JP2007306757A - Switching power circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power circuit of high safety, capable of accurately understanding the operating state of a switching element for accurately detecting abnormality in control, and alarming or forcedly stopping operation, based on this. <P>SOLUTION: The switching power circuit rectifies pulsating flow that occurs on a secondary coil 17b, by turning on/off the DC current supplied to a primary coil 17a of a switching transformer 17 from a power supply 11 by using a switching element 16. It comprises a comparison circuit 32 that outputs an overcurrent detecting signal, if the current which flows the switching element 16 exceeds a predetermined threshold current value; and a protection monitoring circuit 33 which sets the threshold current value and outputs it to the comparison circuit; and if the overcurrent detection signal is received, it decides that there is presence of control abnormality, based on this. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, the DC current supplied to the primary winding of the switching transformer is intermittently turned on and off by switching the switching element, thereby rectifying the pulsating current appearing in the secondary winding and thereby the DC current having a desired voltage value. In particular, the present invention relates to an improvement for ensuring safety by accurately monitoring the state of a switching element.

As the switching power supply circuit as described above, many circuit types have been proposed so far in both the self-excited oscillation type and the separately excited oscillation type. Incidentally, recently, as an inexpensive and efficient circuit system with a simple configuration, an RCC (Ringing Choke Converter) type switching power supply circuit belonging to a self-excited oscillation type (hereinafter referred to as Patent Document 1), for example, is recognized. Simply called "RCC power supply circuit").
JP 2002-204572 A

  FIG. 1 shows a preferred embodiment of the present invention applied to an RCC power supply circuit, as will be described later. Except for the components indicated by the reference numerals in the 30th order in FIG. First, the operation principle of the RCC power supply circuit will be briefly described although well known.

  The DC power supply voltage rectified by the rectifier circuit 12 using a diode bridge, etc., and smoothed by the smoothing capacitor 13 is applied to the control terminal of the switching element 16 via the connection midpoint of the voltage dividing resistors 14 and 15. The When the switching element 16 is composed of a field effect transistor, the control terminal is a gate, and when it is composed of a bipolar transistor, it is a base.

  When the voltage applied to the control terminal exceeds a predetermined level, the switching element 16 is turned on, and the main current path of the switching element 16 in series with the primary winding 17a of the switching transformer 17 is closed. To do. Of course, when the switching element 16 is a field effect transistor, it is a source-drain current path, and when it is a bipolar transistor, it is an emitter-collector current path.

  When the main current path of the switching element 16 is conducted, the DC power supply current from the rectifier circuit 12 is supplied to the primary winding 17a of the switching transformer 17, and thereby the same phase as the primary winding provided in the switching transformer 17 An induced voltage is also generated in the feedback winding 17f, and a control voltage is applied to the control terminal of the switching element 16 via the differential feedback circuit 18 in a direction to further increase the conduction state of the switching element 16, and this positive feedback causes The primary winding current increases more.

  While the primary winding 17a is energized in this way, energy is stored in the primary winding 17a, but the voltage generated in the feedback winding 17f is monitored by the switching control circuit 23. When this voltage reaches a predetermined voltage, the control transistor 24 composed of a field effect transistor or a bipolar transistor is turned on, which turns the switching element 16 off, for example, by pulling the control terminal of the switching element 16 to the ground potential, for example. .

  As a result, when the supply current to the primary winding 17a of the switching transformer 17 is suddenly cut off, the energy accumulated in the primary winding 17a is transferred to the secondary winding 17b, and the current is supplied to the secondary winding 17b. This current is rectified via the rectifier circuit 19 such as the diode 19 and charges the smoothing capacitor 20.

  When the secondary winding energy is reduced through this charging, the current again causes current in the feedback winding 17f to reverse its direction, and the voltage appearing thereby causes the switching transformer 16 to turn through the feedback circuit 18. Thereafter, the switching operation with positive feedback described above is repeated, and a DC voltage output of a predetermined voltage is efficiently obtained on the secondary side of the switching transformer 17.

  Under this switching operation, the output voltage control circuit 21 provided on the secondary side sends the control signal to the primary side, for example, via the photo coupler 22 when the secondary side DC voltage rises above a certain value. To the switching control circuit 23 of the switching element 16, and works to turn off the switching element 16, and the shunt resistor 25 connected in series to the main current path of the switching element 16 increases its current as the current flowing through the switching element 16 increases. The voltage at both ends is raised, and this is also fed back to the switching control circuit 23 to turn off the switching element 16 when it exceeds a predetermined size. It works to protect the DC voltage value.

  However, in the conventional RCC power supply circuit, as described above, the output voltage control circuit 21 is provided on the secondary side of the switching transformer 17 to control the output voltage to a predetermined voltage value, or the main current of the switching element 16 The voltage across the shunt resistor 25 in series with the passage is monitored to detect an overload state of the switching element 16 and try to ensure safety.

  However, such a protective function is, as a matter of course, control, and as a result, the switching element 16 may continue to operate so as to extend the on-time. Or it is not unthinkable that a failure will occur. This means that the product equipped with this switching power supply circuit itself will not work. For example, if it is for driving a water heater, the user will take a bath for several days until the repair is completed. There is a possibility that there will be no situation. Furthermore, it must be considered that the switching element 16 and its peripheral parts generate heat, which may cause fire and smoke in the worst case and may cause harm to the user.

  However, conventionally, there is no way to recognize in real time exactly how much heat is generated in the switching element 16, in other words, how much loss has been reached, and if the input and load conditions change, the constant of the shunt resistor 25 There was also a problem that the operating point had to be changed. Such a point does not change even in the technique disclosed in the above-mentioned Patent Document 1, and the switching transformer primary current is turned on / off even in a switching power supply circuit other than the illustrated RCC power supply circuit. The same problem occurs in conventional circuits having elements.

  The present invention has been made in view of this point, and is capable of accurately grasping the operating state of the switching element, accurately detecting a control abnormality, and alerting or forcibly stopping the operation based on this. In addition, it is desirable to provide a switching power supply circuit with a high level of power, and desirably, even if the circuit load condition or the maximum load current changes, the constants of the circuit components do not need to be changed, and protection monitoring based on a certain standard can be performed. It is intended to provide a switching power supply circuit that can be used.

In order to achieve the above object, in the present invention,
A switching power supply circuit for rectifying a pulsating current appearing in a secondary winding by interrupting a direct current supplied from a power source to a primary winding of a switching transformer by turning on and off the switching element;
A comparison circuit that outputs an overcurrent detection signal when the magnitude of the current flowing through the switching element exceeds a predetermined threshold current value;
A protection monitoring circuit that sets the threshold current value, outputs the threshold current value to the comparison circuit, and determines whether there is a control abnormality based on the overcurrent detection signal;
A switching power supply circuit characterized by comprising:

  In the present invention, for more precise determination, the protection monitoring circuit grasps the current actually flowing through the switching element from the threshold current value set when the overcurrent detection signal is received, and detects the overcurrent. By grasping the switching frequency after receiving the signal, when the actual loss of the switching element obtained through a predetermined calculation function between them exceeds the allowable range, it is determined that the control is abnormal. A switching power supply circuit configured to be proposed is proposed.

  This may be a simpler determination method. For example, when it is recognized that the switching frequency of the switching element has exceeded a predetermined width after receiving an overcurrent detection signal, a control abnormality is determined. A protection monitoring circuit can be built.

  Further, in the above configuration, the protection monitoring circuit can be configured by a microcomputer so that the threshold current value can be easily variably set, so that the load condition or the maximum load current required for the switching power supply circuit has changed. Even in this case, it is possible to cope with this by simply changing only the threshold current value without changing the circuit constants of other circuit components.

  The present invention also proposes a switching power supply circuit having a warning device that emits one or both of a visual alarm and an audible alarm when the protection monitoring circuit determines that the control is abnormal, as a desirable sub-mode.

  In addition to this, or instead of this, the protection monitoring circuit also proposes a switching power supply circuit configured to stop the operation of the switching element when it is determined that the control is abnormal, and in this case, In addition, it is also proposed to provide a latch circuit that allows the switching element to be restarted only when the release operation is preferably performed by an artificial operation such as a button operation or when the power is turned off and then turned on again. To do.

  According to the present invention, it is possible to monitor the loss state of the switching element in real time while maintaining the basic control for controlling the switching by the conventional load current on the secondary side, so that the heat generation state and the switching operation state can be grasped in detail and used. The risk of inconvenience to the elderly can be greatly alleviated. In addition, according to the specific aspect of the present invention, the threshold current value of the comparison circuit can be arbitrarily variably set according to the load condition without changing the circuit constant at all. Reliable protection function can be realized.

  FIG. 1 shows a preferred embodiment of a switching power supply circuit constructed by applying the present invention. In particular, this embodiment is an improvement to the RCC power supply circuit, although not limited thereto, as described above. It has become.

  Since the basic operation description of the RCC power supply circuit is as described above, the following description will be made exclusively for the circuit portion to which the present invention is applied. Simply abbreviated as “element current”) is input to one input (in this case, a reverse-phase input) of the comparison circuit 32 as a voltage-converted value of the current flowing through the shunt resistor 25. The threshold voltage value corresponding to the threshold current value output from the protection monitoring circuit 33 is supplied to the other input of the comparison circuit 32 (in this case, the positive phase input) via the digital / analog converter 36 as necessary. Yes.

  Therefore, when the element current does not exceed the threshold current value, the switching element 16 continues to operate as it is. However, when the element current exceeds the threshold current value, the output of the comparison circuit 32 is inverted, and in this case, it substantially falls to the ground potential. By energizing the photocoupler 35, an overcurrent detection signal indicating that the element current has exceeded the threshold current value is transmitted to the protection monitoring circuit 33.

  The protection monitoring circuit 33 that receives this overcurrent detection signal stores in advance a current value corresponding to how much element current is currently applied based on the above-described threshold voltage value set in advance. Therefore, it can be determined that the control is abnormal depending on the value or the fact that the overcurrent detection signal is received.

  However, preferably, the actual loss of the switching element 16 at that time is indirectly detected through a predetermined calculation function between them when the comparison circuit 32 inverts its output and thereafter. However, since it can be obtained fairly accurately in real time, it may be configured to determine that the control is abnormal when the loss exceeds an allowable range. A simpler determination method may be used. For example, when it is recognized that the switching frequency of the switching element exceeds the predetermined width after receiving the overcurrent detection signal, it can be determined that the control is abnormal.

  In any case, according to the present invention, the device current or the device loss can be accurately grasped in real time, so that it is possible to reliably determine whether or not there is a control abnormality within a necessary and sufficient safety margin. And the result of the abnormality determination can be used more rationally.

  For example, when the oversight detection signal is received by the protection monitoring circuit 33, or when it is determined that the operation state of the switching element 16 has led to failure or burning through the above-described arithmetic function, One or both of a visual alarm and an audible alarm may be generated from the alarm device 34.

  Some of these devices that operate with such a switching power supply have a remote controller, but if there is a liquid crystal display, for example, it is visible by displaying characters or blinking on the display. An appropriate buzzer or the like can be used for an audible alarm.

  In addition, if the protection monitoring circuit 33 determines that certain conditions are met that may cause serious harm to the user, such as ignition or smoke, the switching operation must be forcibly stopped using a latch circuit 37, for example. Can do. That is, the output of the latch circuit 37 acts on the switching control circuit 23 to forcibly turn off the switching element 16 to ensure safety.

  And this forced stop is a release function only by human operation such as operating a button (not shown) unlike the temporary stop by the output voltage control circuit 21 and the like described above due to the function of the latch circuit 37. It is desirable to allow the switching element 16 to be restarted only when the power is turned off or the power is turned off and then on again.

  The protection monitoring circuit 33 may of course be configured as a dedicated hardware device itself, but in the recent technical circumstances, this can be substantially configured by a microcomputer. Then, since the threshold voltage value and the like given to the comparison circuit 32 can be easily changed and set, even if the maximum load current or load condition of the circuit changes, only the variable setting of the threshold voltage value (threshold current value) is sufficient. This eliminates the need to change circuit component constants (requires replacement of circuit components) and provides very reasonable and desirable results, with a constant percentage of the maximum load current of the circuit required from time to time. Various operating points can be set.

  As described above, the present invention has been described with reference to the preferred embodiments. However, as described above, the present invention is naturally applicable to switching power supply circuits other than the illustrated RCC power supply circuit. In the illustrated case, the DC current selectively supplied to the switching transformer primary winding 17a is obtained from a DC power source obtained by rectifying the commercial AC power source 11 with the rectifier circuit 12. However, the switching power source using a battery or the like as the power source It can also be applied to circuits.

1 is a schematic configuration diagram of a preferred embodiment of a switching power supply circuit according to the present invention.

Explanation of symbols

11 AC power supply
12 Rectifier circuit
13 Smoothing capacitor
14, 15 resistance
16 Switching element
17 Switching transformer
17a Switching transformer primary winding
17b Switching transformer secondary winding
17f Switching transformer feedback winding
18 Feedback circuit
19 Rectifier circuit
20 Smoothing capacitor
21 Output voltage control circuit
23 Switching control circuit
25 Shunt resistor
32 Comparison circuit
33 Protection monitoring circuit
34 Alarm device
37 Latch circuit

Claims (7)

A switching power supply circuit for rectifying a pulsating current appearing in a secondary winding by interrupting a direct current supplied from a power source to a primary winding of a switching transformer by turning on and off the switching element;
A comparator circuit for outputting an overcurrent detection signal when the magnitude of the current flowing through the switching element exceeds a predetermined threshold current value;
A protection monitoring circuit that sets the threshold current value, outputs the threshold current value to the comparison circuit, and determines whether there is a control abnormality based on the overcurrent detection signal;
A switching power supply circuit comprising: A switching power supply circuit according to claim 1;
The protection monitoring circuit grasps the current actually flowing through the switching element from the threshold current value set when the overcurrent detection signal is received, and after receiving the overcurrent detection signal. The switching frequency of the switching element is grasped, and when the actual loss of the switching element at that time obtained through a predetermined calculation function exceeds the allowable range, it is determined that the control is abnormal. A switching power supply circuit. A switching power supply circuit according to claim 1;
The protection monitoring circuit is configured to determine a control abnormality when recognizing that the switching frequency of the switching element has exceeded a predetermined width after receiving the overcurrent detection signal. thing;
A switching power supply circuit. A switching power supply circuit according to claim 1;
The protection monitoring circuit is configured by a microcomputer so that the threshold current value can be variably set;
A switching power supply circuit. A switching power supply circuit according to claim 1;
Having an alarm device that emits one or both of a visual alarm and an audible alarm when the protection monitoring circuit determines that the control abnormality has occurred;
A switching power supply circuit. A switching power supply circuit according to claim 1;
The protection monitoring circuit is configured to stop the operation of the switching element when the control abnormality is determined;
A switching power supply circuit. A switching power supply circuit according to claim 6;
A latch circuit that permits re-operation of the switching element only when the release operation is performed by human operation after the stop of the operation of the switching element or when the power supply is once turned off and then turned on again. Having;
A switching power supply circuit.

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