CN112630512A

CN112630512A - FF bus under-voltage indicating circuit

Info

Publication number: CN112630512A
Application number: CN202011430510.4A
Authority: CN
Inventors: 陈宇; 林强; 王文辉; 段汝良; 江竹轩
Original assignee: Zhejiang Supcon Technology Co Ltd
Current assignee: Zhejiang Supcon Technology Co Ltd
Priority date: 2020-12-07
Filing date: 2020-12-07
Publication date: 2021-04-09
Anticipated expiration: 2040-12-07
Also published as: CN112630512B

Abstract

The invention provides a novel FF (foundation field) bus under-voltage indicating circuit which comprises a voltage detecting unit, an indicating lamp unit and a constant current unit, wherein the indicating lamp unit at least comprises an LED and a bypass voltage-regulator tube D1 connected with the LED in parallel, the constant current unit is used for being coupled with a bus power supply end to obtain electricity and providing a constant current power supply for the indicating lamp unit, and the voltage detecting unit is coupled with the bus power supply end, coupled between an LED cathode and a power ground and used for controlling the connection and disconnection of a circuit between the LED cathode and the power ground based on detected bus voltage. The FF bus under-voltage indicating circuit keeps the constant current of the circuit when the lamp is turned off under voltage, does not interfere the bus, and has lower cost compared with the circuit in the prior art.

Description

FF bus under-voltage indicating circuit

Technical Field

The invention relates to the technical field of FF bus communication, in particular to an FF bus under-voltage indicating circuit.

Background

The FF bus network is used for a plurality of instruments to access the bus when arriving near the instrument, a branch protector is arranged in the junction box, the under-voltage of the bus needs to be indicated on the branch protector, and the maintenance and the investigation are convenient. The indicator lights are on in the FF bus 9-32V operating voltage range and are otherwise off (the actual lowest nominal voltage of the different devices may be higher). Overvoltage extinguishing is generally realized by directly turning off the total power supply through an overvoltage turn-off circuit, but undervoltage extinguishing needs additional circuits to realize.

As shown in fig. 1, the prior art low-voltage protection threshold point is set by matching R1 and R2 divider resistors with the voltage reference of the high-side of U1, when the voltage is higher than the threshold value, U1 is turned on, and then the base of Q1 is pulled high and turned on, so that the right-side constant-current lighting circuit working LED lamp is turned on. In the constant current lighting circuit, since the Q1 is turned on, the base of the Q2 is pulled down and conducted through the R5, the U2 is turned on when the voltage drop generated by the current on the R6 reaches the threshold value of the reference U2, so that the base of the Q2 is pulled up to enter a linear region, and finally, the current flowing through the R6 is constant, namely, the current of the LED is also basically constant. When the voltage is lower than the threshold, U1 is not conducted, Q1 is closed, Vbe of Q2 is 0V and is closed, therefore, the lamp is turned off. However, with this circuit, when the voltage fluctuates around the threshold, the constant current circuit is in an unstable region, and the current is large or small, which causes serious bus signal interference and makes communication impossible.

Disclosure of Invention

The invention solves the technical problem of providing a novel FF bus under-voltage indicating circuit, which keeps the constant current of the circuit continuously when the voltage is under-voltage and the lamp is turned off, does not generate interference on a bus, and has lower cost compared with the circuit in the prior art.

In order to solve the problems, the invention adopts the following technical scheme:

the FF bus under-voltage indicating circuit comprises a voltage detection unit, an indicator lamp unit and a constant current unit, wherein the indicator lamp unit at least comprises an LED and a bypass voltage-stabilizing tube D1 connected with the LED in parallel, the constant current unit is used for being coupled with a bus power supply end to obtain electricity and providing a constant current power supply for the indicator lamp unit, and the voltage detection unit is coupled with the bus power supply end, coupled between an LED cathode and a power ground and used for controlling the on-off of a circuit between the LED cathode and the power ground based on detected bus voltage.

In an exemplary embodiment, the voltage detection unit includes at least voltage dividing resistors R7 and R8 coupled in series between a power terminal of the bus and a power ground, and a reference chip U1 coupled between a cathode of the LED and the power ground, wherein a voltage reference terminal of the reference chip U1 is coupled between the resistors R7 and R8.

In another illustrative embodiment, the voltage detection unit comprises at least voltage dividing resistors R251 and R256 coupled in series between a power terminal of the bus and a power ground, and a comparator U7; the INA + pin of the comparator U7 is coupled between the resistors R251 and R256, the OUTB pin is coupled to the cathode of the LED, the VDD pin is coupled to the bus power terminal through the resistor R245, and is coupled to the power ground through the parallel capacitor C100 and the zener diode D29, and the GND pin is coupled to the power ground.

In an illustrative embodiment, the constant current unit is a constant current diode.

In another illustrated embodiment, the constant current unit includes PNP transistors Q1 and Q2, resistors R9 and R10; the emitter of the transistor Q2 and one end of the resistor R9 are coupled to a bus power supply terminal, the other end of the resistor R9 is coupled to the base of the transistor Q2 and the emitter of the transistor Q1, the collector of the transistor Q2 is coupled to the base of the transistor Q1 and to the ground via the resistor R10, and the collector of the transistor Q1 is coupled to the anode of the LED.

Compared with the prior art, the FF bus under-voltage indicating circuit has the following advantages that:

1) through setting up bypass stabilivolt D1, guarantee when instructing LED bright and go out (break-make) because voltage variation, can not cause the electric current in the instruction return circuit to change for the state change of indicating circuit can not produce the interference to bus communication, thereby bus communication's minimum voltage can keep unanimous with the minimum operating voltage lower limit of instrument, has widened bus operating voltage limit, makes the communication voltage range maximize of bus.

2) The reference chip U1 used is a low side reference, which is more versatile and less expensive than a high side reference. Meanwhile, the constant current circuit adopts a triode to limit current, so that the cost is further reduced.

Drawings

Fig. 1 is a schematic circuit diagram of a conventional FF bus brown-out indication circuit.

FIG. 2 is a schematic circuit diagram of a FF under-voltage bus indication circuit according to a first embodiment of the invention.

FIG. 3 is a schematic circuit diagram of a FF under-voltage bus indication circuit according to a second embodiment of the invention.

FIG. 4 is a schematic circuit diagram of a FF under-voltage bus indication circuit according to a third embodiment of the invention.

Detailed Description

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.

Fig. 1 is a schematic circuit diagram of a conventional FF brown-out bus indication circuit. The low voltage protection threshold point is set by matching R1 and R2 divider resistors with a high end side voltage reference U1, when the voltage is higher than the threshold value, U1 is conducted, then the base of Q1 is pulled high and conducted, and the LED lamp operated by the right constant current lighting circuit is turned on. In the constant current lighting circuit, since the Q1 is turned on, the base of the Q2 is pulled down and conducted through the R5, the U2 is turned on when the voltage drop generated by the current on the R6 reaches the threshold value of the reference U2, so that the base of the Q2 is pulled up to enter a linear region, and finally, the current flowing through the R6 is constant, namely, the current of the LED is also basically constant. When the voltage is lower than the threshold, U1 is not conducted, Q1 is closed, Vbe of Q2 is 0V and is closed, therefore, the lamp is turned off. However, with the circuit, near the undervoltage lamp-out threshold, the constant current state cannot be maintained due to the change of the working point of the constant current circuit, which causes sudden change of the current of the lamp-out circuit, resulting in sudden change of the bus impedance and influencing communication. That is, the existing circuit can only work normally when the threshold value is ensured to be over. The amplitude of a bus signal is +/-0.75-1V during single-terminal communication, the lowest voltage is pulled to 8V during 9V power supply, and the bus signal is interfered by a lighting circuit. The lowest working voltage of the instrument is usually lower than 9V required by the bus, and the bus fails in advance due to lighting when the instrument can work, so that the application of the bus is not facilitated.

In order to solve the above problems, the present invention provides a new FF bus under-voltage indication circuit, which includes a voltage detection unit, an indicator light unit and a constant current unit. The indicating lamp unit at least comprises an LED and a bypass voltage-regulator tube D1 connected with the LED in parallel, and the bypass voltage-regulator tube D1 is used for providing a follow current channel for current generated by the second circuit when the LED is extinguished; the voltage detection unit is coupled with the bus power end, coupled between the LED cathode and the power ground and used for controlling the on-off of a circuit between the LED cathode and the power ground based on the detected bus voltage.

The scheme of the invention ensures that the lighting current can not change due to the lamp switch through the bypass voltage regulator tube D1, the lighting circuit can not interfere the bus communication, the lowest voltage of the bus communication can be consistent with the lowest working voltage lower limit of the instrument, and the communication voltage range of the bus is maximized. The scheme of the invention is further illustrated by the following specific examples.

Example 1

As shown in fig. 2, in the illustrated embodiment, the indicator light unit includes at least a light emitting indicator LED and a bypass regulator D1 connected in parallel with the LED. The voltage detection unit at least comprises voltage dividing resistors R7 and R8 which are coupled between a bus power supply end and a power ground in series, and a reference chip U1 which is coupled between an LED cathode and the power ground, wherein a voltage reference end of the reference chip U1 is coupled between the resistors R7 and R8. The constant current unit adopts a constant current tube D33, which is coupled to a bus power supply terminal VCC for taking power and providing a constant current power supply for the LED.

The working principle of the circuit is as follows: the voltage dividing resistors R7 and R8 are used for setting the threshold voltage for lamp extinguishing, when the threshold voltage is exceeded, the U1 works, the LED has low impedance to the ground, at the moment, because the voltage drop of the LED and the U1 is far less than the working voltage of the voltage stabilizing tube D1, the current flows through a series circuit consisting of the LED and the U1, no current flows through the D1, and the LED is lightened. In this process, the current in the lighting circuit does not change due to the lamp switch, so that the entire lighting circuit does not interfere with the bus communication.

In one embodiment, U1 is model TI of LMV 431. Generally, the accuracy of the threshold point is affected by the performance of the device, such as temperature drift, and the application in this embodiment has low requirements on the threshold range, so that other domestic TL431 may be selected, and are more general and cheaper than the high-side standard.

Example 2

As shown in fig. 3, in the present illustrative embodiment, the circuit configuration of the indicator light unit and the voltage detection unit 201 is similar to that in embodiment 1, and the constant current unit 202 is replaced with a high-side constant current circuit composed of transistors including PNP transistors Q1 and Q2, and resistors R9 and R10; the emitter of the transistor Q2 and one end of the resistor R9 are coupled to a bus power supply terminal, the other end of the resistor R9 is coupled to the base of the transistor Q2 and the emitter of the transistor Q1, the collector of the transistor Q2 is coupled to the base of the transistor Q1 and to the ground via the resistor R10, and the collector of the transistor Q1 is coupled to the anode of the LED.

The working principle of the constant current circuit is as follows: after power-up, the base of the Q1 is pulled down by the R10, so that the Q1 is conducted, the base of the Q2 is pulled down by the Q1 at the moment, the voltage of the R10 rises, the Q1 enters an amplification region from a switching state, and the voltage of the base of the Q2 also rises along with the voltage of the Q2 enters a discharge region, so that the voltage of the R10 is lowered, and negative feedback is formed. In a steady state, when the current flowing through Q1 is too large, the voltage drop of R9 is larger than Vbe of Q2, the conduction capability of Q2 is increased, the voltage of R10 is increased, the Vbe voltage of Q1 is reduced, the amplification capability is weakened, and the current flowing through R9 is reduced; when the current flowing through R9 is too small, the reverse is true, and the current finally flowing through Q1 is just Veb/R3 of Q2, so that constant current is formed.

By adopting the circuit, the constant current can be more accurate and stable, so that the stability of the whole circuit is enhanced. Meanwhile, the constant current circuit adopts a triode to limit current, so that the cost is further reduced.

Example 3

As shown in fig. 4, in the present illustrative embodiment, the circuit configuration of the indicator light unit and the constant current unit is similar to that in embodiment 2, and the voltage detection unit employs an integrated chip circuit including voltage dividing resistors R251 and R256 coupled in series between the bus power supply terminal and the power ground, and a comparator U7; the INA + pin of the comparator U7 is coupled between the resistors R251 and R256 and is grounded via the capacitor C99; the pin OUTB is coupled with the cathode of the LED, the pin VDD is coupled with a bus power supply terminal VCC through a resistor R245, and is coupled with a power ground through a capacitor C100 and a voltage stabilizing diode D29 which are connected in parallel, and the pin GND is coupled with the power ground. In this embodiment, the comparator U7 is model number TPS3700 DDCR.

By adopting the circuit, the voltage is more accurately adopted, and the circuit is suitable for occasions with higher requirements on voltage adoption.

By adopting the scheme in the embodiment, the lighting constant-current working voltage can be reduced to be lower than 7V, the lighting-out threshold value point can be designed at will, the impedance characteristic of the bus does not change when the lighting-out prompt is given, and the lowest working voltage depends on the bus instrument and the interface card.

The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims

1. The FF bus under-voltage indicating circuit is characterized by comprising a voltage detection unit, an indicator lamp unit and a constant current unit, wherein the indicator lamp unit at least comprises an LED and a bypass voltage-regulator tube D1 connected with the LED in parallel, the constant current unit is used for being coupled with a bus power supply end to obtain electricity and providing a constant current power supply for the indicator lamp unit, and the voltage detection unit is coupled with the bus power supply end, coupled between an LED cathode and a power ground and used for controlling the connection and disconnection of a circuit between the LED cathode and the power ground based on detected bus voltage.

2. The FF bus brown-out indication circuit of claim 1, wherein the voltage detection unit comprises at least a voltage dividing resistor R7 and R8 coupled in series between the bus power terminal and the power ground, and a reference chip U1 coupled between the LED cathode and the power ground, wherein a voltage reference terminal of the reference chip U1 is coupled between the resistors R7 and R8.

3. The FF bus brown-out indication circuit of claim 1, wherein the voltage detection unit comprises at least voltage dividing resistors R251 and R256 coupled in series between a bus power terminal and a power ground, and a comparator U7; the INA + pin of the comparator U7 is coupled between the resistors R251 and R256, the OUTB pin is coupled to the cathode of the LED, the VDD pin is coupled to the bus power terminal through the resistor R245, and is coupled to the power ground through the parallel capacitor C100 and the zener diode D29, and the GND pin is coupled to the power ground.

4. The FF bus brown-out indication circuit of any of claims 1-3, wherein the constant current unit is a constant current diode.

5. The FF bus brown-out indication circuit of any of claims 1-3, wherein the constant current unit comprises PNP transistors Q1 and Q2, resistors R9 and R10; the emitter of the transistor Q2 and one end of the resistor R9 are coupled to a bus power supply terminal, the other end of the resistor R9 is coupled to the base of the transistor Q2 and the emitter of the transistor Q1, the collector of the transistor Q2 is coupled to the base of the transistor Q1 and to the ground via the resistor R10, and the collector of the transistor Q1 is coupled to the anode of the LED.