JPS6337592B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a switching drive device used in a switching regulator or a PWM (pulse width modulation) control device for a DC motor, in which a switching transistor for switching and driving a load is formed. When the temperature of the IC chip reaches a predetermined limit temperature, the switching mode of the switching transistor is changed from a normal switching mode with a relatively high frequency to a mode determined by the temperature time constant of the IC chip. This is intended to prevent thermal destruction of the IC and application of excessive power to the load by causing the IC to shift to a second switching mode with a lower frequency and a shorter active level period.

Conventionally, a thermal cutoff circuit is formed on the same chip of an IC on which a power transistor is formed, and when the chip temperature of the IC reaches a limit value, the power transistor is cut off and the IC is heated. The concept of protecting against physical damage is well known. For example, Japanese Patent Application Publication No. 30886 of 1980, or T.
D. S. Hamilton: “Hand book of linear
integrated electronics for research”McG
RAW―HILL Book Company (UK) Limited
As shown on page 194 of London (1977).

The present invention realizes a switching drive device in which heat dissipation can be designed extremely efficiently and economically by applying this known concept of heat cutoff to a switching regulator or a PWM control device for a DC motor. It is something.

The configuration of the present invention will be explained below based on the drawings.
FIG. 1 shows a circuit diagram of a DC motor switching drive device according to an embodiment of the present invention. In FIG. 1, a power supply (not shown) connected between the positive power supply terminal 1 and the negative power supply terminal 2 is connected between the collector and emitter of the power supply control transistor 5 in series with the DC motor 3 and the choke coil 4. is connected, a capacitor 6 is connected in parallel with the DC motor 3, a flywheel diode 7 is connected in the opposite direction between the collector of the transistor 5 and the positive power supply terminal 1, and the DC motor The configuration is such that switching power can be supplied to the motor 3.

Further, the output of the frequency generator 8 connected to the DC motor 3 is applied to the inverting input terminal 9a of the comparator 9 via the frequency-voltage converter 100, and the output of the comparator 9 is applied to the PWM modulator 2.
The output of the PWM modulator 200 is applied to the base of the transistor 5 via the transistor 10.

On the other hand, transistors 11, 12, 13, 14,
15, 16, resistance 17, 18, 19, 20, 2
1, 22, and 23 constitute a reference current source circuit 300, and the output of the reference current source circuit 300 is connected to resistors 30, 3 via current distribution transistors 24, 25, 26 and matching resistors 27, 28, 29, respectively.
Both ends of 1 and the emitter are negative side feed line 2a
The base and collector of a transistor 32 connected to

A reference voltage for controlling the rotation speed of the DC motor 3 is generated across the resistor 30, and this reference voltage is applied to the non-inverting input terminal 9b of the comparator 9.
is applied to.

Further, an inverting input terminal 33a of a comparator 33 is connected to a connection point between the collector of the transistor 25 and the resistor 31, and the transistor 26
The non-inverting input terminal 33b of the comparator 33 is connected to the connection point between the collector of the transistor 32 and the base and collector of the transistor 32, and the output of the comparator 33 is applied to the base of the transistor 10 via the diode 34, and is connected to the capacitor 32. 35 is also applied.

Here, the comparator 33, the transistor 32, the resistor 31 (the comparator 33
is of open collector output type. ) constitutes a heat-sensitive switch circuit 400, and the capacitor 35, the diode 34, and the resistor 38 constitute a holding circuit 450.

Now, in the circuit shown in Fig. 1, the speed control loop of the DC motor consisting of the frequency generator 8, the frequency-DC voltage converter 100, the comparator 9, and the PWM modulator 200 is well known (for example, USP 4149116), its detailed explanation will be omitted and only an outline of its operation will be described.

In FIG. 1, a frequency generator 8 generates an output signal with a frequency proportional to the rotational speed of the DC motor 3, and this output signal is transmitted to a frequency-DC voltage converter 10.
0, it is converted into a DC voltage according to its frequency. The output voltage of the frequency-DC voltage converter 100 is compared with the reference voltage generated across the resistor 30 by the comparator 9, and the comparison output is
applied to PWM modulator 200. The PWM modulator 200 generates a rectangular wave signal having a duty according to the magnitude of the input voltage, and
0 to the base of the transistor 5 as a drive signal.

Since these blocks constitute a closed loop, the frequency-to-DC voltage converter 10
The transistor 5 performs a switching operation at a duty such that the output voltage of 0 becomes equal to the voltage across the resistor 30, and the DC motor 3 is controlled to rotate at a constant speed.

On the other hand, the reference voltage source circuit 300 generates a reference voltage with a zero temperature coefficient through the following operation.
That is, the base-emitter forward voltages of transistors 11 and 12 are respectively V _BE1 and V _BE2 ,
The resistance values of resistors 17, 18, and 19 are R ₁₇ ,
When R ₁₈ and R ₁₉ are set, the voltage V _X appearing across the resistor 19 is given by the following equation.

_{V _ _ _ _ _}
Ae, the emitter area of the transistor 12 is N times larger, and the transistor 1
If the emitter currents of 1 and 12 (assumed to be equal to the collector currents) are I ₁ and I ₂ respectively, then V _BE1 = k・T/qln (I ₁ /Io・Ae) (2) V _BE2 = k・T /qln(I ₂ /Io・N・Ae) (3) In equations (2) and (3), k is Boltzmann's constant and q is the electron charge, respectively k=1.38×10 ^-23 joule/〓 q=1.602 ×10 ^-19 coulomb Also, T is the absolute temperature (〓) of the junction, I ₀ is the reverse saturation current per unit area, I ₀ = γ・T ³・exp (−14000/T) (4 ) In equation (4), γ is a constant governed by the diffusion distance of electrons and holes, the diffusion constant, etc.

From _{formulas (} ¹ _{) to} ( ₄ ), _V /N・Ae・γ・T ³・exp(−14000/T)}
] (5) Since the current I ₁ in equation (5) is supplied from the current mirror circuit consisting of the transistors 13 and 14 in FIG. 1, its value is proportional to the value of the current I ₂ , and the emitter current of the transistor 14 is The density is made approximately equal to the emitter current density of the transistor 13 (specifically, the emitter current density of the transistors 14, 1
The temperature coefficient of I ₁ /I ₂ can also be considered to be zero by setting the ratio of the emitter area of 3 to be close to _{I 1} :I ₂ .

Therefore, by appropriately setting the emitter current density I ₁ /Ae of the transistor 11 and the emitter current density I ₂ /N·Ae of the transistor 12,
The temperature and coefficient of V _X become zero.

Here, in order to simplify the explanation, the resistor 20,
The resistance values of 28 and 29 are all the same, and resistance 19,
Letting the resistance values of resistor 31 be R ₁₉ and R ₃₁ , respectively, the reference voltage E _S generated across the resistor 31 is given by the following equation.

E _S =R ₃₁ /R ₁₉・V _X (6) Also, the emitter area of transistor 32 is Ae
Then, the collector-emitter voltage E _D
becomes as follows.

E _D =k・T/qln {I ₂ /Ae・γ・T ³・exp(−14000/T)} (7) Set so that the temperature coefficient of voltage V _X given by equation (5) becomes zero. Then, the reference voltage E _S also has a zero temperature coefficient.

By the way, the emitter current I ₂ of transistor 12
is given by the following equation.

I _{2 = V
When V} ) given by E _D is still −
It has a temperature coefficient of about 2mV/℃. Therefore, even if the current I ₂ is assumed to be constant regardless of temperature in order to simplify the calculation, a large error will not occur.

As an example, if we take a transistor with Ae of 20 microns square and a value of γ of around 500, then the value of I ₂ is
When set to 100 μA, the collector-emitter voltage E _D of transistor 32 at 20°C is
It is 700mV, but it becomes 435mV at 150℃. Therefore, if the value of E _S is set to 435 mV, the output of the comparator 33 is inverted when the junction temperature T reaches 150°C (423〓), and the output of the comparator 33 is , PWM
The output current of the modulator 200 is now absorbed, and as a result, the transistor 5 is cut off.

The temperature of the IC chip may rise abnormally when the armature coil of the DC motor 3 is short-circuited, or when the rotating shaft of the DC motor 3 is restrained by external force for a long period of time and the armature coil is burnt out. ,
Or, as shown in FIG. 4, which will be explained later, a separate output current limiting circuit is provided and that current limiting circuit continues to operate for a long time. In either case, the power loss of the transistor 5 may increase abnormally. This is due to Therefore, by detecting the temperature rise of the IC chip and turning off the transistor 5, the cause of the temperature rise can be eliminated.

Figure 2 is an operation waveform diagram for explaining the operation pattern of the thermal switch circuit, and Figure 2 a, b, c, d
are the power loss in transistor 5, the junction temperature of transistor 32, and the transistor 10, respectively.
5 shows changes in the base potential of the transistor 5 and the base potential of the transistor 5.

Assuming that normal switching control (switching frequency is generally around 50 to 100 KHz) is being performed before time _t1 , the power loss in transistor 5 at that point is small, and the junction of transistor 32 The internal temperature, that is, the chip temperature, is also not much different from the ambient temperature Ta.

At time _t1 , if the rotating shaft of the DC motor 3 is restrained by an external force, the DC motor 3
Since the rotation of is stopped, the frequency generator 8, the frequency-DC voltage converter 100, the comparator 9,
The speed control system using the PWM modulator 200 works to fully accelerate the DC motor 3, and the base potentials of the transistors 10 and 5 rise.

At this time, the power loss in the transistor 5 is the saturation voltage between the collector and emitter and the DC motor 3
For example, if the power supply voltage is 3V
Assuming that the saturation voltage is 0.6V and the series resistance between the DC motor 3 and the chain coil 4 is 4.8Ω,
The collector current of the transistor 5 is 0.5A, and the collector loss is 0.3W.

Furthermore, since current also flows continuously through the transistor 10, the power loss in the drive stage at time _t1 is 0.3W or more, and the transistor 5, which is a heat source,
The junction temperature of the transistor 10 and the transistor 32 disposed near the resistor 36 rises relatively rapidly.

At time t ₂ , when the junction temperature of the transistor 32 reaches the set temperature Ts, the output state of the comparator 33 is reversed and the charge in the capacitor 35 is rapidly discharged via the diode 34 . Therefore, no base current flows through the transistors 10 and 5, and the transistors 10 and 5 are cut off, and the power loss becomes zero.

When the power loss becomes zero, the temperature of the junction decreases from the junction of the transistor 32 following a descending curve depending on the thermal time constant relative to the outside air, so the output of the comparator 33 returns to the original value, and the output of the comparator 33 returns to the original value. Charging of the capacitor 35 is started via the resistor 37 and the resistor 38.

By charging the capacitor 35, the base potential of the transistor 10 gradually rises, and at time _t3 , the transistors 10 and 5 are turned on again, and the junction temperature of the transistor 32 follows the rising curve at time _t1 . When the junction temperature increases at the same rate of increase and reaches Ts at time _t4 , the output state of the comparator 33 is reversed again, causing the transistors 10 and 5 to enter the cut-off state.

Thereafter, the same operation is repeated, and as shown from time t ₃ to t ₅ in FIG. , the charging time to the capacitor 35, that is, the holding circuit 450
The transistor 5 repeats the on-off operation with a repetition period that depends on the power supply blocking time, but the period during which the transistor 5 is in the on state, that is, the active level period of the drive signal of the transistor 5 (FIG. 2 d) The period during which the base potential is at a high potential in the waveform depends on the rate of temperature rise based on the power loss when the transistor 5 is saturated.

As shown after time t ₅ or t ₆ in FIG. 2, when the power loss when the transistor 5 is saturated is small, the junction temperature of the transistor 32 rises slowly, so that the drive signal The active level period becomes longer.

In this way, when the IC chip temperature exceeds a predetermined temperature Ts, the heat sensitive switch circuit 400 operates, and from then on, the thermal time constant of the IC chip with respect to the outside air, the power supply blocking period by the holding circuit, and the temperature rise rate are determined. The heat-sensitive switch circuit 400 and the holding circuit 450 generate signals having a duty based on Ts, and as a result, the temperature of the IC chip does not rise above Ts, so the IC chip can be protected from thermal damage. by the way,
Due to the presence of the holding circuit 450, even if the thermal time constant of the IC chip relative to the outside air is small, a power supply pulse of sufficient width can be applied to the load after recovery from the cut-off state. That is, even if the temperature of the IC chip drops rapidly immediately after the heat-sensitive switch circuit 400 is activated, the power supply to the DC motor 3 via the transistor 5 is stopped until the potential of the capacitor 35 rises to a sufficient value. Therefore, by appropriately selecting the power supply blocking period by the holding circuit 450 (in the embodiment shown in FIG. 1, it is determined by the time constants of the capacitor 35, the resistor 37, and the resistor 38), the IC chip After the temperature of DC motor 3 has fallen to a sufficiently safe range,
It is possible to resupply power to the

In addition, since the DC motor 3 that serves as the load of the transistor 5 is intermittently energized even after the heat-sensitive switch circuit 400 is activated, it will automatically return to its original state if the cause of the abnormal rise in IC chip temperature is removed. Taking the circuit shown in FIG. 1 as an example, the heat-sensitive switch circuit 400 intermittently switches the DC motor 3
For example, if a short circuit occurs in the load due to foreign matter adhering to the undercut portion of the commutator of the DC motor 3, the foreign matter is removed by energizing the DC motor 3 (sparks caused by intermittent energization). It is also possible to eliminate the particles by using a rotor, or to sift them off by vibrations of the rotor, etc.

Further, as shown in FIG. 3, the anode voltage of the diode 34 constituting the holding circuit 450 is applied to the display circuit 500 for warning,
If the configuration is such that current is supplied to, for example, the light emitting diode 50 by 0, when normal switching control is performed, the light emitting diode 50 appears to be continuously lit because the blinking period is extremely short. It looks like the heat sensitive switch circuit 40
0 begins to operate, the light emitting diode 50 blinks at a slow cycle, so that it can be detected at a glance that an abnormality has occurred.

Furthermore, if the present invention is applied to a switching drive IC having an output current limiting function as shown in FIG. 4, the effect will be extremely large.
That is, in FIG. 4, the collector current of the transistor 39 which together with the transistor 5 constitutes a current mirror circuit depends on the collector current of the transistor 5, but the collector current of the transistor 39 is at a limit value supplied by the transistor 40. When the voltage exceeds 0, the transistor 41 turns on, and the comparator 9 and
2 and 43, the collector current of the transistor 5 is ultimately limited to a preset value, but the transistor 5 performs a switching operation. While the collector loss of the transistor 5 is small when the current is on, the collector loss of the transistor 5 becomes extremely large when the current limit operation is started. However, in the circuit of FIG. 4 as well, a transistor 42 and a resistor 31 are arranged near the transistor 5, a heat-sensitive switch circuit 400 constituted by the transistor 41, and a holding circuit constituted by a capacitor 35 and a resistor 38. Circuit 450 prevents abnormal temperature rise of the IC chip.

In general, switching regulators and DC motor switching control devices that perform switching power supply to the load at relatively high frequencies for the purpose of improving power consumption efficiency are used to control the power supply to the load during normal operation. Since a switching transistor consumes only a small amount of power, the heat dissipation design of a switching drive IC that includes the switching transistor is extremely simple, unless abnormal situations are taken into consideration.In most cases, special heat dissipation is It is economical and does not require any equipment, and can improve mounting efficiency.

However, when an abnormal situation occurs, excessive power loss occurs, and if only a simple and economical heat dissipation design is used, the switching IC will be thermally destroyed in a short period of time. By applying the present invention to a switching drive IC, thermal damage to the IC can be prevented even under an economical heat dissipation design.

Although the embodiments shown in FIGS. 1, 3, and 4 apply the present invention to a switching control device for a DC motor, the present invention can also be applied to a general switching regulator. I can do it,
The power supply control transistor 5, which serves as a switching transistor that performs switching power supply to the load, is not necessarily a bipolar transistor but may be an FET.
It may also be a unipolar transistor such as.

As described above, in the switching drive device of the present invention, the first pulse signal (the output signal of the PWM modulator 200 in the embodiment shown in FIG. 1) whose duty changes based on the command value from the control system is input. A switching transistor (transistor 5 in the embodiment) is applied to an electrode, and is formed on the same IC chip as the switching transistor, and when the temperature of the IC chip exceeds a predetermined limit temperature Ts. The heat-sensitive switch circuit 400 operates to cut off the power supply to the input electrode of the switching transistor, and the heat-sensitive switch circuit 400 operates for a predetermined period of time even after the temperature of the IC chip drops and the cutoff of the power supply by the heat-sensitive switch circuit is released. and a holding circuit 450 for blocking power supply to the input electrode of the switching transistor, and when the temperature of the IC chip is lower than the limit temperature, the switching transistor is turned on and off by the first pulse signal. and when the temperature of the IC chip exceeds the limit temperature, a second circuit having a duty based on a thermal time constant of the IC chip with respect to the outside air, a power supply blocking period by the holding circuit, and a temperature increase rate.
The device is characterized in that the switching transistor is turned on and off by the pulse signal of the IC.
Even if the thermal time constant of the chip relative to the outside air is small, it is possible to provide a power supply pulse of sufficient width to the load after recovery from the cut-off state, which not only reliably prevents thermal damage to the IC but also eliminates the cause of the abnormality. If you do so, you can quickly return to your original state.
Furthermore, in some cases, it is possible to eliminate the cause of the abnormal situation, and furthermore, by adding a display means to the output side of the heat-sensitive switch circuit, the occurrence of an abnormal situation can be easily detected. ,
It has a great effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit wiring diagram showing an embodiment of the present invention;
FIG. 2 is an operational waveform diagram of the main part of FIG. 1, and FIGS. 3 and 4 are circuit connection diagrams showing other embodiments of the present invention. 3...DC motor, 4...Chi York coil, 5
...Power supply control transistor (switching transistor), 7...Flywheel diode, 8
...Frequency generator, 200...PWM modulator, 4
00...Thermosensitive switch circuit, 450...Holding circuit, 500...Display circuit.

Claims (1)

[Scope of Claims] 1. A switching transistor to which a first pulse signal whose duty varies based on a command value from a control system is applied to an input electrode, and a switching transistor formed on the same IC chip as the switching transistor. ,
a heat-sensitive switch circuit that operates when the temperature of the IC chip exceeds a predetermined temperature limit to cut off power supply to the input electrode of the switching transistor; and a heat-sensitive switch circuit that operates when the temperature of the IC chip exceeds a predetermined temperature limit; and a holding circuit that blocks power supply to the input electrode of the switching transistor for a predetermined period even after the cutoff of power supply by the IC chip is released, and when the temperature of the IC chip is lower than the limit temperature, the The switching transistor is caused to perform an on/off operation by a pulse signal of 1, and when the temperature of the IC chip exceeds the limit temperature, the switching transistor is
A switch characterized in that the switching transistor is caused to perform an on/off operation by a second pulse signal having a duty based on a thermal time constant of the IC chip with respect to the outside air, a power supply blocking period by the holding circuit, and a temperature rise rate. driving device. 2. A first pulse signal whose duty varies based on a command value from a control system is formed on a switching transistor to which an input electrode is applied, and on the same IC chip as the switching transistor,
a heat-sensitive switch circuit that operates when the temperature of the IC chip exceeds a predetermined temperature limit to cut off power supply to the input electrode of the switching transistor; The circuit includes a holding circuit that blocks the power supply to the input electrode of the switching transistor for a predetermined period even after the power supply cutoff by the circuit is released, and a display means for warning, and a holding circuit that prevents the supply of power to the input electrode of the switching transistor for a predetermined period even after the cutoff of the power supply by the circuit is released, and a display means for warning. When the temperature is lower than the limit temperature, the first pulse signal causes the switching transistor to perform an on/off operation, and when the temperature of the IC chip exceeds the limit temperature, the thermal time constant of the IC chip with respect to the outside air and the above-mentioned The switching transistor is caused to perform an on/off operation by a second pulse signal having a duty based on the power feeding blocking period and the temperature rise rate by the holding circuit, and the output of the holding circuit is applied to the display means to display the holding circuit. A switching drive device characterized in that the switching drive device is configured such that the operation thereof can be identified by the display means.