RU2514200C2 - Circuit and method of monitoring load current and fire alarm control device - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to a circuit and a method of monitoring load current and a fire alarm control device, wherein the circuit comprises a power source, a load current sensing resistor for monitoring the load current and a main switch for controlling connection and disconnection of the power source and further comprises a bias circuit on a metal-oxide-semiconductor field-effect transistor for controlling the main switch, an amplifier circuit for converting the value of the load current passing through the load current sensing resistor to a voltage value, an operational circuit for disconnecting the power supply channel and transmitting a signal indicating the state of the load current when the voltage value exceeds a threshold, and a clamping circuit for holding the overload current signal. Once the load current exceeds a predefined threshold, in other words, when there is overload current, the power supply channel of the power source is disconnected, and the state of overload current is blocked for 50 mcs to avoid compromise of normal power supply of internal circuits of the controller.

EFFECT: enabling use to monitor user device load.

14 cl, 9 dwg

Description

Technical field

The invention relates to the field of electrical engineering, more particularly to a circuit and method for monitoring the load current and a fire alarm control device.

State of the art

The fire alarm control device typically has internal circuits for an AC / DC power supply (AC / DC). User devices for interacting with the controller, on the other hand, receive power from a separate power source, as shown in FIG. one.

It is desirable for users that part of the current from the controller’s power source can be used for their devices in order to avoid the need to install an additional energy source and save costs (see Fig. 2). However, due to the unpredictable load of user devices, if there is no overload current control in place, then the user device can cause an overload of the energy source, adversely affecting the normal power supply of the circuits in the controller.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a load current monitoring circuit that can be used to monitor the load current state of user devices.

To achieve this, the present invention discloses a load current monitoring circuit for detecting said load current, comprising an energy source, a load current sensing resistor for sensing a load current, and a main switch for controlling connection and disconnection of the energy source, and further comprising

a bias circuit on a field effect transistor with a MOS structure to control the actions of the main switch,

an amplifier circuit for converting a load current value passing through a load current sensing resistor into a voltage value,

an operating circuit for shutting off the power path of the circuit and sending a signal indicating the state of the overload current when the voltage value exceeds a threshold,

a latching circuit for holding an overload current signal.

Preferably, the circuit further comprises a reset circuit for resetting the circuit to its initial state from the overload current holding state.

Preferably, the circuit further comprises an indication circuit for indicating whether the circuit is in an overload current state.

Preferably, the bias circuit on the MOS field-effect transistor comprises a coupling capacitor between the power source and the main switch, and said bias circuit on the MOS field-effect transistor controls the actions of the main switch by controlling the gate voltage of the main switch.

Preferably, the main switch is a P-channel MOSFET or an N-channel MOSFET.

Advantageously, said amplifier circuit comprises an operational amplifier with a span equal to a supply voltage for converting a load current value into a voltage value in a predetermined ratio.

Advantageously, said latching circuit comprises an operational amplifier with a span equal to the supply voltage, for comparing the voltage value with a threshold and holding the state of the overload current.

Advantageously, said operating circuit comprises two MOS field-effect transistors that have the same channel type as the main switch and are used to turn off the main switch.

Advantageously, said operating circuit further comprises a light emitting diode (LED) indicating an overload current state that is lit when a field effect transistor with a MOS structure is activated in the operating circuit in case of an overload current condition.

Advantageously, said reset circuit comprises a switch 1 and a switch 2, the switch 1 being a manually operated switching button, or a switch on a field effect transistor with a MOS structure controlled by a logic level, or a solid state relay, or an optocoupler controlled by a controller, so if switch 2 electrically connected to ground, switch 1 is closed to reset the circuit; if the switch 2 is connected before this to the power source, then the switch 1 is closed to disconnect the power path.

Advantageously, said display circuit comprises a microcontroller for overload current monitoring to indicate whether the circuit is in an overload current state by detecting changes in a logic level.

The present invention also provides a fire alarm control device comprising any of the overload current monitoring circuits described above.

The present invention also provides a load current monitoring method for detecting an overload current event in a circuit, the method comprising converting the load current passing through the sensing resistor into a voltage value in a predetermined ratio, comparing the voltage value with a threshold, determining the existence of an overload current state when the voltage value reaches the threshold, shutting off the power path and holding the state of the overload current.

Advantageously, if the existence of an overload current condition is determined, this state is indicated by an LED or an overload current control device controlled by a microcontroller.

When using the load current monitoring circuit, the fire alarm control method and device according to the embodiments of the present invention, so that if only the load current exceeds a predetermined threshold, in other words, if an overload current event occurs, the power supply path of the power source will open and the overload current condition will be blocked for 50 μs to avoid compromising the normal power supply of the internal circuits of the controller.

Description of drawings

The following drawings are intended only to provide an exemplary description and explanation of the present invention, and not to limit the scope of the present invention.

FIG. 1 is a schematic diagram showing that a user device is powered from a separate power source according to the prior art;

FIG. 2 is a schematic diagram showing that the user device is powered by a load current monitoring circuit (built into the output port of the DC power source) of the internal power supply of the fire alarm controller;

FIG. 3 is a schematic diagram showing the structure of a load current monitoring circuit provided by the present invention;

FIG. 4 is a schematic diagram showing the structure of another load current monitoring circuit provided by the present invention;

FIG. 5 is a graph of the waveform of the load voltage and current in one scenario, where the power is on, the load changes, and the reset switch works;

FIG. 6 shows parts of FIG. 5;

FIG. 7 is a graph of the waveform of the load voltage and current in another scenario, where the power is on, the load changes, and the reset switch works;

FIG. 8 is a waveform diagram of a load voltage and current in a third scenario according to the invention, where the power is turned on, the load changes, and the reset switch operates;

FIG. 9 is a flowchart of a method for monitoring a load current provided by the present invention.

Specific Embodiments

In order to obtain a clear understanding of the technical features, objectives, and results of the present invention, specific embodiments of the present invention are described below with reference to the drawings.

The present invention provides a load current monitoring circuit that opens the power supply path and blocks the state of the overload current for 50 μs after the load current exceeds a predetermined threshold, that is, when an overload current event occurs. If necessary, the current can be reset to restore power after eliminating the condition of the overload current. During the initial power-up phase and resetting the power supply, consideration should also be given to controlling the rate at which the voltage increases during power-up.

The load current control circuit contains loads, a power source, a load current sensing resistor for sensing the load current, and a main switch for controlling the connection and disconnection of the energy source, and further comprises a bias circuit 1 on a field effect transistor with a MOS structure, which is used to control the actions of the main switch by control the shutter voltage of the main switch.

Amplifier circuit 2, which is used to convert the value of the load current passing through the load current sensing resistor into a voltage value, since, in the absence of amplification, comparison with a threshold would be more sensitive to accuracy and could easily cause operational errors due to temperature changes or voltage fluctuations .

Operational circuit 3 is used to turn off the power path and send a signal indicating the state of the overload current when the voltage value exceeds a threshold, and, for the present disclosure, the circuit when such a state signal appears is referred to as a circuit in the “overload current state”.

Latch circuit 5, which is used to hold the overload current signal through positive feedback from the operational amplifier, for the purpose of the present disclosure, such an operation on the overload current signal is referred to as “latch”, and the circuit in this state is referred to as a circuit in “latch state” or "State of fixation of the overload current."

In addition, the circuit further comprises a reset circuit 4, which is used to reset the circuit to its initial state from the latching state, and further comprises an indication circuit 6, which is used to inform the microcontroller whether the circuit is in an overload current state.

Moreover, the aforementioned bias circuit 1 on a field effect transistor with a MOS structure contains a coupling capacitor C1 between the energy source V1 and the main switch M1.

Moreover, the main switch M1 is a P-channel high-power field-effect transistor with a MOS structure or N-channel high-power field-effect transistor with a MOS structure.

Moreover, said amplifier circuit 2 comprises an operational amplifier U1 with a span equal to a supply voltage for converting a load current value into a voltage value in a predetermined ratio.

Moreover, the said locking circuit 5 comprises an operational amplifier U2 with a span equal to the supply voltage, for comparing the voltages and blocking the state of the overload current.

Moreover, the mentioned operating circuit 3 contains two field-effect transistors with a MOS structure, M2 and M3, which have the same channel type as the main switch, and are used to turn off the main switch M1 and turn on LED D4, which indicates the state of the overload current.

Moreover, said reset circuit 4 comprises a switch S1 and a switch S2, the switch S1 being a manual switching button, or a switch on a field effect transistor with a MOS structure controlled by a logic level, or a solid state relay, or an optocoupler controlled by a microcontroller, so that if the switch S2 electrically connected to ground, switch S1 closed to reset the circuit; if switch S2 is previously connected to a power source, switch S1 is closed to shut off the power path.

At the same time, said indicating circuit 6 comprises a microcontroller device for monitoring the overload current for detecting the state of the overload current based on changes in the logic level.

Moreover, the aforementioned operating circuit 3 contains LED D4 for indicating the state of the overload current.

As shown in FIG. 3, an embodiment of a circuit according to the present invention comprises a power supply V1, a load current sensing resistor R1 for detecting current and connecting to a power source V1, a main switch M1 for controlling the connection and disconnection of a power source, and a non-bias resistor RS2 to avoid floating drain M1 in the absence of load, and additionally contains a bias circuit 1 on a field effect transistor with a MOS structure for controlling the gate voltage M1, amplifier circuit 2 for converting the load current to a proportional voltage value, an operating circuit 3 for shutting off the power supply path and indicating an overload current state, a reset circuit 4 for resetting from a latching state to an initial state, a latching circuit 5 for holding an overload current protection state, and an indication circuit 6 that informs microcontroller whether the circuit is in a state of overload current. In an embodiment, the main switch M1 may be a P-channel MOSFET or PMOS power transistor, or an MOS power MOS or NOS channel transistor.

The principle of operation of the circuits in accordance with the present invention is described below with reference to the full embodiment.

When the power is turned on, capacitor C1 will provide a short-circuit path between the gate and the source of the main switch M1 to keep it closed. As soon as the power supply becomes stable, capacitor C1 will start to discharge through resistor R5, and the power supply switch M1 will turn on smoothly. This feature allows the circuit to connect to a large capacity power supply. Typically, this type of power supply is characterized by a very slow slew rate of the power-on voltage, for example, 1 V / ms. Similarly, the slow power-on speed also allows the circuit to withstand a large capacitive load or cold filament without causing a large pulsed power-on current.

Using operational amplifiers U1 and U2 (operational amplifiers are characterized by a span equal to the supply voltage and a slew rate of the output voltage of 1 V / μs) and the fast action of switches M2 and M3, switch M1 can be fully closed for 50 μs from the occurrence of an overload current condition.

More specifically, the collector voltage of the triode Q1 is directly proportional to the current through M1 and less than the predetermined threshold for R8 and D2 under normal conditions. As soon as an overload current event occurs, an overhead voltage will be generated at the output of the operational amplifier U2. As a result, M3 is turned off, the gate voltage M2 is reduced by R10 to connect M2, the gate voltage M1 is increased to the same level as the source voltage, hence the disconnection of M1. Thus, based on the response speed from the input change to the output change U1 and U2, M1 can be completely locked for 50 μs from the occurrence of an overload current condition.

To supply a MOSFET field-effect transistor, the nominal pulse current for this period of 50 μs is very high, for example, 100A, which will reduce the requirement for the resistance of the RS8 resistor to limit the current and reduce the output impedance of the circuit.

If the switch S2 is electrically connected before this to ground, then as soon as the overload current state disappears, the state of holding the overload current of the circuit can be reset by closing the switch S1. The M1 switch can smoothly turn on again without restarting the power source. S1 can be a manual switching button, or a switch on a field effect transistor with a MOS structure controlled by a logic level, or a solid state relay, or an optocoupler controlled by a microcontroller. If the reset signal is controlled by a programmable timer, then after eliminating the overload current condition, the circuit may automatically attempt to reset to its original state to automatically restart the power supply without any manual operation. If S2 is previously connected to the power source, M1 will be forced to disconnect after the switch S1 is connected.

If PMOS is used as the main switch, so when the load resistance is 8 Ohms, the load capacitance is 300 μF, the voltage of the power supply increases from 0 V to 24 V with a slew rate of 1 V / ms. Another 8 ohm load resistor is added at 70 ms to increase the load current, resulting in an overload current condition. The last 8 ohm terminating resistor added is removed from the load at 80 ms, the reset switch S1 turns on at 90 ms and then turns off at 100 ms. A short circuit is added to the load at 150 ms and then removed at 160 ms. FIG. 5 is a graph of the waveform of the voltage and load current, and FIG. 6 is a detailed waveform diagram of a short circuit.

Similarly, if PMOS is used as the main switch, when a short circuit occurs in the load and S2 is electrically connected to ground, the voltage of the power supply increases from 0 V to 24 V at a rate of rise of the supply voltage of 1 V / ms. The short circuit is removed from the load, and an 8 ohm load resistor and 300 μF load capacitance are added at 100 ms, the reset switch S1 turns on at 120 ms and then turns off at 130 ms. FIG. 7 shows a graph of waveforms of voltage and load current in this scenario.

In the third scenario, an 8 ohm load resistor is added first, and then switch S2 is connected to a 24 V power supply. The voltage of the power supply increases from 0 V to 24 V with a slew rate of 1 V / ms, the reset switch S1 turns on at 80 ms and then turns off at 100 ms. FIG. 8 shows a graph of the waveform of the voltage and load current in this scenario.

It can be seen that, in the above three different scenarios, as soon as an overload current condition occurs, the power supply path of the power supply will turn off and the overload current condition will be blocked for 50 μs of the overload current condition.

In another aspect, the LED D4 shown in FIG. 3, or a change in the logic level in the display circuit gives a direct indication of the overload current to inform users whether the circuit is in a state of protection against overload current. As shown in FIG. 3, when LED D4 is lit, it gives a direct indication that the circuit is in a state of protection against overload current.

The present invention further provides another embodiment, as shown in FIG. 4, where the main switch M1 is an N-channel high-power MOSFET or NMOS transistor. The detailed principle of operation is essentially the same as in the circuit shown in FIG. 3, so that it does not repeat here.

The present invention further provides a fire alarm control device comprising any of the load current monitoring circuits described above. This device opens the path of the power source and blocks the state of the overload current for 50 μs from the time when the overload current exceeds a predetermined threshold, that is, when the state of the overload current occurs. If necessary, the circuit can also be reset to resume turning on the power source after the overload current condition has been removed. At the stage of initial power-up and reset of the power supply, attention should also be paid to controlling the increased slew rate of the power-on voltage.

In another aspect, the present invention also provides a method for detecting a load current, as shown in FIG. 9, which is used to detect overload current of user devices that are powered by the fire alarm control device. As soon as the power source is turned on (S100a), the main switch is turned on (S100b), the load current passing through the sensing resistor is converted to a voltage value according to a predetermined ratio (S101), the voltage value is compared with a threshold (S102), the normal state of the power source (S103) ) is supported if the voltage value is less than the threshold value, and a decision is made on the state of the overload current (S104) if the voltage value reaches the threshold.

In this case, the power supply path opens, and the state of the overload current is blocked if an overload current event occurs. If the state of the overload current is determined, then this state can be indicated (S105) by means of an LED or an overload current control device controlled by the microcontroller. The latching state of the circuit can be reset (S106) using the reset switch, then the main switch is turned on (S100b), and the load current is continuously monitored.

The above description shows only exemplary embodiments of the present invention and is not intended to limit the scope of protection of the invention. Any modifications, equivalent substitutions and improvements made by a person skilled in the art without deviating from the essence and principle of the invention should be included in the scope of the present invention.

Claims (14)

1. A load current monitoring circuit for monitoring said load current, comprising a power source, a load current sensing resistor for monitoring a load current, and a main switch for controlling connection and disconnection of the power source, and further comprising
a bias circuit of a field-effect transistor with a MOS structure for controlling the actions of the main switch, comprising a coupling capacitor between the energy source and the main switch, providing smooth switching on of the main switch,
an amplifier circuit for converting a load current value passing through a load current sensing resistor into a voltage value,
an operating circuit for shutting off the power path and sending a signal indicating the state of the overload current when the voltage value exceeds a threshold,
a latching circuit for holding an overload current signal. 2. The circuit according to claim 1, further comprising a reset circuit for resetting said circuit to its initial state from the state of fixation of the overload current. 3. The circuit of claim 1, further comprising an indication circuit for indicating whether the circuit is in an overload current state. 4. The circuit according to claim 1, characterized in that said bias circuit of a field effect transistor with a MOS structure controls the actions of the main switch by controlling the gate voltage of the main switch. 5. The circuit according to claim 1, characterized in that said main switch is a P-channel high-power field-effect transistor with a MOS structure or N-channel high-power field-effect transistor with a MOS structure. 6. The circuit according to claim 1, characterized in that said amplifier circuit comprises an operational amplifier with a span equal to the supply voltage for converting the load current value into a voltage value in a predetermined ratio. 7. The circuit according to claim 1, characterized in that the said locking circuit comprises an operational amplifier with a span equal to the supply voltage, for comparing the voltage value with a threshold and holding the state of the overload current. 8. The circuit according to claim 5, characterized in that said operating circuit contains two field effect transistors with a MOS structure, which have the same channel type as the main switch, and are used to turn off the main switch. 9. The circuit of claim 8, wherein said operating circuit further comprises an LED indicating an overload current state that is lit when a field effect transistor with a MOS structure is activated in the operating circuit when an overload current condition occurs. 10. The circuit according to claim 2, characterized in that the reset circuit includes a switch 1 and a switch 2, and the switch 1 is a manually operated switching button, or a switch on a field effect transistor with a MOS structure controlled by a logic level, or a solid state relay, or an optocoupler controlled by a microcontroller, so that if switch 2 is electrically connected to ground, switch 1 is closed to reset the circuit; if switch 2 is previously connected to the power source, then switch 1 is closed to disconnect the power path. 11. The circuit according to claim 3, characterized in that said indication circuit comprises a microcontroller for overload current monitoring, which is used to indicate whether the circuit is in an overload current state by detecting changes in the logic level. 12. A fire alarm control device comprising any of the overload current control circuits according to any one of claims 1 to 11. 13. The method of monitoring the load current to control the load current in the circuit according to any one of claims 1 to 11, the method comprising converting the load current passing through the sensing resistor into a voltage value in a predetermined ratio, comparing the voltage value with a threshold, determining the existence of a current state overload, when the said voltage value reaches the threshold, shutting off the power path and holding the state of the overload current. 14. The method according to item 13, wherein if it is determined that an overload current exists, then this state is indicated by an LED or an overload current control device controlled by a microcontroller.

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