit C/C via the connection line 100 and the conduction control pulse supplied via the connection line 101. The CJN-like width can be set by the time width.

Now, after eight and a half hours have passed since the transistor Q1 was turned off, the control unit C/C sends the above-mentioned conduction control signal and conduction stop control pulse with a 180° phase delay via the connection line 102 and the connection line 103. The conduction control signal and the conduction stop control pulse are supplied to the conduction drive transistor Q5 and the conduction stop control transistor Q6, respectively, and the high power switching transistor Q2' is controlled for a similarly controlled time width through the same process as described above. Turn it on.

By repeating the above operation, an intercurrent current is supplied to the primary side of the main transformer T1, and this is transformed in the same way as in the case of FIG. 1, and the rectifying power diode])3. D4
It is rectified by choke coil CH and capacitor C4.
It favors DC output by waving.

Is the output DC voltage the connection wire 104? The voltage is guided through the control unit (/C), where it is compared with the reference voltage, and depending on the difference,
As shown above, the output voltage is stabilized by controlling the entire time period in which transistors Q1 and Q2 are turned on.

In this embodiment, the output voltage led into the control unit C/C via the connection line 104 is further internally connected to an undervoltage detection conduction cutoff circuit UJ)T. This circuit UL)T detects when the above-mentioned output voltage drops beyond a predetermined specific output voltage range, and the subsequent transistors Q3. Continuity for Q5vc!
This is a circuit that immediately cuts off one of the tilJ control signals.

Now, in this embodiment as well, for exactly the same reason as explained in FIG. It completely prevents it from being driven beyond the low potential side of the power supply.

However, in this embodiment, as shown in FIG. 2, it is connected to the midpoint of the primary side of the current transformer CT. As a result, in the normal state, the transistor Q is
The conduction current of 1 flows through the half of the transistor Ql side on the primary side of the current transformer CT, reaches point P, passes through the primary side of the main transformer T1, and passes through the capacitor C2.
, C3 are discharged and charged.

Furthermore, when the transistor Q2 becomes conductive, the charges discharged to the capacitors C2 and C3 pass through the main transformer TI' to the point P, and then pass through the half of the transistor Q2 side on the primary side of the current transformer CT. It is charged and discharged entirely through the transistor Q2.

In this manner, in the normal state of the current transformer CT, id, the half on the transistor Ql side and the half on the transistor Q2 side operate mutually, so that the influence on the opposite half can be ignored.

Now, the polarity of the winding of the current transformer CT in this embodiment is such that when the same current flows through the primary side of the transistor Ql color transformer CT to the transistor Q2, the magnetomotive forces generated in each half cancel each other out. It is configured to

7t, overcurrent detection resistors R1 and R2 are inserted in each of the secondary sides of the kinded transformer CT, and the voltage generated by the current flowing through each of the resistors 1 and 2 includes a diode. The control unit C/
Cic 4 is connected to the overcurrent detection/continuity cutoff circuit EDT inside the control unit C/C. This circuit E
All of these are detected, and subsequent transistors Q3. Conduction to Q5 101] This is a circuit that immediately cuts off the supply of the control signal.

Now, in this embodiment having the above-described configuration, a case where either one of the protective power diodes DI, D2 and the high-power switching transistors Ql, Q2 causes a failure and short-circuits will be considered.

First, a case where the protective power diode D1 is short-circuited will be described. In this case, when the transistor Q2 is in the ON state 1, the current flowing through the transistor Q2 becomes abnormally large, and as a result, an abnormal voltage is generated in the d current detection resistor R2 on the secondary side of the current transformer CT. The overcurrent detection conduction cutoff circuit EDT in the C/C operates, and the drive to the transistors Ql and Q2 is cut off, so that the transistors Ql and Q2 are turned off. As a result, the free transistor Q2 is prevented from being destroyed, and the adverse effects of short-circuit current on the input power supply side can be almost ignored. Of course, there is no need to insert an a-need on the input side to protect the circuit against this failure.

The above is a case where diode D1 is short-circuited.
It is clear that even if the 1-ode I) 2 is short-circuited, the transistor Q1 will not be destroyed by the same operation, and the adverse effect of the short-circuit current on the input power supply will be negligible.

Next, a case will be described in which the high power switching transistor Q1 is short-circuited (emitter-collector short-circuited). If transistor Q1 fails and short-circuits while transistor Q2 is on, transistor Q
The current flowing through 2 is the current transformer CT
Because almost all of the primary side of the current transformer CTO flows to the short-circuited transistor Q1, the magnetomotive force generated in each half of the current transformer CTO cancels each other out due to the above-mentioned implantation. , the output of the quadratic A law is almost zero. Therefore, the transistor Q2T is driven only by the current supplied from +VCC through the series resistor rs2 and the series diode d8°, so that the conduction current of the transistor Q2 decreases rapidly.

On the other hand, capacitor c2. The capacitors C2 and C will be discharged and charged from the high potential side of the input power supply via the transistor Ql' which is short-circuited with the C31d transformer T1.
Since the capacitance of the transformer T1 is comparatively small, the voltage across the transformer T1 is rapidly discharged and charged, and the voltage across the transformer T1 becomes small. The excitation becomes smaller and therefore the output DC voltage decreases, which is detected by the undervoltage detection conduction cutoff circuit UDT in the control unit C/C via the connection line 104, and the transistor Q
The drive to l, Q2 is cut off and transistor Q2 is turned off.
state. As a result, the transistor Q2 is prevented from being destroyed, and the adverse effects of the short-circuit current on the input power supply side can be almost ignored.

The above is a case where the transistor Q1 is short-circuited, but even when the transistor Q2 is short-circuited, the transistor Q1 is protected from destruction due to the completely similar operation, and the adverse effects of the short-circuit current on the input power supply side are almost negligible. It is clear that

Therefore, there is no need to insert a fuse on the input side to protect the circuit against these failures.

It should be noted that the circuit diagram in FIG. 2 merely shows an actual example, and the present invention is not limited thereto.

As described above, according to the present invention, even if one of the protective gravity diodes or the large power switching transistors is short-circuited due to failure, the normal large gravity It is possible to provide a 1)C-1)'C converter that does not cause a transistor to break down, thereby shorting the input power supply and inducing a serious secondary failure.

As a result, it is no longer necessary to insert an extra fuse on the input side, which was required in the past, which simplifies handling, and in the event of a failure such as the one mentioned above, it does not needlessly destroy all high-power switching transistors, making it much easier for repair workers to do so. a? This has the effect of saving money.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining a conventional VAU, and FIG. 2 is a circuit diagram of an embodiment of the present invention. In the figure, C/C...for control, Q], Q2...human rights, power switching transistor, Q3. Q.5...
... Conduction control transistor, Q4. Q6...
・Conductivity 1] Official transistor, r31. rs
2...Series resistance s d31゜dS2...
・Series diode, 1. R2...Resistance for overcurrent detection, DI, D2...Gravity diode for protection,
D3. D4... Rectifier power diode, TI...
...Main transformer, T2. T3...
... Noculus transformer, CT ... Current transformer, CI, C2, C3, C4 ...
・Condenser @j-, C, H・・Mountain・Choke coil, E
DT...River/Overcurrent detection continuity/disconnection circuit, 'Ul)T...
...Undervoltage detection continuity cutoff circuit.

Claims (1)

[Claims] The output from the conduction driving transistor driven by the conduction control signal and the own conduction current flowing to the primary side of the feedback transformer cause the feedback transformer to
The first string and the second high-power wire are driven by the feedback output generated on the next side, and are periodically and alternately brought into conduction in a normal state, thereby exciting the primary side of the main transformer with the father current. The switching transistor and the inductance of the main transformer? T! −. the main transformer's secondary 1) In the C-DC converter, the primary side of the feedback transformer for the first high-power switching transistor and the second high-power switching transistor for the feedback transformer. The configuration is such that each of the feedback outputs is canceled when a conduction current flows to the high-power switching transistor during the primary side current, and one of the two diodes during excitation in the normal state. If the pieces are short-circuited, the second
The feedback transformer is connected to generate abnormal current information on the next side, and the abnormal current information exceeds a certain threshold. an overcurrent detection conduction cutoff means for detecting fl and cutting off the output of the continuity control signal; and detecting when the voltage of the DC output becomes lower than a specific threshold value, A DC-DC converter comprising: undervoltage detection conduction cutoff means for cutting off output of a control signal.