The present disclosure relates generally to electrical and electronic circuits, and more particularly to backup energy storage systems.
Automotive applications have become increasingly dependent on the use of electronic modules. From the need to increase safety features, to the ongoing push towards vehicle electrification and autonomous driving, the requirement for dependable electronic modules is critical. Vehicles of every facet (e.g. motor vehicles, hybrid electric vehicles, electric vehicles, aircraft, etc) require many electronic modules. These modules provide essential features that must continue working even when an energy supply source is temporarily interrupted. Interruptions, due to disturbances in the vehicle power network, could cause travel complications and potentially irreversible damage in the case of vehicles that are highly dependent on a fully operational electronic network.
Electronic modules, also described as electronic controllers, utilized in automotive vehicles, aircrafts, and similar environments, frequently experience large voltage overshoots and deep under voltage interruptions. Currently, one way to manage power interruptions is with the use of a buffer capacitor. Buffer capacitors are typically connected between the device's input (power supply) and output (load). The most common approach is to place a buffer capacitor after a reverse current blocking element (e.g. a diode). The reverse current blocking element prevents the capacitor from discharging into the input power supply when the voltage at the input power supply is interrupted (i.e. drops below a predetermined voltage level). This backup energy storage architecture has several drawbacks. The capacitance must be large enough to maintain a charge sufficient to keep any intermediate voltage above the minimum input voltage of a downstream component, such as a voltage regulator. The capacitance requirement within this architecture may result in a very bulky capacitor, resulting in an expensive module. Another drawback to this backup energy storage architecture occurs during overvoltage conditions, such as during a “load dump” or “jump start” of a component connected to the voltage limiter. During an overvoltage condition, the capacitor is directly exposed to possible overvoltage. Therefore, in order to maintain the reliability of the circuit, and any connected components, the capacitor must have a voltage rating sufficient to handle the potential overvoltage resulting from the load dump.
The combination of the requirements for a high voltage rating and a large capacitance in this backup energy storage architecture increases the size and cost of the module.
The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings, in which:
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, are only schematic, and are non-limiting. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. It will be appreciated by those skilled in the art that the words “during”, “while”, and “when” as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. Additionally, the term “while” means that a certain action occurs at least within some portion of a duration of the initiating action. The use of the word “approximately” or “substantially” means that a value of an element has a parameter that is expected to be close to a stated value or position. However, as is well known in the art there may be minor variances that may prevent the values or positions from being exactly as stated.
Input supply voltage source 120 has an output for providing an input voltage. Rectifier 130 has a first electrode connected to the output of input supply voltage source 120, and an output. Capacitor voltage limiter 140 has an input connected to the output of rectifier 130, and an output for connecting to the first terminal of external storage capacitor 150. Capacitor voltage limiter 140 provides a voltage to the first terminal of external storage capacitor 150 that is limited to a predetermined voltage. Additionally, capacitor voltage limiter 140 has an output for connecting to an output regulator and/or a load. In this embodiment, capacitor voltage limiter 140 has an output connected to the input of output regulator 170. Output regulator 170 has an output for providing voltage to the input of load 190.
In the illustrated embodiment, input supply voltage source 120 normally supplies power to load 190. External storage capacitor 150 is separated from input supply voltage source 120 by capacitor voltage limiter 140. When input supply voltage source 120 supplies a sufficiently large voltage, capacitor voltage limiter 140 also charges external storage capacitor 150 from input supply voltage source 120 up to a predetermined voltage limit. The charge of external storage capacitor 150 is defined by the operations of capacitor voltage limiter 140. A rectified voltage, transmitted via conductor 132, is received at capacitor voltage limiter 140. Capacitor voltage limiter 140 regulates the voltage received across external storage capacitor 150. Capacitor voltage limiter 140 discontinues charging external storage capacitor 150 when the voltage across external storage capacitor 150 reaches the predetermined voltage limit, as determined by the operations and components of capacitor voltage limiter 140.
In another embodiment, capacitor voltage limiter 140 has a predetermined in-rush current limit. The predetermined in-rush current limit enables fast charging of external storage capacitor 150 while preventing excessive currents during startup.
External storage capacitor 150 supplies power to load 190 during power supply interruptions. When input supply voltage source 120 is interrupted, or its voltage drops below a predetermined voltage, power supply system 100 switches to utilizing external storage capacitor 150 as a power source for load 190. Capacitor voltage limiter 140 allows load current to be conducted from the first terminal of external storage capacitor 150 into load 190, while rectifier 130 prevents the flow of current from external storage capacitor 150 into input supply voltage source 120. In this manner, the output voltage to load 190 remains substantially constant while the voltage rating of external storage capacitor 150 can be made relatively small, thereby reducing its cost.
Voltage source 120 has a positive terminal for providing an input supply voltage, and a negative terminal connected to ground. Input supply voltage source 120 may be, for example, a battery and in automotive applications, a car battery that is subject to output voltage fluctuations, interruptions, and periodic recharging.
Rectifier 130 has an input terminal connected to the output terminal of input supply voltage source 120, and a second terminal connected to a supply node 244 conducting a voltage labeled “Vx”. In the embodiment illustrated in
Capacitor voltage limiter 240 has a first terminal connected to supply node 244, a second terminal connected to a node 254 that conducts a voltage labeled “Vcap”, and a third terminal connected to ground. Capacitor voltage limiter 240 includes a pass element in the form of an N-channel transistor 242, a resistor 246, a resistor 248, a voltage source 256, and a differential amplifier 262. Transistor 242 has a first drain electrode connected to supply node 244, a gate, and a second source electrode. Associated with transistor 242 is a diode 241 having an anode connected to the second source terminal of transistor 242, and a cathode formed in the first drain terminal of transistor 242. The anode is formed by providing a local connection between the second source terminal of transistor 242 and the body of transistor 242. The PN junction is formed between the P− body and the N+ first drain terminal of transistor 242, which functions as the cathode of diode 241. Resistor 246 has a first terminal connected to the second source terminal of transistor 242, and a second terminal. Resistor 248 has a first terminal connected to the second terminal of resistor 246, and a second terminal connected to ground. Voltage source 256 has a positive terminal and a negative terminal connected to ground. Differential amplifier 262 has a non-inverting input connected to the positive output of voltage source 256, an inverting input connected to the second terminal of resistor 246, and an output connected to the gate of transistor 242.
External storage capacitor 250 includes an electrolytic capacitor 252 which has a first terminal connected to node 254, and a second terminal connected to ground. Electrolytic capacitor 252 is designated as being external because it has a voltage and voltage rating not suitable for integration, whereas capacitor voltage limiter 240 is suitable for integration.
Voltage regulator 270 includes a pass element in the form of an N-channel transistor 272, a resistor 274, a resistor 278, and a differential amplifier 276. Transistor 272 has a first drain electrode connected to supply node 244, a gate, and a second source electrode. Resistor 274 has a first terminal connected to node 284 and to the second source terminal of transistor 272, and a second terminal. Resistor 278 has a first terminal connected to the second terminal of resistor 274, and a second terminal connected to ground. Differential amplifier 276 has a non-inverting input connected to the positive output of voltage source 256, an inverting input connected to the first terminal of resistor 278, and an output connected to the gate of transistor 272.
Load 290 includes a capacitor 292 and a resistor 294. Capacitor 292 has a first terminal connected to node 284, and a second terminal connected to ground. Resistor 294 has a first terminal connected to the first terminal of capacitor 292, as well as node 284, and a second terminal connected to ground.
In operation, input supply voltage source 120 and voltage source 256 (Vref), of power supply system 200, are connected. The voltage at supply node 244 (Vx), is equivalent to the input voltage (Vin) minus the value of the cut-in voltage of diode 232. When the value of voltage source 256 is greater than the voltage value conducted at node 254 (Vcap) through the resister divider, differential amplifier 262 makes transistor 242 conductive. The voltage at node 254 increases as electrolytic capacitor 252 is charged by input supply voltage source 120. Differential amplifier 262 continues to keep transistor 242 conductive while Vcap increases, until the voltage on node 254 through the resistor divider is approximately equivalent to voltage source 256. When the voltage on node 254 is approximately equal to voltage source 256, differential amplifier 262 makes transistor 242 non-conductive, therefore limiting further static current from flowing into electrolytic capacitor 252. Input supply voltage source 120 decreases during use as its energy is drained by load 290. When the voltage at supply node 244 is less than the voltage at node 254, less the cut-in-voltage of diode 232, electrolytic capacitor 252 starts supplying current to load 290 through diode 241 and transistor 242. Vcap continues to supply current into load 290 until electrolytic capacitor 252 discharges, or a new battery is connected. When the current drawn by load 290 causes the voltage at node 254 to drop such that the voltage at node 254, is less than Vref, then differential amplifier 262 again makes transistor 242 conductive; thereby, enabling input supply voltage source 120 to recharge electrolytic capacitor 252.
Power supply system 200 utilizes capacitor voltage limiter 240 to limit the voltage across electrolytic capacitor 252 as voltage source 120 charges electrolytic capacitor 252. Once electrolytic capacitor 252 is fully charged, capacitor voltage limiter 240 restricts additional current flow to electrolytic capacitor 252. When input supply voltage source 120 experiences an interruption or undervoltage, capacitor voltage limiter 240 enables electrolytic capacitor 252 to dynamically supply energy to load 290.
In power supply system 200 of
In another embodiment, capacitor voltage limiter 240 utilizes alternate components to limit the voltage across electrolytic capacitor 252. Transistor 242, of capacitor voltage limiter 240, may comprise a junction field effect transistor (JFET). When a JFET, or an equivalent thereof, is utilized as transistor 242, feedback from differential amplifier 262 is optional. Given, for this example, the JFET is an N-type device, the first electrode terminal of transistor 242 is connected to supply node 244, the second electrode terminal of transistor 242 is connected to capacitor 252, and the control, or gate electrode terminal of transistor 242 is connected to ground. Capacitor 252 charges until the voltage at the second electrode of transistor 242 reaches a predetermined voltage, as defined by transistor 242 cutoff voltage (Vgs). When Vgs is reached, the current flowing to capacitor 252 is stopped due to transistor 242 turning off. Additionally, transistor 242 can be a bipolar junction transistor (BJT), silicon controlled rectifier (SCR), or equivalents thereof.
Rectifier 130 could be implemented with other types of passive rectifiers or with synchronous rectifiers. In one embodiment, power supply system 200 can include a regulator, a combination of regulators, or no regulator at all. Voltage regulator 270, of power supply system 200, can comprise any component or a combination of components that enable regulation of the voltage supply to load 290. For example, a combination of a charge-pump regulator and a downstream regulator utilizing a series PMOS pass element may be implemented as regulator 270. Alternatively, power supply system 200 does not require a regulator. When the unregulated voltage is sufficient to power load 290, power supply system 200 provides an unregulated Vx to load 290 via supply node 244.
In one embodiment, the functions of capacitor voltage limiter 240, voltage regulator 270, and load 290 are provided on an integrated circuit configured in one of a first configuration, a second configuration, and a third configuration, or a combination thereof. The first architecture, or configuration, comprises capacitor voltage limiter 240 and voltage regulator 270 combined on a single integrated circuit. The second configuration comprises capacitor voltage limiter 240, regulator 270, and load 290 combined on the single integrated circuit. The third configuration comprises capacitor voltage limiter 240 and regulator 270, combined to function as the load.
While the subject matter of the invention is described with specific preferred embodiments and example embodiments, the foregoing drawings and descriptions thereof depict only typical embodiments of the subject matter and are not therefore to be considered as limiting of its scope, and many alternatives and variations will be apparent to those skilled in the art. Inventive aspects of the present disclosure may lie in less than all features of a single foregoing disclosed embodiment. As just one example, while
Furthermore, some embodiments described herein include some but not other features included in other embodiments, and therefore combinations of features of different embodiments are meant to be within the scope of the disclosure, and form different embodiments, as would be understood by those skilled in the art.
This application claims priority to U.S. Provisional Application No. 62/308515, filed on Mar. 15, 2016, entitled “Temporary Energy Storage for Voltage Supply Interruptions,” invented by Jan Plojhar, and is incorporated herein by reference and priority thereto for common subject matter is hereby claimed.
Number | Date | Country | |
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62308515 | Mar 2016 | US |