The present application is directed to the lighting arts. Typically, high frequency ballast inverter circuits provide power for operating a lamp, and the present application is directed to one of these ballast circuits. More particularly, the present application is directed to a ballast circuit that has the capability to power both a primary and a secondary, backup lamp, and will be described with particular reference thereto.
Typically, in an industrial lighting setting, it is often desirable to have a backup light source available should primary lights fail. Sometimes, in certain settings, it is even required to have automatic backup lighting. Many industrial lighting settings use high intensity discharge (HID) lamps because of their long life, high lumen output, and relative reliability. Yet even the best of light sources will fail from time to time. HID lamps in particular will “drop out” from time to time, meaning that they temporarily stop producing light, but are not dead, or permanently spent.
After lamp drop out, or if power is interrupted to the HID lamp, the lamp cannot be restarted until the lamp cools down. This can take up to twenty minutes, and during that time, the area in which the lamp is fixed will be without light. Temporary lighting is desirable, and often required where failure of primary light sources could present dangerous conditions. Typically, these temporary, backup light sources were powered by their own dedicated drive circuits. It has been typical that these auxiliary drive sources tap the ballasting inductor to provide a 120 V signal to the auxiliary lamp. This means that added space is required in an often already space lacking environment to house the backup drive circuits, and their associated power sources.
When an HID lamp drops out, the voltage inverter of the ballast typically does not simply stop oscillating. The unlit lamp acts essentially as an open circuit as far as the ballast is concerned, but a small amount of current still completes the circuit. Thus the lamp can be re-struck and again ramp up to its steady state operation. In the meantime however, a completely different circuit powers the auxiliary lamp while the primary lamp relights.
The present application presents a new and improved HID ballast inverter circuit that overcomes the above referenced problems and others.
In accordance with one aspect of the present disclosure, a lighting ballast is disclosed. The ballast includes a first inverter switch for providing power to a primary lamp during a first half-cycle of an alternating current lamp drive signal, and a second inverter switch for providing power to the primary lamp during a second half-cycle of the lamp drive signal. A high voltage multiplier portion boosts a signal applied to the primary lamp during a startup phase. A clamping portion clamps voltages within the ballast to levels that the lamp can tolerate. A resonant portion determines an operating resonant frequency of the ballast. An integrated auxiliary lamp power portion providing power to an auxiliary lamp if the primary lamp fails.
With reference to
The inverter 12 includes switches 34 and 36 such as MOSFETs, serially connected between conductors 20 and 24, to excite the resonant circuit 14. Other switches, such as IGBTs, or BJTs could also be used and are certainly contemplated. Typically, the resonant circuit 14 includes a resonant inductor 38 and a resonant capacitor network 40, 76, 78, and 42 for setting the frequency of the resonant operation. The capacitor 42 also acts as a DC blocking capacitor, which prevents excessive DC current from flowing through the lamp 28. A snubber capacitor 44 allows the inverter 12 to operate with zero voltage switching where the switches 34 and 36 turn ON and OFF when their corresponding drain-source voltages are zero.
The switches 34 and 36 cooperate to provide a square wave at a node 46 for exciting the resonant circuit 14. Gate lines, i.e., control lines 48 and 50, running from the switches 34 and 36, respectively, each include a resistance, 52 and 54, respectively. Diodes 56 and 58 are connected in parallel to the resistances 52 and 54, respectively, making the turn-off time of the switches 34 and 36 faster than the turn-on time. Achieving unequal turn-off and turn-on times provides a time when the switches 34 and 36 are simultaneously in the non-conducting states to allow the voltage at node 46 to transition from one voltage state to another voltage state by a use of residual energy stored in the inductor 38.
Gate drive circuitry, generally designated 60 and 62, includes inductors 64 and 66, which are both secondary transformer windings, each mutually coupled to primary winding 38. The gate drive circuitry 60, 62 is used to control the operation of respective switches 34 and 36. More particularly, the gate drive circuitry 60, 62 maintains the switch 34 ON for a first half of a cycle and maintains the switch 36 ON for the second half of the cycle. The square wave is generated at node 46 and is used to excite the resonant circuit 14. Bi-directional voltage clamps 68, 70 are connected in parallel to inductors 64 and 66, respectively. Each clamp 68, 70 includes a pair of back-to-back Zener diodes. The clamps 68, 70 act to clamp positive and negative excursions of gate-to-source voltage to respective limits determined by the voltage ratings of the back-to-back Zener diodes.
The output voltage of the inverter 12 is clamped by diodes 72 and 74 connected in series, which are a part of the clamping circuit 16. The clamping circuit 16 limits the high voltage generated to start the lamp 28. The clamping circuit 16 further includes capacitors 76 and 78, which are essentially connected in series to each other, but are effectively in parallel due to the low impedance of the DC bus. Each clamping diode 72, 74 is connected across an associated capacitor 76, 78. Prior to the lamp 28 starting, the lamp's circuit is essentially open, since an impedance of the lamp 28 is seen as a very high impedance. A high voltage across capacitor 42 is generated by a multiplier 80 (depicted in
With continuing reference to
For a variety of reasons, sometimes, during steady state operation of the ballast 10, the lamp 28 will drop out, that is, temporarily extinguish. In typical lighting applications, backup lights are provided with separate control circuitry and/or power sources. With reference to
The auxiliary lamp 120 in the illustrated embodiment is a 150 W, 120 V quartz lamp, but other lamps are also contemplated. The lamp 120 could also be a compact fluorescent lamp (CFL). In a CFL embodiment, the ballast 10 may include an extra capacitor to boost the voltage to start up the CFL. In other embodiments, the auxiliary lamp 120 could be an incandescent lamp, a halogen lamp, or other known lamp. With some additional rectification, the lamp 120 could even be a series of LEDs. The nominal light output of the auxiliary lamp can be 10% of the HID lamp's 28 output. Industry standards require that the backup lighting have at least approximately 1% of the lumen output of the primary light. Thus, in an industrial lighting setting, an auxiliary lamp that is about 10% as bright as the primary lamp can be included in one of every ten fixtures, yielding the net 1% of standard lumen output.
The inverter 12, before lamp ignition, is operating to supply the multiplier 80 with charge for breaking down the lamp 28. In this instance, and in other instances when the lamp is not lit (e.g., following a lamp drop out) the inverter 12 still oscillates with a low quiescent power. With reference to
With continuing attention to
Once the HID lamp 28 is re-ignited, the auxiliary lamp 120 does not have to extinguish immediately. In one embodiment, the ballast 10 senses the power across the HID lamp 28 and cuts out the auxiliary lamp 120 by opening switch 127 when the HID lamp re-achieves about 30%-70% of its potential lumen output. In the illustrated embodiment, the ballast 10 can cut out the auxiliary lamp 120 when the HID lamp 28 reaches approximately 50% of its potential lumen output. As shown in
Power for the monitor 128 is provided by the ballast 10 via power control circuitry 132. From the detected current, and the DC bus voltage, the power sensor 128 can calculate the average power being applied to the lamp 28. As the lamp 28 ramps back up to steady state operation, the current provided increases. That is, current is proportional to power. Once the power sensor 128 senses that the HID lamp 28 is running at about 50% power, (i.e. 50% lumen output) then the auxiliary lamp 120 switches off. The switch 127 that turns off the auxiliary lamp could be a BJT, MOSFET or IGBT. The switch 127 is driven by a comparator that senses when the bus power is less than a predetermined level. This would indicate that the HID lamp has extinguished. At that point, the comparator turns on the switch. When the power rises above a predetermined level, the comparator turns off the switch.
The signal that drives the switch 127 can be designed to turn off the auxiliary lamp 120 at any desired level. One possibility is to have the total power delivered to the HID lamp 28 and the auxiliary lamp 120 limited to the nominal power setting of the inverter. For example, the auxiliary lamp 120 could be switched off when the bus power reaches its nominal value. If the auxiliary lamp 120 is a 150 W halogen lamp and the HID lamp 28 is a 400 W lamp, this would mean that the switch 127 would extinguish the auxiliary lamp 120 when the HID lamp reaches 250 Watts.
Generally, the ballast is very cost effective. As has been shown, the auxiliary lamp 120 accommodating circuitry can be added to present ballast arrangements with very little modification. Thus, it can be included in every ballast produced, and not limited to the 10% of ballasts, as mentioned above.
While it is to be understood the described circuit may be implemented using a variety of components with different component values, provided below is a listing for one particular embodiment when the components have the following values:
The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.