Patent Description:
Wetting current is a minimum current that a sourcing device (henceforth the device) needs to switch in order to ensure that the switching contacts remain clean and thereby maintain the reliability of the device. If the current sourced to the device is less than the wetting current value recommended by the manufacturer of the device, the reliability of the device cannot be assured. This issue affects relay-based circuits where a minimum switching current is required for the circuit to function properly.

With the advent of electronic monitoring circuits, less and less current is required to operate the electronic input circuits of the destination device which results in higher input impedance and a need for less and less current to be drawn from the sourcing device on activation. The reduction in current results in a reduction in the power consumed by each of the input devices for on-board and wayside equipment. However, this reduction affects effectiveness of current sourcing devices as the minimum wetting current required to switch the device on is not met. To remedy this difficulty, document <CIT> proposed a technical solution. This technical solution presents a programmable circuit for sensing signals, which comprises a programmable current sink circuit. The programmable current sink circuit includes a plurality of inputs coupled to sense input signals received from at least one input/out device, such as a relay contact. The programmable current sink circuit comprises a digital-to-analog converter (DAC) that is programmable to set an adjustable magnitude of current sink so that a proper amount of current is jointly sunk from the plurality of inputs to generate a total sink current. With wetted contacts, the current sink circuit is capable of detecting relay contact status conditions that include whether the contact is closed, the contact is open, or the contacts are contaminated due to corrosion. The current sink circuit can measure the actual sink current for diagnostics and to feedback a value for adjustment.

The following disclosure provides many different examples, for implementing different features of the provided subject matter. Specific examples of components, values, operations, materials, arrangements, or the like, are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Other components, values, operations, materials, arrangements, or the like, are contemplated. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact.

With reference to <FIG>, a power system <NUM> for a device including a wetting input circuit is shown. A current source <NUM> is electrically coupled with an input circuit <NUM> which is in turn electrically coupled with a device <NUM>. The current source <NUM> transmits power to the device <NUM> through the input circuit <NUM>. The device <NUM> has a minimum wetting current value. In some embodiments, the minimum wetting current value is specified by the device <NUM> manufacturer to meet minimum reliability measures. The input circuit <NUM> detects the presence of a current, above a threshold current value equal to the minimum wetting current value of the device <NUM>, from the current source <NUM> and transmits the current to the device <NUM>. When the current from the current source <NUM> is below the threshold current value, the input circuit <NUM> shunts the current so that current is not provided to the device <NUM>.

With reference to <FIG>, a simplified powering circuit <NUM> is shown. A current source <NUM> transmits a current I to a device <NUM>. Device <NUM> has a minimum wetting current Iw. Device <NUM> activates if the current I exceeds the minimum wetting current Iw for the device <NUM>. In some embodiments, device <NUM> is usable as device <NUM> (<FIG>).

With reference to <FIG>, a wetting input circuit <NUM> is shown, in accordance with an embodiment. In some embodiments, wetting input circuit <NUM> is usable as input circuit <NUM> (<FIG>). Wetting input circuit <NUM> comprises a first current detector <NUM>, a control circuit <NUM>, a second current detector <NUM>, and a switch <NUM>. First current detector <NUM> is electrically coupled with an end of a resistor <NUM>, an output terminal <NUM>, a control circuit <NUM>, and switch <NUM>. The other end of resistor <NUM> is electrically coupled with an input terminal <NUM> which is in turn coupled with a current source, e.g., current source <NUM> (<FIG>). In some embodiments, resistor <NUM> is a current limiting resistor. In some embodiments, output terminal <NUM> is electrically coupled with a device, e.g., device <NUM> (<FIG>). The first current detector <NUM> generates a current level signal responsive to detection of a current from input terminal <NUM> (via resistor <NUM>). The first current detector <NUM> transmits the current level signal to control circuit <NUM>. Control circuit <NUM> is a processor-based system, in accordance with some embodiments.

In some embodiments, first current detector <NUM> compares the current received from input terminal <NUM> with the minimum wetting current value. First current detector <NUM> generates a current level signal. If the current received meets or exceeds the minimum wetting current value, first current detector <NUM> generates a current level signal indicating that the minimum wetting current value has been exceeded. If the current received is below the minimum wetting current value, first current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, first current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, first current detector <NUM> does not generate a current level signal. In some embodiments, the current level signal is the current value or a binary value indicative of whether the minimum wetting current value has been exceeded.

Second current detector <NUM> is electrically coupled with an end of a resistor <NUM>, an input terminal <NUM>, and control circuit <NUM>, and switch <NUM>. The other end of resistor <NUM> is electrically coupled with an output terminal <NUM> which is in turn coupled with the current source, e.g., current source <NUM> (<FIG>). In some embodiments, resistor <NUM> is a current limiting resistor. In some embodiments, input terminal <NUM> is electrically coupled with the device, e.g., device <NUM> (<FIG>). Similar to first current detector <NUM>, second current detector <NUM> generates a current level signal responsive to detection of a current from output terminal <NUM> (via resistor <NUM>). The second current detector <NUM> transmits the current level signal to control circuit <NUM>.

In some embodiments, second current detector <NUM> compares the current received from output terminal <NUM> with the minimum wetting current value. Second current detector <NUM> generates a current level signal. If the current received meets or exceeds the minimum wetting current value, second current detector <NUM> generates a current level signal indicating that the minimum wetting current value has been exceeded. If the current received is below the minimum wetting current value, second current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, second current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, second current detector <NUM> does not generate a current level signal. In some embodiments, the current level signal is the current value or a binary value indicative of whether the minimum wetting current value has been exceeded.

Control circuit <NUM> is electrically coupled with first and second current detectors <NUM>, <NUM>, and switch <NUM>. Control circuit <NUM> receives the current level signal from the first and second current detectors <NUM>, <NUM> and generates a switch control signal for controlling switch <NUM>.

If the current level signal indicates that the current is below the minimum wetting current value, control circuit <NUM> causes switch <NUM> to be in an ON mode (also referred to as a conducting or shunted state), i.e., control circuit <NUM> generates a switch control signal (ON signal) to turn on switch <NUM>. If switch <NUM> is shunted, current flows from the first current detector <NUM> through switch <NUM> and to output terminal <NUM> via resistor <NUM> and current detector <NUM>.

If the current level signal indicates that the current meets or exceeds a minimum wetting current value, control circuit <NUM> causes switch <NUM> to be in an OFF mode (also referred to as a non-conducting state), i.e., control circuit <NUM> generates a switch control signal (OFF signal) to turn off switch <NUM>. If switch <NUM> is non-conducting, current flows from the first current detector <NUM> to output terminal <NUM> to the device and returns via input terminal <NUM> to second current detector <NUM> and on to output terminal <NUM> via resistor <NUM>.

A current is transmitted to the circuit <NUM> through input terminal <NUM> and output terminal <NUM>. The wetting input circuit <NUM> has an internal impedance represented by resistors <NUM> and <NUM>. First current detector <NUM> detects the presence of an input current. Current detectors are electronic components which measure the current in the input circuit and provide the measured value to a control circuit. The measured value is either the actual measured value or an ON or OFF value based on threshold detection.

If no current, or a current below a threshold value, is detected by the current detector <NUM>, the current detector <NUM> sends a signal (or a null signal) to control circuit <NUM>. Control circuit <NUM> is a circuit which either commands the switch <NUM> to the ON state (conducting) or the OFF state (not conducting), based on the input from the current detectors. Switch <NUM> is an electronic device or a relay and its function is to allow the switching between the high impedance state of the electronic input and the low impedance state of the electronic input.

The control circuit <NUM> closes switch <NUM> which shunts the input <NUM> and output <NUM>, so that no current flows between them via a connected device, e.g., device <NUM> (<FIG>). If a current at or in excess of a threshold value is detected by the current detector <NUM>, the current detector <NUM> sends a signal to control circuit <NUM>. The control circuit <NUM> opens the switch <NUM> which causes the current to flow from the first current detector <NUM> to the input <NUM>, the connected device, and back to input terminal <NUM>. A second current detector <NUM> detects output current and sends a control signal (or a null signal) to the control circuit in the same fashion. The redundancy of the current detectors <NUM> and <NUM> assure proper operation of the control circuit and detect the failure of either current detector <NUM> or <NUM>. In accordance with an embodiment, when one of the current detectors <NUM> or <NUM> fails then the input circuit continues to function and a failure is reported for maintenance. For proper operation of the circuit, only one of the current detectors <NUM> or <NUM> allows the input circuit to work. In accordance with an embodiment, if both current detectors <NUM> or <NUM> fail, the input circuit is in the safe state, i.e. no input.

With reference to <FIG>, a wetting input circuit <NUM> is shown, in accordance with an embodiment. Wetting input circuit <NUM> is similar to wetting input circuit <NUM> without including a second current detector. In some embodiments, wetting input circuit <NUM> is usable as input circuit <NUM> (<FIG>). Wetting input circuit <NUM> comprises a current detector <NUM>, a control circuit <NUM>, and a switch <NUM>. Current detector <NUM> is electrically coupled with an end of a resistor <NUM>, an output terminal <NUM>, a control circuit <NUM>, and switch <NUM>. The other end of resistor <NUM> is electrically coupled with an input terminal <NUM> which is in turn coupled with a current source, e.g., current source <NUM> (<FIG>). In some embodiments, resistor <NUM> is a current limiting resistor. In some embodiments, output terminal <NUM> is electrically coupled with a device, e.g., device <NUM> (<FIG>). The current detector <NUM> generates a current level signal responsive to detection of a current from input terminal <NUM> (via resistor <NUM>). The current detector <NUM> transmits the current level signal to control circuit <NUM>. Control circuit <NUM> is a processor-based system, in accordance with some embodiments.

In some embodiments, current detector <NUM> compares the current received from input terminal <NUM> with the minimum wetting current value. Current detector <NUM> generates a current level signal. If the current received meets or exceeds the minimum wetting current value, current detector <NUM> generates a current level signal indicating that the minimum wetting current value has been exceeded. If the current received is below the minimum wetting current value, current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, first current detector <NUM> does not generate a current level signal. In some embodiments, the current level signal is the current value or a binary value indicative of whether the minimum wetting current value has been exceeded.

A resistor <NUM> is coupled with an input terminal <NUM>, and switch <NUM>. The other end of resistor <NUM> is electrically coupled with an output terminal <NUM> which is in turn coupled with the current source, e.g., current source <NUM> (<FIG>). In some embodiments, resistor <NUM> is a current limiting resistor. In some embodiments, input terminal <NUM> is electrically coupled with the device, e.g., device <NUM> (<FIG>).

Control circuit <NUM> is electrically coupled with current detector <NUM> and switch <NUM>. Control circuit <NUM> receives the current level signal from the current detector <NUM> and generates a switch control signal for controlling switch <NUM>.

If the current level signal indicates that the current is below the minimum wetting current value, control circuit <NUM> causes switch <NUM> to be in an ON mode (also referred to as a conducting or shunted state), i.e., control circuit <NUM> generates a switch control signal (ON signal) to turn on switch <NUM>. If switch <NUM> is shunted, current flows from the current detector <NUM> through switch <NUM> and to output terminal <NUM> via resistor <NUM>.

If the current level signal indicates that the current meets or exceeds a minimum wetting current value, control circuit <NUM> causes switch <NUM> to be in an OFF mode (also referred to as a non-conducting state), i.e., control circuit <NUM> generates a switch control signal (OFF signal) to turn off switch <NUM>. If switch <NUM> is non-conducting, current flows from the current detector <NUM> to terminal <NUM> to the device and returns via terminal <NUM> to output terminal <NUM> via resistor <NUM>.

A current is transmitted to the circuit <NUM> through input <NUM> and output <NUM>. The input circuit <NUM> has an internal impedance represented by resistors <NUM> and <NUM>. A current detector <NUM> detects the presence of an input current. If no current, or a current below a threshold value, is detected by the current detector <NUM>, the current detector <NUM> sends a signal (or a null signal) to a control circuit <NUM>. The control circuit <NUM> closes switch <NUM> which shunts the input <NUM> and output <NUM>, so that no current flows between them. If a current in excess of a threshold value is detected by the current detector <NUM>, the current detector <NUM> sends a signal to a control circuit <NUM>. The control circuit opens the switch <NUM> which provides the current to the terminal <NUM> to the device and returns via terminal <NUM>.

With reference to <FIG>, a power system <NUM> is shown, in accordance with an embodiment. A power source <NUM> transmits power to a computer through a computer power input <NUM>. The power transmitted by the power source <NUM> generates a current that passes into wetting input circuit <NUM>. In some embodiments, wetting input circuit <NUM> is one or the other of wetting input circuit <NUM> or <NUM>. The wetting input circuit <NUM> has an internal impedance represented by resistor <NUM>. The computer input <NUM> has an internal impedance represented by resistor <NUM>. The impedance presented by resistor <NUM> is larger than the impedance presented by resistor <NUM>. The input circuit <NUM> detects current generated by the power source <NUM>. If the current is below a threshold value, i.e., the minimum wetting current for the computer input <NUM>, the input circuit <NUM> shunts the current through the input circuit and resistance <NUM>. If the current is above a threshold value, i.e., the minimum wetting current for the computer input <NUM>, the input circuit <NUM> provides the current to the computer input <NUM> and resistance <NUM>.

With reference to <FIG>, a wetting input circuit <NUM> is shown. Wetting input circuit <NUM> is similar to wetting input circuit <NUM> and <NUM> with a current control <NUM> in place of a control circuit and switch. The wetting input circuit <NUM> is usable as input circuit <NUM> (<FIG>). Wetting input circuit <NUM> comprises a current detector <NUM> and a current control <NUM>. Current detector <NUM> is electrically coupled with an input terminal <NUM>, an output terminal <NUM> and a current control <NUM>. Input terminal <NUM> is coupled with a current source, e.g., current source <NUM> (<FIG>). The output terminal <NUM> is electrically coupled with a device, e.g., device <NUM> (<FIG>). The current detector <NUM> generates a current level signal responsive to detection of a current from input terminal <NUM>. The current detector <NUM> transmits the current level signal to current control <NUM>. Current control <NUM> is a processor-based system.

The current detector <NUM> compares the current received from input terminal <NUM> with the minimum wetting current value. Current detector <NUM> generates a current level signal. If the current received meets or exceeds the minimum wetting current value, current detector <NUM> generates a current level signal indicating that the minimum wetting current value has been exceeded. If the current received is below the minimum wetting current value, current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. In some embodiments, if no current is received or if the current received is below the minimum wetting current value, current detector <NUM> generates a current level signal indicating that the minimum wetting current value has not been exceeded. If no current is received or if the current received is below the minimum wetting current value, first current detector <NUM> does not generate a current level signal. The level signal is the current value or a binary value indicative of whether the minimum wetting current value has been exceeded.

An input terminal <NUM> is coupled with a current control <NUM>. An output terminal <NUM> is coupled with the current source, e.g., current source <NUM> (<FIG>). The input terminal <NUM> is electrically coupled with the device, e.g., device <NUM> (<FIG>).

Current control <NUM> is electrically coupled with current detector <NUM>. Current control <NUM> receives the current level signal from the current detector <NUM> and controls the current between input terminal <NUM> and output terminal <NUM>.

If the current level signal indicates that the current is below the minimum wetting current value, current control <NUM> allows current to flow from the current detector <NUM> to terminal <NUM>.

If the current level signal indicates that the current meets or exceeds a minimum wetting current value, current control <NUM> allows current to flow from the current detector <NUM> to terminal <NUM> to the device and returns via terminal <NUM> to terminal <NUM>.

Power is generated between input <NUM> and output <NUM>. A current detector <NUM> detects current and provides a control signal to a control circuit <NUM>. If the detected current is above the threshold wetting current value for load <NUM>, the current is provided to the load <NUM>. If the detected current is below the threshold wetting current value for load <NUM>, the current is shunted away from the load <NUM>.

With reference to <FIG>, a simplified power circuit <NUM> is shown. The simplified power circuit <NUM> shows the state of the input circuit <NUM> when the current detected by current detector <NUM> or <NUM> is less than a threshold value and switch <NUM> or <NUM> is closed. A current source <NUM>, for example current source <NUM> (<FIG>) is connected to a switch <NUM> that is opened to indicate that the power to the input circuit <NUM> is turned OFF. Impedance <NUM> is connected to open switch <NUM> and the other end of impedance <NUM> is connected to the current source <NUM>. Impedance <NUM> is connected in series with device <NUM> which has an internal impedance represented by impedance <NUM> A current source <NUM> is disconnected from the device <NUM> (turned off) by switch <NUM>. The current passing through the device <NUM> is zero or insignificant, i.e., below the wetting current of device <NUM>. A shunting path through is connected to the device <NUM>. The current provided to the device <NUM> is approximately zero. The current Io represents the current when the current source is disconnected and is approximately equal to zero. The current IEM represents the current in the circuit due to electromagnetic waves or fluctuations. Any stray current IEM is.

With reference to <FIG>, a simplified power circuit <NUM> is shown. The simplified power circuit <NUM> shows the state of the input circuit <NUM> (<FIG>) when the current detected by current detector <NUM> or <NUM> is greater than a threshold value and switch <NUM> or <NUM> is open. A current source <NUM>, for example current source <NUM> (<FIG>) is connected to a switch <NUM> that is closed to indicate that the power to the input circuit <NUM> is turned ON. Impedance <NUM> is connected to closed switch <NUM> and the other end of impedance <NUM> is connected to an open switch <NUM>. The open switch <NUM> is connected at the other end to the current source <NUM>. Impedance <NUM> is connected in series with device <NUM> which has an internal impedance represented by impedance <NUM> A current source <NUM> is connected to the device <NUM> (turned on) by switch <NUM>. The current passing through the device <NUM> is above the wetting current of device <NUM>. A shunting path is disconnected from the circuit <NUM> by switch <NUM>.

With reference to <FIG>, a method of operating a wetting current control <NUM> is shown, in accordance with an embodiment. An input circuit, for example input circuit <NUM> (<FIG>) is connected to a variable power source, for example current source <NUM> (<FIG>) that provides power to the input circuit when on and provides no power to the input circuit when off in step <NUM>. The current provided by the power source is detected by a current detector, for example current detector <NUM> (<FIG>) or current detector <NUM> (<FIG>) in step <NUM>. The current detector provides a control signal to a control circuit, for example control circuit <NUM> (<FIG>) in step <NUM>. If the control signal indicates that the current has a value equal to or greater than the wetting current of the load in decision step <NUM>, the control circuit opens a switch in step <NUM>. Current is provided to the load in step <NUM>. If the control signal indicates that the current has a value less than the wetting current of the load in decision step <NUM>, the control circuit closes the switch in step <NUM> thereby shunting the current through the switch and away from the load in step <NUM>.

With reference to <FIG>, a power system for on-board electronics <NUM> is shown, in accordance with an embodiment. A power supply <NUM>, for example current source <NUM> (<FIG>) generates a current. The current generated by the power supply <NUM> is detected by input circuit <NUM>, for example input circuit <NUM> (<FIG>). If the current is less than the wetting current of on-board electronics <NUM>, the device <NUM> (<FIG>), the input circuit <NUM> shunts the current away from the on-board electronics <NUM>. If the current is greater than the wetting current of on-board electronics <NUM>, the current is provided to the on-board electronics <NUM>.

With reference to <FIG>, a power system for way-side electronics <NUM> is shown, in accordance with an embodiment. A power supply <NUM>, for example current source <NUM> (<FIG>) generates a current. The current generated by the power supply <NUM> is detected by input circuit <NUM>, for example, the input circuits of <FIG> or <FIG>. If the current is less than the wetting current of way-side electronics <NUM>, for example, the device <NUM> of <FIG>, the input circuit <NUM> shunts the current away from the way-side electronics <NUM>. If the current is greater than the wetting current of way-side electronics <NUM>, the current is provided to the way-side electronics <NUM>.

One or more embodiments of the present disclosure are related to an input circuit for on-board and wayside equipment with respect to the control of the input wetting current for such equipment. One or more embodiments further ensure that under all operating conditions the minimum wetting current for input devices exceeds the recommended manufacturer's wetting current specification. One or more embodiments address the conflicting requirements as stated above without the need to increase power consumption of the electronic input devices.

One or more embodiments are using in railway signaling; however, one or more embodiments of the present disclosure are applicable for input devices needing increased wetting current or greater immunity to EMI. One or more embodiments are suited for vital (safety) circuits where the permissive state of an input is the energized state and where a reduction in power consumption benefits the design. One or more embodiments also find use in electronic equipment requiring larger immunity to EMI in the input OFF state and where wetting current specification points to a need for increased input current due to high impedance input devices.

One or more embodiments of the invention include designing a two-stage electronic input circuit which provides the sourcing device with two values of impedance. A low impedance value when the device is de-energized and a high impedance value when the sourcing device has been detected as energized.

One or more embodiments of the invention include a circuit for controlling an input current, the circuit includes a first input port configured to receive the input current. A current detector detects an input current value of the input current and generates a control signal indicative of the input current value. A first output port outputs an output current to a load. A second output port receives the output current from the load. A control circuit provides a low-impedance path in parallel with the load in response to the control signal indicating the input current value is below a threshold value.

As discussed above, the sourcing devices need to be assured that the wetting current needed when the sourcing device is turned on is larger than the minimum sourcing current specified by the sourcing device manufacturer. When the sourcing device is in the de-energized state no current will flow in the electronic input circuit at which point the input impedance of the electronic input as seen by the sourcing device will be low.

After the sourcing device energizes the input (on state), the current flowing between the source circuit and the electronic input will be high due to the low impedance of the circuit and the current flowing will be above the wetting current threshold. After the electronic input detects that the input has been energized through current detector circuits, the input impedance is increased to a value dictated by the impedance of the computer input. This impedance is much higher and thus results in a reduction of the current flowing in the circuits and the energy used.

The fact that the circuit presents a low impedance input to the sourcing device while the input is de-energized (off state), increases the immunity of the circuit to EMI by shunting electronic noise from the high impedance of the computer input. After the input remains on, the circuit impedance remains high and the current is dictated by the high impedance of the computer input.

After the input de-energizes (off state), the circuit reverts automatically to the low impedance state.

In operation, when the sourcing device is de-energized (OFF state), the current detectors measure a current which is below the detection threshold and provide this information to the control circuit which turns ON (conducting state) the switch. This presents a low impedance input to the sourcing device and shunts the computer input from the external world thus increasing its immunity to stray EMI.

When the sourcing device is energized (ON state), the current flowing in the circuit is due to the low impedance of the circuit and thus at a value greater than the minimum wetting current that the device needs. Thus, at the point of switching ON, the current flowing exceeds the minimum value specified.

Current detectors detect the larger current and thus indicate to the control circuit that the input is energized. Control circuit then turns off switch and the switch stops conducting. As a result, the shunt across the computer input is eliminated and the current flows into the computer input. This turns on computer input although at a lower value as the circuit now contains the high input impedance of the computer input.

While the input remains energized, the current sourced remains at the value dictated by the high impedance of the circuit.

When the sourcing device is de-energized (OFF state), the reduced current is detected by current detectors which informs control circuit which in turn energizes switch. This results in presenting a low impedance value to the sourcing device.

The above sequence of operation continues whenever the sourcing device is turned ON or OFF.

The circuit includes two current detectors in each leg of the circuit to improve reliability of the circuit. In at least some embodiments, the circuit operates with a single current detector. In at least some embodiments, failures of a detector are detected and indicated to the control circuit for maintenance notification.

One or more embodiments of the input circuit, by providing a low impedance current path shunted via the switch, ensure that when an input is energized sufficiently, current flows in the circuit which provides for the necessary wetting current to the sourcing device. After the switch opens as a result of the input being detected as energized by the current sensing detectors, the current in the circuit drops to the current drawn by the high impedance input device. This operation substantially reduces the current used by the circuit, reduces power consumption and provides higher initial input current to assure proper wetting current to the sourcing device only when the input changes from low to high, in at least some embodiments.

One or more embodiments advantageously increases the wetting current to the values specified by the source device manufacturer. One or more embodiments advantageously increases the immunity of the electronic input circuit to EMI by requiring a higher current to turn on the input. One or more embodiments advantageously eliminates the need for additional power devices to increase the input current and thus the need of larger power supplies and heat dissipation resistors.

One or more embodiments avoid the need to increase the current consumption of the devices and avoiding the resulting need to increase the size of power supplies and the added cost of energy. Additionally, one or more embodiments avoid the additional cost accrued as a result of the need to rid the added power and a corresponding increase in cabinet size, wire size, and the addition of fans.

One or more embodiments satisfy the increase of the wetting current specified by a manufacturer without increasing the power consumption. One or more embodiments, increase the immunity to EMI, in particular, when the input is not energized. One or more embodiments reduce power consumption in comparison with other methods for increasing the wetting current by electronic input devices.

In at least one aspect, the present disclosure includes a circuit for controlling a wetting current. The circuit comprises a current detector for measuring a current; a control circuit electrically coupled with the current detector and configured to generate a control signal based on the measured current value; and a switch coupled with the control circuit and configured to have a conducting state and a non-conducting state responsive to the control signal. When the switch is in the conducting state it is configured to shunt current across a device input and when the switch is in the non-conducting state it is configured to allow current to flow to the device input.

In accordance with an embodiment, the input circuit detects current in the input and current limiting resistors. When the current in the input circuit is below a threshold, the switch, such as <NUM> or <NUM>, is closed basically shorting the load. When there is current, the switch, such as <NUM> or <NUM>, is open allowing current to flow to the load in high impedance configuration.

In accordance with an embodiment, the resistor, such as <NUM> or <NUM>, is in series with the load, such as <NUM> or <NUM>, is a high impedance, relative to the current limiting resistor at the input, such as <NUM> or <NUM>.

In accordance with an embodiment, a computer circuit presents both a high impedance and low impedance to a source. In accordance with an embodiment, high impedance is presented to the source load when current is flowing in the circuit above a threshold and a low impedance is presented to the source load when the current is low or zero. In accordance with an embodiment, the low impedance allows for wetting currents when the source input is turning from off to on. A transition from low impedance to high impedance configuration after a short time period when input current is detected from the source. A low impedance configuration is restored when the source current is below a threshold or zero.

In accordance with an embodiment, the circuit is used as an input circuit for external signals in onboard and wayside application, to minimize power consumption and control wetting current. In many applications the status for the input is relays. These relays are connected to a wetting current. Otherwise their reliability is affected. Sometimes the relays are not in the cleanest environment and they need a wetting current to clean the contacts. A wetting current consumes more power and generates heat that needs to be disposed of. The input circuit provides a wetting current and reduces power consumption and heat.

<FIG> is a block diagram of a control circuit <NUM> in accordance with some embodiments.

In some embodiments, control circuit <NUM> is a general purpose computing device including a hardware processor <NUM> and a non-transitory, computer-readable storage medium <NUM>. Storage medium <NUM>, amongst other things, is encoded with, i.e., stores, computer program code <NUM>, i.e., a set of executable instructions. Execution of instructions <NUM> by hardware processor <NUM> represents (at least in part) a control circuit which implements a portion or all of the methods described herein in accordance with one or more embodiments (hereinafter, the noted processes and/or methods).

Processor <NUM> is electrically coupled to computer-readable storage medium <NUM> via a bus <NUM>. Processor <NUM> is also electrically coupled to an I/O interface <NUM> by bus <NUM>. A network interface <NUM> is also electrically connected to processor <NUM> via bus <NUM>. Network interface <NUM> is connected to a network <NUM>, so that processor <NUM> and computer-readable storage medium <NUM> are capable of connecting to external elements via network <NUM>. Processor <NUM> is configured to execute computer program code <NUM> encoded in computer-readable storage medium <NUM> in order to cause system <NUM> to be usable for performing a portion or all of the noted processes and/or methods. In one or more embodiments, processor <NUM> is a central processing unit (CPU), a multi-processor, a distributed processing system, an application specific integrated circuit (ASIC), and/or a suitable processing unit.

In one or more embodiments, computer-readable storage medium <NUM> is an electronic, magnetic, optical, electromagnetic, infrared, and/or a semiconductor system (or apparatus or device). For example, computer-readable storage medium <NUM> includes a semiconductor or solid-state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and/or an optical disk. In one or more embodiments using optical disks, computer-readable storage medium <NUM> includes a compact disk-read only memory (CD-ROM), a compact disk-read/write (CD-R/W), and/or a digital video disc (DVD).

In one or more embodiments, storage medium <NUM> stores computer program code <NUM> configured to cause system <NUM> (where such execution represents to be usable for performing a portion or all of the noted processes and/or methods. In one or more embodiments, storage medium <NUM> also stores information which facilitates performing a portion or all of the noted processes and/or methods. In one or more embodiments, storage medium <NUM> stores library <NUM> of one or more wetting current minimum values as disclosed herein.

Control circuit system <NUM> includes I/O interface <NUM>. I/O interface <NUM> is coupled to external circuitry. In one or more embodiments, I/O interface <NUM> includes a keyboard, keypad, mouse, trackball, trackpad, touchscreen, and/or cursor direction keys for communicating information and commands to processor <NUM>.

Control circuit system <NUM> also includes network interface <NUM> coupled to processor <NUM>. Network interface <NUM> allows system <NUM> to communicate with network <NUM>, to which one or more other computer systems are connected. Network interface <NUM> includes wireless network interfaces such as BLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA; or wired network interfaces such as ETHERNET, USB, or IEEE-<NUM>. In one or more embodiments, a portion or all of noted processes and/or methods, is implemented in two or more systems <NUM>.

System <NUM> is configured to receive information through I/O interface <NUM>. The information received through I/O interface <NUM> includes one or more of instructions, data, wetting current minimum value(s), and/or other parameters for processing by processor <NUM>. The information is transferred to processor <NUM> via bus <NUM>. Control circuit system <NUM> is configured to receive information related to a UI through I/O interface <NUM>. The information is stored in computer-readable medium <NUM> as user interface (UI) <NUM>.

In some embodiments, a portion or all of the noted processes and/or methods is implemented as a standalone software application for execution by a processor. In some embodiments, a portion or all of the noted processes and/or methods is implemented as a software application that is a part of an additional software application. In some embodiments, a portion or all of the noted processes and/or methods is implemented as a plug-in to a software application. In some embodiments, at least one of the noted processes and/or methods is implemented as a software application that is a portion of a control circuit tool. In some embodiments, a portion or all of the noted processes and/or methods is implemented as a software application that is used by control circuit system <NUM>.

Claim 1:
A circuit (<NUM>) configured to control an input current, the circuit (<NUM>) comprising:
a first input port (<NUM>) configured to receive the input current;
a first current detector (<NUM>) configured to detect an input current value of the input current and generate a first control signal indicative of the input current value;
a first output port (<NUM>) configured to output an output current to a load (<NUM>);
a second output port (<NUM>) configured to receive the output current from the load (<NUM>); and
a control circuit (<NUM>) generates a switch control signal for controlling switch (<NUM>), configured to provide a low-impedance path in parallel with the load (<NUM>) in response to the first control signal indicating the input current value below a threshold value, the circuit (<NUM>) further comprising a first series resistor (<NUM>) connecting the first input port (<NUM>) to the current detector (<NUM>); and a second series resistor (<NUM>) connected to the second output port (<NUM>) and an output terminal (<NUM>), wherein a switch (<NUM>) connects between the first output port (<NUM>) and the second output port (<NUM>), wherein the first series resistor (<NUM>) has a lower resistance value than the second series resistor (<NUM>) in series with the load (<NUM>), and wherein the first series resistor (<NUM>) and the second series resistor (<NUM>) are current limiting resistors.