JPS6244367Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is used, for example, in a feedback control device or a DC voltage control device, and detects a DC high voltage in the main circuit, and applies a voltage proportional to the magnitude of this DC high voltage to the main circuit. This invention relates to improvements in insulators for detecting voltage generated in isolated control circuits.

FIGS. 1 and 2 are circuit diagrams showing different examples of this type of conventional voltage detection insulator. That is,
In FIG. 1, transistors 2, 3, resistors 4, 5, 6, diodes 7, 8, 9, and a DC power supply 10 are connected to the input winding of an oscillation transformer 1, and a self-excited oscillation circuit is constructed by these. ing. On the other hand, each output winding 11, 12, 13, 14 of the oscillation transformer 1
A square wave alternating current voltage is generated, and this voltage causes transistors 15, 16, 17, 18, 19, 2
0, 21, and 22 are configured to turn on and off. In addition, a high DC voltage V of the main circuit (not shown) is detected at the input terminal, and this detected voltage V is connected to the resistor 2.
Transistors 15, 17 and 16, 18 are alternately switched by the voltage divided by voltages 5 and 26, thereby supplying voltage to the primary winding of an isolation transformer 27. The induced electromotive force on the primary side of the isolation transformer 27 is alternately switched between the transistors 19, 21 and 20, 22, integrated by the smoothing resistor 37 and the smoothing capacitor 38, and transmitted to the load 28. It's summery. Note that the transistors 15, 17,
19 and 21 are turned on and off at the same time. Oscillation transformer 1 and isolation transformer 2 in the diagram
The black dots shown at 7 indicate the polarity of the windings, and 29 to 36 indicate stabilizing resistors. In such a configuration, the detected voltage V is divided by the resistors 25 and 26 and supplied to the isolation transformer 27, and a voltage proportional to the turns ratio of the isolation transformer 27 is supplied to the load 28.

However, since the oscillation transformer 1 used in the voltage detection insulator with this configuration generates a square wave AC voltage, it must use an iron core with square hysteresis characteristics, and is expensive because it is a ring-shaped sintered iron core. When used for high voltage, not only the withstand voltage of the isolation transformer 27 but also the oscillation transformer 1
The withstand voltage between the windings is also an issue.

Figure 2 shows that in order to solve this problem, the expensive oscillation transformer 1 is not used, and instead a photodiode is used.
Electrical isolation is achieved through optical coupling using phototransistors, making it possible to create a voltage detection insulator with high withstand voltage and low cost. That is, in FIG. 2, when a DC voltage is applied to the input terminals 41 and 42 so that the terminal 41 becomes the anode, the oscillator 43 causes the photodiode 44 to be energized at the oscillation frequency of the oscillator 43, so the phototransistor 45 operates at the oscillation frequency. The switching is repeated. When the phototransistor 45 is turned on and the transistor 46 is turned on, a voltage obtained by dividing the detection voltage V by the resistors 48 and 49 is applied to the primary winding of the isolation transformer 47, and a voltage proportional to the turns ratio of the isolation transformer 47 is applied. is induced on the secondary side of the isolation transformer 47, rectified by the diode 50, and applied to the load 51. The resistors 52 and 53 are used to stabilize the phototransistor 45 and the transistor 46, and the capacitor 54 is used to keep the voltage applied to the resistor 49 constant. Diode 55 and constant voltage diode 5
6 suppresses the back electromotive force generated on the primary side of the isolation transformer 47 when the transistor 46 is turned off;
This is to prevent the transistor 46 from being destroyed. The capacitor 57 is for smoothing the voltage. Next, when the phototransistor 45 and the transistor 46 are off, a voltage proportional to the turns ratio of the sum of the forward voltage drop of the diode 55 and the Zener voltage of the voltage regulator diode 56 is the secondary voltage of the isolation transformer 47. Although induced in the opposite phase,
This is blocked by diode 50.

Since the phototransistor 45 used in FIG. 2 has a larger amplification factor than the general transistor 46,
The equivalent capacitance between the base and collector increases. Therefore, when used in a circuit where the collector potential fluctuates, the switching speed becomes slow.
An example of this will be explained with reference to FIGS. 3 and 4. That is, the current IF shown in FIG. 4 flows from the oscillation circuit 61 shown in FIG. 3 to the photodiode 62, and the current IF shown in FIG.
A phototransistor 6 of a grounded emitter circuit consisting of
A voltage VOUT is output between the emitter and collector of No. 3. As is clear from FIG. 4, the off time of the phototransistor 63 increases, and the oscillation circuit 6
1 frequency cannot be increased. Therefore, in order to reduce the output ripple in the insulator shown in Fig. 2, it is necessary to increase the capacitance of the capacitor 57, but on the other hand, increasing the capacitance has the disadvantage that the response of the insulator becomes slower. .

This idea was made in view of these circumstances, and the purpose is to provide a voltage detection isolator that can reduce the filter time constant and speed up the response time by configuring it to increase the chopper frequency. do.

Examples of this invention will be described below with reference to the drawings. FIG. 5 is a circuit diagram showing an embodiment of this invention. Only the points different from FIG. 2 will be explained, and the same parts as in FIG. 2 will be given the same reference numerals and their explanation will be omitted. That is, a resistor 68 and diodes 69, 7 are connected between the input terminal 41 and the input terminal 42.
0 is connected in series, a capacitor 71 is connected in parallel to the diodes 69 and 70, and the diode 69
The collector of the phototransistor 45 (connected to the collector of the transistor 46 in FIG. 2) is connected to the connection point between the resistor 49 and the capacitor 71, and the diode 72 is connected in series with the resistor 49.

The operation of such a configuration will be explained below with reference to FIG. That is, in FIG. 5, when a DC voltage is applied to the input terminals 41 and 42 so that the input terminal 41 becomes the anode, the photodiode 44 is repeatedly energized by the oscillator 43, and as a result, the phototransistor 45 and the transistor 4
6 repeats switching. The collector potential of the phototransistor 45 is lower than the input DC voltage by the resistor 68.
This is the voltage drop in the diode forward direction obtained by the current flowing through the diodes 69 and 70 via the diodes 69 and 70.
Since the forward voltage drop of the diodes 69 and 70 is approximately constant regardless of the magnitude of the forward current, it is approximately constant regardless of fluctuations in the input voltage. Therefore, the conduction current IF of the photodiode 44 and the collector of the phototransistor 45 shown in FIG.
As is clear from the emitter voltage VCE, the off time of the phototransistor 45 is shortened, and the oscillation frequency can be increased. transistor 4
6 is on, the voltage applied to the primary side of the isolation transformer 47 is the sum of the voltage drops across the resistor 48 and the diode 72, which are divided by the resistors 48 and 49 and the diode 72. A voltage proportional to the primary voltage and the turns ratio of the isolation transformer 47 is induced on the secondary side of the isolation transformer 47, and the induced electromotive force is rectified by the diode 50, smoothed by the capacitor 57, and given to the load 51. . Further, when the transistor 46 is off, the secondary voltage of the isolation transformer 47 is blocked by the diode 50, and the secondary voltage of the isolation transformer 47 is blocked by the diode 50.
A discharge voltage of 7 is applied to the load 51. Note that the diode 72 acts to correct the voltage drop caused by the diode 50 in the output voltage.

FIG. 7 is a circuit diagram showing another embodiment of this invention. In the circuit diagram shown in FIG. 5, only one diode 50 is inserted on the secondary side of the isolation transformer 47, so rectification is performed only for half a cycle. The ripple is made smaller than the one that had a large ripple. That is, a series circuit of resistors 73, 74 and a diode 75 is connected between the input terminals 41, 42, and the neutral point tap on the primary side of the isolation transformer 47 is connected to the resistor 73, 74.
At the same time, one end of the capacitor 76 is connected to this connection point, and the capacitor 76
The other end is connected to the input terminal 42. Also, oscillator 4
Connect another photodiode 77 to the output side of 3,
The collector of the phototransistor 78 that operates thereby is connected to the connection point between the resistor 68 and the diode 69, and the base and collector of the transistor 79 are connected between this emitter and one end of the primary winding of the isolation transformer 47. . Resistors 80 and 81 are connected between the base and input terminal 42 of phototransistor 78 and between the emitter and input terminal 42, respectively. Connect the neutral point tap of the secondary winding of the isolation transformer 47 to the smoothing capacitor 57 whose one end is connected to the diode 50, and the other end of the smoothing resistor 51, and connect it to one end of the secondary winding of the connecting transformer 47. Another diode 82 is connected between the anode of diode 50.
Connect.

The operation of the voltage detection insulator constructed as described above will be explained below with reference to FIG. That is, when a DC voltage is applied to the input terminals 41 and 42 so that the input terminal 41 becomes the anode, the phototransistors 78 and 45 are assumed to repeatedly switch with a phase shift of 180 degrees as shown in FIG. . At this time, the transistor 79 is turned on when the phototransistor 78 is turned on, and the transistor 46 is turned on.
turns on when the phototransistor 45 is on. The voltage applied between the neutral point of the isolation transformer 47 and the terminal 42 is applied to the resistors 73 and 74 and the diode 7.
5, and the voltage generated in the secondary winding of the isolation transformer 47 is the sum of the voltage drops across the resistor 74 and the diode 75, which are divided by 5, and the voltage generated in the secondary winding of the isolation transformer 47 is the voltage divided by
A voltage proportional to the turns ratio of the isolation transformer 47 is generated in different directions of the induced power depending on whether the phototransistor 78 or the phototransistor 45 is turned on. At this time, the collector potentials of the phototransistors 78 and 45 are constant because they utilize the input DC voltage as in the previous embodiment and are the voltage drop in the forward direction of the diodes 69 and 70 via the resistor 68. The phototransistor 78,
The switching time of 45 is shortened, and the switching frequency can be increased. The voltage generated in the secondary winding of the isolation transformer 47 is full-wave rectified by the diodes 50 and 82, smoothed by the capacitor 57, and applied to the load 51.

Note that this invention is not limited to the above-mentioned embodiments, and can be implemented with the following modifications. A plurality of diodes 72 provided in the embodiment of FIG. 5 may be connected in series depending on the turns ratio of the isolation transformer 47, etc. In addition, various modifications can be made without changing the gist of the invention.

According to this invention described above, the input DC voltage is used as the collector potential of the phototransistor, and the voltage drop in the forward direction of the diode is used.
Since the forward current of the diode is almost constant regardless of the magnitude, the collector potential of the phototransistor can be kept constant regardless of fluctuations in the input DC voltage, which shortens the switching time of the phototransistor. It is possible to provide a voltage detection insulator that can increase the chopper frequency, reduce the capacitance of the capacitor that smooths the waveform of the input voltage applied to the load, and increase the response speed.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams of different conventional voltage detection insulators, Figure 3 is a circuit diagram for explaining the shortcomings of Figure 2, and Figure 4 is a circuit diagram of the photodiode and photodiode of Figure 3. Figure 5 is a circuit diagram showing an embodiment of the voltage detection insulator according to this invention; Figure 6 is a diagram of the current waveform of the photodiode and the current waveform between the collector and emitter of the phototransistor; FIG. 7 is a circuit diagram showing another embodiment of the voltage detection insulator according to the present invention, and FIG. 8 is a timing diagram of the phototransistor shown in FIG. 7. 41, 42... Input terminal, 43... Oscillator, 4
4,77...photodiode, 45,78...phototransistor, 46,79...transistor,
47...Isolation transformer, 50, 69, 70, 7
5, 82...Diode, 51-53, 68, 7
3, 74, 80, 81...Resistor, 57...Smoothing capacitor.

Claims (1)

[Scope of utility model registration request] In a voltage detection insulator that chops a DC input voltage by the switching action of a phototransistor and supplies the DC voltage to a load via an isolation transformer, the collector of the phototransistor includes:
A voltage detection insulator configured to provide a voltage obtained by dividing the DC input voltage by a voltage drop in a forward direction of a diode.