JPH08102372A - Television door phone backlight device - Google Patents

Abstract

PURPOSE: To make possible improving a power factor using simple circuit constitution, to make possible producing a DC source voltage without increasing the size of a power transformer, and to feed electricity to a backlight well. CONSTITUTION: An alternating current from an AC power supply is voltage- transformed at a predetermined level by a power transformer 2 and supplied to a feeder circuit for a backlight and to a DC feeder circuit. The alternating current supplied is converted into a direct current by a first rectifying smoothing circuit 3 to produce a DC voltage and applied to a Zener diode 5. The AC is also converted into DC voltage by a second rectifying smoothing circuit 6 and applied to an external circuit. A Zener diode 5 is turned on or off according to the value of the current applied, thus controlling the switching action of switching elements Q1, Q2. Therefore, electricity is fed to the DC feeder circuit during the period of a phase near the peak value of th input current, and is fed to the backlight 4 during the period of a phase other than the peak value. Thus a circuit which feeds electricity to the backlight and feeds direct current using one power transformer can be formed without increasing the size of the power transformer 2, and the power factor of the entire circuit can be improved to a large extent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TV intercom backlight device, and more particularly to a power supply circuit for generating a direct current power supply from an alternating current power supply using a capacitor input type rectifier circuit, and a power supply for supplying power for a backlight. The present invention relates to a TV doorphone backlight device including a circuit.

[0002]

2. Description of the Related Art Generally, in a TV doorphone, an AC power supply is used as an input power supply, and the AC power supply is used to drive a plurality of devices and circuits forming a TV doorphone system.

As is well known, TV intercoms include:
Since there is a monitor for indoor viewing of external images taken outdoors, there is a need for a TV intercom backlight device to power the backlight of the monitor, which is also more traditional than It has been put to practical use.

The TV intercom backlight device is usually a power supply circuit for a backlight of a liquid crystal monitor, for example, a backlight for supplying power required for lighting or dimming an incandescent light bulb.

By the way, in a TV doorphone system, a DC power supply for the purpose of rectifying an input AC power supply to a DC power supply and supplying a DC power supply to an audio output circuit for external communication by the main voice of the TV doorphone. Some are equipped with circuits.

Such a DC power supply circuit normally uses a power transformer for transforming an AC voltage from an AC power source, an AC output transformed by the power transformer, and a DC power source using an electrolytic capacitor. And a capacitor input type smoothing circuit for generating.

In the DC power supply circuit having the above structure, the input AC voltage is transformed by the power transformer, and the transformed AC voltage is supplied to the capacitor input smoothing circuit. The capacitor input smoothing circuit rectifies and smoothes the supplied AC voltage to generate a DC voltage, which is output to the DC power supply output terminal. At this time, the output of the capacitor input smoothing circuit is only the high-level power supply current near the peak value of the input voltage waveform, and the current in other phases with low peak values is not output.

Therefore, in the DC power supply circuit using the capacitor input type smoothing circuit as described above, the power factor of the capacitor input smoothing circuit is extremely small. Therefore, in order to generate a DC power supply of a predetermined level in another circuit such as an audio output circuit, it is necessary to increase the capacity of the power supply transformer as compared with the power consumption. That is, in other words, in order to supply a predetermined level of DC power to a circuit such as an audio output circuit, it must be replaced with a power transformer having a large capacity. That is, in the conventional DC power supply circuit, there is an inconvenience that the cost increases as the size of the power transformer increases.

Therefore, the above-mentioned TV doorphone backlight device is provided with the DC power supply circuit, and a so-called one power supply transformer is shared, and a circuit configuration of the backlight power supply circuit and the DC power supply circuit is provided. Attempts have been made to form. However, in this case, since the power factor of the capacitor input type smoothing circuit is extremely small as described above, the DC power supply cannot be generated well. Therefore, in order to efficiently generate the DC power supply and improve the performance of both the power supply circuit for the backlight, it is essential to improve the power factor of the entire circuit. At present, no such proposal has been made.

[0010]

As described above, since the conventional TV doorphone backlight device is configured by using the capacitor input type smoothing circuit, the power factor of the circuit is small, so that the peak of the input voltage waveform is generated. Only the current near the value is generated as the feeding current. In addition, in order to efficiently generate a DC power supply of a predetermined level, it is necessary to provide a power supply transformer having a larger capacity than the power consumption, resulting in an inconvenience that the cost becomes high. There was a problem that the rate was not improved.

Therefore, the present invention has been made in view of the above problems, and it is possible to improve the power factor with a simple circuit configuration and to generate a DC power supply voltage without increasing the size of the power supply transformer. It is an object of the present invention to provide a TV intercom backlight device that can perform power supply for a backlight as well.

[0012]

According to a first aspect of the present invention, there is provided a TV intercom backlight device according to the present invention, wherein a power transformer for transforming and outputting an alternating current from an alternating current power supply at a predetermined level and an output alternating current from the power transformer. To a DC power supply for supplying power to the backlight of the monitor for image monitoring, and for converting the output AC from the power supply transformer to DC and generating a DC voltage to power an external circuit. In the backlight device of the monitor for image monitoring, comprising the DC power supply circuit of, the backlight power supply circuit supplies power to the DC power supply circuit during a phase period near the peak value of the supplied current, It is characterized in that the phase control is performed so as to supply power to the backlight during the phase period other than the value.

According to another aspect of the present invention, there is provided a TV intercom backlight device, which transforms an alternating current from an alternating current power supply at a predetermined level and outputs the power supply transformer, and converts the output alternating current from the power supply transformer into a direct current. A TV door phone including a backlight power supply circuit for supplying power to the backlight, and a DC power supply circuit for converting output AC from the power transformer into DC to generate DC voltage and supplying power to an external circuit. In the backlight device, the backlight power supply circuit supplies power to the DC power supply circuit during a phase period near the peak value of the supplied current, and supplies power to the backlight during a phase period other than the peak value. It is characterized by performing phase control.

According to another aspect of the present invention, there is provided a TV intercom backlight device according to the present invention, in which a power transformer for transforming and outputting an alternating current from an alternating current power source at a predetermined level and a first rectifying and smoothing output alternating current from the power transformer. A backlight power supply circuit having a dimming means for converting the voltage into direct current using a circuit and supplying power to the backlight using at least two switching elements; and second alternating rectifying and smoothing output alternating current from the power transformer. A TV doorphone backlight device, comprising: a DC power supply circuit for converting a direct current into a direct current using a circuit to generate a direct current voltage and supplying the power to an external circuit. By performing switching by the two switching elements using the optical means, the DC power supply circuit is connected to the DC power supply circuit during the phase period near the peak value of the supplied current. Photoelectrically, the phase period other than the peak value and performing phase control so as to power the backlight.

According to a fourth aspect of the present invention, there is provided a TV intercom backlight device according to the present invention, wherein the second rectifying / smoothing circuit comprises at least four diodes. And a capacitor input type smoothing circuit composed of an electrolytic capacitor connected in parallel with the bridge circuit.

According to a fifth aspect of the present invention, there is provided a TV intercom backlight device according to the present invention, wherein the backlight feeding circuit is the first rectifier connected to the power transformer. A smoothing circuit, a backlight connected to the first rectifying and smoothing circuit, a switching element that performs switching to supply a current based on a phase angle of an input current to the backlight and the DC power supply circuit, And a dimmer that controls the switching operation of the switching element based on the phase angle of the input current.

According to a sixth aspect of the present invention, there is provided a TV intercom backlight device according to the fifth aspect, wherein the dimmer means comprises a Zener diode capable of varying a Zener voltage. The zener diode operates so that it becomes conductive when the voltage value applied by the input current exceeds the voltage of the zener voltage, and it becomes non-conductive when it does not exceed the voltage of the zener voltage. It is characterized by controlling the switching operation by.

[0018]

According to the first and second aspects of the present invention, the alternating current from the alternating current power source is transformed at a predetermined level by the power transformer, and the transformed alternating current supplies the backlight power feeding circuit of the image monitoring monitor and the direct current power feeding. The circuit is used to supply power for the backlight and direct current to the external circuit. At this time, the backlight power supply circuit supplies power to the DC power supply circuit during a phase period near the peak value of the supplied current, and supplies power to the backlight of the image monitoring monitor during a phase period other than the peak value. Phase control is performed. As a result, DC power supply can be performed, and a current in a phase period other than near the peak value can be supplied as a backlight power supply current. Therefore, it is possible to configure a circuit for performing power supply for backlight and DC power supply using one power supply transformer without increasing the size of the power supply transformer, and it is possible to significantly improve the power factor of the entire circuit.

According to the third aspect of the present invention, the alternating current from the alternating current power source is transformed at a predetermined level by the power transformer, and the transformed alternating current is supplied to the backlight power feeding circuit and the direct current power feeding circuit. The supplied alternating current is converted into direct current by the first rectifying and smoothing circuit, and this direct current is applied to the dimming means to supply power to the backlight by using at least two switching elements. Further, the supplied current is converted into a direct current by the second rectifying and smoothing circuit to generate a direct current voltage, which is supplied to an external circuit. At this time,
By the switching operation of the switching element by the dimming means, phase control is performed so that power is supplied to the DC power supply circuit during a phase period near the peak value of the supplied current and power is supplied to the backlight during a phase period other than the peak value. It can be carried out. As a result, DC power supply can be performed, and a current in a phase period other than near the peak value can be supplied as a backlight power supply current. Therefore, it is possible to configure a circuit that performs backlight power supply and DC power supply using one power transformer without increasing the size of the power transformer, and it is possible to significantly improve the power factor of the entire circuit.

In the present invention according to claim 4, the second aspect
By using a capacitor input type smoothing circuit for the rectifying and smoothing circuit of, it is possible to convert the AC output from the power transformer to DC, and also to supply the current only during the phase period near the peak value of the supplied current to the DC There is an advantage that a voltage can be generated.

According to the fifth and sixth aspects of the present invention, the backlight power supply circuit includes the first rectifying / smoothing circuit connected to the power transformer, the backlight, the switching element, and the dimming means. The phase control can be performed so that the backlight power supply and the DC power supply are performed according to the output AC phase of the power transformer. For example,
By using a Zener diode capable of varying the Zener voltage for the light control unit, the Zener diode is turned on / off according to the phase of the input current, and controls the switching operation by the switching element. This allows
The DC power supply circuit can be supplied with a current in a phase period close to the peak value of the input current value, and the backlight can be supplied with a current in a phase period other than the peak value. Furthermore, by changing the Zener diode,
It has an effect that the light of the backlight can be adjusted.
Therefore, it is obvious that the power factor of the entire circuit can be significantly improved.

[0022]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a TV intercom backlight device according to the present invention.

In FIG. 1, a pair of AC power supply input terminals 1
Is supplied with an AC voltage from an AC power supply (not shown). The AC power input terminal 1 is connected to the primary winding side of the power transformer 2, and an AC voltage is supplied to the primary winding side of the power transformer 2. On the other hand, on the secondary winding side of the power supply transformer 2, a backlight power supply circuit for supplying power to and dimming the backlight 4 of the image monitoring monitor is connected, and the power supply transformer 2 and the power supply for the backlight are connected. A first rectifying and smoothing circuit 3 is connected between the circuit and the circuit. The AC voltage transformed by the power transformer 2 is supplied to the first rectifying / smoothing circuit 3.

For example, if the input AC voltage is AC100V, the AC voltage supplied to the first rectifying and smoothing circuit is AC.
It will be about 20V.

The first rectifying / smoothing circuit 3 is a bridge circuit composed of, for example, four diodes, and rectifies and smoothes the supplied alternating current to convert it into direct current and outputs it. In the rectifying / smoothing process at this time, for example, full-wave rectification is performed to rectify the entire one cycle of the input AC, and DC that is a pulsating current is generated.

The output side of the first rectifying / smoothing circuit 3 has positive and negative terminals (not shown), and the positive terminal is connected to a backlight 4 formed of, for example, an incandescent lamp. It The other end of the backlight 4 is connected to the collector of a transistor Q1 which serves as a switching element.
The 1 emitter is connected to the negative terminal of the first rectifying and smoothing circuit 4.

The positive terminal of the first rectifying / smoothing circuit 3 has a transistor Q as another switching element via a bias R1 connected in parallel with the backlight 4.
2 is connected to the collector of the
It is also connected to the base of 1. The emitter of the transistor Q2 is connected to the negative terminal of the first rectifying / smoothing circuit 3.

Further, in this embodiment, a Zener diode 5 is used for effectively switching the two transistors Q1 and Q2, and the cathode of the Zener diode 5 is connected to the first transistor via an additional resistor R2. 1 is connected to the positive terminal of the rectifying and smoothing circuit 3. The anode is connected to the base of the transistor Q2, and is also connected to the positive terminal of the first rectifying / smoothing circuit 3 via the additional resistor R3. Incidentally, three additional resistors R4 to R6 are connected in parallel to the Zener diode 5, and one of the additional resistors is operatively used to divide the voltage by the Zener diode 5.

The Zener diode 5 is, for example, a programmable Zener diode (Texas LM431).
Is usually used, and the Zener diode 5 has a resistor R
The voltage can be divided using 5 and the Zener voltage can be varied arbitrarily. Therefore, when the DC voltage applied to the Zener diode 5 exceeds the Zener voltage, the Zener diode 5 conducts, and when it does not exceed the Zener voltage, the Zener diode 5 operates in a non-conducting state. As a result, the switching by the two switching elements Q1 and Q2 is effectively performed.

On the other hand, on the DC power supply circuit side, the second rectifying / smoothing circuit 6 is connected to the output terminal of the secondary winding of the power transformer 2. This second rectifying / smoothing circuit 6
As shown in FIG. 1, a capacitor input type smoothing circuit similar to that of the prior art is used, and the AC voltage transformed by the power transformer 2 is supplied to this capacitor input type smoothing circuit.

This capacitor input type smoothing circuit 6
Is composed of, for example, a bridge circuit composed of four diodes, and an electric field transistor connected in parallel to the bridge circuit. The supplied AC is rectified and smoothed to be converted into DC, that is, DC voltage. Is generated and output to the pair of DC power supply output terminals 7.

Next, the operation of the TV intercom backlight device having such a configuration will be described in detail with reference to FIG.

FIG. 2 is a waveform diagram for explaining the operation of the TV intercom backlight device shown in FIG.
2A is an output voltage waveform of the power transformer, FIG. 2B is a current waveform flowing in the first rectifying / smoothing circuit, and FIG. 2C is a current waveform flowing in the second rectifying / smoothing circuit of the DC power supply circuit.
FIG. 2D is a waveform of current flowing through the backlight, and FIG.
(E) is a timing chart showing the operation of the transistors Q1 and Q2 which are switching elements.

Now, it is assumed that an AC voltage is supplied from an AC power supply (not shown) to the AC power supply input terminal shown in FIG. Then, the AC voltage is transformed by the power transformer 2 to generate, for example, a sinusoidal AC voltage V1 shown in FIG. This AC voltage V1 is then supplied to the first and second rectifying and smoothing circuits 3 and 6. For example, AC100
When the AC of V is supplied, the power transformer 2 is AC20V
It is transformed into and output.

The alternating voltage V1 shown in FIG. 2 (a) is rectified and smoothed by the first rectifying / smoothing circuit 3 and converted into direct current, that is, the alternating current is full-wave rectified to generate a pulsating direct current. After that, this direct current is supplied to the right side circuit group shown in FIG. At the same time, also on the DC power supply circuit side, the supplied AC is rectified and smoothed by the second rectifying / smoothing circuit 6, and a DC voltage is supplied to the DC power output terminal.

Therefore, in this embodiment, since the Zener diode 5 whose Zener voltage is variable is used, an arbitrary Zener voltage is set in advance so as to have a predetermined voltage value. The setting in this case is a temporary setting and can be freely set when the light of the backlight 4 is adjusted.

When the pulsating DC current supplied from the first rectifying / smoothing circuit is supplied to the circuit group for supplying power, it is applied to the Zener diode 5 when the current value does not reach the peak value. Since the voltage value of the Zener diode 5 does not exceed the Zener voltage, the Zener diode 5 becomes non-conductive. Therefore, no current flows through the transistor Q2, the transistor Q2 turns off as shown in FIG. 2 (e), and a direct current flows through the transistor Q1 via the bias resistor R1, so that the transistor Q1 turns on. As a result, the current corresponding to the phase before the peak value of the current is supplied to the backlight 4.

After that, when the current value supplied to the Zener diode 5 reaches a level near the peak value,
Since the voltage value applied to the Zener diode 5 becomes a voltage value exceeding the Zener voltage, the Zener diode 5 becomes conductive. Therefore, the transistor Q
2 flows a current, the transistor Q2 is turned on as shown in FIG. 2 (e), and the DC current is applied to the bias resistor R1.
Since it does not flow to the transistor Q1 through the transistor Q1, the transistor Q1 is turned off. As a result, no current is supplied to the backlight 4 in the phase near the current peak value. At this time, in the DC power supply circuit, a current corresponding to a phase near the peak value of the DC current flows in the DC power supply circuit, and as a result, the generated DC voltage is supplied to the DC power output terminal 7. Will be done.

When the current value supplied to the Zener diode 5 falls to a level lower than the peak value, the voltage value applied to the Zener diode 5 becomes a voltage value which does not exceed the Zener voltage again. The Zener diode 5 becomes non-conductive. Therefore, no current flows through the transistor Q2, the transistor Q2 is turned off as shown in FIG. 2 (e), and a direct current flows through the transistor Q1 through the bias resistor R1, so that the transistor Q1 is turned on again. As a result, the current can be supplied to the backlight 4 in the phase that has dropped from the vicinity of the peak value of the current. After that, the above-mentioned operation is repeated, and as a result, the backlight current I3 as shown in FIG. It becomes possible to shine. During dimming, as shown by the arrow in FIG. 2B, the phase width increases around the peak value, and the backlight current I3 does not flow during this period.

Therefore, according to this embodiment, in the waveform of the input voltage from the input AC power supply, the current in the phase near the peak value can be supplied to the DC power supply circuit to generate the DC voltage of a predetermined level. Further, the current in the phase other than the peak value can be supplied to the backlight power supply circuit as the backlight current for powering the backlight 4. As a result, the current other than the peak value can be favorably utilized for the power supply for the backlight without being wasted. Therefore, since the power factor of the entire circuit can be improved, a backlight power supply circuit for supplying power to the backlight 4 using the same power transformer without increasing the capacity of the power transformer 2, and other And a DC power supply circuit for supplying DC power to the circuit of FIG.

In the present embodiment, the backlight power supply circuit is constructed by using a plurality of additional resistors R4 to R6. However, the switching operation by the two switching elements when the Zener diode is turned on / off is not performed. ,
It is not so affected, and when it is integrated into an IC, these resistors are included.

[0042]

As described above, according to the present invention, by using the backlight feeding circuit including the Zener diode, the transistors Q1 and Q2, and the bias resistor, the current in the phase near the peak value of the input voltage waveform is reduced. Can be supplied to the DC power supply circuit to generate a DC voltage, and the current can be supplied to the backlight power supply circuit and the backlight current to the backlight in phases other than the peak value. Therefore, the power factor of the entire circuit can be significantly improved. Further, without increasing the size of the power supply transformer, it is possible to configure a television intercom backlight device including a power supply circuit for backlight and a DC power supply circuit by using one power supply transformer.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a TV intercom backlight device according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the TV intercom backlight device shown in FIG.

[Explanation of symbols]

1 ... AC power input terminal, 2 ... Power transformer, 3 ... First rectifying / smoothing circuit, 4 ... Backlight (incandescent light bulb), 5 ... Zener diode, 6 ... Second rectifying / smoothing circuit (capacitor input type smoothing circuit) , 7 ... AC power supply output terminal, Q
1, Q2 ... Transistor, R1 ... Bias resistor, R2-
R6 ... resistance.

Claims (6)

[Claims] 1. A power supply transformer for transforming and outputting AC from an AC power supply at a predetermined level, and a back for converting output AC from the power supply transformer into DC and supplying power to a backlight of an image monitoring monitor. A backlight device for an image monitoring monitor, comprising: a power supply circuit for a light; and a direct current power supply circuit for converting an output alternating current from the power supply transformer into a direct current to generate a direct current voltage to supply an external circuit. The backlight power supply circuit performs phase control so that power is supplied to the DC power supply circuit during a phase period near the peak value of the supplied current and power is supplied to the backlight during a phase period other than the peak value. A backlight device for an image monitoring monitor characterized by: 2. A power supply transformer for transforming and outputting AC from an AC power supply at a predetermined level, and a backlight power supply circuit for converting the output AC from this power transformer into DC and supplying power to the backlight. And a DC power supply circuit for converting an output AC from the power transformer into a DC voltage to generate a DC voltage and supplying the DC voltage to an external circuit, the TV doorphone backlight device comprising: a backlight power supply circuit; Is a power supply to the DC power supply circuit during a phase period near the peak value of the supplied current, and performs phase control such that power is supplied to the backlight during a phase period other than the peak value. apparatus. 3. A power supply transformer that transforms and outputs alternating current from an alternating current power supply at a predetermined level, and an output alternating current from this power supply transformer is converted into direct current by using a first rectifying and smoothing circuit, and at least two switching operations are performed. A backlight power supply circuit having a dimming unit for supplying power to the backlight by using an element, and an output AC from the power transformer is converted into a DC using a second rectifying and smoothing circuit to generate a DC voltage. And a DC power supply circuit for supplying power to an external circuit, wherein the backlight power supply circuit performs switching by two switching elements using the dimming means. As a result, power is supplied to the DC power supply circuit during a phase period near the peak value of the supplied current, and power is supplied to the backlight during a phase period other than the peak value. TV intercom backlight device characterized by performing phase control as described above. 4. The second rectifying / smoothing circuit includes a bridge circuit including at least four diodes,
4. The TV doorphone backlight device according to claim 3, wherein the TV-door intercom backlight is a capacitor input type smoothing circuit composed of an electrolytic capacitor connected in parallel with the bridge circuit. 5. The backlight feeding circuit includes a first rectifying / smoothing circuit connected to the power transformer, a backlight connected to the first rectifying / smoothing circuit, the backlight and the DC power feeding. The circuit includes a switching element that performs switching to supply a current based on the phase angle of the input current, and a dimmer that controls the switching operation by the switching element based on the phase angle of the input current. The TV intercom backlight device according to claim 3. 6. The dimming means is configured by using a Zener diode capable of varying the Zener voltage, and the voltage value applied by the input current of the Zener diode exceeds the voltage of the Zener voltage. 6. The TV intercom backlight device according to claim 5, wherein the switching operation by the switching element is controlled by operating so as to be in a non-conductive state when it does not exceed, and controlling a switching operation by the switching element.