JPS59151526A - Switching circuit - Google Patents

Abstract

PURPOSE:To reduce the current at the inverse mode without losing the switching time at the forward mode by inserting a resistor and a diode in series between the base and emitter of a switching transistor (TR). CONSTITUTION:Resistors R1-R4 and Schottky barrier diodes D11-D14 are inserted in series between the base and emitter of TRs Q1-Q4. When the TRs Q1, Q4 are turned from ON to OFF and a flywheeling current flows to diodes D2, D3 in this constitution, since the diodes D12, D14 are inserted reversely between the base and emitter of the TRs Q2, Q3, the base current hardly flows. Thus, the current value and period in the reverse direction as those of the current at the inverse mode required to flow the next forward mode are made respectively small sufficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a switching circuit that switches and drives an inductive load such as a motor, and more particularly to a switching circuit that requires freewheeling operation.

[Technical background of the invention]

When driving an inductive load, such as a DC motor, by switching entirely, a switching circuit as shown in FIG. 1 has conventionally been used. In the switching circuit shown in Figure 1, the DC power source is voltage ■. , two switching NPN) transistors Ql between the application point and the reference voltage application point (earth).
, Q2 is connected in series, and two more switching NPNs are connected between the same <vcc application point and ground.
)Ran resistor Q8. Q4 are connected in series, and the transistors Q1. (h series connection point A and transistors Q3 and Q4
A DC motor M is connected between the series connection point B and the series connection point B. Furthermore, free-wheeling PN junction diodes D1 to D4 are connected between the collectors and emitters of the transistors Q1 to Q4, respectively, with their anodes facing the emic side, and between the paces and emitters of the transistors Q1 to Q4 are connected. , resistors R1 to R4 for absorbing accumulated carriers of transistors Ql to Q4 are connected, respectively.

That is, in the switching circuit shown in FIG. 1, each of the transistors Q1 to Q4 . It is constructed by providing four unit switching circuits each including a diode Dl'' D4 and each resistor R1 to R4.

In the switching circuit having such a configuration, when the DC motor M is rotated in a fixed direction at a predetermined rotation speed, the switching of transistors Q1 and Q4 is controlled using a predetermined frequency signal, for example.

Also, to rotate in the opposite direction, transistor Q3
and Q2 are switched and controlled by a predetermined frequency signal. Now suppose that transistors Q1 and Q4 are in the on state, and a current flows through the DC motor M as shown by arrow A in Figure 1, then both transistors Q
1 and Q4 are turned off. Then, the current that has been flowing through the DC motor M will now flow through the two freewheeling diodes D2 and D3, as shown by the arrows.

[Problems with background technology]

By the way, each pace of transistors Q1 to Q4.

Resistors R1-R4 connected between the emitters absorb carriers accumulated in each pace region when each transistor Q1-Q4 changes from an on state to an off state, thereby reducing the switching time in forward mode. It is designed to speed up the process. Therefore, in order to further speed up the switching time, it is preferable that the values of the resistors R1 to R4 be much smaller.

On the other hand, considering the free boiling operation, it is preferable that the values of the resistors R, to R4 be larger. For example, attention will be paid to the transistor Q2 during a free boiling operation in which a current flows in the direction indicated by the arrow p after the transistors Ql and Q4 are turned off. Now the collector of this transistor Q2.

A forward current flows through the diode D2 connected between the emitters. At this time, a current flows through the resistor R2 to the transistor Q2, so a current also flows from the emitter to the collector of the transistor Q2. That is, a so-called inverse mode current flows through the transistor Q2, and the value of this current is determined by the resistor R2.
The smaller the value, the more difficult it is. Next, when the transistor Q] is turned on again, in order to turn off the transistor Q2 in the inverse mode, this transistor Q2 is turned on again.
In this case, it is necessary to flow a current in the opposite direction to the current that has been flowing so far, and its value and period become larger or longer depending on the current value in the inverse mode. In other words, if the current value in inverse mode is large, transistor Q
IK requires a large forward current to flow for a long time, so it is a transistor. It is necessary to increase the power of the star Q1 itself and the pace input signal thereof. Therefore, considering the inverse mode, the resistors R1 to R
It is preferable that the value of 4 be larger.

In this way, in a conventional switching circuit that connects a resistor between the pace and emitter of a switching transistor,
Since the effect of setting the value of this resistor in forward mode and inverse mode is contradictory, it is possible to shorten the switching time in forward mode, reduce the power of the switching transistor itself, and reduce the power of the pace input signal. The disadvantage is that it is not possible to satisfy both.

[Object of the Invention] The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to reduce the current in the inverse mode without impairing the switching time in the forward mode, thereby improving the efficiency of switching transistors. An object of the present invention is to provide a switching circuit that can reduce the power consumption of the pace input signal and the pace input signal thereof.

[Summary of the invention]

According to the present invention, a switching circuit is provided in which a resistor and a diode are inserted in series between a switching transistor node and an emitter.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a circuit configuration diagram when this invention is implemented in a switching circuit for switching driving a DC motor in the same way as in FIG. 1, and parts corresponding to those in FIG. 1 are given the same reference numerals. The explanation will be omitted. In this example circuit, the trough) 7. The resistors R1 to R4 are inserted between the bases and emitters of transistors Q1 to Q4, respectively, and the bases 9. Schottky barrier diodes I)tt to D14 are inserted in series with the resistors R1 to R4 between the emitters so that each cand is on the emitter side. That is, each of the 7 sweet rear diodes I) it ~ D1
4 is inserted in the opposite direction to the PN junction between the base and emitter of the transistors Q1 to Q4. Further, a relationship such as VBE>vF is established between each forward voltage vF of the Schottky barrier diode Dll~014 and each base-emitter voltage 'YBE of each transistor Q1~Q4, ,, :0.7V,
V, #0.4~0.5V), and each reverse recovery time tr of Schottky barrier diodes Dll~D14
r and each carrier accumulation time ts of transistors Q1 to Q4
It is assumed that the relationship trr<tBtg holds true between tg and tg.

Note that the above relationship can be easily achieved in a normal Schottky barrier fist diode.

In such a configuration, the transistor Q! +Q4 transitions from the on state to the off state, and the freewheeling current flows through the diode D2. Consider when it is flowing to D3. In this case, transistor Q2. Between the base and emitter of Q3 are each Schottky barrier bone diode D12 in the opposite direction *
Since D13 is inserted, almost no base current flows. Therefore, transistor Q2. Q
The current in the inverse mode shown in step 3 should be an extremely small leakage current, and the value and duration of the current in the opposite direction to the current in the inverse mode that needs to flow in the next forward mode should be sufficiently small. can do. The same holds true when the transistors Ql and Q4 are in the inverse mode. As a result, each transistor Q8~Q
It is not necessary to increase the power of 4 itself and its base input signal, and both can be made small.

On the other hand, considering the switching time of each transistor Q1 to Q4 in the forward mode, the resistors R1 to R4
If the value of is the same as before, the Schottky barrier
The length is increased by the insertion of the diodes I)st to D14. However, since the values of each of the resistors R1 to R4 can be freely set to a low value without considering the inverse mode, there is no fear that the switching time in the forward mode will be impaired compared to the conventional one.

Also, the voltage relationship VB as described above! , > vF is necessary to supply sufficient base current when turning on each transistor Q1 to Q4), and the time relationship trr<t, tg is necessary to hold for each transistor Q1 to Q4. This is because the accumulated carriers of the transistors Ql-Q4 are absorbed by the respective resistors R1''-R4 via the respective Schottky barrier diodes DIl-D14'.

Next, the results of an actual characteristic comparison test between the switching circuit according to the present invention and a conventional one will be explained. FIG. 3 shows the test circuit. In the figure, one end of a coil C having a value of 300 μH is connected to the positive side of the DC power supply Vcc, the collector of a switching NPN transistor Q8 is connected to the other end of the coil C, and the collector of this transistor Q8 is connected to the other end of the coil C. The emitter is connected to the negative electrode side of the DC power supply vcc. Further, at both ends of the coil C, there is a collector of a transistor Q1 in a conventional unit switching circuit as shown in FIG. 4(4) or a unit switching circuit according to the present invention as shown in FIG. 4(B). The emitters are connected to each other.

(1) In such a test circuit, Figure 5 shows the change in current when the transistor Q is turned on and a predetermined current is passed through the coil C, and then the transistor Q8 is turned off. It is a characteristic diagram. Note that the value of resistor R1 is 0.
．． Each is set to 10. FIG. 5(4) shows a case where a conventional unit switching circuit as shown in FIG. 4(4) is connected to the coil C. At this time,
■oc is set to 50V. As shown in FIG. 5 (4), when the current IF in the forward mode is set to 8A, the transistor Ql in the inverse mode
The peak value of the current flowing through the diode D1 reaches as high as 80 A, and the period during which this current flows is as long as 3 μs. On the other hand, Fig. 5 CB) shows the case where the unit switching circuit of this invention as shown in Fig. 4 ■) is connected to the coil C, and cc is 300.
It is set to v. As shown in FIG. 5(B), if
If is set to 5OA, the peak value to is 55'
In addition, the period during which the current flows is only 05 μs.
It is. As described above, in the present invention, the current value and period in the inverse mode can be made sufficiently smaller than in the conventional case.

FIGS. 6 and 7 are circuit diagrams showing modified examples of the invention, respectively. In the example circuit shown in FIG. 2 above, each NP
We have explained the case where the DC motor M is driven only by N ) transistors Q1 to Q4, but in this case, as shown in FIG. , and the source, and an input signal may be supplied to the dart of this MOS transistor Q21. in this case,
When a 7 Lee wheeling current flows through the diode D1,
If the Schottky barrier Φ diode Dll does not exist, current will also flow through the diode parasitically generated between the source and drain of the MOS transistor Q21.

However, by providing a diode DIf, this current can also be blocked. Also, the one in Figure 7 is NP
N) The transistor Ql is composed of two Darlington-connected transistors Qalr Q41, and a resistor R is connected between the base and emitter of the transistor Q41 on the output side.
1 and a Schottky barrier diode Dll are inserted in series.

FIG. 8 is a circuit diagram of another embodiment of the present invention. The embodiment shown in Fig. 2 is a case where the present invention is implemented in a circuit for driving a DC motor, but this is a case where two unit switching circuits are added to make six units as shown in Fig. 8. The induction motor IM is driven by a switching circuit.

Note that this invention is not limited to the above embodiments. For example, in the above embodiment, the case where this invention is applied to a circuit that drives an all-DC motor or an inductor motor is described, but it goes without saying that this invention can be implemented when driving other inductive loads. For example, it can be implemented in a constant voltage constant frequency device such as a switching drive for the primary coil of a transformer.

〔Effect of the invention〕

As explained above, according to the present invention, the current in the inverse mode is reduced without impairing the switching time in the forward mode, thereby reducing the power of the switching transistor and the pace input signal thereof. It is possible to provide a switching circuit that can achieve

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional switching circuit, Fig. 2 is a circuit block diagram of an embodiment of the present invention, Fig. 3 is a diagram showing a test circuit for explaining the present invention, and Fig. 4 is a diagram showing a test circuit for this test. Figure 5 showing the unit switching circuit under test used in the circuit.
The figures are characteristic diagrams obtained with the circuit of FIG. 3, FIGS. 6 and 7 are circuit diagrams of modified examples of the present invention, and FIG. 8 is a circuit configuration diagram of another embodiment of the present invention. Q1-Q4...NPN) transistor (pybolar transistor element), DI-D4...PN junction diode (first diode element), R4-R4 resistor (resistance element), Schottky barrier for D11-D14 Diode (second diode element), M...DC motor (corrosive conductive load). Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 5 (A) (B) Figure 6 Figure 7

Claims (3)

[Claims] (1) A bipolar transistor element that switches and drives an inductive load, and an emitter of this transistor element,
The first for freewheeling operation inserted between the collectors.
the diode element and the pace of the transistor element,
A resistor element inserted between the emitters, and a second diode element inserted in a direction opposite to the PN junction between the transistor element and the emitter and in series with the resistor element. Characteristic switching circuit. (2) The forward voltage of the second diode element is set to be smaller than the pace and emitter voltage of the transistor element, and its reverse recovery time is set to be shorter than the carrier accumulation time of the transistor element. A switching circuit according to claim 1. (3) The switching circuit according to claim 2, wherein the second diode element is a Schottky barrier diode.