JPH03226295A - Load drive circuit - Google Patents

Abstract

PURPOSE:To reduce power loss in a load drive circuit by providing a power supply for feeding a drive transistor with a power having a driving voltage obtained by adding a predetermined offset voltage to the load voltage across a load. CONSTITUTION:Collector of a drive transistor Q1, having non-earth side terminal P1 of a reel motor 2 constituting a load, is connected with a collector power supply amplifier circuit 3 and source power is fed from a DC power supply 4 through the collector and emitter of the drive transistor Q1 to the non-earth side terminal PL of the reel motor 2. Consequently, drive current IDV is fed through the reel motor 2 and a drive current detecting resistor R1 thus driving the reel motor 2. Since only a voltage corresponding to an offset voltage VOFST is applied across the drive transistor Q1 at all times, the transistor Q1 is not overheated upon load voltage drop.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Outline of the invention C. Conventional technology. Problems to be solved by the invention. E. Means for solving the problems. 1. Effects. G2) Configuration of offset voltage circuit and collector power supply amplifier circuit (Figs. 2 to 6 and 12) (G3) Second embodiment (Fig. 7) (G4) Third embodiment (Fig. 8) ) (G5) Fourth embodiment (Figure 9) (G6) Fifth embodiment (Figure 10) (G7) Sixth embodiment (Figure 11) (G8) Other examples H Effect of invention Industry A INDUSTRIAL APPLICABILITY The present invention relates to a load drive circuit, and is particularly suitable for application to a case where a load is driven at a constant current.

B. Summary of the Invention The present invention provides, in a load drive circuit, a drive transistor that provides a power output having a value similar to that of a load voltage generated across a load by applying a predetermined offset voltage to the drive transistor. Excessive heat generation can be prevented, and a highly efficient load drive circuit can be realized.

C. Prior Art For example, in a video tape recorder, a load drive circuit is used as a reel motor drive circuit for driving a take-up reel to drive a load at a constant current.

The reel motor drive circuit utilizes the characteristic proportional to the torque drive current that can be generated in a DC motor.
The tape tension of the magnetic tape wound by the reel is controlled to a constant value, thereby controlling the torque generated from a reel motor constituted by a DC motor to a constant value.

D Problems to be Solved by the Invention In a load drive circuit applied to such a reel motor drive circuit, the output current value is generally selected to be a relatively large value in order to generate a practically sufficient torque. In addition, since the rotational speed of the reel motor has a wide variation range, it is necessary to use a power source with a sufficiently high voltage for practical use.

Incidentally, the torque of a reel motor made of a DC motor is proportional to the drive current value, and the rotation speed is proportional to the voltage. On the other hand, the reel motor needs to rotate the reel at a relatively low speed in the recording/reproducing mode, whereas it is necessary to rotate the reel at a high speed when transferring the magnetic tape at high speed.

Therefore, it has conventionally been thought that a load drive circuit constituting the output stage of a reel motor drive circuit inevitably suffers from large power loss.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a load drive circuit that can further reduce power loss as a load drive circuit.

E Means for solving the problem In order to solve the problem, in the present invention, the load 2
has a drive transistor Q1 connected in series with
Power output ■. 1. In a load drive circuit that supplies VeC to a load 2 through a drive transistor Q1, a predetermined offset voltage ■ with respect to the load voltage VTHL present across the load 2. The driving voltage VC that gave 2,7! (@1
A load drive circuit 3 is provided which supplies a power supply output having a value of 1 to the drive transistor Q1.

F action A predetermined offset voltage ■ with respect to the load voltage V THL.

2. i and drive voltage Vctt. , ) to the collector of the drive transistor Q1, even if the load voltage VTHL changes, there is always an offset voltage V across the drive transistor Q1. By applying only the voltage corresponding to 7, 7, it is possible to prevent the drive transistor Q1 from generating excessive heat when the load voltage decreases, and it is possible to realize a highly efficient load drive circuit.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

(Gl) First embodiment In FIG. 1, 1 indicates the load driving circuit as a whole,
The emitter of a drive transistor Q1, which is an NPN transistor, for example, is connected to the non-ground end P1 of the reel motor 2, which constitutes the load to be driven, and one end is connected to the ground (!1 end P2) of the reel motor 2. A drive current detection resistor R1 is connected to the drive current detection resistor R1.

A collector power supply amplifier circuit 3 is connected to the collector of the drive transistor Ql, and the power output supplied from the DC power supply circuit 4 (consisting of voltage v6. By supplying it to the ground side end P1, a drive current Isv flows through the reel motor 2 and the drive current detection resistor R1, thereby driving the reel motor 2.

In this driving state of the reel motor 2, the detection voltage Vll? obtained at the midpoint of the connection between the drive current detection resistor R1 and the reel motor 2? is compared with the drive input signal et in the comparator circuit 5, and the deviation voltage obtained at the output terminal of the comparator circuit 5 is supplied to the base of the drive transistor Q1 as the drive control signal VIN. , a drive current of 111V corresponding to
A constant current is controlled so that the current flows through the reel motor 2.

In addition to the above configuration, an offset voltage circuit 6 is connected to the emitter of the drive transistor Q1 and the connection midpoint of the reel motor 2, and an offset voltage obtained at both ends of the circuit 6 is connected.
. 2. T is supplied to the collector power supply amplifier circuit 3 as a reference power supply voltage ■□r.

Here, the offset voltage V OF of the offset voltage circuit 6
F? The collector-emitter saturation voltage V C! of the drive transistor Q1 is expressed as the following formula (1): ! A voltage value slightly larger than AT is selected, and as a result, the reel motor terminal voltage (i.e., during the connection between the drive transistor Q1 and the reel motor 2) is applied to the output terminal of the offset voltage circuit 6 as shown in the following equation (2) Voltage at point) ■1, offset voltage ■. A reference input voltage V□, which is higher by 2.7, is obtained and is supplied to the collector power supply amplifier circuit 3.

The collector power supply amplifier circuit 3 is an offset voltage circuit 6
The total gain c for the reference input voltage, including the gain of
The circuit constants are selected so that any becomes a value 1 as shown in the following equation (3), and as a result, the output terminal of the collector power supply amplifier circuit 3 is connected to the output terminal of the collector power supply amplifier circuit 3 as shown in the following equation (4). Offset voltage■. 1. A collector and emitter drive voltage VB, □) approximately equal to A is generated and supplied to the collector of the drive transistor Ql.

In the above configuration, the drive transistor Q1 is configured such that the drive current I A constant current operation is performed to maintain a constant value, and thereby the reel motor 2 is driven with a winding torque such that the tape tensicon of the magnetic tape is constant with respect to the take-up reel.

In this driving state, the collector power supply amplifier circuit 3
An offset voltage V is applied to the input terminal of the reel motor terminal voltage V fML. 2! ? A reference input voltage VIEF having a voltage value as high as
The signal is amplified with an amplification degree of , and is supplied to the collector of the drive transistor Q1. Therefore, the collector of the drive transistor Q1 has a offset voltage (2) from the reel motor terminal voltage VBI supplied to the emitter. By applying a drive voltage higher by 1.7, the drive transistor Q
There is always an offset voltage between the collector and emitter of 1.
. FIT will be given.

Incidentally, when the reel motor 2 is driven at a constant current, the terminal voltage of the reel motor 2,
The value is determined by the rotation speed, drive current, and rotation direction of the reel motor 2. Therefore, the drive mode of the reel motor 2 is the recording mode,
When in playback mode or fast forward mode, it changes accordingly. However, the collector and emitter drive voltage V applied to the collector and emitter of the drive transistor Q1
C1(.,) always changes to the offset voltage voys'r in any mode.

Therefore, in the fast-forward mode, the reel motor terminal voltage V
When TKL rises to a high voltage, the voltage at the collector of the drive transistor Q1 is changed accordingly, so that the drive transistor Q1 can stably control the reel motor 2 with a constant current, and at the same time When the reel motor terminal voltage v7□ decreases due to a decrease in rotational speed due to switching to recording mode or playback mode, drive transistor Q1
Since the collector voltage of the drive transistor Q1 also decreases, an excessive drive voltage is not applied to the drive transistor Q1, and the drive transistor Q1 is not overdriven. The reel motor 2 can be controlled with constant current without fear.

In this way, it is possible to realize a load drive circuit that can drive the drive transistor Q1 at a constant current with high efficiency.

(G2) Configuration of Offset Voltage Circuit and Collector Power Supply Amplifier Circuit The detailed configuration shown in FIG. 2 can be applied as the load drive circuit 1 of FIG. 1.

The comparison circuit 5 includes a differential amplifier circuit ICII, a feedback input resistor R11, and a feedback capacitor C1l.
It has a drive transistor Q1, a reel motor 2,
Conversion gain 1 (A/V) with drive current detection resistor R1
This constitutes a constant current circuit.

Further, the offset voltage circuit 6 has the power supply output voltage V of the power supply circuit 4. (=+5 (V)) at the base, and the constant current output 11 obtained from the constant current circuit consisting of the transistors Qll and G12 forming the current mirror circuit, is applied to the connection midpoint between the drive transistor Q1 and the reel motor 2. voltage dividing resistors R12 and R connected to
13, and this mainly creates a composite resistance of constant current ■1 and voltage dividing resistors R12 and R13 (the effective resistance in the loop of resistor R12 - reel motor 2 - drive current detection resistor R1 - ground is approximately resistor R12) The offset voltage v orst determined by the product of
is supplied as a reference power supply voltage V□r.

In this embodiment, a lead compensation circuit 11 consisting of a capacitor C12 and a resistor R14 is provided between the offset voltage circuit 6 and the connection midpoint of the drive transistor Ql and the reel motor 2. Drive transistor Q from supply amplifier port W13
This is designed to compensate for the delay from the reference power supply voltage v*** while the drive power supply output supplied to the collector of 1 is being processed in the collector power supply amplifier circuit 3.

Collector power supply amplifier circuit 3 is offset voltage circuit 6
The reference power supply voltage vmxr generated in is applied to the non-inverting input terminal of the differential amplifier circuit IC12, and the difference with the reference voltage obtained from the gain setting resistors R21 and R22 is input to the comparator ICl3 of the differential amplifier circuit configuration. .

The comparator ICl3 turns on the switching transistor Q23 via the reverse operation transistors Q21 and G22 when the voltage level becomes lower than the triangular wave voltage generated in the triangular wave generation circuit having the differential amplifier circuit ICI4, By turning off the power supply voltage VCCI when the reference 11tf1 voltage v1,
A pulse width modulated output S12 obtained by performing pulse width modulation to a pulse width corresponding to the voltage level of 2 is obtained at the output terminal of the switching transistor Q23.

This pulse width modulation output S12 is a Schottky diode D.
21, a choke coil L21, and a capacitor C16.The DC rectified output is fed back to the resistor R21, and the DC drive voltage VC! (The DC drive current 1. of Ql+ is supplied to the collector of the drive transistor Q1 as a motor.

In the above configuration, the collector power supply amplifier circuit 3 constitutes a pulse width modulation amplifier circuit using the switching transistor Q23 as a switching element, and its voltage gain G
, is a value determined by the following equation depending on the resistance ratio of voltage gain setting resistors R21 and R22.

For example, set the values of resistors R21 and R22 to R21-22.
0 (kΩ), R22 = 33 (kΩ), the voltage gain G of the pulse width modulation amplifier circuit is -7,66 = 17.69 (dB)...
... The value is approximately (6).

On the other hand, the offset voltage ■ generated in the offset voltage circuit 6. 1. A, (which is equal to the voltage across the resistor R12) is expressed by the product of the constant current (1) and the combined resistance of the parallel resistors R12 and R13, as shown in the following formula (7), so it is constant. Current output II
, the values of resistors R12, R13, and R1 are 1, =0.04
47 (μA), R12=12 [kΩ], R13=
1.8 (kΩ), R1 = 1 (Ω), the value of offset voltage V.F, 7 becomes VOFST'
=, 0.0100 (V) -----
・As shown in -(8), the value is about 0.0700 (V).

In this way, in the offset voltage circuit 6, the reel motor terminal voltage V TNL is changed to the offset voltage vorst.
When obtaining the reference power supply voltage VIEF with an offset of value,
In other words, by selecting 17.69 [dB],
Substantially, the total gain Gmxr of the offset voltage circuit 6 and collector power supply amplifier circuit 3 is CAMF = 1 (=O(ds))
・・・・・・1 as in (9) (=O(dB)
) can be made.

Thus, according to the configuration of FIG. 2, the reel motor terminal voltage ■□, as described above with respect to FIG.

Even if the value of VC changes depending on the operating mode, the collector drive voltage VC! of the drive transistor Q1 changes accordingly. +.

l) Offset voltage■. Since it can be floated to a value offset by 15T, an offset voltage V is always present between the collector and emitter of the drive transistor Q1. ,. A drive voltage equal to that can be given.

In this way, even if the rotational speed of the reel motor 2 decreases and the terminal voltage of the reel motor 2 decreases in the recording mode or the reproduction mode, it is possible to prevent excessive supply voltage from being supplied to the collector of the drive transistor Ql. , it is possible to effectively avoid the risk of causing the drive transistor Q1 to generate excessive heat, and it is possible to realize a load drive circuit with a good division ratio.

Incidentally, as in the conventional case, the power supply voltage supplied to the collector of the drive transistor Q1 cannot be driven even when the terminal voltage of the reel motor 2 becomes high (corresponding to when the reel motor 2 is rotated at high speed in fast-forward mode). If the transistor Q1 is selected to have a sufficiently high constant value so that it can be operated in a range with sufficiently good linearity for practical purposes, when the terminal voltage of the reel motor 2 becomes low (the reel motor 2 is recorded) mode or reproduction mode), the voltage corresponding to the drop in the terminal voltage of the reel motor 2 is excessively increased by the drive transistor Q1.
is supplied to the collector.

As a result, when the reel motor 2 is driven at a constant current, an excessive drive voltage is applied between the emitter and the collector, and the amount of heat generated inside the drive transistor Q1 increases, and the load drive circuit 1 as a whole However, according to the configurations shown in FIGS. 1 and 2, such efficiency can be prevented from occurring.

If we calculate the degree of improvement in efficiency for the embodiment shown in Figure 2, we get:
It will look like this:

For example, in a conventional configuration as shown in FIG. 12 with the same reference numerals assigned to parts corresponding to those in FIG. When the voltage is in the operation mode of -3 [V], the constant current drive current I□ flowing through the drive current detection resistor R1 with a resistance value R1 - 0°2 [Ω] is ■□=
0.5 (A), the heat loss W generated in the drive transistor Ql is W, −(12(V) −3(V) −0,2(Ω))
x0.5 (A) ) x O,5(A)-4,45(W
) ......(10).

On the other hand, in the configuration of FIG. 1, the offset voltage V
OFS? If Vorsr-0,8 (V), the total gain G of the offset voltage circuit 6 and the collector power supply amplifier circuit 3, and □ are selected as Gh and p-1, the voltage between the emitter and the collector of the drive transistor Q1 is vC! is the offset voltage ■. 1. A value equal to a, that is, V, , =
0.8 (V), so the drive transistor Q1
The heat loss W□ occurring at W, −0,5(A
) Xo, 8 (V) = 0.4 (W) (11) In addition to this, the collector voltage VC of the drive transistor Ql is the voltage drop across the resistor R1 = 0.2 [ Ω)
x o,s (A), terminal voltage of reel motor 2 =
3 (VL offset voltage = 0.8 (V) sum voltage, v, = 0.2 (Ω) Xo, 5 (A) + 3
(V) +0.8 (V) = 3.9 (V) (12) Therefore, the output W generated in the collector power supply amplifier circuit 3 is W.

= (12 (V) 3.9 (V)) xo, 5 (A) = 4.05
(W) (13) It should be. By the way, assuming that the efficiency of the collector power supply amplifier circuit 3 is 90% (this value is practical if a pulse width modulation circuit configuration is used), the input power W4 supplied from the power supply circuit 4 is 0 00, the loss W generated in the collector power supply amplifier circuit 3 is W.

=4.5 (W) -4,05 (W) =0.45 (W) (15) As a result, the total loss Wh generated in the drive transistor Ql and collector power supply amplifier circuit 3 is as follows.
is W, = W□ +W.

=0.4(W) +0.45 [W] -0,85[W] (16) become.

Therefore, in the configuration shown in FIG. 1, the total loss Wa
(Equation (16)) can be reduced to approximately 115 compared to the loss W generated in the conventional configuration shown in FIG. 12 (Equation (10)), and in particular, the heat loss Wz ( If we limit ourselves to equation (11), it can be reduced to approximately 1/10 compared to the conventional configuration shown in FIG.

Thus, by using the load drive circuit 1 shown in FIG. 1, the efficiency of the reel motor drive system can be further increased compared to the conventional case shown in FIG. 12.

In addition, in the case of the embodiment shown in FIG. 2, the collector power supply amplifier circuit 3 can obtain an efficiency of approximately 90% with respect to changes in output current as shown in FIG.
As shown in FIG. 4, it is possible to obtain a frequency characteristic in which the output gain is approximately constant in the frequency range up to approximately 2 [kHz].

In the case of the embodiment shown in FIG. 2, in the offset voltage circuit 6, the terminal voltage V?
Transistor Ql that divides NL to form a constant current circuit
In addition to the efficiency of attenuation corresponding to the voltage gain G of the collector power supply amplifier circuit 3 as described above,
The phase lead compensation is performed so as to realize a flat phase characteristic over a wide band with respect to the phase characteristic (FIGS. 5 and 6).

Incidentally, since the collector power supply amplifier circuit 3 is provided with a filter circuit including a choke coil L21 and a capacitor C16 after the switching transistor Q23, its resonance frequency re (FIG. 5) is -12( dsloct) and the phase is rotated by -180 degrees.

Such attenuation and phase rotation are flattened by compensating for the phase advance using voltage dividing resistors R12 and R13 of the offset voltage circuit 6.

Furthermore, in the case of the embodiment shown in FIG. 2, the lead compensation circuit 11 connected in parallel with the voltage dividing resistor R12 leads the input signal to the collector power supply amplifier circuit 3 in phase so as to prevent the clipping phenomenon from occurring in the drive transistor Q1. give compensation.

Incidentally, if the operating band of the collector power supply amplifier circuit 3 is insufficient, if the input signal has high frequency components, the phase will be delayed and the collector drive voltage ■c! (, 1, it becomes impossible to obtain a sufficient output voltage.

Here, if the voltage between the emitter and the collector of the drive transistor Q1 cannot be maintained at a predetermined value, h□ of the drive transistor Q1 decreases, and eventually the drive transistor Q1 causes a clipping phenomenon. On the other hand, in the case of the embodiment shown in FIG. 2, by providing the lead compensation circuit 11, it is possible to compensate for the phase delay occurring in the collector power supply amplifier circuit 3, thereby preventing the clipping phenomenon from occurring in the drive transistor Q1. It can be done.

(G3) Second Embodiment FIG. 7 shows the second embodiment, and the drive current detection resistor R1 in FIG. 1 is omitted, as the corresponding parts to those in FIG. 1 are denoted by the same reference numerals. At the same time, the detection voltage ■ applied to the inverting input terminal of the comparator circuit 5. The reel motor terminal voltage V TWL obtained at the midpoint of the connection between the drive transistor Ql and the reel motor 2 is used as the first voltage.

According to the configuration shown in FIG. 7, the comparator circuit 5 controls the drive transistor Ql at a constant voltage so that the reel motor terminal voltage V TIIL becomes a constant value.

Even in this case, the offset voltage (2) of the offset voltage circuit 6 is applied to the emitter and collector of the drive transistor Q1 in the same manner as described above with reference to FIG. 2.
? By being able to supply a drive voltage corresponding to , it is possible to always supply an appropriate collector voltage to the collector of the drive transistor Q1, and thus drive the drive transistor Q1 efficiently without causing excessive heat generation. I can do it.

(G4) Third Embodiment FIG. 8 shows a third embodiment, in which the load drive circuit 1 drives the reel motor 2 only in the forward direction.

That is, the drive transistor Q1 is an NPN transistor, and supplies the motor terminal voltages vT and L obtained at the midpoint of the connection between the drive transistor Q1 and the reel motor 2 to the adder circuit 21, and also supplies the non-ground voltage of the offset voltage circuit 6 whose one end is grounded. Offset voltage V obtained at the side edges. FS? is supplied to the adder circuit 21 as a second addition input, and its applied output is input to the collector power supply amplifier circuit 3 as a reference voltage □1.

According to the configuration shown in FIG. 8, the adder circuit 21 applies the reference power supply voltage 117, which is higher than the motor terminal voltage VTWL by the offset voltage VOW*T, to the collector power supply amplifier circuit 3.
can be supplied to the collector of the drive transistor Q1 via the offset voltage 2 between the collector and emitter of the drive transistor Q1, thus driving the reel motor 2 in the forward direction. rst can be supplied.

Thus, according to the configuration shown in FIG. 8, the drive transistor Q1 can be driven at a constant current without excessively generating heat.

(G5) Fourth Embodiment On the other hand, in the case of the fourth embodiment shown in FIG. 9, the load drive circuit 1 drives the reel motor 2 in one direction only in the opposite direction.

The drive transistor Q1 is a PNP transistor, and the power supply output VCC of the power supply circuit 4 is connected to the drive current detection resistor R.
By supplying the reel motor 2 through the reel motor 1, a driving current is caused to flow through the reel motor 2 in the opposite direction.

The motor terminal voltage VTT4L obtained at the midpoint of the connection between the reel motor 2 and the emitter of the drive transistor Q1 is applied to the addition input terminal of the current reduction circuit 22, and is also applied to the offset voltage circuit 6 as an offset voltage (2). 1,1 is applied to the subtraction input terminal of the current reduction circuit 220.

As a result, the motor terminal voltage ■
Offset voltage■ from 7□. A reference power supply voltage □, which is lower by WST, is obtained and is applied to the collector of the drive transistor Ql via the collector power supply amplifier circuit 3.

Thus, at the collector of the drive transistor Ql,
Offset voltage ■ compared to the motor terminal voltage V applied to the emitter. 2. A lower collector voltage can be applied, and thus the drive transistor Q1 can be driven with a constant current in the reverse direction without excessively generating heat.

(G6) Fifth Embodiment FIG. 10 shows a fifth embodiment. As shown by assigning the same reference numerals to corresponding parts as in FIG. 2 in the forward or reverse direction while generating approximately the same torque.

In this case, the drive control signal obtained at the output terminal of the comparison circuit 5
, is given to the bases of the forward drive transistor QIF consisting of an NPN) transistor and the reverse direction drive transistor QIR consisting of a PNP) transistor, and the commonly connected emitters are connected to the reel motor 2 and the drive current detection resistor R1. It is grounded.

Motor terminal voltage ■T□ of reel motor 2 is addition circuit 23
At F, the offset voltage ■ of the offset voltage circuit 6.

7. A is added to the forward reference voltage V OFF and supplied to the collector of the forward drive transistor QIF through the forward collector power supply amplifier circuit 3F.

Similarly, the motor terminal voltage V TIIIL is set to the voltage reducing circuit 2.
The offset voltage ■ of the offset voltage circuit 6 is applied to 3R. FAT is subtracted and the reverse reference voltage VIIF obtained at its output terminal is supplied to the collector of the reverse drive transistor QIR through the reverse collector power supply amplifier circuit 3R.

In the above configuration, the forward collector power supply amplifier circuit 3F and the reverse collector power supply amplifier circuit 3R each operate the reel motor 2 in the forward direction by being supplied with the power supply voltage V ((and -VCC) as a power supply. (or reverse direction), forward collector power supply amplifier circuit 3F (or reverse collector power supply amplifier circuit 3F)
R) into an operating state. As a result, the forward drive transistor QIF (or reverse drive transistor QIR) is driven with a constant current, and as a result, the current flowing through the reel drive motor 2 is switched to the forward (or reverse) direction, thereby driving the reel motor in the forward (or reverse) direction. drive in the opposite direction).

Here, when driving the forward drive transistor QIF (or reverse drive transistor QIR) with a constant current, an offset voltage ■ is applied between the collector and emitter of the forward drive transistor QIF (or reverse drive transistor QIR). By being able to supply a drive voltage corresponding to FIT, it is possible to flow approximately the same drive current to the reel motor 2, and as a result, it is possible to generate approximately the same amount of torque in the forward and reverse directions.

(However, by providing collector power supply amplifier circuits 3F and 3R for the forward and reverse directions, the forward and reverse drive transistors QIF and QIR do not generate excessive heat in either direction. The drive can be controlled as follows.

(G7) Sixth Embodiment FIG. 11 shows a sixth embodiment, in which the reel motor 2 is driven in the opposite direction, as shown by assigning the same reference numerals to corresponding parts as in FIG. 10. This is a simplified version of the circuit configuration.

In other words, in the case of FIG. 11, the subtraction circuit 23R and the reverse collector in FIG. 1O are omitted from the source supply amplifier circuit 3R, and the power output VCC of the reverse current f14R is directly connected to the collector of the reverse drive transistor QIR. configured to supply.

According to the configuration shown in FIG. 11, when the forward drive mode is specified by applying the drive input signal e and a signal of positive polarity, a relatively large drive current is caused to flow through the reel motor 2. The reel motor 2 generates large torque.

In this state, an offset voltage v0a, a is applied between the collector and emitter of the forward drive transistor QIF via the forward collector power supply amplifier circuit 3F.
The IF operates without generating excessive heat because the voltage supplied between the emitter and the collector is always maintained at the offset voltage VOF3 even if the motor terminal voltage Va fluctuates.

On the other hand, by switching the voltage of the drive input signal ei to negative polarity, the reverse direction drive transistor QIR
When the reverse drive transistor QIR is in an operating state, a reverse power supply output -■o is directly applied between the emitter and collector of the reverse drive transistor QIR.

Therefore, motor terminal voltage ■4. If becomes smaller, the drive voltage supplied between the emitter and collector of the reverse drive transistor QIR will increase accordingly, but in reality, if the reverse drive current flowing to the reel motor 2 is small and the generated torque is small, then There is no possibility that the reverse direction drive transistor QIR will be in an operating state in which it generates excessive heat.

Therefore, when driving the reverse drive transistor QIR, the subtraction circuit 23R and the reverse collector power supply amplifier circuit 3R can be omitted compared to the case of FIG. 10, and the overall configuration can be further simplified.

Incidentally, the reel motor in a normal tape recording/playback device requires a large torque when winding the tape in the forward direction, but only needs to generate a small torque when winding the tape in the reverse direction. In such a case, the configuration shown in FIG. 11 can be used and is suitable.

(G8) Other Embodiments (1) In the above, an embodiment has been described in which the load drive circuit according to the present invention is used to drive a linear motor of a tape recording/reproducing apparatus having a tape-shaped recording medium. The present invention is not limited to this, but can be widely applied to cases where the power supply voltage supplied to the drive transistor becomes excessive when the load fluctuates, such as in an audio output stage.

(2) In the frequency characteristics of FIG. 4, if the switching frequency of the switching transistor Q23 (FIG. 2) in the pulse width modulation circuit section is changed to a high value, - as shown by the broken line in FIG. It is possible to provide a broadband characteristic so that the constant amplitude characteristic curve portion extends to a high frequency region corresponding to the increase in the switching frequency.

(3) In the embodiment shown in Fig. 7, the configuration was described in which the constant current drive circuit shown in Fig. 1 is driven at a constant voltage. Figures 10 and 11
When the load is driven at a constant voltage in accordance with the configuration shown in the figure, the drive current detection resistor R1 is omitted and the motor terminal voltage VTML is used as the detection voltage (2), as in the case of FIG. , to the comparator circuit 5, it is possible to realize a constant voltage drive type load drive circuit that can obtain the same effect as described above with reference to FIG.

(4) In the above embodiment, the overall gain G of the offset voltage circuit 6 and the collector power supply amplifier circuit 3,
Although the case where □ is set to G and □-1 (formula (9)) has been described, the value of the overall gain G1□ may be set to a value other than 1, which is limited to this.

Incidentally, if the total gain G□P is selected to be 1, the current flowing through the drive transistors Ql, QIF, and QIR will become large and there is a risk that linear control will not be possible. It is sufficient to select a smaller value.

(5) In the above embodiment, a case was described in which a pulse width modulation circuit configuration was used as the collector 1tfl supply amplifier circuit 3, but the point is that the collector voltage is adjusted according to fluctuations in the load current. It is sufficient to use a circuit that can be controlled by

H Effects of the Invention As described above, according to the present invention, the power supply voltage applied between the emitter and collector of the drive transistor that drives the load can be controlled even when the terminal voltage fluctuates due to changes in the operation mode of the load. By being able to maintain a predetermined offset voltage, it is possible to effectively avoid generating excessive heat in the drive transistor, thereby realizing a highly efficient load drive circuit with much smaller power loss.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the load driving circuit according to the present invention, FIG. 2 is a connection diagram showing its detailed configuration, and FIG.
4 and 4 are characteristic curve diagrams showing the operating characteristics of FIG. 2, FIGS. 5 and 6 are characteristic curve diagrams used to explain the phase compensation operation of FIG. 2, and FIGS. FIG. 12 is a block diagram showing the second to sixth embodiments, and a connection diagram showing the conventional configuration. 1... Load drive circuit, 2... Reel motor, 3... Collector power supply amplifier circuit, 4
...Power supply circuit, 5...Comparison circuit, 6.
...Offset voltage circuit. Negative sliding circulation straddle n @ a certain number of times 2nd example a example 7 Prisoner collection springs up'' ← cold circuit Increased II 1 day trace 3n Efficiency characteristic 3 hard [d8] Collector t9L Amplified riJ word 30 shoulder (1 (Bamboo I
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Claims (1)

[Claims] A drive transistor connected in series to a load,
In a load driving circuit that supplies a power output to the load through the drive transistor, a power supply that supplies the drive transistor with the power output having a drive voltage that is a predetermined offset voltage with respect to the load voltage generated across the load. A load driving circuit comprising a supply circuit.