CN101321424B - Hot cathode fluorescent lamp filament current control circuit - Google Patents
Hot cathode fluorescent lamp filament current control circuit Download PDFInfo
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- CN101321424B CN101321424B CN2007100938498A CN200710093849A CN101321424B CN 101321424 B CN101321424 B CN 101321424B CN 2007100938498 A CN2007100938498 A CN 2007100938498A CN 200710093849 A CN200710093849 A CN 200710093849A CN 101321424 B CN101321424 B CN 101321424B
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- fluorescent lamp
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Abstract
The invention provides a filament current control circuit of hot-cathode fluorescent lamp, which is used for accurately controlling the filament current of hot-cathode fluorescent lamp, comprising a filament heating transformer and a filament current control loop. A primary loop of the filament heating transformer is connected with the filament current control loop, and two ends of secondary loop are respectively connected with two ends of a hot-cathode filament of fluorescent lamp. The driving power supply of the fluorescent lamp is connected to a centre tap of the corresponding secondary loop. The filament current control loop comprises a power switch, a control logic, a multiple-input comparator, an oscillator, a reference voltage source, a reference current source, a primary loop current sampling resistor, a filtering capacitor, a filtering resistor and so on. By using the filament current control circuit of hot-cathode fluorescent lamp in this invention, the influence of the lamp tube on the temperature of filament can be reduced, the filament current can be accurately controlled, the temperature of filament can be stabilized, the service life of fluorescent lamp can be prolonged, and the current balance of shunt-wound fluorescent lamp can be realized without using an extra choke coil.
Description
Technical field
The present invention relates to the fluorescent tube Driving technique, specifically relate to the fluorescent tube cathode protection technology, particularly a kind of hot cathode fluorescent lamp filament current control circuit.
Background technology
Hot-cathode fluorescent lamp HCFL is as a kind of energy-conserving light source, be widely used, as shown in Figure 1, the hot cathode of HCFL is positioned at the two ends of fluorescent tube, hot cathode is made by spiral helicine tungsten filament coiled. its surface coverage have can emitting electrons material, when filament temperature one regularly, add certain voltage at the two ends of filament, filament just can heat of emission electronics, excites mercuryvapour collision phosphorus luminous.As shown in Figure 4, according to the structure of negative electrode, utilize the characteristics of electromagnetic field to analyze, it is the closeest to learn that electric field distributes at the two ends of negative electrode, and during filament work, the current density here is also maximum.Common simple Filament of fluorescent lamp heater circuit as shown in Figure 2, lamp tube drive power is from input A, B inserts fluorescent lamp, realizing filament pre-heating by the electric current between filament and the startup electric capacity between the circuit warming up period, after fluorescent lamp is finished ignition operation, heater current is made up of two parts, a part is for making the lamp current of lamp luminescence, a part is the resonant capacitance electric current of control light tube electric voltage, when low-light level, lamp current is very little, have only several milliamperes, and the resonant capacitance electric current is very big, can cause filament under the low-light level situation, to damage easily up to more than 0.6 ampere.As shown in Figure 4, lamp current can flow to the other end on filament from an end, produces a large amount of heat on filament, and makes filament temperature very high and be difficult to accurate control.Figure 3 shows that the filament heating circuit of at present common a kind of hot-cathode fluorescent lamp HCFL electric ballast, lamp tube drive power is from input A, B inserts fluorescent lamp, filament is heated separately by transformer coupled electric current, the filament heating current that the temperature of filament is added simultaneously and the influence of lamp current, as shown in Figure 4, lamp current can flow to the other end from an end on filament in this circuit, electric current by filament comprises filament heating current and lamp current, because lamp current has very big excursion in the light modulation process, and the electric current by filament is altered a great deal, make filament temperature very high and unstable, make filament temperature be difficult to accurate control.Cathode life has determined the life-span of fluorescent lamp, if cathode current is excessive, superheating phenomenon will appear in filament, makes the oxide material accelerated evaporation, causes the tungsten evaporation when serious, fluorescent tube is turned black in early days, the lost of life.Too little as cathode current, the cathode temperature deficiency also can shorten lamp tube service life.Because it is inconsistent with the thermal coefficient of expansion of its surperficial electronic emitting material to form the tungsten filament of filament, what the broad filament electric current of moment can the accelerated electron emissive material peels off, and influences the useful life and the luminous efficiency thereof of fluorescent lamp.
Because the HCFL fluorescent tube is negative resistance charactertistic, promptly electric current is low more, and voltage is high more, and this characteristic of HCFL makes its directly parallel operation, wants balance parallel connection lamp tube current usually, all is that employing adds choke, changes the impedance operator of fluorescent tube, has increased cost.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of hot cathode fluorescent lamp filament current control circuit, adopt this circuit can reduce the influence of lamp current to filament temperature, can accurately control heater current, prolong fluorescent lamp useful life, and do not need to adopt and add the current balance type that choke just can be realized fluorescent lamp in parallel.
For solving the problems of the technologies described above, the technical scheme that hot cathode fluorescent lamp filament current control circuit of the present invention is taked, comprise the filament heating transformer, the filament heating transformer comprises primary coil and secondary coil institute, also comprise the heater current control loop, primary coil connects the heater current control loop, and the secondary coil two ends link to each other with hot cathode filament two ends of fluorescent lamp respectively, and fluorescent lamp drive power supply is connected to the centre cap place of respective secondary.
Described heater current control loop comprises power switch, control logic, multi-input comparator, oscillator, reference voltage source, reference current source, primary current sampling resistor, filter capacitor, filter resistance; Filament heating transformer primary coil one end links to each other with the power switch output, another termination DC power supply, the feedback end of power switch links to each other with primary current sampling resistor, filter resistance, and the other end of filter resistance links to each other with filter capacitor and is connected to reference current source; Electric current and reference current source electric current in the primary current sampling resistor probe power switch, and produce a voltage signal, the RC filter that filter resistance and filter capacitor constituted forms this voltage signal equalization the average feedback signal of switching current, multi-input comparator is according to the voltage of sawtooth signal with the average feedback signal of reference voltage source signal, oscillator generation, produce a pulse-width signal, by the action of control logic power controlling switch.
Secondary coil can be for a plurality of, and each secondary coil two ends links to each other with hot cathode filament two ends of fluorescent lamp respectively, and centre cap connects fluorescent lamp drive power supply.
The filament heating transformer of hot cathode fluorescent lamp filament current control circuit of the present invention is made up of primary coil and secondary coil, primary coil is used for realizing the input to transformer energy, secondary coil is used for realizing the heating to filament, realize the isolated temperature of filament is controlled by the filament heating transformer, and utilize it to weaken the thermal impact of lamp current filament.The secondary coil of filament heating transformer adopts centre cap, utilizes the stray inductance of transformer to realize reducing mean allocation to lamp current the heat that lamp current is produced on filament, and be beneficial to the accurate control of realization to heater current.Because the fluorescent lamp AC driven power inserts to fluorescent lamp from filament heating transformer secondary coil centre cap and powers, the stray inductance of filament heating transformer can make lamp current evenly flow out at the electrode two ends, directly be divided into two parts at the hot cathode two ends behind the fluorescent lamp tube electric current arrival electrode and flow into filament heating transformer secondary coil two ends, flow out through filament heating transformer secondary coil centre cap place then, the part of generation heat has only the fraction electric current from hot cathode filament intermediate flow to two ends on filament, the heat that produced on filament of lamp current will be very low like this, the power of filament heating will be controlled by outside filament heating current, thereby and might realize the accurate control of filament temperature.
The present invention can utilize the characteristics of the response time of RC to realize the soft start and the soft shutoff of power switch pipe, can utilize RC low pass filter and reference current source to realize filament pre-heating and normal operation, can allow the temperature of filament rise or descend with speed more slowly, avoiding filament because of quenching or shock heating, and the accelerated electron emissive material peels off from filament and causes the shortening of electrode life.
The present invention can change the negative resistance charactertistic of HCFL fluorescent tube because of the stray inductance of filament heating transformer secondary coil, thus utilize the filament heating transformer can make a plurality of fluorescent tubes parallel operations simultaneously, and guarantee the balance of lamp current, can reduce cost.
Description of drawings
Fig. 1 is the cathode construction of HCFL;
Fig. 2 is common simple Filament of fluorescent lamp heater circuit;
Fig. 3 is the common heating transformer filament heating circuit of using;
Fig. 4 is the path of lamp current in the common filament heating circuit;
Fig. 5 is the path of lamp current in the filament heating circuit of the present invention;
Fig. 6 is the equivalent electric circuit of lamp current path of the present invention;
Fig. 7 is that the present invention uses BJT to be the embodiment of filament heating circuit switch;
Fig. 8 is that the present invention uses metal-oxide-semiconductor to be the embodiment of filament heating circuit switch;
The soft start schematic diagram that Fig. 9 is made up of the RC circuit;
Figure 10 utilizes the heated by electrodes schematic diagram of same filament heating transformer realization to a plurality of HCFL;
Figure 11 is that HCFL in parallel is by inserting the equiva lent impedance figure of AC power supplies behind the transformer;
Figure 12 is that the parallel connection of many fluorescent tubes drives schematic diagram.
Embodiment
Below in conjunction with the drawings and the specific embodiments the present invention is described in further detail.
Hot cathode fluorescent lamp filament current control circuit of the present invention as shown in Figures 7 and 8, this circuit comprises filament heating transformer 1, filament heating transformer 1 comprises a primary coil and at least one secondary coil, also comprise the heater current control loop, the heater current control loop comprises devices such as power switch 2, control logic 3, multi-input comparator 4, current-controlled switch 5, oscillator OSC, reference voltage source VREF, reference current source IFER, primary current sampling resistor R0, filter capacitor C1, filter resistance R1.Filament heating transformer 1 secondary coil two ends link to each other with hot cathode filament two ends of fluorescent lamp respectively, and fluorescent lamp drive power supply A, B are connected respectively to the centre cap place of corresponding filament heating transformer 1 secondary coil; Filament heating transformer 1 primary coil one end links to each other with power switch 2 outputs, another termination flows power supply always, the feedback end of power switch 2 links to each other with primary current sampling resistor R0, filter resistance R1, the other end of filter resistance R1 links to each other with filter capacitor C1 and is connected to current-controlled switch 5, and current-controlled switch 5 meets reference current source IREF; Primary current sampling resistor R0 is used for the electric current of probe power switch and the electric current of reference current source IREF, produce a voltage signal, the RC filter that this voltage signal process filtering resistance R 1 and filter capacitor C1 are constituted forms its equalization the average feedback signal FB voltage of switching current, multi-input comparator 5 is according to the reference voltage source vref signal, the feedback signal FB voltage of sawtooth waveforms (ramp) signal that oscillator OSC produces and average switching current, produce a pulse-width signal PWM, by the action of control logic 3 (as rest-set flip-flop) power controlling switch 2, live the average current that power switch 2 flows through to stablize.Stable live the electric current that average current that power switch 2 flows through can stable flow be crossed filament heating transformer 1 primary coil, and then the filament heating current that produces of the induction of stable filament heating transformer 1 secondary coil.In circuit of the present invention, because the fluorescent lamp AC driven power inserts to fluorescent lamp from filament heating transformer 1 secondary coil centre cap and powers, directly be divided into two parts at the hot cathode two ends behind the fluorescent lamp tube electric current arrival electrode and flow into filament heating transformer 1 secondary coil two ends, flow out through filament heating transformer 1 secondary coil centre cap place then, the part of generation heat has only the fraction electric current from hot cathode filament intermediate flow to two ends on filament, the stray inductance of filament heating transformer can make lamp current evenly flow out at the electrode two ends, the heat that produced on filament of lamp current will be very low like this, the power of filament heating will be controlled by outside filament heating current, thereby and might realize the accurate control of filament temperature, Fig. 5 is the path of lamp current in the filament heating circuit of the present invention.The equivalent electric circuit of fluorescent lamp tube current path as shown in Figure 6 among the present invention, ZHCFL is a tube impedance, R4 is the very little equivalent resistance of hot cathode filament intermediate flow to two ends, and L4 is the inductance of the two ends of filament heating transformer 1 secondary coil to the centre cap place.
Because the electric current when needed electric current is with operate as normal during filament pre-heating is different, usually need preheat curent enough big, so that filament can fully heat, and only need smaller electric current during operate as normal usually, keep the temperature that filament can emitting electrons, reduce the consumption of filament wattage simultaneously, save electric energy, improve the luminous efficiency of fluorescent tube.Heater current control in the time of preheating and normal operation is as follows:
● the preheating filament Current Control
Current-controlled switch 5 disconnections this moment, the average current of power switch is controlled by VREF fully, the electric current of the power switch primary current sampling resistor R0 that flows through, produce a pulse voltage, the RC low pass filter (LPF) that this voltage is formed via R1 and C1 filters and becomes a direct voltage, when circuit was stablized, this direct voltage equated with VREF. at this moment, the average current that flows through power switch is: I
AVGPH=VREF/R
0
● normally move the filament Current Control
This moment current-controlled switch 5 closures, the average current of power switch is by the difference control of VREF with IREF*R1, this time, the average current of power switch was: I
AVGRUN=(V
REF-I
REF* R
1)/R
0After current-controlled switch 5 closures, IREF can pass through resistance R 1, and R0 flows to ground, and the generation size is V on these two resistance
C=I
REF* (R
0+ R
1) pressure drop because R0 is generally several ohm, and R1 is generally tens of K ohms, so this pressure drop is leading by R1, can be reduced to V
C=I
REF* R1, because the existence of VC is arranged, when current controlled circuit was stablized, the average current that R0 flows through was changed to: I
AVGRUN=(V
REF-V
C)/R
0=(V
REF-I
REF* R
1)/R
0
The closure of current-controlled switch 5 can realize the dynamic adjustments of heater current; The size of reference current can be regulated and control.
The present invention can realize the soft start of heater current.Can utilize RC filter and reference current source IREF to realize the soft start of heater current.Before the work of filament control circuit, with the electric current that doubles filament control circuit working standard electric current average feedback signal FB voltage is charged on the reference voltage V REF earlier, this moment, the duty ratio of pulse-width signal PWM was 0, close this reference current source IREF again, at this moment, feedback signal FB voltage will descend by logarithmic relationship, and the duty ratio of power switch 2 will increase in time gradually simultaneously, until the current stabilization of control loop with power switch 2.Soft start-up process as shown in Figure 9.
When soft shutoff heater current, reference current source charges to the FB end points with the electric current that doubles filament control circuit working standard electric current, at this moment feedback signal FB voltage will rise by logarithm, the duty ratio of power switch 2 also reduces by same sequential simultaneously, until switch cuts out fully, realize the soft shutoff of heater current.Different RC values can be set various soft starts and soft turn-off time.
Because the HCFL fluorescent tube is negative resistance charactertistic, promptly electric current is low more, and voltage is high more.This characteristic of HCFL makes its directly parallel operation, wants balance lamp tube current in parallel usually, all is to adopt to add choke, changes the impedance operator of fluorescent tube.In the filament heating transformer 1 that is adopted in the present invention, the secondary of transformer is entwined on magnetic core by coil, this coil has certain stray inductance, this stray inductance can be used for changing the impedance operator of fluorescent tube, the feasible parallel operation of realizing a plurality of HCFL fluorescent tubes, and do not need to increase extra choking-winding.Be that a plurality of filament heater coils are wound in the heating that realizes on the same filament heating transformer many groups HCFL electrode as shown in figure 10, and realize the driving in parallel of many lamps.Equivalent electric circuit in the stray inductance incoming transport power supply of fluorescent tube adding filament heating transformer 1 as shown in figure 11, the filament heating transformer is secondary to be the center with the tapping point, thereby this tap is to the stray inductance parallel connection of other two taps, form L1 and two stray inductances of L2 respectively at the two ends of fluorescent tube, the equiva lent impedance that this moment, fluorescent tube was connected with this stray inductance is: Z
Eq=j ω * (L
1+ L
2)+Z
HCFLFrom top equation as can be known: when L1+L2 is enough big, ω is enough greatly when (frequency that is AC power supplies is enough high), the equiva lent impedance of fluorescent tube will be dominated at the equivalent inductive reactance under the operating frequency by stray inductance, make the fluorescent lamp load of incoming transport power supply become positive resistance characteristic, thereby the parallel connection that realizes a plurality of HCFL fluorescent tubes drive by the negative resistance charactertistic change.Figure 12 is many lamps schematic diagrames that drive in parallel.
The filament heating transformer 1 of hot cathode fluorescent lamp filament current control circuit of the present invention is made up of primary coil and secondary coil, and primary coil is used for realizing the input to transformer energy, and secondary coil is used for realizing the heating to filament.Realize the isolated temperature of filament is controlled by filament heating transformer 1, and utilize it to weaken the thermal impact of lamp current filament.The secondary coil of filament heating transformer 1 adopts centre cap, utilizes the stray inductance of transformer to realize the mean allocation of lamp current on filament, reduces the heat that lamp current is produced on filament, is beneficial to realize the accurate control to heater current.
Hot cathode fluorescent lamp filament current control circuit of the present invention has reduced the heating of lamp current on filament, has realized that the temperature of filament is mainly controlled by external circuit, and has not been subjected to the influence of lighting tube brightness.Current control loop comprises oscillator, multi-input comparator, reference voltage source, reference current source, control logic, power switch and a signal feedback loop to realize the closed-loop control to heater current, guarantee this electric current stablizing under varying environment, thereby prolong the useful life of filament.
But the electric current that flows through in the current feedback sampled power switch 2, the electric current of the transformer secondary of also can sampling.Outside RC low pass filter is used to realize to the detection of filament heating transformer average current and the dynamic control of heater current.
Adopt filament heating current soft start and soft cut-off method, can allow the temperature of filament rise or to descend with speed more slowly, avoiding filament because of quenching or shock heating, and the accelerated electron emissive material peels off and causes the shortening of electrode life from filament.Can utilize the characteristics of the response time of RC to realize the soft start and the soft shutoff of power switch pipe, can utilize RC low pass filter and reference current source to realize the setting of filament pre-heating electric current and normal operation heater current.
The present invention utilizes the HCFL filamentray structure, by external inductors shunting lamp current, reduces the influence of lamp current to filament temperature, makes to the electric current of filament heating leading by the external control electric current.Can control the elementary average current of transformer by the circuit that oscillator, multi-input comparator, RC filter are formed, thereby control filament temperature.Current controling signal interface (current-controlled switch 5) allows the input pwm signal to realize the dynamic adjustments of filament average current, utilize active control technology, realization finally realizes the accurate control of filament temperature to the accurate control of heater current, thus the useful life of prolonging lamp tube.
Utilize the filament heating transformer can realize lamp tube current balance.The parasitic structure of filament heating transformer can make equivalent inductance of lamp two ends polyphone, by controlling the inductance value of this inductance, can increase the impedance of fluorescent tube, form a ballast inductance, this stray inductance can change the negative resistance charactertistic of HCFL fluorescent tube, so utilizes the filament heating transformer can make a plurality of fluorescent tubes parallel operation simultaneously, and also utilize the parasitic parameter of filament current control circuit to realize lamp tube current balance in parallel, thereby cost is saved in the design that can simplify many lamp ballasts.
Above method can reduce the power that filament consumes, stablize the working temperature of filament, prolong the useful life of HCFL, simultaneously stablizing owing to the filament consumed power, this method also helps improving the luminous efficiency of fluorescent tube, can simplify the Design of Digital Ballast that drives many lamps.
Claims (7)
1. hot cathode fluorescent lamp filament current control circuit, comprise the filament heating transformer, the filament heating transformer comprises primary coil and secondary coil, it is characterized in that, also comprise the heater current control loop, primary coil connects the heater current control loop, and the secondary coil two ends link to each other with hot cathode filament two ends of fluorescent lamp respectively, and fluorescent lamp drive power supply is connected to the centre cap place of respective secondary;
Described heater current control loop comprises power switch, control logic, multi-input comparator, oscillator, reference voltage source, reference current source, primary current sampling resistor, filter capacitor, filter resistance; Filament heating transformer primary coil one end links to each other with the power switch output, another termination DC power supply, the feedback end of power switch links to each other with primary current sampling resistor, filter resistance, and the other end of filter resistance links to each other with filter capacitor and is connected to reference current source; Electric current and reference current source electric current in the primary current sampling resistor probe power switch, and produce a voltage signal, the RC filter that filter resistance and filter capacitor constituted forms this voltage signal equalization the average feedback signal of switching current, multi-input comparator is according to the voltage of sawtooth signal with the average feedback signal of reference voltage source signal, oscillator generation, produce a pulse-width signal, by the action of control logic power controlling switch.
2. hot cathode fluorescent lamp filament current control circuit according to claim 1 is characterized in that, also comprises current-controlled switch, is connected in reference current source with between filter capacitor and the filter resistance.
3. hot cathode fluorescent lamp filament current control circuit according to claim 1 is characterized in that, power switch is the BJT pipe.
4. hot cathode fluorescent lamp filament current control circuit according to claim 1 is characterized in that, power switch is a metal-oxide-semiconductor.
5. according to claim 1,2,3 or 4 each described hot cathode fluorescent lamp filament current control circuits, it is characterized in that the output current of reference current source is adjustable.
6. hot cathode fluorescent lamp filament current control circuit according to claim 1, heater current control loop feedback current is sampled in the electric current of transformer secondary.
7. according to claim 1,2,3,4 or 6 each described hot cathode fluorescent lamp filament current control circuits, secondary coil is a plurality of, each secondary coil two ends links to each other with hot cathode filament two ends of fluorescent lamp respectively, and centre cap connects fluorescent lamp drive power supply.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007100938498A CN101321424B (en) | 2007-06-05 | 2007-06-05 | Hot cathode fluorescent lamp filament current control circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007100938498A CN101321424B (en) | 2007-06-05 | 2007-06-05 | Hot cathode fluorescent lamp filament current control circuit |
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| Publication Number | Publication Date |
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| CN101321424A CN101321424A (en) | 2008-12-10 |
| CN101321424B true CN101321424B (en) | 2011-11-02 |
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| CN103281854B (en) * | 2012-11-22 | 2016-04-13 | 南京恒瑞医疗科技有限公司 | Adopt the X-ray production apparatus filament supply of high side current detection technique |
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| US5920155A (en) * | 1996-10-28 | 1999-07-06 | Matsushita Electric Works, Ltd. | Electronic ballast for discharge lamps |
| CN1228671A (en) * | 1998-01-05 | 1999-09-15 | 国际整流器有限公司 | Fully intergrated ballast IC |
| CN1457623A (en) * | 2000-05-12 | 2003-11-19 | O2米克罗国际有限公司 | Integrated circuit for lamp heating and dimming control |
| CN1630452A (en) * | 2003-12-15 | 2005-06-22 | 上海贝岭股份有限公司 | A fluorescent lamp filament preheating startup apparatus based on frequency conversion technique and design method thereof |
| CN1794893A (en) * | 2004-12-20 | 2006-06-28 | 东芝照明技术株式会社 | Discharge lamp lighting device and lighting system |
-
2007
- 2007-06-05 CN CN2007100938498A patent/CN101321424B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5920155A (en) * | 1996-10-28 | 1999-07-06 | Matsushita Electric Works, Ltd. | Electronic ballast for discharge lamps |
| CN1228671A (en) * | 1998-01-05 | 1999-09-15 | 国际整流器有限公司 | Fully intergrated ballast IC |
| CN1457623A (en) * | 2000-05-12 | 2003-11-19 | O2米克罗国际有限公司 | Integrated circuit for lamp heating and dimming control |
| CN1630452A (en) * | 2003-12-15 | 2005-06-22 | 上海贝岭股份有限公司 | A fluorescent lamp filament preheating startup apparatus based on frequency conversion technique and design method thereof |
| CN1794893A (en) * | 2004-12-20 | 2006-06-28 | 东芝照明技术株式会社 | Discharge lamp lighting device and lighting system |
Non-Patent Citations (3)
| Title |
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| JP特开2004-178943A 2004.06.24 |
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| JP特开2007-87711A 2007.04.05 |
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