Design of digital dimming electronic ballast based on PICl6F628 and optocoupler

“The 32W/T8 fluorescent lamp digital dimming DALI Electronic ballast launched on this article makes use of a microcontroller PICl6F628. The microcontroller acts as an interface between the dimming ballast controller IR21592 and DALI. The digital dimming DALI digital ballast design features a PFC increase circuit primarily based on the L6561 controller and a ballast circuit primarily based on the IR21592 controller. It additionally features a PICl6F628 microcontroller and an optocoupler isolation circuit for connecting DALI. The dimming vary of this digital dimming digital ballast is 1% to 100%, and it has excellent security safety capabilities, excessive effectivity and excessive energy issue.

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Writer: Wang Shouzhi, Mao Xingwu

introduction

Dimmable fluorescent lamps have apparent power-saving results in ballasts, so that they have been quickly developed and utilized in recent times. A fluorescent lamp is a low-pressure gasoline discharge lamp, which is a non-resistive load. Due to this fact, the dimming management know-how of fluorescent lamps is rather more sophisticated than that of incandescent lamps. Fluorescent lamp dimming know-how is split into two varieties: analog dimming and digital dimming. For the dimming of the compact energy-saving lamp desk lamp, analog know-how is often used. For dimming fluorescent lamps used for lighting in properties, workplaces, procuring malls, workshops and different locations, digital dimming options are adopted. The digital dimming digital ballast represents the longer term improvement course of the lighting equipment.

Fluorescent lamp dimming is achieved by adjusting the facility of the lamp tube. There are two methods to regulate the lamp energy: one is to regulate the frequency to alter the impedance of the ballast output stage LC community to regulate the lamp present, thereby altering the lamp energy and lamp brightness; the opposite is to regulate the lamp present and the lamp voltage. To regulate the lamp energy. The dimming ballast IR21592/IR21593 produced by IR Firm adopts the section dimming scheme.

1 Digital Addressable Lighting Interface (DALI)

Digital dimmable digital ballasts want to make use of DALI. The digital addressable lighting interface (DALI) worldwide normal prIEC929 is a communication protocol and technique for interfacing lighting gadgets on a two-wire community. The DALI protocol is 16 bits and helps as much as 64 particular person addressing of ballasts, and 16 teams are broadcast to the whole lighting community. Along with the protocol, DALI additionally helps optical attenuation, logarithmic dimming, reside on-site and fault detection.

For all lighting environments, DALI permits totally different management and administration. DALI makes use of the identical management system to manage (transmit and obtain) 64 totally different digital ballasts. The transmission command can attain a single ballast or a bunch of ballasts, and understand the dimming vary from 100% to 1%. Via digital management, the sunshine stage could be exactly adjusted based on totally different lighting wants. DALI incorporates 256 brightness ranges and a logarithmic dimming curve, as proven in Determine 1. It's simpler to manage higher at decrease gentle ranges and is extra delicate to human eyes.

2 Design scheme of digital dimming digital ballast

2.1 The composition of digital dimming digital ballast

The block diagram of the digital dimming digital ballast is proven in Determine 2. This system primarily consists of 3 components, specifically the energetic energy issue correction (PFC) increase pre-converter primarily based on the controller L6561, the ballast circuit primarily based on the controller IR21592 and the digital dimming management circuit. As well as, it additionally incorporates enter EMT filters, bridge rectifiers and safety circuits. Shuning management circuit gives DALI and software program, and the ballast could be immediately related to DALI 2 one-line enter or the system it's primarily based on. Use RS232/DALI converter to connect with PC, the aim is to show. The microcontroller PICl6F628 controls the ballast circuit primarily based on IR21592, and IR21592 controls the ballast circuit based on the sign acquired from the microcontroller.

2.2 The communication between the microcontroller and the skin world and IR21592

The microcontroller acts as an interface between DALI and IR21592. The communication between the microcontroller and the skin world is realized by two indicators, TX and RX. TX is the sign despatched from the community to the microcontroller, and RX is the sign despatched from the microcontroller to the community, as proven in Determine 3. A digital interface ensures excessive voltage isolation between the DALI enter and the output stage of the ballast.

The communication between the microcontroller PICl6F628 and IR21592 is accomplished with 4 indicators. Amongst them, the sign despatched from pin 9 of PICl6F628 to pin 4 of IR21592 is used for dimming, and the sign despatched from pin 10 of the microcontroller to pin 9 of IR21592 is used to shut or conduct the ballast, and it's acquired on pin 11 and pin 12 of PICl6F628. The sign is used for fault detection. The microcontroller controls the three pins of IR21592. That's, pin 4 (DIM, management lamp brightness), pin 9 (SD, energetic excessive stage makes IR21592 flip off) and pin 7 (FMIN, logic “0” makes IR21592 disabled).

IR21592 pin 4 (DIM) wants an analog dimming voltage of 0.5 to 5V, and the corresponding lamp energy stage is 1% to 100%. In O. At 5V enter, the section shift of lamp present is the most important, lamp energy is the bottom, and the sunshine is the darkest; at 5V enter, akin to the minimal section shift and most lamp energy, the lamp output is “full gentle” (100%). PICl6F628 pin 9 outputs a PWM sign, filtered by means of R25 and C17 and transformed into an analog voltage enter to pin 4 (DIM) of IR21592, offering 256 voltages of various ranges. Skinny folks want from digital dimming, and the output voltage is logarithmic quite than linear. At decrease gentle ranges, the human eye is extra delicate to it as a consequence of its linearity. The minimal lamp energy and most lamp energy could be set by exterior resistors on pin 6 (MIN) and pin 5 (MAX) of IR21592.

2.3 Software program

The DALI execution software program has a comparatively massive capability. Determine 4 exhibits the move chart of the software program in a easy type. The detailed supply code is sealed within the CD to be used in design.

After this system is began from initialization, the microcontroller is positioned within the loop and the enter information is checked. If legitimate information is acquired and the tackle matches the ballast-determined tackle, the group matches the particular group member, or the info is a broadcast command, it's filtered and screened. Instructions are divided into two varieties: normal and particular. After filtering and screening, this system is directed to the suitable command and executed instantly. All instructions are divided into 4 classes, specifically arc energy management instructions, configuration instructions, question instructions and particular instructions. Arc gentle energy management instructions are often utilized in lighting programs. Such command occupancy indicators are despatched to the ballast controller, and the sunshine stage is adjusted by pulse width modulation; configuration instructions are used for ballast settings, together with most and minimal gentle thresholds, Attenuation time, price and discipline stage, and so on., and the info is often saved within the EEPROM space and maintained; question instructions are used to get suggestions from the ballast. Via applicable question instructions, gentle attenuation, lamp, normal Details about faults and energy; devoted instructions are distinctive, and such instructions won't have an effect on the tackle. All ballasts on DALI reply to a devoted command.

2.4 The connection between DALI and microcontroller

The connection between the microcontroller and DALI is realized by means of an optocoupler, as proven in Determine 5. Utilizing the optical coupler, the DALI two-wire enter turns into 4 indicators. Of those 4 indicators, one is a communication allow sign (ENABLE), one is a transmit sign (TX_DALI), one is a obtain sign (RX-DALI), and the opposite is a receive-drive sign (RECEIVE-DRIVE). Amongst them, the transmitted sign and the acquired sign immediately have an effect on the extent on DALI. Utilizing the communication enabling sign and receiving a driving sign to manage the communication circuit could make the ballast acquire very low energy. Throughout regular operation, PICl6F628 could make the communication circuit activate utilizing the communication allow sign. When information begins to be despatched to the ballast, the communication allow sign present is decrease than 100μA. With a purpose to precisely transmit information, this present isn't adequate. To ensure that the sign to have a very good transmission by means of the isolation and preserve the reception of a driving sign, the present must be elevated to 0. Above 5mA. With a purpose to transmit all the info, obtain a drive sign, allow the time to be lengthy sufficient, after which cease, as proven in Determine 6. This technique can successfully cut back energy and present consumption.

To detect the enter information, the built-in comparator of PICl6F628 units the edge stage. The information detection threshold is ready on pin 1 (RA2) of PICl6F628. With a purpose to obtain the high-level logic on DALI, it's transformed to 5V logic on the microcontroller, and transformed to a high-voltage logic stage on DALI.

2.5 Microcontroller energy provide

After the lamp is triggered, the facility provide present on PIC16F628 pin 14 (VDD) is offered by the cost pump circuit on the output of the ballast half-bridge. Throughout regular operation of the microcontroller, the interior frequency is 4 MHz. When the voltage VSD on IR21592 pin 9 (SD) is “2V, the half bridge is lower off and the cost pump circuit is disabled. The present on PICl6F628 pin 14 (VDD) is equipped by the bridge rectifier output by way of a excessive resistance Resistor (270 kΩ). The microcontroller enters sleep mode and consumes little or no present. To get up the microcontroller to begin working once more, it's essential to provide sufficient present. Determine 7 exhibits a communication instance when the sunshine is turned off.

3 The precise circuit of digital dimming 36W/T8 fluorescent lamp digital ballast

Based mostly on IR21592 and managed by the microcontroller PICl6F628, the precise circuit of the 32W/T8 fluorescent lamp digital dimming digital ballast is proven in Determine 8. The AC line enter voltage vary of the digital dimming digital ballast is 185~265V, and the full harmonic distortion (THD) of the enter present is 2V, and the shutdown safety is carried out; the fourth is over-temperature safety, so long as the IC2 junction temperature TJ>165℃, then Enter the fail-safe mode. Within the fail-safe mode, the oscillator is turned off, the half-bridge circuit stops working, and the facility switches S2 and S3 are each turned off.

4 Conclusion

The 32W/T8 fluorescent lamp digital dimming DALI digital ballast launched on this article makes use of a microcontroller PICl6F628. The microcontroller acts as an interface between the dimming ballast controller IR21592 and DALI. The digital dimming DALI digital ballast design features a PFC increase circuit primarily based on the L6561 controller and a ballast circuit primarily based on the IR21592 controller. It additionally features a PICl6F628 microcontroller and an optocoupler isolation circuit for connecting DALI. The dimming vary of this digital dimming digital ballast is 1% to 100%, and it has excellent security safety capabilities, excessive effectivity and excessive energy issue.