JP2012248480A - Electric field emission type lamp drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive an electric field emission type lamp with constant power in a simple circuit configuration, thereby avoiding increase in a device size or rise in cost due to the increased number of circuit components.SOLUTION: In a power control circuit section 20, a reference voltage Vr is applied to an inverted input terminal (- terminal) of a comparator CP, while a resistor R1 is connected to a non-inverted input terminal (+ terminal) for an input voltage Vin to be input thereto for comparison purpose, with the cathode electrode of a lamp L also connected and further grounded to earth via a resistor R2. The reference voltage Vr is applied to the inverted input terminal (- terminal) of the comparator CP and a voltage (voltage across the resistor R2) applied to the non-inverted input terminal (+ terminal) are compared, based on which electrical continuity of a control element Q is controlled by the output of the comparator, and gate voltage control of the lamp L via a gate voltage stabilization circuit section 10 is exerted. Furthermore, constant power control for driving the lamp L with constant power against fluctuations in a lamp voltage Va is also exerted.

Description

  The present invention relates to a drive device for a field emission lamp that excites a phosphor by light emitted from an electron emission source.

  In recent years, field emission lamps have been developed compared to conventional lamps such as incandescent bulbs and fluorescent lamps. In this type of lamp, a positive voltage is applied to a cathode electrode having an electron emission source in a vacuum container to cause electron field emission, and the emitted electron collides with a phosphor on the anode electrode to emit fluorescence. By appropriately controlling the voltage of the gate electrode provided between the cathode electrode and the anode electrode, light emission with high luminance can be obtained with low power consumption.

  In order to drive such a field emission lamp, a high-voltage DC voltage from a switching power supply or the like is necessary. For example, Patent Document 1 discloses a floating capacitance of a step-up transformer that boosts a switched input voltage. By using the resonance circuit that uses the power supply and matching the on / off timing of the switching signal to the resonance condition of this resonance circuit, the loss due to the components of the power supply circuit is eliminated to increase the voltage conversion efficiency and the overall circuit configuration A technique is disclosed that can be simplified to reduce the size and cost and reduce the cost.

JP 2009-238414 A

  However, it is inevitable that field emission type lamps have variations in characteristics of electron emission sources and phosphors, variations in manufacturing of the distance between electrodes, and variations in lamp characteristics due to aging. There is a problem that the conditions are different for each lamp. For this reason, when the field emission lamp is driven with a constant power, the circuit configuration of the driving device becomes complicated and the number of circuit components increases, leading to an increase in size and cost of the entire driving device.

  The present invention has been made in view of the above circumstances, and can drive a field emission lamp with a constant power with a simple circuit configuration, thereby avoiding an increase in size and cost of the apparatus due to an increase in circuit components. An object of the present invention is to provide a driving device for a field emission lamp.

  According to the field emission lamp driving apparatus of the present invention, a cathode electrode having an electron emission source and an anode electrode having a phosphor are disposed in a vacuum container at a predetermined interval, and the cathode electrode and the anode electrode are disposed between the cathode electrode and the anode electrode. A driving device for a field emission lamp having a tripolar structure in which a gate electrode is disposed, wherein a gate voltage stabilization circuit unit applies a stabilized gate voltage to the gate electrode of the field emission lamp, and the anode electrode The gate voltage applied from the gate voltage stabilizing circuit unit is set so that the sum of the voltage proportional to the lamp voltage applied to the voltage and the voltage proportional to the lamp current flowing through the cathode electrode becomes a constant reference voltage. And a power control circuit unit that controls and drives the field emission lamp with a constant power.

  According to the present invention, a field emission lamp can be driven with a constant power with a simple circuit configuration, and an increase in size and cost of the apparatus due to an increase in circuit components can be avoided.

Circuit block diagram of lamp driver Power control circuit block diagram Explanatory diagram showing the relationship between lamp power and lamp voltage Other configuration diagram of power control circuit

Embodiments of the present invention will be described below with reference to the drawings.
First, a first embodiment of the present invention will be described. In FIG. 1, reference numeral 1 denotes a lamp driving device 1 that drives a field emission lamp L. The field emission lamp L collides electrons emitted from an electron emission source in a vacuum with a phosphor at high speed. This is a well-known cold cathode field emission type light emitting device for exciting and emitting phosphors. Hereinafter, the field emission lamp L is simply referred to as “lamp L”.

  The lamp driving device 1 has a three-pole structure in which a cathode electrode having an electron emission source and an anode electrode having a phosphor are arranged at a predetermined interval inside a vacuum vessel, and a gate electrode is arranged between the cathode electrode and the anode electrode. The lamp is the driving target. Therefore, the lamp driving device 1 generates a predetermined DC high voltage from the input voltage VGin, applies the stabilized gate voltage Vg to the gate electrode G of the lamp L, and the gate voltage stabilization. The power control circuit unit 20 that controls the gate voltage of the lamp L applied via the control circuit unit 10 and drives the lamp L with constant power is configured as a main part.

  Specifically, the gate electrode G of the lamp L is connected to the output terminal of the gate voltage stabilizing circuit unit 10 and is connected (grounded) to the ground GND via the resistors Rg1 and Rg2. The connection portion of the resistors Rg1 and Rg2 is connected to the gate voltage stabilization circuit portion 10 in order to control the voltage applied to the gate electrode G of the lamp L, and the voltage across the resistor Rg1 is detected to detect the gate voltage stabilization circuit. Input to the unit 10. Further, a control element Q composed of a field effect transistor (FET) or the like is interposed in parallel between the resistor Rg2 and the ground GND, and conduction of the control element Q is controlled by the power control circuit unit 20.

  An anode voltage (lamp voltage) Va higher than the gate voltage Vg is applied to the anode electrode A of the lamp L from a power supply circuit (not shown).

  As shown in FIG. 2, the power control circuit unit 20 is mainly configured by a comparator (comparison circuit) CP that drives and controls the control element Q. Specifically, the output side of the comparator CP is connected to the control input terminal of the control element Q, and is connected to the input voltage Vin side via the resistor R3. On the input side of the comparator CP, a reference voltage Vr generated by a resistor R4 and a diode D from an external input voltage Vin is applied to an inverting input terminal (-terminal), while a non-inverting input terminal (+ terminal). ) Is connected to a resistor R1 as a first resistor for inputting the input voltage Vin for comparison, and is connected to a cathode electrode of the lamp L, and is further grounded via a resistor R2 as a second resistor. Has been.

  The input voltage Vin to the power control circuit unit 20 is a voltage based on the lamp voltage Va and is a voltage proportional to the lamp voltage Va. Such a voltage proportional to the lamp voltage can be generated by using, for example, a transformer in a power supply circuit that generates a high-voltage lamp voltage, a voltage doubler rectifier circuit, or the like.

  The power control circuit unit 20 having such a configuration includes a reference voltage Vr applied to the inverting input terminal (− terminal) of the comparator CP and a voltage (both ends of the resistor R2) applied to the non-inverting input terminal (+ terminal). Voltage) and control the control element Q to control the gate voltage of the lamp L via the gate voltage stabilizing circuit unit 10 and drive the lamp L with constant power against the fluctuation of the lamp voltage Va. Perform constant power control.

First, the gate voltage control of the lamp L will be described. When the impedance of the control element Q is Z, the combined resistance R between the gate electrode G of the lamp L and the ground GND is given by the following equation (1). Accordingly, assuming that the current flowing through the combined resistance R (Rg1, Rg2, Z) is Ig, the gate voltage Vg of the lamp L is given by the following equation (2).
R = Rg1 + (Rg2 × Z) / (Rg2 + Z) (1)
Vg = (Rg1 + (Rg2 × Z) / (Rg2 + Z)) × Ig (2)

  Therefore, if the gate voltage stabilization circuit unit 10 controls the voltage VRg1 across the resistor Rg1 connected to the gate electrode G to be a constant value, the current Ig (= VRg1 / Rg1) becomes a constant value, and the comparator The gate voltage Vg of the lamp L can be controlled by varying the impedance Z by controlling the conduction of the control element Q with CP.

  Specifically, when the lamp voltage Va is constant, when the gate voltage Vg increases, the current (lamp current) Ik that flows from the cathode electrode K to the ground GND through the resistor R2 on the non-inverting input terminal (+ terminal) side of the comparator CP. Increases and the voltage across the resistor R2 increases. When the voltage across the resistor R2 exceeds the reference voltage Vr, the output of the comparator CP becomes high level, the control element Q is controlled in the ON (conduction) direction, and the impedance Z decreases.

  As a result, as can be seen from the equation (2), the gate voltage Vg of the lamp L decreases, and the lamp current Ik decreases as the gate voltage Vg decreases. That is, when the lamp voltage Va is constant, the gate voltage Vg is controlled so that the voltage across the resistor R2 becomes equal to the reference voltage Vr, and the lamp current Ik is controlled.

On the other hand, when the lamp voltage Va fluctuates, the power control circuit unit 20 detects the fluctuation of the voltage across the resistor R2 due to the fluctuation of the lamp current Ik so that the voltage across the resistor R2 becomes equal to the reference voltage Vr. By controlling the gate voltage, the power of the lamp L is controlled to be constant. That is, when the input voltage Vin (voltage proportional to the lamp voltage Va) to the power control circuit unit 20 is set so as to satisfy the condition of the following expression (3), the current flowing through the resistors R1 and R2 under this condition: Iin can be expressed by equation (4).
Vin >> Vr (3)
Iin≈K1 × Va (4)
Where K1: coefficient

Therefore, since the lamp power P is P = Va × Ik, the lamp power P can be approximately calculated by the following equation (5) using the relationship of the equation (4).
P = Va × Ik
≒ K2 x Iin x Ik (5)
K2: coefficient

Here, the voltage V2 across the resistor R2 can be obtained from the sum of the current Iin from the voltage proportional to the lamp voltage Va and the lamp current Ik, as shown in the following equation (6).
V2 = R2 × (Iin + Ik) (6)

Accordingly, when V2 = Vr, the lamp power P in the equation (5) can be expressed by the following equation (7).
P ≒ K2 × (K1 × Va × Vr / R2-K1 2 × Va 2) ... (7)

  FIG. 3 shows the relationship between the lamp voltage Va and the lamp power P according to the equation (7). When Iin = Ik (R2 × Iin = R2 × Ik = 0.5 Vr), the lamp power P is 100. %. Therefore, the gate voltage of the lamp L is controlled via the control element Q so that the voltage V2 (= R2 × (Iin + Ik)) that is the non-inverting input of the comparator CP is equal to the constant reference voltage Vr that is the inverting input. As a result, the lamp L can be driven with a constant power even if the lamp voltage Va fluctuates.

  The above power control circuit unit 20 generates the comparison voltage V2 to be compared with the reference voltage Vr in the comparator CP using the two resistors R1 and R2, and has a simple circuit configuration with a small number of parts and noise resistance. However, since the current Iin equal to the lamp current Ik flows from the input voltage Vin which is a voltage proportional to the lamp voltage Va, the power consumption of the circuit slightly increases.

  For this reason, the power control circuit unit 20 may have a circuit configuration as shown in FIG. That is, by adding a resistor R12 as a third resistor between the resistor R1 and the resistor R2, and connecting the connection point between the resistor R1 and the resistor R12 to the non-inverting input terminal (+ terminal) of the comparator CP. The reference voltage Vr is compared with the sum of the voltage across the resistor R12 and the voltage across the resistor R2, and the gate voltage of the lamp L is controlled via the control element Q.

Specifically, assuming that the current flowing through the resistor R2 through the resistor R1 and the resistor R12 by the input voltage Vin is Iin ′, the voltage across the resistor R12 is V12, and the voltage across the resistor R2 is V2, the following (8) to ( The resistors R1, R12, and R2 are set so as to satisfy the condition of the expression 10).
Vin >> V12 + V2 (8)
Va >> V2 (9)
Ik >> Iin '(10)

Under the conditions of the equations (8) to (10), the voltage V2 across the resistor R2 is approximately proportional to the lamp current Ik, and the voltage V12 across the resistor R12 is approximately proportional to the input voltage Vin. For this reason, the both-ends voltage V12 of the resistor R12 can be approximated by the following equations (11) and (12) using the lamp voltage Va.
V2 ≒ R2 x Ik (11)
V12 ≒ K3 × Va (12)
K3: coefficient

Here, when the gate voltage of the lamp L is controlled via the control element Q so that the voltage (V12 + V2) becomes equal to the reference voltage Vr (V12 + V2 = Vr), the lamp power P is expressed by the following equation (13). Can be expressed.
P≈ (Vr × Va−K3 × Va ² ) / R2 (13)

  The relationship between the lamp voltage Va and the lamp power P according to the equation (13) is the same as that in FIG. 3, and when V12 = V2 (when V12 = V2 = 0.5 Vr), the lamp power P is 100%. Become. In the circuit configuration of FIG. 4, the gate voltage of the lamp L is controlled via the control element Q so that the voltage (V12 + V2) which is the non-inverting input of the comparator CP is equal to the constant reference voltage Vr which is the inverting input. The current Iin ′ from the input voltage Vin can be made much smaller than the lamp current Ik, and the lamp L can be driven with a constant power while reducing the power consumption of the circuit.

  As described above, in the present embodiment, a voltage proportional to the lamp voltage with a simple circuit configuration using several resistors (resistors R1, R2 or resistors R1, R12, R2) provided on the comparison input side of the comparator CP. The lamp L can be driven at low power by controlling the gate voltage so that the sum of the voltage and the voltage proportional to the lamp current becomes a constant reference voltage, avoiding the increase in size and cost of the device due to the increase in circuit parts. Thus, a small and inexpensive drive device can be realized.

DESCRIPTION OF SYMBOLS 1 Lamp drive device 10 Gate voltage stabilization circuit part 20 Power control circuit part CP Comparator (comparison circuit)
R1 resistance (first resistance)
R2 resistance (second resistance)
R12 resistance (third resistance)

Claims (4)

Field emission having a tripolar structure in which a cathode electrode having an electron emission source and an anode electrode having a phosphor are arranged at a predetermined interval inside a vacuum vessel, and a gate electrode is arranged between the cathode electrode and the anode electrode. Type lamp drive device,
A gate voltage stabilization circuit unit that applies a stabilized gate voltage to the gate electrode of the field emission lamp;
The gate voltage stabilization circuit unit applies the constant voltage so that the sum of the voltage proportional to the lamp voltage applied to the anode electrode and the voltage proportional to the lamp current flowing through the cathode electrode becomes a constant reference voltage. And a power control circuit section for controlling the gate voltage and driving the field emission lamp with a constant power. The power control circuit unit is
2. The gate voltage according to claim 1, wherein when the lamp voltage is a constant voltage, the gate voltage is controlled so that a voltage proportional to the lamp voltage is equal to a voltage proportional to the lamp current. Field emission lamp driving device. The power control circuit unit is
A first current is passed through a first resistor from a voltage proportional to the lamp voltage, and the lamp current and the first current via the first resistor are grounded through a second resistor. A circuit to flow to,
A comparison circuit for comparing the voltage across the second resistor and the reference voltage;
3. The field emission lamp driving apparatus according to claim 1, wherein the gate voltage is controlled by an output of the comparison circuit so that a voltage across the second resistor is equal to the reference voltage. . The power control circuit unit is
A first current is allowed to flow from a voltage proportional to the lamp voltage to a second resistor via a first resistor, and the first current via the lamp current, the first resistor, and the second resistor. A circuit for passing current to ground through a third resistor;
A comparison circuit that compares the sum of the voltage across the second resistor and the voltage across the third resistor with the reference voltage;
The gate voltage is controlled by an output of the comparison circuit so that a sum of a voltage across the second resistor and a voltage across the third resistor is equal to the reference voltage. 3. A field emission lamp driving apparatus according to 1 or 2.

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