JPH06164352A - Pulse transformer driving circuit - Google Patents

Abstract

PURPOSE:To obtain a pulse transformer driving circuit which can reduce a generated noise. CONSTITUTION:This pulse transformer driving circuit is provided with switching elements Q1 and Q2 which invert the direction of a current supplied to the primary winding of a pulse transformer T1 according to high and low variation in the level of a pulse signal generated by a pulse generating means OS and a capacitor C2 for ringing suppression is connected to the primary winding of the pulse transformer T1 substantially in parallel. In this case, the above 'substantially' means that an element having low impedance to high frequencies may be interposed between the primary winding of the pulse transformer T1 and capacitor C2 for ringing suppression.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse transformer drive circuit for driving a pulse transformer for transmitting a pulse signal used for switching or the like to a load such as a switching element.

[0002]

2. Description of the Related Art FIG. 5 shows a circuit diagram of an example of a conventional pulse transformer drive circuit. This pulse transformer drive circuit
The output terminal of the pulse generating means OS such as a pulse oscillator connected between the power supply V _CC and the ground is connected via the resistor R ₁ to the bases of the _two switching elements Q ₁ and Q _{2 which} are transistors of serial inverter configuration. Connected. Connected to one end of the primary winding of the pulse transformer T ₁ series connected two connection points switching elements Q _1, Q ₂ a (emitter) through a coupling capacitor C _1, a pulse transformer T ₁ The other end of the primary winding is connected to ground.

Two switching elements Q₁, Q₂In series
The circuit is the power supply V_CCConnected between the ground and
It Pulse transformer T₁Both ends of the secondary winding of
MOS field effect transistor Q₃Gate and saw
It is connected to each. Pal with the above configuration
The operation of the transformer drive circuit will be described with reference to FIG.
It From the pulse generation means OS, the pattern as shown in FIG.
Russ signal is resistance R₁Two switches connected in series through
Ching element Q₁, Q₂It is commonly input to each base.
When the pulse signal is high level, switching element Q
₁Current i to the base of₁Flows in, switching element Q₁
Is turned on and the DC blocking capacitor C ₁Through pal
Trans T₁Current i in the primary winding of₃Flows. pulse
When the signal is low level, switching element Q₂The
Current i₂Flows out, switching element Q₂Is o
DC blocking capacitor C₁Pulsed through
Lance T₁Current i in the primary winding of₃Current i opposite to_Four
Flows.

Therefore, the switching elements Q ₁ , Q ₂
At the connection point of A, that is, the point A, as shown in FIG.
A voltage having the same waveform as the output voltage of the pulse generating means OS will appear. By a coupling capacitor C _1, since the DC component of the voltage at point A is removed, the connection point between the primary winding and a coupling capacitor C ₁ pulse transformer T _1, that is, the point B, A pulse voltage (AC rectangular wave voltage) that swings positively and negatively as shown in FIG. 6C appears.

[0005] primary winding of the pulse transformer T _1, since the AC rectangular wave voltage shown in FIG. 6 (c) mentioned above is added, the pulse like AC rectangular wave voltage in the secondary winding of the transformer T ₁ is MOS that is generated and is the secondary load of the pulse transformer T _1.
Type field effect transistor Q ₃ between the gate and source of FIG.
A voltage as shown in (d) is applied, and this voltage drives the MOS field effect transistor on and off.

The pulse transformer drive circuit configured as described above is often used when the reference potentials on the primary side and the secondary side of the pulse transformer T ₁ are different. For example, it is used to drive a switching element on the high side of a series inverter device that converts a DC voltage into an AC voltage.

[0007]

However, such a pulse transformer drive circuit has the following problems. That is, the pulse transformer T ₁ has a main purpose of transmitting a pulse signal, and ideally, the degree of coupling between the primary side and the secondary side is preferably 1.0. However, in reality, it is almost impossible to set the coupling degree to 1.0. As a result, ringing (P ₁ and P _{2 in} FIGS. 6 (c) and 6 (d)) occurs at the timing near the voltage polarity reversal in the voltage across each of the primary and secondary windings of the pulse transformer T ₁ . It will be. This ringing causes high-frequency noise, which adversely affects the space in which the pulse transformer drive circuit is installed and the power supply environment for supplying power to the pulse transformer drive circuit.

FIG. 7 shows a circuit diagram of another example of the pulse transformer drive circuit. This pulse transformer drive circuit is configured for the purpose of reducing ringing in the pulse transformer drive circuit of FIG. 5, and a diode clamp circuit is added to the circuit of FIG. That is, the diodes D ₁ and D ₂ are connected in antiparallel to the switching elements Q ₁ and Q ₂ , respectively.

However, even if such a diode clamp circuit is provided, it is effective in reducing noise in a low frequency range, but is not necessarily effective in reducing noise in a high frequency range of several hundred MHz. It was Therefore,
An object of the present invention is to provide a pulse transformer drive circuit that can effectively reduce the generated noise.

[0010]

The pulse transformer drive circuit of the present invention is directed to the direction of the current supplied to the primary winding of the pulse transformer in response to the high / low change of the level of the pulse signal generated from the pulse generating means. A switching element for reversing is provided, and a ringing suppressing capacitor is substantially connected in parallel to the primary winding of the pulse transformer. In addition,
The term "substantially" means that a low impedance element with respect to a high frequency may be interposed between the primary winding of the pulse transformer and the ringing suppressing capacitor.

[0011]

According to the structure of the present invention, the pulse transformer 1
Since a ringing suppressing capacitor is connected in parallel to the secondary winding, ringing that occurs when the direction of the current supplied to the primary winding of the pulse transformer is reversed by the switching element according to the change in the level of the pulse signal. The current due to can be made to flow through the ringing suppressing capacitor. As a result, ringing can be suppressed, and thus noise generated due to ringing is reduced.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a circuit diagram of a pulse transformer drive circuit according to a first embodiment of the present invention. This pulse transformer drive circuit is provided with switching elements Q ₁ and Q ₂ that reverse the direction of the current supplied to the primary winding of the pulse transformer T ₁ in accordance with the change in the level of the pulse signal generated from the pulse generation means OS. , A ringing suppressing capacitor C ₂ is connected in parallel to the primary winding of the pulse transformer T ₁ .

The difference from the conventional example of FIG. 5 is that a ringing suppressing capacitor C ₂ is added.
Is the same as that shown in. In FIG. 1, the pulse transformer T ₂ of the 2 rather than MOS-type field effect transistor Q ₃ in winding shows a state of connecting the common load LD which includes a MOS field-effect transistor Q _3.

The capacitance of the ringing suppressing capacitor C ₂ is set to a sufficiently small value.
The level is a level that basically does not change the primary side waveform of the pulse transformer T ₁ , and the current i flowing from the switching element Q ₁ through the DC blocking capacitor C ₁ and the ringing suppressing capacitor C _{2 in the} arrow direction.
₁₁ or the current i ₁₂ flowing from the switching element Q ₂ through the DC blocking capacitor C ₁ and the ringing suppressing capacitor C _{2 in} the direction of the arrow causes the collector currents of the switching elements Q ₁ and Q ₂ to become excessive. It's a level you don't have.

[0015] Naturally currents i _11, i _12, because it is influenced by the power supply voltage V _CC, the power supply voltage V _CC, in such a pulse transformer drive circuit is generally a low voltage (e.g., 24V or less), ringing If the suppression capacitor C ₂ is set to an appropriate value, it is possible to prevent the switching elements Q ₁ and Q ₂ from being adversely affected. Since the ringing suppressing capacitor C ₂ as described above is connected in parallel to the primary winding of the pulse transformer T ₁ , in the period 0 to t ₁ in FIG. ₁₃ flows in the direction of the arrow, and during the period t _{1 to} t ₂ , similarly, the current i ₁₄ due to ringing flows in the direction of the arrow when ringing occurs, and as a result, ringing can be suppressed.

To suppress ringing, a capacitor is more effective than a diode, and among the capacitors,
Ceramic capacitors with excellent high frequency characteristics are effective. FIG. 2 shows a circuit diagram of a pulse transformer drive circuit in which the load LD is the same MOS type field effect transistor Q ₃ as in FIG. The operation of this circuit is as described in the description of FIG. 5 and FIG. 1, and thus detailed description will be omitted.

The circuit as shown in FIG. 2 was applied to drive the high-side switching element of the serial inverter to manufacture a ballast for a fluorescent lamp, and the radiation noise was measured. As a result, the radiation noise is about 10 in almost the entire range of 30 to 300 MHz.
dB reduced, especially about 4 in the 200-250 MHz band
It was confirmed that it was reduced by 0 dB and it was effective to connect the ringing suppressing capacitor C ₂ .

According to the pulse transformer driving circuit, since the ringing suppression capacitor C ₂ to the primary winding of the pulse transformer T ₁ are connected in parallel, 1 of the pulse transformer T ₁
A current due to ringing generated when the direction of the current supplied to the next winding is reversed by the switching elements Q ₁ and Q ₂ according to the change in the level of the pulse signal can be passed through the ringing suppressing capacitor C ₂ . As a result, ringing can be suppressed, and therefore noise generated due to ringing can be reduced. In this case, the radiation noise in the band of 30 to 300 MHz can be reduced, and particularly the radiation noise in the band of 200 to 250 MHz can be greatly reduced.

[Second Embodiment] FIG. 3 shows a circuit diagram of a pulse transformer drive circuit according to a second embodiment of the present invention. In this pulse transformer drive circuit, a ringing suppressing capacitor C ₂ is connected in parallel to the primary winding of a pulse transformer T ₁ via a DC blocking capacitor C ₁ having a low impedance for high frequencies, that is, a pulse transformer. A ringing suppressing capacitor C ₂ is substantially connected in parallel to the primary winding of T ₁ , and other configurations are similar to those of the circuit of FIG.

Also in this embodiment, the capacitance of the DC blocking capacitor C ₁ is equal to the ringing suppressing capacitor C ₂
It is sufficiently larger than the capacitance of No. 1 and has the same action and effect as the embodiment of FIGS. 1 and 2 with respect to ringing. [Third Embodiment] FIG. 4 is a circuit diagram of a pulse transformer drive circuit according to a third embodiment of the present invention. The pulse transformer driving circuit includes a switching element Q in addition to the capacitor C ₂ for parallel become ringing suppression to _2, the ringing suppression capacitor C ₃ to be parallel with the switching element Q ₁
Is added, and other configurations are similar to those in FIG.

The above ringing suppressing capacitor C
_{3 is} also connected in parallel to the primary winding of the pulse transformer T ₁ via a DC power supply (V _CC ). The ringing suppressing capacitor C ₂ forms a ringing suppressing current loop via the ground line, whereas the ringing suppressing capacitor C ₃ forms a ringing suppressing current loop via the power supply line.

In this embodiment, the same effect as the above embodiment can be obtained. In this embodiment, both ringing suppressing capacitors C ₂ and C ₃ are provided, but the ringing suppressing capacitor C ₂ may be omitted. Further, in each of the above-described embodiments, in order to drive the pulse transformer T ₁ , two switching elements Q ₁ and Q _{2 form} a series inverter, but the primary winding of the pulse transformer T ₁ is driven. The connection configuration of the switching elements may be any configuration and is not limited to the series inverter. In short, as long as the ringing suppressing capacitor is substantially connected in parallel to the primary winding of the pulse transformer T ₁ , the circuit configuration and the types of constituent elements are not particularly limited.

[0023]

According to the pulse transformer drive circuit of the present invention, since the ringing suppressing capacitor is substantially connected in parallel to the primary winding of the pulse transformer, the direction of the current supplied to the primary winding of the pulse transformer is increased. Can be suppressed by causing a current due to ringing that occurs when the switching element reverses according to the change in the level of the pulse signal to flow through the ringing suppression capacitor, thus reducing the noise generated due to ringing. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a pulse transformer drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific example of the load in FIG.

FIG. 3 is a circuit diagram showing a configuration of a pulse transformer drive circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a pulse transformer drive circuit according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of an example of a conventional pulse transformer drive circuit.

FIG. 6 is a time chart of each part of the pulse transformer drive circuit of FIG.

FIG. 7 is a circuit diagram showing a configuration of another example of a conventional pulse transformer drive circuit.

[Explanation of symbols]

OS pulse generation means Q ₁ , Q ₂ switching element R ₁ resistance C ₁ DC blocking capacitor C ₂ ringing suppression capacitor LD load T ₁ pulse transformer Q ₃ MOS field effect transistor

Claims (1)

[Claims] 1. A pulse generator for generating a pulse signal, and a direction of a current supplied to a primary winding of a pulse transformer is reversed in response to a change in level of a pulse signal generated by the pulse generator. A pulse transformer drive circuit comprising a switching element for controlling the ringing and a ringing suppressing capacitor substantially connected in parallel to the primary winding of the pulse transformer.