JPH07240676A - Drive circuit - Google Patents

Abstract

PURPOSE:To prevent production of a radio noise and to prevent a switching loss at turn-off from being increased. CONSTITUTION:A switching element (Q1) comprising a MOS transistor(TR) and a drive element (Q2) driving the switching element are provided to the circuit and a current is supplied.from the switching element to a load (L1). A capacitor (C1) for extending a switching time is connected between a gate and a drain of the switching element. A setting circuit (R1, R2, D1) makes a time change rate of a voltage across the capacitor in the vicinity of a threshold voltage nearly equal to each other at turn-on and turn-off of the switching element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit, and more particularly to a drive circuit for switching a current flowing through a load.

[0002]

2. Description of the Related Art Conventionally, as a drive circuit for a switching element, there is one disclosed in Japanese Patent Application Laid-Open No. 2-123816. This drive circuit has an M having a capacitive control input terminal.
For input terminals of switching elements such as OS transistors,
Connects an inductor, a diode, a capacitor, and a bipolar transistor, which is a drive element, and uses the energy stored in the inductor during the ON period of the drive element to control the flyback voltage when the drive element is turned off. It is used as the drive voltage of the element.

[0003]

In the above-described conventional drive circuit, when the MOS transistor is switched at high speed to turn on / off the load, the harmonic components of the switching element output voltage waveform, stray capacitance, and wiring inductance are generated. Radio noise is generated due to parasitic vibration.

As a countermeasure against this radio noise, it is conceivable to add a low-pass filter to the output of the switching element to remove the radio noise. In this case, however, the increase in the number of parts constituting the low-pass filter causes an increase in cost and an increase in installation space. There's a problem.

In addition, in order to suppress the generation of radio noise by lengthening the turn-on period of the load (transient period when the current starts to flow through the load) and the turn-off time (transient period when the current of the load stops), the gate / drain of the MOS transistor is suppressed. It is conceivable to add a capacitor between them to make the output waveform of the switching element a trapezoidal waveform, but the turn-on time and turn-off time will differ if the capacitor is simply added. Therefore, if the turn-on time is set to be sufficient to suppress the radio noise at turn-on, the turn-off time becomes excessive, the switching loss increases, and the amount of heat generation increases.

The present invention has been made in view of the above points,
An object of the present invention is to provide a drive circuit which prevents generation of radio noise and prevents increase of switching loss at turn-off by making turn-on time and turn-off time substantially the same for a predetermined time.

[0007]

The drive circuit according to the present invention comprises an M
A drive circuit that includes a switching element including an OS transistor and a drive element that drives the switching element, and that supplies a current from the switching element to a load to drive the load, and is connected between a gate and a drain of the switching element. And a capacitor for extending the switching time,
And a setting circuit for setting the time change rates of the voltage across the capacitor in the vicinity of the threshold voltage when the switching element is turned on and when the switching element is turned off to be substantially the same.

The switching element is a P-channel MOS transistor, and the setting circuit includes a first resistor connected between the power source and the driving element and a gate between the driving element and the switching element. It is composed of a second resistor and a diode connected in parallel with each other.

Further, the switching element is an N-channel MOS transistor, and the setting circuit includes a first resistor connected between the power source and the driving element and a gate between the driving element and the switching element. And a second resistor connected.

[0010]

In the present invention, since the rate of change of the voltage between both ends at the time of turn-on and the time of turn-off of the capacitor for extending the switching time are substantially the same, the turn-on time and the turn-off time can be made substantially the same for a predetermined time. Generation of radio noise can be prevented by extending the time and the turn-off time, and since the turn-off time does not become excessive, an increase in switching loss can be prevented.

The switching element is a P channel M.
In the case of the OS transistor, the setting circuit can be configured by the first and second resistors and the diode.

Further, the switching element is an N channel M
In the case of the OS transistor, the setting circuit can be configured only by the first and second resistors, and the diode is unnecessary.

[0013]

1 is a circuit diagram of a driving circuit according to the present invention. This drive circuit is used, for example, as a drive circuit for a damping force control stepping motor of an electronically controlled air suspension system.

In the figure, an active high control signal is input from the CPU to the terminal 10 and supplied to the base of the NPN transistor Q ₂ which is a driving element.

The emitter of the transistor Q ₂ is grounded,
The collector is the anode of the diode D ₁ and the first resistor R
It is connected to one end of each of the _first and second resistors R ₂ . The cathode of the diode D ₁ and the other end of the resistor R ₂ are connected to the gate of a P-channel MOS transistor, which is a switching element, and the other end of the resistor R ₁ has a voltage V _IG (= 12V).
Is connected to the power terminal of.

The source of the MOS transistor is connected to the power supply terminal, the capacitor C ₁ for extending the switching time is connected between the gate and the drain, and the drain is connected to one end of the exciting coil L ₁ of the stepping motor.
The other end of the exciting coil L ₁ is grounded.

Here, since the capacitor C ₁ for extending the switching time is selected as a capacitance channel which is 10 times or more the feedback capacitance C _rss of the MOS transistor Q ₁ , C _{rs s} can be ignored. Turn of the capacitor C ₁ (L ₁ starts to flow a current to), (to stop the current flowing in L ₁₎ off Tokio s gate-source voltage V _GS of the MOS transistor Q ₁ is at the threshold voltage V _th The charging / discharging current I _clu and the charging / discharging current I _{cld at a} certain time are set to be the same.

Since the charging / discharging current I _cld at V _GS = V _th at turn-off passes through the resistor R ₁ and the diode D ₁ from the power source, the forward voltage drop of the diode D ₁ is represented by V _F and expressed by the following equation.

I _Cld = (V _th −V _F ) / R ₁ (1) Further, the charge / discharge current I _Clu at V _GS = V _th at turn-on is grounded from the capacitor C ₁ through the resistor R ₂ and the transistor Q _2. Is expressed by the following equation. I _Clu = (V _IG −V _th ) / R ₂ (2) Here, V _IG = 12 V, V _th = 2.5 V, V _F = 0.6.
When V is set, the following relationships are obtained by substituting the equations (1) and (2) into I _cld = I _clu .

R ₂ = (9.5 / 1.9) R ₁ Therefore, for example, when R ₁ = 4.7 kΩ, R ₂ = 24 kΩ
, The turn-on time and the turn-off time can be made substantially the same.

The operation waveforms at this time are shown in FIG. turn
When turned on, the control signal at the terminal 10 is as shown in FIG.
Time t₀When it rises at, transistor Q₂By continuity of
Resistance R₂Through capacitor C₁Voltage across the
Sensor C₁Excitation coil L₁Based on the connection point with
As shown in FIG. 2D, the MOS transistor Q is lowered. ₁
Gate-source voltage V_GSAt time t₁At threshold
Field voltage V_th(For example, when the drain current is 10mA
V_th= 2.5V). At this point MOS Transis
Q₁Starts conducting, and the MOS transistor Q₁Encouraging
Magnetic coil L₁Voltage applied to V₀Is shown in FIG.
It rises almost linearly.

After the MOS transistor Q ₁ is completely turned on at time t ₂ , the capacitor C ₁ is charged in the negative direction as shown in FIG. 7D by the time constant of the capacitor C ₁ and the resistor R ₂ . Along with this, the gate-source voltage V _GS rises as shown in FIG. However, after time t _2, the applied voltage V _{0 to the} coil L ₁ is constant as shown in FIG.

Next, at the time of turn-off, at time t ₃ , terminal 1
When 0 control signal falls, the blocking of the transistor Q _2, the voltage across the capacitor C ₁ through the resistor R ₁ and a diode D ₁ is increased as shown in FIG. 1 (D), the voltage V
_GS decreases. At time t ₄ , the voltage V _GS changes to the threshold voltage V _th (for example, when the drain current is 1 A, V _th = 3.
0 V), the MOS transistor Q ₁ starts to shut off, and the voltage V ₀ applied to the exciting coil L ₁ is (C) in the figure.
As shown in FIG.

After the MOS transistor Q ₁ is completely cut off at time t ₅ , the capacitor C ₁ is charged in the positive direction by the time constant of the capacitor C ₁ and the resistor R _1, and the voltage V _GS is accordingly increased. It decreases as shown in (B).

In this way, both the turn-on time T ₁ and the turn-off time T ₂ shown in FIG. 2 (C) can be set to a predetermined time of several hundred microseconds, whereby the radio noise at turn-on and turn-off is reduced. Occurrence can be prevented. The turn-off time T ₂ is the turn-on time T ₁
Therefore, it is possible to prevent an increase in switching loss and an increase in heat generation amount due to this.

By the way, as shown in FIG.
Mode D₁To remove the resistance R₁Is a MOS transistor Q₁
It is conceivable to connect between the gate and source of the. MO
V of S transistor_GS・ I_DCharacteristic V_GS<V_thWhen
Drain current I_DIs about 10 mA, V_th<V_GS<
V_thDrain current I in the range of +0.5_DIs 1_ADegree
It In the circuit shown in FIG. 3A, the MOS transistor Q
₁Capacitor C at turn-on₁Is the resistance R₁
Through the current (V_IG-V_th) / R₁Is discharged in the turn
Capacitor C when off₁Is the current V_th/ R₂Is charged with
It (V_IG-V _th) / R₁= V_th/ R₂Then turn
On time and turn off time can be the same, but V_IG= 12
V, V_th= 2.5V and R₁/ R₂≈4 / 1
It must be a transistor Q₁, Q₂V when on_IG
Is resistance R₁, R₂Is divided by the MOS transistor Q₁
Gate-source voltage V_GSIs the threshold voltage V
_thThe resistance between drain and source is as high as about 10Ω.
The operation is in a saturated region, and the loss at the time of turning on is large.
The amount of heat is large and practical application is impossible. On the other hand, in FIG.
In the embodiment, as shown in FIG.₁, Q
₂V when on_GSRises to 12V, so drain
・ The source-to-source resistance is about 0.2Ω, which is sufficiently low
Since it operates in the range, the amount of heat generated is small, and it can be put to practical use.
It

Considering the response of the stepping motor, the motor response is improved as the electromagnetic energy extinguishing ability of the exciting coil L ₁ at the time of turning off the MOS transistor Q ₁ . Considering a drive circuit shown in FIG. 1 which does not have a diode D _{1 and} whose turn-off time cannot be set sufficiently long, since electromagnetic energy remains in the exciting coil L ₁ after turn-off, a kick voltage is applied to the MOS transistor Q ₁ to destroy it. May occur.

As a countermeasure against this, as shown in FIG.
Magnetic coil L₁Flywheel diode D in parallel with₂To
Provided, this flywheel when kick voltage is applied
Turn on the diode to extinguish the arc, or as shown in Fig. 3 (C).
Diode D₃And Zener diode D_zAnd set
When the kick voltage is applied, the MOS transistor Q
₂It is conceivable to turn on and extinguish the arc. But hula
Ewheel diode D ₂Is provided, even after turn off
A return current flows in the same direction as when turning on. Diode D₁of
The forward voltage is as small as 0.9V, and it is necessary to turn it off for extinguishing the arc.
The time for the return current to flow after turning off is relatively long. An example
For example, in a 4-phase stepping motor, for example, phase A turns
The reverse A phase turns on at the same time as it turns off, but the above reason
When a reflux current flows in phase A, the movement (rotation) of the motor is blocked.
It is stopped and the response deteriorates. Also, the diode D₃And Tsu
Zener diode D_zAnd MOS transistor
Q₂When turned on, the arc is extinguished at high speed and responsiveness is secured.
However, there is a problem that the number of parts increases.

On the other hand, in the configuration of the present invention shown in FIG. 1, by setting the turn-off time to the time when the exciting coil L ₁ is sufficiently extinguished, the response of the step motor can be improved without adding any parts.

FIG. 4 shows a circuit diagram of a second embodiment of the circuit of the present invention. This circuit uses an N-channel MOS transistor Q ₃ as a switching element, and an active low control signal is input to the terminal 11 to cause a transistor Q ₂
Supplied to the base of. The emitter of the transistor Q ₂ is grounded, the collector is connected to the power source of the voltage V _IG via the resistor R _1, and is connected to the gate of the MOS transistor Q ₃ via the resistor R ₂ .

The source of the MOS transistor Q ₃ is grounded, and the drain is connected to the power supply via the exciting coil L ₁ . A capacitor C ₁ for extending the switching time is connected between the gate and drain.

Considering the charging / discharging current I _clu of the capacitor C ₁ when V _GS = V _{th at} the time of turn-on (transistor Q ₂ off), the current I _clu is _derived from the resistor R ₁ ,
Since it passes through R ₂ , it is expressed by the following equation.

I_Clu= (V_IG-V_th) / (R₁+ R₂) (3) Also turn off (transistor Q₂ON) V_GS=
V_thCapacitor C when₁Charge / discharge current I_cldThinking
Then, the current I_CldIs the capacitor C₁To resistance R ₂And
Langista Q₂Since it flows to the ground through
I will be told.

I _cld = V _th / R ₂ (4) Here, the formulas (3) and (4) are substituted into I _Clu = I _cld ,
Substituting V _th = 2.5V and V _IG = 12V, the following relationship is obtained.

R ₂ = R ₁ · (2.5 / 7) Therefore, for example, when R ₁ = 10 kΩ, R ₂ = 3.6 kΩ
By selecting, the turn-on time and the turn-off time can be made substantially the same.

Also in this embodiment, both the turn-on time and the turn-off time can be set to predetermined times, the generation of radio noise can be prevented, and the switching loss and the amount of heat generation at turn-off can be prevented from increasing. Is the same as. Further, in this embodiment, since the diode is unnecessary, the cost can be reduced.

FIG. 5 shows a circuit diagram of a four-phase stepping motor drive circuit using the circuit of the present invention. In the figure, circuits 20a, 20b, 20c and 20d surrounded by broken lines correspond to the drive circuit of FIG. 1, and these circuits 20a to 20d are supplied with control signals via terminals 21a to 21d, respectively. 4-phase exciting coil La of the stepping motor 22,
Each of Lb, Lc, and Ld is energized.

The overcurrent detection circuit 23 includes circuits 20a and 20b.
If the source current of the MOS transistor Q ₁ becomes excessive, the resistance R ₁₀ detects this and the PNP transistor Q ₁₀
Is turned on, and the circuit 20 is connected through the diodes D ₁₁ and D _12.
The MOS transistors a and 20b are forcibly turned off. Overcurrent detection circuit 24 is the circuit 20c, it detects the overcurrent 20d, diode D ₁₃ performs the same operation as the overcurrent detection circuit 23, D ₁₄ through the circuit 20c, 20
d is controlled.

When an overcurrent is detected by the overcurrent detection circuits 23 and 24, the transistor Q ₁₀ is turned on, and after being delayed for a predetermined time by the delay circuit composed of the resistor R ₁₀ and the capacitor C ₁₀ , the inverter Q ₁₀ is turned on. It is reversed at 25. When the output of the inverter 25 becomes low level based on the above-mentioned overcurrent detection,
Terminal 21a~21d is forced to a low level, whereby the circuit 20a~20d all the transistors Q ₁ is turned off, thereby preventing wasteful power consumption.

Further, when the overcurrent state continues due to a short circuit of the wire harness or the like, the mode is shifted to the intermittent energization mode to prevent the transistor Q ₁ from being heated.

By the way, the MO of each of the circuits 20a to 20d is
The diodes D _{21 to} D ₂₄ connected to the drain of the S transistor Q ₁ are for obtaining the flywheel effect of the coils La to Ld and for applying an electromagnetic brake when the rotation of the stepping motor 22 is stopped.

Further, the Zener diode D _z1 is provided when the surge voltage such as load dump is superimposed on the power supply voltage V _IG ,
A gate between the gate and source of the MOS transistor Q ₁
It is prevented that the voltage exceeding the source breakdown voltage V _GSS is applied and Q ₁ is damaged.

[0043]

As described above, according to the drive circuit of the present invention, since the time change rates of the both-end voltages at the turn-on and the turn-off of the capacitor for extending the switching time are substantially the same, the turn-on time and the turn-off time are the same. Can be made to be almost the same in a predetermined time, and the generation of radio noise can be prevented by extending the turn-on time and turn-off time, and the turn-off time does not become excessive, preventing switching loss and heat generation from increasing. It is possible and extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a circuit of the present invention.

FIG. 2 is a signal waveform diagram of each part of the circuit of FIG.

FIG. 3 is a diagram for explaining a conventional circuit.

FIG. 4 is a circuit diagram of a circuit of the present invention.

FIG. 5 is a circuit diagram of a stepping motor drive circuit to which the circuit of the present invention is applied.

[Explanation of symbols]

Q ₁ , Q ₃ MOS transistor Q ₂ transistor R ₁ first resistor R ₂ second resistor C ₁ capacitor

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H03K 17/04 E 9184-5J 17/567 17/695

Claims (3)

[Claims] 1. A drive circuit comprising a switching element composed of a MOS transistor and a drive element for driving the switching element, wherein the drive circuit supplies a current to the load from the switching element to drive the load. It has a capacitor connected between the drains for extending the switching time, and a setting circuit for making the time change rate of the voltage across the capacitor in the vicinity of the threshold voltage at the time of turning on and off of the switching element substantially the same. Drive circuit characterized by. 2. The drive circuit according to claim 1, wherein the switching element is a P-channel MOS transistor, and the setting circuit includes a first resistor connected between a power source and the drive element, and the drive element. And a diode connected between the switching element and the gate of the switching element in parallel with each other, and a drive circuit. 3. The drive circuit according to claim 1, wherein the switching element is an N-channel MOS transistor, and the setting circuit includes a first resistor connected between a power source and the drive element, and the drive element. And a second resistor connected between the gate of the switching element and the gate of the switching element.