JP3268725B2 - DC voltage detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply, and more particularly to an effective DC voltage detector applicable to a power supply which needs to insulatedly detect a DC voltage signal proportional to a DC voltage.

[0002]

2. Description of the Related Art Conventionally, this type of detecting means is implemented by a circuit as shown in FIG. That is, the DC voltage Vin is divided by the resistors 30 and 31 as the first detector, and the DC voltage Vin is non-insulated to output Vout. Alternatively, means for dividing a DC voltage Vin by a voltage divider 32 as a second detector and converting the divided signal into a frequency (hereinafter referred to as a V / F converter 33), which is implemented by a circuit as shown in FIG. , A frequency proportional to the voltage is obtained, the frequency is insulated by a photocoupler 34, and a voltage proportional to the frequency is generated by means for converting the frequency into a DC voltage (hereinafter referred to as an F / V converter 35). , The DC voltage Vin is detected and the DC output Vout is output.

FIG. 6 shows an application example of the prior art. 6 is a device that receives AC power from an AC input 51 and supplies power to an AC power load 58. As a specific example, an induction motor control device (VVVF
Device), an uninterruptible power supply (UPS device), and the like. The power conversion device 50 is a device that normally controls an AC power by converting an input AC voltage 51 into a direct current 55 rectified by a rectifier 52 into an alternating current by an inverter 56 and controlling the converted alternating current voltage 59. DC voltage detector 5
Reference numeral 4 denotes a DC voltage detector that detects the DC voltage 55 output from the rectifier 52 and supplies a detection voltage signal Vout to an inverter controller 57. Thereby, the inverter 56 is controlled at the time of abnormality such as when the voltage of the AC input decreases or rises, and the inverter 56 is protected from the abnormality of the input voltage.

[0004]

However, in the above prior art, the voltage to be detected and the output detection signal are non-insulated in the first DC voltage detector. For example, in the power converter 50 shown in FIG. The potential of the controller 57 becomes the same as the potential of the rectifier 52, a high voltage such as several hundred volts is applied to the inverter controller 57 operating at a low voltage, and the inverter controller has a high withstand voltage such as several hundred volts. Semiconductors are required. Further, the second detector requires a large number of parts to be realized,
There is a problem that expensive parts such as the / F and F / V converters are required.

[0005]

According to a first aspect of the present invention, there is provided an insulating transformer having one primary winding and two secondary windings for insulating a detected voltage and a detected output voltage signal, and a primary winding of the insulating transformer. A first shunt resistor on the wire side, a diode bridge for alternately switching the current of the primary winding of the isolation transformer, and a diode bridge for switching on and off and alternately switching the current of two secondary windings of the isolation transformer. Two switches, an oscillator that drives the two switches, a stabilized DC voltage source that keeps the secondary voltage of the isolation transformer constant, and an output detection voltage signal that is provided at the outputs of the two switches and detects the output current. Is a DC voltage detector including a second shunt resistor for converting the voltage to a DC voltage.

The two switches are alternately switched to alternately switch the two winding currents on the secondary side of the insulating transformer, so that the DC current on the primary side of the insulating transformer is switched. The current of the primary winding of the insulating transformer is switched, and the current reduced by the first shunt resistor due to the detected voltage flows through the diode bridge to the primary side of the insulating transformer in a positive polarity and a negative polarity. By alternately switching the primary current of the insulating transformer, magnetic saturation of the insulating transformer is prevented, and the current is transmitted from the primary side to the secondary side. At this time, a current transmission error due to the exciting current of the insulating transformer is reduced by keeping the exciting current of the insulating transformer constant by the stabilized DC voltage source. The current transmitted to the secondary side of the insulating transformer is converted into a voltage by the second shunt resistor, and a DC output is obtained.

According to a second aspect of the present invention, there is provided an insulating transformer having two primary windings and two secondary windings for insulating a detected voltage and a detected output voltage signal, and a first winding provided on a primary winding side of the insulating transformer.
A shunt resistor, a diode for alternately switching the current of the primary two windings of the insulating transformer, and two switches for turning on and off and alternately switching the current of the two secondary windings of the insulating transformer. An oscillator that drives the two switches, a stabilized DC voltage source that keeps the secondary voltage of the isolation transformer constant, and an output current that is provided at the outputs of the two switches and that converts the output current to an output detection voltage signal. A DC voltage detector comprising a second shunt resistor.

[0008] The two switches are alternately switched to alternately switch the two winding currents on the secondary side of the insulation transformer, so that the DC current on the primary side of the insulation transformer is switched to two windings. The current of the primary winding of the insulating transformer is alternately switched to the two windings, and the current reduced by the first shunt resistor by the detected voltage flows alternately to the primary winding of the insulating transformer by the diode. .
By alternately switching the primary current of the insulating transformer to the two windings, magnetic saturation of the insulating transformer is prevented, and the current is transmitted from the primary side to the secondary side. At this time, a current transmission error due to the exciting current of the insulating transformer is reduced by keeping the exciting current of the insulating transformer constant by the stabilized DC voltage source. The current transmitted to the secondary side of the insulating transformer is converted into a voltage by the second shunt resistor, and a DC output is obtained.

[0009]

FIG. 1 shows a first embodiment of the present invention.
This will be described below. The present invention relates to a shunt resistor 2 and a shunt resistor 1 shown in FIG.
5, an insulating transformer 7 for electrically insulating the shunt resistor 2 and the shunt resistor 15 from each other, and two secondary windings 7b and 7c of the insulating transformer 7 being connected to a secondary-side electric circuit of the insulating transformer 7. The switch 11 and the switch 1 that perform on / off operations to alternately flow the current I2 flowing through the switch 18
2, an oscillator 13 for turning on and off the switch 11 and the switch 12 alternately, and an operation of the switch 11 and the switch 12 for alternately switching the current I1 flowing through the primary side electric circuit 17 of the insulating transformer 7. , A DC voltage source 10 and a transistor 14 as means for stabilizing an applied voltage on the secondary side of the insulating transformer, and a secondary side DC voltage source 9 of the insulating transformer 7. It is a feature.

In FIG. 1, a switch 11 and a switch 12 are alternately turned on and off by an oscillator 13. When the switch 11 is off and the switch 12 is on, the current I2 supplied by the DC voltage source 9 and flowing through the current reducing resistor 8
Flows through the secondary winding 7b of the insulating transformer 7 and flows through the shunt resistor 15. On the other hand, when the switch 11 is turned on and the switch 12 is turned off, the current I2 supplied from the DC voltage source 9 and flowing through the current reducing resistor 8 flows through the secondary winding 7c of the insulating transformer 7 and the shunt resistor Flow 15 By turning on and off the switches 11 and 12, the voltage V72 of one secondary winding 7b of the insulating transformer 7 is switched to the voltage V73 of the other winding 7c. By switching the voltage applied to the secondary winding of the insulating transformer 7 from the windings 7b to 7c, the voltage V of the primary winding 7a of the insulating transformer 7 is changed.
71 switches from positive polarity to negative polarity.

The voltage V7 of the primary winding 7a of the insulating transformer 7
When 1 is positive, the cathode of the diode 3 has a positive polarity and the anode of the diode 6 has a negative polarity, so that the diodes 3 and 6 do not conduct and the diodes 4 and 5 conduct. On the other hand, when the voltage V71 of the primary winding 7a of the insulating transformer 7 is negative, the cathode of the diode 4 has a positive polarity, and the anode of the diode 5 has a negative polarity. And the diode 6 conducts. A current proportional to the DC input voltage Vin reduced by the shunt resistor 2 due to the switching of the diode flows through the primary winding 7a of the transformer 7, and the DC is applied to the secondary windings 7b and 7c without magnetic saturation of the transformer 7. A current proportional to the input voltage Vin flows. The secondary winding current of the transformer 7 flowing in proportion to the DC input voltage Vin is guided to the shunt resistor 15 by the switches 11 and 12, and the shunt resistor 15
Is converted to a DC output voltage Vout and output as a voltage proportional to Vin.

Here, the DC voltage source 10 has a purpose of keeping the voltages V72 and V73 of the secondary windings 7b and 7c of the transformer 7 constant and keeping the exciting current of the transformer 7 constant. The base of the PNP transistor 14 is connected to the anode side of the shunt resistor 15, and the voltage V of the secondary windings 7b and 7c of the transformer 7 due to the voltage fluctuation of the shunt resistor 15 is changed.
72 and V73 are compensated. For example, when the voltage of the shunt resistor 15 becomes zero while the switch 11 is on,
The base current of the transistor 14 becomes maximum, the transistor 14 becomes fully conducting, and the collector-emitter voltage becomes zero if the semiconductor voltage drop is ignored.
In this state, the voltage V73 of the secondary winding 7c of the transformer 7 becomes equal to the voltage of the DC voltage source 10. On the other hand, switch 1
When 1 is on, the voltage of the shunt resistor 15 is, for example, 1
If the voltage is 0 V, the base current of the transistor 14 decreases and the transistor 14 becomes unsaturated,
The emitter-to-emitter voltage, if we ignore the semiconductor voltage drop,
10V. In this state, the voltage V73 of the secondary winding 7c of the transformer 7 becomes equal to the voltage of the DC voltage source 10 as described above. By keeping the exciting current constant, the current flowing through the transformer 7 becomes a value proportional to Vin, and the output voltage Vo
ut becomes a value proportional to the input voltage Vin. That is,
If the turns ratio of the transformer 7 is one to one, the output voltage Vout
Is the ratio of the resistance of the shunt resistor 15 to the resistance of the shunt resistor 2 and is proportional to the input voltage Vin.

Next, an embodiment of the second invention will be described with reference to FIG. The present invention includes a shunt resistor 2 and a shunt resistor 15 for dividing the DC voltage 1 shown in FIG.
An insulating transformer 77 for electrically insulating the shunt resistor 2 from the shunt resistor 15 and two secondary windings 77c and 77d of the insulating transformer 77 flow through the secondary-side electric circuit 18 of the insulating transformer 77. A switch 11 and a switch 12 for performing an on / off operation in order to allow the current I2 to flow alternately; an oscillator 13 for turning on and off the switch 11 and the switch 12 alternately;
Diodes 78 and 79 for alternately switching the current I1 flowing in the primary side electric circuit 17 of the insulating transformer 77 by the operation of the switch 12 and the DC voltage of means for stabilizing the applied voltage on the secondary side of the insulating transformer 77 It is characterized by comprising a power source 10, a transistor 14, and a secondary DC voltage source 9 of the insulating transformer 77.

In FIG. 2, the switch 11 and the switch 12 are alternately turned on and off by the oscillator 13. When the switch 11 is off and the switch 12 is on, the current I2 supplied by the DC voltage source 9 and flowing through the current reducing resistor 8
Flows through the secondary winding 77c of the insulating transformer 77 and flows through the shunt resistor 15. On the other hand, when the switch 11 is on and the switch 12 is off, the current I2 supplied from the DC voltage source 9 and flowing through the current reduction resistor 8
Flows through the secondary winding 77d and flows through the shunt resistor 15. By turning on and off the switches 11 and 12, the voltage V of one secondary winding 77c of the insulating transformer 77 is changed.
From 83, the voltage is switched to the voltage V84 of the other winding 77d.
The voltage applied to the secondary winding of the insulating transformer 77 is
By switching from c to 77d, the isolation transformer 7
The voltage of the primary winding 7 changes from the positive polarity to the negative polarity in the winding 77a. Further, the voltage of the winding 77b switches from negative polarity to positive polarity.

When a positive voltage is applied to the primary winding 77a of the insulating transformer 77, the cathode of the diode 78 has a positive polarity, and the cathode of the diode 79 has a negative polarity. 79 conducts. On the other hand, when a positive voltage is applied to the primary winding 77b of the primary winding 77b of the insulating transformer 77, the cathode of the diode 79 has a positive polarity, and the cathode of the diode 78 has a negative polarity. Does not conduct, and the diode 78 conducts. A current proportional to the DC input voltage Vin reduced by the shunt resistor 2 due to the switching of the diode flows through the primary winding 77a or 77b of the transformer 7, and the transformer 77 does not magnetically saturate and the secondary windings 77c and 77d , A current proportional to the DC input voltage Vin flows. DC input voltage Vin
The secondary winding current of the transformer 77 flowing in proportion to the current is guided to the shunt resistor 15 by the switches 11 and 12, and the DC output voltage Vou is output by the shunt resistor 15.
t is output as a voltage proportional to Vin.

Here, the DC voltage source 10 is connected to the voltages V83 and V84 of the secondary windings 77c and 77d of the transformer 77, respectively.
To keep the exciting current of the transformer 77 constant. By connecting the base of the PNP transistor 14 to the anode side of the shunt resistor 15, the shunt resistor 1
5, secondary windings 77c, 7
The voltage V83 and V84 of 7d are compensated. For example, when the voltage of the shunt resistor 15 becomes zero while the switch 11 is on, the base current of the transistor 14 becomes maximum, the transistor 14 becomes fully conductive, and the voltage between the collector and the emitter becomes the semiconductor voltage drop. If you ignore, it becomes zero. In this state, the secondary winding 7 of the transformer 77 is
The voltage V83 of 7d becomes equal to the voltage of the DC voltage source 10. On the other hand, when the switch 11 is on, the shunt resistor 1
If the voltage of 5 is, for example, 10 V, the base current of the transistor 14 decreases, the transistor 14 becomes unsaturated, and the collector-emitter voltage becomes 10 V if the semiconductor voltage drop is ignored. In this state, the voltage V84 of the secondary winding 77d of the transformer 77 becomes equal to the voltage of the DC voltage source 10 as described above. By keeping the exciting current constant, the current flowing through the transformer 77 becomes a value proportional to Vin, and the output voltage Vout becomes a value proportional to the input voltage Vin. That is, the winding ratio of the transformer 77 is 1
If the ratio is one, the output voltage Vout is the input voltage Vi based on the ratio of the resistance of the shunt resistor 15 to the resistance of the shunt resistor 2.
n.

[0017]

FIG. 3 shows an embodiment of the present invention. The embodiment of FIG. 3 is different from the first embodiment of FIG.
0 to two series diodes 20 and switch 11
And 12 are changed to a field effect transistor.
When two series diodes 20 are used as the DC voltage source 10, a voltage of about 1.4 V is generated between the terminals of the two series diodes 20 when the transistor 14 is turned on.
Further, 0.7 V is applied between the emitter and the base of the transistor 4.
Occurs, and a voltage of about 0.7 V is generated by using a field effect transistor for the switch 11 or the switch 12. In this state, the secondary winding 7b or 7c of the transformer 7
Is applied with a stable DC voltage of 2.8V. Other operations are the same as in the embodiment of FIG. 1, and if the winding ratio of the transformer 7 is 1: 1, the output voltage Vout is the input voltage Vin based on the ratio of the resistance of the shunt resistor 15 to the resistance of the shunt resistor 2.
Is proportional to By using a field effect transistor for the switches 11 and 12, the switches 11 and 12 can be reduced to several tens.
It can operate at a high frequency of 0 kHz, and the transformer 7 can be downsized.

[0018]

As described above, the diode bridge 18 for switching the DC voltage to the primary side, and the switch 1 on the secondary side of the transformer 7 having one primary winding and two secondary windings.
By providing 1 and 12 and switching at a high frequency of about 100 kHz by the oscillator 13, it is possible to reduce the size of the insulating transformer, and to form an insulated DC voltage detection circuit with a simple configuration with a very small number of parts and a low cost. .

[Brief description of the drawings]

FIG. 1 is a circuit according to an embodiment of the first invention.

FIG. 2 is a circuit according to an embodiment of the second invention.

FIG. 3 is a circuit diagram of an embodiment of the first invention.

FIG. 4 is a basic circuit of a first example of the related art.

FIG. 5 is a basic circuit of a first example of the related art.

FIG. 6 illustrates an application of an embodiment of the present invention.

[Explanation of symbols]

 1 DC voltage to be detected Vin 2,15 Shunt resistor 3,4,5,6,78,79 Diode 7,77 Insulation transformer 7a Primary winding 7b, 7c Insulation transformer 7 Secondary winding 8 Reduction Current resistor 9 DC voltage source 10 Stabilized DC voltage source 11, 12 Switch 13 Oscillator 14 Transistor 17, 19 Electrical path 18 Diode bridge 20 Two series diodes 21, 22 Field effect transistor 23 Detection output signal 50 Power converter 51 Inverter 77a, 77b Primary winding of the insulation transformer 77 77c, 77d Secondary winding of the insulation transformer 77

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-250704 (JP, A) JP-A-4-17297 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 19/165 G05F 1/10 301 H02M 1/00

Claims (2)

(57) [Claims] An insulation transformer having one primary winding and two secondary windings for insulating a voltage to be detected and a detection output voltage signal; a first shunt resistor on a primary winding side of the insulation transformer; A diode bridge for alternately switching the current of the primary winding of the isolation transformer, two switches for turning on and off and alternately switching the current of two secondary windings of the isolation transformer, and driving the two switches. Oscillator, a stabilized DC voltage source for keeping the secondary voltage of the isolation transformer constant, and a second shunt resistor provided at the outputs of the two switches and converting the output current to an output detection voltage signal DC voltage detector. 2. An insulating transformer having two primary windings and two secondary windings for insulating a voltage to be detected and a detection output voltage signal, and a first shunt resistor on a primary winding side of the insulating transformer. A diode for alternately switching the current of two primary windings of the insulating transformer, two switches for turning on and off and alternately switching currents of two secondary windings of the insulating transformer, and the two switches. , A stabilized DC voltage source for keeping the secondary voltage of the insulating transformer constant, and a second shunt provided at the outputs of the two switches and converting the output current to an output detection voltage signal DC voltage detector consisting of a resistor.