JP3302779B2 - I / O isolated current / current converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input / output insulated type current / current converter, and more particularly to an input / output insulated type current / current converter capable of signal isolation without a power supply without preparing an independent insulated power supply (auxiliary power supply). It relates to a current converter.

[0002]

2. Description of the Related Art Conventionally, most of industrial instruments such as an ON-line process instrument and the like have a microcomputer incorporated therein. A digital circuit incorporates arithmetic control by the microcomputer into components constituting the instrument. The signal from the digital circuit is DA
A signal is received from a sensor or other load attached to the end of the analog output cable via a converter.

In this type of industrial equipment, even if one end of a load is connected to a certain potential, the influence is not caused on the instrument main body side (transmission or reception side). An input / output insulation type current / current converter is interposed at a predetermined position between the loads.

[0004] Further, even in a device in which a digital circuit and an analog circuit are mixed in the above-mentioned instrument and a signal is received via a DA converter or an AD converter, the influence of noise on the receiving side or the transmitting side is cut off. For this purpose, an input / output insulated current / current converter is provided on the input / output circuit side of the analog circuit. For this type of input / output insulated current / current converter, it is common to use a converter capable of signal isolation without a power supply without preparing an independent insulated power supply for convenient system expansion. .

The circuit configuration of such a converter will be briefly described with reference to FIG.
A self-excited DC-DC converter composed of r ₁₁ , Tr ₁₂ , R ₁₁ , and R ₁₂ is configured, while a rectifier is configured on the output side by D _{11 to} D ₁₄ . In this configuration, it oscillates the addition of a DC signal (input current) to the input side in accordance with the principles of the DC-DC converter, and the Ic ₁₁ when the transistor Tr ₁₁ is ON, Ic ₁₂ when transistor Tr ₁₂ is ON is respectively trans The current flows through the CT windings N ₁₁ and N ₁₂ . At this time, if a transistor having a high current amplification factor is used for the transistors Tr ₁₁ and Tr ₁₂ , almost Is (input current) = Ic
Flows through the core and is transmitted to the secondary side. Therefore, a current almost equal to the input current Is can be taken out by rectifying and taking out this current as necessary.

[0006]

However, in the above circuit, when the input current becomes 4 mA or less, particularly when the input current becomes 1.8 mA or less as shown in FIG. The output current obtained in the above is likely to be unstable. Therefore, in the above circuit, the current width range that can be converted with high accuracy is 1.8 mA.
It is limited to the above.

In the above circuit, the transistors Tr ₁₁ and Tr
_In order to take a configuration that turns on alternately with ₁₂ , in other words, T
duty ratio is ON / OFF 50% without ON pulse width of the ON pulse width and Tr ₁₂ of the r ₁₁ overlap each other. Therefore, at the rising and falling portions of the pulse, settling (time delay) occurs due to the influence of the inductance of the transistor or the transformer, and as a result, the output current on the secondary side of the transformer is smaller than the input current on the primary side. This makes it difficult to perform high-precision current / current conversion.

[0008] In view of the above technical problems, the present invention has a low current of 4 mA or less, especially 1 mA or less, on the input signal side.
It is an object of the present invention to provide an input / output insulated current / current converter capable of performing current / current conversion with high accuracy and high linearity even with a current of 0 mA or more.

[0009]

According to the present invention, an upper circuit connected to the upper potential side of the input current and a lower circuit connected to the lower potential side are connected in series, and the upper circuit is connected to the upper circuit side. A constant voltage positive and negative power supply generating means, a rectangular wave generating means for generating a rectangular wave pulse based on one of the positive / negative power supply from the generating means, and 180 ° from the rectangular wave.
Means for generating two modulation outputs in which the Hi-level side pulses having different phases overlap each other are provided. On the other hand, the current. In addition to the transformer and the rectifier for the secondary side current, the modulation output generated on the upper circuit side is used as the current. The present invention is characterized in that a pair of push-pull MOSFETs is provided in a transformer.

[0010]

According to the present invention, the higher-order circuit, which is higher in potential, has the signal DC current (1 to 20) obtained from the input terminal.
mA), a positive and negative power source of a constant voltage is generated, and a square wave pulse oscillator and a pulse modulator are provided on the negative power source side, whereby two Hi-level side pulses 180 ° out of phase are overlapped with each other. Generate output. The two modulation outputs are added between the gates and sources of two P-CH enhancement MOSFETs, for example, on the lower circuit side, and the FET and the current transformer are driven to Push-PuLL, so that all of the input current is converted to the current transformer. (N: n = n: n), and the same current as the input current can be taken out to the secondary side of the current transformer. It is possible to obtain an insulated current-current converter capable of performing high-accuracy conversion even at the minimum input current value (1 mA or less) at which the oscillation circuit of (1) stably oscillates.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just.

FIG. 1 is a circuit diagram showing an input / output insulated current / current converter that does not use an insulated power supply (auxiliary power supply) according to an embodiment of the present invention. This conversion circuit connects the upper circuit 10 connected to the upper potential side of the input DC current and the lower circuit B connected to the lower potential side in series, and
On the side, a constant voltage (positive) power supply generating means 1 comprising resistors R ₁ and R ₂ and an output variable micropower voltage reference element IC _O , capacitors C ₁ and C _2, and a switch capacity voltage converter IC _1. Negative power supply generating means 2
When made from an oscillator IC ₂ resistors R _3, R ₅ condenser C _3, the rectangular wave generating means 3 for generating a square wave of 50% duty ratio based on the negative power supply -V _H, pulse modulation IC _3, the variable resistor 1 consisting of R ₄ and condenser C ₄
Means 4 for generating two modulated outputs having a phase shift of 80 °.

On the other hand, the lower circuit B side outputs the modulation output to the current. Transformer CT (turn ratio n: n = n: n) with P
A pair of P-channel MOSFE flowing in a ush-Pull
T (low ON resistance, cut-off time, gate-source voltage is low), current. It comprises a pair of rectifier diodes (Schottky diodes) RE ₁ and RE ₂ for rectifying the secondary current of the transformer CT, and a filter 5.

Next, the operation of the circuit will be described.
First, in the unsteady state where the input current starts to flow, the terminal
A pair of MOSFETTr ₁ in the lower part the circuit B when from outside the T ₁ starts to flow DC input current I _in, Tr ₂ are both for OFF, the electrolytic <br/> input current I _in the upper portion circuit 10 out flow through the condensers C _5. Next, the upper circuit 10
Oscillator IC ₂ normally oscillates and the lower MOSFET
Tr ₁ and Tr ₂ are driven and shift to a steady state. Constant and shifted to the steady state, the input current I _in is having flows stably, resistors R _1, R _2, and the voltage value by the voltage reference element ICO + V _H = 1.25 a _{(1 + R 2 / R 1} ) Voltage power supply is generated. The + V _H capacitor C ₁ from the power supply, C _2, with a voltage converter IC _1, + V _H 0 of the power supply
volt side i.e. the point E to generate a negative power supply -V _H. (Note the voltage value of -V _H is determined by the gate-source voltage value for the P-channel MOSFET is switched ON for use with the lower portion circuit B)

On this -V _H power supply, a rectangular wave with a 50% duty output is generated using an oscillator IC ₂ , a resistor R ₃ , and an R ₅ capacitor C _3, which consume a small amount of current. This rectangular wave is phase-shifted by 180 ° as shown in FIG. 2 by a pulse modulation circuit IC _{3 and a} variable resistor R ₄ and a capacitor C ₄ .
Pulse width modulation is performed by generating two pulse waves and changing the duty ratio so that the pulse widths on the Hi level side overlap each other. For example, the waveform at point A before modulation has a duty ratio of 50% and the Hi level is almost equal to the power supply voltage E.
LOW level is the minus power supply potential minus
A V _H. Then, the waveform at the point B and the waveform at the point C after the rectangular wave pulse is modulated are modulated so that the phase is shifted by 180 ° and the LOW level is narrowed by the time τ. The time τ is equal to the input current I _in on the upper circuit 10 side.
Output current I _out of the lower portion circuit B side to adjust the variable resistor R ₄ to be equal.

Points B and C are located in lower circuit B, respectively.
MOSFETTr₁, Tr_Two Gate G₁, G_Two Connected to
And Tr₁, Tr_Two Source S₁, S_Two Is drained to potential E
D 1, D_Two Is connected to the primary side of the transformer CT
You. The secondary side of the transformer CT is a rectifier diode RE.₁,
RE_Two And the load Re (0 to 250) through the filter 5.
Ω).

Therefore, according to such a circuit configuration, the upper part circuit
Since the entire input current I _in on the road 10 can be flowed through the primary side of the transformer CT by Push-Pull, an output current I _out equal to the input current can be taken _out on the secondary side of the transformer CT, and high accuracy can be obtained. Isolated current over-current conversion not only possible, even it is possible to convert even beyond 20mA with high accuracy from the oscillation start minimum current of the oscillator Ic ₂ Top section circuit 10. That is, specifically, FIG.
As shown in B, it is possible to provide a converter capable of converting an input current exceeding 1.8 mA or less and an input current exceeding 0.6 mA with high accuracy even if exceeding 20 mA.

[0018]

As described above, according to the present invention, the current / current conversion can be performed with high accuracy and high rectilinearity even with a weak current of 4 mA or less, particularly 1 mA or less on the input signal side. And so on.

[Brief description of the drawings]

FIG. 1 is an insulated power supply (auxiliary power supply) according to an embodiment of the present invention.
FIG. 3 is a circuit diagram showing an input / output insulated current / current converter that does not use a circuit.

FIG. 2 shows rectangular pulse waves at points A, B, and C shown in FIG.

FIG. 3 is a characteristic diagram of input and output currents of the converter shown in FIG.

FIG. 4 is a circuit diagram showing an input / output insulated current / current converter according to the related art.

[Explanation of symbols]

10 Upper circuit B Lower circuit 1 Constant voltage positive and negative power supply generating means 2 Square wave generating means 3, 4 Modulation output generating means CT Current. Transformer 5 Secondary current rectification means Tr ₁ , Tr _{2 A} pair of MOSFETs

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 19/00-19/32 H02M 3/28 H03F 3/38

Claims (1)

(57) [Claims] An upper circuit connected to an upper potential side of an input current and a lower circuit connected to a lower potential side are connected in series, and a positive and negative constant voltage is connected to the upper circuit side. Negative power supply generating means, rectangular wave generating means for generating a rectangular wave pulse based on either positive or negative power supply from the generating means, and Hi-level side pulses 180 ° out of phase with the rectangular wave overlap each other. Means for generating two modulation outputs are provided on the lower circuit side. In addition to the transformer and the rectifier for the secondary side current, the modulation output generated on the upper circuit side is used as the current. Push-Pu in transformer
An input / output insulated current / current converter characterized by having a pair of MOSFETs flowing at 11 l.