CN201590942U - Electronic ballast of FM (frequency modulation) light-dimming fluorescent lamp - Google Patents

Abstract

The utility model relates to a frequency modulation adjustable fluorescent lamp electronic ballast, comprising an EMC filter rectifier circuit, an input voltage sampling circuit, a PFC boost circuit, a half-bridge drive circuit, a DC-AC half-bridge inverter circuit, an ignition circuit, Microprocessor, lamp current and lamp voltage sampling circuit; the EMC filter rectifier circuit is connected with the PFC booster circuit, the PFC booster circuit is connected with the half-bridge drive circuit and the microprocessor, and the half-bridge drive circuit is connected with the DC-AC half-bridge The inverter circuit is connected, the DC-AC half-bridge inverter circuit is connected with the ignition circuit; the lamp current and voltage sampling circuit is connected with the microprocessor. The beneficial effects of the utility model: instead of using a dedicated control integrated circuit, a general-purpose microcontroller is used to realize the dimming through pulse frequency modulation. The overall structure is simple, and various dimming interfaces can be conveniently expanded to realize digital dimming. Light.

Description

A frequency-modulated electronic ballast for dimmable fluorescent lamps

technical field

The utility model relates to an electronic ballast, in particular to a two-stage half-bridge mode, a fluorescent lamp electronic ballast which realizes dimming by adjusting the inverter frequency of the half-bridge.

Background technique

With the improvement of people's requirements for lighting quality, traditional fixed brightness fluorescent lamps can no longer meet people's needs for changing visual effects, and are not conducive to saving energy. The appearance of dimmable high-frequency fluorescent lamps not only meets people's need to change visual effects, but also achieves the purpose of energy saving. However, the commonly used methods are as follows: First, use the thyristor to control the chopping control of the AC input mains current, or connect the thyristor in series in the lamp branch circuit to perform chopping control on the lamp current. Although this method realizes It is relatively simple, but it affects the circuit and power factor, and the dimming range is limited; second, the pulse duty ratio dimming method, which realizes the output power by adjusting the pulse ratio of the power switch tube in the high frequency inverter. For example, the FMS7401 of FAIRCHILD Company and the L6574 of ST Company are both control integrated circuits with pulse duty cycle dimming function. If the duty ratio is too small, the power switch tube cannot be guaranteed to work in the ZVS state, which reduces the reliability of the electronic ballast circuit and increases the EMI radiation of the electronic ballast.

Utility model content

The technical problem to be solved by the utility model is to provide an electronic ballast for fluorescent lamps that adopts the pulse frequency modulation dimming method to realize dimming. , overcome the shortcoming existing in the prior art.

In order to solve the above-mentioned technical problems, the utility model adopts the following technical solutions: a frequency-modulated electronic ballast for dimmable fluorescent lamps, including an EMC filter rectifier circuit, an input voltage sampling circuit, a PFC boost circuit, a half-bridge drive circuit, a DC- AC half-bridge inverter circuit, ignition circuit, microprocessor, lamp current lamp voltage sampling circuit; described EMC filter rectifier circuit is connected with PFC booster circuit, PFC booster circuit is connected with half-bridge drive circuit, microprocessor, The half-bridge drive circuit is connected to the DC-AC half-bridge inverter circuit, and the DC-AC half-bridge inverter circuit is connected to the ignition circuit; the lamp current and voltage sampling circuit is connected to the microprocessor; the EMC filter rectifier circuit is connected to the input voltage sampling circuit , the input voltage sampling circuit is connected with the microprocessor.

As a preference of the present utility model, the electronic ballast for frequency-modulated dimmable fluorescent lamps further includes an auxiliary power supply circuit, and both the microprocessor and the half-bridge drive circuit are connected to the auxiliary power supply circuit.

As a preference of the present invention, the microprocessor is AT90PWM2B, and the input voltage sampling circuit, the lamp voltage and lamp current sampling circuit, the PFC boost circuit and the half-bridge inverter circuit are all controlled by the microprocessor.

As a preferred option of the present invention, the electronic ballast for frequency-modulated dimmable fluorescent lamps also includes a filament preheating circuit, which preheats the filament through four secondary coils T1B, T1C, T1D and T1E coupled with the BUCK step-down inductor T1A A filament preheating circuit is formed, and the filament preheating circuit is connected with a half-bridge inverter circuit.

As a preferred option of the present invention, the electronic ballast for frequency-modulated dimmable fluorescent lamps is provided with three kinds of dimming interfaces: SWITCH dimming, 0-10V analog dimming and DALI dimming.

As a preferred option of the present invention, the DC-AC half-bridge inverter circuit is composed of two power switch tubes Q1 and Q2 driven by a half-bridge driver, a DC blocking capacitor C1, a BUCK step-down inductor T1A and a resonant capacitor C2. The working frequency of the bridge inverter circuit is used to adjust the voltage at both ends of the resonant capacitor C2 to realize stepless dimming within a wide power range of 1-100%.

Beneficial effects of the utility model: the design of this electronic ballast for dimmable fluorescent lamps does not use a dedicated control integrated circuit, but a general-purpose micro-controller, which is realized by pulse frequency modulation and dimming method, and the overall structure is simple. Various dimming interfaces can be easily expanded to realize digital dimming. It can drive two T8 36W lamps of various common brands such as OSRAM, and realize stepless dimming within the power range of 1-100% by adjusting the working frequency of the inverter half-bridge. Thanks to active power factor correction, the power factor of the electronic ballast remains above 0.99 throughout the dimming range. The electronic ballast can expand three kinds of dimming interfaces: SWITCH dimming, 0-10V dimming and DALI dimming. It can form a digital and intelligent lighting control management system. The DALI interface lighting management system described in the utility model has been tried out in large shopping malls and large office places.

Description of drawings

Fig. 1 is the block diagram of the circuit structure of the electronic ballast described in the utility model;

Fig. 2 is the schematic diagram of the electronic ballast described in the utility model;

Fig. 3 is the preheating and ignition voltage waveform diagram of the electronic ballast described in the utility model;

Fig. 4 is a waveform diagram of lamp voltage and lamp current when the electronic ballast described in the present invention works at low frequency;

Fig. 5 is a waveform diagram of lamp voltage and lamp current when the electronic ballast described in the present invention works at high frequency;

Fig. 6 is a logarithmic dimming curve diagram of the electronic ballast described in the present invention;

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail:

As shown in Figures 1 and 2, a frequency-modulated electronic ballast for dimmable fluorescent lamps described in the present invention includes an EMC filter rectifier circuit, an input voltage sampling circuit, a PFC boost circuit, a half-bridge drive circuit, a DC- AC half-bridge inverter circuit, ignition circuit, microprocessor, lamp current lamp voltage sampling circuit; described EMC filter rectifier circuit is connected with PFC booster circuit, PFC booster circuit is connected with half-bridge drive circuit, microprocessor, The half-bridge drive circuit is connected to the DC-AC half-bridge inverter circuit, and the DC-AC half-bridge inverter circuit is connected to the ignition circuit; the lamp current and voltage sampling circuit is connected to the microprocessor; the EMC filter rectifier circuit is connected to the input voltage sampling circuit , the input voltage sampling circuit is connected with the microprocessor.

The microprocessor is AT90PWM2B, and the input voltage sampling, lamp voltage and lamp current sampling, PFC circuit and half-bridge inverter circuit are all controlled by the microprocessor, which is an electronic ballast with full digital control. The DC-AC half-bridge inverter circuit is composed of two power switches Q1 and Q2 driven by the half-bridge drive circuit, DC blocking capacitor C1, BUCK step-down inductor T1A and resonant capacitor C2. By changing the operating frequency of the half-bridge inverter circuit to adjust the voltage across the resonant capacitor C2 (that is, the lamp voltage) to realize stepless dimming within the power range of 1-100%. The electronic ballast described in the utility model adopts the voltage-type filament preheating starting mode, and before the fluorescent lamp is started and ignited, the filament is preheated by four secondary coils T1B, T1C, T1D and T1E coupled with the BUCK step-down inductor T1A , including SWITCH dimming, 0-10V analog dimming and DALI dimming three dimming interfaces.

The circuit structure of the electronic ballast is shown in Figure 2. It is a modification of the voltage-fed series resonant half-bridge inverter circuit. The capacitor C ₁ replaces the two half-bridge series capacitors of the traditional half-bridge inverter circuit. The capacitor C ₁ provides a current loop for the power switch tube. The driving of the inverter half-bridge, the dimming control of fluorescent lamps, the end-of-life detection of fluorescent lamps, fault diagnosis and circuit protection and other functions are all realized based on microcontrollers, and it is a digitally controlled electronic ballast. The microcontroller adopts Lighting AVR MCU AT90PWM2B specially designed by ATMEL for lamp ballast products. This MCU has a working frequency up to 8MHz and does not require an external crystal oscillator. It is especially suitable for high-voltage and high-current electronic ballast products. It contains The PSC (Power Stage Controllers) module that can work up to 64MHz can be used for inverter half-bridge drive and dimming control of fluorescent lamps. The high-precision AD conversion channel can be used for sampling signals such as input voltage, lamp voltage and lamp current. Abundant IO ports make it possible for the ballast to expand various dimming interfaces. As shown in Figure 2, the AC mains input of 220V/50Hz is corrected by active power factor to obtain a 400V DC regulated output, which is used as the input of the half-bridge inverter. The auxiliary power supply generates 5V and 15V voltages as the power supply required by the microcontroller and half-bridge driver. The half-bridge driver drives two power switch tubes Q ₁ and Q ₂ to form a DC-AC half-bridge inverter circuit. The operating frequency of the inverter is completely controlled by the PSC module of the AT90PWM2B single-chip microcomputer.

The working process of filament preheating is as follows:

The start of fluorescent lamps is divided into preheat start and non-preheat start. Non-preheat start, that is, cold start, means that the lamp electrode is not heated, and the high open circuit voltage is used to cause the field emission of the electrode to trigger the lamp to start. The starting voltage is relatively high. For the T8 36W lamp tube, the open circuit voltage at start should be Above 800V. In the process of high-voltage cold start, an excessively long and excessively large continuous glow discharge current is often generated, resulting in excessive sputtering of the filament material, causing premature blackening of the tube walls at both ends of the fluorescent lamp, and shortening the life of the fluorescent lamp tube. The preheating start is to slowly heat the lamp electrode to the electron emission temperature before the lamp is triggered to conduct, which can greatly reduce the starting voltage to about 300V and prolong the life of the lamp. As shown in Figure 2, the output of the electronic ballast for dimmable fluorescent lamps is a double-lamp parallel structure, and a balanced transformer voltage type filament preheating circuit is used, and T _1B , T _1C , T _1D , T _1E The voltage on the four filament windings realizes the preheating of the filament. When the microcontroller controls the inverter half-bridge to work at a frequency of 80KHz, the filament is preheated. The preheating time can be flexibly controlled by the microcontroller according to actual needs , There is a voltage applied to both ends of the filament during the whole working process of the lamp, and the balance transformer _T2 keeps the working current of the two lamps consistent.

The ignition and start-up process of fluorescent lamps is as follows:

The lamp branch is composed of DC blocking capacitor C ₁ , ballast inductance T _1A and resonant capacitor C ₂ . When the circuit is powered on, the lamp load has not been ignited and is in a high-resistance state. Capacitor C ₁ , ballast inductance T _1A and capacitor C ₂ form a series resonant circuit. Since the capacity of capacitor _C1 is much larger than that of _C2 , the resonant frequency of the circuit is mainly determined by the parameters of ballast inductance _T1A and capacitor _C2 , and the fluorescent lamp is triggered by the high voltage generated on capacitor _C2 when the circuit resonates ignition. After the lamp load is ignited, its impedance becomes smaller, the LC series circuit is detuned, and T _1A acts as a ballast. In the design of the electronic ballast for dimmable fluorescent lamps described in the utility model, C ₁ =0.1uF, T _1A =1.4mH, C ₂ =0.01uF, by the formula $f_0=1/\left(2\mathrm{\π}\sqrt{\mathrm{LC}}\right)$ The series resonant frequency f ₀ ≈42.5KHz of the circuit can be obtained. When the inverter half-bridge operates at a frequency around 45KHz, series resonance ignition occurs. The ignition voltage waveform at both ends of the resonant capacitor _C2 is shown in Figure 3. It can be seen from the figure that due to the filament preheating starting method, when the voltage across the capacitor _C2 reaches about 380V, the fluorescent lamp is triggered to start, and then enters the normal working state. The entire ignition process only takes about 150ms, which helps to prolong The working life of the lamp.

The dimming control process of fluorescent lamps is as follows:

After the fluorescent lamp starts normally, it can be dimmed and controlled. The dimming of electronic ballasts for fluorescent lamps discussed in this paper is a frequency modulation dimming method, that is, through the microcontroller to adjust the operating frequency of the half-bridge inverter circuit, the impedance of the ballast inductor will change accordingly, thereby changing the size of the lamp current , to achieve dimming control, the higher the frequency, the dimmer the light. The dimming range is completely determined by the frequency modulation range. By reasonably selecting parameters such as the operating frequency of the ballast inductor core, a wide range of stepless dimming can be achieved. When the half-bridge inverter frequency changes within the range of 40-75KHz, it corresponds to 100%-1% of the luminous brightness respectively. Figure 4 and Figure 5 are respectively the voltage and lamp current waveforms at both ends of the fluorescent lamp when working at low frequency and high frequency, where channel 1 is the lamp voltage waveform, and channel 2 is the lamp current waveform. It can be seen from the figure that the lamp voltage and lamp current are similar high-frequency sine waves in the entire dimming range, which reduces the aging of the lamp tube and significantly avoids the stroboscopic effect of fluorescent lamps. Because human eyes are more sensitive to low-brightness levels than high-brightness levels, electronic ballasts for dimmable fluorescent lamps provide 256-level logarithmic dimming control characteristics. The dimming curve is shown in Figure 6. When the light is bright The actual lamp power adjustment amount corresponding to each dimming level is larger, and vice versa. This nonlinear logarithmic dimming control characteristic is a linear change relative to the visual characteristics of the human eye.

Based on a microcontroller, the electronic ballast is extended with the following dimming interfaces:

(1) SWITCH dimming interface. As shown in Figure 2, the dimmer switch is connected to the mains input AC terminal, and the sinusoidal AC signal is input to the IO port of the microcontroller after half-wave rectification and step-down. When the switch is pressed, the microcontroller detects Low level, otherwise high level. The micro-controller obtains the dimming signal according to whether the dimming switch is pressed and the length of time it is pressed. The specific working process is as follows: after the power is turned on, the dimmer switch is pressed and then released, the ballast lights up the fluorescent lamp and returns to the power level when it was turned off last time; when the dimmer switch is pressed next time and then immediately When it is released, it will turn off the fluorescent lamp and save the current power state; when the fluorescent lamp is on, press and hold the switch, the ballast will dim until it is the brightest or the darkest state; when it is pressed again When the switch is pressed and held, the light will be dimmed in the opposite direction until it reaches the brightest or darkest state. The dimming method is easy to operate and the implementation cost is the cheapest.

(2) 0-10V analog dimming interface. As shown in Figure 2, the 0-10V DC analog voltage generated by the potentiometer is input to the AD channel of the microcontroller through optocoupler isolation, and the microcontroller uses the voltage level as the dimming signal. This dimming method is currently the most commonly used.

(3) DALI dimming interface. Digitally Addressable Lighting Interface (DALI) is a communication protocol related to the interconnection of electronic ballasts jointly formulated by major European electronic ballast manufacturers. promotion and use. Each DALI lighting control system can connect up to 64 electronic ballasts through twisted pair cables. There is bidirectional communication between the controller and the electronic ballasts. The controller can send switching and dimming commands to the electronic ballasts, or Send status information query commands such as the current brightness level and lamp failure to the electronic ballast to form a digital lighting control management system.

A high-performance dimmable electronic ballast for fluorescent lamps is designed and implemented based on a microcontroller, which can better drive two T8 36W lamps of various common brands such as OSRAM, and adopts the method of adjusting the operating frequency of the inverter half-bridge Realize stepless dimming within the power range of 2%~100%. Thanks to active power factor correction, the power factor of the electronic ballast remains above 0.99 throughout the dimming range. The electronic ballast can expand three kinds of dimming interfaces: SWITCH dimming, 0-10V dimming and DALI dimming. It can form a digital and intelligent lighting control management system. The DALI interface lighting management system described in the utility model has been tried out in large shopping malls and large office places.

Claims (6)

1. A frequency modulation type dimmable electronic ballast for fluorescent lamps, characterized in that it includes an EMC filter rectifier circuit, an input voltage sampling circuit, a PFC boost circuit, a half-bridge drive circuit, a DC-AC half-bridge inverter circuit, an ignition circuit, microprocessor, lamp current and lamp voltage sampling circuit; the EMC filter rectifier circuit is connected to the PFC boost circuit, the PFC boost circuit is connected to the half-bridge drive circuit and the microprocessor, and the half-bridge drive circuit is connected to the DC-AC The half-bridge inverter circuit is connected, the DC-AC half-bridge inverter circuit is connected with the ignition circuit; the lamp current and voltage sampling circuit is connected with the microprocessor; the EMC filter rectifier circuit is connected with the input voltage sampling circuit, and the input voltage sampling circuit is connected with the microprocessor device connection. 2. The electronic ballast for a frequency-modulated dimmable fluorescent lamp according to claim 1, further comprising an auxiliary power supply circuit, the microprocessor and the half-bridge drive circuit are both connected to the auxiliary power supply circuit. 3. A frequency-modulated electronic ballast for dimmable fluorescent lamps according to claim 1, characterized in that: the microprocessor is AT90PWM2B, input voltage sampling circuit, lamp voltage lamp current sampling circuit, PFC boost Both the circuit and the half-bridge inverter circuit are controlled by a microprocessor. 4. A frequency-modulated electronic ballast for dimmable fluorescent lamps according to claim 1, characterized in that it also includes a filament preheating circuit, through T1B, T1C, T1D and T1E coupled with BUCK step-down inductor T1A A secondary coil preheats the filament to form a filament preheating circuit, and the filament preheating circuit is connected to the half-bridge inverter circuit. 5. A frequency-modulated electronic ballast for dimmable fluorescent lamps according to claim 1, characterized in that it is equipped with three kinds of dimming interfaces: SWITCH dimming, 0-10V analog dimming and DALI dimming. 6. A frequency-modulated electronic ballast for dimmable fluorescent lamps according to any one of claims 1-5, characterized in that: the DC-AC half-bridge inverter circuit is driven by a half-bridge driver with two power Switching tubes Q1, Q2, DC blocking capacitor C1, BUCK step-down inductor T1A and resonant capacitor C2, by changing the operating frequency of the half-bridge inverter circuit to adjust the voltage across the resonant capacitor C2 to achieve a wide power of 1 to 100% Stepless dimming within a range.

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