JPS60142713A - Electronic ac voltage variable device - Google Patents

Abstract

PURPOSE:To attain systematically the voltage control of a comparatively light load by switching a current flowing to an input diode of a photocoupler of a bias circuit by means of a power MOSFET so as to vary the voltage of the load. CONSTITUTION:One terminal of the AC input of a diode bridge 11 is connected to the load 4 and the other terminal is connected to an AC power supply VI respectively, and a drain and a source of the MOSFET12 are connected to a DC output of the bridge 11. A fixed resistor 9 is connected between the drain and gate of the FET12 and a bias circuit including plural fixed resistors 19 and diodes 18 is connected between the gate and source. An output transistor section of the plural photocouplers 20 is connected to the bias circuit. Then the voltage applied to the load 4 is made variable by the switch operation of the current flowing to the input diode of the coupler 20.

Description

[Detailed Description of the Invention] Industrial Application Field 2 ・1 The present invention performs voltage control of a relatively light load connected to an AC power source, and is mainly used for speed control of induction motors, electric power for lights, heaters, etc. Suitable for control, etc.

Conventional configuration and its problems A conventional example will be explained using FIGS. 1 to 3.

FIG. 1 shows a generally widely known variable output voltage type autotransformer (hereinafter referred to as a slideac).

1 is AC power supply, 2 is Slydac, 3 is Slydac 2
output tap, 4 is the load. The power supply voltage v of the AC power supply 1 applied to the input of the large-sized slide duck 2 decreases in proportion to the position of the output tap 3, and is applied to the load 4 as a load voltage vL. Power supply voltage v and load voltage v
The state of L is shown in FIG. 3 using solid lines and broken lines, respectively.

The method of varying the AC output voltage using SLIDAC 2 has a simple structure and is relatively inexpensive, so it is widely used, but its disadvantages are that it is heavy and has a mechanical structure, making it unsuitable for control as a system. It can be said that Furthermore, since the factor that determines the output voltage is mechanical contact, there is also the problem that long-term reliability and environmental reliability are low.

Next, FIG. 2 shows an example of an electronic alternating voltage variable system.

6. 6 is a diode, 7 is an NPN) transistor, 8 is a PNP) transistor, 9 is a fixed resistor, and 10 is a variable resistor. 1 and 4 are the same as in FIG.

The base voltages of the NPN transistor 7 and the PNP transistor 8 are determined by the fixed resistor 9 and the variable resistor 1o, the emitter potential is determined, and therefore the voltage applied to the load 4 is determined. Transistors 7 and 8 correspond to the positive and negative phases of the AC power supply 1, and the difference between the voltage applied to the AC power supply 1 and the voltage applied to the load 4, that is, the voltage drop is consumed as vcE of the transistors 7 and 8. Ru. Diodes 5 and 6 are necessary to block base-collector current when the respective transistor 7.8 is reverse biased.

With the circuit shown in Figure 2, the power supply voltage ■ and the load voltage vL
The voltage waveform of is shown in FIG.

According to FIG. 2, the load voltage ■L can be varied by varying the variable resistor 10, but the transistors 7 and 8, which mainly consume power, are two elements, and the collectors are isolated from each other. There is a limit to miniaturization and cost reduction due to the necessity of In addition, a load voltage vL is always applied to both ends of the variable resistor 1o included in the base of the transistor 7.8, and as a result, the variable resistor 1o is connected to the AC power source 1.
A withstand voltage equivalent to the voltage vI is required, and insulation is also required in order to safely vary the output. Therefore, in order to systemize this circuit using a microconbeater or the like, an insulated, high-voltage control element is required, and the circuit is not suitable for a compact system.

Purpose of the Invention Therefore, the present invention aims to overcome the problems of the above-mentioned conventional examples and provide power control for relatively light loads with a simple circuit configuration that can be systemized. .

Structure of the Invention In order to achieve this object, the present invention has the following structure.

That is, in the present invention, one end of the AC input of the diode bridge is connected to a single-phase AC power supply through a load, and the other end is directly connected to a single-phase AC power supply, and the drain and source of the power MO8FET are connected to the DC output of the diode bridge. , a fixed resistor is connected between the drain and the gate of the power MO8FET, and a bias circuit including a plurality of fixed or variable resistors and a diode is connected between the gate and the source, and a plurality of fixed or variable resistors are connected between the gate and the source. The output transistor parts of a plurality of photocouplers are connected in parallel to a bias circuit including a variable resistor and a diode, and the voltage applied to the load is varied by switching the current flowing through the input diode of the photocoupler. It is configured to do this.

Description of examples Detailed explanation of the present invention is shown in Fig. 4 and Fig. 6 in Part 6 \- A schematic diagram is shown.

In the figure, a voltage obtained by subtracting the load voltage vL from the power supply voltage v is applied between the drain and source of the FET 12 (hereinafter abbreviated as drain voltage Ds), and the drain voltage is set by a fixed resistor 9 and a variable resistor 10. and DC power supply vDc (
or voltage vF) is applied between the gate and source (hereinafter abbreviated as gate voltage vGs).

The DC power supply vDc includes a diode section 18, a fixed resistor 15,
It is composed of a capacitor 16, and the gate voltage vG
A DC bias is applied to s.

7 and 8 are characteristic diagrams of the FET 12.

Figure 7 shows the IDS''-■GS characteristics.Usually, FET
has a threshold voltage vTH, and when the gate voltage vGs exceeds the threshold voltage vTH, O
The drain current IDS flows into the N region.

The DC power supply vDc shown in FIG. 6 compensates for this threshold voltage vTH, and by selecting an appropriate value, the waveform of the load voltage vL is improved.

FIG. 8 shows ID5-vDS characteristics. Gate voltage ■G
The relationship between the drain current IDS and the drain voltage vDs can be determined using s as a parameter. The dash-dotted line in FIG. 7 indicates the operating point of the circuit shown in FIG. Therefore, P indicates the peak drain current value when V L = V r. vDpH-1: Indicates the peak drain voltage value when vL=O, that is, vDs cape v■. When the gate voltage vGsO value is increased, the operating point moves so that the drain current IDs increases and the drain voltage vDs decreases.

Furthermore, since the power supply voltage V is an alternating current voltage, the operating point line shown by the dashed line moves in the direction of the arrow in FIG. 7 depending on the voltage phase.

Therefore, when the value of the variable resistor 10 shown in FIG. 4 is set to a certain value, the operating point A is set at one point on the operating line connecting IDP-vDP. Depending on the phase of the power supply voltage (■), the operating point moves approximately on a straight line connecting the operating point A and the origins of (DS) and (Ds).

FIG. 9 shows the relationship between the power supply voltage v and the load voltage vL.

Since the aforementioned gate threshold IT voltage vTH is compensated by the DC power supply ■Dc, the load voltage vL is almost similar to the power supply voltage VI.

However, when analyzed strictly, when the DC power supply vDc is a relatively high value as shown in Figure 9 (,), when the load voltage ■L is high, it is close to a sine wave, but when the load voltage ■L is low, it is trapezoidal. Get closer to the waves. Further, when the DC power supply voltage VL is relatively low, as shown in FIG. 9(b), when the load voltage vL is low, it approaches a sine wave, and when it is high, it approaches a triangular wave. This is because the gate threshold voltage decreases as the drain current decreases. That is, the load voltage v
There is a correlation that the region where L is low requires a low value of the DC bias of the gate, that is, the value of the DC power supply ■Dc.

FIG. 4 shows an example in which voltage correction of the gate DC bias is performed.

In place of the DC power supply vDc in FIG.
Then, the gate threshold voltage vTH
As compensation for the forward drop voltage VF of the diode section 18
is adopted.

Figure 6 shows the diode IF-VF4? It is a sex diagram.

This IF-VF characteristic is shown in FIG. It closely approximates the 5-vGs characteristic of FET12. By combining these two approximate characteristics, the influence of the threshold voltage VTR of the gate of the FET 12 is completely canceled, so that the voltage waveforms of the power supply voltage V and the load voltage VL can be almost approximated. This situation is shown in FIG. 10(d).

Further, Figures 10), (b), and (a) show the waveforms of the drain voltage vDs, gate voltage vGs, and forward drop voltage vF of the diode section 18, respectively. It is shown that the forward drop voltage vFO value decreases as the drain voltage VDS decreases, and the gate voltage vGs also decreases.

General [FET gate threshold voltage vTH
Although there are many variations within a certain range, the diode 18
The threshold voltage vTH can be easily corrected by adjusting the type and number of diodes in the section.

1o＼- Next, an embodiment according to the present invention is shown in FIG.

19 is a fixed resistor section, 20 is a photocoupler section, and 21 is a switch section. The variable resistor 10 in FIG. 4 is replaced with a fixed resistor section 19, and the output transistor of each photocoupler of the photocoupler section 2o is connected corresponding to each fixed resistor. If all the switches of the switch section 21 are OFF, all the output transistors of the photocoupler section 20 are OFF, and the combined resistance value of the fixed resistor section 19 is the sum of the values of all the fixed resistors. The highest voltage is output to the load 4.

Next, when any switch other than the switch 22 of the switch section 21 is turned on, the output transistors of the photocouplers of the photocoupler section 20 corresponding to this switch are turned on in order from the top, and the combined resistance value of the fixed resistor section 19 is As a result, the load voltage VL applied to the load 4 decreases. Furthermore, when the switch 22 of the switch section 21 is turned on, the output transistors of all seven optical couplers of the photocoupler section 2o are turned on, and the gate voltage vGs becomes 0 and F.
ET12 is turned OFF, and the load voltage output to the load 4 becomes O. If load 4 is specified here, the load voltage v
L is for ON of each switch 22 of the switch section 21,
Each is uniquely determined.

Further, if a variable resistor is used in the fixed resistor section 19, it becomes possible to change the load voltage VI, or to reset the load voltage VL when the load 4 becomes a different load.

Effects of the Invention According to the present invention, power control for relatively light loads can be provided compactly and inexpensively, and systemization can be easily achieved.

The first feature is that the power control element can be realized with one element.

Second, the voltage applied to the part that controls the output (fixed resistor section 19 in FIG. 11) is low. Since this voltage is the gate voltage vGs, it can normally be controlled with an upper limit of about 10V. Therefore, the control voltage is extremely low for controlling an AC power source of 100 V or 20 OV, and if a photocoupler is used, it can be easily combined with a microcomputer or the like to form a system.

Furthermore, the circuit configuration is extremely simple and can be constructed at low cost, and even in the event of an abnormality such as a short circuit or open circuit of each component, the load is placed on the power supply side of the circuit, so it has the advantage of high safety. are doing. Furthermore, the distortion of the load voltage VL can be kept within a range that does not cause any practical problems.

As described above, it has various excellent effects, and is the most suitable means for systematically controlling the voltage of relatively light loads.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional example using a slider, Figure 2 is a circuit diagram of a conventional example using a transistor, and Figure 3 is a circuit diagram of a conventional example using a transistor.
Figure 2 is a voltage control waveform diagram, Figure 4 is a circuit diagram showing the previous example of the present invention, Figure 5 is a diode IF-V characteristic diagram, and Figure 6 is another example of the present invention. Figure 7 is the FET's 5-vGs characteristic diagram, Figure 8 is the FET's S-VDB characteristic diagram, Figure 9 is the voltage control waveform diagram using the circuit in Figure 6, and Figure 9 is the voltage control waveform diagram using the circuit in Figure 6. Fig. 10 is a voltage control waveform diagram, and Fig. 11 is a circuit diagram showing an embodiment of the present invention.
... Fixed resistor, 18 ... Diode,
19... Fixed resistor section, 2o... Photo coupler section, 21... Switch section, 22...
···switch. Name of agent: Patent attorney Toshio Nakao and 1 other person, 1
Figure 3 @ 4 Figure 11.5I! l VF (V) Figure 6 Figure 7 Guan Figure 8 vr) r(v) os Figure 9 (OL) (b)

Claims (1)

[Claims] One end of the AC input of the diode bridge is connected through the load,
The other end is directly connected to a single-phase AC power supply, and a power MO8FET is connected to the DC output of the diode bridge.
Connect the drain and source of the power MO8F
A fixed resistor is connected between the drain and the gate of the ET, and a bias circuit including a plurality of fixed or variable resistors and a diode is connected between the gate and the source, and a plurality of fixed or variable resistors are connected between the gate and the source. The output transistors of a plurality of photocubes 2 are connected in parallel to a bias circuit including a diode and a diode, and the voltage applied to the load is varied by switching the current flowing through the input diode of the photocoupler. AC voltage variable device.