JP2007124152A - Receiver unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver unit capable of preventing beat disturbance caused by a switching noise from a self-excitation switching power source, using a low-cost circuit configuration. <P>SOLUTION: An AM receiver unit includes an AM receiver 14 for receiving AM broadcast, a self-excitation switching power source 11 for supplying operation power to the AM receiver 14, a dummy load 12 provided as a load of the self-excitation switching power source 11, a switch means 13 inserted in a current path of the dummy load 12 for switching the current path connection on and off, a switching frequency detection means 15 for detecting the switching frequency of the switching power source 11, and a control means 16 for controlling to open/close the switch means 13 so that the switching frequency detected by the switching frequency detection means 15 comes into a predetermined range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a receiving apparatus, and more particularly, to a receiving apparatus that can prevent beat failure caused by the switching frequency of a self-excited switching power supply with a low-cost configuration.

  When a switching power supply is used in an apparatus that receives an AM broadcast, the harmonics of the switching frequency of the switching power supply may be close to the frequency of the AM broadcast to be received. In such a case, a beat failure occurs between the harmonic wave and the AM broadcast to be received, and the broadcast becomes very difficult to hear.

  FIG. 6 is an explanatory diagram showing the relationship between radio waves and harmonics of AM broadcasting. The relationship between harmonics and beat disturbance will be described with reference to FIG. In the figure, 201 indicates the carrier frequency of AM broadcast, and 202 indicates the frequency band of the carrier frequency 201 of AM broadcast. D is the frequency bandwidth of the carrier frequency 201 of AM broadcasting.

  Here, it is assumed that the harmonic has a frequency indicated by 301. In this case, since it overlaps within the frequency band occupied by the carrier frequency 201 of AM broadcasting, a beat failure occurs due to interference. When this beat failure occurs, the beat failure disappears if the frequency of the harmonic 301 is shifted to a frequency indicated by 302, for example.

  Conventionally, a method has been proposed in which a load resistance is provided on the secondary side of a switching power supply, and the switching frequency is shifted by changing the load current to prevent beat failure (see, for example, Patent Document 1). However, when the load current continuously fluctuates like an audio signal, the switching frequency of the switching power supply also changes constantly, so that some of the harmonics may cause a beat again with the reception frequency of the tuner. In order to avoid this completely, it is necessary to provide several types of load resistors and switch the load resistors.

Utility Model Registration No. 3098365

  However, the configuration in which a plurality of load resistors are provided in order to prevent a beat failure has a problem that the number of circuit parts increases and the circuit cost increases.

  The present invention has been made in view of the above, and an object of the present invention is to provide a receiver capable of preventing beat failure caused by switching noise of a self-excited switching power supply with a low-cost circuit configuration. .

  In order to solve the above-described problems and achieve the object, the present invention provides a switching power supply capable of voltage control by varying a switching frequency, a receiving unit capable of receiving a broadcast, and a broadcast received by the receiving unit. And a switching frequency control unit that changes a switching frequency of the switching power supply based on the frequency received by the receiving unit.

  Exemplary embodiments of a receiving apparatus according to the present invention are explained in detail below with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment, and not all combinations of features described in the embodiment are necessary for the solving means of the invention. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or that are substantially the same.

(Embodiment)
FIG. 1 is a diagram showing a configuration of an AM receiving apparatus according to an embodiment of the present invention. The AM receiver shown in FIG. 1 includes a switching power supply 11, a dummy load 12, a switch unit 13, an AM receiver 14, a switching frequency detection unit 15, and a control unit 16.

  The AM receiver 14 receives AM broadcasts. The self-excited switching power supply 11 supplies operating power to the AM receiver 14. The switching power supply 11 is, for example, a PFM power supply or an RCC power supply. The dummy load 12 is a load on the secondary side of the switching power supply 11, and is composed of, for example, a connection point between the switching power supply 11 and the AM receiver 14 and one load resistor connected between the ground. Can do.

  The switch means 13 is inserted in the current path of the dummy load 12, and opens and closes the connection of the current path. The switching frequency detection means 15 detects the switching frequency of the switching power supply 11. As a switching frequency detection method of the switching frequency detection means 15, for example, a method of detecting the current value of the current path between the switching power supply 11 and the AM receiver 14 to detect the switching frequency of the switching power supply 11, There is a method of directly detecting the switching frequency from the output waveform.

  The control means 16 controls opening and closing of the switch means 13 so that the switching frequency detected by the switching frequency detection means 15 falls within a predetermined range. Since the switching frequency of the switching power supply 11 can be changed by opening and closing the switch means 13, beat failure due to switching noise of the switching power supply 11 can be prevented.

  FIG. 2 is a diagram illustrating a schematic configuration example of the AM receiving apparatus according to the first embodiment. The AM receiver shown in FIG. 1 includes a switching power supply (hereinafter referred to as “SMPS”) 101, a dummy load 102, a switch unit 103, an AM receiving unit 104, a current detection unit 105, a microcomputer 106, and a switch drive. Part 107.

  The AM receiver 104 receives an AM broadcast at a frequency designated by the user via an input unit (not shown). The SMPS 101 is a self-excited switching power supply, and is composed of, for example, a PFM power supply or an RCC power supply, and supplies operation power to the AM receiver 104.

  The dummy load 102 is a load on the secondary side of the SMPS 101 and is connected between the connection point of the SMPS 101 and the AM receiver 104 and the ground. The dummy load 102 is composed of one load resistor R10. One terminal of the load resistor R10 is connected to a connection point between the SMPS 101 and the AM receiving unit 104, and the other terminal is connected to the transistor Q1 of the switch unit 103. Connected to the collector.

  The switch unit 103 is inserted into the current path of the load resistor R10 and functions as switch means for opening and closing the connection of the current path of the load resistor R10. For example, the switch unit 103 includes a transistor Q1 and a base resistor R20. The transistor Q1 has a collector connected to one end of the load resistor R10, a base connected to the microcomputer 106 via the base resistor R20 and the switch drive unit 107, and an emitter grounded.

  When the control signal input from the switch drive unit 107 according to the control signal from the microcomputer 106 is “H” level, the transistor Q1 closes the connection of the current path of the load resistor R10, and the control signal is “L”. In the case of the level, the connection of the current path of the load resistor R10 is opened. The switching frequency of the above-described SMPS 101 is low when the load on the secondary side is heavy, and is high when the load is light. For this reason, when the connection of the switch unit 103 is closed and the connection of the current path of the load resistor R10 is closed, the switching frequency is reduced corresponding to the increase in the load due to the load resistor R10. Therefore, the switching frequency of the SMPS 101 can be changed by the microcomputer 106 controlling the opening and closing of the connection of the switch unit 103 via the switch drive unit 107.

  The current detection unit 105 functions as a switching frequency detection unit, detects a current flowing in a current path between the SMPS 101 and the AM reception unit 104, and outputs a voltage value corresponding to the current value to the microcomputer 106. The current detection unit 105 includes a current detection resistor R1 connected in series between the current paths of the SMPS 101 and the AM reception unit 104, resistors R2, R3, R4, R5, and R6, an operational amplifier OP, and a capacitor C1. The current value flowing through the current detection resistor R1 is converted into a voltage value by the resistors R2, R3, R4, R5, R6, the operational amplifier OP, and the capacitor C1, and is output to the microcomputer 106.

  The microcomputer 106 functions as switching frequency detection means and control means, and controls the overall operation of the AM receiver. Specifically, the microcomputer 106 detects the switching frequency of the SMPS 101 based on the voltage value input from the current detection unit 105. For example, a table indicating the relationship between the voltage value and the switching frequency is held, and the switching frequency can be calculated based on the input voltage value with reference to this table.

  Then, the microcomputer 106 controls the opening / closing of the switch unit 103 so that the detected switching frequency of the SMPS 101 falls within a predetermined range in order to prevent beat failures caused by the switching frequency of the SMPS 101 (for example, , PWM signal) is output to the base of the transistor Q1 via the switch drive unit 107. That is, the microcomputer 106 monitors the switching frequency of the SMPS 101, controls the opening and closing of the switch unit 103, and sets the switching frequency of the SMPS 101 within a predetermined range, so that the switching frequency of the SMPS 101 is changed from the frequency at which beat failure occurs to a different frequency. Shift.

  FIG. 3 is a flowchart for explaining the operation of the microcomputer 106. FIG. 4 is a diagram showing a spectrum of radio waves of AM broadcasting. In FIG. 4, ft represents the reception frequency of the AM receiver 104, fi represents an intermediate frequency, fLo (= ft ± fi) represents a local frequency, and image (= ft ± 2fi) represents an image frequency.

  In FIG. 3, the microcomputer 106 monitors the switching frequency (fsw) of the SMPS 101 via the current detection unit 105 when the AM reception unit 104 receives an AM broadcast (step S1). The microcomputer 106 confirms how many times the received frequency ft is approximately the switching frequency (fsw) of the monitored SMPS 101, and stores the absolute value as n. (Step S2) The microcomputer 106 determines whether or not the switching frequency (fsw) is within a predetermined range. Specifically, it is determined whether the absolute value of the difference between the integral multiple (n times) of the reception frequency ft and the switching frequency fsw is more than a predetermined (X kHz) (step S3). This is because a beat failure occurs even when a frequency that is an integral multiple of the switching frequency is received. X is a constant set at the time of product design, and is set to about 10 kHz, for example.

  If the microcomputer 106 determines in step S3 that the absolute value of the difference between the received frequency ft and the switching frequency fsw is an integer multiple (n times) is greater than or equal to a predetermined distance (“Yes” in step S3), Since it does not occur or is considered to be very slight, the operation of the switch unit 103 is left as it is (step S5).

  On the other hand, when the microcomputer 106 determines in step S3 that the absolute value of the difference between the integer multiple (n times) of the reception frequency ft and the switching frequency fsw is not greater than a predetermined value (“No” in step S3), The open / close state of the switch unit 103 is switched (step S4). As a result, the switching frequency of the SMPS 101 changes, so that a beat failure can be avoided. Therefore, it is preferable that the dummy load 102 in the present embodiment has a resistance value enough to sufficiently separate the frequency value obtained by multiplying the reception frequency ft of the AM receiver 104 by n times the switching frequency fsw.

  In this way, by controlling the difference between the integer multiples (n times) of the reception frequency ft and the switching frequency fsw to be a predetermined distance or more, beat failure due to the switching frequency of the SMPS 101 can be prevented.

  In the above example, the absolute value of the difference between the integer multiple (n times) of the reception frequency ft and the switching frequency fsw is used as the condition for controlling the opening / closing operation of the switch unit 103, but other conditions may be used. For example, (1) | n × fsw−fi |> XkHz, or (2) | n × fsw− (ft ± fi) |> XkHz, or (3) | n × fsw− (ft ± 2fi) | Conditions such as> X kHz can also be used. The example of (1) uses the absolute value of the difference between the intermediate frequency of the AM receiving unit 104 and the integral multiple (n times) of the switching frequency fsw. The example of (2) uses an absolute value of a difference between an integer multiple (n times) of the local frequency and the switching frequency fsw. The example of (3) uses an absolute value of a difference of an integer multiple (n times) of the image frequency and the switching frequency fsw. By controlling the opening and closing of the switch unit 103 so as to satisfy these conditions, a beat failure can be prevented. The conditions (1) to (3) are examples, and all of these combinations may be satisfied, or any of them may be satisfied.

  As described above, according to the first embodiment, the dummy load 102 serving as the load of the SMPS 101, the switch unit 103 that is inserted into the current path of the dummy load 102 and opens and closes the connection of the current path, the SMPS 101, and the AM receiving unit. A current detection unit 105 that detects a current value of a current path between the switches 104, and a switching frequency of the SMPS 101 is detected based on the current value detected by the current detection unit 105, so that the switching frequency falls within a predetermined range. Since the switching frequency of the SMPS 101 is monitored, the switching frequency of the SMPS 101 that constantly fluctuates can be constantly shifted to a frequency at which no beat disturbance occurs, and self-excited switching is provided. Power supply switching noise can cause It is possible to prevent the door failure at a low cost circuit structure.

  Further, according to the first embodiment, when the switching range of the SMPS 101 is (fsw) and the reception frequency of the AM receiver 104 is (ft), according to the first embodiment, | n × fsw−ft |> Xkhz (however, , N is an integer, and X is a constant), the switch unit 103 is controlled, so that the occurrence of a beat failure can be prevented at high speed and high accuracy.

  The SMPS 101 is not limited to a power source for driving the AM receiving unit 104. For example, even if the power supply for the AM receiver 104 is a dropper power supply and the SMPS 101 is used in an amplifier, the SMPS 101 used in the amplifier may cause a beat when receiving an AM broadcast. Even in such a case, occurrence of a beat failure can be prevented by using the present invention.

  FIG. 5 is a diagram illustrating a schematic configuration example of an AM receiving device according to the second embodiment. In the AM receiving apparatus according to the first embodiment, the current detection unit 105 is provided in order to detect the switching frequency of the SMPS 101. In contrast, the second embodiment has a configuration in which the switching frequency (fsw) is directly detected from the output waveform of the SMPS 101 without providing a current detection unit. 5, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals, description of common parts is omitted, and only different points will be described.

  The SMPS 101 attenuates the switching voltage output of the SMPS 101 in the voltage conversion unit 200 (for example, attenuates the output of about 100 V to about 5 V) and outputs it to the microcomputer 106. Calculate the switching frequency.

  According to the second embodiment, since the switching frequency is directly detected from the output of the SMPS 101, it is not necessary to provide a current detection unit, and the circuit configuration can be further reduced in cost.

  As described above, the receiving apparatus according to the present invention is useful for preventing beat failure when supplying operating power to an AM tuner with a self-excited switching power supply, and can be widely applied to audio apparatuses.

It is a figure which shows the structure of AM receiver which concerns on embodiment of this invention. 1 is a diagram illustrating a schematic configuration example of an AM receiving device according to Embodiment 1. FIG. It is a flowchart for demonstrating operation | movement of the microcomputer of FIG. It is a figure which shows the spectrum of the electromagnetic wave of AM broadcast. FIG. 10 is a diagram illustrating a schematic configuration example of an AM receiving device according to a second embodiment. It is explanatory drawing which shows the relationship between the electromagnetic wave of AM broadcast, and harmonic noise.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Switching power supply 12 Dummy load 13 Switch means 14 AM receiving part 15 Switching frequency detection means 16 Control means 101 SMPS
102 dummy load 103 switch unit 104 AM reception unit 105 current detection unit 106 microcomputer 107 switch drive unit 200 voltage conversion unit

Claims (5)

A switching power supply capable of voltage control by varying the switching frequency;
A receiver capable of receiving broadcasts;
A reception frequency detection unit for detecting a broadcast frequency received by the reception unit;
A switching frequency control unit that changes a switching frequency of the switching power supply based on the frequency received by the receiving unit;
A receiving apparatus comprising: A current load section serving as a load of the switching power supply;
Switching frequency detection means for detecting the switching frequency of the switching power supply,
The reception according to claim 1, wherein the switching frequency control unit changes the switching frequency so that the frequency received by the receiving unit and a frequency that is an integral multiple of the switching frequency do not overlap. apparatus. The current load part is composed of a plurality of resistors,
A switch means inserted in the current path of the plurality of resistors, and opens and closes the connection of the current path;
Control means for controlling opening and closing of the switch means such that the switching frequency detected by the switching frequency detection means falls within a predetermined range;
The receiving apparatus according to claim 2, further comprising: The switching frequency detection means includes
Current detection means for detecting a current value of a current path between the switching power supply and the receiver;
Detecting means for detecting a switching frequency of the switching power supply based on a current value detected by the current detecting means;
The receiving device according to claim 2, further comprising:   The receiving device according to claim 2 or 3, wherein the switching frequency detecting means detects a switching frequency directly from an output waveform of the switching power supply.

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