WO2008019531A1

WO2008019531A1 - High-frequency generator

Info

Publication number: WO2008019531A1
Application number: PCT/CN2006/002026
Authority: WO
Inventors: Waikei Huen; Yun Li; Lock Kee Rocky Poon
Original assignee: Waikei Huen; Yun Li; Lock Kee Rocky Poon
Priority date: 2006-08-10
Filing date: 2006-08-10
Publication date: 2008-02-21

Abstract

A high-frequency generator includes a direct current - direct current conversion unit which is used for converting input direct current voltage to high voltage direct current, and high frequency oscillation output unit which is used for converting the converted direct current voltage to high frequency output voltage, it also includes protector, which detects direct voltage which is input to the direct current - direct current conversion unit. The protector couples to the direct current - direct current conversion unit and stops the work of the direct current - direct current conversion unit when the input direct current voltage value is too low.

Description

High frequency generator

The present invention relates to a high frequency generator as a novel power source, and more particularly to a high frequency generator for driving an electrodeless discharge lamp and a radio. Background technique

In today's era, oil resources are becoming increasingly tense. As society progresses, people's demand for energy is growing. In view of environmental protection requirements, people want to use clean energy such as solar energy or wind energy as a source of electrical energy.

The electrical energy generated by the solar cells or the electrical energy generated by the wind turbine typically needs to be stored in the battery first, and then powered by the battery to the powered device. However, typically, a low DC voltage such as 12V can be supplied by means of a battery or the like. In order to supply power to a powered device, it is often necessary to convert the DC voltage into an output of a desired waveform and voltage value.

As an example of electrical equipment, discharge lamps (such as cold cathode fluorescent lamps) have a wide range of applications, such as backlighting for road lighting and liquid crystal displays. When a solar cell is used to power a discharge lamp, a low-current DC voltage directly or indirectly supplied by the solar cell is converted by a conversion circuit into a high-frequency high-voltage sine wave output voltage required for a discharge lamp (such as a cold cathode fluorescent lamp) to reduce the circuit. Loss and achieve high luminous efficiency.

Prior art conversion circuits typically implement voltage conversion and frequency control in the same stage, which typically includes an output transformer through which voltage is supplied to the powered device. A converter for driving a discharge lamp is disclosed, for example, in U.S. Patent Application Serial No. 2004/0056607, in which an input DC voltage is first converted to a high amplitude ripple voltage by a regulator circuit and then passed through an output transformer. The direct drive circuit converts the ripple voltage into an output voltage. Although the converter includes Two-stage circuit, but the previous stage circuit generates ripple voltage, which is mainly used to control the output voltage value. The voltage conversion and frequency control are still realized by the latter stage circuit.

Due to the presence of distributed parameters in the transformer, it is not suitable to use a transformer to convert energy in a high frequency circuit. Moreover, since the output transformer needs to withstand both high frequency and high voltage, the parameters of the output transformer itself are very high. For example, to increase the pressure resistance of a transformer, a larger transformer must be designed. Therefore, due to the use of the output transformer, the conventional conversion circuit is only suitable for outputting a low-frequency low-voltage AC voltage, and has the disadvantages of low efficiency, large loss, and large volume, resulting in great waste of energy.

Moreover, in a direct drive circuit that uses an output transformer to generate a high-frequency high-voltage output voltage, if the high-frequency output voltage is fed back to the control circuit to provide a protection mechanism, the protection circuit may malfunction, and the high-frequency signal may also be converted. The device itself generates interference, which reduces the operational reliability of the converter. Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel high frequency generator which is highly reliable and small in size.

According to the present invention, there is provided a high frequency generator comprising a DC-DC converter for converting an input DC voltage into a high voltage DC voltage, and a high frequency oscillation output device for converting a high voltage DC voltage into a high frequency output The voltage is further characterized by: a protection device that detects a DC voltage input to the DC-DC converter and is coupled to the DC-DC converter, and stops the DC when the value of the input DC voltage is too low - The operation of the DC converter.

In a preferred embodiment, in the high frequency generator of the present invention, the protection device further detects an output current of the DC-DC converter, and stops the operation of the DC-DC converter when the value of the output current is too high. .

As another preferred embodiment, in the high frequency generator of the present invention, the high frequency oscillation output device uses a high voltage direct current power source as a working power source, and includes two A half-bridge oscillating circuit composed of a CMOS field effect transistor has an LC series resonant circuit connected to the half bridge, and the gates of the two FETs are respectively connected to the same polarity end of the first winding of the transformer (also referred to as the same name end). And the non-homopolar end of the second winding (also referred to as a non-identical end), the third winding of the transformer is connected in the LC series resonant circuit, and once the half-bridge oscillating circuit starts to work under the driving of the oscillating circuit, The half-bridge oscillating circuit maintains its own oscillation.

In the present invention, the protection device does not directly detect the high frequency output voltage signal, but detects the DC input voltage and the output current of the DC-DC converter to achieve undervoltage or overcurrent protection. Since the protection device detects the DC signal, it does not cause a problem that the high-frequency signal causes the protection circuit to malfunction, thereby ensuring the operational reliability of the generator.

Moreover, in a preferred embodiment of the present invention, the high-frequency output signal is outputted by the series LC resonant network, and the switching frequency of the two FETs is controlled by the LC series resonant frequency, so that the high-frequency characteristics are good, the high-voltage loss is small, and the nonlinearity is low. Small size, light weight, high reliability, and stable output frequency. Also, since the series LC resonance network is employed, the high frequency oscillation output device can be easily designed to operate at a high frequency of, for example, 2.65 MHz.

Since only the control transformer is used in the high-frequency oscillation output device, the control transformer only needs to withstand a very low voltage during operation, and therefore, it is required to withstand high voltage and operate at high frequency as compared with the prior art. In the case of an output transformer, the volume of the transformer can be greatly reduced, and as a result, a small-sized high-frequency generator can be obtained. DRAWINGS

Figure 1 is a circuit block diagram of a high frequency generator in accordance with the present invention;

Figure 2 is a circuit diagram of the electromagnetic compatibility filter circuit of Figure 1;

Figure 3 is a circuit diagram of the oscillation drive circuit of Figure 1; 4 is a circuit diagram of the boost converter and rectifier circuit of FIG. 1; FIG. 5 is a circuit diagram of the power supply overload and undervoltage protection sampling circuit of FIG. 1; FIG. 6 is a circuit diagram of the high frequency oscillation output circuit of FIG.

Figure 7 is a waveform diagram at each node in Figure 2-6. detailed description

1 shows a circuit block diagram of a high frequency generator according to the present invention, comprising five circuit modules, namely: an electromagnetic compatibility filter circuit 1, an oscillation drive circuit 3, a boost converter and a rectifier circuit 2, a power supply overload and an undervoltage protection. The sampling circuit 4 and the high frequency oscillation output circuit 5.

A DC voltage of, for example, 12 V is input to the input terminal of the high frequency generator, and filtered by the electromagnetic compatibility filter circuit 1, the DC voltage is input to the boost converter and rectifier circuit 2. The step-up conversion and rectification circuit 2 is driven by the oscillation drive circuit 3 so that the DC voltage is first boost-converted into a high-voltage sine wave voltage, and then rectified to obtain, for example, a DC high voltage of about 400V. The power overload and undervoltage protection circuit 4 detects the input voltage and the output current of the high frequency generator, and stops controlling the operation of the oscillation driving circuit 3 when the input voltage is too low or the output current is too large, so as to protect the high frequency occurrence of the present invention. Device.

The DC high voltage obtained by the rectification is input to the high frequency oscillation output circuit 5, and the high frequency oscillation output circuit operates at a frequency of 2.65 MHz, thereby converting the input DC high voltage into a high frequency sine wave output high voltage.

Next, the operation of each circuit module of the high frequency generator of the present invention will be specifically described with reference to Figs.

FIG. 2 shows a circuit diagram of the electromagnetic compatibility filter circuit 1. The electromagnetic compatibility filter circuit 1 includes an insulative fuse connected in series on the input line for preventing overcurrent, and further includes capacitors C1, C2, C3, C4 connected in parallel on the input line and a choke line mounted on the input line. Ll, select the parameters of each component to filter out clutter and interference signals in the power grid, and suppress the operating frequency of the high-frequency oscillation output circuit, ie 2.65MHz The electromagnetic wave and its higher harmonics, thereby eliminating the electromagnetic radiation interference of the circuit of the present invention to the outside, and further comprising a diode D1 connected in parallel to the input line for preventing polarity reversal at the input end due to misoperation Possible damage to the circuit of the present invention.

Fig. 3 shows a circuit diagram of the oscillation drive circuit 3. The oscillating drive circuit 3 is a conventional two-way output pulse width modulation (PWM) control circuit. In Fig. 4, an integrated circuit UC3525 from Texas Instruments is used as an example.

The integrated circuit U2 includes an externally controllable internal oscillation circuit, the pin 5 is an external capacitor terminal of the internal oscillator, and the pin 6 is an external resistor terminal of the internal oscillator. The pulse width can be adjusted by adjusting capacitor C17 connected in series between pin 5 and ground. The oscillation frequency can be adjusted by adjusting resistor R27 connected in series between pin 6 and ground.

An integrated internal voltage regulator is also included in integrated circuit U2, and the resulting reference voltage is output from pin 16. Resistors R29 and R24 form a bias circuit that is connected in series between pin 16 and ground to provide this reference voltage to pin 2.

An integrated error amplifier is also included in integrated circuit U2, and pins 1 and 2 are the two inputs of the internal error amplifier. Resistors R23 and R24 form a bias circuit connected in series between the approximately 400V DC voltage output of boost converter and rectifier circuit 2 and ground. Pin 1 is connected to the node between resistors R23 and R24 for detection. External line voltage. As described above, the pin 2 receives the reference voltage. When the external line voltage drops, the internal error amplifier outputs a signal that activates the PWM latching circuit inside the integrated circuit U2 to stop the output.

Pin 8 of integrated circuit U2 is the soft start terminal, and capacitor C16 is connected in series between pin 8 and ground as a soft start capacitor. When the PWM latch circuit is activated, capacitor C16 begins to discharge. After a certain period of time, the pulse width modulation control circuit is restarted. The soft start time can be changed by adjusting the capacitance of capacitor C16.

The pin 10 of the integrated circuit U2 is a closed end and is connected to the following description. The load and undervoltage protection circuit 4 will turn off the pulse width modulation control circuit when the input voltage of the high frequency oscillation generator is too low or the output current is too high.

Pins 11 and 14 of integrated circuit U2 are the respective outputs of the two outputs. The waveform signals generated at the nodes h, i are shown in Fig. 7, in which the waveforms of the two output square wave signals of the integrated circuit U2 are the same, and the phases are 180 degrees out of phase. The square wave signals are applied to the control terminals of the switching transistors Q1 and Q2, respectively, such that the switching transistors are alternately turned on or off.

Fig. 4 shows a circuit diagram of the boost converter and rectifier circuit 2. The boost converter and rectifier circuit 2 includes a transformer L2 having a center tap on the primary side. The center tap of the primary side of the transformer L2 is connected to the high potential output of the electromagnetic filter circuit 1, the two inputs of the primary side are connected to the current terminals of the switching transistors Q1 and Q2, respectively, and the two outputs of the secondary side are Connect to a full bridge rectifier. The control terminals of the switching transistors Q1 and Q2 are connected to the oscillation drive circuit 3 already explained above to receive the drive control signal. Driven by the two square wave signals output from the oscillating drive circuit 3, the switching transistors Q1 and Q2 are alternately turned on, so that current flows from the center tap, and then alternately flows out from the two input terminals on the primary side through the corresponding switches. The transistor is grounded to thereby generate an AC output voltage having a frequency of, for example, 50 Hz and a waveform symmetrical with respect to the ground potential due to coupling on the secondary side, and a signal waveform generated at the node b is shown in FIG. At the same time, the output voltage reaches an amplitude of, for example, about 400 V due to the voltage conversion of the transformer.

The AC voltage from the secondary output of transformer L2 is supplied to the full bridge rectifier circuit. At the output of the full-bridge rectifier circuit, a filter network consisting of capacitor C15 and inductor L3 and resistors R10, R11, and R12 is provided. The AC voltage is processed by the full bridge rectifier circuit rectification and filtering network to generate a converted DC high voltage.

The oscillation drive circuit 3, the boost converter and the rectifier circuit 2 constitute a DC-DC converter.

FIG. 5 shows a circuit diagram of the power supply overload and undervoltage protection sampling circuit 4. Can This circuit is constructed using a conventional two-way operational amplifier, and Texas Instruments' dual operational amplifier integrated circuit LM358 (hereinafter referred to as ϋΐ) is selected as an example.

The pins 3, 2, and 1 of the two operational amplifiers U1 are the non-inverting input, the inverting input, and the output of one of the operational amplifiers, respectively, and the pins 5, 6, and 7 are the non-inverting inputs of the other operational amplifier, Inverting input and output. Pin 8 is the power supply and is connected to the 12V supply voltage.

A sampling resistor 5 is connected in series to the negative output of the full-bridge rectifier circuit in the boost converter and rectifier circuit 2 of Fig. 3 for detecting current. The in-phase input pin 5 and the inverting input pin 6 of the two operational amplifiers IJ1 are coupled across the sampling resistor R5. When the current output by the full bridge rectifier circuit is too large (for example, in the case of a load short circuit), a high level is generated at the output terminal 7, the diode D2 is turned on, and the high potential signal is supplied to the integrated circuit U1. The pin 10 causes the integrated circuit U1 to stop the operation of the pulse width modulation control circuit, thereby implementing overload protection.

Resistors R19, R18 and variable resistor R17 are connected in series between the input 12V DC voltage and ground, and a voltage stabilizing diode D5 is connected between the node of resistors R19 and R18 and ground. As will be understood by those skilled in the art, the resistors R19, R18, the variable resistor R17 and the Zener diode D5 form a conventional voltage stabilizing circuit to provide a stable voltage for the non-inverting input terminal 3 as a reference voltage. . The inverting input pin 2 is connected to the input of the high frequency generator via a resistor R21 to detect the input 12V DC voltage. Select the parameter of Zener diode D5 so that when the input voltage is 12V, provide a suitable reference voltage at pin 3, so that the signal output at pin 1 is less than the potential required to turn on diode D3, at this time diode D3 It is in the cutoff state.

On the other hand, when the input voltage is lowered, the reference voltage of pin 3 remains unchanged, and the voltage of pin 2 decreases, so that a high potential signal is output at pin 1, turning on diode D3, and The high potential signal is supplied to the pin of the integrated circuit U1 10, causing the integrated circuit to stop the operation of the pulse width modulation control circuit, thereby implementing undervoltage protection.

Fig. 6 shows a circuit diagram of the high frequency oscillation output circuit 5.

Transistors Q5 and Q6 form a start-up circuit. When the power is turned on, the charging of the capacitor C13 is started, and the base potential of the transistor Q5 rises to be turned on. The current flows through the emitter and collector of the transistor Q5, charges the capacitor C14, and the potential of the control terminal of the transistor Q6 rises to be turned on, thereby turning on the diode D6.

The control transformer L5 includes windings N1, Ν2 and Ν3 which are formed on the same core so as to be coupled to each other. The winding Ν2 is connected to the control terminal of the switching transistor Q3, and the winding Ν3 is connected to the control terminal of the switching transistor Q4. The same polarity end of each winding is shown by black dots in Fig. 6.

The main part of the high-frequency oscillation output circuit 5 is a half-bridge oscillation circuit including switching transistors Q3 and Q4, inductors L4 and L5, and a capacitor C10. Inductor L4 and capacitor C10 form a series LC resonant network connected between the midpoint of the half bridge (ie, the node between switching transistors Q3 and Q4) and the same polarity end of winding N1 of transformer L5, the non-homopolar of winding N1 The ground is grounded.

After the diode D6 is turned on, current flows through the diode D6 into the winding N2 of the transformer L5, and at the same time, the capacitor C11 is charged, causing the potential of the point e to rise, thereby turning on the switching transistor Q3. The half-bridge oscillating circuit starts operating under the driving of the oscillating circuit.

When the switching transistor Q3 is turned on, a 400 V DC voltage is applied to the point g through the two current terminals of the switching transistor Q3, and the capacitor C10 is charged via the inductor L4. When the resonant frequency is 2.65 MHz, the current iL reaches a maximum value. At this time, the left side and the right side of the inductor L4 are positive potential and negative potential, respectively, and the left side and the right side of the capacitor C10 are also positive potential and negative potential, respectively, and the winding N1 of the transformer L5 reaches the highest polarity end. Potential. Due to the coupling relationship, the winding N2 of the transformer L5 and the same polarity end of the winding N3 (the black point in Fig. 6) also reach the highest potential, so that the e point potential is low and the f point potential is high, so that the switching transistor Q3 is turned off and the switching transistor is turned off. Q4 is turned on.

When the switching transistor Q3 is turned off and Q4 is turned on, the g point passes through the two current terminals of the switching transistor Q4 to the ground, so that the potential of the point is lowered. The current in the inductor L4 cannot be abruptly changed, so that an induced electromotive force of opposite polarity is generated in the inductor L4, that is, the left side and the right side of the inductor L4 are a negative potential and a positive potential, respectively. The voltage across capacitor C10 cannot be abrupt, so that current iL is reversed, flowing through the two current terminals of switching transistor Q4 to ground, thereby discharging the electrical energy stored by inductor L4 and capacitor C10. Accordingly, the potential is lowered at the respective polarity ends of the windings N1, N2 and the winding N3 of the transformer L5, causing the potential at the point _{e to} be high and the potential at the point f to be low, so that the switching transistor Q3 is turned on and the switching transistor Q4 is turned off, so that the half The bridge oscillating circuit maintains its own oscillation.

Referring to FIG. 7, a square wave signal having a phase difference of 180 degrees is generated at points e and f, respectively, acting on the control terminal of Q4 of the switching transistor Q3, so that the switching transistors Q3 and Q4 are alternately turned on and off, and output at the point g. The signal waveform is shown in Figure 7.

Diodes D8 and D9 are connected in series between the control terminal and the current terminal of the switching transistor Q3 to protect the switching transistor Q3 from breakdown due to the back electromotive force of the winding N2. Resistor R15 and capacitor C11 are connected in parallel between the control terminal and the current terminal of the switching transistor Q3, and the resonance frequency is set at about 2.65 MHz to ensure an accurate output frequency.

Similarly, diodes D10 and D11 are connected in series between the control terminal and the current terminal of switching transistor Q4 to protect switching transistor Q4 from breakdown due to the back EMF of winding N3. The resistor R16 and the capacitor C12 are connected in parallel between the control terminal and the current terminal of the switching transistor Q3, and the resonance frequency is set at about 2.65 MHz to ensure an accurate output frequency.

The resistor R13, the capacitor C8 and the diode D7 constitute a protection circuit. When the power supply voltage fluctuates, the voltage across capacitor C8 cannot be abrupt, thereby protecting switching transistor Q3. When the power supply voltage rises, the resistor R13 and the diode D7 are divided to The switching transistor Q3 is protected.

The output signal is taken from the node between the inductor L4 and the capacitor C10 in the series LC resonant network. The output signal is corrected by the parallel capacitor C9 and resistor R14 to smooth the rising and falling edges of the output signal. See Figure 7. An approximate sine wave is obtained at point d.

By way of example, in accordance with the present invention, the output signal is an approximately sinusoidal voltage having a frequency of 2.65 MHz and an amplitude of approximately 400V.

The invention can be used in conjunction with a solar cell for generating a high frequency and high voltage output voltage to drive electrical equipment, such as an electrodeless discharge lamp. The use of the high frequency generator of the present invention for driving a discharge lamp achieves optimum luminous efficiency.

While the invention has been described in terms of the embodiments of the embodiments, the invention For example, for an example of an integrated circuit given, other types of products, or products of the same function from other manufacturers, may be purchased, or formed using discrete components.

In this document, a detailed description of a conventional circuit (e.g., an electromagnetic compatibility filter circuit and a boost converter and a rectifier circuit using a transformer) is for ease of understanding of the present invention and is not intended to limit the present invention. Moreover, in accordance with the teachings of the present invention, sinusoidal output voltages of other amplitudes and frequencies can be implemented as desired by varying the parameters of the respective components. Therefore, the performance parameters presented herein are not intended to limit the invention.

All of the above modifications and implementations are within the scope of the invention.

Claims

Rights request

A high frequency generator comprising a DC-DC converter for converting an input DC voltage into a high voltage DC voltage, and a high frequency oscillation output device for converting a high voltage DC voltage into a high frequency output voltage, The method further includes: a protection device that detects a DC voltage input to the DC-DC converter and couples with the DC-DC converter, and stops the DC-DC converter when the value of the input DC voltage is too low work.

2. The high frequency generator according to claim 1, wherein said protection means comprises a first operational amplifier, a Zener diode is coupled between an input of said first operational amplifier and ground to provide a reference voltage, said first operation Another input of the amplifier is coupled to the input of the DC-to-DC converter, and an output of the first operational amplifier is coupled to the closed end of the DC-DC converter, and when the input DC voltage is low At the predetermined value, the first operational amplifier outputs a signal to activate the closed end of the DC-DC converter.

A high frequency generator according to claim 1, wherein said protection means further detects an output current of said DC-DC converting means, and stops the operation of said DC-DC converting means when the value of said output current is too high.

4. The high frequency generator according to claim 3, wherein said protection means comprises a second operational amplifier, and a sampling resistor is connected in series between said DC-DC converting means and said high-frequency oscillation output means, the second operation Two inputs of the amplifier are coupled to both ends of the sampling resistor, respectively, and an output of the second operational amplifier is coupled to a closed end of the DC-DC converter, and

When the value of the current flowing through the sampling resistor is greater than a predetermined value, the second operational amplifier outputs a signal to activate the closed end of the DC-DC converter.

5. The high frequency generator according to claim 1, wherein said high frequency oscillation output means comprises a vibrating circuit and a half bridge oscillating circuit.

6. The high frequency generator according to claim 5, wherein said half bridge oscillation circuit comprises first and second transistors connected in series between the power source and ground, a node coupled between the first and second transistors, and a ground An inter-connected LC resonant network, a control transformer including first and second windings coupled to respective control terminals of the first and second switching transistors, the control transformer further comprising coupling between the series LC resonant network and ground Third winding,

Wherein, the oscillating circuit is coupled to the control end of the first switching transistor, and when the high frequency oscillating output device is just beginning to operate, the oscillating circuit provides a signal to the first switching transistor to drive the half bridge oscillating circuit to start operating.

By the coupling of the control transformer, current changes of the series LC resonant network are respectively applied to the control terminals of the first and second switching transistors, so that the first and second switching transistors are alternately turned on, thereby the half bridge oscillation The circuit itself maintains oscillation, and

A high frequency output voltage is output from a node between the inductor and the capacitor in the series LC resonant network.

7. The high frequency generator according to claim 6, wherein the control terminals of said first and second switching transistors are respectively coupled to the same polarity end of the first winding of said transformer and the non-inverting end of said second winding .

The high frequency generator according to any one of claims 1 to 7, wherein said DC-DC converting means comprises an oscillating driving circuit and a step-up converting and rectifying circuit, said oscillating driving circuit providing two output signals, said liter The voltage conversion and rectification circuit includes third and fourth switching transistors, a step-up transformer including a center tap on the primary side and coupled to the third and fourth switching transistors, respectively, and a secondary side coupled to the secondary side of the step-up transformer Rectification full bridge,

The square wave output signal of the oscillating drive circuit is applied to the control terminals of the third and fourth transistors to control the third and fourth switching transistors to be alternately turned on.