Patent Application
20120218243
1. Technical Field
The disclosure relates to electronic devices, and particularly to a power supply system and a display device using the same.
2. Description of Related Art
A display device is driven by a power supply system. The power supply system of the display device provides stable power to the display device according to load of the display device. However, the display device generally displays images in a scanning mode, which would lead to a high transient response and subsequently cause the power to be unstable. Correspondingly, the unstable power reduces quality of the images displayed.
The switch circuit 220 receives external power signals Vin, and converts the external power signals Vin into first alternating current (AC) power signals, and outputs the first AC power signals to the transformer 230. In one embodiment, the first AC power signals are square wave signals. The transformer 230 converts the first AC power signals into second AC power signals. In one embodiment, the second AC power signals are sine wave signals. The output filter circuit 240 filters the second AC power signals from the transformer 230 into high voltage output power signals suitable to drive the display screen 30. In other embodiment, the power supply system 20 comprises an electromagnetic interference (EMI) filter circuit, an input filter circuit, a switch circuit 220, a transformer 230, and a filter circuit 240, which are connected in series. The EMI filter circuit receives the external power signals Vin, and filters EMI from the external power signals Vin. The input filter circuit is connected to the EMI filter circuit and the switch circuit 220, to filter the external power signals Vin and output direct current (DC) power signals to the switch circuit 220. The switch circuit 220 converts the DC power signals from the input filter circuit into first AC power signals, and outputs the first AC power signals to the transformer 230. The transformer 230 converts the first AC power signals into second AC power signals. The output filter circuit 240 filters the second AC power signals from the transformer 230 into high voltage output power signals suitable to drive the display screen 30.
The transforming circuit 250 is electronically connected to the scanning circuit 40, and adjusts amplitude of the scanning signals output by the scanning circuit 40 to generate adjusted scanning signals. The superposition circuit 260 is connected to the output filter circuit 240 and the transforming circuit 250, to sample the high voltage output power signals output by the output filter circuit 240 and to get the adjusted scanning signals output by the transforming circuit 250. The superposition circuit 260 further superposes the sampled high voltage output power signals and the adjusted scanning signals together to generate a superposition signal, and sends the superposition signal to the controller 270. The controller 270 controls on or off of the switch circuit 220 to output adjusted suitable power signals to drive the display screen 30 according to the superposition signal. Thus, transient response of the high voltage output power signals and quality of images of the display device are improved due to the superposition scanning signal.
The third resistor R3 and the variable resistor Rh are connected in series between the output of the output filter circuit 240 and the output of the transforming circuit 250 in turn. The fourth resistor R4 is connected between the output of the transforming circuit 250 and the ground. The microchip T1 stabilizes voltage, and comprises an anode grounded and a reference pole connected to the output of the transforming circuit 250. The fifth resistor R5 and the second capacitor C2 are connected in series between a cathode of the microchip T1 and the output of the transforming circuit 250 in turn. In the embodiment, the microchip is a TL431 microchip. The photocoupler Q1 comprises a light emitting diode and a transistor. An anode of the light emitting diode is connected to the output of the output filter circuit 240, and a cathode of the light emitting diode is connected to the cathode of the microchip T1. A collector of the transistor is connected to a second reference power supply VCC, and an emitter of the transistor is connected to the controller 270.
In the embodiment, total voltage of the first reference power supply Vref and voltage on the first resistor R1 is set between maximum voltage and minimum voltage of the scanning signals. The scanning signals from the scanning circuit 40 are input to the non-inverting input of the comparator B1 via the first resistor R1. If the voltage of the non-inverting input of the comparator B1 is less than breakdown voltage of the zener diode ZD, the voltage of the non-inverting input of the comparator B1 is compared with the voltage of the inverting input of the comparator B1. If the voltage of the scanning signals is the maximum voltage, the voltage of the non-inverting input of the comparator B1 is greater than the voltage of the first reference power supply Vref. Thus, the comparator B1 generates logic 1, and the transforming circuit 250 outputs logic 1, which is corresponding to the scanning signals with the maximum voltage.
If the voltage of the scanning signals is minimum, the voltage of the non-inverting input of the comparator B1 is less than the voltage of the first reference power supply Vref. The comparator B1 generates logic 0, and the transforming circuit 250 outputs logic 0, which is corresponding to the scanning signals with the minimum voltage. That is, the transforming circuit 250 outputs the adjusted scanning signals with different amplitude from that of the scanning signals. Thus, the adjusted scanning signals are superposed with the sampled high voltage output power signals together to generate the superposition signal to improve the transient response and the quality of the images.
In the embodiment, the zener diode ZD protects the comparator B1 from damage. If the voltage of the non-inverting input of the comparator B1 reaches the breakdown voltage of the zener diode ZD, the zener diode ZD is broken down to make the voltage of non-inverting input of the comparator B1 stable. Thus, the comparator B1 is protected.
The power supply system 20 superposes the sampled high voltage output power signals and the scanning signals with adjusted amplitude together to generate the superposition signal, and sends the superposition signal to the controller 270, which improves the transient response to supply a stable power to the display screen 30. Thus, the quality of the images displayed by the display screen 30 is improved.
The foregoing disclosure of the various embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201120049803.8 | Feb 2011 | CN | national |
