JP2007060787A - Power supply transformer protection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply transformer protection system that can detect the abnormal temperature of a power supply transformer without exchanging components and without upsizing a device due to an increase in the number of part items. <P>SOLUTION: The power transformer protection system measures voltages applied to both ends of a winding resistor by detecting a voltage proportional to a voltage induced at a secondary winding of the power supply transformer by a voltage detection resistor, whereby a load of the power supply transformer is predicted without substantially generating an error, thus protecting the power supply transformer from being overheated. The cost of a part can be reduced compared with the case that a current value generated at the secondary winding of the power supply transformer is measured. Furthermore, since an average value of voltages outputted by the voltage detection resistor in a certain period is employed when protecting the power supply transformer, the temperature of the power supply transformer is not abruptly raised even if a voltage applied to a primary winding is temporarily changed, and a wasteful operation such as an immediate protection operation can be prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power transformer protection system that protects a power transformer from overheating by predicting a temperature rise due to heat generation during operation of the power transformer.

  Conventionally, when an abnormal load is applied to the power transformer, the following can be prevented in order to prevent the occurrence of a fire due to overheating of the power transformer and other parts, and to prevent damage to the equipment provided with this power transformer. Configured as follows. FIG. 1 is a circuit diagram showing a configuration in which a current flowing through a power transformer is detected by a voltage across a resistor.

  (1) A thermal fuse is provided on the primary side of the power transformer, and when the temperature reaches an abnormal temperature, the fuse is blown to disconnect the primary side of the power transformer.

  (2) When the temperature detection circuit detects an overheat abnormality, the switching element is configured not to perform the switching operation but to maintain the conduction state and to fuse the fuse element (see, for example, Patent Document 1).

(3) As shown in FIG. 1, a small resistor (R1), for example, 0.1Ω, is connected in series to the secondary winding of the power transformer T1 on the main power supply line, and both ends of the resistor R1 are connected. When the current is detected from the voltage and the load on the transformer is predicted to be large, the microcomputer M1 is configured to suppress or stop part of the operation of the load RL to reduce power consumption.
Japanese Patent Laid-Open No. 2003-174771

  In the configuration of (1), the thermal fuse is blown when a large load is applied to the power transformer, so that failure of other parts of the apparatus can be prevented. However, if the temperature fuse is blown, the apparatus cannot be used again unless the power transformer is removed and the temperature fuse is replaced, and there is a problem that the trouble of replacing the power transformer is complicated.

  In the configuration (2), the current fuse is less expensive than the thermal fuse and is easy to replace. However, a plurality of fuse elements must be prepared in advance in preparation for fusing. In addition, the fuse element has to be exchanged every time it is blown, and there is a problem that it is troublesome.

  In the configuration (3), since the power consumption of the load RL is reduced before the thermal fuse is blown, the power transformer can be protected. However, it is necessary to use an expensive resistor having a rated power of several W class and a large size as the resistor R1 for current detection. For this reason, there is a problem that the cost is increased and a large space is required to attach the resistor, so that the apparatus is increased in size. Further, as shown in (3), when the current is detected by the resistor R1, there is a problem that an increase in the amount of heat generated due to the temperature characteristic of the transformer winding resistance value cannot be detected and an error occurs. For example, the primary-side winding resistance of the power transformer increases by 40% when the temperature is 125 ° C. compared to when the temperature is 25 ° C.

  Therefore, an object of the present invention is to provide a power transformer protection system capable of detecting an abnormal temperature of a power transformer without replacing parts and without increasing the size of the apparatus due to an increase in parts. .

  The present invention has the following configuration as means for solving the above problems.

(1) a power transformer including a primary winding connected to a commercial AC power source and a secondary winding for supplying an induced voltage to a load;
A voltage detection resistor connected in parallel to the power transformer and outputting a voltage proportional to the voltage induced in the secondary winding of the power transformer;
Determination means for determining whether or not a difference between an average value and a reference value for each first period of the voltage output by the voltage detection resistor is equal to or greater than a reference value;
When the determination means determines that the average value of the first period is greater than or equal to a reference value, protection means for limiting the operation of the load;
It is provided with.

  In this configuration, the voltage applied to both ends of the winding resistance of the power transformer is measured by detecting the voltage proportional to the voltage induced in the secondary winding of the power transformer by the voltage detection resistor, so there is almost no error. By predicting the load of the power transformer, the power transformer can be protected from overheating. Moreover, compared with the case where the electric current value of the secondary winding of a power transformer is measured, component cost can be reduced. Furthermore, when protecting the power transformer, the average value of the voltage output by the voltage detection resistor over a certain period is used, so even if the voltage applied to the primary winding is unstable and fluctuates temporarily, the power transformer Since the temperature does not rise suddenly, useless operations such as immediately performing a protective operation can be prevented. Therefore, the protection operation can be accurately performed by predicting the temperature rise of the power transformer.

  (2) The determination means sets the voltage data output by the voltage detection resistor when there is no load immediately after start-up or when the load is minimum to an initial value of a reference value, and as the reference value for each predetermined period, The voltage detection resistor is updated to the maximum value of the voltage data output during the period.

  In this configuration, the determination unit updates the reference value to the maximum value of the voltage data during the certain period. Therefore, even when the voltage applied to the primary winding continuously fluctuates, the power transformer can be protected without being affected by it.

  (3) When the protection unit operates, the determination unit changes a period for calculating an average value of the voltage data to a second period shorter than the first period, and the protection unit does not operate for the third period. The period for calculating the average value of the voltage data is returned to the second period.

  When the protection means operates continuously, the power transformer is likely to generate heat and become high temperature, so it is necessary to frequently determine whether or not a protection operation is necessary. On the other hand, when the protection means does not operate for a while, there is a high possibility that the heat generated by the power transformer has subsided, so there is no problem even if the determination interval for determining whether or not the protection operation is required is long. In this configuration, when the protection means operates continuously, the period for determining whether or not the difference between the average value of the voltage output from the voltage detection resistor and the reference value is equal to or greater than the reference value is shortened. If the protection means does not operate for a while, the determination period is lengthened. Therefore, the determination as to whether or not the protection operation is necessary and the protection operation can be accurately performed according to the operation state of the power transformer.

  The power transformer protection system of the present invention can accurately perform protection operation by predicting the temperature rise of the power transformer, so that the power transformer will not be abnormally overheated, and there is no need to replace or repair the power transformer. It is. Further, by appropriately performing the protection operation, it is possible to use a power transformer having a smaller size than usual, and it is possible to reduce the size of a device incorporating this system. Furthermore, the detection error can be reduced compared to a system that detects the temperature rise of the power transformer by current detection, and there is no need to use an expensive resistor with a rated power of several W class and a large size. Since it is good, the part cost can be reduced and the mounting space for the part can be reduced.

  FIG. 2 is an equivalent circuit diagram of the power transformer. Causes of temperature rise due to heat generation of the power transformer include loss due to copper loss (loss due to winding resistance) and iron loss (sum of core hysteresis loss and eddy current loss). When the load is so large that the thermal fuse element is blown, copper loss is dominant as the cause of the temperature rise. Therefore, FIG. 2 shows an equivalent circuit of a power transformer in which the resistance of the primary winding is equivalently moved to the secondary side while paying attention to the copper loss and omitting the winding resistance. In FIG. 2, T2 is an ideal power transformer, and R2 is an equivalent resistance of the primary winding and the secondary winding of the power transformer T2.

  Here, since the load P applied to the power transformer is P = I × ΔV (I: current, ΔV: voltage applied to both ends of the winding resistance), if the voltage ΔV can be known, the load of the power transformer is predicted. It becomes possible. In addition, the winding resistance value of the power transformer increases as the temperature rises. However, since the voltage ΔV = I × R2, when the voltage ΔV is measured, the change in the current and the change in the winding resistance value should be measured together. become. Therefore, the error can be reduced by measuring the voltage ΔV compared to the method of measuring the current I.

  FIG. 3 is a circuit diagram showing a configuration of a power transformer protection system that detects the voltage ΔV. In the power transformer protection system 1, an unstable DC voltage obtained by rectifying and smoothing the voltage induced in the secondary winding of the power transformer T3 by the diode D1 and the capacitor C1 is applied to the load RL. The voltage induced in the secondary winding of the power transformer T3 is divided by the voltage dividing resistors R3 and R4 and taken into the A / D port of the microcomputer M2. Furthermore, a capacitor C2 is connected in parallel to the voltage dividing resistor R4 in order to prevent the voltage from fluctuating due to noise or the like. In addition, the microcomputer M2 is configured to limit the operation of the load RL according to the voltage of the voltage dividing resistor R4. For example, the load RL is provided with a limiter circuit and a volume circuit (not shown). When the voltage of the voltage dividing resistor R4 exceeds a certain value, the microcomputer M2 operates the limiter circuit and the volume circuit to consume the load. Suppress power. Thereby, it is possible to protect the power transformer T3 from overheating.

  Here, for example, in a residential building, there are a time zone in which a plurality of electric devices are used at once, a time zone in which some of the electric devices are used, and a time zone in which almost no electric devices are used. In this way, when the load on the entire residential building fluctuates greatly in one day, the voltage of the commercial power supply also fluctuates in the range of 5V to 10V. For this reason, if the protection operation of the power transformer is performed without taking this voltage fluctuation into consideration, the power transformer may not be protected accurately. Therefore, in the power transformer protection system 1 of the present invention, even if the device 2 incorporating this system is installed in a place where the voltage supplied from the outside is not stable, the microcomputer can perform the protection operation of the power transformer without any problem. The operation of M2 is set.

  In the configuration shown in FIG. 3, the voltage input to the A / D port of the microcomputer M2 is processed as follows. FIG. 4 is a flowchart for explaining the operation of the microcomputer.

  When the power of the device 2 incorporating the power transformer protection system 1 is turned on and starts operating, the microcomputer M2, which is a control unit, captures voltage data at the time of no signal immediately after the power is turned on (s1), and the reference initial value and (S2).

  Subsequently, the microcomputer M2 takes in the voltage data (s3), and compares the voltage data with the MAX value (s4). Here, it is assumed that an initial value is set in advance for the MAX value, or 0 is set in the initial state. At this time, if the acquired voltage data is larger than the MAX value, the voltage data is set as the MAX value (s5). On the other hand, when the acquired voltage data is less than or equal to the MAX value, the voltage data is not replaced. Thereby, voltage data (voltage value) when the load of the power transformer is the lightest can be set to the MAX value.

  When a certain time (for example, 1 minute) elapses (s6), the average value of the data taken in the certain time is calculated (s7). Further, the control unit calculates a voltage ΔV that is a difference between the average value and the reference value (s8). Then, the control unit compares ΔV with a certain reference value Vr (s9), and when ΔV is larger than a certain reference value Vr, it determines that the load of the power transformer is large and reduces the power consumption. A protection operation such as lowering is performed (s10). On the other hand, when ΔV is equal to or smaller than a certain reference value Vr, the protection operation is not performed.

  Further, the processes of steps s3 to s10 are repeated until a certain measurement time (temporarily 15 minutes) elapses. When a certain measurement time elapses (s11), the current MAX value is replaced with a reference value (s12). . Then, the processes of steps s3 to s12 are repeated.

  By performing the above processing, the current temperature of the power transformer T3 and the temperature rise can be predicted, and the protection operation can be accurately performed.

  In the processing described with reference to FIG. 4, it is preferable to appropriately set the reference values for determining each measurement time and overload in accordance with the characteristics of each product and the performance of the transformer. For example, when the device incorporating the power transformer protection system is configured to detect the moment when the load is light, it is possible to obtain a more accurate value by taking in the reference value at the time of the light load. . Specifically, when the device incorporating the power transformer protection system is an amplifier and can detect that muting is being performed, voltage data may be acquired and set as a reference value during muting.

  Further, in the process described with reference to FIG. 4, it is possible to set the fixed time for determining the elapse of the measurement time in step s <b> 6 depending on whether the protection operation of the power transformer is performed. . For example, since the temperature of the power transformer is considered to be low at the beginning of the power supply of the device incorporating the power transformer protection system of the present invention, a certain time for judging the passage of the measurement time is, for example, 5 minutes (first period) Set to. An operation is performed so as to calculate an average value of the voltage data every 5 minutes. On the other hand, when the protection operation of the power transformer described in step s10 has been performed even once, the temperature of the power transformer is high, so that a certain time for determining the elapse of the measurement time is, for example, 1 minute (second period) ). An operation is performed so as to calculate an average value of the voltage data every minute. Also, if the power transformer protection operation has not been performed once, for example, after 10 minutes (third period) has passed since the power transformer protection operation, the temperature of the power transformer is lowered. Therefore, the fixed time for determining the passage of the measurement time is returned to 5 minutes (first period). In this way, by calculating the average of the voltage data according to the state of the power transformer protection operation, the number of determinations for performing the protection operation can be reduced.

  In the processing described with reference to FIG. 4, the power transformer is set to perform the protection operation when the voltage ΔV is larger than a certain reference value Vr. For example, a plurality of reference values Vr1, Vr2, Vr3. . . And the level of the protection operation of the power transformer may be set finely according to the value of the voltage ΔV. For example, “When the value of voltage ΔV is Vr1 <ΔV ≦ Vr2, the volume circuit is operated to lower the volume. When the value of voltage ΔV is Vr2 <ΔV ≦ Vr3, the limiter circuit is operated. The operation of the load RL is limited.When the value of the voltage ΔV is Vr3 <ΔV, the operation of the load RL is stopped. ”For example, the protection operation of the power transformer can be performed. .

  In the processing described with reference to FIG. 4, the maximum value of the acquired voltage data is replaced with the MAX value, and this MAX value is replaced with the reference value at regular intervals. However, the present invention is not limited to this. Other methods are possible. For example, when setting the reference initial value, measure the voltage (commercial power supply voltage) supplied from the outside at this time, measure the commercial power supply voltage at regular intervals, and change the voltage value. It is also possible to set so that the reference initial value is changed in proportion to.

  Next, a specific example when the power transformer protection system of the present invention is applied to a power amplifier will be described. FIG. 5 is a circuit diagram of a power amplifier to which the power transformer protection system of the present invention is applied. FIG. 6 is a graph showing the winding temperature of the power transformer when a music signal is input to the power amplifier.

  The power amplifier 11 shown in FIG. 5 has a configuration in which the power transformer protection system shown in FIG. 3 is provided for the + B power source.

  The power amplifier shown in FIG. 5 has a rating of 120 W / 6Ω, and performs the protective operation of the power transformer T3 when the voltage drop ΔV is 0.6 V or more. As the protection operation of the power transformer T3, the output is limited to 33 W (9.9 V / 3Ω) by clipping the signal to the final stage (Amp1) of the power amplifier. The microcomputer M2 initially performs abnormality determination every 5 minutes. Further, once the microcomputer M2 performs the protection operation of the power transformer, the abnormality determination frequency is changed every minute. On the other hand, if the protection operation of the power transformer is not performed for 5 minutes, the microcomputer M2 returns the abnormality determination frequency every 5 minutes.

  In the power amplifier shown in FIG. 5, the voltage at the A / D port of the microcomputer M2 is 2.89V as the reference value Vr in a certain period. At this time, the voltage of the + B power supply is 60.7V. Further, as described above, when the voltage drops by 0.6 V at the A / D port of the microcomputer M2, it is set so as to be determined to be abnormal. Therefore, when the voltage of the A / D port of the microcomputer M2 becomes 2.29 V or less, the microcomputer M2 performs a protection operation of the power transformer. When the voltage of the A / D port is 2.29V, the voltage of the + B power supply is 48.1V.

  When a music signal with an average output of 80 W / 3Ω is input to the power amplifier 11, as shown in FIG. 6, at the beginning of operation, the abnormality determination is set to be performed every 5 minutes. It has risen to 120 ° C. However, after that, the abnormality determination is performed every minute, the protection operation of the power transformer is performed, and when the voltage ΔV becomes 0.6V or less, the operation of stopping the protection operation of the power transformer is repeated. The temperature can be suppressed to around 90 ° C.

  As described above, the power transformer protection system according to the present invention can accurately perform the protection operation by predicting the temperature rise of the power transformer, and therefore can prevent abnormal overheating of the power transformer.

It is the circuit diagram which showed the structure which detects the electric current which flows into a power transformer with the both-ends voltage of resistance. It is an equivalent circuit diagram of a power transformer. It is a circuit diagram which shows the structure of the power supply transformer protection system which detects voltage (DELTA) V. It is a flowchart for demonstrating operation | movement of a microcomputer. It is a circuit diagram of a power amplifier to which the power transformer protection system of the present invention is applied. It is a graph which shows the coil | winding temperature of a power transformer when a music signal is input into a power amplifier.

Explanation of symbols

1-power transformer protection system 2-device 11-power amplifier C1, C2-capacitor D1-diode M1, M2-microcomputer P-load R1-resistor R3, R4-voltage dividing resistor RL-load T1, T2, T3-power transformer

Claims (3)

A power transformer including a primary winding connected to a commercial AC power source and a secondary winding for supplying an induced voltage to a load;
A voltage detection resistor connected in parallel to the power transformer and outputting a voltage proportional to the voltage induced in the secondary winding of the power transformer;
Determination means for determining whether or not a difference between an average value and a reference value for each first period of the voltage output by the voltage detection resistor is equal to or greater than a reference value;
When the determination means determines that the average value of the first period is greater than or equal to a reference value, protection means for limiting the operation of the load;
A power transformer protection system characterized by comprising:   The determination means sets the voltage data output by the voltage detection resistor when there is no load immediately after startup or when the load is minimum to an initial value of a reference value, and as a reference value every predetermined period, The power transformer protection system according to claim 1, wherein the voltage transformer is updated to a maximum value of voltage data output from the voltage detection resistor.   The determination unit changes the period for calculating the average value of the voltage data to a second period shorter than the first period when the protection unit operates, and the voltage data if the protection unit does not operate for the third period. The power transformer protection system according to claim 1, wherein a period for calculating an average value of the power transformer is returned to the second period.

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