Abstract: For the purpose of preventing generation of burning or disconnection of an inrush current preventing resistor (3) when making and breaking of an AC power supply are frequently repeated, energy to be charged to a smoothing capacitor (4) at the time of making the power supply is calculated from the capacitance of the smoothing capacitor (4) of a capacitor-input type rectifying circuit and value of a rectifying smoothing DC voltage, and a mean power is calculated from the energy and the number of times of power making and breaking within a predetermined period of time. If the mean power exceeds an allowable power of the inrush current preventing resistor (3) for preventing an inrush current at the time of making the power supply, warning by an alarm display or an alarm output and power non-making interlock are carried out, and driving of a load-side device is stopped.

Abstract: A heater control device that prevents a flickering by driving a fixing heater in a phase controlling at a fixed phase angle for predetermined duration when an image forming apparatus starts power supplying to the fixing heater.

Abstract: A power circuit including means for preventing the generation of an inrush current during the power circuit's initial operation without increasing the size of the power circuit is described. The power circuit comprises an output transistor for supplying a current from a power supply to an output terminal, and a differential amplifier for controlling the current supplied by the output transistor in such a manner as to regulate a voltage at the output terminal based on a preset reference voltage. A limiting transistor is provided as a source follower on a current path at the output stage of the differential amplifier. The gate potential of the output transistor is controlled using the source potential of the limiting transistor. Before the power circuit starts to operate, an operation controller charges a capacitor to control the gate potential of the limiting transistor so that during the initial operation of the power circuit, the capacitor is discharged by using a current source.

Abstract: The present invention provides a protection circuit for, and method of, sensing a transient condition and limiting a current, and a power supply having a filter incorporating the protection circuit or method. In one embodiment, the protection circuit includes: (1) a current-limiting component coupled between the filter and a return node, (2) a bypass switch coupled across the current-limiting component, (3) a load-current return switch series-coupled between an output of the power supply and the return node and (4) a control circuit that senses a transient condition in the power supply and controls at least one of the bypass switch and the load-current return switch.

Abstract: An electrical power supply (EPS) including a voltage regulator (SR1) and an inrush current limiter (ICL1) having a current limiting circuit (CL1) and a support capacitor (C1). Charging current spikes produced in particular when the electrical power supply (EPS) is switched on are limited by the current limiting circuit (CL1). The current limiting circuit (CL1) is connected in series with the support capacitor (C1), thus preventing load current from flowing through the current limiting circuit. A step-up converter circuit (SUC) is connected upstream of the current limiting circuit (CL1) with the particular purpose of increasing the voltage (V). An advantage of the arrangement is that, due to the step-up converter circuit (SUC), the support capacitor (C1) has considerably improved support characteristics with regard to the switching regulator (SR1).

Abstract: A current limiting circuit in which, when the input DC voltage is raised from zero volts to the reference voltage, an output DC flows through the connected load only when the value of the input DC voltage rises to a value above an undervoltage threshold value which is below the reference voltage.

Abstract: A power supply with a programmable voltage slew rate is disclosed for generating a regulated voltage at a predetermined set-point. The power supply includes a programmable current source for generating a controllable level of current flow and a capacitive element coupled to the current source. The capacitive element is responsive to the current flow to establish a reference voltage that varies linearly with respect to variations in the current flow. The power supply additionally includes a power device having a control element disposed in sensed communication with the reference voltage and an output for driving a load. The output is operative to generate an output voltage following that of the reference voltage.

Abstract: A power supply includes a diode bridge rectifier. The diode bridge rectifier output provides direct current to a primary capacitor. A current-limiting resistor is connected in series with the rectifier output and the primary capacitor. The current-limiting resistor acts to limit inrush current to the primary capacitor when the power supply is turned on. A triac is coupled in parallel with the current-limiting resistor. When charged, the primary capacitor provides a primary signal and primary current to a switched load, which includes a first winding of a transformer and a load switching device. The transformer also has a second winding connected in series with the triac's gate terminal. When the primary signal reaches a satisfactory level, the load switching device switches the load, causing current transients in the first winding. The first winding current transients, in turn, induce current in the second winding and in the triac gate terminal.

Abstract: A hard disk drive for supplying a power supply voltage by monitoring a power supply voltage and method of controlling the same. The hard disk drive includes a power supply monitor circuit for monitoring an initially supplied power supply voltage, and a controller for supplying a prescribed reference voltage to the power supply monitor circuit, and for controlling the power supply voltage generated when initially activating a spindle motor by varying a permissible variation level of the power supply voltage of the power supply monitor circuit.

Abstract: A controlled DC power supply for a refrigeration appliance is disclosed for reducing heat dissipation and power loss. The refrigeration appliance has AC-powered components, such as compressors and fans, and DC-powered components, such as relays and solenoids. The relays operate to supply AC power from an AC input to the AC-powered components. The relays are selectively activated or deactivated by the controller through enable signals in response to factors such as time and/or temperature. The power supply has an AC-to-DC power conversion circuit for converting AC power at an AC input to one or more DC power outputs for powering DC-powered components. When a group of DC-powered components powered by the same DC power output, such as a group of relays, do not require DC power, the controller selectively disables or reduces a portion of the AC-to-DC power conversion circuit to reduce power consumption and heat dissipation therein.

Abstract: The present invention teaches a variety of startup modes for operating a boost type switching power supply. A linear charging mode couples the input voltage directly to the output voltage, thereby precharging the output capacitor of the switching power supply. The linear mode serves to reduce inrush battery current and limit the stress voltage on the power switching devices. A pseudo-buck mode, preferably entered into after the linear mode has precharged the output capacitor, operates the boost type switching power supply in a manner providing power to the output essentially as a buck type switching power supply would. This results in continuous charging of the output capacitor, thereby reducing startup time and increasing power efficiency. The pseudo-buck mode also enables step-down voltage generation with boost type circuitry. A pseudo-boost mode facilitates a smooth transition between the pseudo-buck and traditional boost modes.

Abstract: Apparatus and method for limiting current in a direct voltage network of a HVDC power distribution system. A direct voltage network is connected to an alternating voltage network through a VSC-converter. At least one parallel connection including a semiconductor switching element is connected in series with the direct voltage network. A surge diverter is connected in parallel with the semiconductor switching element. During a high current condition in the direct voltage network, the switching element is switched off interrupting the current flow which is then diverted through the surge diverter which reduces the current flowing in the direct voltage network. By inserting a plurality of parallel connections, and selectively turning off a number of the semiconductor switching elements, a number of different levels of over current conditions in the direct voltage network may be controlled.

Abstract: A current limiter for a rectifier circuit includes a fixed resistor 50 and a positive temperature coefficient (PTC) resistor 100 connected in series across a control switch 70. The control switch is connected between a rectifier output and a smoothing capacitor 20. If the switch fails to operate, the PTC resistor heats up, increasing its resistance in the presence of an abnormal current. The increased resistance will limit the current supplied to the rectifier output terminals 40.

Abstract: For use with a protection circuit having an in-rush current control element that controls in-rush current into a power converter, a control circuit, a method of controlling the in-rush current control element and a power supply employing the control circuit and method are provided. In one embodiment, the control circuit includes: (1) a sensor, coupled to the in-rush current control element, that senses an in-rush current through the in-rush current control element and produces an intermediate signal and (2) a controller, coupled to the sensor and the in-rush current control element, that controls the in-rush current control element to limit the in-rush current when the intermediate signal exceeds a first reference current signal and to substantially interrupt the in-rush current when the intermediate signal exceeds a second reference current signal.

Abstract: A method and system for allowing a power supply circuit to limit inrush current and to use a small current specification switch. The power supply circuit comprises a transformer that receives a power signal from a primary circuit and supplies power of a selected voltage to a secondary circuit, to which a load is coupled. The primary circuit comprises a rectifier for providing a rectified power signal to the transformer, a power supply controller for controlling the transformer, and a small current specification switch coupled between a kick resistor and the power supply controller, where the kick resistor functions to activate the power supply controller when the circuit is first turned on.

Abstract: A semiconductor device drive circuit comprises first drive means for driving an IGBT, second drive means for driving the IGBT at lower speed than the first drive means, switch means for switching output of the first drive means and output of the second drive means for supply to a gate of the IGBT, and current decrease start point detection means for detecting a current decrease start point when a transition is made from a first period in which change in a collector current is moderate to a second period in which change in the collector current is abrupt when the IGBT is turned off. The switch means is operated so as to use the first drive means in the first period and the second drive means in the second period in response to output of the current decrease start point detection means.

Abstract: A dimmable fluorescent lamp including a feedback circuit for drawing sufficient current to maintain an appropriate charge across the buffer capacitor. A bypass capacitor provides a path for diverting a portion of the power which would otherwise be fed back to the buffer capacitor during low level dimming. Consequently, overboost voltages across the buffer capacitor during low level dimming are substantially reduced.

Abstract: In an overcurrent protection circuit, when a control section turns on a switch in response to a signal from a microcomputer so that power is supplied from a power source to an IC card, a signal controlling section prevents the overcurrent protection circuit from functioning even if a current greater than a predetermined level is detected by a current detecting section, until a voltage of the IC card is stabilized. When the control section turns off the switch in response to a signal from the microcomputer, the power supply from the power source to the IC card is stopped, thereby preventing a malfunction of the overcurrent protection circuit, even if the microcomputer goes out of control or malfunctions.

Abstract: This apparatus and method controls and limits the flow of in-rush current and maintains a supply voltage to a peripheral device during power surges. The apparatus and method essentially isolate and limit in-rush current flow to an in-rush circuit comprising a capacitive load and series resistor connected directly to the power bus at one end and to a reference potential at the other end. A switching device is coupled to the series resistor. A current sensing circuit is coupled to the series resistor. During initial start-up or "hot plugging" of the device, a control circuit turns "off" the switching device causing the load to be charged from the power bus through the resistive device for a pre-selected time interval, after which the switching circuit is turned "on" to bypass the resistive device and connect the load and the peripheral device to the power bus.

Abstract: A direct current (DC) powered process instrument start up circuit includes an energy storage device, a switching regulator circuit, a variable impedance circuit, and a voltage measurement circuit. The energy storage device is coupled between first and second power supply terminals. The switching regulator circuit is coupled to the energy storage device and has a regulated voltage output. The variable impedance circuit is coupled between the energy storage device and the first power supply terminal and has an impedance control input. The voltage measurement circuit has a measurement input coupled to the energy storage device and a measurement output coupled to the impedance control input.

Abstract: A switching regulator circuit using a common switch network on a single IC for providing step-up and step-down DC--DC conversion is provided. The switching regulator uses switched capacitor techniques and hence avoids EMI, parasitic and stability concerns particular to inductors and transformers. The converter circuit includes control circuitry for sensing the voltage differential between the input and output to determine whether step-up or step-down mode is to be used. The control circuitry also senses the voltage differential between the input and output and enables the minimum number of switch sections needed to fully regulate the output, using the highest switch resistance possible to minimize inrush current from the input to the output.

Abstract: A power supply unit has an output transistor and two resistors connected in series between a power source line and a ground potential point. The output electrode of the output transistor is connected to an output terminal. Between the output terminal and the ground potential point, a capacitor is connected. When a starting switch is turned on, the output transistor starts conducting. A current limiting circuit is also provided to limit the current that flows through the output transistor when it starts conducting. The current limiting circuit bypasses part of the output current of a comparator to the ground potential point.

Abstract: A large inrush of electrical current flow occurs during a short interval after switch closure, when power is applied to a conventional electronic ballast commonly used for fluorescent lighting. This inrush current flows as the main filter capacitor in the ballast charges to its steady state value. For a lighting circuit that contains a multiplicity of ballasts, the combined magnitude of the inrush is potentially large enough to cause contact failure of the switching device due to arcing and contact welding. The invention features a circuit for limiting inrush current having a current-limiting resistor that is active for a brief interval during startup. The resistor is subsequently bypassed from the principal current path by a switching transistor. The transistor is controlled by electrical signals normally present in conventional electronic ballasts. The advantage of the inventive circuitry is the use of only two inexpensive components to accomplish inrush current protection.

Abstract: An overcurrent breaking circuit includes a semiconductor switch inserted in a main current path; a current detector circuit for detecting a current passing through the main current path; a logic circuit for switching off the semiconductor switch when the current detector circuit detects a current exceeding a set value for an overcurrent level; a first unit for prohibiting the logic circuit from performing an operation for switching off the semiconductor switch even if the current detector circuit detects a current exceeding the set value for a first short time period immediately after the semiconductor switch is switched from a breaking state to a conductive state; and a second unit for prohibiting the logic circuit from performing an operation for switching off the semiconductor switch for a second short time period even if the current detector circuit detects a current exceeding the set value when the semiconductor switch remains in a conductive state.

Abstract: A motor starter circuit providing recovery of the energy trapped in the motor windings when the supply voltage and current have opposite polarities by selectively controlling actuation of a plurality of high speed switches. The circuit, for use with a multiphase motor and power source that provides positive and negative voltage alternations which result in the generation of a load current in the motor having positive and negative alternations, includes a plurality of switch-diode combinations electrically configured such that for a given pair of supply voltage/load current polarities, only one diode of each combination may be forward biased.

Abstract: A power supply inrush current control circuit includes a current-limiting resistor connected in series with a first relay, a second relay connected in parallel with the current-limiting resistor and first relay, a power factor correction stage connected in series with the parallel combination of first relay and current-limiting resistor, and second relay, a holdup capacitor connected to an output of the power factor correction stage and a DC/DC converter connected to the output of the power factor correction stage. A first timer is connected to the second relay, a second timer is serially connected to the first timer and to the power factor correction stage, and a third timer is serially connected to the second timer and to the DC/DC converter.

Abstract: The present invention relates to a switching device for selecting a voltage between an a.c. voltage and a d.c. voltage using the ground as a reference, meant to be controlled by a two-state signal, using the ground as a reference and of the same sign as the d.c. voltage, including means for adjusting the turn-on time of a switch in the selection of the d.c. voltage.

Abstract: This apparatus and method controls and limits the flow of in-rush current to a peripheral device coupled to a main power supply unit through a power bus and a ground bus. The apparatus and method essentially isolate and limit in-rush current flow to a capacitive load until operational current flow occurs to the peripheral device. A switching device is coupled to the power bus and the ground bus through a load. A resistive device is coupled to the power bus and the ground bus through the load. A control circuit is connected to the switching device. During initial start-up or "hot plugging" of the device, the control circuit turns "off" the switching device causing the load to be charged from the power bus through the resistive device until a predetermined condition occurs whereupon the switching circuit is turned "on" to bypass the resistive device and connect the load and the peripheral device to the power bus.

Abstract: A new and improved rectifier power supply operates in a low voltage mode of operation and a high voltage mode of operation without user intervention and includes an inrush current limiting device that is in circuit during a predetermined period of time during start up and bypassed during steady state operation in the low voltage mode of operation. In the high voltage mode of operation, when inrush current is reduced relative to the low voltage mode of operation, the inrush limiting device always remains in circuit. As there is no power loss associated with the inrush limiting device in the steady state low voltage mode of operation, the power supply has an improved efficiency and reliability and a reduced cost as it can be rated for continuous operation only in the high voltage mode of operation when the input current is lowest and device dissipation is least.

Abstract: A power supply control circuit is provided for preventing sudden inrush current which is produced when a power switch of an electronic device is turned on. The power supply control circuit includes a main power supply which receives an alternating current (AC) voltage and supplies a first predetermined voltage to a system and outputs a second predetermined voltage independent of an amplitude of the AC voltage, a subsidiary power supply which receives the second predetermined voltage and outputs a power voltage; and a controller which is operated by the power voltage and outputs a switch control signal to control a flow of the first predetermined voltage of the main power supply.

Abstract: An electronic power supply circuit (50) that includes a rectifying circuit (14), a boost converter (16), an in-rush current reduction circuit (52), and a bulk capacitor (18). The in-rush current reduction circuit (52) includes an in-rush current limiting resistor (54) and a bypass capacitor (56) that are connected in parallel with each other. An improved version of the in-rush current reduction circuit (52) includes a bypass diode (58) connected in parallel with the in-rush current limiting resistor (54) and bypass capacitor (56) which is oriented to provide a path for current flowing out of bulk capacitor (18). One particular application of the disclosed circuit is for use in an electronic ballast for fluorescent lamps.

Abstract: A device and associated method for limiting a current surge in a capacitor connected to the output of a rectifying bridge having its input connected to an a.c. voltage, the bridge being a composite bridge and being associated with means for synchronizing the turning-on of the bridge from zero crossings of the voltage of the a.c. power supply.

Abstract: A system on an aircraft that eliminates hot-swapping of circuit boards to prevent damage to the circuit board connector interfaces. The system supplies power to a circuit card only when there is an effective coupling between a circuit card connector and an opposite mating connector. A power control circuit responds to a card present signal which indicates when the circuit card connector is coupled to the opposite mating connector. A logic circuit converts the card present signal to a power supply enable signal. A main power supply receives the power supply enable signal and provides power to the circuit card only when the circuit card connector and the opposite mating connector are appropriately coupled.

Abstract: A surge suppression circuit for gradually charging a capacitance of a device being hot plugged into a system, such as a disk drive being hot plugged into a RAID system. Without reliance on a permanently turned-on series element, such as a pass transistor, the surge suppression circuit uses a trigger circuit in combination with either a current limiting circuit or a slew rate control circuit. The current limiting circuit relies on a current sensing resistor in combination with a transistor that turns on when a voltage reaches a certain level across the current sensing resistor. The slew rate control circuit relies on a feedback mechanism that includes a capacitor and a resistor for maintaining a substantially constant rate of charging the capacitance of the device being hot plugged.

Abstract: A circuit unit to be inserted or removed by live wire work into or from a system having a plurality of circuit units and a power source to supply power to the plurality of circuit units includes a first circuit to supply power to the circuit unit from the power source when the circuit unit is inserted into the system; and a second circuit to supply power to the circuit unit in normal operation after the circuit unit is inserted into the system. The first circuit nearly stops supplying power about the time when the second circuit starts supplying power and by this arrangement, it becomes possible to vary the timing of inrush currents attending on a supply of power from a plurality of power sources. A removal permission indicator can be installed which can be turned on by a voltage supplied from the power source under a condition that permission to remove the unit has been issued.

Abstract: An apparatus for retrofitting an HID light fixture is described in several embodiments. The apparatus is coupled in series with the secondary winding and the HID lamp of the HID light fixture. A first retrofit capacitor replaces the light fixture capacitor of the HID light fixture. A switching device is coupled in series with a second retrofit capacitor and couples the first and second retrofit capacitors in parallel in response to a normal power mode control input so that the HID lamp provides normal intensity lighting at normal power. The switching device uncouples the first and second retrofit capacitors from being in parallel in response to a low power mode control input so that the HID lamp provides low intensity lighting at low power.

Abstract: An input protection circuit for an instrumentation system which receives an input signal and which is adapted for providing a current and/or voltage limited version of the input signal to a measurement system. The input protection circuit of the present invention utilizes an optocoupler and also includes circuitry which protects the optocoupler from damage if an over-voltage condition is detected. The input protection circuit includes a comparator which is operable to disable or turn off the optocoupler when the current limited version of the input signal exceeds a preset value. The input protection circuit preferably includes a resistor connected in parallel with the optocoupler. which provides an alternative path for the input signal when the optocoupler has been cut off. The present invention thus provides an improved input protection circuit which also protects the optocoupler from damage if an over-voltage condition is detected, but still allows the input signal to be measured during this time.

Abstract: In an active plug-in circuit, a mode setting section sets either a plug-in mode or a regular mode, depending on the power source voltage of a package. When the plug-in mode is set, a power consumption controller maintains an electronic circuit built in the package in a low power consumption mode. After the power source voltage of the electronic circuit has been stabilized, the mode setting section sets the regular mode. The circuit reduces the variation of power source current to occur when a power source pin mounted on a package connector is connected to the corresponding terminal of a mother board connector and on the transition from the plug-in mode to the regular mode.

Abstract: An electrical device for controlling heater has a power supply connected in parallel with a heater or the like. A reducer such as a resistor is provided for reducing electrical current flowing into the heater. A switch can be operated by a controller to connect the heater to the electrical power supply or to connect the heater and the reducer in series to the electrical power supply. The controller operates the switch to disconnect the heater from the electrical power supply after operating the switch to connect the heater and the reducer in series to the power supply. Thus, even at a timing when the load of the power supply is the maximum and the capacitor charging current to the power supply increases, the change in the current through the heater becomes gradual, and the harmonic components in the current do not increase by using the reducer even if the timing of the maximum load overlaps with the timing of the stop of power supply to the heater.

Abstract: A power conversion circuit for providing a rectified supply voltage to an output capacitor. The power conversion circuit includes: a rectifying circuit; a power factor correction circuit; a resistor for limiting inrush current, the resistor being operatively connected between the rectifying circuit and the power factor correction circuit, the capacitor being connected to the output of this power factor correction circuit; and a switch that is operatively connected for short circuiting the resistor, the output capacitor being connected across the output terminals of the power factor correction circuit, the switch being activated when the output voltage of the power factor correction circuit exceeds a predetermined threshold.

Abstract: To substantially reduce harmonic distortion and improve the power factor of n operating circuit for a fluorescent lamp, a smoothing circuit (G) is interposed between the outputs from a power rectifier (GL) and an inverter (WR) supplying the fluorescent lamp (L) with high-frequency energy. The smoothing circuit includes a two electrolytic capacitor (C1, C2)--three diode (D1, D2, D3) network, which is so connected, and the diodes so polarized that, during charging of the capacitors, a series circuit is established with one (D2) of the three diodes in series with the two capacitors. For discharge of the capacitors to supply the inverter when the rectified voltage is lower than the capacitor voltage, the two capacitors (C1, C2), through the other two diodes (D1, D3), are connected in parallel to supply the inverter. To substantially reduce harmonic distortion to less than about 30% and improve the power factor of the circuit to above 0.

Abstract: A device for detecting the short circuiting of the switches of a converter circuit arrangement is disclosed. The device is magnetically coupled to the current limiter coil and comprises a conductor loop which is preferably arranged at the end of the current limiter coil. On short circuiting, a voltage is induced in the conductor loop. This voltage is converted in a detection circuit into a voltage pulse and fed to an evaluation logic circuit. In the evaluation logic circuit, the period of the induced voltage pulse is evaluated and, if appropriate, load-relieval actuation is initiated.

Abstract: A power control circuit is provided for coupling a load to a power source. It includes a transistor for coupling said load to the power supply through the transistor dependent upon a control voltage applied to a control terminal of the transistor, a charge pump circuit having its output connected to the transistor control terminal to apply a controlled turn on signal to the transistor when the charge pump is activated, wherein the controlled signal gradually increases until the transistor is biased into its fully on state.

Abstract: A lamp protection device includes a circuit to prevent a lamp from being switched on at full line voltage and which provides for the gradual heating of the filament to reduce the expansion rate of the filament. The circuit is connected to a switched alternating current power source and to an incandescent bulb. The circuit includes two silicon controlled rectifiers which are connected in reverse parallel configuration. One of the silicon controlled rectifiers being connected to a capacitor to prevent the full sinusoidal AC current from reaching the lamp until a time delay has expired after the lamp is turned on. A reference switch is connected to the other silicon controlled rectifier to permit the bulb to be turned on only when the AC voltage crosses zero.

Abstract: A zero inrush visual or visual/audible alarm circuit which includes a transistor switch and resistor combination connected in series with a storage capacitor provides inrush resistance for a period following initial power-on. The transistor switch may be controlled by a microcontroller or a simple timer.

Abstract: A power supply system including a thermal current limiting device operating due to high temperatures. At predetermined temperatures, the device acts to incrementally control the output of a power supply. An implementation of the device may be found in a voltage or power regulator wherein a constant output voltage or power is desired. As temperature increases, the power supply system is not switched off, rather current output is adjusted in a controlled manner thereby eliminating the need for the device to be entirely shut down for a time period. A back-up battery is used to provide supplementing current needed by the load.

Abstract: A field-effect transistor incorporates a diode which is disposed between a battery power source and an inverter. A rush-current suppressive starting circuit is provided in a stage anterior to the field-effect transistor. The transistor is shifted to its conducting state while the on-resistance of the transistor is gradually lowered to thereby limit a charging current to a power smoothing capacitor. In an off-state of a main switch, a charge stored in the current smoothing capacitor is released therefrom via a stabilized power circuit and a controller which is a power load to the circuit.

Abstract: A zero power circuit includes an upper power supply voltage pad, battery pad, a power control circuit, and a suppression circuit. The power control circuit provides power to the zero power circuit by switching between the battery pad and the upper power supply voltage pad. The suppression circuit is connected in series between the power control circuit and the battery pad. The suppression circuit includes a resistor connected in series between the battery pad and the power control circuit, wherein current flowing through the transistor during a latch condition causes the voltage to drop across the resistor, suppressing the latchup condition to the battery pad. The suppression circuit also includes a transistor connected in parallel with the resistor, the transistor having a gate, wherein a first signal applied to the gate turns off the transistor and a second signal applied to the gate turns on the transistor, wherein the resistor is shorted when the transistor is turned on.

Abstract: An UPS system provides a true input power walk-in. The UPS adjusts the level of power supplied from an input port to a load on an output port as a function of a level of current of a power supplied from a backup power source to the load on the output port.

Abstract: Main power supply circuit includes an inrush current suppressing circuit serially connected between its rectifying circuit and a load, this inrush current suppressing circuit being composed of a current limiting resistor and an FET switch that is serially connected to this resistor. An auxiliary power supply circuit provides power for a control circuit of the main power supply circuit, and, after the power supply switch is closed, a delay circuit monitors rise of a charge voltage of a smoothing capacitor within the main power supply circuit as well as rise of control circuit voltage of the auxiliary power supply circuit and establishes a delay time. After the elapse of the delay time, the FET switch is turned ON and the inrush current suppressing circuit is closed. The inrush current suppressing circuit is then short circuited within a short time period and the load operation is continued.