Patent Grant
8294384
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
This application claims benefit of the following patent application(s) which is hereby incorporated by reference: Japanese Patent Application No. JP2008-215809, filed Aug. 25, 2008.
Not Applicable
Not Applicable
The present invention relates to an electronic ballast for a discharge lamp having at least two lighting modes with different light outputs, and a lighting fixture using such ballast.
In a discharge lamp of a thermionic cathode type such as a fluorescent lamp, lamp illumination performance and a lamp life can be secured by maintaining an appropriate filament temperature in the lamp.
In the present specification, a lead wire current obtained during illumination is divided into a current referred to as a lead wire current which includes a lamp current (i.e. large current side), and a current referred to as a constant preheating current which flows via filaments (i.e. small current side). Indexes employed in the vertical axis in
A curve D in
That is, it can be said that a filament temperature suitable for illumination can be maintained in the vicinity of rated illumination of a discharge lamp by constantly preheating filaments using the lamp current. Dimming control, on the other hand, requires a larger constant preheating current to maintain the appropriate filament temperature in accordance with a lower lamp output.
As stated above, it is a well-know fact that a required amount of the constant preheating current is increased when dimming the discharge lamp.
An operation in an electronic ballast for a discharge lamp will be explained referring to a first conventional example shown in
A low frequency AC power source sent from a commercial power source 10 is rectified by a diode bridge including diodes D1 to D4 in a step-up chopper circuit 11. The voltage is stepped up by a step-up chopper circuit including a choke coil L1, a transistor Q1 and a diode D5. Obtained at both ends of an electrolytic capacitor C2 is a DC voltage of, for example, about 300V. This DC voltage is converted into a high frequency current in inverter 12 and used as a lighting current for a discharge lamp 13.
The inverter 12 has a half bridge inverter circuit including a pair of transistors Q2 and Q3, and an inverter control circuit 14 drives the transistors Q2 and Q3 to be turned on/off alternately to output high frequency power. The high frequency power is supplied to the discharge lamp 13 via filaments by passing through a DC blocking capacitor C4 and the inductor L2.
A control power source circuit 15 which includes a step-down chopper circuit or similar circuit generates a DC low voltage (e.g. 12V) which is supplied to the inverter control circuit 14 and a chopper control circuit 16. The chopper control circuit 16 may include a control IC (e.g. MC33262 made by Motorola, Inc.) and generates a gate control signal for the transistor Q1 in the step-up chopper circuit 11. The inverter control circuit 14 provides each gate of the transistors Q2 and Q3 in the inverter 12 with a signal oscillated by using a versatile control IC (e.g. μPC494 made by NEC cooperation) via a driver circuit (e.g. IR2111 made by International Rectifier Corp.).
When power is applied, the chopper control circuit 16 and the inverter control circuit 14 starts oscillation to bring an output voltage Vdc in the step-up chopper circuit 11 to about 300V and an oscillation frequency in the inverter 12 to fp=95 kHz. At this time, a voltage obtained at the filaments of the discharge lamp 13 is lower than a lamp starting voltage, which means the discharge lamp 13 does not light.
High frequency power outputted from the inverter 12 is also made to flow into a transformer T2 through a capacitor C9. Power induced to a secondary side of the transformer T2 causes a current to flow into the filaments of the discharge lamp 1 through capacitors C7 and C8. This current obtained before the discharge lamp 13 starts is a required preheating current of, for example, about 700 mA.
Preheating is carried out for two to three seconds and is followed by reducing an oscillation frequency in the inverter 12 to fs=80 kHz. As a result, the voltage at the lamp filaments is increased to a required starting voltage, whereby the lamp illuminates. Thereafter, the oscillation frequency in the inverter circuit 12 is reduced to fr=55 kHz to bring the discharge lamp 13 into a rated lighting state.
In the case where lamp dimming is desired (luminance which is lower than rated luminance), a dimming control signal is sent to the inverter control circuit 14. Therefore, the oscillation frequency in the inverter circuit 12 is changed to fd=75 kHz for the discharge lamp 13 to be in a dimmed lighting state.
As dimming control is deepened with an increased oscillation frequency in the inverter circuit 12, the filament current is increased as understood from the filament current curve in
It is therefore made possible to appropriately secure a required preheating current before the lamp starts and a constant preheating current during dimming control.
An operation of an electronic ballast will also be explained by referring to a second conventional example in
The control circuit 4 which controls the inverter circuit 12 and the preheating circuit 5 carries out each control of filament preheating, starting and lighting for the discharge lamp 13 after the AC power source 10 is supplied to start the inverter 12. The control circuit 4 includes: a timer circuit 41 for setting each switching time to switch operations in the inverter 12 from a preheating state to a starting state, and from the starting state to a lighting state, and switching time to switch operations in the preheating circuit 5 from a preheating current supplying state to a preheating current stopping state respectively, and outputting a control signal corresponding to each switching time. A frequency setting circuit 42 sets each operating frequency in the inverter 12 in the preheating state, the starting state and the lighting state in accordance with each control signal outputted from the timer circuit 41. A driving circuit 43 outputs a driving signal to determine switching of the switching elements in the inverter 12 on the basis of a frequency set by the frequency setting circuit 42. An inverter 44 outputs a control signal δ obtained by inverting a control signal Y which is outputted from the timer circuit 41 to control preheating switching element SW1.
An operation of the control circuit 4 will be explained below by using a timing chart shown in
Next, after passing the time t1, the control signal α is switched from “L” to “H” for switching to a starting state (i.e. starting mode) to apply a voltage required for starting to both ends of the discharge lamp 13. An amount of time t2 to maintain the starting state is set by a control signal β outputted by the timer circuit 41, during which the inverter 12 is subjected to a switching operation at a frequency fs (fs<fp) set for the starting state.
Next, after passing the time t2, the control signal β is switched from “L” to “H” for switching to a lighting state (i.e. lighting mode) to supply power required for rated lighting of the discharge lamp 13. At the time t2 and thereafter, the control signal α is set to “H” and the control signal β is set to “H”, wherein the inverter circuit 12 is subjected to a switching operation at a frequency fr (fr<fs<fp) set for the lighting state at this time to realize lighting of the discharge lamp 13 by a predetermined output.
In the present conventional example, the control signal δ obtained by inverting the control signal Y which is switched from “L” to “H” at time t3 set as t1<t3<t2 is used to turn on the preheating switch element SW1 up to the time t3 so as to supply a preheating current, and the preheating switch element SW1 is turned off at the time t3 and thereafter to stop supplying a preheating current If.
More specifically, a preheating current is made to flow in filaments in the precedent preheating period and a constant preheating current supplied to the filaments is stopped after stable lighting. Therefore, power consumption by a constant preheating current which is unnecessary in normal lighting and adverse effects to a lamp life are prevented.
In the electronic ballast described as the first conventional example, a lighting output and a constant preheating current are appropriately supplied as stated above by a combination of the two independent resonant circuits including a main resonant circuit for supplying lighting power and a preheating resonant circuit for supplying filament preheating power, and the interrelationship therebetween is largely affected by variations in the characteristics of components which constitute the resonant circuits, thereby making it difficult to design the circuits.
In designing the preheating resonant circuit so as to have relatively fewer effects from component variations, the design needs to be realized such that preheating power applied to filaments has fewer variations resulting from a frequency characteristic in an inverter operating range during lighting, and preheating power exhibits an output curve which is substantially flat relative to variations of lighting power. In this case, a current which makes little difference to a current in a dimming control state is made to flow into filaments even in a full-lighting mode in which a constant preheating current is unnecessary, causing concern about an increased power loss without contributing to a light output and adverse effects to a lamp life.
Meanwhile, in the electronic ballast described as the second conventional example, the constant preheating current is stopped after achieving stable lighting, thereby eliminating the concern considered as a problem in the first conventional example about power loss without contributing to a light output and adverse effects to the lamp life. However, this configuration will result in having an insufficient preheating current because no constant preheating current is supplied during dimming control, and there is another concern about adverse effects such as premature filament failure.
The present invention was achieved by taking the above problems into consideration, having an object to improve efficiency of an electronic ballast by cutting off an unnecessary constant preheating current in a full-lighting mode and thereby reducing power loss which does not contribute to a light output. The invention also prevent problems related to a short life of a discharge lamp such as premature filament failure by maintaining an appropriate filament temperature during lighting resulting from securing a constant preheating current in a dimming control mode with a reduced light output.
A first aspect of the present invention is characterized by an electronic ballast as shown in
A second aspect of the present invention is based on the electronic ballast according to a first aspect of the present invention, wherein the preheating circuit constitutes an LC resonant circuit including the primary winding of the winding component T2 and a serially connected capacitance C9. An oscillation frequency in the electronic ballast during lighting is operated to be higher than a resonant frequency in the first resonant circuit (including L2 and C3) with a lamp current flowing therein, and lower than a resonant frequency in a preheating resonant circuit (including T2 and C9).
A third aspect of the present invention is based on the electronic ballast according to the first or second aspect of the present embodiment, having a first lighting mode (i.e. full-lighting mode) and a second lighting mode (i.e. dimming control mode) allowing an operation over a plurality of stages with a light output less than that of the first lighting mode as shown in
A fourth aspect of the present invention is based on the electronic ballast according to any one of the first to third aspects and makes it possible to realize a light output control over a plurality of stages with a visually continuous dimming operation. The amount of a preheating current is controlled in accordance with a lighting mode by changing the switch Q4 to operate corresponding to a lighting control signal or a signal secondarily generated from the lighting control signal as shown in
A fifth aspect of the present invention is a lighting fixture including the electronic ballast according to any one of the first to fourth aspects of the present invention.
According to the first and second aspects of the present invention, a power loss without contributing to a light output due to a constant preheating current flowing into filaments serving as a current path can be reduced in a lighting mode with a large light output in which an appropriate filament temperature can be maintained by a lamp current. An appropriate filament temperature can be maintained by securing the constant preheating current flowing into the filaments serving as a current path in a lighting mode with a small light output in which an appropriate filament temperature cannot be maintained only by a lamp current, so that problems related to premature filament failure (i.e. short life of lamp) can be prevented.
According to the third aspect of the present invention, power consumption can be efficiently converted into a light output and filament overheating can also be prevented in a first lighting mode. This prevents blackening of the lamp bulb, premature filament failure, and premature emitter exhaustion. Meanwhile, in a second lighting mode to obtain power saving and lighting effects by suppressing power consumed in a lamp, these effects can be obtained while preventing premature blackening of the lamp bulb, filament failure, and emitter exhaustion.
According to the fourth aspect of the present invention, it is possible to establish any amount of a filament current in accordance with the degree of a dimming control for a lamp without requiring an operation performed for a constant preheating current by a resonance effect, thereby making it easier to design a circuit for supplying preheating power.
Shown in
In this embodiment, an AC voltage of 100V and 50/60 Hz supplied from a commercial power source 10 is rectified to a DC voltage with a peak value of about 141V by a diode bridge including diodes D1 to D4. The DC voltage is stepped up by a step-up chopper circuit including a choke coil L1, a transistor Q1 and a diode D5. Obtained at both ends of an electrolytic capacitor C2 connected to an output end of the step-up chopper circuit is a DC voltage of, for example, about 300V. This DC voltage is converted into high frequency power in a subsequent inverter 12 and used as lighting power for a discharge lamp 13.
The inverter 12 has a half bridge inverter circuit including serially connected transistors Q2 and Q3, and provides a high frequency rectangular wave voltage at a connection point between the switching transistors Q2 and Q3, by a control circuit 17 which carries out a high frequency switching operation to turn on the transistors Q2 and Q3 alternately. The high frequency voltage is converted into lighting power of a substantially sinusoidal wave by a resonance action of an inductor L2 and a capacitor C3. This lighting power is supplied to the discharge lamp 13 via a step-up transformer T and a DC blocking capacitor C4. The discharge lamp 13 which is a thermionic cathode fluorescent lamp is connected to the lighting device via a lamp socket.
The control circuit 17 may include an integrated circuit (or other components) to control a lighting output of the discharge lamp 13 to a predetermined output by driving the transistor Q1 in step-up chopper circuit 11 and the transistors Q2 and Q3 in the inverter 12 in response to signals for turning on/off and dimming control or other signals sent from a dimming control output circuit 18 such as a remote control signal receiving device.
High frequency power outputted from the inverter circuit 12 is also made to flow into a transformer T2 through a capacitor C9. Power induced to a secondary side of the transformer T2 causes a current to flow into filaments of the discharge lamp 13 through capacitors C7 and C8. Also connected in series to the capacitor C9 and the transformer T2 is a transistor Q4 whose switching operation is used to switch an amount of current supplied to the filaments. The transistors Q1 to Q4 may be MOSFETs or other semiconductor switching elements.
A driving signal for the transistor Q4 is supplied from an output terminal of a comparator 19 which has a positive input terminal for inputting a fixed voltage Vref and a negative input terminal for inputting a dimming control level signal Vdim from the dimming control output circuit 18 to the control circuit circuit 17.
The dimming control level signal Vdim corresponds to a smoothed DC voltage which is increased as a light output is controlled to be higher and is decreased as a light output is reduced by a dimming control. If it is assumed that a dimming control level signal obtained in a maximum light output is Vdim1 and a dimming control level signal obtained in a minimum light output is Vdim2, a relationship therebetween relative to the fixed voltage Vref will be Vdim2<Vref<Vdim1.
More specifically, the transistor Q4 is turned off to stop supplying a constant preheating current in a lighting mode with a dimming control level equal to or greater than nominal or rated brightness. Here, if an impedance element such as a capacitor is connected in series with the transistor Q4, supplying a constant preheating current can be suppressed by turning off the transistor Q4. On the contrary, in a lighting mode with a dimming control level equal to or less than rated or nominal brightness, the transistor Q4 is turned on to supply a constant preheating current.
Note that, in shifting the discharge lamp 13 from a turned-off state to a turned-on state by a lighting signal inputted upon power supply or from a remote control transmitter, the dimming control level signal Vdim is fixed to an “L” level during a preheating period prior to lamp lighting and the transistor Q4 is turned on to supply a preheating current.
In
In accordance with reduction of a light output, a preheating current undergoes a transition to a direction in which the preheating current becomes insufficient as shown in a lighting state b. The transistor Q4 is switched from a turned-off state to a turned-on state when a light output reaches a fixed point or less (i.e. less than 0.7 on the horizontal axis) and begins supplying a constant preheating current. This is followed by increasing the constant preheating current as a light output decreases thereafter and carrying out an operation at a point along a target dimming control curve B on the dimming control data sheet. That is, an appropriate filament temperature is maintained during lighting.
An electronic ballast according to a second embodiment of the present invention will be explained. It has basically a same circuit configuration as the first embodiment (i.e. circuit shown in
The fluorescent lamp has lighting modes including a first lighting mode (i.e. full-lighting mode) with a large light output, and a second lighting mode (i.e. dimming control mode), allowing an operation over a plurality of stages with a light output smaller than that of the first lighting mode.
If the full-lighting button 21 is pressed in the transmitter 20 to realize the first lighting mode (i.e. full-lighting mode), the transistor Q4 arranged in the preheating resonant circuit is turned off to bring a constant preheating current into substantially 0 [A].
If the preference button 22 is pressed in the transmitter 20 to realize the second lighting mode (i.e. dimming control mode), the transistor Q4 arranged in the preheating resonance circuit is turned on to supply the constant preheating current.
In
In the second lighting mode (i.e. dimming control mode), the constant preheating current is supplied to increase the constant preheating current as a light output is decreased thereafter, followed by an operation at a point along the target dimming control curve B on the dimming control data sheet. That is, an appropriate filament temperature can be maintained during lighting.
In the case of carrying out a feedback control for a lamp light output by power consumed in the inverter, power required for constant preheating is also combined for feedback, wherein there is a danger that a discontinuous change may happen in switching to a constant preheating current in the middle of continuously reducing a light output as shown in the first embodiment (refer to
An unexpected operation may also happen in response to a power saving operation by a user in the first embodiment such that a light output is slightly reduced due to decreased discharge lamp lighting power before and after switching the transistor Q4 from a turned-off state to a turned-on state. As understood from
An electronic ballast according to a third embodiment of the present invention will be explained with reference to
The preheating resonant circuit does not have a resonance effect to increase a constant preheating current as light output decreases as shown in the first and second embodiments. Also, the capacitor C9 has a sufficiently large capacitance so that a resonance frequency calculated for the preheating resonant circuit is much smaller than an operating frequency in the inverter. A constant preheating current is obtained when the transistor Q4 is turned on and is characterized as being substantially flat relative to a change in a light output, that is an oscillation frequency.
Meanwhile, inputted from the dimming control output circuit 18 (such as a remote control signal receiving circuit) to the control circuit 17 is a DIM signal which determines a dimming control level. The DIM signal is a duty cycle signal with a frequency of 1 kHz, having an ON time which is made larger in accordance with a smaller light output. In order to realize a dimming control level corresponding to this signal, the light output is controlled by the control circuit 17. The DIM signal is further used to drive the transistor Q4 to be turned on/off.
Therefore, an appropriate filament temperature can be maintained in accordance with each lamp output mode by carrying out an operation to increase/decrease an amount of time to supply a constant preheating current, which is characterized as being flat by nature as stated above, in response to a lighting control signal.
Moreover, in the case where light outputted from a lamp is subjected to a feedback control by power consumed in the inverter, power required for constant preheating is also combined for feedback, so that there is a danger that a discontinuous change may happen in switching to a constant preheating current in the middle of reducing a light output continuously. Such a visual sense of incompatibility can be eliminated by applying stepwise changes to an effective value of the constant preheating current in the same manner with the light output.
Note that the transistor Q4 is controlled to be turned on/off in the present embodiment by using a duty cycle signal (of 1 kHz) for dimming control without making any changes, but it may be replaced with a control to turn on/off the transistor Q4 by an output of a PWM control circuit which is arranged to convert the dimming control level signal Vdim made of a smoothed DC voltage as shown in
Thus, although there have been described particular embodiments of the present invention of a new and useful electronic ballast with preheat current control, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-215809 | Aug 2008 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5170099 | Ueoka et al. | Dec 1992 | A |
| 5502423 | Okude et al. | Mar 1996 | A |
| 5644480 | Sako et al. | Jul 1997 | A |
| 5920155 | Kanda et al. | Jul 1999 | A |
| 6054815 | Sugita et al. | Apr 2000 | A |
| 6057652 | Chen et al. | May 2000 | A |
| 6636005 | Wacyk et al. | Oct 2003 | B2 |
| 6828740 | Takahashi et al. | Dec 2004 | B2 |
| 6963176 | Onishi et al. | Nov 2005 | B2 |
| 20070296355 | Hamamoto et al. | Dec 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 2002231483 | Aug 2002 | JP |
| 20050019142 | Jan 2005 | JP |
| 2006188641 | Jul 2006 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20100109548 A1 | May 2010 | US |
