JPH10163834A - Drive circuit of load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have an output characteristic of a Darlington circuit as a single transistor in a low current area and to have both characteristics of double transistors in a high current area by connecting a diode between the collector of a transistor of a preceding stage and the collector of a transistor of a subsequent stage. SOLUTION: A transistor TR1 of a prestage and a transistor TR2 of a poststage are undergone Darlington connection, and a diode D5 is connected so that the collector of the TR1 of the preceding stage may be connected to a cathode between both collectors. With such a structure, output current of two stage types can be acquired. That is, first, an output of a single transistor appears and then, from the midst an output of double transistors appears. Then, when a high current area is needed, the double output can be used and when a low current area is needed as output current, this circuit can be used as a single type, and furthermore, low VCE (sat) that is a characteristic of a single transistor can drive the low current area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a load, and more particularly to a driving circuit for a load such as a motor or a lamp which is driven with a large current at the time of starting and a small current in a steady state.

[0002]

2. Description of the Related Art Power devices are semiconductors that perform power conversion and control, and their application fields have been significantly expanded. Particularly, bipolar transistors have been used for inverter control of motors and the like as shown in FIG.

This bipolar transistor is difficult to increase in breakdown voltage and current as compared with a thyristor, but is not available in a thyristor in that a main current can be cut off / conducted by a base signal and high-speed switching is possible. Have advantages. In addition, it has high breakdown strength such as reverse bias SOA (safe operation area) and short-circuit strength for inverter applications.

Accordingly, while new power devices such as MOSFETs and IGBTs are receiving attention, they are still widely used as core elements even today. Specific descriptions of these are described in, for example, Transistor Technology, September issue, 1994, in particular, pages 216 to 22.
This is described in detail on page 3. FIG. 7 shows an example of a conventional Darlington circuit, in which a preceding transistor TR1 and a following transistor TR2 are Darlington connected. This property is generally

[0005]

(Equation 1)

Here, hFE1, hFE2 << hFE1 × hFE2
So

[0007]

(Equation 2)

[0008] Also

[0009]

(Equation 3)

[0010]

(Equation 4)

## EQU1 ## Where hFE1, VCE (sat)
1. VBE (sat) 1 is a current amplification factor of a preceding transistor, a collector-emitter saturation voltage, and a base-emitter saturation voltage. HFE2, VCE (sat) 2, VB
E (sat) 2 is the current amplification factor of the transistor at the subsequent stage, the saturation voltage between the collector and the emitter, and the saturation voltage between the base and the emitter.

On the other hand, as a technique having a different purpose from the present application, there is JP-A-58-7532. In this publication, a speed-up diode is connected between the base and the emitter of the first-stage transistor in order to improve the switching speed when the Darlington transistor is turned off. In this technology, when the collector current of the Darlington transistor is reduced, the base transistor IBC flows in the forward direction in the collector junction of the preceding stage transistor because the preceding stage transistor is excessively driven. The recovery current flows through the emitter junction of the preceding transistor and flows into the speed-up diode (at this time, the latter transistor is already turned off), and the former transistor is destroyed, so that the collector of the former transistor and the latter transistor are destroyed. A diode is connected between the collectors.

That is, this publication is intended to prevent the destruction of the preceding transistor at the time of turn-off, and is not a technique which pays attention to power loss at the time of startup and steady driving of the Darlington transistor as described later.

[0014]

The advantages of the Darlington type are that the current amplification factor hFE is high and the base current required for driving is small as shown in equation (2), but the disadvantages are as shown in equation (3). Another problem is that the collector-emitter saturation voltage VCE (sat) is high and the power loss is high. For example, looking at the output characteristic waveform A (vertical axis: collector current, horizontal axis: collector-emitter voltage VCE) of the conventional Darlington transistor shown in FIG.
It is on the order of V, and it can be seen that it is necessary to use a saturation region (the portion where VCE (sat) is the lowest) in order to reduce the power loss.

For example, considering the driving of the motor, at the time of start-up requiring a large current, when the point S is used and when the driving current becomes small and the driving current becomes small and the point T is used for driving, VCE is about 1 V It is set between about 2V. In particular, since the steady state of the motor occupies most of the driving period, it is necessary to reduce VCE (sat) in the steady state. This motor is used in various fields, for example, an air conditioner operates all day. Ventilation fans are also operating without rest.
The same applies to lamps and the like. In these, a large current flows instantaneously at the time of startup, and when a steady state is reached, the load impedance is reduced, and they are driven with a current much smaller than the drive current at the time of startup. Since this steady state occupies most of the driving period, it is very important to suppress the power loss here from the viewpoint of energy saving and the like.

Next, the Darlington circuit shown in FIG. 7 will be analyzed with reference to FIGS. Since a transistor has a PN junction formed from a base to a collector and a base to an emitter, it can be interpreted that the transistor includes two diodes. Therefore, as can be seen from FIG. 8, it can be interpreted that the Darlington circuit includes four diodes D1 to D4 and two switching elements S1 and S2. That is, diodes D1 and D2 are forwardly directed from point n to point i, from point n to point k, and from point k to point j and from point k to point m.
Are connected in the forward direction, and when a current flows from the point n to the point k, the switch S1 is operated, a current amplified from the point i to the point k flows, and the transistor TR1 is turned on. When the amplified current flows through the switch S2, the switch S2 is operated, and a further amplified current flows from the point j to the point m.
2 can be assumed to be on.

The point to be noted here is that if the potential at the point h (point i) is lower than the point n, a part of the base current flowing from the point n flows toward the point h (point i). Further FIG.
I will explain using. 5 V is applied between the base and the emitter of the Darlington transistor, and 35
0Ω is connected, and a load R (for example, a motor or a lamp) is connected to the collector side. It is also assumed that a power supply of 100 V is applied between the load R and the emitter. When S3 is turned on, 1.4V is generated as VBE (sat), about 10mA flows as base current, and the transistor T
R1 turns on, the emitter current of the preceding transistor TR1 is input to the base of the following transistor TR2, and the transistor TR2 turns on. At this time, point C is
VCE (sat) = VCE (sat) 1 + VCE (sat) 2 = approximately 1.0. At the point B, about 1.4 V is generated with respect to GND. Therefore, the potential of the point C (about 1 V) becomes lower than that of the point B (about 1.4 V), and a part of the base current is changed to the point C. Through the diode D1.

In this operation, the transistor TR1 is turned off to reduce the base current of the transistor TR1, and the emitter current of the transistor TR1 is reduced. Therefore, the transistor TR2 also operates to turn off. As a result, the current flowing through the load R decreases, and the point C tends to increase from 1V. This point C rises from 1 V and is about 1.4
If the voltage exceeds V, the base current flowing to the point B does not flow to the point i (point h), and all the current flows to the transistor TR1.
The transistor TR1 turns on, and as a result, the transistor T1
R2 is also turned on, and VCE (sat) becomes about 1V. That is, VCE (sat) becomes a constant voltage while repeating this. That is, VCE (sat) is affected by the change of the point C, and keeps a relatively high VCE (sat).

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. First, an NPN-type Darlington transistor is used, and the collector of the preceding transistor or the collector of the preceding transistor is used from the base of the preceding transistor. A diode for blocking a current flowing from the base of the preceding transistor to the collector of the following transistor via the collector of the preceding transistor, and when the voltage of the anode electrode of the diode is lower than the voltage of the cathode electrode, By blocking the collector current of the transistor and turning on the subsequent transistor substantially with the base current flowing between the base and the emitter of the preceding transistor, the first rising curve is obtained as the collector current curve of the Darlington transistor. Set and die When the voltage at the anode electrode of the transistor is higher than the voltage at the cathode electrode, the collector current of the preceding transistor flows, and the emitter current flowing between the base and emitter and between the collector and emitter of the preceding transistor substantially reduces the current of the latter transistor. By turning on the transistor, a second rising curve is further set in the middle of the first rising curve, and when a current larger than a steady current is required, the second rising curve is used. When the load is driven and a steady current is required, the problem is solved by driving the load using the first rising curve.

When the output current of the Darlington circuit requires a high current range at the time of startup, the output of the Darlington circuit operating in Darlington is utilized. When the output current of the Darlington circuit requires a low current region in a steady state, If the transistor TR2 in the subsequent stage is used by being used as a single type, the transistor TR2 can be driven at a low VCE (sat) of the single type by the transistor TR2 in a steady state, so that power loss can be suppressed.

The specific characteristics of a single transistor are as follows:
VCE (sat) ≒ 0.3 V (point W), VBE (sat) ≒ 0.7 V, which are generally low. In addition, by turning on only the transistor TR2 without turning on the transistor TR1, the characteristics using a single transistor TR2 are obtained. Can be approached. That is, in the single transistor, in the output characteristics (vertical axis: collector current, horizontal axis: collector-emitter voltage VCE) of FIG.
Since the voltage rises from CE ≒ 0 V, the rising voltage of VCE can be reduced.

That is, in the low current region where the output current of the Darlington circuit is in a steady state, the transistor TR2
Is substantially driven by a base current flowing between the base and the emitter of the preceding transistor TR1, and in a high current region when the output current of the Darlington circuit is activated, the succeeding transistor TR2 is connected between the base and the emitter of the preceding transistor TR1. By driving the transistor TR2 with the emitter current flowing between the collector and the emitter, the Darlington circuit can be used at the time of startup, and only the transistor TR2 at the subsequent stage can be amplified and used as a single type in the steady state.

Specifically, when the emitter current is small, the diode cuts off the current path from the point h in FIG. 4 to the collector of TR1, and the base current of TR1 is reduced to TR2 without TR1 exhibiting an amplification effect. When the emitter current is large, the current path from point h to the collector of TR1 is made conductive, and about hFE1 times the base current of TR1 is input to the base of TR2. That is, when a low current is required in a steady state as shown by a waveform B in FIG.
It has the advantage of being driven down to 0.3V.

The first means has been described using an NPN-type Darlington transistor. The second means uses an NPN-type Darlington transistor.
It is replaced with an NP-type Darlington transistor. In either case, the driving in the steady state can be driven with a small VCE (sat) according to the above-described principle, and the power loss can be suppressed as a whole driving circuit. Thirdly, a configuration in which three or more stages are used to handle large currents is applied to the first and second means.

[0025]

Embodiments of the present invention will be described below. First, the output characteristics of the transistor, that is, the vertical axis is the collector current, and the horizontal axis is the collector-emitter voltage FIG.
Considering the graph of FIG. 1, the rise of VCE is smaller in the single transistor than in the double transistor configuration of the Darlington circuit. The waveform A in the figure is the output waveform of the conventional Darlington transistor of FIG.
Standing up from a degree. Waveform B is a waveform of the present invention, and has a first rising curve VCE rising from about 0 V, and a second rising curve from VCE about 1.5 V. A waveform C rising from VCE = 0 V is an output waveform of a known single transistor. The rising points of the first and second stages can be changed depending on the types of diodes described later and the number of series-connected diodes.

First, a motor is considered as a load of the Darlington transistor, and it is assumed that a collector current Ic of point S of FIG. (Here, the required current at the time of start-up and at the time of steady-state changes variously depending on the type of load, but it can be dealt with by selecting the transistor TR1 at the front stage and the transistor TR2 at the back stage. In the output waveform A of the conventional Darlington circuit, the start-up VCE
= 1.3V and VCE = 0.8V at steady state. However, when driving a load such as a motor, steady operation occupies most of the driving time. The motor requires a large amount of current and a large current when the motor is started, and this torque is reduced as the steady state is reached. Further, there is a case where a large current is suddenly required during the steady driving (this case is tentatively referred to as a restart). For example, considering an air conditioner, it is a time when the cooling operation of the air conditioner needs to be rapidly performed due to a sudden temperature rise during steady driving. In other words, it is a case where the motor starts up and shifts to a steady state, and a large current is required at one time in the steady state. This cooling operation is only a moment in consideration of the driving period.

Therefore, if the Darlington circuit of the present invention is used, in the conventional Darlington circuit, VCE = 0.8 V in the steady state.
However, by adopting the Darlington circuit, VCE can be set to 0.5 V or less, and power loss can be reduced by reducing VCE. On the other hand, in order to make the waveform B, when a high current region is required as the output current of the Darlington circuit, the output of the Darlington circuit operating in Darlington is utilized, and when a low current region is required as the output current of the Darlington circuit, Can be obtained by using the transistor TR2 in the subsequent stage as a single type.

For example, in FIGS. 7 and 8, when driving at a low current, the points h and k are disconnected, and if a base current from the outside is separately input to the point k, the transistor TR in the subsequent stage
2 operates as a single. In the case of a high current at the time of startup (or at the time of restart), if point h and point k are connected, it operates as Darlington and can supply a high current. That is, in the case of a low current, the waveform C is output as a single transistor, and in the case of a high current, the waveform of a Darlington-connected double transistor can be output. For example, in the waveform B of FIG. At the time of (or at the time of restart), VCE at the point V is about 1.8 V, and at the time of steady state, the VCE at the point W can be driven at about 0.2 V.

Next, a more specific example will be described with reference to FIG. What is important here is that the present invention is applied to a load such as a motor or a lamp which requires a large current at the time of starting (or at the time of restarting) and requires less current at a steady state than at the time of starting (or at the time of restarting). In the case where a low current is required as the output current of the Darlington circuit, the rear transistor TR2 is replaced with the front transistor TR2.
It is substantially driven by a base current flowing between one base-emitter.

When a high current is required as the output current of the Darlington circuit The transistor TR2 in the subsequent stage is replaced by the transistor TR1 in the preceding stage.
Is driven by an emitter current flowing between the base and the emitter and between the collector and the emitter. Between the collector of the preceding transistor TR1 and the collector of the succeeding transistor TR2 so that
(Refer to FIG. 3), specifically, to provide a diode or a resistor as shown in FIG.

When the emitter current at the terminal E is small, the current limiting means L cuts off the current path from the point h to the collector of the transistor TR1, whereby the base current of the transistor TR1 is amplified by the transistor TR1. Input to the base of the transistor TR2 and the emitter current at the terminal E is large, the current path from the point h to the collector of the transistor TR1 is made conductive, and hFE (TR1) times the base current of the transistor TR1 is applied to the base of the transistor TR2. It is made to be input.

In FIG. 4, a diode D5 is connected to the collectors of TR1 and TR2 so that current can flow from the point h to the collector of TR1 (so that the base current of TR1 does not flow into the point h). It is connected. FIG. 5 shows a further analysis of this as shown in FIG. A current flows through the base terminal B, and a current flows from the point n to the point k.
Operates, a current flows from the point i to the point k, and the transistor once turns on. When a current flows from the point k to the point m, the switch S2
Operates, and a current twice as large as hFE flows to the terminal E through the points h, j, and m. As a result, the potential VBE between the terminal B and the terminal E
Becomes about 1.4V, and VCE (sat) between the point C and the point E becomes about 1.0V.

Here, in the conventional circuit diagram 8, the base current flows through the point D1 toward the point h, but in the present invention, since the diode D5 is provided, the base current inputted from the terminal B is D1. It does not flow from point i to point h.
Therefore, all base currents input to the terminal B are equal to the point k.
Flowing towards. On the other hand, point h is 0.2 V at point W in FIG.
Degree, point i is VBE (sat) 2 + VCE (sat) 1 = 0.7V +
Although it is about 0.3 V = 1 V, almost no current flows through the diode D5 because it is connected in the opposite direction to the potential. Then, even if S1 turns on once, T
Since no current is supplied from the collector of R1 to the emitter, S1 tends to turn off, so that a current hFE1 times the base current does not flow through TR1 (amplifying action is not exhibited). That is, finally, only the current of the terminal B is changed from the point k to T
Input to the base of R2, TR2 only amplifies the base current of TR1, and eventually the Darlington circuit operates with the characteristics of a single TR.

In the case of a high current, as can be seen from the waveform in FIG. 11, the larger the collector current Ic, the larger the VCE. For example, operating at point V, VCE =
It becomes about 1.8V. That is, point h is 1.8 V and point i is 1
Since it is V, the current from the terminal C flows from the point i to the point k by turning on S1 via the diode D5. Therefore, a current obtained by adding the collector current and the base current that are hFE1 times the base current of the terminal B flows to the base of TR2, and furthermore, TR2
It operates as a normal Darlington (double transistor).

In the conventional waveform, the value of the point S in the waveform A shows a high value of VCE = 1.3 V, and the present invention shows a high value of VCE = 1.8 V. However, when starting (or restarting), the driving time is considered. Since it is only a moment, the power loss is not so large considering the length of the driving period. Subsequently, the adjustment of the rising will be described with reference to FIG. The case where a PN diode and a Schottky barrier diode are used as the diodes will be described.

First, in the case of a PN diode, the potential at point i is
VBE (sat) 2 + VCE (sat) 1, and the potential Vh at the point h is
When the potential becomes 0.7 V higher than the potential at the point i, a current flows into the collector of TR1. This point is the second rising edge of the waveform B in FIG. Next, when a Schottky barrier diode is used, the potential Vh at the point h becomes VBE
When the voltage becomes 0.3 V higher than (sat) 2 + VCE (sat) 1, a current flows into the collector of TR1. Therefore, the more the diode with the smaller ON voltage is used, the closer the rising voltage VCE (sat) of the second stage can be made to approach the conventional Darlington output waveform A. That is, if a diode having a small on-voltage is used, the point V of the waveform B can be moved further to the left, and the VCE voltage at the time of starting (at the time of restarting) can be reduced.

Conversely, if a PN diode is used rather than a Schottky barrier diode, the point V can be moved to the right. Further, by using a plurality of diodes, it can be moved further to the right. That is, by using a plurality of Schottky diodes, a plurality of PN diodes, or a mixture of both, the second rising curve can be moved to the right.

As described above, the present invention is applied to driving a load having a steady state, such as a motor or a lamp, which requires a large current at the time of starting (or restarting) and requires less current than at the time of starting (or restarting). It has been described that the power loss can be reduced by adopting the Darlington circuit. FIG. 1 specifically shows this, and is a part of FIG. 9 or FIG.

In FIG. 1, a resistor R is a load such as a motor or a lamp in which the current at the time of starting (or at the time of restarting) is larger than the current in a steady state, such as a motor or a lamp. + Power supply voltage is connected and point E is connected to ground. In the steady state, since the collector current is in the current region of the first rising curve, VCE is about 0.2 V, and the voltage at the point i is about 1 V. Therefore, the diode D5
As a result, the base current of TR1 does not flow toward the point h, and the points h and i are reverse-biased for the diode D5, so that no current flows to the diode, and the base current indicated by the arrow A is the base current of the TR2 as it is. Flows to Here, the arrow A indicates that the current does not flow to the emitter due to the diode D5. Therefore, the current of arrow A is amplified,
A current flows through TR2 as indicated by an arrow c.

Next, at the time of starting (or at the time of restarting), a large current is required. Therefore, the current flowing through the Darlington transistor shifts to the second curve, and VCE becomes 1.8 V. Since the point i is about 1 V, the current supplied from the terminal C flows in the direction of arrow A, and the emitter current amplified by TR1 flows to the base of TR2, and is amplified and flows as shown by arrow C.

As described above, the value of VCE can be reduced by connecting the diode D5 to the Darlington transistor during steady driving of a load such as a motor or a lamp, thereby reducing the power loss of the entire driving circuit. be able to. Here, FIG. 6 shows Darlington connection using three NPN-type TRs, and a diode is connected between the preceding collector and the interrupted collector as shown in FIG. In this case, a diode may be further connected between the collector of the interrupted TR and the collector of the subsequent TR.

Although the description is omitted, as shown in FIG.
Needless to say, a Darlington circuit in which a plurality of P-type transistors are connected has the same effect. FIG.
Indicates a part of the inverter circuit, and terminals A and B
, A DC rectified by a rectifier circuit is input, and three pairs of Darlington elements connected in series are connected in parallel. Base currents are input to the base terminals a to f from the control circuit, and, for example, TR1 and TR4, TR3 and TR6, and TR5 and TR2 are sequentially turned on to drive the motor. Here, when the six Darlington-connected transistors are in a steady state, VCE can be reduced as compared with a conventional Darlington-connected transistor, and as a result, power loss can be suppressed.

Also, instead of an NPN transistor, a PNP
It may be composed of a transistor. In this case, as shown in FIG. 2, the emitter of the preceding transistor TR1 is connected to the base of the following transistor TR2, and the collector of the preceding transistor TR1 is connected to the collector of the following transistor TR2 via the diode D5. The diode D5 is arranged so that no current flows from the point h to the collector of the transistor TR1 because the transistor is a PNP transistor.

[0044]

As described above, when a diode is connected between the collector of the preceding transistor and the collector of the following transistor, the output characteristics of the Darlington circuit are both single transistors in the low current region and both double transistors in the high current region. Characteristic can be provided.

Therefore, in the low current range, a drive circuit for a load with a reduced VCE voltage can be provided. In particular, when driving a motor or a lamp, the driving voltage V in a steady state, which is a low current region,
CE can be reduced, and power loss can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a load drive circuit diagram for explaining an embodiment of the present invention.

FIG. 2 is a load drive circuit diagram for explaining the embodiment of the present invention.

FIG. 3 is a Darlington circuit diagram for describing an embodiment of the present invention.

FIG. 4 is a Darlington circuit diagram for describing an embodiment of the present invention.

FIG. 5 is an analysis diagram for explaining the operation of FIG. 4;

FIG. 6 is a diagram illustrating a Darlington circuit when three transistors are used.

FIG. 7 is a diagram illustrating a conventional Darlington circuit.

FIG. 8 is an analysis diagram for explaining the operation of FIG. 7;

FIG. 9 is a circuit diagram when a load is connected to the Darlington circuit.

FIG. 10 is a diagram of an inverter circuit that drives a motor.

FIG. 11 is a diagram illustrating output characteristics of the present invention and a conventional Darlington transistor.

[Explanation of symbols]

 TR1 preceding transistor TR2 following transistor D5 diode

Claims (3)

[Claims] 1. An NPN-type Darlington transistor having a base electrode, a collector electrode, and an emitter electrode, a load connected to the collector electrode and requiring a larger current than a steady state current during a driving period, Two NPNs constituting Darlington transistor
A type transistor, and a diode that blocks a current flowing from the base of the preceding transistor to the collector of the preceding transistor or from the base of the preceding transistor to the collector of the following transistor via the collector of the preceding transistor. A drive circuit for at least a load, comprising: when a voltage of an anode electrode of the diode is lower than a voltage of a cathode electrode, blocking a collector current of the preceding transistor, and flowing a base current between a base and an emitter of the preceding transistor. Setting a first rising curve as a curve of the collector current of the Darlington transistor by substantially turning on the transistor at the subsequent stage. When the voltage of the anode electrode of the diode is higher than the voltage of the cathode electrode, the first rising curve is set. The collector current of the transistor of the preceding stage flows, and the transistor of the subsequent stage is substantially turned on by the emitter current flowing between the base and the emitter and between the collector and the emitter of the preceding stage transistor. When the second rising curve is set and a current larger than the steady current is required, the driving is performed using the second rising curve. When a steady current is required,
A driving circuit for a load, wherein the driving is performed using the first rising curve. 2. A PNP-type Darlington transistor having a base electrode, a collector electrode and an emitter electrode, a load connected to the emitter electrode and requiring a larger current than a steady state current during a driving period, Two PNPs constituting Darlington transistor
A type transistor, and a diode for blocking a current flowing from the collector of the preceding transistor to the base of the preceding transistor or from the collector of the following transistor to the base of the preceding transistor via the collector of the preceding transistor. A drive circuit for at least a load comprising: a base current flowing between an emitter and a base of the preceding transistor, wherein the collector current of the preceding transistor is blocked when a voltage of an anode electrode of the diode is lower than a voltage of a cathode electrode. Setting a first rising curve as a curve of the collector current of the Darlington transistor by substantially turning on the transistor at the subsequent stage. When the voltage of the anode electrode of the diode is higher than the voltage of the cathode electrode, the first rising curve is set. The collector current of the transistor of the first stage flows, and the latter stage transistor is turned on substantially by the emitter current flowing between the emitter and the base and between the emitter and the collector of the previous stage transistor. When the second rising curve is set and a current larger than the steady current is required, the driving is performed using the second rising curve. When a steady current is required,
A driving circuit for a load, wherein the driving is performed using the first rising curve. 3. The load driving circuit according to claim 1, wherein said Darlington transistor is composed of three or more stages.