JPH0313770Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a variable output inductive load circuit in which the output of an inductive load such as a capacitor motor is made variable by controlling an AC power supply by switching using transistors.

Conventionally, in this type of circuit, as shown in Figure 1,
Diodes 8, 9, 10, 1 are connected in antiparallel between a pair of AC power receiving terminals consisting of a first terminal and a second terminal 2 connected to the output ends of the AC power supply 3, respectively.
Four transistors 4, 5, 6, and 7 are connected in series in this order, and the first and second transistors 4, 5 are connected to each other in series.
An inductive load 12 is placed on both ends of the first set of switches consisting of
is connected. In addition, the first switch of the first set of switches
and the conduction direction of the second transistors 4 and 5 and the third and fourth transistors 6 and 7 of the second set of switches.
The conduction directions of NPN transistors are opposite to each other, and PNP transistors are opposite to each other. Therefore, by making the bases of the transistors in each group common and allowing the base current to flow, it is possible to conduct bidirectional conduction for each group. Conductive properties are given.

In this circuit, to change the output of the inductive load (hereinafter simply referred to as load) 12, the pulse generator 1 is connected directly to the common base of the first set of switches, and through the inverter 14 to the common base of the second set of switches.
This is done by applying variable duty pulses from 3 onwards and alternately turning on and off the first set of switches and the second set of switches. In other words, when the second set of switches is on and the first set of switches is off,
Current flows from the power supply 3 to the load 12, and the second set of switches is turned off and the power flowing into the load becomes zero.At the same time, the first set of switches is on, so that the current due to the accumulated energy of the inductive load 12 is turned on. The load power is controlled by varying the on/off time ratio by shunting the current to the first set of switches to prevent abnormal voltage transients that would normally occur at the inductive load end when the switch is turned off.

However, in the on/off operation of the transistor by the base drive pulse, there is a slight delay in the off operation compared to the on operation due to base accumulated carriers. Therefore, when switching between the first set of switches and the second set of switches, there is a period in which both switches are in the on state, and during this period, short-circuit current that does not pass through the load flows between the first and second terminals. Since the current flows between the two switches and causes an overload of the transistor, it was necessary to insert a protective resistor 15 in series with the first set of switches.

The purpose of the present invention is to provide a variable output inductive load circuit that does not form a short current circuit when switching the current on and off, thus eliminating the need for a transistor protection resistor and improving efficiency. It's about doing.

The variable output inductive load circuit of the present invention has a pair of AC power receiving terminals consisting of a first terminal and a second terminal, and a diode connected in antiparallel to the first and second terminals in the order of first to fourth. four first to fourth transistors connected in series between the two terminals, and the third transistor whose conduction directions are opposite to each other.
and a fourth transistor, and an inductive load connected in parallel to the set of transistors; The transistor has a configuration including a resistor connected therebetween, and a pulse generator that generates a variable duty pulse to be applied to the bases of the first and fourth transistors whose conduction directions are opposite to each other.

Next, the present invention will be explained with reference to examples.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

In Fig. 2, four transistors 4, 5, 6, and 7 with diodes connected in antiparallel are connected in series between the first terminal 1 and the second terminal 2, unlike the conventional example. However, in the case of Fig. 2, the second and third
NPN transistors 5 and 6 constitute a first set of switches, and an inductive load 12 is connected between both ends thereof. On the other hand, the second set of switches is formed of first and fourth transistors 4 and 7 separated on both sides with the load 12 in between and conduction directions facing each other. Resistors 16 and 17 are connected between the first terminal 1 and the base of the third transistor 6 and between the second terminal 2 and the base of the second transistor 5, respectively. Then, variable duty pulses are applied from the variable duty pulse generating circuit 13 only to the transistors of the second set of switches.

Further, FIGS. 3a to 3d are waveform diagrams of main parts for explaining the operation of the variable output inductive load circuit shown in FIG. 2, respectively.

The operation of the circuit of the present invention will be explained with reference to FIG. 2 and FIGS. 3a to 3d.

First, the terminal 1 of the AC power supply 3 shown in FIG.
When the terminal 2 is negative and the transistor 4 is turned on by the pulse from the pulse generating circuit 13, the resistor 16 and the transistor 6 are connected from the terminal 1.
A current flows through the base-collector of the diode 11 and reaches the terminal 2.

That is, generally NPN like transistor 6
The basic structure of a transistor is a connected body of an N-type semiconductor, a P-type semiconductor, and an N-type semiconductor.The terminal connected to the P-type semiconductor is the base, and one of the N-type semiconductors is the base.
The terminal connected to the N-type semiconductor is called the collector, and the terminal connected to the other N-type semiconductor is called the emitter. Therefore, the distance between the base and emitter is P
Since it has a diode structure, which is a connection between a type semiconductor and an N type semiconductor, the base potential is higher than the emitter potential by a certain degree (for example, 0.6V).
degree), current flows from the base to the emitter. Similarly, since the base-collector is connected to a P-type semiconductor and an N-type semiconductor, that is, it has a diode structure, the potential of the base is higher than the potential of the collector (for example,
(about 0.6V), current flows from the base to the collector.

In this state, the base of the transistor 6 is connected to the positive side of the power supply, and the collector is connected to the negative side of the power supply, so that current flows from the base to the collector.

Further, as at time _t1 shown in FIGS. 3A to 3D, a current also flows from the terminal 1 through the transistor 4, the inductive load 12, and the diode 11 to the terminal 2. At this time, since no current flows through the base of the transistor 5, the transistor 5 is in an off state, and since a positive voltage is applied to the cathode of the diode 9, no current flows through the diode 9 either.

Next, when the pulse from the pulse generating circuit 13 disappears and the transistor 4 turns off, the accumulated energy of the inductive load 12 generates a voltage in the inductive load 12 in the direction of continuing the current flowing, and the transistor 4 A positive voltage is applied to the collector of , and a current flows from terminal 1 through resistor 16, the base/emitter of transistor 6, diode 9, inductive load 12, and diode 11 to terminal 2, so transistor 6 turns on. As shown at time _t2 shown in FIGS. 3a to 3d, the transistor 6 and diode 9 are
A circulating current flows through the inductive load 12.

Next, when the transistor 4 is turned on again by a pulse from the pulse generating circuit 13, the transistor 5 is turned off because no current is supplied to the base of the transistor 5, and a positive voltage is applied to the cathode of the diode 9. As a result, current no longer flows through the diode 9, and as shown in Fig. 3 a to d.
The operation returns to the same operation as at time t ₁ shown in .

The case where the terminal 1 of the AC power supply 3 is positive and the terminal 2 is negative has been described above, but the operation is similar when the terminal 1 of the AC power supply 3 is positive and the terminal 2 is negative. That is, transistors 4 and 7, diodes 8 and 11,
The operation is simply that the resistors 16 and 17, the transistors 6 and 5, and the diodes 10 and 9 are replaced, respectively, and the details will be omitted.

Furthermore, the operation at the time of switching the polarity of the AC power supply 3 will be explained.

For example, just before time _t3 shown in FIGS. 3a to 3d, as described above, the terminal 1 connects the resistor 16, the base and collector of the transistor 6, and the diode 1.
A current is flowing through 1 to terminal 2, but the voltage (for example, 0.6V) required for the voltage of AC power supply 3 to flow between the base and collector of transistor 6,
Forward voltage drop of diode 11 (for example,
0.6V), no current flows into the base of transistor 6.

In other words, the voltage of AC power supply 3 is set to V ₃ , and the circuit described above (terminal 1 → resistor 16 → base of transistor 6
If the current flowing through the collector → diode 11 → terminal 2 is I _b , and the resistance value of the resistor 16 is R ₁₆ , then I _B = V ₃ −0.6V − 0.6V/R ₁₆ , and the power supply voltage V ₃ is 1.2V. (that is, the sum of the voltage required for current to flow between the base and collector of transistor 6 and the forward voltage drop of diode 11), the base current I _B will no longer flow through transistor 6.

In addition, silicon-based diodes and diodes between the base and collector of transistors, etc.
When the voltage is increased to about 0.6V or higher, current suddenly begins to flow.

For example, if AC power supply 3 of 50Hz, AC100V is (0.6V
+0.6V) to OV, During this period, no current flows to the base of transistor 6,
There is sufficient time for the transistor to remain on for a short period of time (approximately several microseconds).
Therefore, no short circuit current flows from terminal 2 through transistor 7, transistor 6, transistor 5 or diode 9, diode 8.

Further, when both the transistors 4 and 7 are in the off state and the polarity of the AC power supply ₃ is switched as at time _t4 shown in FIG. , the current flows through the base and emitter of transistor 5, diode 10, load 12, and diode 8 to terminal 1, turning transistor 5 on, so that inductive load 1
A circulating current flows from the transistor 2 through the transistor 5 and the diode 10 to the inductive load 12.

Furthermore, the voltage of the AC power supply 3 is the voltage necessary for the base current of the transistor 5 to flow, that is, the voltage between the base and emitter of the transistor 5 (for example,
0.6V), the forward voltage drop of diode 10 (for example, 0.6V), and the forward voltage drop of diode 8 (for example, 0.6V). AC power supply 3, resistor 17, base of transistor 5
Inductive load 12 through the emitter and diode 10
Since the current flows, the transistor 5 remains on, and the circulating current continues to flow. In this case, a current also flows from the inductive load 12 through the diode 8, the resistor 16, and the base/collector of the transistor 6 to the inductive load 12, but only a small amount flows and does not affect the circulating current. Furthermore, when the stored energy of the inductive load 12 is exhausted, the resistor 16 and the transistor 6 are connected to the terminal 1.
The current flows only through the base, collector, and diode 11 to the terminal 3.

As explained above, in this embodiment, since the first set of switches formed by the second and third transistors 5 and 6 are always off in the conduction direction that bypasses the load 12, the second set of switches is It will not turn on at the same time as the other switch. Furthermore, since the freewheeling circuit caused by the transient voltage of the load 12 is always turned on, no abnormal transient voltage occurs across the load 12 .

Therefore, according to the present invention, there is no need to provide a protection resistor to prevent overload of the transistor, which was required in the conventional circuit shown in FIG. Not only can the cost be lowered, but the conventional loss caused by short-circuit current is eliminated, so efficiency can be improved accordingly.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an example of a conventional variable output inductive load circuit, and FIG. 2 is a circuit diagram of an embodiment of the present invention.
FIGS. 3a to 3d are waveform diagrams of main parts for explaining the operation of the variable output inductive load circuit shown in FIG. 2, respectively. 1...First terminal, 2...Second terminal, 4, 5,
6, 7...first to fourth transistors, 8,
9, 10, 11...Anti-parallel diode, 12...
Inductive load, 13... variable data pulse generator, 15, 16... resistance.

Claims (1)

[Scope of utility model registration request] A pair of AC power receiving terminals consisting of a first terminal and a second terminal, and diodes connected in antiparallel to the first terminal and the second terminal in the order of first to fourth.
The transistor is connected in parallel to a set of four first to fourth transistors connected in series between the terminal and the second and third transistors whose conduction directions are opposite to each other. a resistor connected between the first terminal and the base of the third transistor and between the second terminal and the base of the second transistor, respectively;
A variable output inductive load circuit comprising: a pulse generator that applies variable duty driving pulses to the bases of the first and fourth transistors whose conduction directions are opposite to each other.