JPS62296790A - Motor driving circuit - Google Patents

Abstract

PURPOSE:To suppress a blind sector in a motor driving circuit by providing level shift diodes for a voltage corresponding to base-emitter voltage of the transistor circuit of an output stage in the preceding stage. CONSTITUTION:Sine wave signal generated from a signal source 1 is applied to the base of a transistor Q1 of a buffer stage 3 via an input amplification stage 2. The collector of the transistor Q1 is connected to a series circuit of a resistor R2 and diodes D1 and D2. Forward voltage VD generated respectively on the diodes D1, D2 is used for a level shift. The output of the transistor Q1 is fed to the base of the transistor Q2 of an output stage 4. Signal current I2 flowing through a load R1 is detected by a resistor R3 for current feedback to the input amplification stage 2. As a result, a blind sector on a driving circuit can be reduced by the slight change of the circuit.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Summary] By raising the base potential of the output stage of a motor drive circuit such as a VCM (voice coil motor).

Eliminate dead zones.

[Industrial application field]

The present invention relates to a motor drive circuit such as a VCM used in a magnetic disk drive or the like, and more particularly to a technique for eliminating a dead zone that occurs at the output stage of a DC feedback amplifier that constitutes a VCM drive circuit.

[Conventional technology]

A typical magnetic disk drive uses a VCM (voice coil motor) to control the seek operation of the head. The VCM is driven by a drive circuit configured as a DC feedback amplifier.

FIG. 5 shows a basic circuit constituting such a VCM drive circuit, and in reality, two of these basic circuits are used to bridge-drive the VCM.

In FIG. 5, 1 is a signal source and 2 is a manual amplification stage.

3 is a buffer stage, 4 is an output stage, and 5 is a level converter.

Q,,Q2,Q,is a transistor,R,,R2゜R3
is the resistance I RL is the load (VCM in this case).

V, , VZ, V:l is power supply potential + ■O+ vl
+v2 is the signal voltage, 1. , I2 represents a signal current (emitter current), and VBE represents a voltage between the base and emitter of the transistor.

The signal source 1 generates a sinusoidal signal and only during its positive half cycle, in the output stage 4, a signal current I2 is applied to the load RL.
is caused to flow and driving is performed.

Input amplification stage 2. Buffer stage 3. The output stages 4 are directly coupled to each other, and the signal voltage Vl generated across the current detection resistor R3 provided in the output stage 4 is fed back to the input amplification stage 2 via the level converter 5.

By the way, in the output stage 4, the transistors Q2 and Q3 are connected in a Darlington manner. For this reason.

Each transistor Q2. Q3 base-emitter voltage■
1 overlap, raising the base potential of the input side transistor Q2 by 2V++t, creating a so-called Fuwazai zone.
As shown in FIG. 6, this causes an idle running period in the output. This will be explained below using two equations.

First, the relational expression between +v2 and 12 is.

Vz =Rz Iz =2Vgi+R3I2 ---
-----■ If this is shown in a graph, it will be as shown in FIG. 7 (al). Also, the relational expression between vo and I1 is.

7゜=■□+R+1+ ・−・・−・
・It is represented by ■, and by substituting the 0 expression into the 0 expression, the relational expression between + vO and I2 is obtained. Furthermore, the gain G of the subsequent stage viewed from the output of the input amplification stage 2 is calculated by ignoring the offset.

It becomes vO. If the equation 0 is shown as a graph, it will be as shown in FIG. 7(b).

Based on this equation 0, the conditions for flowing It are:

It turns out that. That is, if it is desired to minimize vo, it is necessary to increase R2 or decrease R8.

However, when this condition is satisfied, the slope of the graph in FIG. 7(b) becomes smaller and the gain G expressed by equation 0 becomes larger, making the two circuits unstable.

[Problem that the invention seeks to solve]

In conventional VCM drive circuits, unsteady zones tend to occur.

There was a problem in that the drive current of the VCM was cut off, resulting in an idle running period. In order to eliminate this dead zone, a method is generally used to increase the gain, but as a result, it is impossible to avoid instability of the two circuits.

The present invention attempts to easily reduce the dead zone without using a method of increasing the gain of one circuit.

[Means for solving problems]

Therefore, in the present invention, the level gap between the output stage and the previous stage is compensated for by inserting a level shift diode commensurate with the base-emitter voltage of the output stage transistor circuit in the stage before the output stage of the motor drive circuit. This suppresses the dead zone.

FIG. 1 shows the basic structure of the present invention in an exemplary manner.

The illustrated configuration is compared to the conventional circuit shown in FIG.

In FIG. 1, 1 is a signal d, and 2 is a manual amplification stage.

3 is a buffer stage, 4 is an output stage, and 5 is a level converter.

Q+, Qz, Qs are transistors, D, , D2 are level shift diodes, R1+ Rz, R3 are resistors, RL is load, V, , V, , V3 is power supply potential * v
O+ vl + v2' is the signal voltage, Ill 1
2 is the signal current, ■. is the forward voltage of the diode, V
! IE represents the voltage between the base and emitter of the transistor.

A sinusoidal signal generated from a signal source 1 is applied to a single-power amplification stage 2. The output of input amplifier stage 2 is applied to the base of transistor Q, of buffer stage 3.

Transistor Q is a PNP type transistor, with a resistor R1 on the emitter side and a resistor R2 on the collector side.
and diodes D+ and D2 are provided in series.

Forward voltage ■ generated in diodes D, , and Dffi, respectively. is used for level shifting.

The collector of transistor Q is directly connected to the base of transistor Q2 of output stage 4. Transistor Q2 is Darlington-connected to transistor Q3, has a load RL (ie, VCM) on its collector side, and has a resistor R1 on its emitter side.

The signal current I2 flowing through the load RL is detected by a resistor R3, and the current is fed back to the input amplifier stage 2 via the level converter 5.

The signal current (2) flows only during approximately the positive half cycle of the sinusoidal signal generated by the signal source (1).

[Effect]

This is because the level shifting diodes D+ and Dz are provided in series with the resistor R2 on the emitter side of the transistor Ql constituting the buffer stage 3.

The signal voltage v2' is increased by 2cm compared to the signal voltage v2 in the conventional circuit shown in FIG.

Figure 2(a), (bl is v2 for I, respectively
This figure shows a comparison of the changes between V2' and V2'.

In Figure 1, the relationship between ■2', 1+, and Iz is 9
It is given by the following formula.

v*'=RtIt+2VD=2VBz+Ry
If--------・-・■ From formula 0.

is obtained. On the other hand, the relationship between + vO and I is.

It is given by the following formula.

VO=V BE + RI I I
−'−−”■■ Substitute the expression.

is obtained.

Figure 3 is a graphical representation of this ②. As shown in the figure, the change in vo for +I2 is.

In order to minimize vo, it is desirable that the value of the starting point be small. For this value, +VIE is almost ■. IVII when equal to
It becomes E. In this case, if r vo is made larger than ■, + rz can flow. This value V8t has the advantage of not affecting the value of the starting point in the case of the conventional circuit shown in FIG. 7 (bl), that is, the gain.

〔Example〕

FIG. 4 shows the configuration of an embodiment of a VCM drive circuit according to the present invention.

In Figure 4, ■ is a signal source, 2A, 2B are input amplification stages, 3A, 3B are buffer stages, 4A, 4B are output stages, 5A
, 5B is a level converter, Q, A, QIll Qz^
, QzlI, Q, A, Q, ,, Q4A,
Q4I+ is a transistor, DIA+ DIR
+ DZAI D28 is a diode and RL respectively
represents the load (VCM).

The illustrated embodiment circuit uses two basic circuits of the present invention shown in FIG. 1, each having a positive half cycle and a negative half cycle of sine wave drive, and one load Rt
This corresponds to the case where the two are driven alternately. In the figure, the circuit on the left operates in a positive half cycle, and the circuit on the right operates in a negative half cycle.

Therefore, the input amplification stage 2A takes in only the positive half cycle of the sine wave signal generated by the signal source 1 and inverts and amplifies it.
On the other hand, the input amplification stage 2B is configured to take in only the negative half cycle and perform non-inverting amplification.

Buffer stages 3A and 3B and output stages 4A and 4B.

Each has the same circuit configuration and is placed symmetrically, especially the output stage 4.
A and 4B are configured to bridge-drive the load RL.

Specifically, in the positive half cycle, Q, , Q
4A is driven *Q3mI Q4m remains off.

Q4A-RL → Q, +RL in the path of A, the drive current flows from right to left, and in the negative half cycle, Q3111
Q4B is driven, and Q, A, and Q4A are turned off.

Q a s = RL = Q 1! On route l, R
t, the drive current flows from left to right.

Buffer stages 3A and 3B include level shifting diodes DIA+ D2A+ Dll+ DA, respectively.
Since B is inserted, the dead zone is kept small, and the idle running period that occurs at the boundary between the positive half cycle and the negative half cycle becomes extremely short.

〔Effect of the invention〕

According to the present invention, the dead zone in the VCM drive circuit can be significantly reduced with a slight modification of two circuits and at a low cost.Moreover, the stability of the circuit is not impaired, but rather is improved, so the operating characteristics are improved. and reliability can be improved.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of the present invention, and FIG. 2 is an explanatory diagram showing the effect of inserting a level shift diode. FIG. 3 is an explanatory diagram showing the current drive characteristics of the circuit of the present invention in which a level shift diode is inserted, FIG. 4 is a configuration diagram of an embodiment of the present invention, FIG. 5 is a configuration diagram of a conventional VCM drive circuit, and FIG.
This figure is an explanatory diagram of the effect of the dead zone generated in the VCM drive circuit of FIG. 5, and FIG. 7 is an explanatory diagram of the conventional dead zone suppression method. In Figure 1. l: Signal source 2: Input amplification stage 3: Buffer stage 4: Output stage 5 Two-level converter Q+, Qz, Qs: ) transistor D+, D
t diode for two-level shift R+, Rz,
R8: Resistance

Claims (1)

[Claims] A level shift diode that generates a voltage approximately equivalent to the voltage between the base and emitter of the output stage transistor circuit is inserted into the output section of the transistor circuit in the previous stage of the output stage to increase its output potential. - A motor drive circuit characterized by eliminating the dead zone by compensating the emitter voltage.