JPH09261951A - Pulse transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the saturation of the flux of a pulse transformer and improve the characteristics of the transformer. SOLUTION: A driving power supply Vcc is connected to the middle point (winding ratio: n1 /n2 ) of the primary winding of a pulse transformer Tr1. A pulse-type transmission signal e, is inputted to the one end of the primary winding through a first switch Q1 and a second switch S1 which is connected to the other end of the primary winding in common is provided and controlled so as to be closed in synchronisen with the trailing of the pulse signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a pulse transformer, and more specifically to prevent saturation of transformer magnetic flux to improve the characteristics.

[0002]

2. Description of the Related Art Generally, a pulse transformer is used for transmitting and receiving data in a digital device, and in particular, DC is used on the transmitting side.
Used when insulation is required. FIG. 4 is a block diagram showing a typical usage example of the pulse transformer. In FIG. 4, PT ₁ is a pulse transformer, R ₁ is a current limiting resistor, and Q ₁ is a transistor, which are connected in series. The drive power supply (DC power supply) V _cc is connected to both ends of this series circuit, and the pulse signal e _s to be transmitted is the transistor Q ₁
Applied between the base and the emitter. The secondary side of the pulse transformer PT ₁ has a secondary winding with a midpoint tap. The midpoint tap is at the terminal T ₀ and each end of the secondary winding is a terminal.
They are connected to T ₁ and T ₂ , respectively.

A diode D ₁ and a resistor R are provided between terminals T _{0 and} T _1.
2 , the diode D ₂ and the resistor R ₃ are connected in series between the terminals T _{2 and} T ₀ , respectively, and the terminal T ₀ is connected to the common COM of the circuit. The connection point between the diode D ₁ and the resistor R ₂ is connected to the set terminal S of the RS flip-flop Q ₂ , and the connection point between the diode D ₂ and the resistor R ₃ is connected to the reset terminal R of the RS flip-flop Q _2. The output e ₀ can be obtained from the flip-flop Q terminal.

FIG. 5 is a waveform diagram showing the operation of the circuit having the above configuration.
It is. Transistor Q for switching₁Shown in (a)
Repetitive period T, ON time T_sPulse signal e_SEnters
Forced, transistor Q₁Turns on the pulse transformer
PT₁DC power source V on the primary side of_ccCurrent i flows from. pulse
Transformer PT₁Let L be the input inductance of_Two, R _Three
Is large enough, the current i is i = V_cc/ R₁(1-e^{-Lt / R1}).

That is, as shown in (b), time t₁≒ L / R₁After
Current i is resistance R₁And a constant current determined by the DC power supply Vcc
Become. Pulse transformer PT₁Current i increases in the secondary winding of
Time t₁, The voltage proportional to the time change of the current i
Pressure is induced. Time t when the current i is decreasing_TwoAs well
It is. Therefore, the pulse voltage of the waveform shown in (c) and (d)
Is terminal T₀−T₁Between terminals T_Two−T₀Occur in between. Terminal T₀−T₁
Between terminals T_Two−T₀Voltage e generated during each₁, E_TwoIs Daio
Code D₁， D_TwoRectified by R-S flip-flop Q _TwoInput
Signal (e) (f).

[0006] Therefore, RS flip-flop Q ₂ at the rising edge of the pulse signal e _s (i) is set, the pulse signal e _S
Resets at the falling edge of. As a result, a signal of the pulse voltage having the same waveform as the pulse signal (a) is obtained at the Q terminal of the RS flip-flop Q ₂ as shown in (g). In this case, the size of the pulse transformer PT ₁ is such that the product E of the peak value Es and the on-time T _S is E when the peak value of the pulse signal e _S is Es.
Determined by s · T _S.

[0007]

By the way, in such a pulse transformer, when a DC signal is input to the primary winding side, the transformer is saturated and a large current flows. FIG. 6 (a),
(B) shows the relationship between the increase of the current and the time when the pulse of the voltage Vcc is input. When the exciting inductance of the transformer is L, the current increases at dI / dt = (1 / L) Vcc. The transformer is saturated (A = saturation point). In the figure, it means that the magnetic flux is saturated and the inductance becomes 0 at time t _s . That is, the magnetic flux of the transformer must always operate within this operating point range.

FIGS. 7 (a) and 7 (b) show the relationship between the pulse train input and the operating point, which shows the state of the operating point when a pulse train of ± 5 V and a duty of 50% is input, and the average voltage of the input is At 0V, the operating point of the transformer is ± Φ centered on 0
It is operating with magnetic flux. Next, when driving the pulse transformer with a unipolar voltage, it is necessary to consume magnetic energy and reset the magnetic flux while the transistor is off.

FIGS. 8A and 8B show the output state on the secondary winding side when a unipolar voltage is input to the pulse transformer. The pulse train (a) is input to the primary side. In this case, the OFF time is insufficient, the magnetic energy cannot be reset, and the 0 level shifts (err), and the output (b) on the secondary side also shifts (err ').

That is, the operating point of the magnetic flux changes to either one in proportion to the time during which the + or-voltage is applied. Then, such movement of the operating point causes disturbance of the waveform on the secondary side. The present invention has been made to solve the above-mentioned problems, and after one pulse is transmitted, the magnetic flux is always returned to the original position so that the operating point of the magnetic flux does not deviate, and a pulse transformer with no waveform distortion is provided. The purpose is to provide.

[0011]

In order to achieve this object, the present invention provides a pulse transformer according to the first aspect of the invention.
A drive power source is connected in the middle of the secondary winding (winding ratio n ₁ : n ₂ ), and a pulsed transmission signal is input to one end of this primary winding via the first switch, and The second switch connected to common is provided at the other end of the primary winding, and switching is performed so that the second switch is turned on in synchronization with the fall of the pulse signal. Is connected to a drive power source in the middle of the primary winding of the pulse transformer (winding ratio n ₁ : n ₂ ), and a pulsed transmission signal is applied to one end of the primary winding via a first switch. Is input, the cathode of the diode is connected to the other end of the primary winding, and the anode side is connected to the common. Hereinafter, detailed description will be given based on an example of an embodiment of the present invention.

[0012]

1 is a block diagram showing an outline of a pulse transformer according to claim 1 of the present invention. In FIG. 1, the same elements as those of FIG. 4 shown in the conventional example are denoted by the same reference numerals and the description thereof will be omitted. However, in the present invention, in the middle of the primary side winding (turning ratio n ₁ : N ₂ ) drive power supply (DC power supply + V
cc) is connected, and the transistor Q ₁ is connected to the n ₂ end of this winding through the resistor R ₁ (herein, this transistor is referred to as a first switch).

A pulsed transmission signal e _S is input via the first switch Q ₁ and a second switch S ₁ connected to the common by switch-on is provided at one end of the winding n ₁ . Although omitted in the figure, the transmission signal e _S
Is turned on and off according to the timing of the reference clock, and the second switch S ₁ is turned on in synchronization with the fall of the pulse signal e _s to be transmitted.

FIG. 2 is a waveform diagram showing the operation of the first and second switches of the pulse transformer. Transistor Q ₁ to the repetition period T, such as shown in FIG. (B) of the switching pulse signal e _S ON time t ₀ is input, the pulse transformer PT ₁ the transistor Q ₁ is turned on is first switch
Current i flows from the DC power supply V _cc to the winding side of the n ₂ of. Then, in synchronization with the fall of the on time t ₀ , the pulse transformer P
The second switch S ₁ provided on the n ₁ winding side of T ₁ is turned on as shown in (b), and the magnetic flux is reset for a time of t _R. As a result, an output as shown in (c) is obtained on the secondary side of the pulse transformer PT ₁ .

The density of this pulse signal train is determined by the winding on the primary winding side.
Linear ratio (n₁: N_Two) Are the same, t ₀+ T_RThat is, 2t₀of
The cycle can be shortened. Therefore n_TwoReduce
If t_R= (N_Two/ N₁) ・ T₀ And the baud rate (modulation speed) is 1 / {1+ (n_Two/ N₁)} ・ T₀ It becomes possible to raise it up to.

Further, when the baud rates are the same, the pulse width can be widened by shortening the reset time, and it is possible to drive to a position close to the ET product of the transformer, so that the S / N is improved. Can be made.

FIG. 3 shows an embodiment of claim 2 of the present invention. The difference from FIG. 1 is that the cathode of the diode is connected to the other end (n ₁ ) of the primary winding and the anode side is common. According to such a configuration, the exciting current I ₁ flows to the winding n ₂ side when the first switch Q ₁ is on, and the reset current flows to the diode D ₃ side when the first switch Q ₁ is off. I ₂ will flow. This reset current causes the magnetic energy to become a regenerative current and return to the power supply Vcc, increasing the efficiency. Further, in this case, the winding ratio (n ₁ :
If n ₂ ) is approximately the same, the duty ratio of the transmission signal is approximately 5
Although it is 0%, a duty ratio of 50% or more is possible if n ₁ <n2.

[0018]

As described above, according to the first aspect of the present invention, the drive power source is connected in the middle of the winding on the primary side of the pulse transformer (winding ratio n ₁ : n ₂ ), and A pulsed transmission signal is input to one end (n ₂ side) of the winding through the first switch, and a second switch connected to the common is provided at the other end (n ₁ side) of the primary winding. , The second switch is turned on in synchronization with the fall of the pulse signal, and in the middle of the primary side winding of the pulse transformer (turning ratio n ₁ : n ₂ ) Is connected to a driving power source, and a pulsed transmission signal is input to one end (n ₂ side) of the primary winding through the first switch and to the other end (n ₁ side) of the primary winding. Since the cathode of the diode is connected, it is possible to increase the baud rate.
Further, when the baud rate is the same, the pulse width can be widened by shortening the reset time. Further, since it is possible to drive to a position close to the ET product of the transformer, the S / N can be improved.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing an example of an embodiment of claim 1 of the present invention.

FIG. 2 is an explanatory diagram showing waveforms of the circuit shown in FIG.

FIG. 3 is a main part configuration diagram showing an example of an embodiment of claim 2 of the present invention.

FIG. 4 is a configuration diagram showing a typical usage example of a pulse transformer.

5 is a waveform chart showing the operation of the circuit of FIG. .

FIG. 6 is a diagram showing a relationship between an increase in current and time when a pulse of voltage E is input.

FIG. 7 is a diagram showing a relationship between a pulse train input and an operating point.

FIG. 8 is a diagram showing a state of output on the secondary winding side when a unipolar voltage is input.

[Explanation of symbols]

 PT₁ Pulse transformer  Q₁ 1st switch e_s Pulse signal Q_Two R-S flip-flop S₁ Second switch Vcc drive power supply (DC power supply)

Claims (2)

[Claims] 1. A drive power source is connected in the middle of a winding on the primary side of a pulse transformer (winding ratio n ₁ : n ₂ ).
A pulsed transmission signal is input to the end through the first switch, and a second switch connected to the common is provided at the other end of the primary winding, and the second switch is provided in synchronization with the fall of the pulse signal. A pulse transformer characterized by switching so that two switches are turned on. _{2. A} drive power source is connected in the middle of the winding on the primary side of the pulse transformer (winding ratio n ₁ : n ₂ ).
A pulse transformer characterized in that a pulsed transmission signal is input to the end via a first switch, the cathode of a diode is connected to the other end of the primary winding, and the anode side is connected to common.