JPS58213316A - Ac constant voltage device - Google Patents

Abstract

PURPOSE:To attain accurate constant voltage control with inexpensive constitution, by measuring a time between a zero cross signal and an output of a comparator with a reference clock, in an AC constant voltage device controlled digitally. CONSTITUTION:The time between the zero cross signal and the output of the comparator 6 comparing an input voltage and a reference voltage (voltage at point A) is measured with the reference clock of the microcomputer 7 and an accurate input voltage is obtained from the measured time. A prescribed load voltage is obtained with the control of the phase of continuity angle from the obtained input voltage by using the microcomputer 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC voltage constant device that can be applied to lamp regulators and the like, and particularly relates to a 5 AC voltage constant device that performs digital control.

For example, in copying machines, facsimile machines, etc., power supplies used for fixing devices, exposure lamps, etc. must be stabilized because fluctuations in power supply pressure can have a significant adverse effect on images.

In recent years, a method has been devised in which an input voltage is A/D converted by an A/D converter, the input voltage is measured, and the output voltage is controlled using a microcomputer.

Cheap A/D converters used in this method have the disadvantage of slow conversion speed and wide measurement errors in input voltage, and if you try to use an A/D converter that eliminates these disadvantages, it will be expensive. There are circumstances in which it is difficult to introduce because it sticks to things.

The present invention has been made in order to overcome the drawbacks of the above-mentioned conventional examples in devices that perform digital control, and provides an AC constant voltage device that is inexpensive and capable of accurate constant voltage control. The purpose is to

To do this, the time from the zero-crossing signal to the output of the comparison circuit between the input voltage and the reference voltage is measured using the highly accurate reference clock of the microcomputer, and from the obtained time. This is a VC device that obtains an accurate input voltage, controls the output voltage from the obtained input voltage using a microcomputer, and obtains a constant voltage.The present invention will be described below based on the illustrated embodiments. explain.

FIG. 1 is an electrical circuit diagram showing one embodiment.

In the figure, 1 is an AC power supply, 2 is a load connected to both ends of this AC power supply l, 3 and 4 are diode doves and ridges, and 5 is a switch for turning on and off the power supplied by the AC power supply 1 to the load 2.
6 is a comparator that compares the power supply voltage with the reference voltage and outputs an output, 7 is a microcomputer, 8 is a triac.
is a photocoupler.

R7~R1 again! is a resistor, V is a variable resistor, D is a diode, ZD is a Zener diode, T is a transformer, T is a coil, C1 to C8 are capacitors, Tr,, T
r is a transistor.

The operation of the circuit configured in this manner will be explained below.

The AC voltage applied to the load 2 is applied to the base of the transistor Tr through the transformer T1 and the diode bridge 3. When current flows through the base, the transistor Tr
l is conductive, so the potential at the 0 point is zero, but when the AC waveform reaches the zero crossing point and no current flows to the base, the transistor Tr becomes non-conductive, and the potential at the 0 point becomes high level. . In other words, a zero-crossing pulse synchronized with the zero-crossing point can be obtained in CA.

This zero-cross pulse enters the microcomputer 7's boat INI.

On the other hand, the power supply voltage is full-wave rectified by the diode bridge 3 and input to the e terminal of the comparator 6 through the resistor R8. In this comparator 6, the resistance R0,
The reference voltage created by diode D8, Zener diode ZD, and variable resistor VR is compared with the above-mentioned power supply voltage to output an output. The output of this comparator 6 is input to the boat INp of the microcomputer 7.

The voltage at point D is the output of comparator 6, but since the power supply voltage is input to the O terminal and the reference voltage is input to the This is a low level output.

The time from the zero cross pulse to the fall or rise of the output of the converter 6 is proportional to the magnitude of the power supply voltage as shown in FIG.

In other words, the waveform at point B (power supply voltage) is the voltage at point A (reference voltage)
When K is large, the time t! from the zero cross pulse at point 0 to the rise of the output waveform (output of the controller 6) at point D is longer than the time t1 when it is small.

Therefore, this time 1. ,． 1. By measuring , it is possible to convert it to the power supply voltage.
However, the relationship between the power supply voltage and time is stored in the ROMvc, and the microcomputer 7 [executes it]. For time measurement, use the microcomputer 70 reference clock pulse.

This will also be described in detail in the memory map later, but data for performing phase control to keep the load voltage constant with respect to the power supply voltage determined by the microcomputer 7 is stored in the ROM. A trigger timing pulse for the triac 5 is output from the output port 0UTO of the microcomputer 7 in accordance with the voltage. The output of the output port 0UTO operates the transistor Tr to make the photocoupler 8 conductive. This signal is then applied as a trigger signal to the gate of the triac 5 through the diode bridge 4, thereby turning on the triac 5. By turning on the triac 50, power from the AC power supply 1 is supplied to the load 2. In addition, resistor R4, capacitor CI
constitutes a snubber circuit for suppressing the sudden rate of voltage rise, and resistor RA and capacitor C8 are provided to increase the dv/dt withstand capability of photocoupler 8.

To measure the power supply voltage mentioned above, from the zero cross point,
It is sufficient to count the time until the output of comparator 6 falls or rises, but since it is necessary to measure the power supply voltage after the try book 50 is turned on, we need to count the time until the output of comparator 6 rises. I decided to measure it.

FIG. 3 shows the relationship between the intersection angle between the power supply voltage and the reference voltage.

This sets the reference voltage to 80 iV and the power supply voltage to SOV ~
This is the case where it is 120■.

FIG. 4 is a memory map schematically showing ROM addresses and stored data. This is measured using the pulse count value, which is the time tA from the zero-crossing pulse to the rising edge of point D (output of the comparator 6) in FIG. This sets the power supply voltage.

For example, in the case of 5 milliseconds, the power supply voltage is 80V, and in the case of 7.2 milliseconds, it is 104V.
It turns out that.

In order to keep the load voltage constant with respect to the changing power supply voltage, it is sufficient to use a phase control device for the conduction angle and to make the effective value voltage constant.

Figure 5 shows a constant load voltage of 80V and a power supply voltage of 80V.
It is a trigger phase angle characteristic diagram when it is set to ~120V.

Based on this trigger phase angle characteristic, the relationship between the trigger signal timing (time tn from zero cross pulse) and power supply voltage is stored in the ROM as shown in FIG.

That is, when the power supply voltage is 80V, the load 2 must be fully energized, so tB is zero, that is, the triac 5 is turned on from the zero cross. As a matter of course, as the power supply voltage increases, the value of tB also increases (that is, the conduction angle increases to provide a constant effective value voltage).

The operation waveforms described above are summarized as shown in FIG.

In Figure 7, (1) is the power supply waveform, (2) is the rectified waveform at point B, (3) is the comparator 6 output waveform at point D, and (4) is the rectified waveform at point B.
) shows the zero cross pulse at point 0, (5) shows the phase control waveform at point F, and (6) shows the triac-on signal waveform (trigger timing signal) at point E.

(4) The tA waiting time (proportional to the power supply voltage) and the 1B time (trigger timing signal generation time) are proportional.

The present invention is as described above, and with this device, it is possible to simplify the circuit for measuring AC power supply voltage, and to improve the accuracy of measurement by using the reference clock pulse of a microcomputer.

[Brief explanation of the drawing]

Fig. 1 is a control circuit diagram according to an embodiment of the present invention, Fig. 2 is a waveform diagram showing differences in comparison circuit output due to changes in power supply voltage, and Fig. 3 shows the intersection angle between the power supply voltage and the reference voltage. Figure 4 is a memory map showing the relationship between time from zero-cross pulse and power supply voltage, Figure 5 is a trigger phase angle characteristic diagram,
FIG. 6 is a memory map showing the relationship between power supply voltage and phase control element firing data, and FIG. 7 is a waveform diagram showing waveforms at various parts. 1...AC power supply, 2...Load, 5...
...Triac as a phase control device, 6...
. . . Comparison circuit, 7 . . . Microcomputer, Tr, . . . Transistor as a zero cross detection circuit. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 (2) Fig. 7

Claims (1)

[Claims] Compare the power supply voltage and the reference voltage in a device that has an AC power supply, a load supplied with power from the AC power supply, and a phase control device connected between the load and the AC power supply, and keeps the load voltage constant through phase control. a comparator circuit that outputs an output, a zero-cross detection circuit that detects the zero-crossing point of the power supply waveform, a counting means that counts the time from the zero-crossing point to the output of the comparator circuit, and a phase control circuit that determines the phase control angle based on this counted value. An alternating current constant voltage device comprising control angle selection means.