Abstract: In view of the high-pressured sodium lamp operating feature as well as the work under high-frequency mode’s flaw, uses the electric current track technology, has designed one kind of low frequency high-pressured sodium lamp electron ballast, and has designed the reliable logical control starting circuit. Finally, gives the experimental result.
Key word: High-pressured sodium lamp; Electronic ballast; Closed loop; Electric current track
Introduction
The high-pressured sodium lamp (the HPS lamp) is one performance outstanding high strength gas electric discharge lamp (the HID lamp), its merit is the light effect is high, the life is long, the light color is good, therefore the application is widespread. Is the same with all gaseous discharge electro-optic light, the high-pressured sodium lamp also assumes negative V-I characteristic, needs the ballast to suppress the lamp electric current, when starts needs 3~4kV the gas breakdown voltage. The traditional inductance ballast volume is big, the power factor low (can only achieve 0.3~0.4), moreover is not strong to the network voltage fluctuation’s adaptiveness, therefore, the development performance-to-price ratio high electron ballast substitutes for the inductance ballast is ultimately. Already developed the high-pressured sodium lamp electron ballast is the high frequency electronic ballast mostly, under the high-frequency mode, the high-pressured sodium lamp easy blow-out, to coexist in the acoustic resonance question. In order to avoid the acoustic resonance, the operating frequency needs to revolve the center frequency high and low change frequently, but this causes not the small difficulty to the control, for this reason this article proposed one kind based on the electric current follow-up control low frequency electronic ballast.
1 control principle and circuit analysis
Circuitry diagram as shown in Figure 1. The main circuit divides into two levels, the first level for the rectification and APFC (active power factor compensating circuit), the second level to invert the electric circuit. May see, the electronic ballast materially is a typical AC/DC/AC transfer network.
1.1 rectifications and APFC
The diode does not control the rectification the input voltage, although is the sine, but the input current actually serious distortion, the massive uses will create the severely impair to the electrical network. Simultaneously the input current overtone production’s noise will also affect the electric circuit movement. APFC can make the electric circuit power input factor to enhance to 0.95 above; The input current basic is the sine wave, the harmonic content big reduction. Here uses UC3854 the control the Boost electric circuit to take the APFC electric circuit (Figure 2). UC3854 is the high power factor adjustment chip which American Unitrode Corporation produces, this chip uses the voltage electric current double closed-loop control, the electric current inner rim use mean current mode control. The voltage detection signal and the synchronized signal multiplication assigns as the electric current, Rs is the electric current examination resistance. The output voltage may carry on the control in the wide range, according to the earlier stage need, here controls in 380V. UC3854 as well as control circuit’s power source from the accessory power supply, the accessory power supply is instead stirs up the converter constitution by the PDM keyer UC3844 control, it may provide the multi-channel outputs.
1.2 contravariant parts and current feedback control
The contravariant electric circuit is the electronic ballast most important part, usually uses half bridge to invert or the entire bridge inversion electric circuit. Half bridge inversion electric circuit’s output voltage is the entire bridge’s half, in the power tube electric current equal situation, the entire bridge electric circuit’s output is half bridge’s 2 times, but multipurpose 2 power tubes. Considers the 400W high pressure sodium lamp two trigger voltages in 150~190V, and the APFC output voltage is 380V, therefore, half bridge electric circuit outputs the voltage can definitely meet the needs which two times trigger, moreover half bridge electric circuit and the entire bridge electric circuit power tube’s voltage stress is the same, but the former cost is lower than the latter, therefore, uses half bridge inversion electric circuit in here (Figure 3).
The electronic ballast is essentially the limit winds through lamp’s electric current. According to the reaction control rule, the wish controls some quantity, introduces this quantity the negative feedback to be possible. Shown in Figure 3 the contravariant electric circuit analysis situs in fact was still one kind of high frequency converter structure, to cause to wind through the high-pressured sodium lamp’s electric current is the low-frequency current, here uses stagnates the link comparison electric current track PWM control. Its principle like chart 3 in the dashed line frame shows, it by stagnates the link comparator constitution. Assigns electric current signal ig and current feedback signal if misses the ig-if achievement to stagnate the link comparator’s input, loses through it controls S2 and the S3 make-and-break. Supposes lamp electric current iL direction as shown in Figure 3, when S2 (or D2) breakover, iL increases, when S3 (or D3) breakover, iL reduces. Supposes stagnates the link comparator’s link widely for δi, if the current feedback coefficient is k (=if/iL), electric current iL and (ig ΔI) in the /k scope assumes the zigzag track in (ig-Δ I) /k to assign the electric current, as shown in Figure 4. For simplicity, the electric current demand signal is from the network voltage sine wave signal.
S2 and the S3 cut has two kind of patterns, respectively is the bipolarity cut and the unipolarity cut. When bipolarity cut, regardless of assigns electric current ig to be in alternation negative alternation S2 and S3 is the supplementary make-and-break. When unipolarity cut, when ig half period, S3 shuts off throughout, S2 carries on cuts the wave; When negative half period, S2 shuts off, S3 cuts the wave. The unipolarity cut principle analysis see Figure 4, namely in the t0~t1 time interval, the S2 breakover, electric current iL increases; To the t1 time, iL increases to (ig(t1) ΔI) /k is slightly bigger than a spot, stagnates the link comparator movement, S2 shuts off, inductance L electric discharge, iL after electric capacity C2, diode D3 after flow; Until the t2 time, drops to (ig(t2) - δi) /k is slightly smaller than a spot, the S2 breakover, iL will increase again. ig is in negative half period to be possible to make the similar analysis. Cuts the pattern with the bipolarity to compare, the unipolarity cut has the following merit:
1) has a power tube movement, the switching loss is bipolarity cut half;
2) main circuit various physical quantities dynamic stress, if dv/dt and di/dt are smaller than the bipolarity cut patterns, therefore, is smaller than the bipolarity electric circuit to control circuit’s disturbance.
But the unipolarity pattern’s control circuit must attach some simple logical control electric circuit.
The inductance L size with stagnated the link width 2ΔI to decide the turn-on frequency height. When other conditions are certain, the turn-on frequency and inductance L and stagnate the link width the product to be in reverse proportion. Because the power MOSFET turn-on frequency is very high, therefore, namely can satisfy the request with the small inductance.
2 starting circuit’s design
The starting circuit uses the logical control, cannot take the high pressure quarantine measures, simplified the main circuit, and can the instantaneous start. Principle of work as shown in Figure 5. Is very easy using the LC vibration principle to produce the radio impulse, in the main circuit after flow inductance L takes the LC oscillator vice-side, the original vice-side number of windings ratio supposes for 1∶20. The primary side 300V voltage from the control accessory power supply, vice-side can produce the 6kV pulse theoretically. Because in the LC oscillation circuit the string has thyristor SCR, when triggering under the L both sides can only produce on negative trigger pulse. M1, M2, M3 is three logical control signal, when three signals all for high level, only will then produce the high pressure trigger pulse.
M1 imitates on the C3 voltage to certain value, becomes the high level.
M2 uses for to judge whether to have the lamp electric current, has when the lamp electric current is the low level, forbids to start; Moreover on the M2 signal has the time delay function, after avoids the lamp extinguishment, presents the hot start; After the lamp restores the cold clean criticality, M2 becomes the high level, the permission start.
M3 and the power tube S2 driving signal synchronization, causes when the S2 breakover can produce the trigger voltage. Like this when the L both sides have the high voltage, S2 is at the conducting state, has avoided the trigger voltage to power tube’s destruction.
3 experimental results
The experimental sodium lamp model is NG400, city electricity voltage 230V, the dynamic storage oscilloscope model is TDS3012. The coil in terminal voltage and current waveform as shown in Figure 6. The electronic ballast’s power factor can achieve above 0.97, the harmonic distortion also obtains suppresses effectively, showed that constitutes the APFC performance by UC3854 to be good. Figure 7 is when the steady work the lamp current waveform, basically is the sine wave which requests, the electric current peak-to-peak value is 6.5A, the effective value is 4.6A. Actual enters the line segment power is 412W, lamp power 387W, designs the electronic ballast efficiency to achieve 0.94.
4 conclusions
the 400W high pressure sodium lamp electron ballast experimental result indicated that the electric circuit work is stable, does not have the acoustic resonance, meets the permanent power requirements basically. Explained that this kind of design proposal is more reasonable. Designs the triggering circuit starts quickly, and cannot take the quarantine measures.
