JPH08251919A - Self-excited converter - Google Patents

Abstract

PURPOSE: To obtain a self-excited converter in which overcurrent protection can be realized through simple circuitry. CONSTITUTION: A thyristor 35 in a starting current interruption circuit 30 is turned ON by a voltage induced in the drive winding 4c of a transformer 4 upon starting a self-excited converter. Consequently, the current flowing through the path of a starting resistor 9, a resistor 8, a capacitor 7, a resistor 6 and the drive winding 4c of the transformer 4 is interrupted. Since the positive feedback voltage of the drive winding 4c of transformer 4 drops below the threshold voltage VTH of an MOS-FET 5 upon occurrence of overcurrent, the MOS-FET 5 is not conducted and self-oscillation thereof is stopped to interrupt the DC output. Since the output voltage detection means and oscillation stopping means can be eliminated, overcurrent protection can be realized through simple circuitry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a self-exciting converter device,
In particular, it relates to a self-excited converter device having an overcurrent protection function.

[0002]

2. Description of the Related Art Self-exciting converter device, that is, self-exciting RC
C (ringing choke converter) has been widely used as a DC power supply with a simple circuit configuration and a small output capacity (50 W or less). For example, the conventional self-excited converter device shown in FIG. 4 has an AC power supply 1, a diode bridge 2 connected to the AC power supply 1, and a smoothing capacitor 3 connected between the output terminals of the diode bridge 2.
And a primary winding 4a of a transformer 4 connected to both ends of the smoothing capacitor 3 and a MOS-FET as a switching element
5 through a series circuit, a resistor 6 and a capacitor 7
The drive winding 4c of the transformer 4 connected to the gate terminal (control terminal) of the OS-FET 5, the resistor 8 connected to the capacitor 7, and the starting resistor 9 connected between the diode bridge 2 and the resistor 8. And a rectifying diode 10 and an output capacitor 11 connected to the secondary winding 4b of the transformer 4.
And a rectifying and smoothing circuit composed of. The AC power supply 1, the diode bridge 2, and the smoothing capacitor 3 form a DC power supply. 4, 12 is a gate control transistor, 13 is a current detection resistor, 14 is a resistor, 15 is a capacitor, 16 is a constant voltage diode, 17 is a photocoupler, 17a is a light emitting part, 17b is a light receiving part, and 18 is an error. Amplifier, 19 is a reference power source, 20, 21 are resistors for voltage division, 22,
23 is an output terminal, 24-26 are resistors, 27 is a capacitor, and 28 and 29 are diodes.

Next, the operation of the self-exciting converter device shown in FIG. 4 will be described. At the time of starting the device, a starting current flows through the gate terminal of the MOS-FET 5, the capacitor 7, the resistor 6, and the drive winding 4c of the transformer 4 via the starting resistor 9 and the resistor 8, and the input capacitance of the MOS-FET 5 and The capacitor 7 is charged and the voltage across the capacitor 7 increases linearly. When the voltage V _{G at} the gate terminal of the MOS-FET 5 exceeds the threshold voltage V _TH between the gate and the source (FIG. 5), the MOS-FET 5 is turned on,
The current _ID starts to flow through the primary winding 4a of the transformer 4, the MOS-FET 5, and the current detection resistor 13. At this time, positive feedback is applied, a voltage is induced in the drive winding 4c of the transformer 4 and applied to the gate terminal of the MOS-FET 5, and
The ON state of the FET5 is maintained and the current I _D continues to flow,
It increases linearly. Along with this, the voltage drop of the current detection resistor 13 due to the current I _D and the voltage generated across the parallel circuit of the resistor 14 and the capacitor 15 from the one end A of the drive winding 4c of the transformer 4 via the diode 28 and the resistor 26. And the feedback voltage of the light receiving portion 17b of the photocoupler 17 are added, and the added voltage is applied to the base terminal of the gate controlling transistor 12. The voltage applied to the base terminal of the gate control transistor 12 increases linearly, and when the applied voltage exceeds the threshold voltage between the base and the emitter of the gate control transistor 12, the gate control transistor 12 is turned on. When the gate control transistor 12 is turned on, the gate current of the MOS-FET 5 is bypassed by the gate control transistor 12, and the MOS-FET 5 is turned off. MOS-
When the FET 5 is turned off, the primary winding 4 of the transformer 4
The energy stored in a is released and a counter electromotive force is generated in the secondary winding 4b, and a DC output is generated between the output terminals 22 and 23 via the rectifying diode 10 and the output capacitor 11. On the other hand, a back electromotive force is also generated in the drive winding 4c of the transformer 4, and the back electromotive force causes the diode 29 and the resistor 2
The voltage of the base terminal of the gate control transistor 12 decreases through 4 and 25.
Turns off. When the energy for conducting the rectifying diode 10 falls below the value, the rectifying diode 10 becomes non-conducting and the secondary winding 4b of the transformer 4 is opened so that ringing occurs and an oscillating voltage is generated in the drive winding 4c of the transformer 4. To do. When this oscillating voltage exceeds the threshold voltage V _TH of the MOS-FET 5, the MOS-FET 5 is turned on again and the current I _D flows and oscillation continues. M at this time
The waveform of the voltage V _GS between the gate and source terminals of the OS-FET 5 is shown in FIG. In FIG. 5, V _C7 is the charging voltage of the capacitor 7, V _R is the oscillating voltage of the drive winding 4c of the transformer 4 due to ringing, and V _P is the drive winding 4c of the transformer 4.
The positive feedback voltage component of is shown.

The constant voltage correction operation of the DC output between the output terminals 22 and 23 is as follows. Output terminals 22 and 23
The DC output voltage V _OUT between them is divided by the voltage dividing resistors 20 and 21, and the voltage at the voltage dividing point of the voltage dividing resistors 20 and 21 is compared with the voltage V _REF of the reference power source 19 by the error amplifier 18. Here, when the DC output voltage V _OUT rises above a specified value, the output of the error amplifier 18 rises, and the photo coupler 17
The light output of the light emitting portion 17a increases and the current of the light receiving portion 17b increases. As a result, the gate control transistor 12
Of the gate control transistor 12
Since the timing of turning on is advanced, MOS-F
The ON period of ET5 is shortened, and as a result, the DC output voltage V
_Operates to lower _OUT . On the contrary, when the DC output voltage V _OUT drops below the specified value, the DC output voltage V _OUT is increased by the operation opposite to the above. By the above operation, the DC output of the self-excited converter device shown in FIG. 4 is stabilized.

[0005]

By the way, DC-DC
One of the important items that a power supply device such as a converter, an inverter, or a switching power supply should have is "when an overcurrent occurs,
In other words, the output is shut down when an output current that exceeds the maximum current flows or is about to flow. ”
There is something. The easiest way to do this is to stop the oscillation of the switching element. Therefore, in the conventional power supply device, it is generally performed to stop the oscillation of the switching element to cut off the output when an overcurrent occurs. However, in the self-excited converter device, the output signal of the control circuit is detected by detecting the presence or absence of the feedback signal and the overcurrent detection signal like the separately excited converter device including the control circuit that outputs the ON / OFF control signal of the switching element. It is not easy to stop the oscillation of the switching element by shutting off. Therefore, in the self-exciting converter device shown in FIG. 4, it is detected that the DC output voltage V _OUT drops when an overcurrent occurs, and the MOS-FET 5 is detected.
Although it is sufficient to forcibly stop the self-excited oscillation of the (switching element), there are drawbacks that the output voltage detection means and the oscillation stop means are required, the circuit configuration becomes complicated, and the number of parts increases.

Therefore, an object of the present invention is to provide a self-excited converter device capable of performing overcurrent protection with a simple circuit configuration.

[0007]

A self-excited converter device according to the present invention comprises a DC power supply, a series circuit of a primary winding of a transformer connected to the DC power supply, and a switching element,
A drive winding of the transformer connected to the control terminal of the switching element, and a starting resistor connected between the DC power supply and the drive winding of the transformer, by self-oscillation of the switching element. A DC output is generated from the secondary winding of the transformer through a rectifying and smoothing circuit. In this self-excited converter device, a starting current cutoff circuit that cuts off the starting current flowing through the starting resistor and the driving winding by the voltage generated from the driving winding of the transformer after starting is provided, and when the overcurrent occurs, the The self-excited oscillation of the switching element is stopped when the positive feedback voltage of the drive winding drops below a predetermined value. A series circuit of a variable resistor and a rectifying element may be connected between the starting current cutoff circuit and the control terminal of the switching element.

[0008]

The starting current cutoff circuit is activated by the voltage generated from the drive winding of the transformer after starting the device, and the starting current flowing through the starting resistor and the drive winding of the transformer is cut off. As a result, the ringing in the transformer is reduced when an overcurrent is generated, the positive feedback voltage of the drive winding of the transformer is reduced to a predetermined value or less, the self-excited oscillation of the switching element is stopped, and the DC output is cut off. Therefore, since the output voltage detecting means and the oscillation stopping means are not required, overcurrent protection can be performed with a simple circuit configuration. Furthermore, if a series circuit of a variable resistor and a rectifying element is connected between the starting current cutoff circuit and the control terminal of the switching element, the load seen from the drive winding of the transformer becomes heavier, which causes overcurrent. At this time, the positive feedback voltage of the drive winding of the transformer is further reduced, and the self-excited oscillation of the switching element can be more surely stopped. Further, by changing the resistance value of the variable resistor, the starting current flowing through the drive winding of the transformer can be adjusted.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a self-exciting converter device according to the present invention will be described below with reference to FIGS. However, in FIG.
Then, parts that are substantially the same as the parts shown in FIG. 4 are given the same reference numerals, and descriptions thereof will be omitted. As shown in FIG. 1, the self-exciting converter device of this embodiment is provided with a starting current cutoff circuit 30 between a drive winding 4c of a transformer 4 and a starting resistor 9. The starting current interruption circuit 30 includes a series circuit of a delay resistor 31, a diode 32, and a capacitor 33 connected in parallel with the drive winding 4c of the transformer 4, a resistor 34 connected in parallel with the capacitor 33, and a starting resistor. Connection point of 10 and resistor 11 and diode bridge 17
Thyristor 35 connected between the negative output line of
And a resistor 36 connected between the gate terminal of the thyristor 35 and the negative side output line of the diode bridge 17,
It is composed of a constant voltage diode 37 connected between a resistor 34 and a resistor 36. In FIG. 1, 38 indicates an external shutdown transistor. The other circuit configuration is substantially the same as the circuit configuration of FIG.

Next, the operation of the self-excited converter device shown in FIG. 1 will be described. The normal self-oscillation operation and the constant voltage correction operation are substantially the same as the operation in the self-excited converter device shown in FIG. At the time of starting the circuit of FIG. 1, a starting current flows through the gate terminal of the MOS-FET 5, the capacitor 7, the resistor 6, and the drive winding 4c of the transformer 4 via the starting resistor 9 and the resistor 8, and The input capacitance and the capacitor 7 are charged, and the voltage across the capacitor 7 increases linearly. At the same time, a voltage is generated in the drive winding 4c of the transformer 4, and the capacitor 33 is charged in the starting current cutoff circuit 30 via the delay resistor 31 and the diode 32. When the charging voltage of the capacitor 33 exceeds the sum value of the breakdown voltage of the constant voltage diode 37 and the threshold voltage of the thyristor 35, the thyristor 35 is turned on, and the capacitor 7, the resistor 6, the transformer 6, the transformer 7, the resistor 6, and the transformer 8 are turned on. The starting current flowing through the path of the drive winding 4c of No. 4 is cut off. For this reason, the charging voltage of the capacitor 7 decreases, but in the normal operation, the positive feedback voltage of the drive winding 4c of the transformer 4 is sufficiently high, so that the gate voltage of the MOS-FET 5 does not become insufficient. Further, when the thyristor 35 is turned on, the resistor 8 is inserted in parallel with the drive winding 4c of the transformer 4, so that the impedance of the gate terminal of the MOS-FET 5 lowers, but during normal operation the gate of the MOS-FET 5 is reduced. There is no shortage of voltage.

When an output current exceeding the maximum current flows to the output side due to a short circuit between the output terminals 22 and 23, the overcurrent protection is activated, so that the ringing in the transformer 4 is reduced and the drive winding 4c is generated. The oscillating voltage V _R becomes lower than the threshold voltage V _TH of the MOS-FET 5 as shown by the solid line in FIG. Therefore, the positive feedback voltage of the drive winding 4c of the transformer 4 is lowered and the MOS-FET 5 cannot be conducted.
The self-oscillation of OS-FET5 stops. As a result, the DC output is reliably cut off when an overcurrent occurs. Note that FIG. 2 shows the MOS after the activation current cutoff circuit 30 is activated.
-The waveform of the voltage V _GS between the gate and source terminals of the FET 5 is shown, and the broken line portion of FIG. 2 shows the oscillating voltage V _R generated in the drive winding 4c of the transformer 4 during normal operation. Smoothing capacitor 3
When the voltage across both ends becomes low, the current flowing through the thyristor 35 through the starting resistor 9 becomes less than the holding current, so the thyristor 35 is turned off and returns to the starting state. Also,
In the circuit of FIG. 1, the external shutdown transistor 38
A self-excited oscillation of the MOS-FET 5 can be forcibly stopped by externally applying a shutdown signal to the base terminal of the MOS transistor to turn on the external shutdown transistor 38.

The self-exciting converter device shown in FIG. 1 can be modified. For example, the self-exciting converter device shown in FIG. 3 has a thyristor 35 and a MOS-
A series circuit 40 of a variable resistor 42 and a diode 41 as a rectifying element is connected between the gate terminal of the FET 5 and the FET 5. The other circuit configuration is substantially the same as the circuit configuration of FIG. In the circuit of FIG. 3, when the thyristor 35 in the starting current cutoff circuit 30 is turned on, the diode 41
Becomes conductive and the parallel circuit of the resistor 8 and the variable resistor 42 is inserted in parallel with the drive winding 3c of the transformer 3,
The impedance of the gate terminal of MOS-FET5 is shown in Fig. 1.
In comparison with the circuit of (3), the load is further reduced, and the load seen from the drive winding 3c becomes heavier. As a result, the positive feedback voltage of the drive winding 4c of the transformer 4 is further reduced as compared with the circuit of FIG. 1, so that the self-excited oscillation of the MOS-FET 5 can be more surely stopped when an overcurrent occurs. Further, by changing the resistance value of the variable resistor 42, it is possible to adjust the starting current flowing in the path of the capacitor 7, the resistor 6 and the drive winding 4c of the transformer 4.

In the self-excited converter device of the above embodiment, the starting current cutoff circuit 30 is activated by the voltage generated from the drive winding 4c of the transformer 4 after the device is started, and the capacitor 7 is passed through the starting resistor 9 and the resistor 8. , The resistor 6, and the starting current flowing in the path of the drive winding 4c of the transformer 4 are cut off. Therefore, when overcurrent occurs, the ringing in the transformer 4 decreases, and the positive feedback voltage of the drive winding 4c of the transformer 4 becomes lower than the threshold voltage V _TH of the MOS-FET 5,
The self-excited oscillation of the MOS-FET 5 is stopped and the DC output is cut off without fail. Therefore, the output voltage detecting means and the oscillation stopping means are unnecessary, and the overcurrent protection can be performed with a simple circuit configuration. Further, since the external shutdown transistor 38 is provided, if the startup current cutoff circuit 30 becomes inoperable due to, for example, damage to the thyristor 35, the external shutdown transistor 38 is turned on to activate the MOS-FET 5 itself. Excited oscillation can be forcibly stopped.

The embodiment of the present invention is not limited to the above-mentioned embodiments, but can be modified. For example, in each of the above embodiments, an example using a MOS-FET as a switching element is shown, but a bipolar transistor, a junction type F
Other switching elements such as ET (J-FET) and SCR (reverse blocking 3-terminal thyristor) may be used. It is also possible to divide the secondary winding 4b of the transformer 4 into a plurality of windings each having a different number of turns and connect a rectifying / smoothing circuit to each secondary winding to form a multi-output self-exciting converter device. is there.

[0015]

In the self-excited converter device of the present invention, overcurrent protection can be performed with a simple circuit configuration.
There is an advantage that the number of parts can be reduced and the manufacturing cost can be reduced to obtain an inexpensive self-exciting converter device.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a self-exciting converter device showing an embodiment of the present invention.

FIG. 2 shows M after the activation of the starting current interruption circuit of FIG.
Waveform diagram showing changes in the gate-source voltage V _GS of the OS-FET

FIG. 3 is an electric circuit diagram showing a modified example of FIG.

FIG. 4 is an electric circuit diagram showing a conventional example of a self-exciting converter device.

FIG. 5 is a waveform diagram showing changes in the gate-source voltage V _GS of the MOS-FET during self-excited oscillation.

[Explanation of symbols]

1. ． ． AC power supply, 2. ． ． Diode bridge,
3. ． ． Smoothing capacitor, 4. ． ． Transformer, 4
a. ． ． Primary winding, 4b. ． ． Secondary winding, 4c. ． ． Drive winding, 5. ． ． MOS-FET (switching element),
6,8,14. ． ． Resistance, 7, 15. ． ． Capacitors,
9. ． ． Starting resistor, 10. ． ． Rectifier diode, 1
1. ． ． Output capacitor, 12. ． ． Gate control transistor, 13. ． ． Current detection resistor, 16. ． ． Constant voltage diode, 17. ． ． Photo coupler, 17a. ． ．
Light emitting part, 17b. ． ． Light receiving part, 18. ． ． Error amplifier,
19. ． ． Reference power source, 20, 21. ． ． Voltage dividing resistor, 2
2, 23. ． ． Output terminals, 24-26. ． ． Resistance, 2
7. ． ． Capacitors, 28, 29. ． ． Diode, 3
0. ． ． Startup current interruption circuit, 31. ． ． Delay resistor, 3
2. ． ． Diode, 33. ． ． Capacitors, 34, 3
6. ． ． Resistance, 35. ． ． Thyristor, 37. ． ． Constant voltage diode, 38. ． ． External shutdown transistor, 41. ． ． Diode, 42. ． ． Variable resistance

Claims (2)

[Claims] 1. A series circuit of a direct current power supply, a primary winding of a transformer connected to the direct current power supply, and a switching element,
A drive winding of the transformer connected to the control terminal of the switching element, and a starting resistor connected between the DC power supply and the drive winding of the transformer, by self-oscillation of the switching element. In a self-excited converter device for generating a DC output from a secondary winding of the transformer through a rectifying / smoothing circuit, a start-up resistor and a start-up flowing through the drive winding by a voltage generated from the drive winding of the transformer after start-up. A self-excited oscillation of the switching element is stopped by providing a starting current interruption circuit for interrupting the current, and the positive feedback voltage of the drive winding of the transformer is reduced to a predetermined value or less when an overcurrent occurs. Excitation converter device. 2. The self-exciting converter device according to claim 1, wherein a series circuit of a variable resistor and a rectifying element is connected between the starting current cutoff circuit and a control terminal of the switching element.