阅读说明：本技术 半导体开关管的驱动电路、驱动芯片及驱动控制方法 (Drive circuit, drive chip and drive control method of semiconductor switch tube ) 是由 文鹏 林官秋 曾国梁 于 2021-08-20 设计创作，主要内容包括：本发明揭示了一种半导体开关管的驱动电路、驱动芯片及驱动控制方法,所述驱动电路能耦接一半导体开关管,所述驱动电路包括基极驱动电流控制电路及基极发射极控制电路；基极驱动电流控制电路耦接所述半导体开关管的基极,用以在所述驱动电路处于第一状态下控制所述半导体开关管导通；还用以在所述驱动电路处于第二状态下控制所述半导体开关管基极的电流小于设定阈值；基极发射极控制电路用以在设定条件达到时控制所述半导体开关管的基极及发射极之间短路。本发明提出的用于半导体开关管的驱动电路、驱动芯片及驱动控制方法,可在满足设定条件时强制关断半导体开关管,提高驱动控制的可靠性,防止半导体开关管因长时间工作在放大区而损坏。(The invention discloses a drive circuit, a drive chip and a drive control method of a semiconductor switch tube, wherein the drive circuit can be coupled with the semiconductor switch tube and comprises a base drive current control circuit and a base emitter control circuit; the base electrode driving current control circuit is coupled with the base electrode of the semiconductor switch tube and used for controlling the semiconductor switch tube to be conducted when the driving circuit is in a first state; the current of the base electrode of the semiconductor switching tube is controlled to be smaller than a set threshold value when the driving circuit is in a second state; the base emitter control circuit is used for controlling short circuit between the base and the emitter of the semiconductor switch tube when a set condition is reached. The driving circuit, the driving chip and the driving control method for the semiconductor switch tube provided by the invention can forcibly turn off the semiconductor switch tube when set conditions are met, improve the reliability of driving control and prevent the semiconductor switch tube from being damaged due to long-time work in an amplification region.)

1. A driving circuit of a semiconductor switch, the driving circuit being capable of being coupled to a semiconductor switch, the driving circuit comprising:

the base electrode driving current control circuit is coupled with the base electrode of the semiconductor switch tube and used for controlling the semiconductor switch tube to be conducted when the driving circuit is in a first state; the current of the base electrode of the semiconductor switching tube is controlled to be smaller than a set threshold value when the driving circuit is in a second state; and

and the base emitter control circuit is used for controlling short circuit between the base and the emitter of the semiconductor switching tube when the set condition is reached.

2. The driving circuit of the semiconductor switching tube according to claim 1, wherein:

the base emitter control circuit includes:

a first end of the second switch tube is coupled with the base electrode of the semiconductor switch tube, and a second end of the second switch tube is coupled with the emitter electrode of the semiconductor switch tube; and

and the second switching tube driving circuit is coupled with the second switching tube and used for controlling the conduction of the second switching tube when a set condition is reached.

3. The driving circuit of the semiconductor switching tube according to claim 1, wherein:

the setting condition includes reaching at least one of the following conditions:

(1) the current flowing through the semiconductor switch tube reaches a first threshold value and exceeds a set time;

(2) the current flowing through the semiconductor switch tube reaches a second threshold value; wherein the second threshold is greater than the first threshold;

(3) the semiconductor switch tube has entered the amplification region.

4. The driving circuit of the semiconductor switching tube according to claim 1, wherein:

the base drive current control circuit includes:

the first switching tube is coupled with the base electrode of the semiconductor switching tube;

the first switching tube driving circuit is coupled with the first switching tube and used for controlling the switching state of the first switching tube;

the semiconductor switch tube driving circuit is coupled with the base electrode of the semiconductor switch tube through the first switch tube and used for driving the semiconductor switch tube to work when the first switch tube is conducted.

5. The driving circuit of the semiconductor switching tube according to claim 4, wherein:

the driving circuit further comprises a PWM modulation circuit, and the PWM modulation circuit is used for modulating a PWM signal; the output end of the PWM modulation circuit is coupled with the input end of the first switching tube driving circuit.

6. The driving circuit of the semiconductor switching tube according to claim 5, wherein:

the base driving current control circuit is coupled with the PWM modulation circuit;

the first state refers to a state in which the PWM modulation circuit outputs a set PWM signal;

the second state is a state where a current flowing through the semiconductor switch tube reaches a first threshold value.

7. The driving circuit of the semiconductor switching tube according to claim 4, wherein:

the driving circuit further includes:

an amplitude modulation circuit for generating a first voltage signal corresponding to a first threshold;

a first comparator, wherein the non-inverting input terminal of the first comparator is coupled to the voltage of the emitter of the semiconductor switch tube, and the inverting input terminal of the first comparator is coupled to a first voltage signal corresponding to the first threshold; the output end of the first comparator is coupled with the first switch tube driving circuit.

8. The driving circuit of the semiconductor switching tube according to claim 7, wherein:

the driving circuit further includes: and the timing unit is respectively coupled with the first comparator and the second switch tube driving circuit and is used for timing the set output of the first comparator.

9. The driving circuit of the semiconductor switching tube according to claim 2, wherein:

the driving circuit further includes:

an amplitude modulation circuit for generating a second voltage signal corresponding to a second threshold;

a second comparator, wherein the non-inverting input terminal of the second comparator is coupled to the voltage of the emitter of the semiconductor switch tube, and the inverting input terminal of the second comparator is coupled to a second voltage signal corresponding to the second threshold; the output end of the second comparator is coupled with the second switch tube driving circuit.

10. The driving circuit of the semiconductor switching tube according to claim 2, wherein:

the driving circuit further comprises an amplification area judging module, wherein the amplification area judging module is used for judging whether the semiconductor switch tube enters an amplification area or not; the output end of the amplification area judging module is coupled with the second switching tube driving circuit.

11. A drive control method of a semiconductor switching tube is characterized by comprising the following steps:

controlling the semiconductor switching tube to be conducted when a driving circuit of the semiconductor switching tube is in a first state;

when a driving circuit of the semiconductor switching tube is in a second state, controlling the driving current of the base electrode of the semiconductor switching tube to be smaller than a set threshold value;

and when the set condition is reached, controlling short circuit between the base electrode and the emitter electrode of the semiconductor switch tube.

12. The method of claim 11, wherein:

the setting condition includes at least one of the following conditions:

(1) the current flowing through the semiconductor switch tube reaches a first threshold value and exceeds a set time;

(2) the current flowing through the semiconductor switch tube reaches a second threshold value; wherein the second threshold is greater than the first threshold;

(3) the semiconductor switch tube has entered the amplification region.

13. The method of claim 11, wherein:

the drive control method further includes: and when the set condition is reached, controlling the conduction of a second switching tube which is coupled with the base electrode and the emitter electrode of the semiconductor switching tube.

14. The method of claim 11, wherein:

the driving circuit comprises a PWM modulation circuit;

the first state refers to a state in which the PWM modulation circuit outputs a set PWM signal;

the second state is a state where a current flowing through the semiconductor switch tube reaches a first threshold value.

15. A driving chip of a semiconductor switch tube is characterized by comprising: a driving circuit of a semiconductor switching tube according to any one of claims 1 to 10.

Technical Field

The invention belongs to the technical field of microelectronics, relates to a driving circuit, and particularly relates to a driving circuit, a driving chip and a driving control method of a semiconductor switching tube.

Background

Triode (BJT for short) is current-driven semiconductor switch tube, I in figure 1_B(t) is the base drive current of the BJT, Vce (t) is the voltage between the collector and emitter of the BJT, and ic (t) is the BJT collector current. The switching times are as defined in the above figure: time delay time: td-t 1' -t 0; rise time: tr-t 2' -t 1; storage time: ts-t 4' -t 3; the falling time is as follows: and tf is t5-t 4.

Unlike MOSFET, the driving time sequence of BJT has one more storage time stage, which can last for several us, reflecting "current tailing" effect of BJT. The BJT storage time changes along with the change of the working state, and the control of the switching tube is influenced to a certain extent. In order to turn off the BJT controllably, not only the driving current of the BJT needs to be reduced to 0, but also a negative current needs to be applied, which is called "forced turn-off" as shown in fig. 2. The forced turn-off process is to forcibly extract excess carriers of Base, which wastes circuit energy; the moment when IB is reduced to 0 is commonly referred to as the "pre-close breakpoint".

In the Flyback circuit, a current flowing through the BJT is approximately a triangular wave. Pre-turning off the BJT when the inductive current reaches a threshold Ic 1; when the inductive current reaches a threshold Ic2, the BJT is forced to be switched off; according to IC IB + IE, when pre-off, IB drops to 0, so IC has a drop, as shown in fig. 3.

The design of pre-shutdown and forced shutdown of the BJT needs to be compromised: if the pre-closing break point and the forced closing break point are too close, more energy is wasted, and BJT loss is large; if the pre-off break point and the forced off break point are too different, the BJT may work in the amplification region (as shown in fig. 4), and the loss is large, which may cause the chip to be damaged. Therefore, the drive current of the BJT is difficult to design and often has a certain experience.

In view of the above, there is a need to design a new driving circuit for a switching transistor so as to overcome at least some of the above-mentioned disadvantages of the existing driving circuits.

Disclosure of Invention

The invention provides a drive circuit, a drive chip and a drive control method of a semiconductor switch tube, which can improve the reliability of drive control and prevent the switch tube from being damaged due to long-time work in an amplification region.

In order to solve the technical problem, according to one aspect of the present invention, the following technical solutions are adopted:

a driving circuit of a semiconductor switch tube, the driving circuit can be coupled with a semiconductor switch tube, the driving circuit comprises:

the base electrode driving current control circuit is coupled with the base electrode of the semiconductor switch tube and used for controlling the semiconductor switch tube to be conducted when the driving circuit is in a first state; the current of the base electrode of the semiconductor switching tube is controlled to be smaller than a set threshold value when the driving circuit is in a second state; and

and the base emitter short-circuit control circuit is used for controlling the short circuit between the base and the emitter of the semiconductor switching tube when the set condition is reached.

As an embodiment of the present invention, the base-emitter control circuit includes:

a first end of the second switch tube is coupled with the base electrode of the semiconductor switch tube, and a second end of the second switch tube is coupled with the emitter electrode of the semiconductor switch tube; and

and the second switching tube driving circuit is coupled with the second switching tube and used for controlling the conduction of the second switching tube when a set condition is reached.

As an embodiment of the present invention, the setting condition includes reaching at least one of the following conditions:

(1) the current flowing through the semiconductor switch tube reaches a first threshold value and exceeds a set time;

(2) the current flowing through the semiconductor switch tube reaches a second threshold value; wherein the second threshold is greater than the first threshold;

(3) the semiconductor switch tube has entered the amplification region.

As an embodiment of the present invention, the base drive current control circuit includes:

the first switching tube is coupled with the base electrode of the semiconductor switching tube;

the first switching tube driving circuit is coupled with the first switching tube and used for controlling the switching state of the first switching tube;

the semiconductor switch tube driving circuit is coupled with the base electrode of the semiconductor switch tube through the first switch tube and used for driving the semiconductor switch tube to work when the first switch tube is conducted.

As an embodiment of the present invention, the driving circuit further includes: a PWM modulation circuit for modulating a PWM signal; the output end of the PWM modulation circuit is coupled with the input end of the first switching tube driving circuit.

As an embodiment of the present invention, the base driving current control circuit is coupled to the PWM modulation circuit;

the first state refers to a state in which the PWM modulation circuit outputs a set PWM signal;

the second state is a state where a current flowing through the semiconductor switch tube reaches a first threshold value.

As an embodiment of the present invention, the driving circuit further includes:

an amplitude modulation circuit for generating a first voltage signal corresponding to a first threshold;

a first comparator, wherein the non-inverting input terminal of the first comparator is coupled to the voltage of the emitter of the semiconductor switch tube, and the inverting input terminal of the first comparator is coupled to a first voltage signal corresponding to the first threshold; the output end of the first comparator is coupled with the first switch tube driving circuit.

As an embodiment of the present invention, the driving circuit further includes: and the timing unit is respectively coupled with the first comparator and the second switch tube driving circuit and is used for timing the set output of the first comparator.

As an embodiment of the present invention, the driving circuit further includes:

an amplitude modulation circuit for generating a second voltage signal corresponding to a second threshold;

a second comparator, wherein the non-inverting input terminal of the second comparator is coupled to the voltage of the emitter of the semiconductor switch tube, and the inverting input terminal of the second comparator is coupled to a second voltage signal corresponding to the second threshold; the output end of the second comparator is coupled with the second switch tube driving circuit.

As an embodiment of the present invention, the driving circuit further includes: the amplification area judging module is used for judging whether the semiconductor switch tube enters the amplification area or not; the output end of the amplification area judging module is coupled with the second switching tube driving circuit.

According to another aspect of the invention, the following technical scheme is adopted: a driving control method of a semiconductor switching tube comprises the following steps:

controlling the semiconductor switching tube to be conducted when a driving circuit of the semiconductor switching tube is in a first state;

when a driving circuit of the semiconductor switching tube is in a second state, controlling the driving current of the base electrode of the semiconductor switching tube to be smaller than a set threshold value;

and when the set condition is reached, controlling short circuit between the base electrode and the emitter electrode of the semiconductor switch tube.

As an embodiment of the present invention, the setting condition includes at least one of the following conditions:

(1) the current flowing through the semiconductor switch tube reaches a first threshold value and exceeds a set time;

(2) the current flowing through the semiconductor switch tube reaches a second threshold value; wherein the second threshold is greater than the first threshold;

(3) the semiconductor switch tube has entered the amplification region.

As an embodiment of the present invention, the drive control method further includes: and when the set condition is reached, controlling the conduction of a second switching tube which is coupled with the base electrode and the emitter electrode of the semiconductor switching tube.

As an embodiment of the present invention, the driving circuit includes a PWM modulation circuit;

the first state refers to a state in which the PWM modulation circuit outputs a set PWM signal;

the second state is a state where a current flowing through the semiconductor switch tube reaches a first threshold value.

According to another aspect of the invention, the following technical scheme is adopted: a driving chip of a semiconductor switch tube comprises the driving circuit of the semiconductor switch tube.

The invention has the beneficial effects that: the driving circuit, the driving chip and the driving control method for the semiconductor switch tube provided by the invention can forcibly turn off the semiconductor switch tube when set conditions are met, improve the reliability of driving control and prevent the semiconductor switch tube from being damaged due to long-time work in an amplification region.

Drawings

FIG. 1 is a timing diagram illustrating the driving of a conventional BJT.

Fig. 2 is a timing diagram of the conventional BJT driving with a negative current forced turn-off.

FIG. 3 is a diagram illustrating the BJT collector current falling after the BJT is forced to be turned off.

FIG. 4 is a diagram illustrating the BJT collector current falling after the BJT is forced to be turned off.

FIG. 5 is a diagram illustrating the operation of a conventional BJT to an amplification region.

Fig. 6 is a schematic diagram of a driving circuit of a semiconductor switch in an embodiment of the invention.

Fig. 7 is a schematic diagram of a driving circuit of a semiconductor switch according to an embodiment of the invention.

FIG. 8 is a control timing diagram of the driving circuit according to an embodiment of the present invention.

Fig. 9 is a schematic diagram illustrating the operation principle of the amplification area determination module according to an embodiment of the present invention.

Detailed Description

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.

The description in this section is for several exemplary embodiments only, and the present invention is not limited only to the scope of the embodiments described. It is within the scope of the present disclosure and protection that the same or similar prior art means and some features of the embodiments may be interchanged.

The steps in the embodiments in the specification are only expressed for convenience of description, and the implementation manner of the present application is not limited by the order of implementation of the steps.

"coupled" or "connected" in this specification includes both direct and indirect connections, such as through some active device, passive device, or electrically conductive medium; but also may include connections through other active or passive devices, such as through switches, follower circuits, etc., that are known to those skilled in the art for achieving the same or similar functional objectives.

Fig. 6 is a schematic diagram illustrating a driving circuit of a semiconductor switch device according to an embodiment of the present invention, and fig. 7 is a schematic diagram illustrating a driving circuit of a semiconductor switch device according to an embodiment of the present invention; referring to fig. 6 and 7, the driving circuit can be coupled to a semiconductor switch Q1 (for example, a current-driven semiconductor switch BJT), and the driving circuit includes: a base drive current control circuit 1 and a base emitter control circuit 2.

The base driving current control circuit 1 is coupled to the base of the semiconductor switch Q1 for controlling the semiconductor switch Q1 to be turned on when the driving circuit is in a first state; the base driving current control circuit 1 is further configured to control the current at the base of the semiconductor switching tube Q1 to be smaller than a set threshold (e.g. 0, or other set thresholds) when the driving circuit is in the second state.

The base-emitter control circuit 2 is used for controlling the short circuit between the base and the emitter of the semiconductor switch tube Q1 when the set condition is reached.

In an embodiment of the present invention, the setting condition includes at least one of the following conditions: (1) the current flowing through the semiconductor switch tube reaches a first threshold (for example, the first threshold may correspond to the current flowing through the semiconductor switch tube when Vcs is Vcs _ ref 1), and exceeds a set time; (2) the current flowing through the semiconductor switch tube reaches a second threshold value (for example, the second threshold value may correspond to the current flowing through the semiconductor switch tube when Vcs is Vcs _ ref 2); where Vcs _ ref2 is greater than Vcs _ ref 1; (3) the semiconductor switch tube has entered the amplification region (which can be determined by the amplification region determination module 7). The characteristic of the input to the amplification region is that the on-resistance of the semiconductor switching tube increases significantly.

In one embodiment, the driving circuit further includes an amplification region determination module (e.g., a BJT amplification region determination module) 7; the amplification region determination module 7 is used for determining whether the semiconductor switch Q1 has entered the amplification region; the output terminal of the amplification region determination module 7 is coupled to the input terminal of the second switching tube driving circuit 20. The amplification region determination module 7 determines whether the BJT has entered the amplification region according to whether the reference voltage VFB exceeds a certain threshold. And the reference voltage VFB voltage signal can be obtained by dividing the auxiliary winding voltage through a resistor.

Fig. 9 shows a basic principle of the amplification region determining module, when the BJT is fully turned on, the reference voltage VFB has a certain negative voltage, and when the BJT enters the amplification region, the reference voltage VFB gradually increases to a positive value, so that it can be determined that the BJT has entered the amplification region, and the BJT must be turned off as soon as possible.

Referring to fig. 7, in an embodiment of the present invention, the base-emitter control circuit 2 may include: a second switch tube S2 and a second switch tube driving circuit (also called as S2 driver) 20. A first terminal of the second switch transistor S2 is coupled to the base of the semiconductor switch transistor Q1, and a second terminal of the second switch transistor S2 is coupled to the emitter of the semiconductor switch transistor Q1 (BJT); the second switch driving circuit 20 is coupled to the second switch Q1 for controlling the second switch Q1 to conduct when a set condition is reached.

Referring to fig. 7, in an embodiment of the invention, the base driving current control circuit 1 may include: a first switch transistor S1, a first switch transistor driving circuit (also referred to as S1 driver) 10, and a semiconductor switch transistor driving circuit (also referred to as BJT driver) 11. The first switch tube S1 is coupled to the base of the semiconductor switch tube Q1; the first switch driving circuit 10 is coupled to the first switch S1 for controlling the switching state of the first switch S1. As shown in fig. 8, when the PWM signal is at a first level (e.g., high level), the first switching tube driving circuit controls the first switching tube to conduct. When the current flowing through the triode BJT reaches a first threshold value Vcs _ ref1, the first switch tube driving circuit controls the first switch tube to be turned off. The semiconductor switch driving circuit 11 is coupled to the base of the semiconductor switch Q1 through the first switch S1, and is used for driving the semiconductor switch Q1 to operate when the first switch S1 is turned on.

As shown in fig. 7, in an embodiment of the present invention, the driving circuit further includes a PWM modulating circuit 3, the PWM modulating circuit 3 is configured to modulate a PWM signal; the output end of the PWM modulation circuit 3 is coupled to the input end of the first switching tube driving circuit 10.

In one embodiment, the base driving current control circuit 1 is coupled to the PWM modulation circuit 3. The first state is a state in which the PWM modulation circuit outputs a set PWM signal (the PWM signal is used to provide a driving current for the base of the semiconductor switch Q1, so as to control the semiconductor switch Q1 to be turned on); the second state is a state where a current flowing through the semiconductor switch tube reaches a first threshold value.

As shown in fig. 7, in an embodiment of the present invention, the driving circuit further includes: an amplitude modulation circuit (for example, a Vcs amplitude modulation module) 4, a first comparator 5, a second comparator 6, and a timing unit 8. The amplitude modulation circuit 4 is configured to generate a first voltage signal corresponding to a first threshold and a second voltage signal corresponding to a second threshold. The non-inverting input terminal of the first comparator 5 is coupled to the voltage of the emitter of the BJT, and the inverting input terminal of the first comparator 5 is coupled to the first voltage signal corresponding to the first threshold; the output terminal of the first comparator 5 is coupled to the first switching tube driving circuit 10. The non-inverting input terminal of the second comparator 6 is coupled to the voltage of the emitter of the BJT, and the inverting input terminal of the second comparator 6 is coupled to the second voltage signal corresponding to the second threshold; the output terminal of the second comparator 6 is coupled to the second switch driving circuit 20. The timing unit 8 is coupled to the first comparator 5 and the second switch driving circuit 20, respectively, for timing a set output (an output when the current flowing through the BJT reaches a first threshold) of the first comparator 5.

The condition that the current flowing through the BJT exceeds a certain time after reaching the first threshold value is met, and the timing unit 8 can be triggered to start timing when the current flowing through the BJT reaches the first threshold value; and triggering the second switch tube S2 between the base and the emitter of the BJT to conduct when the timing reaches a certain time threshold.

Fig. 8 reveals the meaning of the condition that the second switch transistor S2 is turned on more than a certain time after the BJT current reaches the first threshold value Vcs _ ref 1. After the BJT current reaches the first threshold value Vcs _ ref1, if the BJT current cannot reach the second threshold value Vcs _ ref2 within a certain time, indicating that the BJT is already in the amplifying state, the BJT must be forced to turn off as soon as possible.

The invention also discloses a driving chip of the semiconductor switch tube, which comprises the driving circuit of the semiconductor switch tube.

The invention further discloses a driving control method of the semiconductor switch tube, which comprises the following steps:

controlling the semiconductor switching tube to be conducted when a driving circuit of the semiconductor switching tube is in a first state; when a driving circuit of the semiconductor switch tube is in a second state, controlling the driving current of the base electrode of the semiconductor switch tube to be 0;

and when the set condition is reached, controlling short circuit between the base electrode and the emitter electrode of the semiconductor switch tube. In an embodiment of the present invention, the setting condition includes at least one of the following conditions: (1) the current flowing through the semiconductor switch tube reaches a first threshold value and exceeds a set time; (2) the current flowing through the semiconductor switch tube reaches a second threshold value; wherein the second threshold is greater than the first threshold; (3) the semiconductor switch tube has entered the amplification region.

In an embodiment of the present invention, the driving control method further includes: and when the set condition is reached, controlling the conduction of a second switching tube which is coupled with the base electrode and the emitter electrode of the semiconductor switching tube.

In one embodiment, the driving circuit includes a PWM modulation circuit; the first state is a state in which the PWM modulation circuit outputs a set PWM signal (the PWM signal is used to provide a driving current for the base of the semiconductor switch Q1, so as to control the semiconductor switch Q1 to be turned on); the second state is a state where a current flowing through the semiconductor switch tube reaches a first threshold value.

In summary, the driving circuit, the driving chip and the driving control method for the semiconductor switch tube provided by the invention can forcibly turn off the semiconductor switch tube when the set condition is met, improve the reliability of the driving control, and prevent the semiconductor switch tube from being damaged due to long-time operation in the amplification region.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The description and applications of the invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. Effects or advantages referred to in the embodiments may not be reflected in the embodiments due to interference of various factors, and the description of the effects or advantages is not intended to limit the embodiments. Variations and modifications of the embodiments disclosed herein are possible, and alternative and equivalent various components of the embodiments will be apparent to those skilled in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other components, materials, and parts, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.