JPS636909Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a frequency modulator working/standby switching control circuit for detecting a failure in an FM modulator including an APC circuit and switching to a backup FM modulator.

Conventionally, in this type of switching control circuit, the confirmation time is usually set to several seconds, taking into account the unstable time it takes for the APC circuit to lose its lock and pull back into the reference frequency when the power is momentarily cut off. That is, as shown in FIG. 1, the first FM modulator 1 and the second FM modulator 2 are in a working/standby relationship, and the coaxial switch 3 switches the output of either one to the next stage unit. Connected to 4. Further, a directional coupler 5 is provided between the coaxial switch 3 and the next stage unit 4, and a part of the high frequency output of the FM modulator 1 or 2 is converted to a DC level by a detector 6. By adding it to the level comparator 7, if the FM modulator output level is lower than the control limit value, the relay circuit 8
is operated, the closing contact is passed to the primary side of the photo coupler 9, and the timer circuit 10 connected to the secondary side of the photo coupler 9 is put into operation.
Next, the output of the timer circuit 10 is output from the AND circuit 11.
and 12 input terminals, and changes from the L level to the H level τ seconds after the input side of the timer circuit 10 changes from the H level to the L level. Therefore, if the coaxial switch 3 is currently connected to select the FM modulator 1, no current will flow to the light emitting diode side of the photo coupler 13, so the current will not flow to the photo transistor side of the photo coupler 13. The collector is at H level, so the output of the AND circuit 11 is at H level, and the flip-flop circuit 15 is set.
Make contact 7 in the make state. Therefore, as a result of current flowing through the coil of the coaxial switch 3 through the closed contact of the relay circuit 17, the coaxial switch 3 is placed in the selected state of the FM modulator 2.

However, in this circuit, even if APC failure is not caused by a momentary power outage in the main power supply, but is caused by an actual APC circuit failure such as a failure of the reference crystal oscillator, the output will be interrupted for several seconds before switching to the standby unit. It had the disadvantage of being accompanied by

The purpose of this invention is to add a power failure detection circuit to the above circuit, and in the case of a momentary power failure of the main power supply, the failure detection circuit is prohibited until the APC circuit is completely stabilized after the power is restored. In the event of a failure in the APC circuit, the failure is instantly detected and automatically switched from the working FM modulator to the standby FM modulator.
It is an object of the present invention to provide an automatic switching control circuit which solves the above-mentioned drawbacks and minimizes the time during which the output is cut off due to failure of the working device.

In other words, the present invention eliminates the time confirmation circuit that was conventionally placed after detecting a failure, adds a power failure detection circuit in its place, and places a time confirmation circuit after the same circuit, so that the APC circuit can be activated in the event of a momentary main power failure. It takes time to confirm that it works stably, but pure
It has the feature of immediately detecting APC circuit failure and automatically switching to a backup device.

The present invention will now be described in detail with reference to drawings of embodiments of the present invention.

FIG. 2 shows an embodiment of the present invention.
A first FM modulator 11 including an APC circuit, and a second FM modulator 11 including an APC circuit.
One of the outputs of the FM modulator 12 is selected by a coaxial switch 13, and the selected output is applied to a unit 14 at the next stage. Furthermore, a directional coupler 15 exists between the coaxial switch 13 and the next stage unit 14, and extracts a part of the output level of the FM modulator.
It is passed to the detector 16, where it is converted to a DC level,
The same output is applied to a level comparator 17 for level comparison. The output of the level comparator 17 is transmitted to the detector 16
When the DC level of is lower than the preset control limit value, it changes from H level to L level,
The relay circuit 18 is set to operate, and the make contact of the relay circuit is connected to the primary side of the photo coupler 19. On the other hand, the secondary side of the photo coupler 19 is connected to one of the input terminals of an AND circuit 21 via an inverter 20. The anode terminal on the primary side of the photo coupler 24 is connected via a resistor to a power source (voltage V ₁ ) obtained by rectifying the main power source, and the cathode terminal is connected to ground. Therefore, in the photo coupler, when the main power supply is normal, the primary side light emitting diode is always in a light emitting state and the secondary side phototransistor is in an on state. Now, if the collector terminal of the secondary side phototransistor of the same photocoupler is connected to an uninterruptible power supply (voltage V _c ) via a resistor, when the main power is cut off, the secondary side phototransistor will be in an OFF state. Therefore, the photocoupler's circuit performs power outage detection operations. The secondary side of the photo coupler 24 is connected to a timer circuit 25 that performs an active low operation, and when the secondary side of the photo coupler 24 changes from an off state to an on state, that is, from an H level to an L level, the timer starts operating and lasts for τ seconds. Afterwards, the output level of the timer circuit is converted from L to H level. Therefore, the timer circuit operates when the main power is initially turned on or when the power is restored after a power outage. The output of this timer circuit 25 is connected to the other input terminal of the AND circuit 21, and by keeping it at L level for τ seconds after the main power is turned on, even if the FM modulator output is cut off, the inverter circuit 20 Even if the output level of the AND circuit 21 is at the H level, the output level of the AND circuit 21 is at the L level. Next, the output terminal of the AND circuit 21 is connected to one side of the input terminals of the AND circuits 22 and 23, while the switching state from the output coaxial switch 13 is transmitted to the AND circuits 22 and 23 through the photo coupler 26. When the FM modulator 1 is used, an H level is applied to the remaining input terminal of the AND circuit 22, and when the FM modulator 2 is used, an H level is applied to the remaining input terminal of the AND circuit 23. Further, the output terminals of the AND circuits 22 and 23 are connected to the set and reset terminals of a flip-flop circuit 28, respectively, and the Q output of the flip-flop circuit is transmitted to the coil of a relay circuit 30 via an inverter circuit 29, and the coaxial switching Vessel 1
Based on the connection status of 3 and the failure detection of the FM modulator,
On/off control of the coil current is performed, and control is performed to automatically switch the coaxial switch 13 to the preliminary modulator side.
For example, in the past, when the main power supply was normal, the FM
When an APC error occurs during use of the modulator 1 and an output interruption is detected by the level comparator 17, the output of the AND circuit 22 becomes H level, the flip-flop circuit 28 enters the set state, and the output level of the flip-flop circuit 29 changes. becomes H level, and the output of inverter 29 becomes L level. As a result, current flows through the coil of relay circuit 30 and the make contact closes. Therefore, the coil of the coaxial switch 13 is also excited, and the FM modulator 2 is selected. Since the automatic switching operation described above does not provide any particular confirmation time during control, it is performed almost instantaneously (100ms or less) after the APC of the FM modulator occurs.

On the other hand, if an instantaneous power failure occurs in the main power supply and the FM modulator is temporarily out of APC, the timer circuit 25 operates as described above and waits for τ until the APC circuit operates stably. Seconds are AND circuit 2
In No. 1, fault detection is prohibited, so switching malfunctions are prevented.

As explained above, this invention adds a circuit that prohibits failure detection only when the power is turned on.
Conventionally, automatic switching due to a modulator failure would require a few seconds of output interruption, but as long as the main power supply is normal,
Automatic switching is possible instantaneously (less than 500msec), so
When used in FM broadcasting equipment or television audio broadcasting equipment, it has the effect of providing a highly reliable broadcasting transmission system with less stoppage time.

It should be noted that although the above embodiments were mainly explained using the configuration of the IC circuit, the same effect can be achieved by replacing the relay circuit with a relay circuit, which is a part of the claims of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional embodiment, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 11, 12...FM modulator, 13...
...Coaxial switch, 17...Level comparison circuit, 24...
...Photo coupler for power failure detection, 25...Timer circuit, 21...Failure detection AND circuit.

Claims (1)

[Scope of utility model registration request] A control circuit that switches between a working frequency modulator and a standby frequency modulator, the circuit including a changeover switch that selects the output of the two modulators, and a control circuit that detects the output level of the changeover switch and sets a predetermined level. a first detector that outputs a first detection signal when the power is turned off, a second detector that outputs a second detection signal when the power is turned off, and a detection signal of the second detector that is delayed by a predetermined time. a delay circuit that receives the output of the first detector and the output of the delay circuit, and when only the first detection signal is detected, immediately switches the changeover switch to detect the first and second detection signals. and a logic circuit that switches the changeover switch based on the first detection signal with a delay of the delay time of the delay circuit after the second detection signal is no longer output when the signal is detected. Features: Frequency modulator active/standby switching control circuit.