JP2001203091A - Constant power control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant power control device to control a lamp connected to an invertor circuit with high accuracy in constant power. SOLUTION: A voltage reduction chopper circuit CH is connected to a DC power source E to supply output voltage Vout of the voltage reduction chopper circuit CH into a full bridge invertor circuit IV. A lamp La is connected to the full bridge invertor circuit IV through a current limiting reactor LZ. A computation part CTa computes the lamp voltage VIa on the base of the output voltage Vout of the voltage reduction chopper circuit CH to compensate the power loss. An on-off control part CTb controls a switching transistor Qx on the base of the output signal of the computation part CTa to control the lamp La in constant power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant power control device for accurately controlling a lamp connected to an inverter circuit with a constant power.

[0002]

2. Description of the Related Art A lamp control device using an inverter circuit has been applied to various uses because of its advantages such as instantaneous lighting and flicker prevention. As a power supply of such a lamp control device, a commercial frequency voltage output from a commercial power supply is rectified and smoothed and converted to a DC voltage, or a DC voltage of the DC power supply is converted to a predetermined DC voltage by a chopper circuit, and further, In some cases, the output voltage of the chopper circuit is converted into an AC voltage by an inverter circuit, and the AC voltage is supplied to the lamp to turn on the lamp.

FIG. 2 is a circuit diagram showing an example of a lamp control device. In FIG. 2, a DC voltage of a DC power supply E is supplied to a step-down chopper circuit CH. Step-down chopper circuit CH
Is a reactor Lx, a switching transistor Qx,
It is composed of a free wheel diode FD and a capacitor C. For example, a MOSFET or the like is used as the switching transistor Qx. CTx is the switch Q
x, which is a first control circuit that controls the output voltage Vout and the output current Iout of the step-down chopper circuit CH.

Since the configuration of the step-down chopper circuit CH is well known, a detailed description of its operation will be omitted. However, by appropriately selecting the ON / OFF cycle of the switch Qx by the first control circuit CTx, the step-down chopper circuit CH is selected. From the output side of the circuit CH, a DC voltage Vout obtained by reducing the input voltage Vin to a predetermined voltage is obtained.

[0005] Ra and Rb are voltage dividing resistors, and Rc is a resistor for detecting an output current. IV is a full bridge inverter circuit connected to the output side of the step-down chopper circuit CH, La is a lamp connected to the full bridge inverter circuit IV, L
z is a current limiting reactor. The lamp La is for a liquid crystal projector, for example.

The full-bridge inverter circuit IV is provided with switches Q1 to Q4.
As 1 to Q4, for example, electronic switches such as MOSFETs are used. The full-bridge inverter circuit IV alternately turns on and off a set of switches Q1 and Q2 and a set of switches Q3 and Q4.

CTy is a full-bridge inverter circuit IV.
To control the on / off operation of each of the switches Q1 to Q4.
And outputs control signals S1 to S4. The output frequency of the full-bridge inverter circuit IV is controlled by appropriately selecting the timing for outputting the control signals S1 to S4.

When the switches Q1 and Q2 of the full-bridge inverter circuit IV are turned on and the switches Q3 and Q4 are turned off by the second control circuit CTy, a current flows in the lamp La in the direction of arrow i1. When the switches Q3 and Q4 are turned on and the switches Q1 and Q2 are turned off, a current flows in the direction of arrow i2.

Thus, a set of switches Q1 and Q2,
By properly selecting the cycle for turning on and off the set of switches Q3 and Q4 alternately, the full bridge inversion is performed.
An AC voltage having a predetermined output frequency is generated from the inverter circuit IV, and the AC voltage is applied to the lamp La.

When the lamp La, which is a load of the step-down chopper circuit CH, is used for a liquid crystal projector as described above, constant power control is performed on the load. The output voltage Vout and the output current Iout of the step-down chopper circuit CH are converted into a first control circuit CTx
, The output power Pout of the step-down chopper circuit CH can be calculated. By controlling the step-down chopper circuit CH so as to keep the output power Pout constant, it is considered that the power Pla of the lamp La is under constant power control.

[0011]

However, due to the on-resistance of each of the switches Q1 to Q4 of the full-bridge inverter circuit IV and the resistance of the current limiting reactor Lz,
The power Pla of the lamp La is lower than the output power Pout of the step-down chopper circuit CH. The power loss Pz when the two switches are turned on is expressed by z
Then, Pz = z × (Iout) 2. here,
Assuming that the ON resistance of one switch Q1 is rp and the resistance of the current limiting reactor Lz is rq, z = (2 × rp) +
(Rq).

As described above, when the two switches of the full-bridge inverter circuit IV are turned on, the loss power Pz
Has occurred. For this reason, when the output power Pout of the step-down chopper circuit CH is made constant, and it is considered that the power Pla of the lamp La is being controlled with constant power, an error occurs and accurate constant power control of the lamp is performed. There was a problem that can not be.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a constant power control device for precisely controlling a lamp connected to an inverter circuit with constant power.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a constant power control device comprising a DC power supply, a control unit for the DC power supply, an inverter circuit connected to the DC power supply, and an inverter circuit. A control circuit for controlling the output frequency of the inverter circuit, wherein the control unit calculates the lamp voltage by an approximate expression based on the output voltage of the DC power supply, and corrects the power loss. This is achieved by supplying the output power of the DC power supply to the inverter circuit and controlling the lamp at a constant power.

According to the above-mentioned feature of the present invention, the lamp voltage is calculated by an approximate expression based on the output voltage of the DC power supply, and the output power of the DC power supply is supplied to the inverter circuit by correcting the loss power. Therefore, constant power control of the lamp can be accurately performed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below with reference to the circuit diagram of FIG. In FIG. 1, the same parts as those in the circuit diagram of the conventional example in FIG. 2 or corresponding parts are denoted by the same reference numerals. In FIG. 1, CTa is an operation unit that performs an approximate operation of a lamp voltage for power correction, and CTb is an on / off control unit of the switching transistor Qx.

The output power of the step-down chopper circuit CH is Pou
t, assuming that the loss power when two switches of the full-bridge inverter circuit IV are turned on is Pz, the lamp La
Is Pla = Pout−Pz. In the present invention, the lamp power Pla is controlled at a constant power. Here, if the output voltage of the step-down chopper circuit CH is Vout and the output current is Iout, Pout =
Vout × Iout, Pz = z × (Iout) 2.

Therefore, the electric power Pla of the lamp La is:
Pla = Iout (Vout−z · Iout). Here, the loss voltage Vz is calculated as follows: Vz = z · Iout = D
(Constant), Pout = Pla + Pz = Iou
t · Vla + Iout · D = Iout (Vla + D),
It is represented by The lamp voltage Vla is Vla = Vo.
ut−Vz.

Since it is difficult to accurately determine the lamp voltage Vla by measurement, the lamp voltage Vla
Assuming that z = constant, the calculation is approximately performed using the above equation. As described above, by approximately calculating the lamp voltage Vla, the output power Pout from the step-down chopper circuit CH is calculated.
Can be obtained as a value obtained by correcting the loss power Pz. Thus, by controlling the output power Pout of the step-down chopper circuit CH in consideration of the loss power Pz, constant power control of the lamp power Pla is performed.

Further, the above-mentioned Pla = Iout (Vout-
By transforming the expression of z · Iout), z (Iout)
t) 2-Vout · Iout + Pla = 0 is obtained. By multiplying each side of this equation by z, (z · Iout)
2-Vout.z.Iout + z.Pla = 0 is obtained.

Here, since z · Iout = Vz,
The above equation is given by (Vz) 2−Vout · Vz + z · Pla =
It becomes 0. Thus, Equation 1 is established as follows.

[0022]

(Equation 1)

Since the lamp voltage Vla = Vout-Vz, Equation 2 is obtained by modifying Equation 1.

[0024]

(Equation 2)

Assuming that A and B are constants, Equation 2 is given by Vla =
A · Vout−B. That is, the ramp voltage Vla is changed to the output voltage V of the step-down chopper circuit CH.
This is predicted by out. As described above, Vz
= Z.Iout = D (constant), and when performing constant power control of lamp power, in practice, accurate constant power control cannot be performed because the output current Iout fluctuates.

However, Vla = A.Vout-B
When the lamp voltage Vla is determined by the approximate expression, the output current Iout is not included in the approximate expression. For this reason,
The constant power control of the lamp power can be performed easily and accurately.

In FIG. 1, the calculation unit CTa calculates the lamp voltage Vla = A · Vout−B by the approximate expression as described above, and outputs the calculated voltage to the on / off control unit CTb. The on / off control unit CTb controls the switching transistor Qx based on the signal input from the calculation unit CTa and the output current Iout of the step-down chopper circuit CH, and
The constant power control of a is performed.

That is, the output power Pout of the step-down chopper circuit CH is controlled in consideration of the loss power Pz as described above, and the constant power control of the lamp power Pla is performed.

In the above example, the DC power from the step-down chopper circuit is supplied to the full-bridge inverter circuit to which the lamp is connected. In addition, a DC power source such as a step-up / step-down chopper is used. Can be. The lamp is not limited to a lamp used for a special purpose for a liquid crystal projector, and may be a general discharge lamp such as a fluorescent lamp. Further, the present invention can be applied to a case where a lamp is connected to a half-bridge inverter circuit instead of the full-bridge inverter circuit.

[0030]

As described above, according to the present invention, the lamp voltage is calculated by an approximate expression based on the output voltage of the DC power supply.
Since the output power of the DC power supply is supplied to the inverter circuit after compensating for the loss power, the lamp can be controlled with constant power with high accuracy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a constant power control device according to a preferred embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional constant power control device.

[Explanation of symbols]

 E DC power supply CH Step-down chopper circuit CTa Calculation section CTb ON / OFF control section IV Full bridge inverter circuit La lamp CTx First control circuit CTy Second control circuit Lz Current limiting reactor

Claims (1)

[Claims] 1. A DC power supply, a control unit for the DC power supply, an inverter circuit connected to the DC power supply, a lamp connected to the inverter circuit, and a control for controlling an output frequency of the inverter circuit. A control circuit that calculates the lamp voltage by an approximate expression based on the output voltage of the DC power supply, corrects the power loss, and supplies the output power of the DC power supply to the inverter circuit. A constant power control device, characterized in that the constant power control is performed.