CN-115118260-B - Improved switch with hysteresis

Abstract

The present disclosure relates to an improved switch with hysteresis, and more particularly to a switching circuit comprising an input terminal connected to a base of a first transistor via a first resistor, the first transistor being an NPN bipolar gate transistor, the switching circuit further comprising a second resistor connected between the base of the first transistor and ground and comprising an output line or terminal connected to a collector of the first transistor, and wherein an emitter of the first transistor is grounded, the circuit further comprising a second transistor which is a PNP bipolar gate transistor, wherein a collector of the second transistor is connected to the base of the first transistor via a third resistor and an emitter of the second transistor is connected to the input terminal, and wherein an emitter of the second transistor is further connected to the base of the second transistor via a fourth resistor and the base of the second transistor is further connected to the output terminal via a fifth resistor and a diode.

Inventors

• HE JIANMIN

Assignees

• 德尔福知识产权有限公司

Dates

Publication Date

20260512

Application Date

20220218

Priority Date

20210323

Claims (2)

1. 1. A switching circuit comprising an input terminal (1) connected to a base of a first transistor (Q1) via a first resistor (R3), the first transistor being a NPN bipolar gate transistor (Q1), the switching circuit further comprising a second resistor (R5) connected between the base of the first transistor (Q1) and ground, and comprising an output line or an output terminal (3) connected to a collector of the first transistor (Q1), and wherein the switching circuit further comprises a second transistor (Q2) which is a PNP bipolar gate transistor, wherein the collector of the second transistor (Q2) is connected to the base of the first transistor (Q1) via a third resistor (R8), the emitter of the second transistor (Q2) is connected to the input terminal (1), and wherein the emitter of the second transistor (Q2) is further connected to the output terminal (Q2) via the second resistor (R11) and the base of the fifth transistor (Q2) is connected to the output terminal (Q1) via the second resistor (R2) and the fifth transistor (Q2) is turned on when the second transistor (Q2) and the base (Q1) is connected, thereby enhancing the on-current to the base of the first transistor (Q1) via the collector of the second transistor (Q2) and the third resistor (R8).
2. 2. Switching circuit according to claim 1, wherein the diode (D1) is electrically connected between the fifth resistor (R10) and an output line/output terminal (3).

Description

Improved switch with hysteresis Technical Field The present disclosure relates to solid state switches and switching circuits and simple switch/switching circuits including Bipolar Junction Transistors (BJTs). Background The single BJT switch has no hysteresis. An unstable input voltage to the base at or near a threshold level (e.g., with noise) may cause the switch to repeatedly turn on and off. More complex designs that can be used for multiple BJTs (three or more BJTs) or comparator solutions are used to overcome this problem and create hysteresis. It is an object of the present invention to overcome this problem and to create a simpler and cheaper switching circuit comprising hysteresis. By adding another BJT (PNP) switch to boost the on-current to the NPN base, the problem is solved that a single BJT NPN open collector switch without hysteresis is susceptible to an unstable input voltage at the threshold level of the BJT base. Disclosure of Invention In one aspect, a switching circuit is provided comprising an input terminal connected to a base of a first transistor (Q1) via a first resistor (R3), the first transistor being an NPN bipolar gate transistor (Q1), the switching circuit further comprising a second resistor (R5) connected between the base of the first transistor (Q1) and ground and comprising an output line or terminal connected to a collector of the first transistor (Q1), and wherein an emitter of the first transistor (Q1) is grounded, the circuit further comprising a second transistor (Q2) being a PNP bipolar gate transistor, wherein a collector of the second transistor (Q2) is connected to the base of the first transistor (Q1) via a third resistor (R8). An emitter of the second transistor (Q2) is connected to the input terminal, and wherein the emitter of the second transistor (Q2) is further connected to a base of the second transistor (Q2) via a fourth resistor (R11), and the base of the second transistor (Q2) is further connected to the output terminal (3) via a fifth resistor (R10) and a diode (D1). The diode (D1) may be electrically connected between the fifth resistor (R10) and an output line/terminal (3). Drawings The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a known simple switching device; Fig. 2 shows a known switching device with a comparator; FIG. 3 shows an example of the invention, and Fig. 4 illustrates the operation of the circuit of fig. 3. Detailed Description Fig. 1 shows a known simple switching device having an input line 1 or terminal (e.g. from a switching source 2) connected via a resistor R3 to the base of a BJT (NPN) labeled Q1. A resistor R5 is included between the base and ground. An output line/terminal 3 is shown which is effectively connected to the collector of Q1. Thus, this describes a conventional open collector NPN BJT switch with BJT Q1. R3 is used to limit the current to the base and R5 is used to ensure that Q1 is turned off when there is no voltage at the input. As mentioned above, the circuit has no hysteresis, and therefore there is no Schmitt (Schmitt) trigger or hysteresis in the typical open collector NPN switch below. Noise on the input may trigger the switch to turn on and off, which means that it may be unstable. A known solution is to use an add comparator to add hysteresis. Fig. 2 shows such a device. Furthermore, the comparator 4 requires another power supply, since the comparator requires a regulated voltage. These additional requirements/components mean that the circuit is more complex and expensive. Invention of the invention In one example, the circuit provides a switch with an efficient and reliable hysteresis. Fig. 3 shows an example. As in fig. 1, there is an input line or terminal 1 (e.g., electrically connected or connectable to a switching source 2) that is connected to the base of a BJT (NPN) (labeled Q1) via a resistor R3. The circuit includes a resistor R5 connected between the base of Q1 and ground. An output line or terminal 3 is shown which is effectively connected to the collector of Q1 and can be considered an open collector output. The emitter of Q1 is directly connected to ground (earth). In addition, the circuit includes another BJT, labeled Q2, which is a PNP transistor. The collector of Q2 is connected to the base of Q1 via resistor R8 and the emitter of Q2 is connected to input line/terminal 1. The emitter of Q2 is also connected to the base of Q2 via resistor R11, the base of Q2 is also connected to the output terminal via resistor R10 and diode D1, diode D1 being located between resistor R10 and output line/terminal 3. Alternatively, the positions of the resistor R10 and the diode may be interchanged. The resistor R10 may be located between (i.e., electrically connected to) the diode and the terminal 3. Thus, the circuit effectively provides a schmitt trigger switch by adding the second BJT Q2 as a PNP BJT, as well as resistors R8, R11,