JPH0669308B2 - Motor drive circuit - Google Patents

Description

The present invention relates to a motor drive circuit for driving a brushless motor or the like.

[Conventional technology]

FIG. 3 is a circuit diagram showing one phase of a drive circuit of a conventional three-phase brushless motor. In the figure, reference numeral 1 denotes an upper driver, which is composed of transistors Q _{1 to} Q ₆ and resistors R _{1 to} R ₄ . Transistors Q ₁ , Q ₂ , Q ₃ and Q ₆ are NPN
Transistors, and transistors Q ₄ and Q ₅ are PNP transistors.

The transistor Q ₁ has its base connected to the input terminal 2 and its emitter connected to the output terminal 3 and is turned on according to H / L of the input terminal 2.
/ OFF to control the operation / non-operation of the upper driver 1.

The transistors Q ₂ and Q ₃ form a current mirror circuit with the transistor Q ₂ as a reference. The emitters of these transistors are connected to the collector of transistor Q ₁ via resistors R ₁ and R ₂ , respectively. The collector of the transistor Q ₂ is connected to the power supply voltage V _CC .

The transistors Q ₄ and Q ₅ form a current mirror circuit with the transistor Q ₄ as a reference. The collector of the transistor Q _{4 is connected to} the collector of the transistor Q ₃ , and the emitter is connected to the power supply voltage V _CC via the resistor R ₃ . The emitter of the transistor Q ₅ is connected to the power supply voltage V _CC .

The transistor Q ₆ is a power transistor, the base of which is connected to the collector of the transistor Q ₅ and the output terminal 3 via the resistor R ₄ , the collector of which is connected to the power supply voltage V _CC and the emitter of which is connected to the output terminal 3. . Output terminal 3
Is connected to GND5 via an external capacitor C for preventing oscillation and back electromotive force.

4 is a lower driver, it is configured by the transistors Q ₇ to Q ₁₂ and resistors R ₅ to R _8. Then, the transistor Q ₈ · Q ₉ and Q ₁₂ are NPN transistors, the transistor Q ₇ ·
Q ₁₀ and Q ₁₁ are PNP transistors.

The base of the transistor Q ₇ is connected to the input terminal 2 and the emitter is connected to the output terminal 3, and the transistor Q ₇ is OF depending on H / L of the input terminal 2.
F / ON to control non-operation / operation of the lower driver 4. That is, the transistors Q ₁ and Q ₇ have a push-pull configuration.

The transistors Q ₈ and Q ₉ form a current mirror circuit with the transistor Q ₈ as a reference. The emitters of these transistors are connected to GND ₅ via resistors R ₅ and R ₆ , respectively. And the collector of transistor Q ₈ is transistor Q ₇
Connected to the collector.

The transistors Q ₁₀ and Q ₁₁ form a current mirror circuit with the transistor Q ₁₀ as a reference. And the transistor
The emitter of Q ₁₀ is directly connected to the power supply voltage V _CC through the resistor R _7, and the emitter of transistor Q ₁₁ is directly connected. Also, the collector of the transistor Q ₁₀ is connected to the collector of the transistor Q ₉ .

Transistor Q ₁₂ is a power transistor whose base is connected to the collector of transistor Q ₁₁ and through resistor R ₈ to GND.
Connected to 5, collector is output terminal 3, emitter is GND
5 connected to each.

Next, the operation will be described. Now, a three-phase differential waveform in which the phase is shifted by 120 ° from the Hall amplifier (not shown) as shown in FIG. 4 is similar to the circuit shown in FIG.
It is assumed that one phase (U phase, V phase, W phase) is input to input terminal 2. The potential of the three-phase differential input waveform is always the power supply voltage V _CC.
It is assumed that it is between the and GND5. For example, the voltage V _UH higher than the midpoint potential V _ref for the U phase, the voltage V _VL lower than the midpoint potential V _{ref for} the V phase, and the same voltage V _WM as the midpoint potential V _{ref for the} W phase are input terminals 2 of each phase. In the U-phase, the transistor Q ₁ turns on to turn on the other transistors Q _{2 to} Q ₅ that form the upper driver 1, thereby supplying current to the base of the transistor Q ₆ and turning on the transistor Q ₆ Turns on,
The emitter current of the transistor Q ₆ is supplied to a U-phase motor coil (not shown) connected to the output terminal 3.
In this case, since the transistor Q ₇ is off, the lower driver 4 does not operate.

In the V phase, when the transistor Q ₇ is turned on, the other transistors Q _{8 to} Q ₁₁ forming the lower driver 4 are turned on.
And supplies current to the base of the transistor Q _12, the transistor Q ₁₂ is turned ON, current flows from the motor coil of V-phase, not shown is connected to the output terminal 3 is supplied to the collector of the transistor Q _12, It flows to GND5. In this case, since the transistor Q ₁ is off, the upper driver 1 does not operate.

Since the midpoint potential V _ref is input to the W phase, both the transistors Q ₁ and Q ₇ are turned off, and the upper and lower drivers 1 and 4 of the W phase do not operate.

That is, in the above case, the current supplied to the U-phase motor coil flows to the V-phase motor coil.

In this way, the three-phase differential input is (V _UH , V _VL , V _WM ) → (V
_UH , V _VH , V _WL ) → (V _UM , V _VH , V _WL ) → (V _UL , V _VH , V _WH ) →
The current changes from (V _UL , V _VM , V _WH ) → (V _UM , V _VL , V _WH ) to (U phase to V phase) → (U phase to W phase) → (V
Phase to W phase) → (V phase to U phase) → (W phase to U phase) →
(W-phase to V-phase) to drive the motor. Then, by changing the amplitude of the three-phase differential waveform,
Controls the drive capacity of the motor.

Next, the three-phase differential waveform input to the input terminal 2 becomes a full swing (the amplitude of the three-phase differential waveform becomes large, the potential of "H" approximates to the power supply voltage V _CC , and the potential of "L" approximates to GND5. , The saturation voltage V of the upper and lower drivers 1 and 4 when the motor driving capacity is about to drop)
_{Above CE (sat) and below} V _{CE (sat)} (when the motor drive circuit exhibits the maximum drive capacity, the maximum voltage drop in the motor drive circuit) is determined. Below, the transistor
The base-emitter voltages of Q ₁ , Q ₆ and Q ₇ are V _BE1 , V _BE6 and V respectively.
And _BE7, each of the collector-emitter voltage of the transistor Q _5, Q ₁₂ and _{V CE5 · V CE12, V BE1} ≒ V BE6 ≒ V BE7 ≒ V BE ... (1) V BE> V CE5, V BE> V CE12 … (2) The relationship is established.

First, the saturation voltage V of the upper driver 1
_{Ask on CE (sat)} . Considering that the potential of "H" is close to the power supply voltage V _CC during full swing of the three-phase differential waveform, the potential difference between the output terminal 3 and the input terminal 2 is V _BE1 , and the potential difference between the output terminal 3 and the power supply voltage V _CC. Since V _BE6 + V _CE5 , V _BE1 <V _BE6 + V _CE5 (3) from the equations (1) and (2). Therefore, the condition for the upper driver 1 to operate, that is, the saturation voltage V _{CE (sat)} for turning on the transistors Q ₁ , Q ₅ and Q ₆ is V _{CE (sat)} = V _BE6 + V _CE5 (4 ).

Next, the saturation voltage V of the lower driver 4
_{Under CE (sat)} is requested. Considering that the potential of “L” is close to GND5 during full swing of three-phase differential waveform, the potential difference between output terminal 3 and input terminal 2 is V _BE7 , and the potential difference between output terminal 3 and GND5 is V _CE12 . , (1) and (2), V _BE7 > V _CE12 (5). Therefore, under the condition for the lower driver 4 to operate, that is, _under the saturation voltage V _{CE (sat)} for turning on the transistors Q ₇ and Q ₁₂ , is V _{CE (sat) lower} = V _BE7 (6). Therefore, the voltage applied to both ends of the motor coil (not shown) connected to the output terminal 3 of each phase is V _CC- (V _{CE (sat) upper} + V _{CE (sat) lower} ) = V _CC -V _BE6 -V _CE5 -V _BE7 (7)

[Problems to be solved by the invention]

Since the conventional motor drive circuit is configured as described above, the saturation voltage V _{CE (sat) above} and _below V _{CE (sat) of} the upper and lower drivers 1 and 4 is relatively large and is applied to both ends of the motor coil. Since the voltage is small, there is a problem that the motor drive capacity is small.

The present invention has been made to solve the above problems, and has a small voltage drop in the motor drive circuit.
The purpose is to obtain a motor drive circuit with a large motor drive capability.

[Means for solving problems]

A motor drive circuit according to the present invention is a motor drive circuit in which a plurality of phases of differential inputs are input to the bases of a PNP transistor and an NPN transistor, and a push-pull system drives a motor according to the inputs.
A first level shift circuit is provided between the emitter of the transistor and the output, and the emitter potential of the PNP transistor is set higher than the potential of the output.

[Action]

The first level shift circuit according to the present invention reduces the voltage drop in the motor drive circuit by increasing the emitter potential of one of the push-pull type PNP transistors higher than the output potential, and increases the voltage applied across the motor coil. To do.

〔Example〕

FIG. 1 is a circuit diagram showing one phase of a motor drive circuit according to an embodiment of the present invention. In the figure, the difference from the conventional one is that the emitter of the transistor Q ₇ and the output terminal 3
That is, a diode D ₁ for level shift is inserted between and. The cathode of the diode D ₁ is connected to the output terminal 3, the anode is connected to the power supply voltage V _CC via the resistor R ₉ , and is also connected to the emitter of the transistor Q ₇ . Other configurations are similar to those of the conventional circuit shown in FIG.

Next, the operation will be described. A three-phase differential waveform with a phase shift of 120 ° from each other is input to the input terminal 2 of each phase from a Hall amplifier (not shown) as shown in Fig. 4, and a rotating current flows through the motor coil of each phase, driving the motor. The operation performed is the same as the conventional one.

Next, the saturation voltage V _{CE (sat) above} and _below V _{CE (sat)} of the upper and lower drivers 1 and 4 when the three-phase differential waveform input to the input terminal 2 is fully swung are determined. Hereinafter, the forward voltage drop of the diode D ₁ is V _D1, and V _D1 ≈V _BE (8) Other conditions are the same as in the conventional example.

First, the saturation voltage V of the upper driver 1
_{The CE (sat)} is the same as the formula (4) shown in the conventional example.

Next, the saturation voltage V of the lower driver 4
_{Under CE (sat)} is requested. Considering that the potential of "L" is close to GND5 when the three-phase differential waveform is full swing,
Since the potential difference between the output terminal 3 and the input terminal 2 is V _D1 −V _BE7 and the potential difference between the output terminal 3 and the GND 5 is V _CE12 , V _D1 −V _BE7 ≈V _BE −V _BE = 0 ((1)) 9) and V _D1 −V _BE7 <V _CE12 (10). Therefore, under the condition for the lower driver 4 to operate, that is, _under the saturation voltage V _{CE (sat) for turning on the} transistors Q ₇ and Q ₁₂ , the _lower V _{CE (sat)} = V _CE12 (11). Therefore, the voltage across the motor coil is connected to each phase of the output terminal _{3 V CC - (V CE (} sat) _above + V _{CE (sat) below) = V CC -V BE6 -V CE5} -V CE12 … (12). Comparing equations (7) and (12) under the conditions of equations (1) and (2), the voltage drop (V _{CE (sat) above} + V _{CE (sat) in the} motor drive circuit is found in this embodiment. _(Lower ) is small and the voltage across the motor coil is large.

FIG. 2 is a circuit diagram showing another embodiment according to the present invention. The difference from the embodiment of FIG. 1 is that level shifting diodes D ₂ and D ₃ are further provided. diode
The anode of D ₂ is connected to the output terminal 3, the cathode is connected to the GND 5 through the resistor R _10, and the emitter of the transistor Q ₁ . The diode D ₃ has an anode connected to the input terminal 2 and a cathode connected to the base of the transistor Q ₁ . With this configuration, the same effect as that of the above-described embodiment is obtained, and the emitter potential of the transistor Q ₁ is lower than the output terminal 3 by V _BE , so that the transistor Q ₇
Since the emitter potential of is increased by V _BE , the transistors Q _{1 to} Q ₅ when the upper driver 1 is operating and Q _{7 to} Q ₁₁ when the lower driver 4 is operating have a potential margin, and the power supply voltage V
It is possible to operate even if _CC is low potential.

Further, in the above-described embodiment, the case where the differential input has three phases has been described, but any other multi-phase input such as two-phase or four-phase has the same effect as that of the above-described embodiment.

〔The invention's effect〕

As described above, according to the present invention, the first level shift circuit is provided between the emitter and the output of one of the push-pull PNP transistors that receive differential inputs of a plurality of phases,
Since the emitter potential of the PNP transistor is set to be higher than the output potential, the voltage drop in the motor drive circuit can be reduced, and as a result, the voltage applied to both ends of the motor coil is high and the motor drive capability is high. There is an effect that.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, FIG. 3 is a circuit diagram showing a conventional motor drive circuit, and FIG. It is a wave form diagram which shows a phase differential input. In the figure, 2 is an input terminal, Q ₁ is a PNP transistor, Q ₇
Is an NPN transistor and D ₁ is a diode. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] 1. A PNP transistor and an N are provided for a plurality of phases of differential inputs.
In a motor drive circuit that is input to the base of a PN transistor and drives a motor according to the input by a push-pull method, a first level shift circuit is provided between the emitter and the output of the PNP transistor, and the emitter of the PNP transistor is provided. A motor drive circuit characterized in that a potential is made higher than the potential of the output. 2. A second level shift circuit is further provided between the base of the NPN transistor and the input, and the second level shift circuit is provided.
Making the base potential of the N transistor lower than the potential of the input, and further providing a third level shift circuit between the emitter of the NPN transistor and the output,
The motor drive circuit according to claim 1, wherein the emitter potential of the NPN transistor is lower than the output potential. 3. The motor drive circuit according to claim 2, wherein the first, second and third level shift circuits are diodes.