JP4513456B2 - DC-DC converter transformer magnetism detector - Google Patents

Description

  The present invention relates to protection against magnetic saturation of a transformer in an insulation type DC-DC converter, and more particularly, to an apparatus for detecting a magnetic bias of a transformer without using an expensive current detector or a capacitor for removing a DC component. .

FIG. 4 shows an example of a conventional circuit. In FIG. 4, 1 is a DC power source, 2 to 5 are semiconductor switch elements, 6 is a transformer, 7 to 10 are diodes, 11 is a reactor, and 12 is a load.
When semiconductor switch elements 2 and 5 are turned on, a positive voltage is applied to the primary winding of transformer 6, and when semiconductor switch elements 3 and 4 are turned on, a negative voltage is applied. By applying positive and negative voltages alternately, high-frequency alternating current is input to the primary winding of the transformer 6. This is transformed and insulated by the transformer 6, then rectified by a diode rectifier composed of diodes 7 to 10, and smoothed by the reactor 11 to apply a DC voltage to the load 12. The voltage applied to the load 12 can be controlled by changing the time ratio at which the semiconductor switch elements 2 to 5 are turned on / off by the pulse width control circuit 15.
Here, an unintended DC voltage component may be applied to the transformer 6 due to a difference in characteristics of the semiconductor switch elements 2 to 5 and a variation in transmission time of the on / off signal. When a DC voltage component is applied, the transformer 6 is demagnetized, and in extreme cases, magnetic saturation is reached. When magnetic saturation occurs, not only can the power not be normally transmitted to the load, but also the transformer 6 is almost equal to a short circuit, so that an overcurrent is generated, which causes damage to the semiconductor switch elements 2-5.

As means for preventing this, the primary winding current of the transformer 6 is detected by the current detector 13, and the DC component is extracted by the DC component detector 14 composed of a low-pass filter or the like, and this is input to the pulse width controller 15. By controlling so that the direct current component is reduced, the demagnetization is suppressed. An example of the above method is shown in Patent Document 1, for example.
JP 9-168278 (4 pages, Fig. 1 and Fig. 2) Japanese Patent Laid-Open No. 11-98835 (6 pages, FIGS. 1 to 3 and others)

  In this conventional example, the current detector 13 needs to have a wide band from high-frequency alternating current to direct current, and is required to be highly accurate in order to capture a slight direct current component contained in the alternating current. In general, such detectors are expensive. As another method for preventing demagnetization, there is a method of removing a direct current component by inserting a capacitor in series with a transformer as disclosed in Patent Document 2, for example. However, a large current flows through the capacitor, so a large capacitor is required. In particular, a large capacity device is disadvantageous in terms of price and size.

  Converting direct current to alternating current, connecting the transformer input to the output of the so-called inverter, connecting the input of the rectifier circuit consisting of a plurality of diodes to the output of the transformer, and connecting the series circuit of the reactor and load to the output of the rectifier circuit In the DC-DC converter, the circulating diode connected in parallel to the output of the rectifier circuit, the continuity detecting means for detecting the continuity of at least two of the diodes in the rectifier circuit, and the conduction time of the diode Time comparison means for comparison, and during the circulation period, only the excitation current flows through the diodes of the rectifier circuit, and the bias is detected by imbalance of the on-time of each diode.

  By detecting the difference in conduction time between at least two rectifier diodes, it is possible to detect demagnetization without using an expensive current detector or capacitor for removing a DC component as in the past, thereby reducing demagnetization. realizable.

FIG. 1 shows a first embodiment of the present invention, and FIG. 2 shows its operation. The same parts as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 1, 101 is a free-wheeling diode, 102 and 103 are voltage detectors, and 104 is a time difference measuring device.
In the semiconductor switch elements 2 to 5, the semiconductor switch elements 2 and 5 are alternately turned on and the semiconductor switch elements 3 and 4 are alternately turned on similarly to the operation of FIG. When the semiconductor switch elements 2 and 5 are turned on, a voltage is applied to the transformer 6, an exciting current flows through the transformer 6, and the diodes 7 and 10 are conducted to the secondary winding to connect the reactor 11 and the load 12. Current flows through the path. Next, when the semiconductor switch elements 2 and 5 are turned off, the current of the reactor 11 is held by the smooth action of the reactor 11, and this current flows through the freewheeling diode 101.
Here, there may be a path through the rectifier diodes 7 to 10 as the current path. However, in this path, two diodes are connected in series, and a forward voltage is generated twice. . This period is called a reflux period. Next, when the semiconductor switch elements 3 and 4 are turned on, a voltage is applied to the transformer 6, an exciting current flows through the transformer 6, and the diodes 8 and 9 are conducted to the secondary winding to connect the reactor 11. Current flows in a path through the load 12. Next, when the semiconductor switch elements 3 and 4 are turned off, the current of the reactor 11 is held by the smoothing action of the reactor 11, and this current flows through the freewheeling diode 101. Here, there may be a path through the rectifier diodes 7 to 10 as the current path. However, in this path, two diodes are connected in series, and a forward voltage is generated twice. .
The method of providing the freewheeling diode 101 is a method that is generally used to reduce the loss during the freewheeling period. At this time, the exciting current of the transformer 6 tries to continue to flow from the primary side to the secondary side, but when flowing through the primary side, the voltage of the DC power source 1 is applied in the direction of decreasing the current, whereas it flows through the secondary side. Since only two forward voltages of 7 to 10 much smaller than that are required, the exciting current flows on the secondary side. For example, if the excitation current is positive on the primary side when entering the recirculation period, the excitation current becomes negative on the secondary side, so that the transformer 6 → the diode 9 → the reactor 11 → the load 12 → the diode 8 → the transformer 6 flows and diodes 8 and 9 become conductive. Similarly, assuming that the excitation current has a negative polarity when entering the reflux period, the diodes 7 and 10 are conductive because the excitation current has a positive polarity on the secondary side.

When no magnetism has occurred, the excitation current has a positive and negative equal waveform, so that the conduction times of the diodes 7 and 10 and the diodes 8 and 9 are equal. On the other hand, when the demagnetization occurs, the conduction time becomes uneven. As shown in FIG. 2, when the exciting current is positively biased, the diodes 8 and 9 are always conducted during the circulation period, and the conduction times of the diodes 7 and 10 and the diodes 8 and 9 are uneven. By detecting this, the occurrence of bias can be detected.
Although it is possible to conduct the diode by detecting each current, voltage detectors 102 and 103 for detecting the voltage between the anode and the cathode are provided in FIG. These detect the occurrence of forward voltage in the diodes 8 and 10, and do not require a reverse voltage detection function. Further, since the forward voltage value itself does not matter, accuracy is not necessary. For the same reason, variations in forward voltage of individual diodes do not become a problem. As the voltage detector, there are a method using a series circuit of resistors and a method using a series circuit of resistors and an amplifier.

The difference in conduction time between the diodes 8 and 10 is measured by the time difference measuring device 104. The time difference measuring device 104 includes a counter or an integrator. The required value here is the conduction time difference in the reflux period, but the time difference between the period in which the positive voltage is applied to the transformer 6 and the period in which the negative voltage is applied in the steady state is sufficiently small. There is no problem to measure.
Based on the measurement results of the time difference measuring device 104, the pulse width controller 15 adjusts the on-time of the semiconductor switch elements 2 and 5 and the on-time of the semiconductor switch elements 3 and 4 so as to reduce the conduction time difference. It is suppressed.

FIG. 3 shows a second embodiment of the present invention. The difference from Fig. 1 is that the transformer secondary winding is a center tap, and further a center tap rectifier circuit using two diodes 7 and 9 as rectifier diodes. Reference numeral 103 denotes a point where the voltage detector 102 is attached to the diode 9. In this configuration, the freewheeling diode 101 and the series circuit of the rectifier diode 7 or 9 and the transformer secondary winding are connected in parallel during the freewheeling period. Therefore, the forward direction of the freewheeling diode 101 is used to flow the freewheeling current to the freewheeling diode. A voltage smaller than that of the rectifier diodes 7 and 9 is selected.
Other operations are the same as those in FIG. That is, when the semiconductor switch elements 2 and 5 are turned on, a voltage is applied to the transformer 6, an exciting current flows through the transformer 6, and a diode 7 is conducted to the secondary winding to connect the reactor 11 and the load 12. Current flows through the path. Next, when the semiconductor switch elements 2 and 5 are turned off, the current of the reactor 11 is held by the smooth action of the reactor 11, and this current flows through the freewheeling diode 101. Here, there may be paths through the rectifier diodes 7 and 9 as current paths. However, since the forward voltage of the freewheeling diode 101 is selected to be smaller than the forward voltage of the diodes 7 and 9, the current flows to the freewheeling diode 101. Flowing.

Next, when the semiconductor switch elements 3 and 4 are turned on, a voltage is applied to the transformer 6, an exciting current flows through the transformer 6, and a diode 9 is conducted to the secondary winding to cause the reactor 11 and the load 12. Current flows through the path. Next, when the semiconductor switch elements 3 and 4 are turned off, the current of the reactor 11 is held by the smoothing action of the reactor 11, and this current flows through the freewheeling diode 101. Here, there may be paths through the rectifier diodes 7 and 9 as current paths. However, since the forward voltage of the freewheeling diode 101 is selected to be smaller than the forward voltage of the diodes 7 and 9, the current flows to the freewheeling diode 101. Flowing. When no magnetization is generated, the excitation current has a positive and negative equal waveform, so that the conduction period of the diode 7 and the conduction time of the diode 9 are equal.
On the other hand, when the demagnetization occurs, the conduction time becomes uneven. As in FIG. 2, when the exciting current is positively biased, the diode 9 always conducts during the circulation period, and the conduction time between the diode 7 and the diode 9 becomes uneven. By detecting this, the occurrence of bias can be detected. The difference in conduction time between the diodes 7 and 9 is measured by the time difference measuring device 104. The time difference measuring device 104 includes a counter or an integrator. The required value here is the conduction time difference in the reflux period, but the time difference between the period in which the positive voltage is applied to the transformer 6 and the period in which the negative voltage is applied in the steady state is sufficiently small. There is no problem to measure.

 Based on the measurement results of the time difference measuring device 104, the pulse width controller 15 adjusts the on-time of the semiconductor switch elements 2 and 5 and the on-time of the semiconductor switch elements 3 and 4 so as to reduce the conduction time difference. It is suppressed.

  The present invention relates to a demagnetization prevention circuit of a full-bridge type switching regulator, and can detect the demagnetization of a transformer without using an expensive current detector or capacitor. It can be applied to switching regulators using DC transformers, DC-DC converters, high-voltage power supplies, and the like.

1 shows a first embodiment of the present invention. The operation waveform of FIG. 1 is shown. 2 shows a second embodiment of the present invention. A conventional example is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... DC power supply 2-5 Semiconductor switch element 6 ... Transformer 7-10 ... Diode 11 ... Reactor 12 ... Load 13 ... Current detector 14 ... DC component detector
DESCRIPTION OF SYMBOLS 15 ... Pulse width amplifier 101 ... Freewheeling diode 102, 103 ... Voltage detector 104 ... Time difference measuring device

Claims (1)

Converting direct current to alternating current, connecting the input of a transformer to the output of a so-called inverter, connecting the input of a rectifier circuit consisting of a plurality of diodes to the output of the transformer, and connecting a series circuit of a reactor and a load to the output of the rectifier circuit In the DC-DC converter formed by
Wherein the wheeling diode connected in parallel to the output of the rectifier circuit, conduction detecting means for detecting the conduction for at least two diodes of the previous SL in the rectifier circuit to flow only exciting current to the diode of the rectifier circuit in refluxing period And a time comparison means for comparing the conduction times of the two diodes. A transformer demagnetization detecting device for a DC-DC converter.

Images