JPH0664090B2 - Current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a secondary output AC current, which is generated by intermittently transforming a detected current supplied to the primary side of a saturable transformer by a transistor switch, into a resistance element. Regarding a current detection device for detecting a current to be detected based on a voltage obtained by supplying,
A magnetic multi-vibrator constructed by combining a complementary FET switch with a saturable transformer is used to enable current detection with good characteristics by a small device with a simple configuration.

(Prior Art) Recently, a DC-DC converter using high-frequency switching, a PWM type small AC uninterruptible power supply, or the like has been widely used as a power supply for information processing equipment using a microcomputer. However, since these power supply devices require current detection such as output current or battery current for overcurrent protection, high efficiency, etc., an inexpensive small current detection device is required.

Therefore, in general, as a current detection device, a device in which a resistor is connected in series to a conducting wire through which a current flows and a voltage generated according to Ohm's law is read across the resistor to detect the value of the current is used. Since it has the simplest configuration and does not require any special adjustment and can easily detect current, it has been widely used in power supply devices with a relatively small power capacity such as a small DC constant voltage power supply. ing.

Further, in a high power power supply device and the like in which it is often necessary to insulate the detected circuit from the detection output circuit, it is often difficult to detect the current by inserting a resistor.Therefore, a DC transformer using a saturable magnetic core should be used. The advantages are that the required space is narrower than that of the current detector by inserting the resistor, the loss is less, and the detection circuit and the detection output circuit can be easily insulated. Therefore, it has been widely used in various fields as a current detector for a high power supply device.

(Problems to be Solved by the Invention) However, in the current detection device using the resistor insertion, when the current capacity of the power supply to be detected becomes large, the power consumed by the detection resistor becomes large. There is a problem in that the power efficiency of the device is lowered and it is difficult to miniaturize the resistor because it is necessary to process heat generated by the resistor.

In addition, a conventional current detection device using a DC transformer of a saturable magnetic core needs to use a plurality of saturable magnetic cores, an AC power supply for resetting the detection device, and a detection output. Therefore, there is a problem that only the current flowing in one direction can be detected because the current is taken out through the rectifier. Therefore, a conventional current detecting device using a DC transformer with a saturable magnetic core is used as a current detecting device for overcurrent protection and current control in an inverter device, an AC uninterruptible power supply device, etc., which have been widely used recently. Have many problems to be solved, such as downsizing of the detection device and bipolarization.

Among various current detection methods that have been conventionally used for high power, the current detection method that detects DC current or low frequency current in a non-contact manner is DC current transformer method using saturable magnetic core, saturable There are an instantaneous current detection method using a magnetic core, a current detection method using a Hall element and a magnetic core, a current detection method using a magnetic multivibrator, etc., each of which has good results and is used in various technical fields. However, in any of the methods, the conventional current detection device has many types and a large number of components, and many of them require complicated adjustment in order to maintain good characteristics of the device. With the miniaturization and cost reduction of power supply devices, the appearance of a small-sized, low-cost current detection device with a small number of component parts and a small number has been awaited.

(Means for Solving the Problems) An object of the present invention is to solve the above-mentioned conventional problems and to detect a direct current or a low-frequency alternating current for overcurrent protection or current limitation of a current device or the like. To provide a current detection device capable of detecting a direct current or a low-frequency alternating current with a lossless circuit and a detection output circuit in a non-contact state with an extremely simple circuit configuration using a magnetic core. is there.

In order to achieve the above-mentioned object, the present invention utilizes a phenomenon similar to that of a mixing amplifier circuit using a magnetic multivibrator circuit in principle, and a complementary field effect transistor (FET) is used as a switch element of the magnetic multivibrator circuit. ) Or a field effect transistor equivalent to a complementary type is used to effectively utilize the characteristics of the field effect transistor, so that the number of component parts is extremely small, the cost is excellent, the current detection device has a good linearity and a good operating range. Is to be realized.

That is, the current detection device of the present invention supplies a current to be detected to the primary winding of a transformer having a saturable magnetic core, and a resistance element is provided between one end of the secondary winding of the transformer and the ground potential. And a field effect transistor having a gate winding wound around the magnetic core and connected to the other end between the other end of the secondary winding and the DC phase source, and By connecting a circuit element that supplies a voltage having a polarity opposite to that of the DC voltage source to the secondary winding during the off period to the other end, the detected current supplied to the primary winding can be dealt with. The detected current is detected based on the voltage induced in the resistance element.

(Operation) Therefore, according to the present invention, a current detection device capable of performing non-contact current detection with low loss and excellent characteristics is realized by a simple circuit configuration, and a DC constant voltage power supply device, an inverter device, an AC It can be effectively applied to a power failure power supply device, a battery charging device, an electric motor control drive device, and the like.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

As described above, the present invention is, in principle, for example, "A Switching DC-to-AC Converter Having an Output.
Frequency Proportional to the DC Input Voltoge) ''
AIEE Transactions pt.1, vol.74, July 1955, pp.322〜2
4 or "An Improved Squ
are-Wave Oscillator Circuit) ”IRE Transaction on
Circuit Theory, vol.CT-4, Sept. 1957, pp.276-79 and other magnetic multivibrator circuits, for example, "The Magnetic Mixing Amplifier" I
EEE Transaction on Magnetics, Dec.1972, vol.MAG8, N
The same phenomenon as in the mixing amplifier circuit of o.4, pp.780 to 785 is used, but a complementary FET is used as a switching element of the magnetic multivibrator circuit, and
By effectively utilizing the characteristics of ET, the number of parts is extremely small,
The present invention realizes a current detecting device which is excellent in economical efficiency and has good linearity and operating range. An example of a basic circuit configuration of the current detecting device of the present invention is shown in FIG.

In the current detection circuit device of the basic configuration shown in FIG.
A transformer T ₁ is formed by passing a lead wire through the center hole of a small toroidal magnetic core I to form a primary winding N ₁ and winding a lead wire around an annular portion at a winding ratio of 1: n to form a secondary winding N _2. configured, as well as connecting the source electrode of FET ₁ and FET ₂ which form a complementary to each other at one end of the secondary winding N _2, FET ₁ and
Direct-current voltage sources + E and -E are connected to the drain electrode of the FET ₂ , respectively. Further, the gate electrodes of FET ₁ and FET ₂ are connected to a gate winding N _G , which is a secondary winding N ₂ wound with an appropriate winding ratio, to keep each FET in an ON state or an OFF state. To do so. Further, the secondary winding N ₂ and the other end connected to the resistor R, detects the resistor voltage drop E ₀ from the secondary current I ₂ appears to R, and its secondary current I ₂
The primary current I ₁ having a ratio of n: 1 can be detected.

In the current detection device of the present invention having such a basic circuit configuration, when the FET ₁ is in the ON state, a positive voltage is supplied from the DC voltage source + E to the secondary winding N ₂ via the FET _1, and The magnetic flux density in the toroidal magnetic core I increases according to the time integration of the positive voltage. When positive saturation is reached due to the increase in the manner in which the magnetic flux density in the toroidal magnetic core I increases, the gate
Driven by the transient vibration generated in the resonance circuit formed by the saturation inductance of N _G and the gate-source capacitance of the FET, the on / off state is switched between FET ₁ and FET ₂ ,
The on state commutates from FET ₁ to FET ₂ . As a result of the commutation in the ON state, the supply of the positive voltage from the DC voltage source + E via the FET ₁ is cut off, and the DC voltage source −E to the secondary winding N ₂ via the FET ₂ in the ON state. Is supplied with a negative voltage,
The magnetic flux density in the toroidal magnetic core I decreases according to the time integration of the negative voltage. When the magnetic flux density in the toroidal magnetic core I reaches negative saturation due to such a decrease, in the same manner as when the above-mentioned positive saturation is reached, conversely,
_The ON state is commutated from ₂ to FET ₁ , and then FET ₁
・ Between FET _{2 the} on / off state is repeated alternately and alternately.

In the circuit configuration shown in FIG. 1 in which ON / OFF state alternating inversion between FET ₁ and FET ₂ is repeated, if a toroidal magnetic core I having a small exciting current is used, the current flows through the gate winding N _G.
The gate winding I _G of the FET is significantly smaller than the primary and secondary currents I ₁ and I ₂ , and can be considered to be almost zero. Therefore, the primary winding N ₁ and the secondary winding N ₂ The equal ampere-turn law is established between the output resistor R and the primary current I ₁ between both ends of the output resistor R.
The output voltage E ₀ proportional to That is, except for one period during commutation in the on / off state, the equal ampere-turn law expressed by the following equation (1) is established with the holding magnetomotive force of the toroidal magnetic core I being F _C.

(N ₁ · I ₁ ) + (N ₂ · I ₂ ) + (N _G · I _G ) = F
_C (1) Then, the gate impedance of the FET has an extremely high value in a steady state excluding the transient state during commutation, and as described above, the gate current I _G is so small that it can be ignored, Further, if a magnetic core having a sufficiently small magnetomotive force is used, the primary windings N ₁ and N 2 follow the law of equal ampere-turn.
If the winding ratio to the next winding N ₂ is 1: n, the secondary current I ₂ is expressed by the following equation (2).

I ₂ = I ₁ / n (2) If the output resistance is R, the output voltage E ₀ is expressed by the following equation (3).

E ₀ = I ₁ · R / n (3) Then, while the FET ₁ is in the ON state, the secondary winding N ₂
The voltage applied is (E-E _0), the voltage applied to the secondary winding N ₂ during a period in which FET ₂ is in the on state (-
E-E ₀ ), and as described above, the secondary winding N ₂
Toroidal magnetic core I determined by the time integration of the voltage supplied to
The magnetic flux Φ inside is expressed by the following equation (4) or equation (5) depending on which FET is in the ON state.

While FET ₁ is on: When FET ₂ is on: Here, the winding voltage is constant, the magnetic flux Φ changes from the negative saturation magnetic flux −Φs to the positive saturation magnetic flux + Φs while the FET ₁ is on, and the magnetic flux Φ is positive while the FET ₂ is on. Since the saturation magnetic flux + Φs changes to the negative saturation magnetic flux −Φs, if the period during which the FET ₁ is on is (T ₁ ) and the period during which the FET ₂ is on is (T ₂ ), The following expressions (6) and (7) are established.

2Φs · N ₂ = (E−E ₀ ) · (T ₁ ) (6) −2Φs · N ₂ = (− E−E ₀ ) · (T ₂ ) (7) Therefore, each period (T ₁ ) and ( T ₂ ) is expressed by the above equations (6) and (7) as equations (8) and (9), respectively.

(T ₁ ) = 2Φs · N ₂ / (E−E ₀ ) (8) (T ₂ ) = 2Φs · N ₂ / (E + E ₀ ) (9) Further, the oscillation frequency f is expressed by the above formulas (8) and (8). It is expressed by the following expression (10) from 9).

f = 1 / {(T ₁ ) + (T ₂ )} = {E ² − (R · I ₂ ) ² } / 4 · E · Φs · N
₂ (10) Further, from the above-mentioned equation (4), it is understood that the change in the magnetic flux Φ becomes zero when E = E ₀ . Therefore, the theoretical operating range of the current detecting device having the first illustrated configuration with respect to the change of the primary current I ₁ is narrower than the range represented by the following equation (11).

E> E ₀ = I ₁ · R / n (11) Regarding the current detection device of the present invention having the first basic configuration shown in the above, which operates as described above, the detected output voltage E ₀ and the oscillation frequency with respect to the change of the primary current I ₁ The experimental results of measuring f are shown in FIG. In the experimental results shown in the figure, the change characteristic of the current detection output voltage E ₀ with respect to the change of the primary current I ₁ is:
It can be seen that good linearity is obtained, which is in good agreement with the above equation (3). Similarly, the oscillation frequency f with respect to the change of the primary current I ₁ depends on the denominator of the intermediate term {(T ₁ ) + (T ₂ )} in the equation (10), and the period required for commutation is actually Since they are added, the value will be slightly lower than the value determined by equation (10).

In the circuit configuration shown in FIG. 1, however, the saturation of the magnetic core I causes the FET ₁ and the FET ₂ acting as switch elements to repeatedly switch between the on / off states, and oscillation is sustained. The mechanism of on-state commutation between FETs that is repeatedly and alternately performed to sustain oscillation can be explained by the resonance phenomenon between the saturation inductance of the saturable magnetic core and the gate-source capacitance of the FET. That is, first, when the FET ₁ is in the ON state and the magnetic flux of the toroidal magnetic core I has not reached the saturation magnetic flux yet,
The internal resistance of the gate at ₁ is extremely high, and therefore FET ₁ is maintained in the ON state by the positive voltage supplied from the power supply voltage + E to the gate electrode through the FET _{1 in the} ON state and the gate winding _NG in order. However, when the magnetic flux Φ of the toroidal magnetic core I reaches the saturation magnetic flux Φs, the inductance value exhibited by the gate winding N _G sharply decreases, and a resonance circuit composed of a relatively small saturation inductance and the gate-source capacitance of the FET. Is formed, and the resonance of the circuit causes FE
The polarity of the gate voltage of T ₁ and FET ₂ is reversed, resulting in an on-state commutation between FET ₁ and FET ₂ . That is, since the gate current required to alternately switch a pair of FET switches is supplied by the resonance current when the magnetic core is saturated, it is during the on-state commutation of the FET switch pair.
The power consumed at the gate to drive the ET pair will be very low.

Further, since the FET used as the switch element in the current detection device of the present invention does not have the charge accumulation time as seen in the bipolar transistor, the oscillation frequency by switching the FET switch element can be set extremely high. Therefore, by setting the oscillation frequency to be extremely high, it is possible to easily reduce the size of the filter inserted in the current detection circuit in order to remove the noise appearing at the input and output ends when the switch is switched.

Next, in the basic circuit configuration shown in FIG.
Positive and negative voltages are supplied from the pair of voltage sources to the secondary winding of the current transformer via the FET switch, while the positive voltage is supplied by the single voltage source via the single FET. FIG. 3 shows an example of the configuration of the current detecting device of the present invention, which is adapted for practical use by supplying a negative voltage to the secondary winding of the current transformer. In the circuit configuration shown in FIG. 3, instead of the FET ₂ and the negative voltage source -E in the circuit configuration shown in FIG.
By connecting the series connection of the diode D and the small-sized transformer T ₂ acting as a choke coil in parallel with the FET ₁ , the same operation and effect as the circuit configuration shown in the first illustration can be obtained. That is, first, FET ₁ is in the ON state, the energy is positive current from the voltage source + E flows through the primary winding N ₃ of the transformer T ₂ stored in transformer T _2, then, FET ₁
Is turned off by the resonance in the resonance circuit of the saturation inductance of the magnetic core I and the capacitance between the gate and the source described above, a negative voltage is generated by inverting the positive voltage generated in the secondary winding N ₄ by the action of the diode D. 1 by winding N ₃ is supplied to the secondary winding N ₂ of the transformer T _1, the magnetic core I of the transformer T ₁ by the negative voltage reaches a negative saturation, FE
T ₁ is turned ON state again, just as in the circuit configuration of the first illustrated, so that the repeated alternating inversion of the on-off state is performed.

(Effects of the Invention) As is apparent from the above description, according to the present invention, various remarkable effects as described below can be obtained.

(1) It is possible to detect a direct current and a low-frequency alternating current in the form of a voltage drop that occurs in the resistor without contacting the circuit to be detected.

(2) Since the FET is used as the switching element for DC / AC conversion, the base resistance used in the conventional magnetic multivibrator using the bipolar transistor is unnecessary, and the number of constituent parts is reduced.

(3) Since the use of the FET does not cause non-linearity due to the base current, excellent current detection characteristics due to the output voltage can be obtained.

(4) Since the FET does not have the charge storage time as seen in a bipolar transistor, the switching frequency can be set high, and therefore the filter for removing switching noise can be easily miniaturized.

(5) Since a pair of complementary FETs or a circuit element having an equivalent function is used, the number of windings wound around the magnetic core of the DC-AC converting transformer can be reduced.

(6) Enhanced FET with current-voltage characteristics that rises from zero
By using, stable start-up and stable oscillation durability can be easily obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic configuration example of the current detection device of the present invention, and FIG. 2 is a characteristic curve diagram showing an example of output voltage characteristics and oscillation frequency characteristics with respect to changes in input current in the current detection device of the present invention. FIG. 3 is a circuit diagram showing another configuration example of the current detection device of the present invention. T ₁ , T ₂ …… Transformer, N ₁ , N ₃ …… Primary winding N ₂ , N ₄ …… Secondary winding _NG …… Gate winding FET ₁ , FET ₂ …… Field effect transistor R ...... Resistor, D ...... Diode

Claims (1)

[Claims] 1. A current to be detected is supplied to a primary winding of a transformer having a saturable magnetic core, and a resistance element is connected between one end of a secondary winding of the transformer and a ground potential. A field effect transistor having a gate winding wound around the magnetic core and connected to the other end is connected between the other end of the secondary winding and the DC voltage source, and the field effect transistor is turned off during the off period of the field effect transistor. By connecting a circuit element that supplies a voltage having a polarity opposite to that of the DC voltage source to the secondary winding, to the other end,
A current detection device, wherein the detected current is detected based on a voltage induced in the resistance element corresponding to the detected current supplied to the primary winding.