JPS61173492A - High frequency lighting apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-frequency lighting circuit for a light source used in optical reading devices for characters and images, copying machines, and the like.

2. Description of the Related Art A block diagram of the configuration of a conventional high frequency lighting circuit is shown in FIG. In a conventional high-frequency lighting circuit, a drive circuit 2 rectifies and smoothes an AC input voltage V in a rectifier and smoothing circuit 4, and turns the output of the rectifier and smoothing circuit 4 into ○N-0FF by a pulse generated by a variable pulse width generation circuit 1. The light source 3 was driven by

Problems to be Solved by the Invention In such a conventional high-frequency lighting circuit, when the input AC voltage V fluctuates as shown in FIG. 7 (al), the driving voltage V changes as shown in FIG. , (di. In this case, if the pulse width period is 7, the pulse duty ratio is α, and the load resistance of the light source is R in each case, the effective value of the power is P1°. C,
A problem arises in that the amount of light from the light source fluctuates.

However, a photodetector is provided to detect variations in the light intensity of the light source 3, and the output pulses of the variable pulse width generation circuit are Changing the duty α solves the problem with variations in the amount of light, but problems such as the installation location of the photodetector itself and the temperature characteristics of the detector with respect to the heat emitted by the light source arise.

The present invention has been made in view of the above, and an object of the present invention is to provide a high-frequency lighting circuit that can obtain a stable amount of light with respect to input AC voltage with a simple configuration without using a photodetector or the like. do.

Means for Solving the Problems In order to solve the above problems, the present invention steps down the input AC voltage, rectifies and smoothes the output, and divides the voltage. From the output after voltage division, calculate the pulse width of the output pulse of the variable pulse width generation circuit so that the effective value of the lighting power of the light source is constant.
It is something to control.

Effect of the Invention With the above-described configuration, the present invention can control the pulse width of the output pulse of the variable pulse width generation circuit so that the effective value of the lighting power of the light source is constant. You can get the amount of light.

Embodiment FIG. 1 is a block diagram showing an embodiment of the high frequency lighting circuit of the present invention. In Figure 1, 5 is the input AC power supply 11
6 is a rectifier and smoothing circuit that rectifies and smoothes the output of the transformer 5; 7 is a rectifier and smoothing circuit 6;
8 is a pulse output from the variable pulse width generating circuit 1, and the output of the squaring circuit is 0N-
9 is an average value circuit that averages the output of the analog switch 8; 1o is an average value circuit 9
This is a comparator that compares the output of the reference voltage generator 12 with the output voltage vREF of the reference voltage generator 12.

FIG. 2 is an explanatory diagram of the operation of the present invention.

The operation of one embodiment of the present invention will be described below with reference to FIGS. 1 and 2. If the amplitude of the input AC voltage Y11 is vo, the step-down ratio of the transformer 5 is 1. Assuming that the voltage dividing ratio of resistors R1 and R2 is 2, the output of the squaring circuit 7 is shown in (a) in FIG.
It has a waveform like l. However, let X = (2 on the bill) 2. A second pulse width generating circuit 10 generates this output.
Period T shown in figure [bl.

Turn analog switch 8 to 0N- with a pulse of duty α.
When turned OFF, the output of analog switch 8 is
When this output is passed through the average temporary circuit 9t, it becomes a waveform as shown in Fig. 2(d) K. On the other hand, the power applied to the light source is as shown in Equation 1. niαVo
', /' EL, the power applied to the light source is correlated with the output of the average value circuit 9.

If the input AC voltage Y11 fluctuates, as described above, the power applied to the light source will fluctuate, so the amount of light will fluctuate.

Therefore, for example, if the input AC voltage y fluctuates, the fluctuation @v0
has become smaller, the output voltage vREF of the reference voltage generator set at the time of the original input AC voltage is compared with the output of the average value circuit 9, and the output of the comparator 10 is used to generate a variable pulse. O of the pulse generated by the width generating circuit 1
The N ratio is set to be large so that the reference voltage vREF and the output of the average value circuit 9 match. Therefore, even if the input AC voltage fluctuates, the puff −αV0 applied to the light source
'/R is always constant, so there is no variation in the amount of light.

Other embodiments of the present invention will be described. FIG. 3 is a block diagram of another embodiment, in which 13 is an analog/digital converter (A/D converter) and 14 is a division circuit.

The operation will be explained using FIG. NREF is the effective value of the power at the time of reference lighting, P is the step-down ratio of the transformer, and 12 is the voltage division ratio. If the resistance value of the light source is R, NREF=p, ux
It is set as (kl・k2)2. X is the output of the square circuit 7 when the input AC voltage V fluctuates, and V is the amplitude of Y.
o, then I = (2 in vokl) 2, so the output y of the divider circuit 14 becomes y;P -F'L7''Io, and this y is divided into 0
Control as N-OFF ratio.

For example, input AC voltage V is the reference input AC voltage 9
If the number is doubled, the division circuit will be overloaded, so if the output pulse duty of the variable pulse width generation circuit 1 is made constant, a constant amount of light can be obtained even when the input AC voltage fluctuates. It will be done.

Next, a third embodiment of the present invention will be described. FIG. 4 shows a configuration diagram of the third embodiment. 16 is A/D converter 1
16 is an output port that outputs the processed data, 17 is a CPU, 1s
is a ROM that stores the program of CPU1 (5), 19 is a RAM that stores data, and CPU17.ROM1
B, RAM19゜input port 16 and output port 16
are connected to each other by an address path and a data bus to form a microcomputer.

First, the CPU 17 sends the input AC voltage y through a transformer, and converts it into a rectified, smoothed, and divided voltage of 1 to 2V.

(However, k is the step-down ratio of the transformer 6, and 2 is the resistor R1.
, R2, and vo is the amplitude of the input AC voltage y. ) is A/D converted by the A/D converter 13, and this data is read through the input port 14. CPU17
The data read by is processed in the microcomputer, and the variable pulse width generation circuit 1 outputs appropriate duty ratio data to the input AC voltage y through the output port 16.
Output to.

Next, processing within the microcomputer will be explained.

Figure fa5 is a flowchart of processing within the microcomputer. QPUl 7 issues an A/D start signal and the A/D conversion is completed.

Assuming that the effective power of the reference light source stored in the memory is P, the following equation must be satisfied in order to keep the light amount of the light source constant.

P = e2・α/R・・・・・・・・・・・・Old・
(2) where a is the pulse duty and R is the resistance value of the light source. Therefore, from equation (2), α = (2/vO for kl)・P-R・l1...old...(3), and in advance, Ref=P-R・(2 for kl
)2 is calculated and used as reference data, α=Ref/v
The pulse duty α is determined simply by performing the calculation of 0. This calculation is performed within the software, and the output port
6, the pulse duty data α is output to the variable pulse width generation circuit 1. The variable pulse width generation circuit 1 outputs a pulse of duty α according to the supplied pulse duty data α. As a variable pulse width generation circuit,
For example, PTM (programmable timer)
etc.

Effects of the Invention As described above, according to the present invention, a stable amount of light can be obtained without using a photodetector or the like, regardless of fluctuations in the input AC voltage.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a high-frequency lighting device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of each part for explaining the device, and FIG. 3 is a block diagram of a high-frequency lighting device according to a second embodiment of the present invention. 4 is a block diagram of a high frequency lighting device according to a third embodiment of the present invention, FIG. 6 is a flowchart for explaining the same device, FIG. 6 is a plot diagram of a conventional high frequency lighting device, and FIG. FIG. 7 is a waveform diagram for explaining a conventional high frequency lighting device. 1...Variable pulse width generation circuit, 2...
Drive circuit, 3.6... Rectification and smoothing circuit, 7...
... Square circuit, 8 ... Analog switch, 9
...Average value circuit, 10 ...Comparator, 1
2...Reference voltage generator, 13...A/
D Converter, 14... Division circuit, 16...
...Input port, 16...Output port, 17.
...CPU. 18...ROM, 19...RAM0 Name of agent Patent attorney Toshi Nakao and 1 other person aQ
) Figure 2 (a-2 (b) (Shen 2 Buddha Kvo2□ Figure 5 Figure 6)

Claims (4)

[Claims] (1) A transformer that steps down the input AC voltage, a rectifier and smoothing circuit that rectifies and smoothes the output of the transformer, and a variable pulse width generator that drives a high frequency lighting circuit, and the output of the rectifier and smoother circuit. A high-frequency lighting device characterized in that the output pulse width of the variable pulse width generator is calculated and controlled so that the effective value of the lighting power of the light source is constant. (2) A reference voltage generator that sets a voltage proportional to the effective value of the lighting power of the light source, a squaring circuit that squares the output of the rectifying and smoothing circuit, and the output of this squaring circuit as the output pulse of the variable pulse width generator. an average value circuit that averages the output of the analog switch, and a comparator that compares the output of the average value circuit with the output of the reference voltage generator; 2. The high frequency lighting device according to claim 1, wherein the pulse width of the variable pulse width generator is increased or decreased. (3) An A/D converter that converts the output of the rectifying and smoothing circuit from analog to digital, a squaring circuit that squares the output of this A/D converter, and a division circuit that divides the output of this squaring circuit by a reference signal. 2. The high frequency lighting device according to claim 1, wherein the output pulse width of the variable pulse width generator is varied in proportion to the output of the dividing circuit. (4) It is equipped with an A/D converter that A/D converts the output of the voltage dividing circuit, and a microcomputer consisting of a CPU, ROM, RAM, input port, and output port, and the output of the A/D converter is controlled by software. The output pulse width of the variable pulse width generation circuit is varied by reading data from the input port, calculating the square, and dividing the data for setting the effective value of the lighting power of the light source by the result and outputting the resultant data from the output port. A high frequency lighting device according to claim 1, characterized in that: