JPH07169002A - Magnetic head driving circuit - Google Patents

Abstract

PURPOSE:To eliminate the error in the direction of a current applied to a magnetic head which is produced immediately after the recording start when a recording signal is supplied to the magnetic head of a magnetic head driving circuit in which the recording signal which is applied to the magnetic head of a magnetic field modulation recording system is driven by auxiliary coils and two switching devices with low voltage power supplies. CONSTITUTION:A recording signal which is applied to the head coil 6a of the magnetic head 6 of a magnetic field modulation system which is provided between respective series circuits composed of auxiliary coils 7 and 8 and switching devices 11 and 12 is driven by high voltages generated by low voltage power supplied 9 and 10. In a magnetic head driving circuit like this, a recording stand-by circuit 24 which turns on both the switching devices 11 and 12 in a stand-by status in which the recording signal is not supplied to the switching devices is provided in a control circuit which performs the ON/OFF control of the switching devices 11 and 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic head drive circuit suitable for use in a magnetic head for magneto-optical recording.

[0002]

2. Description of the Related Art Conventionally, as a recording system of a rewritable type optical disc as a magneto-optical disc, an optical modulation system in which a DC magnetic field is applied to a magnetic film and a laser beam is modulated by a signal for recording, and a continuous oscillation laser are used. A magnetic field modulation method is known in which light is applied to a magnetic film and the magnetic field is modulated with a recording signal.

FIG. 5 is a schematic diagram for explaining a recording method of such a magnetic field modulation system. Reference numeral 1 is a rewritable magneto-optical disk, which has a television (Tb) and iron (Tb) on a transparent substrate such as polycarbonate. A magnetic layer 3 made of a magnetic material such as Fe) or cobalt (Co) is coated, and the magnetic layer 3 is magnetized upward, for example. By irradiating the magneto-optical disk 1 with a continuous wave laser beam through the lens 5 by the optical pickup 4 and raising the magnetic layer 3 to the Curie temperature or higher, the magnetization direction of the spot irradiated with the laser beam is easily downward. The record is made by reversing.
In this case, as the recording signal supplied to the coil of the magnetic head 6 as the magnetic field modulating means for overwriting, the modulation magnetic field can be obtained by switching the direction of flowing through the coil at high speed in accordance with the recording data. When a pulsed recording signal is supplied to the magnetic head 6 having such a coil inductance L and internal resistance R, the current cannot be reversed at high speed because of the time constant τ = L / R, and CNR (carrier / noise). Lower. Therefore, it is necessary to apply a high voltage in order to switch the recording signal at high speed. However, there was a problem that the driving power had to be increased when a high voltage was applied.

In order to solve such a problem, the rise time of the recording signal sent to the coil of the magnetic head 6 is shortened,
A magnetic head drive circuit that can be driven with low drive power is disclosed in Japanese Patent Application Laid-Open No. 63-94406 and is known.

FIG. 6 shows the configuration of the magnetic head drive circuit disclosed in the above publication. In FIG. 6, 6a is a head coil of the magnetic head 6 having an inductance L _H. Both ends A and B of the head coil 6a are connected to DC power supplies 9 and 10 via auxiliary coils 7 and 8, respectively, and the other ends of the DC power supplies 9 and 10 are grounded. Further, the head coil 6a
Both ends A and B of the first and second switching elements 11
And 12 respectively, the other ends of these switching elements 11 and 12 are respectively grounded, and a recording signal is supplied from the input terminal 13 to the switching element 11 via the inverter circuit 14 or without the inverter circuit 14. A recording signal is provided to and 12.

The inductances L ₁ and L ₂ of the auxiliary coils 7 and 8 are the inductance L of the head coil 6a.
It is selected to be sufficiently larger than _H and L ₁ = L ₂ > L _H. DC power supplies 9 and 10 and a field effect transistor (FE
The switching elements 11 and 12 composed of T) and the like have a circuit configuration in which they are alternately turned “on” and “off” based on a recording signal, and a current I necessary for recording is supplied to the auxiliary coils L ₁ and L ₂ and the magnetic head 6. It is designed to supply ₁ and I ₂ .

In the above-described conventional magnetic head drive circuit, the back electromotive force is generated when the switching elements 11 and 12 are alternately switched to the connection points A and B at both ends of the auxiliary coils 7 and 8 and the head coil 6a. By using a high voltage (several hundreds of volts) that is generated, a current I _H having a reverse direction and substantially the same value can be made to flow to the head coil 6a in a short time such as a switching time, and the driving power can be made extremely small. It is made to be possible.

[0008]

In the conventional magnetic head drive circuit shown in FIG. 6, since the head coil 6a of the magnetic head 6 and the auxiliary coils 7 and 8 have internal resistances, the respective internal resistance values are set to R _H and R. _{If 1} and R ₂ are used, FIG. 6 can be equivalently rewritten as shown in FIG. 7. At the time of recording with this drive circuit, the two switching elements 11 and 12 are turned "on" and "off" in synchronization with the recording signal to invert the direction of the current I _H flowing through the head coil 6a of the magnetic head 6. Therefore, one of the switching elements 11 and 12 is always in the “off” state in the standby state.

Here, in FIG. 6, the inductances of the auxiliary coils 7 and 8 are L ₁ and L ₂ (L ₁ = L ₂ = L _X ),
The internal resistances are R ₁ and R ₂ (R ₁ = R ₂ = _RL ), and the currents flowing through the auxiliary coils 7 and 8 are I ₁ and I _{2, respectively.}
And Further, the inductance of the magnetic head 6 is L _H , the internal resistance is R _H , the current flowing in the switching element 11 is I, and the voltages of the DC power supplies 9 and 10 are E.
And

Considering the state in which the switching element 11 is "on" and the switching element 12 is "off", the currents I ₁ and I ₂ flowing through the auxiliary coils 7 and 8 in the standby state are the current I on the vertical axis. If time t is plotted on the horizontal axis,
In the steady state, I = I as shown by curves 15 and 16 in FIG.
₁ + I ₂ , I ₁ = E / _RL , I ₂ = E / ( _RL + _RH )
Therefore, the current I ₁ flowing through the auxiliary coil 7 is larger than the current I ₂ flowing through the auxiliary coil 8 (I ₁ > I ₂ ).

Here, if the energy accumulated in the coils of the auxiliary coils 7 and 8 is W _L1 and W _L2 , respectively, then W _{L1
^{= L X · I 1 2/}} 2, W L2 = relation L _X · I _{² 2/2} next magnitude becomes I _1> naturally from the relationship I ₂ W _L1> W _L2. Therefore, the energy W _L2 stored in the auxiliary coil 8 is smaller than the energy W _L1 stored in the auxiliary coil 7. Further, when the switching element 11 is "off" and the switching element 12 is "on", these relationships are naturally reversed.

Now, assuming that the recording signal 17 as shown in FIG. 9A is supplied to the input terminal 13 of FIG. 6 from the recording standby period, the switching element 11 outputs the recording signal 17 as shown in FIG. The switching signal 18 inverted by the circuit 14 is supplied to the switching element 11
Is turned on, and the switching element 12 receives the recording signal 1
The switching signal 19 of FIG. 9C, which is in phase with 7, is supplied to bring it to the “off” state.

In such a magnetic head drive circuit, the head coil 6a of the magnetic head 6 which is in the standby state with the switching signals 18 and 19 shown in FIGS. 9B and 9C is shown in FIG.
As shown by D, the current I _H = I ₂ flowing in the head coil 6a of the magnetic head 6 immediately after the start of recording is deviated from the reference potential value by + E / R _L + _RH. The current I ₁ on the side of the correction coil 7 is large, and the current I ₂ on the side of the correction coil 8 is small, so that the magnetic head is in the section from t = a to t = b (for example, 0.1 seconds) during the transition when the recording signal is input. Current I _H flowing in the head coil 6a of No. 6 =
There is a problem that I ₂ is in the ± direction and is in an unbalanced state as shown by the transient waveform 20 in FIG. 9D, and good magnetic field modulation recording cannot be performed.

The present invention is intended to provide a magnetic head drive circuit which solves the above problems, and its purpose is to input the recording signal 17 from a recording standby state in which the recording signal 17 is not input. Immediately after the magnetic head 6
The present invention intends to eliminate imbalance in the ± direction of the currents flowing in the magnetic field, and to obtain a magnetic field modulation recording that is excellent.

[0015]

As shown in FIG. 1, the magnetic head drive circuit of the present invention has inductances L ₁ and L _{2 which are} larger than the inductance L _H of the head coil 6a of the magnetic head 6. The head coil 6a of the magnetic head 6 is arranged between a series circuit composed of two switching elements 11 and 12 connected in series with two auxiliary coils 7 and 8 each having In a magnetic head drive circuit configured to control the switching elements 11 and 12, two switching elements 11 and 12 are provided together with the control means 14, 21, 22 and 23 during recording standby. It is provided with a recording standby circuit 24 for turning it "on".

[0016]

In the present invention, two switching elements 11 and 12 are used.
In the standby state in which the recording signal 17 is not input, the switching elements 11 and 12 are both turned “on”, and the two switching elements 11 and 1 are set immediately after the recording is started.
Since the recording standby circuit 24 is provided so as to alternately control "on" and "off" of No. 2, the difference in the direction of the current flowing to the head coil 6a of the magnetic head 6 when the recording signal 17 is input from the recording standby state is set. It is possible to obtain a magnetic head drive circuit that can be eliminated and can perform excellent magnetic field modulation recording.

[0017]

The present invention will be described in detail below with reference to the drawings. First, the principle configuration of the magnetic head drive circuit of the present invention and its operation waveforms are shown in FIGS. In FIG. 3, parts corresponding to those in FIG. 7 are designated by the same reference numerals, and redundant description will be omitted. FIG. 3 shows an equivalent circuit of the magnetic head drive circuit in the standby state before the pulse-shaped signal as the recording signal is supplied, that is, in the state where the recording signal is not supplied.

The principle of the present example is that in order to correct the excessive difference in the direction of the recording signal flowing through the head coil 6a of the magnetic head 6 that occurs immediately after the start of recording, it is set to 2 during recording standby.
A recording standby circuit 24 for holding both the switching elements 11 and 12 in the “on” state is provided, and after the recording signal 17 is input, the switching elements 11 and 12 are alternately controlled to be “on” and “off”. It was done.

That is, the switching elements 11 and 1 in FIG.
Both 2 are in the "on" state. At this time, the steady-state currents flowing through the auxiliary coils 7 and 8 are I ₁ and I ₂
Then, R ₁ = R ₂ = _RL , I ₁ = I ₂ = E / _RL , and the respective energy W _L1 and W _L2 accumulated in the two auxiliary coils 7 and 8 is W _L1 = W _L2 = L _X (E / R) ² /
It can be placed with 2 equal.

Therefore, the switching elements 11 and 12 before the recording signal 17 as shown in FIG. 4A is applied to the magnetic head 6.
4B and FIG. 4C, after both are turned on, the recording switching signals 18 and 19 are supplied to the head coil 6a for driving.
As shown in D, in the recording standby state, the magnetic head current I _H
= 0, you can start recording from t = a,
Since the current flowing through the head coil 6a of the magnetic head 6 can be flowed in a well-balanced manner with reference to zero regardless of the ± directions, good magnetic field modulation recording is possible.

FIG. 1 shows an embodiment of the construction of a specific magnetic head drive circuit based on the above principle. FIG. 2 is a waveform diagram for explaining the operation of FIG. In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals.

In FIG. 1, a magnetic head 6 is for performing magneto-optical recording on a magneto-optical disk by a magnetic field modulation method, and a head coil 6 having an inductance L _H and a resistance R _H.
a is wound. Of course, the magnetic head 6 may be an electromagnet having a coil wound around a magnetic core or the like like a solenoid coil.

One end A of the head coil 6a of the magnetic head 6 is connected to the drain of a first N-type junction field effect transistor (JFET) 11 which constitutes a switching element. The JFET 11 constitutes a source-grounded switching circuit, and the source is grounded. One end A of the head coil 6a is further connected to one end of an auxiliary coil 7 having a _first inductance L ₁ and a resistance component R ₁ .
This inductance L ₁ has a sufficiently large value as compared with the inductance L _H of the head coil 6a. The first
The other end of the auxiliary coil 7 is connected to the positive terminal of the first DC power supply 9, and the negative terminal of the first DC power supply 9 is grounded.

The other end B of the head coil 6a is also connected to the drain of the second N-type JFET 12 which constitutes a switching element, constitutes a source-grounded switching circuit, and the source is grounded. The other end of the head coil 6a is connected to one end of a second auxiliary coil 8 having an inductance L ₂ and a resistance component R ₂ , and this inductance L ₂ is L ₁
= Is the L ₂ as compared with the inductance L _H of the head coil 6a is made sufficiently large value. The other end of the second auxiliary coil 8 is connected to the positive terminal of the second DC power supply 10, and the other end of the second DC power supply 10 is grounded.

The recording signal 17 supplied to the input terminal 13 is applied to the gate of the first JFET 11 by the inverter circuit 14,
21 and 22, and the recording signal 17 is supplied to the gate of the second JFET 12 through the inverter circuit 14, the recording standby circuit 24, and the inverter circuit 23, and constitutes the first and second switching elements. JFE
T11 and 12 are alternately turned "on" in synchronization with the recording signal.
It is designed to be "off" controlled.

The recording standby circuit 24 connected between the inverter circuits 14 and 23 is in a standby state where the recording signal is not supplied to the gates of the first and second switching elements, that is, the JFETs 11 and 12, and the first and second switching elements. J
This is a circuit for making the FETs 11 and 12 both "on", and time constant circuits 26 to 2 having different charge and discharge constants.
9 and the switching element 30.

A resistor 25 is connected between the recording standby circuit 24 and the inverter circuits 14 and 23, and the resistor 2
The third switching element 30 is connected between the connection point C of the inverter 5 and the inverter circuit 23 and the ground. The third switching element 30 is a JFET, the drain of which is connected to the connection point C and the source of which is grounded. A resistor 28 is connected in parallel with the resistor 25 and between the output end of the inverter circuit 14 and the gate of the third JFET 30. A series circuit of a diode 26 and a resistor 27 is connected in parallel with the resistor 28. The anode side of the diode 26 in this series circuit is connected to the resistor 27, the cathode side is connected to the output end of the inverter circuit 14, and the resistor 28 and the third circuit are connected.
A capacitor 29 is connected between the connection point with the gate of the JFET 30 and the ground.

The resistor 28 and the capacitor 29 form a charging circuit, and the charging time constant determined by the resistance value R _{3 of the} resistor 28 and the capacitance C ₁ of the capacitor 29 is selected so as to be longer than the longest period of the recording signal 17. Similarly capacitor 2
9, the resistance value R ₄ of the resistor 27 forming the discharge circuit and the forward resistance of the forward diode 26, and the capacitor 2
The discharge time constant determined by the capacitance C ₁ of 9 is selected to be sufficiently smaller than the shortest period of the recording signal 17.

In the above configuration, the case where N-type JFETs are used as the first to third switching elements has been described.
It is obvious that normal NPN-type and PNP-type transistors and inverter circuits corresponding to these can be used as well as N-type JFETs and N-type and P-type MOSFETs, and inverter circuits 14, 21, 22, 23 are also NAND. Alternatively, it is obvious that a NOR circuit and an operational amplifier (OP amplifier) can be used.

The operation of the magnetic head drive circuit having the above configuration will be described with reference to the timing waveform diagram of FIG. The recording signal 17 shown in FIG. 2A is supplied to the input terminal 13, and the standby period 3
In the case of 1, the recording signal is “OFF” and in the L state, and is supplied to the inverter circuit 14. At the output end of the inverter circuit 14, the recording signal 17 having the output waveform 32 shown in FIG.
Is inverted and brought into the H state in the standby period 31. Therefore, in this standby state, the capacitance C _{1 of the} capacitor 29 is charged through the resistance value R ₃ of the resistor 28, the charging potential is added to the gate of the third JFET 30, and the third JFET 30 is turned “on”.

Therefore, in the standby period 31, the output waveform 32 which has been brought into the H state by the inverter circuit 14 is brought into the L state and supplied to the inverter circuit 23. Since this waveform is formed as the input waveform 33 as shown in FIG. 2C, it is inverted by the inverter circuit 23 and becomes the H state in the standby period 31 as shown in FIG. 2D and the input waveform 34 of the second JFET 12 is formed. As supplied to the gate. Thus, the second FET 12 is "turned on".

On the other hand, the output waveform 32 of the inverter circuit 14 shown in FIG. 2B is in the H state during the standby period 31,
The inverter circuit 21 inverts the signal to generate an L signal, and the inverter circuit 22 inverts the signal to generate an H signal, which is supplied to the gate of the first JFET 11. Therefore, as shown in FIG. 11 input waveforms 35 are obtained and the first JFET 11 is "turned on".

Therefore, the first and second JFETs 11 and 12 are both in the "on" state while the recording signal 17 in the standby state 31 is not supplied, and the current I _H flowing in the magnetic head 6, that is, the currents I ₁ and I _2. Can be made equal, the magnetic head current can be I _H = 0 as shown in FIG. 2F.

Next, when the recording signal 17 is supplied at the recording start time of t = a, the H signal is supplied to the input terminal 13 as shown in FIG. 2A, and the cathode side of the diode 26 is an inverter circuit as shown in FIG. 2B. The L signal inverted at 14 is added and the electric charge accumulated in the capacitor 29 is rapidly discharged through the discharging circuit of the resistor 27 and the diode 26, and the input waveform 33 of the inverter circuit 23 is the L signal as shown in FIG. 2C. 2E, the input waveform 35 of the second JFET 12 maintains the H signal state as shown in FIG. 2E.
Holds the "on" state. Next, when the recording signal changes from H to L, the output of the inverter circuit 14 changes from L to H, and the gate of the third JFET 30 changes due to the charging constant of the resistance value R _{3 of the} resistor 28 and the capacitance C ₁ of the capacitor 29.
Although the charge constant gradually goes from L to H, since the charge constant is longer than the longest period of the recording signal, the recording signal becomes L before the threshold voltage at which the third JFET 30 turns “on” is exceeded, and the shortest recording signal is obtained. The discharge constant circuit resistor 27 and the diode 26, which are shorter than the cycle, are rapidly discharged again and the L state is maintained. That is, the third JFET 30
Is an “on” state in the recording standby state, and is kept “off” while the recording signal is being input if it is “off” once at t = a when the recording signal starts. The input signal of 23 is the inverter circuit 1
The result of the output of 4 is directly input. On the other hand, the first J
The gate of the FET 11 is L at t = a as shown in FIG. 2D.
Therefore, the first JFET 11 is turned "off", and then the first and second JFETs 11 and 12 are alternately turned "on" and "off" in synchronization with the recording signal 17, so as shown in FIG. 2F. In the transient state immediately after the recording start t = a of the recording signal 17 from the standby period 31, the direction of the current I _H of the magnetic head 6 falls from zero to one direction without making a difference, and the currents can flow in good balance. It will be possible.

Although the standby circuit 24 is provided on the side of the second switch element 12 in the embodiment shown in FIG. 1, the first switch 24 is turned off when the first recording signal is supplied to the first switch element 11. It is obvious that the recording standby circuit 24 may be provided on the gate side of the element 11.

[0036]

According to the magnetic head drive circuit of the present invention,
When two switching elements and an inductance are alternately applied to the head coil of the magnetic head, a switch standby circuit is provided in the switch control circuit to supply a recording signal to the magnetic head just after the start. An excessive difference in the current direction is removed, and a current is applied to the magnetic head in a well-balanced manner, and good magnetic field modulation recording is possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a magnetic head drive circuit of the present invention.

FIG. 2 is an explanatory diagram of operating waveforms of the magnetic head drive circuit of the present invention.

FIG. 3 is a diagram illustrating the principle of a magnetic head drive circuit according to the present invention.

FIG. 4 is a principle waveform explanatory diagram of a magnetic head drive circuit of the present invention.

FIG. 5 is an explanatory diagram of a magnetic field modulation method used in a conventional magnetic head drive circuit.

FIG. 6 is a circuit diagram of a conventional magnetic head drive circuit.

FIG. 7 is a diagram illustrating the principle of a conventional magnetic head drive circuit.

FIG. 8 is an explanatory diagram of a current flowing through an auxiliary coil in a recording standby state of a conventional magnetic head drive circuit.

FIG. 9 is a waveform explanatory diagram of a conventional magnetic head drive circuit.

[Explanation of symbols]

 6 Magnetic head 7,8 Auxiliary coil 9,10 DC power supply 11,12,30 Switching element 14,21,22,23 Inverter circuit 24 Recording standby circuit

Claims (3)

[Claims] 1. A head coil of a magnetic head is arranged between a series circuit composed of two switching elements connected in series with two auxiliary coils having an inductance larger than that of the head coil of the magnetic head, In a magnetic head drive circuit configured to control a switching element according to a recording signal, a recording standby circuit for causing a control means for controlling the switching element to turn on both of the two switching elements during recording standby. A magnetic head drive circuit comprising: 2. The magnetic head drive circuit according to claim 1, wherein the recording standby circuit includes a time constant circuit having different charge / discharge constants and a switching element. 3. The recording standby circuit is provided in either one of control means for alternately turning “on” and “off” the two switching elements at the time of recording so that the direction of the magnetic head current generated immediately after the start of recording is controlled. The magnetic head drive circuit according to claim 1 or 2, wherein a transient difference is prevented.