CN201393275Y - Voltage conversion circuit of liquid crystal television - Google Patents

Abstract

The utility model discloses a voltage conversion circuit of a liquid crystal television, which comprises a voltage pulse circuit, a voltage boosting circuit and a voltage reduction circuit connected to the voltage pulse circuit to receive the voltage pulse output from the voltage pulse circuit, and an output and voltage reduction circuit connected to the voltage reduction circuit. Feedback circuit between voltage pulse circuits. The voltage conversion circuit of the liquid crystal television of the utility model can provide stable +5V voltage and +33V voltage, the circuit is simple and reliable, the stability is good, and the cost is low.

Description

A voltage conversion circuit for LCD TV

【Technical field】

The utility model relates to the technical field of televisions, in particular to a voltage conversion circuit of a liquid crystal television.

【Background technique】

LCD TV motherboards generally require a +5V voltage, which is generally provided by the LCD TV power supply. However, this makes the LCD TV power supply very complicated, and at the same time increases the connection line between the power supply and the motherboard, making the assembly process It also gets complicated. As the market competition becomes more and more fierce, TV manufacturers widely use separate high-frequency tuners in order to reduce costs, and this tuner requires a tuning voltage of about +33V. Therefore, in addition to the +5V voltage, the LCD TV motherboard needs to add a +33V voltage. At present, this kind of tuning voltage is generally achieved by discrete components to achieve voltage doubling or by using a dedicated conversion chip. However, the use of discrete components to achieve voltage doubling will lead to the use of more components, complex circuit structure, difficult parameter configuration of components in the circuit, greater influence by temperature and other conditions, and low stability; and through dedicated conversion Chip implementation is more complicated and costly. Therefore, it is necessary to study and provide a voltage conversion circuit with good stability and low cost for LCD TVs, which can simultaneously convert to +5V voltage and +33V voltage.

【Content of utility model】

In order to solve the above problems, the main purpose of this utility model is to provide a voltage conversion circuit for LCD TVs with good stability and low cost.

To achieve the above object, the technical solution of the utility model is:

A voltage conversion circuit for a liquid crystal television, comprising a voltage pulse circuit, a voltage boost circuit and a voltage drop circuit connected to the voltage pulse circuit to receive the voltage pulse output from the voltage pulse circuit, and a voltage pulse circuit connected between the output of the voltage pulse circuit and the voltage pulse circuit feedback circuit between them.

Further, the voltage pulse circuit is connected to +12V voltage input.

Further, the boost circuit is also connected to a +12V voltage input.

Further, the step-up circuit is used to convert the input +12V voltage into a +33V tuning voltage and output a +33V voltage; and the step-down circuit is used to convert the voltage pulse output by the voltage pulse circuit into a +5V voltage, Output +5V voltage.

Further, the feedback circuit is used to sample the +5V voltage and feed it back to the voltage pulse circuit to output a stable +5V voltage.

Compared with the prior art, the voltage conversion circuit of the liquid crystal television of the utility model can provide stable +5V voltage and +33V voltage, the circuit is simple and reliable, the stability is good, and the cost is low.

【Description of drawings】

Fig. 1 is a block diagram of the utility model;

Fig. 2 is the schematic circuit diagram of the utility model.

【Detailed ways】

Please refer to Fig. 1, the voltage conversion circuit of a kind of liquid crystal television of the present invention, comprises the voltage pulse circuit that connects +12V voltage input, is connected with the voltage pulse circuit to receive the voltage boost circuit that the voltage pulse circuit outputs the voltage pulse circuit and step-down voltage circuit, and a feedback circuit connected between the output of the step-down circuit and the voltage pulse circuit. Wherein, the boost circuit is also connected with a +12V voltage input; the boost circuit is used to convert the input +12V voltage into a +33V tuning voltage, and output a +33V voltage; the step-down circuit is used to convert the voltage pulse The voltage pulse output by the circuit is converted into +5V voltage, and the +5V voltage is output; and the feedback circuit is used to sample the +5V voltage and feed it back to the voltage pulse circuit to output a stable +5V voltage.

The +12V voltage is the output voltage of the LCD TV power supply, and this voltage is input to the voltage pulse circuit and the boost circuit. The voltage pulse circuit converts the +12V voltage into a voltage pulse output, and the voltage pulse is output to the boost circuit and the step-down circuit; the voltage pulse circuit adjusts the output current according to the voltage fed back by the feedback circuit to stabilize the +5V voltage output. Under the control of the above-mentioned voltage pulse, the booster circuit converts the +12V voltage into a +33V voltage output, which is the tuning voltage. The step-down circuit directly converts the input voltage pulse into +5V output, and inputs it to the feedback circuit. The feedback circuit samples the +5V voltage and feeds it back to the voltage pulse circuit to adjust the output current of the voltage pulse circuit so that the step-down circuit outputs a stable +5V voltage.

Please refer to FIG. 2, the voltage pulse circuit includes a power management IC U22, a first resistor R271, a second resistor R275, a first capacitor C344, and a second capacitor C345. Wherein, the +12V voltage is connected to the power management ICU22 through the first resistor R271. The second resistor R275 is connected in series with the second capacitor C345 and forms a parallel circuit with the first capacitor C344. One end of the parallel circuit is connected to the power management IC U22, and the other end is grounded. The power management IC adopts APW7080, which adopts the current control mode and has a very wide voltage input and voltage output. After the input +12V voltage is converted by the voltage pulse circuit, the voltage pulse ULX with a high level amplitude of +12V, a frequency of 380KHZ and a specific duty cycle is output. The voltage pulse ULX is divided into two circuits, one of which is used as a boost circuit The switch control pulse of the other way is used as the input pulse of the step-down circuit.

The boost circuit includes a transistor Q49, a first diode D54 connected to the transistor Q49, a voltage regulator transistor D33, a grounding resistor R72 and a grounding capacitor C270. The transistor Q49 is an NPN transistor, and the voltage pulse ULX is connected to the base of the transistor Q49 through the third resistor R245. The collector of the transistor Q49 is connected to the anode of the first diode D54. And the +12V voltage is also connected to the anode of the first diode D54 through the lower inductor L21. The first inductance L21 is the energy storage inductance of the booster circuit, and the regulator tube D33 uses a regulator tube with a voltage regulation range of 31V to 35V, which is the same as the tuning voltage range of the high-frequency tuner; the grounding capacitor C270 is Energy storage capacitor; the third resistor R245 and the triode Q49 form a control switch. In order to ensure that the triode Q49 can be turned on quickly and completely, the value of the third resistor R245 is 6.8K or less. When the pulse ULX is at low level, the base level of the transistor Q49 is lower than 0V, and the transistor Q49 is cut off; the current of the energy storage inductor L21 passes through the first diode D54, the first diode D54 is turned on, and the voltage at point A The magnitude is the sum of the tuning voltage and the voltage drop of the first diode D54, the voltage at point A is greater than +12V, the current in the inductor L21 decreases, the energy storage inductor L21 provides energy to the load and the grounding capacitor C270, and C270 charges and stores energy. When the pulse ULX is at a high level, the base of the transistor Q49 is at a high level, the transistor Q49 is saturated and turned on, the voltage at point A is about 0.3V, which is lower than +33V, the current in the first inductor L21 increases, and the second and second The pole tube D54 is not conducting, and the grounding capacitor C270 discharges to provide energy to the load. The voltage pulse ULX controls the transistor Q49 to alternately cut off and conduct in saturation, so that the first inductor L21 and the grounding capacitor C270 continuously release and store energy, and convert the +12V voltage into a voltage of about +33V. D33 makes the output +33V less affected by the load, and outputs a stable +33V voltage.

The step-down circuit includes a second diode D34, a second inductor L22, a voltage stabilizing capacitor C268, and a decoupling capacitor C342. Wherein, the second diode D34 is a freewheeling diode, and the second inductor L22 is an energy storage inductor. Take appropriate values for each component in the step-down circuit. During the high level period of the pulse ULX, ULX is +12V, and point B is +5V; the current of the second inductor L22 increases to store energy; the second diode D34 cut off, no current flows. When the pulse ULX is at low level, point B is still at +5V due to the voltage stabilizing effect of the voltage stabilizing capacitor C268, and the current of the second inductor L22 decreases to release energy; the second inductor L22 freewheels through the second diode D34, The second diode D34 is turned on. The input voltage pulse ULX makes the second inductor L22 continuously charge and discharge, and converts the +12V point voltage into +5V voltage.

The feedback circuit includes a fourth resistor R274 and a fifth resistor R276, wherein one end of the fifth resistor R276 is grounded. The feedback circuit samples the +5V voltage and feeds it back to the power management IC U22, and adjusts the output current through the internal adjustment of the power management IC U22 to stabilize the +5V output voltage.

The best embodiment described above is only to set forth and illustrate the utility model, but is not limited to any specific form disclosed, and many modifications and changes are possible.

Claims (8)

1. A voltage conversion circuit of a liquid crystal television, comprising a voltage pulse circuit, is characterized in that: a voltage boosting circuit and a step-down circuit connected to the voltage pulse circuit to receive the voltage pulse output by the voltage pulse circuit, and a voltage step-down circuit connected to the voltage pulse circuit Feedback circuit between output and voltage pulse circuit. 2. The voltage conversion circuit of a liquid crystal television according to claim 1, wherein the voltage pulse circuit is connected to a +12V voltage input. 3. The voltage converting circuit of a liquid crystal television as claimed in claim 2, wherein the voltage boosting circuit is also connected to a +12V voltage input. 4. The voltage conversion circuit of liquid crystal television as claimed in claim 3, is characterized in that: described step-up circuit is used for converting the input +12V voltage into +33V tuning voltage, output +33V voltage; The circuit is used for converting the voltage pulse output by the voltage pulse circuit into +5V voltage and outputting the +5V voltage. 5. The voltage converting circuit of a liquid crystal television according to claim 4, wherein the feedback circuit is used to sample the +5V voltage and feed it back to the voltage pulse circuit to output a stable +5V voltage. 6. The voltage conversion circuit of LCD TV as claimed in claim 5, characterized in that: said voltage pulse circuit includes a power management IC (U22), a first resistor (R271), a second resistor (R275) and a first Capacitor (C344), second capacitor (C345); wherein, the +12V voltage is connected to the power management IC (U22) through the first resistor (R271), and the second resistor (R275) is connected in series with the second capacitor (C345) to the first The capacitor (C344) forms a parallel circuit, one end of the parallel circuit is connected to the power management IC (U22), and the other end is grounded. 7. The voltage conversion circuit of LCD TV as claimed in claim 6, characterized in that: said boost circuit includes a triode (Q49), a first diode (D54) connected to the triode (Q49), and a voltage regulator tube (D33), grounding resistor (R72) and grounding capacitor (C270); the triode (Q49) is an NPN triode, and the voltage pulse ULX is connected to the base of the triode (Q49) through the third resistor (R245), and the triode (Q49 ) is connected to the anode of the first diode (D54), and the +12V voltage is also connected to the anode of the first diode (D54) through a low inductor (L21). 8. The voltage conversion circuit of LCD TV according to claim 7, characterized in that: said feedback circuit includes a fourth resistor (R274) and a fifth resistor (R276), wherein one end of the fifth resistor (R276) is grounded .

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