JPH048670Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial field of application> The present invention is a current/current converter using the principle of a single-stone forward converter type switching regulator.
The present invention relates to current isolators, and particularly to improvements that reduce insertion loss.

<Prior Art> Generally, detection signals of physical variables such as temperature, pressure, flow rate, etc. by sensors are converted into a unified DC signal of 4-20 mA. This converted signal is sent from the transmitting side to the receiving side and processed by an indicator or controller on the receiving side.

FIG. 1 is a circuit diagram illustrating the principle of a conventional single-stone forward converter type switching regulator. This circuit uses a switching transistor Q1 and an isolation transformer T as main components. The transformer T insulates the input terminals 1 and 2 and the output terminals 3 and 4, and the terminals 2 and 4 are selected as common terminals. The transformer T has a primary winding N1 on the input side connected to input terminals 1 and 2, a third winding N3 connected thereto and wound in the same direction as the primary winding N1, and a third winding N3 on the output side. It has a single secondary winding N2. The winding directions of the primary winding N1, the secondary winding N2, and the third winding N3 are selected to be on the anode side, as shown by the black dots in the figure. The common side terminal of the primary winding N1 is designated as 6, the connection terminal with the third winding N3 is designated as 5, and the other end of the third winding N3 is designated as 9. Capacitor C is connected between terminals 1 and 2, and diode D
is used to connect terminals 2 and 9, and the cathode side faces the third winding N3. The switching transistor Q1 has a collector connected to terminal 6 and an emitter connected to terminal 2, and performs a switching operation between the collector and emitter in response to an on/off control signal applied to the base.

The output side circuit is the anode side terminal 7 of the secondary winding N2.
, a reverse current blocking diode D2 having an anode terminal connected thereto, a cathode terminal of this reverse current blocking diode D2 connected to one end, and the other end 8 of the secondary winding N2.
has a smoothing capacitor C2 connected to the other end,
A load RL is connected in parallel with this smoothing capacitor C2 via output terminals 3 and 4.

The operation of the device configured in this manner will be described next. This single-stone forward converter transmits power to the output side when the switching transistor Q1 is on, that is, during a period when the collector and emitter are conducting.

Next, the function of the third winding N3 will be explained.
In a state where there is no third winding N3 on the input side, a high voltage is induced at one end 5 of the primary winding N1 as a reference and at the other end 6 immediately after Q1 is turned off, and this induced voltage is added to the input voltage Vin. Collector with voltage Q1
It acts between the emitsa. In this case, there is a risk that Q1 will be destroyed by the high voltage, so a third winding N3 is provided to protect Q1.

Since a voltage is induced in the third winding N3 immediately after Q1 is turned off, a reset current _iRI flows through the capacitor C along the path shown by the dotted line in the figure. This reset current _iRI flows in the direction of charging the capacitor C, and the excitation energy accumulated during the ON period of Q1 is fed back to the capacitor C during the OFF period of Q1. Generally, since the capacitor C has a large capacity, the input voltage will not rise due to the reset current _iRI . At this time, the voltage of the third winding N3 is the input voltage
Since it is clamped to Vin, the voltage E _f induced in the primary winding N1 satisfies the following relationship.

E _f =(n1/n3)·Vin (1) Here, n1 and n3 are the numbers of turns of the primary winding N1 and the third winding N3, respectively. Therefore, the collector-emitter voltage V _CE of Q1 is limited to the sum of the input voltage Vin and the collector-emitter voltage V _CE , and destruction of Q1 is prevented.

This circuit consisting of capacitor C and diode D is connected in series with third winding N3 and is called a reset circuit. The reset circuit is Q
has the function of discharging and consuming the energy remaining in the transformer T immediately after turn-off during the off-period of Q1.

<Problem to be solved by the invention> However, in the conventional device, the residual energy is not consumed in the reset circuit during the off period of Q1, and the residual energy is not transmitted to the output side, so if this circuit is used as a current/current isolator, There was a problem that insertion loss increased.

The purpose of the present invention is to solve these problems, and to provide a current/current isolator with a simple configuration, low insertion loss, and characteristics that allow transmitting current to be transmitted to the receiving load without error. shall be.

<Means for Solving the Problems> The present invention achieves the above object by connecting an input current source to the primary winding of the transformer via a transformer T that insulates the input side and the output side, and a switching transistor Q1. a first diode D2 whose anode terminal is connected to the anode terminal of the main secondary winding N2 of the transformer; one end connected to the cathode terminal of the first diode and the other end; In a current/current isolator comprising a series circuit of a smoothing capacitor C2 connected to a common side terminal of the main secondary winding, and an output side circuit that supplies a direct current to a load RL connected to the smoothing capacitor. , has the following configuration.

That is, the reset secondary winding N22 is connected in series with the main secondary winding of the transformer, and the anode terminal is connected to the terminal 10 of the reset secondary winding on the side that is not connected to the main secondary winding. It is characterized by comprising a second diode D22 whose cathode terminal is connected to a connection point between the first diode and the smoothing capacitor.

<Function> Each component of the present invention has the following functions. The reset secondary winding and the second diode, together with the smoothing capacitor, form a reset circuit in which the energy remaining in the transformer immediately after the switching transistor is turned off is charged to the smoothing capacitor during the off period, so that the residual energy is removed. It is effectively supplied to the load and insertion loss is reduced.

<Example> The present invention will be explained below using the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. In FIG. 2, parts having the same functions as those in FIG. In the figure, transformer T has a primary winding N1, a main secondary winding N2 and a reset secondary winding N22,
Here, it is assumed that the number of turns of each winding is equal and that each self-inductance is L. Constant current source Iin
represents the DC input current applied to input terminals 1 and 2. Terminal 7 is one terminal of the main secondary winding N2,
Terminal 8 connects the main secondary winding N2 and the reset secondary winding N2.
2 common connection point, terminal 10 is the reset secondary winding N
This is the other terminal of 22. Backflow blocking diode D
Reference numeral 22 has an anode side connected to the terminal 10 and a cathode side connected to the cathode side of the backflow blocking diode D2, and is also connected to the smoothing capacitor C2 and the output terminal 3.

The operation of the device configured in this manner will be described next. When the switching transistor Q1 is now turned on and a current Iin flows through the primary winding N1, a positive voltage is induced between one end 8 and the other end 7 of the main secondary winding N2. The current due to this voltage passes through the reverse blocking diode D2, charges the smoothing capacitor C2, flows to the load RL, and supplies power to it. Q
Just before 1 switches from on to off, L・I _io
2/2 Joule of energy is stored in transformer T. At the moment Q1 turns off, the current due to this stored energy flows through the reverse blocking diode D.
22, smoothing capacitor C2 and load RL
is released. The current released to the smoothing capacitor C2 charges the smoothing capacitor C2 and increases its terminal voltage, and the charge charged in the smoothing capacitor C2 is charged during the ON period of Q1 and remains without being discharged to the load RL. Q1
Current flows through the load RL during the off-period.

Thus, a DC current corresponding to the input current Iin is transmitted to the load RL through the on/off of Q1, and ideally, no current loss occurs in the circuit consisting of the transformer T, smoothing capacitor C2, and backflow blocking diodes D2 and D22. . Therefore, the input current Iin
can be transmitted to the load RL without error. Note that the circuit consisting of the reset secondary winding N22, the reverse current blocking diode D22, and the smoothing capacitor C2 is
Like the reset circuit shown in the figure, this is also a reset circuit because it has the function of resetting the residual energy of transformer T during the off period of Q1.

The embodiment shown in FIG. 2 prevents excessive current from flowing through the switching transistor Q1 when a specified load is connected to the output terminals 3 and 4 and the isolator is operating normally. It has the advantage of reducing insertion loss. However, when the load RL is released, the reverse blocking diode D2 and the smoothing capacitor C connected to the reset secondary winding N22 on the output side of the transformer T
2 has the disadvantage that it is not possible to reset the residual energy of transformer T during the off-period of Q1.

The circuit shown in FIG. 3 is a second embodiment of the present invention in which the residual energy of the transformer T can be reset during the off-period of Q1 even when the load RL is open. In this second embodiment, a part of the power supplied from the input current source Iin is further transferred to the switching transistor Q.
This circuit is also used as a driving power source for an oscillator that generates one on/off control signal. This figure is similar to FIG. 2 in that the transformer T is provided with a reset secondary winding N22, and has a reset circuit for the transformer T including a backflow blocking diode D2, a smoothing capacitor C2, and a load RL. Furthermore, the input side of the transformer T is provided with a third winding N3 connected to the primary winding N1, and a reset circuit including a diode D3 and a capacitor C is provided between the terminals of the third winding N3, as shown in FIG. It is similar to Here, in order to distinguish between the reset circuit on the output side and the reset circuit on the input side of the transformer T, the former will be referred to as the first reset circuit and the latter as the second reset circuit. The Zener diode Dz is an element that generates a constant voltage Vz between its terminals, and the constant frequency rectangular wave oscillator OSC is a circuit driven by a constant voltage Vz flowing through the Zener diode Dz. The output signal If of the OSC controls on/off between the collector and emitter of the switching transistor Q1.

The operation of the device configured in this manner will be described next. Primary winding N1 of transformer T, main secondary winding N2,
The number of turns of the third winding N3 and the reset secondary winding N22 are the same. Load RL between output terminals 3 and 4
In normal operating conditions when the input terminals 12 and 16 are connected, the voltage Vin between the input terminals 12 and 16 is higher than the output voltage Vo, and the second reset circuit including the diode D3 and the capacitor C connected to the third winding N3 is Do not work. Therefore, only the first reset circuit operates, substantially similar to the embodiment of FIG. 2, and the input current Iin is transmitted to the load RL without error. Furthermore, when the load RL is open, the first reset circuit becomes incapable of resetting, and the second reset circuit operates to reset the switching transistor Q.
1 can be prevented from being applied with excessive voltage.

The circuit indicated by the broken line in FIG. 3 is a configuration diagram of a modified embodiment of the present invention. Here, the winding n3 of the third winding N3 is made smaller than the function n22 of the reset secondary winding N22, and one end 9 of the third winding N3 is connected to the capacitor C as shown by the broken line in the figure. At the same time, the cathode side of the diode D3 is connected to the anode side instead of the cathode side of the Zener diode Dz.

Even with this configuration, only the first reset circuit operates in a normal operating state in which the load RL is connected between the output terminals 3 and 4. Further, when the load RL is in an open state, the second reset circuit can be operated.

<Effect of the invention> As explained above, according to the invention, the reset secondary winding N22 and the reverse current blocking diode D22 constitute a reset circuit together with the smoothing capacitor C2, and the reset secondary winding N22 and the reverse current blocking diode D22 form a reset circuit together with the smoothing capacitor C2. The residual energy is charged to the smoothing capacitor C2 during the off period, and the residual energy is effectively supplied to the load, reducing insertion loss.

In addition, as in the embodiment shown in Fig. 3, if a second reset circuit that operates when the load RL is open is provided on the input side of the transformer T in addition to the reset circuit on the output side, the load RL is opened. It is possible to release the residual energy of the transformer T even when the load is
In the normal state where the RL is connected, the above-mentioned effect is exhibited, and the practical effect is great.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram explaining the principle of a conventional single-stone forward converter type switching regulator, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 3 is a circuit diagram illustrating an embodiment of the present invention. This is Example 2. C, C2...Capacitor, D2, D22, D3
...Diode, Dz...Zener diode,
Iin...Input current source, N1...Primary winding, N2...
...Main secondary winding, N22...Reset secondary winding, N
3...Third winding, Q1...Switching transistor, RL...Load, T...Transformer.

Claims (1)

[Claims for Utility Model Registration] (1) A transformer T that insulates the input side and the output side, a circuit that supplies current from an input current source to the primary winding of the transformer via a switching transistor Q1, and the transformer. a first diode D2 whose anode terminal is connected to the anode terminal of the main secondary winding N2 of the device;
and a series circuit of a smoothing capacitor C2, one end of which is connected to the cathode terminal of the first diode, and the other end of which is connected to the common side terminal of the main secondary winding, and a load connected to the smoothing capacitor.
A current/current isolator comprising: an output side circuit for supplying direct current to RL; a reset secondary winding N22 connected in series with the main secondary winding of the transformer; and an anode terminal connected to the reset secondary winding N22. Connected to the terminal 10 on the side not connected to the main secondary winding of the next winding,
A current/current isolator comprising: a second diode D22 whose cathode terminal is connected to a connection point between the first diode and a smoothing capacitor. (2) The transformer further includes a third winding N3 connected in series with the primary winding of the transformer on the input side, and the load on the output side is in an open state between the terminals of the third winding. A second reset circuit is provided which performs a reset operation when the load is connected to the output terminal, and the reset circuit including the second diode and the smoothing capacitor performs the reset operation only in a normal state in which the load is connected to the output terminal. Scope of claim for utility model registration No. 1
Current/current isolator as described. (3) The input current source supplies current to the series circuit of the switching transistor and the primary winding of the transformer via the Zener diode Dz, and generates a constant frequency oscillator by the constant voltage generated between the terminals of the Zener diode. 2. The current/current isolator according to claim 1, which is a utility model and is characterized in that it drives an OSC and controls the switching transistor intermittently based on the output of the oscillator.