JPH097786A - Fluorescent lamp illumination circuit using piezoelectric acoustic transformer and illumination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and light power source and a compact and light control circuit, which have stabilized optical intensity, by using a DC-AC high-voltage transformer having a ceramic transformer, of which output is controlled by a regulator circuit. SOLUTION: An input DC power source 35 supplies the low-voltage DC to a regulator circuit 20 and a high-voltage transformer 20. The high-voltage transformer 20 has a ceramic step-up transformer, and supplies the low-voltage DC, which is input from a terminal 21, converts to the high-voltage AC sufficient for driving a fluorescent lamp 15, and supplies it to a terminal 16. The regulator circuit 25 detects the signal, which shows largeness of the current of the fluorescent lamp 15, as a feedback signal, and controls the output of the high-voltage transformer 20 so as to adjust the optical intensity of the fluorescent lamp 15. A compact and light fluorescent lamp having a stabilized optical intensity and a control circuit can be obtained by using a ceramic step-up transformer, which can be miniaturized. Lifetime of the fluorescent lamp 15 can be prolonged.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a driving circuit for a fluorescent lamp. The invention particularly relates to fluorescent lamp power circuits that utilize certain ceramic material piezoelectric properties to produce a high frequency, high voltage excitation output for driving the lamp.

[0002]

Fluorescent lamps are being used more and more in systems that require an efficient and wide range of visible light sources. For example, portable computers such as laptop computers and notebook computers improve the contrast or brightness of the display by illuminating the liquid crystal display from behind or from the side. Fluorescent lamps have also been used to illuminate vehicle dashboards, and are also considered for use with battery-powered emergency exit lighting systems in commercial buildings.

Fluorescent lamps are also being considered for use in the low voltage applications mentioned above. This is because the fluorescent lamp can emit light over a wider area than an incandescent lamp. Particularly in applications requiring long battery life, such as portable computers, higher fluorescent lamp efficiency may result in longer battery life, lighter battery weight, or both.

In low voltage applications such as those described above, power supplies and control circuitry must be used to operate the fluorescent lamp. Power is typically supplied by a DC power supply in the range of 3-20 volts, but typically about 1000 volts RM is required to start a fluorescent lamp.
An AC voltage source of S (root mean square) is required, and about 200 volts RMS or more is required to maintain effective lighting. The excitation frequency for fluorescent lamps is typically around
It is in the range of 20 kHz to about 100 kHz. Therefore,
The power supply circuit needs to convert the available low voltage DC input to the required high frequency, high voltage AC output.

Conventionally known fluorescent lamp power supply circuits have utilized various drive circuits for converting low voltage DC into high frequencies. Here, the low voltage AC has a substantially sinusoidal waveform. The low voltage AC is then applied to the primary coil of the magnetic boost transformer. The secondary coil of the step-up transformer creates the high frequency, high voltage AC needed to start the circuit and maintain lighting. The output voltage of the step-up transformer has a well-known relationship with the input voltage. That is, N2 / N1
= V2 / V1. Here, N1 is the number of turns of the primary coil, N2 is the number of turns of the secondary coil, V1 is the input voltage, and V2 is the output voltage. Ratio N2 / N1
Is commonly known as the "turn ratio."

The use of magnetic step-up transformers to provide high voltage for the above applications is widespread and well known. Such transformers use the well-known magnetic technique to achieve low to high voltage conversion. However, the use of magnetic step-up transformers in power circuits for computer backlights has certain undesirable characteristics.

Some key disadvantages of previously known fluorescent lamp power supplies and control circuits are imposed and avoided on the ability to minimize the size of the power supply circuit by using a magnetic step-up transformer. There is no size limit.

For example, the ultimate goal in a typical laptop computer system is to maximize the viewing area of a "clamshell" (ie, the lid that contains the display) while still allowing for the size of the outside of the computer. The goal was to minimize the size of the power supply circuitry that drives the computer display.
For a long time, the power circuit for the display must be contained in the shell itself, and in the main body (typically the main circuit, including hard disk and floppy disk drive, keyboard, battery, etc.) It was useless. The reason is that a high frequency, high voltage AC signal is required to drive the backlight.
This is because the signal causes loss and noise on the extended line. Driving a clamshell display from the mains power supply circuit causes a large loss and, as a result, does not work well.

[0009]

Due to the size characteristics of magnetic step-up transformers and the number of turns originally required to obtain the desired input / output characteristics for driving fluorescent backlit displays, it has been a conventional practice. There have been limitations to making technology smaller power circuits. Higher output voltages require more turns, which in turn leads to larger magnetic transformer sizes.

Another disadvantage of lamp drive power circuits using magnetic step-up transformers is that the failure of the magnetic transformer can be destructive to itself and to surrounding elements. Due to the high voltage involved in driving fluorescent lamps and the inability of magnetic transformers to handle high voltage related failures,
When the output terminal of the magnetic step-up transformer is short-circuited, a large amount of heat is released from the transformer to surrounding electronic components. A short circuit between the two windings in the secondary coil leads to the same result. Therefore, the short circuit may damage or destroy the display in addition to destroying the driving electronic component.

Furthermore, a short circuit between two windings in a magnetic transformer is difficult to prevent. First, the high number of turns in the secondary winding is necessary to produce the desired output voltage. Second, to minimize the outer size of the magnetic components, the windings are compressed to fit in the most compact package. Therefore, the insulation between each winding is
It is minimized and is subject to deterioration.

The use of magnetic transformers presents another disadvantage when the fluorescent lamp breaks. A broken lamp is essentially an open circuit, an infinite resistance for power circuits. When the circuit detects such a high load, the power supply will try to drive it at a higher voltage (eg, 2-3 times the normal voltage), resulting in a potentially dangerous high voltage condition. Subsequent shorts at the output or between the transformer windings cause catastrophic failure not only of the transformer itself, but of the surrounding components. If the computer is in a delicate environment, such as a laptop computer used in an airplane, then such a failure causes or triggers risks not limited to the computer.

When used in a power supply circuit for driving a fluorescent lamp, a broadband device is used.
The nature of the magnetic transformer as a vice) presents additional disadvantages. If no conversion is made between the output stage of the power circuit and the input stage of the fluorescent lamp, the fluorescent lamp
Since a sine wave (AC) input signal is required, the power supply circuit must produce a sine wave output. Magnetic transformers, like other broadband devices, require a sinusoidal input to produce a sinusoidal output. Therefore, the magnetic transformer cannot directly receive the square wave. In order for a magnetic transformer to provide a sine wave output, the square wave must be converted to a sine wave before it is applied to the magnetic transformer. The required conversion process increases the complexity of the power supply circuit design.

In view of the above discussion, for a fluorescent lamp using a device with unique basic characteristics that is more conductive to the device used as a step-up transformer than the characteristics of conventional magnetic coil transformers. It is desirable to provide a power supply and control circuit for the.

It is also desirable to provide a power supply and control circuit for a fluorescent lamp that uses a step-up transformer that can be made smaller in all dimensions than conventional magnetic transformers.

It is further desirable to provide a power supply and control circuit for a fluorescent lamp that can be made smaller than conventional circuits using magnetic transformers.

It is further desirable to provide a power supply and control circuit for a fluorescent lamp that is simpler in construction than conventional magnetic power supply circuits.

Further, as a result of being relatively safe even if a high voltage-related failure occurs in the step-up transformer, a fluorescent lamp that does not radiate a large amount of heat to the electronic parts around the transformer or induce a failure. It is desirable to provide a power supply and control circuit for.

It is further desirable to provide a power supply and control circuit for a fluorescent lamp that uses a step-up transformer that has a relatively high internal resistance and is resistant to high voltage operation.

It is further desirable to provide a power supply and control circuit for a fluorescent lamp that uses a transformer that does not require a sinusoidal input to produce a high frequency, high voltage AC output.

The present invention has been made to solve the above problems, and its purpose is as described below.

An object of the present invention is to provide a fluorescent lamp using a device having inherent basic characteristics of higher conductivity for a device used as a step-up transformer than that of a conventional magnetic coil transformer. It is to provide a power supply and a control circuit.

It is also an object of the present invention to provide a power supply and control circuit for a fluorescent lamp that uses a step-up transformer that can be made smaller in all dimensions than conventional magnetic transformers.

Yet another object is to provide a power supply and control circuit for a fluorescent lamp that can be made smaller than conventional circuits using magnetic transformers.

Still another object is to provide a power supply and control circuit for a fluorescent lamp which has a simpler structure than the conventional power supply circuit using magnetism.

Still another object is that even if a high voltage related failure occurs in the step-up transformer, it is relatively safe, and as a result, a large amount of heat is radiated to the electronic parts around the transformer or the failure is induced. The purpose of the present invention is to provide a power supply and control circuit for a fluorescent lamp that does not burn.

Yet another object is to provide a power supply and control circuit for a fluorescent lamp using a step-up transformer having a relatively high internal resistance and withstanding high voltage operation.

Yet another object is to provide a power supply and control circuit for a fluorescent lamp that uses a transformer that does not require a sinusoidal input to produce a high frequency, high voltage AC output.

[0029]

SUMMARY OF THE INVENTION A fluorescent lamp lighting circuit according to the present invention is a circuit for lighting a fluorescent lamp from a DC power source, which comprises an input connected to the DC power source, an output, and a feedback for controlling the output. A DC-AC converter having a regulator having a control terminal for receiving a signal and a ceramic transformer connected to the output of the regulator, the A-A converter being sufficient for the fluorescent lamp to emit light.
A DC-AC converter for generating a C signal at an output terminal, and a monitoring element for monitoring a current indicating a current flowing through the fluorescent lamp and generating a feedback signal indicating a current flowing through the fluorescent lamp. Includes a monitoring element that is coupled to the regulator to regulate the light emitted by the lamp, thereby achieving the above objectives.

In one embodiment, the lamp and the converter are connected such that the lamp is isolated from the converter.

In one embodiment, a feedback signal adjusting circuit for adjusting the current supplied by the fluorescent lamp in response is further provided.

In one embodiment, the AC signal produced by the DC-AC converter is substantially sinusoidal at the output terminal.

In one embodiment, the fluorescent lamp is connected to a ballast capacitor.

In one embodiment, the monitoring element produces a feedback signal proportional to the current delivered by the fluorescent lamp.

In one embodiment, the monitoring element includes an impedance connected in series with the regulator control terminal, and the feedback signal includes a voltage developed across at least a portion of the impedance.

In one embodiment, the monitoring element includes a first impedance connected in series with the regulator control terminal, and the feedback signal includes a voltage generated across at least a portion of the first impedance. And the feedback signal conditioning circuit includes a variable impedance connected in series to at least a portion of the first impedance, the variable impedance having a tuning range sufficient to change the intensity of the fluorescent lamp. .

In one embodiment, the regulator is a switching regulator.

In one embodiment, the regulator is a current mode switching regulator.

The fluorescent lamp lighting circuit according to the present invention is DC
A circuit for lighting a fluorescent lamp from a power supply, the regulator having an input connected to a DC power supply, an output, a control terminal for receiving a feedback signal for controlling the output, and a ceramic transformer. A DC-AC converter connected to the output, the DC-AC converter generating an AC signal at an output terminal, a coupling element coupling the lamp to the converter, and a current flowing by the fluorescent lamp. A monitoring element for monitoring the indicated current and producing a feedback signal indicative of the current drawn by the fluorescent lamp, the feedback signal being coupled to the regulator to modulate the light emitted by the lamp. And, which achieves the above object.

In one embodiment, the coupling element isolates the lamp from the converter.

[0041] In one embodiment, a feedback signal adjusting element for adjusting the current supplied by the fluorescent lamp in response is further provided.

In one embodiment, the AC signal produced by the DC-AC converter is substantially sinusoidal at the output terminal.

In one embodiment, the fluorescent lamp is connected to a ballast capacitor.

In one embodiment, the monitoring element produces a feedback signal proportional to the current passed by the fluorescent lamp.

In one embodiment, the monitoring element includes an impedance connected in series with the regulator control terminal, and the feedback signal includes a voltage developed across at least a portion of the impedance.

In one embodiment, the monitoring element includes a first impedance connected in series with the regulator control terminal, and the feedback signal includes a voltage generated across at least a portion of the first impedance. And the feedback signal adjusting element includes a variable impedance connected in series to at least a portion of the first impedance, the variable impedance having an adjustment range sufficient to change the intensity of the fluorescent lamp. .

In one embodiment, the regulator is a switching regulator.

In one embodiment, the regulator is a current mode switching regulator.

The fluorescent lamp lighting circuit according to the present invention is DC
A circuit for lighting a fluorescent lamp from a power supply, the regulator having an input connected to a DC power supply, an output, a control terminal for receiving a feedback signal for controlling the output, and a ceramic transformer. A DC-AC converter connected to the output, the DC-AC converter generating an AC signal at the AC output, and a first terminal coupled to the AC output of the converter, the fluorescent light A ceramic step-up transformer having a second terminal coupled to the lamp; a monitoring element for monitoring a current indicative of the current supplied to the fluorescent lamp and for producing a feedback signal that regulates the light emitted by the lamp. The above-mentioned object is achieved thereby.

In one embodiment, the second terminal and the lamp are coupled such that the lamp is isolated from the converter.

In one embodiment, the fluorescent lamp further includes a tuning element for varying the feedback signal for responsively varying the current drawn by the fluorescent lamp.

In one embodiment, the monitoring element includes a rectifier for rectifying a current flowing through the first terminal, a resistor connected in series with the rectifier, and a resistor connected in series for the rectifier. A capacitance for filtering a current, the feedback signal comprising a voltage developed across the capacitance.

One embodiment further comprises a variable resistor coupled to the monitoring element for varying the magnitude of the feedback signal and responsively varying the current drawn by the fluorescent lamp.

The fluorescent lamp lighting circuit according to the present invention is DC
A circuit for lighting a fluorescent lamp from a power supply, the current mode switching having an input connected to a DC power supply, an output, and a control terminal adapted to receive a signal controlling the current produced at the output. A ceramic step-up transformer having a regulator, an oscillator for producing an AC voltage coupled to the output of the switching regulator, and a first terminal and a second terminal coupled to the fluorescent lamp, the ceramic step-up transformer being produced by the oscillator. In order to convert the AC voltage at the second terminal into an AC voltage high enough to light the fluorescent lamp, the first terminal is
A ceramic boost transformer coupled to the oscillator and a sensing element including an impedance adapted to sense an input current at the input of the switching regulator to generate a feedback signal proportional to the input current. Wherein the current sensing element is connected to flow the feedback signal to the control terminal of the switching regulator in order to adjust the current passed by the fluorescent lamp and the intensity of the light emitted by the fluorescent lamp. And a sensing element which is provided, thereby achieving the above object.

In one embodiment, the fluorescent lamp is isolated from the switching regulator and the oscillator.

The fluorescent lamp lighting circuit according to the present invention is DC
A circuit for lighting a fluorescent lamp from a power supply, the current mode switching regulator having an input connected to a DC power supply, an output, and a control terminal for receiving a signal controlling a current generated at the output, and the switching. A ceramic step-up transformer having an AC voltage producing an AC voltage coupled to the output of a regulator and a first terminal and a second terminal coupled to the fluorescent lamp, the AC voltage produced by the oscillator being At the second terminal, the first terminal is proportional to the input current and a ceramic step-up transformer coupled to the oscillator to convert the fluorescent voltage to an AC voltage high enough to ignite the fluorescent lamp. An impedance adapted to sense an input current at the first terminal of the transformer to generate a feedback signal. A sensing element including the current sensing element for causing the feedback signal to flow to the control terminal of the switching regulator in order to adjust the current drawn by the fluorescent lamp and the intensity of light emitted by the fluorescent lamp. And a connected sensing element, whereby the above-mentioned object is achieved.

In one embodiment, the fluorescent lamp is isolated from the switching regulator and the oscillator.

The fluorescent lamp lighting circuit according to the present invention is DC
A circuit for lighting a fluorescent lamp from a power supply, the DC-AC converter having at least one fluorescent lamp, an input connected to a DC power supply, an output, and a control terminal for receiving a feedback signal for controlling the output. And a ceramic step-up transformer coupled to the output of the converter that produces at the output terminal a high voltage AC sufficient to cause the fluorescent lamp to emit light, so as to generate a current through the fluorescent lamp. A ceramic step-up transformer to which the output terminal is coupled, and a current flowing through the converter is monitored to detect a current flowing through the fluorescent lamp,
A sensing that produces a feedback signal indicative of the magnitude of the current flowing through the fluorescent lamp and couples the feedback signal to the converter to adjust the current flowing through the fluorescent lamp and the intensity of the light emitted by the fluorescent lamp. And an element, thereby achieving the above object.

In one embodiment, the fluorescent lamp is isolated from the converter.

The method of lighting a fluorescent lamp according to the present invention is DC
A method of lighting a fluorescent lamp from a power source, the method comprising: converting DC power into AC voltage; flowing the AC voltage through the fluorescent lamp using a ceramic transformer to cause the fluorescent lamp to emit light. Detecting the current delivered by the fluorescent lamp by monitoring the current indicative of the current delivered by the fluorescent lamp during the steps of converting to a high voltage AC signal sufficient to generate current and during the converting step. And generating a feedback signal indicative of the magnitude of the monitored current,
DC power to high voltage A in response to the feedback signal
Controlling the conversion to C regulates the current passed by the lamp and the intensity of the light emitted by the lamp, which achieves the above objectives.

In one embodiment, the sensing step monitors the current isolated from the lamp.

In one embodiment, the method further comprises adjusting the feedback signal to adjust the current drawn by the fluorescent lamp in response.

In one embodiment, in the step of controlling, the DC power is a substantially sinusoidal high voltage A.
Converted to C.

In one embodiment, the feedback signal is proportional to the current drawn by the fluorescent lamp.

The operation will be described below.

The above objects of the present invention are accomplished in accordance with the principles of the present invention by a power supply and control circuit and method for driving a fluorescent lamp from a low voltage DC power supply using a ceramic step-up transformer. The regulator element is D
It is powered by the C power supply and is connected to the DC-AC element, the output of which is now connected to the first terminal of the lamp. The booster circuit, under the control of the regulator element, transforms the low voltage DC supplied by the input DC power supply into a high voltage sine wave AC sufficient to operate the fluorescent lamp.

In one embodiment of the invention, the second terminal of the lamp is connected to a circuit which detects and produces a signal indicative of the magnitude of the current flowing through the lamp. This current sense signal is fed back to the regulator to regulate the current delivered to the lamp by the ceramic transformer. As a result, the current through the lamp, and thus the intensity of the light emitted by the lamp, is adjusted as a function of the current feedback signal.

In another embodiment, according to another aspect of the invention, the two terminals of the fluorescent lamp are coupled across the AC output of the ceramic transformer so that the lamp is connected to the drive circuit. It is in a floating state without being directly connected. The output of the fluorescent lamp is indirectly regulated by a circuit that monitors the lamp drive power.
As a result, asymmetries in the lamp drive are reduced resulting in a more uniform distribution of energy and light output over the length of the lamp.

[0069]

The above objects and advantages of the present invention will be apparent from the following detailed description with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

A cold cathode fluorescent lamp (CCFL) often used for backlight illumination requires high frequency and high voltage driving. Typically such lamps have about 1000 volts to start and about 200-500 volts to maintain a glow.
RMS (root mean square) is required. Excitation frequencies are typically in the range of 20-100 kHz.

The high voltage required for fluorescent lamp displays is usually not available through the circuitry used inside the computer, so it must be produced by circuitry in the form of a voltage converter. Without exception, the high voltage can be generated by driving the step-up transformer with a low voltage AC waveform. To achieve low-to-high voltage conversion, previously known step-up transformers used well-known magnetic techniques.

The present invention takes advantage of the piezoelectric properties of certain ceramic materials that replace magnetic transformers. Due to the resonant properties of such ceramic materials, they self-resonate. By using a ceramic material instead of a magnetic material in the transformer, the drive circuit is simpler and smaller, thus saving display size and weight.

FIG. 1 is a block diagram of a fluorescent lamp power supply and control circuit 10 that implements the principles of the present invention.

As shown in FIG. 1, the input DC power source 35 is
Supply power to the circuit. The power supply 35 may be any DC power supply. For example, in a portable computer such as a laptop or notebook computer, power supply 35 is a nickel-cadmium or nickel-hydrogen battery that provides 3-5 volts. Or, if the circuit of the present invention is used with a vehicle dashboard, the power source 35 may be a 12-14 volt vehicle battery and power source. Similarly, the fluorescent lamp 15
May be any type of fluorescent lamp. For example, when illuminating the display of a portable computer, the fluorescent lamp 15 may be a cold cathode fluorescent lamp or a hot cathode fluorescent lamp.

The input DC power source 35 is the regulator circuit 2
5 (at terminal 27) and high voltage converter 20 (at terminal 2)
1) and a low voltage DC. The regulator circuit 25 can be a linear or switching type regulator, but a switching regulator is preferred for maximum efficiency. The output of the regulator circuit 25 is taken from the terminal 28. The terminal 26 is
It is a feedback terminal provided to receive a feedback signal, whereby the regulator circuit 2
The output of 5 is controlled. If the regulator circuit 25 is a switching regulator, the feedback terminal 26 produces the duty cycle of the switching transistor of the regulator, as controlled to regulate the output.

Further, the regulator circuit 25 includes the lamp 15
Current feedback element coupled to terminal 17 of
(Not shown) may be included. The feedback element is the current I _LAMP carried by the fluorescent lamp 15.
Tell the size of. The regulator circuit 25 is the lamp 1
By utilizing the feedback from 5, the gain in the high voltage converter 20 is adjusted and thereby the intensity of the fluorescent lamp 15.

The high voltage converter 20 includes a piezoelectric element (not shown in FIG. 1) such as a ceramic step-up transformer for producing a high voltage AC. The high voltage converter 20 receives the low voltage DC input at the terminal 21 from the input DC power supply 35,
High voltage A large enough to drive the fluorescent lamp 15.
The C output is produced at the output terminal 23. The AC voltage produced by the converter 20 is typically 100 volts or more. The terminal 22 is a terminal 28 of the regulator circuit 25.
A control terminal connected to receive a control signal from the control terminal. The control signal regulates the output of high voltage converter 20 as described below. The output of the converter 20 is the terminal 16 of the lamp.
At 15 (typically via a conventional ballast capacitor not shown).
In order to maximize operating efficiency and minimize radiation of high frequency disturbances, the converter 20 converts the DC power into a sine wave A
Convert to C power.

The circuit of FIG. 1 operates as follows. The high voltage converter 20 is combined with the regulator circuit 25 to provide high voltage AC power to the fluorescent lamp 15. The current I _LAMP flowing through the fluorescent lamp 15 is the regulator circuit 25.
Is detected by the current feedback element in. By coupling the feedback loop with the feedback terminal of the regulator circuit 25, the output of the regulator circuit 25 is modulated as a function of the magnitude of _ILAMP . This time, the output of the regulator circuit 25 is the converter 20.
Controls and modulates the output of. As a result, the fluorescent lamp 15
The magnitude of the current I _{LAMP conducted} by, ie the intensity of the light emitted by the lamp, is adjusted to a substantially constant value. By including the lamp 15 in the current feedback loop along with the regulator 25, the lamp current and light intensity are adjusted so that they are substantially constant as input power, lamp characteristics or ambient environmental factors change. Maintained. Independent of the lamp impedance or supply voltage, the circuit 10 provides a lamp current I _LAMP.
Functions to keep the value substantially constant. Therefore, if the impedance of the lamp increases or decreases as the lamp itself ages, the control circuit 10
Adjusts such changes appropriately so that a regulated constant current and lamp intensity can be maintained. When the power supply voltage fluctuates, the control circuit 10 makes the same adjustment. Thus, these features of the invention can extend the useful life of fluorescent lamps in some applications.

Of course, those skilled in the art will appreciate that other circuit technologies and configurations can be used to provide variable control of the lamp current. For example, a similar lamp intensity control operation can be realized by adding a signal (not shown) for adjusting the loop gain to the feedback point (terminal 26 of the regulator circuit 25).

FIG. 2 is a plot of the impedance of a ceramic transformer having a resonance frequency at 100 kHz with respect to frequency. Theoretically, the device impedance of a ceramic transformer is zero at resonance and infinite at non-resonant frequencies. As shown in FIG. 2, the impedance of the device is negligible at the resonance point and rises rapidly to high impedance at other frequencies. Therefore, if the frequency is tuned to approach the resonance point from either direction, the impedance suddenly drops to its minimum value in a spike shape. The steep non-linear slope formed on either side of the impedance spike is sometimes called the "skirt".

FIG. 3 shows a lamp driving circuit 30 according to the present invention.
0 shows one embodiment to illustrate the use of lamp current feedback in high voltage conversion and simple resonant modes. Input terminals 121 and 122 of the comparator 120
Are biased in their linear region by a combination of resistors 91, 92 and 93. Comparator 120
Behaves like a voltage source at output terminal 124.

The comparator 120 may be a general comparator.
Comparator 120 may comprise, for example, a comparator LT-1011 available from Linear Technology Corporation of Milpitas, Calif. (Hereinafter "linear"), and a power stage circuit for providing current gain. By amplifying the output current of the comparator, the power stage circuit drives the current flowing into the input terminal 221 of the ceramic transformer 220 with an appropriate magnitude. Such power stage circuits are well known in the art. The inductor 50 boosts the voltage and impedance-matches the input impedance of the ceramic transformer 220 to the output voltage drive of the comparator 120.

Positive feedback through the terminal 122 of the comparator 120 is achieved by a piezoelectric ceramic transformer.
An oscillation occurs at the resonance frequency of the transformer 220, and the positive feedback maintains the oscillation frequency at the resonance point. Positive feedback may occur at non-resonant frequencies, but the order of magnitude is lower than at resonance.

The positive feedback path is typically made through, for example, quartz crystal. However, in the present invention, the path is through the ceramic transformer 220,
The feedback signal is sent from the terminal 222 of the ceramic transformer 220 to the comparator 120. As a result, the oscillating signal from the comparator 120 occurring at the resonant frequency causes an acoustic wave in the ceramic transformer 220. This acoustic wave is converted to a high voltage by the inherent nature of the operation of the ceramic transformer 220. The voltage at the transformer output terminal 223 drives the fluorescent lamp 15.

Like the quartz crystal, the ceramic transformer 22
Zero also exhibits significant harmonic and overtone modes.
Due to the piezoelectric properties of ceramic transformer 220, the ceramic transformer acts as a narrow band filter. This is the opposite of the broadband devices realized by conventional magnetic transformers. As a result, the acoustic wave input to the ceramic transformer 220 need not be substantially sinusoidal.
The output of comparator 120 (at terminal 124) is a square wave drive signal applied to ceramic transformer 220.
The transformer 220 behaves as a very resonant filter for the acoustic waves that result from propagating therein. Further, the transformer 220 has a high voltage gain. As a result of these effects, a high voltage sine wave is obtained at the output terminal 223, and this sine wave has the advantage that it matches the drive characteristics of the lamp 15. Therefore, optimum driving can be performed.

The regulator 250 fixes or adjusts the magnitude of the output of the comparator 120 at terminal 124 by sending a control signal to the terminal 123 of the comparator 120 to adjust the input flowing into the ceramic transformer 220. The regulator 250 receives the feedback signal FB at the feedback terminal 260, which controls the regulator output. Regulator 25
0 may be a step-down switching regulator, for example, a Linear LT-1076 switching regulator coupled to a typical step-down network as is well known in the art. The signal received at the feedback terminal 260 is the regulator 2
The operating point of the regulator 250 is set so that the output voltage of 50 is lower than the input voltage.

Also shown in FIG. 3 is a current feedback element 30 which is coupled to terminal 17 of lamp 15 at terminal 32. The feedback element 30 produces a feedback signal FB at the terminal 31 which is indicative of the magnitude of the current I _{LAMP conducted} by the lamp 15. Various types of current feedback circuits can be used as the element 30. However, preferably, the element 30 is
The signal FB at terminal 31, including the current sensing impedance connected between terminal 32 and ground, is the voltage developed across that impedance. Therefore, this voltage is proportional to the magnitude of the current I _LAMP . A variable resistor 34 is connected between the terminal 33 of the current feedback element 30 and the ground. The variable resistor 34 is
It is used for adjusting the magnitude of the feedback signal FB, that is, for adjusting the loop gain and the intensity of the fluorescent lamp 15.

The operating current of the lamp 15 (that is, the light intensity of the lamp) is adjustably controlled by adjusting the feedback gain via the variable resistor 34. By changing the resistance, the magnitude of the feedback signal FB provided to the regulator 250 is changed,
Eventually, the magnitude of the lamp current I _LAMP also changes accordingly. Since the fluorescent lamp has a high impedance and is essentially a current driven device, changing the magnitude of _ILAMP will change the intensity of the lamp 15. Changing the resistance 34 thus helps to adjust the lamp intensity.

FIG. 4 is a schematic diagram of one embodiment of the fluorescent lamp power supply and control circuit of FIG.

As shown in FIG. 4, the input DC power supply 35 is
Provides power for the fluorescent lamp power supply and control circuit 100. The input DC power supply 35 may be any conventional power supply, such as the push-pull high voltage converter circuit 3.
20 and switching regulator circuit 125 are used to provide a low DC voltage (eg, about 3-20 volts). Switching regulator 125 may be any of a number of commercially available switching regulators, such as Linear's LT-1072 integrated circuit switching regulator. When implemented using the LT-1072 switching regulator, the regulator circuit 125 includes a feedback terminal 126, a power supply 35
A power supply terminal 127 and an output terminal 128 connected to.

The converter circuit 320 is a current drive type high voltage push-pull circuit, and is supplied with DC from the input DC power source 35.
Converts power to a high voltage sine wave AC. The piezoelectric properties of the ceramic transformer 220 at resonance make it a high gain, boost device with negligible internal impedance. At the non-resonant frequency, the ceramic transformer 220 behaves as a high impedance circuit for acoustic waves propagating therein (theoretically an almost open circuit). As shown in FIG. 2, at the "skirt" frequency, the ceramic transformer 220 has an intermediate range of impedance.

In FIG. 4, as the converter 320, a conventional magnetic transformer 321 and ceramic transformer 220 are used. The converter 320 is self-oscillating.
Circuit. Transistors 322 and 323 conduct when out of phase and switch each time transformer 321 saturates. Transformer 3 during the entire cycle
The magnetic flux density in the 21 core changes between a saturation value in one direction and a saturation value in the opposite direction. During the cycle time when the magnetic flux density changes from a negative minimum value to a positive maximum value, one of transistors 322 and 323 is on. For the rest of the cycle time, the other transistor turns on.

Switching of transistors 322 and 323 begins when the magnetic flux density of transformer 321 begins to saturate. At that time, the inductance of transformer 321 suddenly decreases to zero, resulting in a sudden increase in collector current through the transistor in the on state. The current spike is the transformer bias winding 321 of the transformer 321.
detected by a. Transistors 322 and 32
The base terminal of 3 is coupled to the bias winding 321a so that the current spike is fed back to the base of the transistor that produces it. As a result, the transistor exits saturation and enters the cutoff state, which eventually causes the transistor to turn off. Therefore, the current in the transformer 321 decreases sharply,
The transformer winding voltage is reversed in polarity so that the other transistor, which was previously off, is turned on. This switching operation is then repeated for the second transistor.

Referring again to FIG. 4, the transistor 32
2 and 323 switch on and off alternately with a duty cycle of about 50%. Transformer 3
The output of 21 is the high (compared to the input of transformer 321) voltage drive provided to the input of ceramic transformer 220. The ceramic transformer 220 now boosts this voltage signal to a level sufficient to drive the lamp 15.

The ceramic transformer 220 is the main voltage boosting device in the converter 320 for driving the lamp 15. As a result, the transformer 321 does not have to generate an output voltage of the magnitude required by conventional lamp drive circuits that use magnetic transformers. Transformer 321
Need only provide a voltage signal sufficient to optimize the input drive to the ceramic transformer 220. Therefore,
Secondary winding 321c and primary winding 321 of transformer 321
The turns ratio of b is significantly smaller than the turns ratio of a magnetic transformer in a conventional lamp drive circuit. Therefore, transformer 3
21 is much smaller than typical magnetic transformers used in conventional lamp drive circuits and does not impose high voltage structure constraints corresponding to large turns ratios.

Capacitor 324 coupled between the collectors of transistors 322 and 323 reduces RF emissions from the circuit without adversely affecting the operation of ceramic transformer 220. Capacitor 324 is equivalent to transistors 322 and 32 without capacitor 324.
Driving the magnetic transformer 321 with square wave voltage oscillations at the collector of 3 closer to a sine wave. In addition, the capacitor 324 also helps tune the oscillation to the resonant frequency of the ceramic transformer 220.

Oscillation frequency (generated at resonance point)
Is firstly a capacitor 32 connected between the magnetic transformer 321, the collectors of the transistors 322 and 323.
4, fluorescent lamp 15, and ballast capacitor 360
It is determined by the combination of the characteristics of. The resonant frequency inherent in ceramic transformer 220 is a function of the physical parameters of this device.

The magnetic transformer 321 comprises a transistor 322.
And 323 boost the sine wave voltage at the collectors of the ceramic transformer 22 and the secondary winding 321c.
Generate sufficient AC voltage to drive zero. The ceramic transformer 220 is now sufficient to boost the output voltage of the magnetic transformer 321 to drive the fluorescent lamp 15 (shown connected to the transformer 220 through a ballast capacitor 360). It produces a high voltage AC waveform. Ballast capacitor 360 is used in lamp 15 to minimize the sensitivity of the circuit to lamp characteristics.
Insert a controlled impedance in series with. In some embodiments of the invention, ballast capacitor 360.
Can be omitted due to the capacitive characteristics of the output drive provided by the ceramic transformer 220. A converter 320 in connection with the current mode switching regulator circuit 125.
Operates as described above to supply a controlled AC current at a high voltage at the terminal 16 of the fluorescent lamp 15. Inductor 143 connected to terminal 128 of regulator 125 and emitters of transistors 322 and 323
Is an energy storage element for the switching regulator 125. Inductor 143 also sets the magnitude of the collector current of transistors 322 and 323, ie the energy delivered to lamp 15 through transformer 220. The Schottky diode 142 connected between the input DC power supply 35 and the inductor 143 maintains the current through the inductor 143 during the off cycle of the switching regulator circuit 125. Resistor 157 connects transistors 322 and 323.
DC bias each base of the.

The current (I _LAMP ) transmitted to the lamp 15 by the transformer 220 is the lamp 15 and the diode 144.
And a feedback loop including the feedback circuit 130 adjusts to a substantially constant value. The diode 144 cooperates with the diode 143 to half-wave rectify the lamp current I _LAMP . Diode 143 shunts the negative portion of each cycle of I _LAMP to ground, and diode 144 feeds the positive portion of this current (representing half the lamp current I _LAMP ) into feedback circuit 130.
Shed on.

The feedback circuit 130 includes a resistor 151.
And a capacitor 152 connected in series between the cathode of the diode 144 and the ground. This produces a voltage across capacitor 152 that is proportional to the magnitude of _ILAMP . This voltage (FB) is the feedback pin (terminal 12) of the switching regulator 125.
6). With the above connection, the feedback control loop for regulating the lamp current is closed. Resistance 1
Resistor 1 connected in parallel with 51 and capacitor 152
46 and 147 allow DC regulation in the voltage (FB) appearing at the feedback pin.

When the circuit 100 of FIG. 4 is activated, the feedback pin 12 of the switching regulator circuit 125 is
The voltage (FB) at 6 is generally the regulator circuit 1
25 internal reference voltages (for example, in the case of the LT-1072 above,
1.23 volts) lower. Therefore, the regulator circuit 1
At 25 output terminals 128, full duty cycle modulation occurs. As a result, the inductor 143 conducts the current flowing from the magnetic transformer 321 through the transistors 322 and 323 into the inductor 143. This current is deposited on the ground while being switched by the operation of the regulator. This switching operation is
It controls the average current I _LAMP of the lamp 15. The amount of this average current is set by the magnitude of the feedback signal FB at the feedback terminal 126.

The feedback loop uses the switching regulator 125 to modulate the output of the converter 320 to whatever value is needed to maintain a constant current in the lamp 15. However, the magnitude of the constant current can be changed by the variable resistor 147. Since the intensity of the lamp 15 is directly related to the magnitude of the current flowing through the lamp, the variable resistor 147 can adjust the intensity of the lamp 15 smoothly and continuously over the selected intensity range.

Those skilled in the art will appreciate that the circuit of FIG. 4 can be modified in many ways without departing from the spirit and scope of the invention. For example, the intensity of the lamp 15 is
Besides the variable resistance 147, it can be changed by introducing the signal S variably into the feedback loop as shown in FIG. The signal S serves to change the loop gain of the feedback loop by changing the magnitude of the feedback signal FB provided to the regulator 125. Similar to the variable resistor 147 of FIG. 4, the lamp 15 is introduced by introducing the signal S of FIG.
The intensity of can be changed.

For example, the signal S of FIG. 5 may be taken from the output of a conventional photocell or other photodetector circuit (not shown) that monitors the intensity of ambient light. Such circuitry allows the fluorescent lamp power supply and control circuitry to compensate or adjust the fluorescent lamp intensity in response to the intensity of ambient light in its environment. Thus, when the intensity of light around the environment is low, the intensity of the fluorescent lamp is adjusted to a high value. Similarly, when the intensity of light around the environment is high, the intensity of the fluorescent lamp is adjusted to a low value. Of course, those skilled in the art will appreciate that the signal S may in fact be derived from any other circuit, in order to vary the intensity of the fluorescent lamp in one desired way. Furthermore, those skilled in the art will appreciate that within the scope of the invention, further modifications can be made to various circuit configurations for driving multiple fluorescent lamps.

A further extension of the circuit 100 of FIG. 4 is shown in FIG. In FIG. 6, there is no secondary winding of the conventional magnetic transformer 321. As a result, ceramic transformer 220 is directly connected to the collectors of transistors 322 and 323.

The converter 320 is also a self-oscillation type circuit. The operation of the circuit of FIG. 6 is the same as the operation of the circuit of FIG. Since the secondary winding of the magnetic transformer 321 is omitted in FIG. 6, the magnetic transformer 321 can be made smaller than the magnetic transformer of FIG. The primary winding 321b of the magnetic transformer 321 fully optimizes the input drive to the ceramic transformer 220.

7-9 illustrate various exemplary configurations of another embodiment according to further aspects of the present invention. In these configurations, the output of the fluorescent lamp is indirectly monitored and the lamp is floating across a 4-terminal ceramic transformer. FIG. 10 shows an exemplary configuration of an embodiment in which a conventional magnetic transformer and a three-terminal ceramic transformer are used and are in a floating state across the output terminals of the magnetic transformer.

7-10 show simple schematics of circuits for adjusting a fluorescent lamp over an extended intensity range, in which the lamp intensity is more pronounced along the longitudinal axis of the lamp. It is constant. While the circuits shown in FIGS. 7-10 are particularly effective for operating cold cathode fluorescent lamps, the circuits of FIGS. 7-10 are also used to drive hot cathode fluorescent lamps.

As shown in FIG. 7, the DC-AC converter 24
8 drives the input terminal of the ceramic transformer 520.
The converter 248 is a simplified representation of the various elements shown in FIG. 1 and includes at least the elements of the regulator 25 and the DC-AC converter. The output terminals of the ceramic transformer 520 are connected to both ends of the cold cathode fluorescent lamp 15. Conventional ballast capacitor 160
Is also connected in series to the lamp 15, as also shown. As also provided for FIG. 4, this capacitor may be omitted in other embodiments while still utilizing the principles of the present invention.

Regulation of lamp 15 is accomplished by providing a feedback signal to converter 248. The feedback signal generated across impedance 210 (indicated by a resistor in the figure, although any other suitable impedance may be used) is:
Proportional to the input current. The feedback signal is lamp 1
5 is coupled to the converter 248 to regulate the current flowing therethrough, so that the amount of light emitted by the lamp 15 is regulated. This feedback signal, which indirectly monitors the lamp drive power, differs from the configuration shown in FIGS. 1, 3 and 4-6, where the feedback signal is extracted directly from the lamp output circuit. Further impedance 210
Is preferably a variable impedance that the transducer 248 receives corresponding user input to vary the intensity of the lamp 15.

Indirectly measuring the floating lamp 15 connected across the output terminals of the ceramic transformer 520 and the drive power supplied to the lamp in order to isolate the lamp from its drive circuit. Has the effect that it does not include the connections that result in asymmetrical drive in the lamp 15. This results in a more evenly distributed electric field within the lamp, which can enhance the lamp's ability to emit light uniformly over its entire length at low operating currents.

A further advantage is that the overall efficiency of the lamp drive circuit is improved. This is because the net energy loss due to parasitic capacitance is reduced. The parasitic capacitance exists along the line connected to any terminal of the fluorescent lamp 15. The amount of energy loss due to a capacity is directly proportional to the voltage drop across that capacity. If the lamp 15 is floating instead of grounded at one terminal, the parasitic capacitance at the high voltage end of the lamp 15 will have less voltage swing (if the low voltage end of the lamp 15 is grounded, The voltage swing will be half of what it would otherwise be). The energy loss due to these capacities is therefore low. This result leads to a net reduction in parasitic capacitance energy loss, and therefore also an increase in overall circuit efficiency.

FIG. 8 shows another method of indirectly monitoring the drive to the lamp 15. In FIG. 8, the converter 248
The current flowing through the feedback (ground) terminal of the is monitored through an impedance 215 (shown as a resistor, but other suitable impedances) connected in series between the converter 248 and ground. . The voltage developed across impedance 215 is used as a feedback signal and is coupled to the feedback terminal of converter 248 as shown to control lamp drive as described above. A disadvantage of the FIG. 8 approach compared to FIG. 7 is that it requires additional signal processing in or around the converter 248 in order to obtain good regulation as the operating conditions change. This is because the feedback line of the converter 248 is
This is because it typically includes a very non-linear signal component.

FIG. 9 illustrates yet another method of indirectly monitoring the drive supplied to the lamp 15. In this figure, the feedback signal FB is the ceramic transformer 5
It is generated by sampling a portion of the 20 input AC voltage signals. The feedback loop includes a capacitor 200 having one end coupled to the input terminal of ceramic transformer 520. The other terminal of the capacitor 200 is connected to the anode of the diode 225 and the first terminal of the impedance 230. The other terminal of impedance 230 is coupled to ground, while the cathode of diode 225 is coupled to the feedback input terminal of converter 248.

FIG. 10 shows a method of indirectly monitoring the input drive to the lamp 215, where a conventional magnetic transformer is used with a three terminal ceramic transformer. In FIG. 10, the lamp 15 is in a floating state across the output terminal of the ceramic transformer 220 and the output terminal of the magnetic transformer 321. Therefore, the lamp 15 is isolated from the converter 248 and operates similarly to FIG.

Other circuit configurations for indirectly monitoring the drive to the lamp 215 can be used and are shown in FIGS.
Circuit is not an exhaustive list of such circuits,
It is only representative. Those skilled in the art will appreciate that in order to indirectly monitor the drive of the lamp, it is not necessary to float the lamp from the drive circuit.
Which of the indirect measurement techniques shown in FIGS.
It may be applied to any of the lamp configurations shown in FIG.

FIG. 11 is a block diagram of a further exemplary configuration of the present invention that utilizes the piezoelectric properties of ceramic transformer 220. In FIG. 11, the input DC power supply 35 supplies the voltage control signal (VC) to the terminal 612 of the operational amplifier 610. The operational amplifier 610 is a voltage controlled oscillator 620.
An output DC voltage signal that sets the operating frequency of the (VCO) is generated. The DC voltage signal is proportional to the feedback signal FB detected at the feedback pin (terminal 611) of the operational amplifier 610. The DC voltage signal is used to drive the voltage controlled oscillator 620 to produce the AC output signal. The magnitude of the AC signal is amplified by driver 630 and the output of driver 630 is used to drive ceramic transformer 220. The ceramic transformer 220 outputs a boosted sinusoidal voltage waveform to drive the lamp 15. Current I flowing through the lamp 15
_LAMP is fed back to create the sensed feedback signal FB at the feedback pin (terminal 611) of operational amplifier 610, closing the feedback loop. The current sense feedback loop regulates the lamp drive.

The oscillation frequency in the system of FIG. 11 is
It is controlled by an operational amplifier 610 (which senses the voltage control signal VC and the feedback signal FB) coupled to the oscillator 620. Unlike the embodiment of the invention of FIGS. 1, 3-6 and 10, the embodiment of FIG. 11 does not perform constant operation at the resonant frequency of the ceramic transformer 220.
Instead of maintaining operation at full resonance and changing only the amount of power supplied to the lamp drive circuit, FIG. 11 shows a system in which the operating frequency varies over resonant and non-resonant frequencies. The voltage control signal VC controls the system shown in FIG.
5 can be adjusted to drive at a non-resonant frequency. Attempting to drive the lamp 15 at the "skirt" frequency shown in FIG.
It causes 20 to operate at a lower resonance than full resonance. Therefore, the ceramic transformer 220 does not flow a full drive current to the lamp 15. Therefore,
The light intensity of the lamp 15 is not completely "on". At frequencies other than the resonance point and the skirt, the ceramic transformer 220 draws no drive current through the lamp 15.

Varying the operating frequency of the system by adjusting the voltage control signal VC is a function of the lamp 15
It can be used to reduce the intensity of light. The range of light intensities is full, ie, substantially “on” (at full resonance) to full, ie, substantially “off” (at frequencies outside the “skirt”), It also includes the intermediate weak light emission obtained by driving the lamp 15 at the skirt frequency.

FIG. 12 is a schematic block diagram of another embodiment of the present invention according to the principle of the circuit shown in FIG.

In the circuit of FIG. 12, the input driver 71
0 produces a pulse width modulated output signal for driving MOS transistors 720 and 730. The input driver 710 includes a regulator. Transistors 720 and 730 then alternately switch on and off with a maximum duty cycle of about 50%. Transistor 720 is on and transistor 730
When is off, inductor 750 charges and current passes through transistor 720 to ceramic transformer 22.
Flows to zero. When transistor 720 is off and transistor 730 is on, inductor 750 is discharged and current is drawn through transistor 730 to ground.

The inductor 750 is the ceramic transformer 2
The input impedance of 20 is impedance matched with the output voltage drive of transistors 720 and 730. Inductor 750 also provides a voltage boost to drive ceramic transformer 220. The piezoelectric properties of transformer 220 act as a narrow band filter, as opposed to the wide band devices provided by conventional magnetic transformers. As a result, the acoustic waves input to transformer 220 need not be substantially sinusoidal. However, the capacitor 740 may be used to reduce RF radiation from the circuit. Capacitor 740 blocks the DC signal component and, if capacitor 740 is absent, transistors 720 and 730.
At the output terminal 723 of the above, the signal which is the square wave voltage oscillation is smoothed.

The resonant frequency inherent in the ceramic transformer 220 is a function of the physical parameters of the device. The ceramic transformer 220 boosts the input voltage to create an AC waveform with a voltage high enough to drive the fluorescent lamp 15.

The feedback control loop around the lamp 15 applies the feedback signal FB to the input driver 710.
It is closed by the path that returns to. This feedback loop senses the lamp current I _LAMP , and this information sets the operating point of the input driver 710. The pulse width of the driver 710 modulated by the output sets the possible drive for the piezoelectric transformer. The operating current of the lamp 15 is
It can be controlled by adjusting the value of the variable resistor 760. By changing the resistance, the input driver 71
The magnitude of the feedback signal FB applied to 0 changes, and eventually the lamp current I _LAMP changes correspondingly. Since a fluorescent lamp has a high impedance and is essentially a current driven device, changing the magnitude of _ILAMP will change the intensity of the lamp 15.

Those skilled in the art will appreciate that the power supply and control circuit of the present invention can be implemented using configurations other than those shown and described above. Such modifications are also within the scope of the invention and are limited only by the scope of the claims.

[0126]

According to the present invention, at least the following effects can be obtained. It is possible to provide a power supply and a control circuit for a fluorescent lamp using a device having an inherent basic characteristic that the conductivity is higher than that of a device used as a step-up transformer than the characteristic of a conventional magnetic coil transformer.

It is also possible to provide a power supply and control circuit for a fluorescent lamp that uses a step-up transformer that can be made smaller in all dimensions than conventional magnetic transformers.

Furthermore, it is possible to provide a power supply and control circuit for a fluorescent lamp that can be made smaller than conventional circuits using magnetic transformers.

[Brief description of drawings]

FIG. 1 is a block diagram of a fluorescent lamp power supply and control circuit that implements the principles of the present invention.

FIG. 2 is a graph plotting the impedance characteristic of an example ceramic transformer used in accordance with the principles of the present invention against frequency.

3 is a schematic block diagram of one embodiment of the fluorescent lamp power supply and control circuit of FIG.

FIG. 4 is a schematic block diagram of another embodiment of the fluorescent lamp power supply and control circuit of FIG.

5 is a schematic block diagram of another embodiment of the fluorescent lamp power supply and control circuit of FIG. 1. FIG.

FIG. 6 is a schematic block diagram of another embodiment of the fluorescent lamp power supply and control circuit of FIG.

FIG. 7 is a schematic showing an exemplary configuration of another embodiment according to another aspect of the invention in which the output of a fluorescent lamp is indirectly monitored and the lamp is floating instead of grounded at one terminal. It is a block diagram.

FIG. 8 is a schematic showing an exemplary configuration of another embodiment according to another aspect of the invention in which the output of a fluorescent lamp is indirectly monitored and the lamp is floating instead of being grounded at one terminal. It is a block diagram.

FIG. 9 is a schematic showing an exemplary configuration of another embodiment according to another aspect of the invention in which the output of a fluorescent lamp is indirectly monitored and the lamp is floating instead of being grounded at one terminal. It is a block diagram.

FIG. 10: The output of the fluorescent lamp is indirectly monitored, 1
FIG. 6 is a schematic block diagram illustrating an exemplary configuration of another embodiment according to another aspect of the invention in which the lamp is floating instead of grounded at one terminal.

FIG. 11 is a block diagram of yet another embodiment of a fluorescent lamp power supply and control circuit implementing the principles of the present invention.

12 is a schematic block diagram of still another embodiment of the fluorescent lamp power supply and control circuit of FIG. 1. FIG.

[Explanation of symbols]

10 Fluorescent Lamp Power Supply and Control Circuit 15 Fluorescent Lamp 16, 17, 21, 22, 23, 26, 27, 28 Terminal 20 High Voltage Converter 25 Regulator Circuit 35 Input DC Power Supply

Claims (36)

[Claims] 1. A circuit for lighting a fluorescent lamp from a DC power supply, the regulator having an input connected to the DC power supply, an output, and a control terminal for receiving a feedback signal for controlling the output, and a ceramic transformer. A DC-AC converter connected to the output of the regulator, comprising: D generating at the output terminal an AC signal sufficient for the fluorescent lamp to emit light.
A C-AC converter and a monitoring element for monitoring a current indicating a current flowing through the fluorescent lamp and generating a feedback signal indicating a current flowing through the fluorescent lamp, the feedback signal comprising:
A fluorescent lamp lighting circuit comprising: a monitoring element coupled to the regulator to regulate light emitted by the lamp. 2. The fluorescent lamp lighting circuit according to claim 1, wherein the lamp and the converter are connected so that the lamp is isolated from the converter. 3. The fluorescent lamp lighting circuit according to claim 1, further comprising a feedback signal adjusting circuit that adjusts a current supplied from the fluorescent lamp in response. 4. The fluorescent lamp lighting circuit according to claim 1, wherein the AC signal generated by the DC-AC converter is substantially sinusoidal at the output terminal. 5. The fluorescent lamp lighting circuit according to claim 1, wherein the fluorescent lamp is connected to a ballast capacitor. 6. The fluorescent lamp lighting circuit as claimed in claim 1, wherein the monitoring element produces a feedback signal proportional to a current passed by the fluorescent lamp. 7. The fluorescence according to claim 6, wherein the monitoring element includes an impedance connected in series to the regulator control terminal, and the feedback signal includes a voltage generated across at least a part of the impedance. Lamp lighting circuit. 8. The monitoring element includes a first impedance connected in series to the regulator control terminal, the feedback signal includes a voltage developed across at least a portion of the first impedance,
The feedback signal adjustment circuit includes a variable impedance connected in series to at least a portion of the first impedance, the variable impedance having an adjustment range sufficient to change the intensity of the fluorescent lamp. The fluorescent lamp lighting circuit according to item 3. 9. The fluorescent lamp lighting circuit according to claim 1, wherein the regulator is a switching regulator. 10. The fluorescent lamp lighting circuit according to claim 1, wherein the regulator is a current mode switching regulator. 11. A circuit for lighting a fluorescent lamp from a DC power supply, the regulator having an input connected to the DC power supply, an output, and a control terminal for receiving a feedback signal for controlling the output, and a ceramic transformer. A DC-AC converter connected to the output of the regulator, the DC-AC converter generating an AC signal at an output terminal; and a coupling element coupling the lamp to the converter. A monitoring element for monitoring a current indicating a current flowing by the fluorescent lamp and generating a feedback signal indicating a current flowing by the fluorescent lamp, wherein the feedback signal is
A fluorescent lamp lighting circuit comprising: a monitoring element coupled to the regulator to regulate light emitted by the lamp. 12. The fluorescent lamp lighting circuit according to claim 11, wherein the coupling element isolates the lamp from the converter. 13. The fluorescent lamp lighting circuit according to claim 11, further comprising a feedback signal adjusting element that adjusts a current supplied from the fluorescent lamp in response. 14. The fluorescent lamp lighting circuit according to claim 11, wherein the AC signal generated by the DC-AC converter is substantially sinusoidal at the output terminal. 15. The fluorescent lamp lighting circuit according to claim 11, wherein the fluorescent lamp is connected to a ballast capacitor. 16. The fluorescent lamp lighting circuit of claim 11, wherein the monitoring element produces a feedback signal that is proportional to the current passed by the fluorescent lamp. 17. The fluorescence according to claim 16, wherein the monitoring element includes an impedance connected in series to the regulator control terminal, and the feedback signal includes a voltage generated across at least a part of the impedance. Lamp lighting circuit. 18. The monitoring element includes a first impedance connected in series to the regulator control terminal, the feedback signal includes a voltage developed across at least a portion of the first impedance, 14. The feedback signal conditioning element comprises a variable impedance connected in series with at least a portion of the first impedance, the variable impedance having a tuning range sufficient to change the intensity of the fluorescent lamp. Fluorescent lamp lighting circuit according to. 19. The fluorescent lamp lighting circuit according to claim 11, wherein the regulator is a switching regulator. 20. The fluorescent lamp lighting circuit according to claim 11, wherein the regulator is a current mode switching regulator. 21. A circuit for lighting a fluorescent lamp from a DC power supply, the regulator having an input connected to the DC power supply, an output, and a control terminal for receiving a feedback signal for controlling the output, and a ceramic transformer. A DC-AC converter connected to the output of the regulator, comprising:
A DC-AC converter for generating an output, a ceramic step-up transformer having a first terminal coupled to the AC output of the converter and a second terminal coupled to the fluorescent lamp, and the fluorescent lamp Monitor the current indicating the current supplied to
A fluorescent lamp lighting circuit comprising: a monitoring element for generating a feedback signal for adjusting the light emitted by the lamp. 22. The fluorescent lamp lighting circuit as claimed in claim 21, wherein the second terminal and the lamp are coupled so that the lamp is isolated from the converter. 23. The fluorescent lamp lighting circuit of claim 21, further comprising an adjusting element that changes a feedback signal for responsively changing the current that the fluorescent lamp draws. 24. The monitoring element includes a rectifier for rectifying a current flowing through the first terminal, a resistor coupled in series with the rectifier, and a resistor coupled in series with the resistor for filtering the rectified current. 22. The fluorescent lamp lighting circuit according to claim 21, wherein the feedback signal comprises a capacitance including a voltage generated across the capacitance. 25. The fluorescent lamp lighting of claim 24, further comprising a variable resistor coupled to the monitoring element that changes the magnitude of the feedback signal and responsively changes the current passed by the fluorescent lamp. circuit. 26. A circuit for lighting a fluorescent lamp from a DC power supply, the control terminal adapted to receive an input connected to the DC power supply, an output and a signal controlling the current produced at the output. A current mode switching regulator having: and A coupled to the output of the switching regulator,
A ceramic step-up transformer having an oscillator for producing a C voltage and a first terminal and a second terminal coupled to the fluorescent lamp, wherein the AC voltage produced by the oscillator is applied to the fluorescent lamp at the second terminal. In order to convert the AC voltage high enough to ignite, the first terminal is connected to a ceramic step-up transformer coupled to the oscillator and to generate a feedback signal proportional to the input current. A sensing element including an impedance adapted to sense an input current at the input of a switching regulator, the sensing element for adjusting a current drawn by the fluorescent lamp and an intensity of light emitted by the fluorescent lamp. A sensing element to which the current sensing element is connected so as to flow the feedback signal to the control terminal of the switching regulator; Fluorescent lamp lighting circuit is provided. 27. The fluorescent lamp lighting circuit according to claim 26, wherein the fluorescent lamp is isolated from the switching regulator and the oscillator. 28. A circuit for lighting a fluorescent lamp from a DC power supply, the current mode having an input connected to the DC power supply, an output, and a control terminal for receiving a signal controlling the current produced at the output. A switching regulator and A coupled to the output of the switching regulator,
A ceramic step-up transformer having an oscillator for producing a C voltage and a first terminal and a second terminal coupled to the fluorescent lamp, wherein the AC voltage produced by the oscillator is applied to the fluorescent lamp at the second terminal. In order to convert the AC voltage high enough to ignite, the first terminal is connected to a ceramic step-up transformer coupled to the oscillator and to generate a feedback signal proportional to the input current. A sensing element comprising an impedance adapted to sense an input current at the first terminal of a transformer for adjusting the current drawn by the fluorescent lamp and the intensity of the light emitted by the fluorescent lamp. A detection element to which the current detection element is connected so as to flow the feedback signal to the control terminal of the switching regulator. Lamp lighting circuit. 29. The fluorescent lamp lighting circuit according to claim 28, wherein the fluorescent lamp is isolated from the switching regulator and the oscillator. 30. A circuit for lighting a fluorescent lamp from a DC power supply, comprising: at least one fluorescent lamp, an input connected to the DC power supply, an output, and a control terminal for receiving a feedback signal for controlling the output. Have D
A C-AC converter and a ceramic step-up transformer coupled to the output of the converter that produces a high voltage AC at the output terminal sufficient to cause the fluorescent lamp to emit light, the current flowing through the fluorescent lamp. To detect the current flowing through the fluorescent lamp by monitoring the current flowing through the converter and a ceramic step-up transformer to which the output terminal is coupled so as to determine the magnitude of the current flowing through the fluorescent lamp. Fluorescent lamp ignition comprising a sensing element for generating a feedback signal indicative of and coupling the feedback signal to the converter to regulate the current drawn by the fluorescent lamp and the intensity of the light emitted by the fluorescent lamp. circuit. 31. The fluorescent lamp lighting circuit according to claim 30, wherein the fluorescent lamp is isolated from the converter. 32. A method of lighting a fluorescent lamp from a DC power source, the method comprising: converting DC power into an AC voltage; and converting the AC voltage using a ceramic transformer to emit light into the fluorescent lamp. , Converting the fluorescent lamp to a high voltage AC signal sufficient to generate a current flowing through the fluorescent lamp, and monitoring the current indicative of the current drawn by the fluorescent lamp during the converting step. Sensing a current flow, generating a feedback signal indicative of the magnitude of the monitored current, and responsive to the feedback signal from DC power to a high voltage A
Controlling the current passed by the lamp and the intensity of the light emitted by the lamp by controlling the conversion to C. 33. The method according to claim 32, wherein in the detecting step, a current isolated from the lamp is monitored. 34. The method of claim 32, further comprising adjusting the feedback signal to adjust the current drawn by the fluorescent lamp in response. 35. The method according to claim 32, wherein in the controlling step, the DC power is converted into a substantially sinusoidal high voltage AC. 36. The method of lighting a fluorescent lamp of claim 32, wherein the feedback signal is proportional to the current passed by the fluorescent lamp.