CN201142635Y - A DC-AC inverter boost circuit - Google Patents

Abstract

The utility model is suitable for the field of backlight power supply circuits, and provides a DC-AC inverter boost circuit, including a boost transformer, and also includes: a backlight control unit for generating a pulse width modulation signal; and a pulse width of the backlight control unit A half-bridge driver chip connected to the output terminal of the modulation signal; two switching devices connected to the half-bridge driver chip and controlled by it to be turned on and off alternately, the first switching device in the two switching devices receives power factor correction The DC voltage signal of the circuit, and is connected with the non-nominal end of the primary winding of the step-up transformer, and the second switching device is connected with the non-nominal end of the primary winding of the step-up transformer; and connected with the step-up transformer The capacitor connected to the terminal of the primary winding of the same name. The utility model converts the DC voltage output from the power factor correction circuit into the driving high voltage required by the backlight of the LCD screen, etc., subtracts the DC step-down process before the traditional boost, reduces the cost, and improves the efficiency.

Description

A DC-AC inverter boost circuit

technical field

The utility model belongs to the field of backlight power supply circuits, in particular to a DC-AC inverter boost circuit.

Background technique

In order to provide high-voltage power supply for backlights such as LCD screens, the existing inverter booster circuit usually boosts low-voltage DC power such as 12V and 24V to generate high-voltage AC power such as 1000V required for backlight driving. Direct current, the existing inverter boost circuit also needs to convert the higher voltage direct current into low voltage direct current through a direct current-direct current (DC-DC) circuit, which makes the realization of the entire backlight drive circuit more complicated and costly , and due to the high precision of the voltage value of the low-voltage direct current, the working efficiency of the circuit is also reduced.

Utility model content

The purpose of this utility model is to provide a DC-AC inverter boost circuit, which aims to solve the problem that the existing backlight drive circuit needs to generate backlight drive high voltage through DC-DC and DC-AC two-stage circuits successively, so that the circuit realizes The problem of high cost and low efficiency.

The utility model is achieved in this way, a DC-AC inverter step-up circuit, including a step-up transformer, is characterized in that the circuit also includes:

A backlight control unit generating a pulse width modulated signal;

A half-bridge driver chip connected to the pulse width modulation signal output end of the backlight control unit;

Two switching devices connected to the half-bridge driver chip and controlled by it to turn on and off alternately, the first switching device of the two switching devices receives the DC voltage signal of the power factor correction circuit, and communicates with the booster connected to the opposite end of the primary winding of the step-up transformer, the second switching device is connected to the opposite end of the primary winding of the step-up transformer; and

A capacitor connected to the terminal of the same name of the primary winding of the step-up transformer.

The utility model directly converts the DC voltage output from the PFC circuit into the driving high voltage required to light the backlight of the LCD screen, thereby subtracting the DC-DC step-down process before the traditional boost, which not only reduces the cost , also improves efficiency.

Description of drawings

Fig. 1 is a circuit diagram of a DC-AC inverter boost circuit provided by the utility model.

Detailed ways

In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not intended to limit the utility model.

The DC-AC (DC-AC) inverter boost circuit provided by the utility model directly converts the DC voltage output from the power factor correction (PFC) circuit into the driving high voltage required for lighting the backlight of the LCD screen and the like. , minus the DC-DC step-down process before the traditional step-up, not only can reduce the cost, but also can improve the efficiency.

Fig. 1 has shown the circuit diagram of the DC-AC inverter step-up circuit that the utility model provides, and details are as follows:

The IN1 terminal and IN2 terminal of the backlight control chip IC2 are respectively connected to one end of the resistor R11 and the resistor R12, the other end of the resistor R11 is connected to the same-named terminal 1 of the primary winding of the isolation transformer T2, and the other end of the resistor R12 is connected to the primary winding of the isolation transformer T2 The opposite end of 2. There are 2 groups of secondary windings of the isolation transformer T2, among which, the terminal 3 with the same name of the first group of secondary windings is respectively connected to one end of the resistor R6 and one terminal of the resistor R7, and the terminal 4 of the second group of secondary windings with the same name is connected to the resistor R9 and the resistor R7 respectively. One end of R10, the opposite end of the first group of secondary windings and the same end of the second group of secondary windings are connected to the hot ground, and the other ends of the resistor R7 and the resistor R10 are also connected to the hot ground.

The other end of the resistor R6 is connected to the base of the P-type transistor Q3 and the base of the N-type transistor Q4, the collector of the transistor Q3 is connected to the power supply voltage VCC through the resistor R5, and the emitter of the transistor Q3 is connected to the emitter of the transistor Q4. The signal terminal S1 and the collector of the transistor Q4 are connected to the hot ground; the other end of the resistor R9 is connected to the base of the P-type transistor Q5 and the base of the N-type transistor Q6, and the collector of the transistor Q5 is connected to the power supply voltage VCC through the resistor R8. The emitter of Q5 is connected to the signal terminal S2 with the emitter of the transistor Q6, and the collector of the transistor Q6 is connected to the thermal ground.

The signal terminals S1 and S2 are respectively connected to the HIN and LIN terminals of the half-bridge driver chip IC1, the VCC terminal of the half-bridge driver chip IC1 and the anode of the diode D0 are connected to the power supply VCC, and the cathode of the diode D0 is respectively connected to the VB of the half-bridge driver chip IC1 end and one end of the capacitor C3, the other end of the capacitor C3 is connected to the VS end of the half-bridge driving chip IC1, and the COM end of the half-bridge driving chip IC1 is connected to the thermal ground.

The HO terminal of the half-bridge drive chip IC1 is connected to one end of the resistor R1, and the other end of the resistor R1 is respectively connected to the gate of the MOS transistor Q1, one end of the capacitor C1, one end of the resistor R2, and the negative pole of the Zener diode ZD1, the capacitor C1 and the resistor The other end of R2 and the anode of the Zener diode ZD1 are connected to the VS end of the half-bridge driver chip IC1, and the other end of the capacitor C1 is also connected to the thermal ground through the capacitor C4. The LO end of the half-bridge driver chip IC1 is connected to one end of the resistor R3, and the other end of the resistor R3 is respectively connected to the gate of the MOS transistor Q2, one end of the capacitor C2, one end of the resistor R4, and the negative electrode of the Zener diode ZD2, and the capacitor C2 and The other end of the resistor R4 and the anode of the Zener diode ZD2 are connected to the thermal ground.

The source of the MOS transistor Q1 and the drain of the MOS transistor Q2 are connected to the opposite terminal 1 of the primary winding of the step-up transformer T1, the drain of the MOS transistor Q1 is connected to the signal terminal PF, and the source of the MOS transistor Q2 is connected to the thermal ground. The same-named terminal 2 of the primary winding of the step-up transformer T1 is connected to the thermal ground through the capacitor C5.

The secondary winding of the step-up transformer T1 is connected to the backlight, and there are 2 groups in total, in which the terminal 3 with the same name of the secondary winding of the first group and the terminal 4 with the same name of the secondary winding of the second group are respectively connected to the signal terminals HVO1 and HVO2, and the terminal The same-named terminal 5 of one group of secondary windings and the different-named terminal 6 of the second group of secondary windings are respectively connected to signal terminals A and B.

The signal terminal A is respectively connected to one end of the resistor R15, the cathode of the diode D3, and the anode of the diode D1, and the other end of the resistor R15 and the anode of the diode D3 are connected to the cold ground; the signal terminal B is respectively connected to one end of the resistor R16 and the anode of the diode D4. The cathode and the anode of the diode D2 are connected, and the other end of the resistor R16 and the anode of the diode D4 are connected to the cold ground. The cathode of the diode D1 and the cathode of the diode D2 are respectively connected to one end of the resistor R13 and the resistor R14, the other end of the resistor R13 is connected to the I_SNS end of the backlight control chip IC2, and the other end of the resistor R14 is connected to the cold ground.

The two pulse width modulation (Pulse Width Modulation, PWM) signals output by the IN1 terminal and IN2 terminal of the backlight control chip IC2 with a phase difference of 180° are isolated from heat and cold by the isolation transformer T2, and then passed through the wireless circuit composed of triodes Q3 and Q4 respectively. The output transformer (Output Transformerless, OTL) power amplifier circuit, and the OTL power amplifier circuit composed of transistors Q5 and Q6 enhance the driving capability, and then transmit it to the half-bridge driver chip IC1 through the signal terminals S1 and S2.

The half-bridge driving chip IC1 drives the MOS transistors Q1 and Q2 to be turned on alternately according to the input PWM signal. When Q1 is turned on and Q2 is not turned on, the direct current (DC) voltage signal output by the power factor correction (PFC) circuit will be transmitted to the primary winding of the transformer T1 through the signal terminal PF through Q1, driving the transformer T1 to work, and at the same time, the capacitor C5 is charging, and when Q1 is not conducting and Q2 is conducting, capacitor C5, the primary winding of T1 and Q2 form a discharge circuit, and continue to drive the transformer T1 to work by discharging the voltage on capacitor C5, so that the transformer During the alternate conduction of MOS tubes Q1 and Q2, T1 generates two high-voltage sinusoidal alternating current (AC) signals with a phase difference of 180° on the secondary winding, which are transmitted to the backlight of the LCD screen through the signal terminals HVO1 and HVO2 respectively. , to provide high voltage drive.

In the process of the above-mentioned half-bridge driver chip IC1 controlling Q1 and Q2 to be turned on alternately, Zener diodes ZD1 and ZD2 will protect the gate voltages of Q1 and Q2 from overvoltage respectively, and the circuit composed of capacitor C1 and resistor R2 in parallel is When the MOS transistor Q1 is not conducting, it discharges its gate charge, and the circuit composed of capacitor C2 and resistor R4 discharges its gate charge when Q2 is not conducting, and the VS of the above-mentioned half-bridge driver chip IC1 The terminal is used as the HO reference ground.

While the transformer T1 outputs the high-voltage AC signal, the transformer T1 also outputs two current signals through the signal terminals A and B, and the current detection circuit composed of the diode D3 and the resistor R15 and the current detection circuit composed of the diode D4 and the resistor R16 respectively control the current. After detection, it is rectified by diodes D1 and D2 respectively, and fed back to the backlight control chip IC2. The backlight control chip IC2 will judge whether it is over-current or open circuit according to the current signal fed back, so that it can be adjusted by IN1 when it is over-current or open circuit. , The output signal at the IN2 terminal makes the working current of the circuit return to normal or enter the protection state. The two groups of current detection circuits, rectifier diodes D1, D2 and resistors R13, R14 form a current feedback circuit, which not only detects and feeds back the output current of the transformer T1, but also feeds backlight current.

The DC-AC (DC-AC) inverter boost circuit provided by the utility model directly converts the DC voltage output from the PFC circuit into the driving high voltage required to light the backlight of the LCD screen, etc., and subtracts the traditional boost voltage. The previous DC-DC step-down process has been proved by experiments to not only increase the efficiency by 10%, but also reduce the cost by 10%, achieving real energy saving and cost saving.

The above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present utility model shall be included in this utility model. within the scope of protection of utility models.

Claims (10)

1. A DC-AC inverter step-up circuit, comprising a step-up transformer, characterized in that the circuit also includes: A backlight control unit generating a pulse width modulated signal; A half-bridge driver chip connected to the pulse width modulation signal output end of the backlight control unit; Two switching devices connected to the half-bridge driver chip and controlled by it to turn on and off alternately, the first switching device of the two switching devices receives the DC voltage signal of the power factor correction circuit, and communicates with the booster connected to the opposite end of the primary winding of the step-up transformer, the second switching device is connected to the opposite end of the primary winding of the step-up transformer; and A capacitor connected to the terminal of the same name of the primary winding of the step-up transformer. 2. The DC-AC inverter boost circuit according to claim 1, wherein the two switching devices are N-channel MOS transistors, and the drain of the first MOS transistor among the two MOS transistors The pole receives the DC voltage signal of the power factor correction circuit, the source of the first MOS transistor and the drain of the second MOS transistor are connected to the opposite end of the primary winding of the step-up transformer, and the two MOS The source of the second MOS transistor in the tube is grounded. 3. The DC-AC inverter boost circuit according to claim 2, characterized in that the circuit further comprises two Zener diodes, the cathode of the first Zener diode among the two Zener diodes is connected to The gate of the first MOS transistor is connected, the anode of the first zener diode is connected to the half-bridge driver chip, and the cathode of the second zener diode in the two zener diodes is connected to the second zener diode. The gate of the MOS transistor is connected, and the anode of the second Zener diode is grounded. 4. The DC-AC inverter and step-up circuit according to claim 3, characterized in that the circuit further comprises two sets of RC parallel circuits connected in parallel with the two Zener diodes respectively. 5. The DC-AC inverter and step-up circuit according to claim 1, wherein the step-up transformer has two sets of secondary windings, and the two sets of secondary windings are also connected to the backlight control unit . 6. The DC-AC inverter boost circuit according to claim 5, characterized in that, in the two sets of secondary windings of the step-up transformer, the opposite end of the first set of secondary windings is connected to the second set of secondary windings. The same-named end of the primary winding outputs a high-voltage AC signal, and the same-named end of the first group of secondary windings and the different-named end of the second group of secondary windings are connected to the backlight control unit. 7. The DC-AC inverter and boost circuit according to claim 6, characterized in that, the circuit further comprises terminals with the same name as the first group of secondary windings and different terminals of the second group of secondary windings. The name terminal and the current feedback circuit connected to the backlight control unit. 8. The DC-AC inverter boost circuit according to claim 7, wherein the current feedback circuit comprises two sets of current detection circuits composed of resistors and diodes connected in parallel, and two rectifier diodes. 9. The DC-AC inverter boost circuit according to claim 1, characterized in that, the circuit further comprises an isolation transformer and a power amplifier circuit, the primary winding of the isolation transformer and the pulse width modulation of the backlight control unit The signal output terminal is connected, the secondary winding of the isolation transformer is connected with the power amplifier circuit, and the power amplifier circuit is connected with the half-bridge driver chip. 10. The DC-AC inverter boost circuit according to claim 9, characterized in that there are two groups of secondary windings of the isolation transformer and the power amplifier circuit, and the two groups of power amplifier circuits are respectively connected to the Among the two sets of secondary windings of the isolation transformer, the same-named ends of the first set of secondary windings and the opposite-named ends of the second set of secondary windings are connected.

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