This application claims the priority of Korean Patent Application No. 10-2009-0064343 filed on Jul. 15, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an alternating current (AC) detection circuit applicable to a power supply such as that of a plasma display panel (PDP), and more particularly, to an AC detection circuit for a power supply, which is configured to detect an AC input and output a square wave signal using a square wave generating part such as a shunt regulator.
2. Description of the Related Art
In general, a switching mode power supply (SMPS) applicable to a plasma display panel (PDP) TV set employs a sequence circuit so as to protect a PDP driving board. In order to employ such a sequence circuit, an alternating current (AC) detection circuit detecting AC input is required, as well as a brownout circuit blocking the sequence circuit when a low voltage is inputted.
An AC detection signal outputted from an AC detection circuit is commonly created in a direct current (DC) waveform and a square waveform, according to an AC signal's forms.
In an AC detection circuit employing the DC waveform, a sequence circuit is controlled and a brownout circuit is configured by using a Zener diode and a transistor.
Like this, a configuration using the Zener diode and the transistor uses an excessive resistance value in an input port so as to reduce the influence of standby power consumption and embody the operational characteristics of the sequence circuit and the brownout circuit, thereby causing circuit design review (CDR) problems in the case of the Zener diode and the transistor. Also, there are many components required, so the problem of cost is encountered.
The following descriptions are of circuits detecting an AC voltage using a Zener diode according to the related art. An AC detection circuit employing a DC waveform is configured to be active high by using a transistor, a Zener diode, and a photodiode. Such a circuit uses approximately twenty-seven components.
This circuit is configured to perform the conversion of an AC voltage to a DC voltage using a first Zener diode and a capacitor such as a ceramic capacitor or a film capacitor, allow a current to flow through a second Zener diode when the converted voltage is higher than a breakdown voltage in the second Zener diode, cause the current to operate a transistor, and generate an AC detection signal accordingly.
Since such an AC detection circuit according to the related art uses the Zener diode and the transistor, a complex circuit configuration is required for a bias and the protection of the Zener diode from surges. This causes an increase in the number of components, resulting in an increase in the area required for the increased components and a production cost.
An aspect of the present invention provides an alternating current (AC) detection circuit for power supply, which is configured to detect an AC and output a square wave signal using a square wave generating part such as a shunt regulator, thereby greatly reducing the number of required components.
According to an aspect of the present invention, there is provided an AC detection circuit for power supply, the AC detection circuit including: a rectifying part rectifying an AC voltage; a voltage division part dividing the voltage rectified by the rectifying part according to a preset division ratio; a voltage stabilization circuit part stabilizing the voltage divided by the voltage division part; and a first square wave generating part connected to a first operation voltage terminal, comparing the voltage stabilized by the voltage stabilization circuit part with an internal reference voltage, and generating a first square wave signal having a duty ratio according to comparison results between the stabilized voltage and the internal reference voltage.
According to another aspect of the present invention, there is provided an AC detection circuit for power supply, the AC detection circuit including: a rectifying part rectifying an AC voltage; a voltage division part dividing the voltage rectified by the rectifying part according to a preset division ratio; a voltage stabilization circuit part stabilizing the voltage divided by the voltage division part; a first square wave generating part connected to a first operation voltage terminal, comparing the voltage stabilized by the voltage stabilization circuit part with an internal reference voltage, and generating a first square wave signal having a duty ratio according to comparison results between the stabilized voltage and the internal reference voltage; and a second square wave generating part connected to a second operation voltage terminal, interlocked with the first square wave generating part, and generating a second square wave signal.
The second square wave generating part may be configured as a photocoupler connected to each of the first and second operation voltage terminals and generating the second square wave signal. The photocoupler may include a photodiode having an anode connected to the first operation voltage terminal and a cathode connected to a first output port; and a phototransistor having a collector connected to the second operation voltage terminal, a base receiving light from the photodiode, and an emitter connected to a second output port, generating the second square wave signal by receiving the light from the photodiode, and outputting the second square wave signal through the second output port.
The rectifying part may be a half-wave rectifying part half-wave rectifying the AC voltage.
The voltage division part may include a plurality of resistors connected in series between an output port of the rectifying part and a ground.
The voltage stabilization circuit part may include a first capacitor connected between a first division node preset in the voltage division part and the ground.
The first square wave generating part may include a shunt regulator having a cathode connected to the first output port, an input port connected to an output port of the voltage stabilization circuit part, and an anode connected to the ground.
The AC detection circuit may further include a protection circuit part having a capacitor connected between a first connection node connected to the first output port and the first division node.
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
The invention may, however, be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. The exemplary embodiments are provided to assist in a comprehensive understanding of the invention.
Referring to
Referring to
Also, referring to
Here, the photocoupler may include a photodiode PD having an anode connected to the first operation voltage Vcc1 terminal and a cathode connected to a first output port OUT1, and a phototransistor PT having a collector connected to the second operation voltage Vcc2 terminal, abase receiving light from the photodiode PD, and an emitter connected to a second output port OUT2. The phototransistor PT receives the light from the photodiode PD, generates the second square wave signal V2square, and outputs the second square wave signal V2square through the second output port OUT2.
Referring to
The voltage division part 200 may include a plurality of resistors connected in series, divide voltage at an intermediate node preset between the plurality of resistors, and output the divided voltage. Here, the number of series-connected resistors or the resistance values thereof may be variable according to the actual states of a power supply.
For example, as shown in
The voltage stabilization circuit part 300 may include a first capacitor C31 connected between a first division node N1, preset in the voltage division part 200, and the ground, so as to stabilize the voltage by removing AC components such as ripple contained in the voltage or noise components.
The first square wave generating part 400 may include a shunt regulator SR having a cathode connected to the first output port OUT1 outputting the first square wave signal V1square, an input port connected to an output port of the voltage stabilization circuit part 300, and an anode connected to the ground. Here, the cathode is connected to the first operation voltage Vcc1 terminal through a resistor R41.
Meanwhile, as shown in
Hereinafter, the operation and effect of the invention will be described in detail with reference to the accompanying drawings.
Referring to
Here, the rectifying part 100 halfwave rectifies an AC voltage Vac of 90V or more and outputs the rectified voltage to the voltage division part 200. For example, the rectifying part 100 may be configured as a rectifying diode. In this case, the rectifying diode halfwave rectifies the AC voltage and outputs the rectified voltage to the voltage division part 200.
The voltage division part 200 divides the rectified voltage according to a preset division ratio. For example, the voltage division part 200 may include a plurality of resistors having resistance values which are set to divide the AC voltage into a higher voltage than an internal reference voltage of the first square wave generating part 400 in a normal state.
As an example, referring to
The voltage stabilization circuit part 300 stabilizes the voltage Vd divided by the voltage division part 200 so as to improve voltage detection accuracy, and then supplies the stabilized voltage Vds to the first square wave generating part 400. Accordingly, the first square wave generating part 400 may be able to operate more accurately.
For example, the voltage stabilization circuit part 300 may include the first capacitor C31. In this case, the first capacitor C31 allows the voltage between the first division node N1, preset in the voltage division part 200, and the ground, to be smoothed. This smoothing of the first capacitor C31 allows the voltage Vds, inputted from the voltage stabilization circuit part 300 to the first square wave generating part 400, to be stabilized.
Then, the first square wave generating part 400 compares the voltage Vds stabilized by the voltage stabilization circuit part 300 with an internal reference voltage Vref and outputs a square wave signal having a duty ratio according to comparison results between the voltage Vds and the internal reference voltage Vref.
That is, as shown in
The configurations for the first square wave generating part 400 will be described in detail with reference to
The first square wave generating part 400 may be configured as a shunt regulator SR having a cathode connected to the first output port OUT1, an input port connected to the output port of the voltage stabilization circuit part 300, and an anode connected to the ground. Here, the shunt regulator SR turns on when an input voltage Vds inputted through the input port is higher than an internal reference voltage Vref, otherwise it turns off.
Specifically, when the shunt regulator SR turns on, a low-level square wave signal is outputted. On the other hand, when the shunt regulator SR turns off, a high-level square wave signal is outputted.
That is, when the shunt regulator SR turns on, a low-level first square wave signal V1square is outputted through the first output port OUT1. On the other hand, when the shunt regulator SR turns off, a high-level first square wave signal V1square is outputted through the first output port OUT1.
Meanwhile, in the case that the AC detection circuit for power supply further includes the second square wave generating part 600, the second square wave generating part 600 is connected to terminals of first and second operation voltages Vcc1 and Vcc2 and interlocked with the first square wave generating part 400, thereby generating a second square wave signal V2square.
More particularly, referring to
In this case, referring to
In contrast, the photodiode PD of the photocoupler turns off when the shunt regulator SR turns off. The current fails to be coupled to the phototransistor PT through the photodiode PD of the photocoupler, so the phototransistor PT does not operate. Accordingly, the second operation voltage Vcc2 is outputted as a high-level second square wave signal V2square through the second output port OUT2.
As described above, as compared to a conventional circuit using a Zener diode, this invention provides the advantages of a great reduction in both the number of required components and manufacturing costs. Also, an AC voltage, applicable to a power supply such as that of a plasma display panel (PDP), is detected, and a square wave signal can be supplied to the secondary side of a power transformer as well as to the primary side thereof.
As set forth above, according to exemplary embodiments of the invention, the AC detection circuit applicable to a power supply such as that of the PDP is configured to detect an AC input and output a square wave signal using the square wave generating part such as a shunt regulator, whereby the number of required components is greatly reduced and the manufacturing cost is reduced accordingly.
While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
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10-2009-0064343 | Jul 2009 | KR | national |