Abstract: A switch mode power supply (SMPS) converter is periodically run backwards by using a synchronous switch instead of the normally used commutating diode. By running the SMPS converter backwards the SMPS output capacitor can be discharged very quickly to provide a fast turn off of (no current through) the LED's, thereby solving the color shift problem. This enables positioning the output voltage of the SMPS up or down by actively charging or discharging the bulk output capacitor. Having the capability of actively charging or discharging the bulk output capacitor allows generation of a current source comprising substantially square, e.g., substantially full current when on and substantially no current when off, current pulses that are preferable for driving LED lighting applications.

Abstract: A circuit regulator is used to generate a pulse-width-modulation signal, so as to control a power to be selectively input or not input to a primary side of a switching power supply. The circuit regulator includes a synchronous timing pulse generation circuit, outputs a starting pulse after performing signal process of time delay, timing pulse regulation, and synchronization control on a pulse-width-modulation signal and a discharging time signal of a secondary side, and accordingly effectively controls a pulse starting time of the pulse-width-modulation signal. Therefore, the synchronous timing pulse generation circuit can be applied to the circuit regulator, so as to further effectively prevent an inductor current of the switching power supply from entering a Continuous Conduction Mode (CCM).

Abstract: A switching power controller circuit comprises a first terminal pin for a high potential of a power supply for the controller circuit, a second terminal pin for providing output of switch drive signals and for receiving feedback signals, and a third terminal pin for receiving external current signals and for a low potential of the power supply. The switching power controller further comprises a clock generator, a pulse width modulation (PWM) generator, a reference generator, a power switch driver, a feedback signal sampler, a PWM comparator and a floating sampler.

Abstract: A method of operating a DC-DC converter according to the current mode control is provided. A current measuring signal for determining a turn-off time of a converter switching element is supplied to a PWM controller and a voltage that is proportional to the current measuring signal is compared by a comparator to a reference voltage. When the reference voltage is exceeded, the converter switching element is turned off.

Abstract: A control circuit and method are provided for a flyback converter converting an input voltage to an output voltage, to compensate for an entry point of a burst mode of the flyback converter, so that the entry point is not affected by the input voltage, and audible noise resulted from a higher input voltage is reduced without impacting the light load efficiency of the flyback converter.

Abstract: An example power supply in accordance with the teachings of the present disclosure includes a switch, an energy transfer element, a controller, an input filter, and a switch clamp circuit. The energy transfer element is coupled to the switch and the controller is coupled to control the switch to regulate an output of the power supply. The input filter is coupled to receive an input voltage of the power supply and includes a first input filter capacitor coupled to a node and a second input filter capacitor coupled to the node. The switch clamp circuit is also coupled to the node to clamp a voltage across the switch in response to a voltage at the node.

Abstract: In one embodiment, a quasi-resonant power supply controller is configured to select particular valley values of a switch voltage to determine a time to enable a power switch. The valleys values are selected responsively to a range of values of a feedback signal.

Abstract: Switching mode power supplies and associated methods of control are disclosed herein. In one embodiment, a method for controlling a switching mode power supply includes determining whether the switching mode power supply is in a burst mode. If the switching mode power supply is in the burst mode, the method includes recording a switching time with and without switching pulses to obtain a current value of an equivalent frequency and generating a peak current limit that decreases as a load becomes lighter based on the equivalent frequency, thereby maintaining the equivalent frequency at the current value above an audible range. If the switching mode power supply is not in the burst mode, the method includes continuing to monitor whether the switching mode power supply is in the burst mode.

Abstract: An offline AC-DC converter circuits including an overvoltage detection module, a current limiting module, a PWM module and a switch control module coupled to the above modules. The overvoltage detection module, the current limiting module and the PWM module share a common input terminal. The sampled current signal and the sampled voltage signal are provided at the common input terminal by way of time-division multiplexing. With the time-multiplexed terminal, overvoltage detection for the output voltage is performed during the period when the power transistor is cut off and a current through the power transistor is detected during the period when the power transistor conducts. The two signals are input by way of time-division multiplexing, which are not affected by each other. Accordingly, overvoltage in the output voltage can be precisely detected without additional terminals, and thus the overvoltage can be controlled.

Abstract: An interleaved flyback converter device with leakage energy recycling includes: two flyback converters and an input power. Each flyback converter includes a capacitor, a switch, two diodes, and a transformer. The input power is connected to the capacitors of the two flyback converters respectively. By using the capacitors as input voltage, the two flyback converters are provided with lower voltage rating. The diodes are used to recycle leakage energy directly, and to clamp voltage on power components. Therefore, in addition to enhancing efficiency via recycling leakage energy, the two flyback converters have lower switching losses due to lower switching voltage.

Abstract: An example controller includes a comparator coupled to receive a feedback signal representative of an output of the power converter. A counter is coupled to receive an output of the comparator and a feedback sampling signal. The counter is coupled to sample the output of the comparator in response to the feedback sampling signal. A state machine is coupled to receive a feedback time period signal. The state machine is coupled to control switching of the power converter according to one of a plurality of operating conditions in response to the counter and the feedback time period signal. A period of the feedback time period signal is substantially greater than a period of the feedback sampling signal. The state machine is coupled to be updated in response to the feedback time period signal.

Abstract: The present invention relates to an adapter power supply, which includes a switching unit for switching a DC voltage; a transformer which has a primary winding connected to the switching unit, a secondary winding electromagnetically coupled to the primary winding, and an auxiliary winding electromagnetically coupled to the primary winding; a rectifier for rectifying a voltage outputted from the transformer; and a controller for controlling the switching unit to operate according to the PWM scheme in a normal operation mode, and to operate according to a quasi-resonant scheme in a standby mode, by detecting information of a load connected to the rectifier.

Abstract: An oscillator with time-variant frequency deviation for a power supply includes a signal generator for generating a first signal according to a clock signal and a comparing unit for adding an offset to at least one of the first signal and a threshold voltage corresponding to the first signal and for comparing the first signal and the threshold voltage after completion of the offset adding, to generate the clock signal whose frequency deviates with variation of the added offset.

Abstract: A flyback DC-DC converter is disclosed herein. The flyback DC-DC converter includes a transformer, a voltage divider and a controller. The transformer receives a DC input voltage and converts the DC input voltage to a DC output voltage. The voltage divider is coupled to a first secondary winding of the transformer, and generates a feedback signal indicative of the DC output voltage. The controller is coupled to the transformer via an input switching circuit and controls the input switching circuit to regulate the DC output voltage according to the feedback signal. A skip operation is triggered if the voltage of the feedback signal is higher than a preset reference voltage at the end of a turn-off period of the input switching circuit, and the voltage of the feedback signal is changed to zero during the skip operation.

Abstract: A digital dynamic delay modulator and the method thereof are applied to a flyback converter. A first input voltage signal from the flyback converter is received and compared with a threshold voltage to determine whether a counting condition is matched. When the counting condition is matched, an integer predetermined count number is counted to determine a delay time. After finishing the counting, a first output signal is generated to turn on a switching device for the flyback converter. The slope of the first input voltage signal is detected when the switching device is turned on, and the slope is used to adjust the count number with integer increment/decrement. Therefore, the delay time for switching the flyback converter can be precisely controlled in digital and dynamic manner.

Abstract: A digital device generates a fixed duty cycle signal with an internal oscillator after a Power-On-Reset (POR). This fixed duty cycle signal is output on a signal pin that normally is used for a PWM control signal. The fixed duty cycle signal is used to stimulate the voltage generation circuits so as to power up the digital device for initialization thereof. Once the digital device has powered-up and initialized, the digital device switches over to normal operation for control of the power system.

Abstract: A secondary circuit of a flyback power converter has a resistor network to monitor the output current of the flyback power converter, so as to generate a voltage to apply to a base of a bipolar junction transistor to thereby provide a collector signal for output feedback. The resistor network has a temperature-dependent resistance to compensate the temperature dependence of the base-emitter voltage imparted to the output current and thereby stable the output current.

Abstract: During a soft start period at the time of startup, a PWM control is carried out. After the soft start period ends, the PWM control is converted into a frequency control, so that stress of a switching element is suppressed and the audible oscillation frequency is removed. As a result, it is possible to obtain a switching power supply device having high power conversion efficiency.

Abstract: System and method for regulating an output voltage of a power conversion system. The system includes an error amplifier coupled to a capacitor. The error amplifier is configured to receive a reference voltage, a first voltage, and an adjustment current and to generate a compensation voltage with the capacitor. The first voltage is associated with a feedback voltage. Additionally, the system includes a current generator configured to receive the compensation voltage and generate the adjustment current and a first current, and a signal generator configured to receive the first current and a second current. The signal generator is further configured to receive a sensing voltage and to generate a modulation signal. Moreover, the system includes the gate driver directly or indirectly coupled to the signal generator and configured to generate a drive signal based on at least information associated with the modulation signal.

Abstract: A power supply may comprise a pulse-width-modulation (PWM) controller; a synchronous rectifier having a forward metal oxide field effect transistor (MOSFET) and a catch MOSFET; a forward gate driver; a catch gate driver; and the PWM controller connected so that a low output of the PWM controller facilitates operation of the catch MOSFET and so that the low output precludes operation of the forward MOSFET. The power supply may include a self powered synchronous rectifier that may be constructed with delay times that are independent of lot-to-lot and temperature-related timing variations of MOSFETS.

Abstract: A start-up circuit for a power adapter and method of operating the same. In one embodiment, the power adapter includes a start-up circuit configured to provide an initial bias voltage for the power adapter. The power adapter also includes a crowbar circuit configured to turn on the start-up circuit upon loss of an ac mains voltage supplied to the power adapter.

Abstract: A flyback power converter with multiple outputs has a transformer, a low-voltage output circuit, a high-voltage output circuit, and a secondary side post regulator circuit is provided. The transformer has a first secondary winding and a second secondary winding. The low-voltage output circuit has a low-voltage output capacitor and a rectifier unit, and is coupled to the first secondary winding to generate a low voltage output. The high-voltage output circuit has a high-voltage output switch and a high-voltage output capacitor, and is coupled to the second secondary winding to generate a high voltage output. The secondary side post regulator circuit adjusts on-time of the high-voltage output switch according to a feedback signal to have the energy stored in the high-voltage capacitor transmitted to the low-voltage capacitor to lower down the voltage level of the high output voltage.

Abstract: A light-emitting diode driver circuit includes: a first-rectifier circuit to output a first-rectified voltage; a transformer including primary and secondary coils and an auxiliary coil inductively coupled to the primary or secondary coils, the primary coil being applied with the first-rectified voltage; a transistor connected in series to the primary coil; a second-rectifier circuit to output a second-rectified voltage obtained by rectifying a voltage generated in the auxiliary coil; a capacitor to be charged with the second-rectified voltage; and a control circuit to control on and off of the transistor based on a charging voltage of the capacitor so that the charging voltage becomes equal to a predetermined voltage, the secondary coil outputting a voltage that varies with a frequency corresponding to a frequency of the first-rectified voltage and that corresponds to a turns ratio between the primary and secondary coils, as a voltage for driving a light-emitting diode.

Abstract: During a soft start period at the time of startup, a PWM control is carried out. After the soft start period ends, the PWM control is converted into a frequency control, so that stress of a switching element is suppressed and the audible oscillation frequency is removed. As a result, it is possible to obtain a switching power supply device having high power conversion efficiency.

Abstract: An isolated primary circuit regulator is applied to a primary side of a transformer of a power supply. The isolated primary circuit regulator outputs a switching signal, and switches the transformer by using the switching signal, thereby stabilizing an output current. The isolated primary circuit regulator includes a discharge time detector, an oscillator, a pulse width modulator and a control circuit. The discharge time detector is used for detecting a discharge time of a switching current generated at a secondary side of the transformer. The oscillator is used for generating an oscillation signal. The control circuit is used for outputting an adjustment signal. The pulse width modulator outputs a switching signal according to the oscillation signal output by the oscillator and the adjustment signal output by the control circuit. The switching signal has a duty cycle and a frequency corresponding to the oscillation signal and the adjustment signal.

Abstract: A power conversion apparatus and an over current protection (OCP) method thereof are provided. The OCP method includes generating a pulse-width-modulation (PWM) signal according to a loading status of an electronic device, so as to switch a power switch in the power conversion apparatus and thus making the power conversion apparatus providing an output voltage to the electronic device; generating an OCP reference signal with variable slope according to a feedback signal related to the loading status of the electronic device and a system operation voltage of a PWM controller chip in the power conversion apparatus that is used for generating the PWM signal; and comparing a sensing voltage corresponding to a current following through the power switch on a resistor, and the OCP reference signal with variable slope to determine whether to activate an OCP mechanism to control the PWM controller chip whether to generate the PWM signal.

Abstract: In order to convert an input power to one or more DC power levels that are provided to an output load, some aspects of the present disclosure relate to techniques for driving a switching regulator as a function of a pulsed voltage signal. In particular, this pulsed voltage signal is provided substantially at a target frequency, but exhibits frequency jitter that causes the pulsed voltage to vary slightly from the target frequency in time. The frequency jitter has a frequency range that varies as a function of the output load.

Abstract: Current control method and apparatus are disclosed. A current limiter is coupled to a switch connected in series with an energy transfer element of a power supply. The current limiter detects a current flowing through the switch and, when the current exceeds a current limit signal, turns off the switch. A limit signal generator provides the current limit signal, detects the maximum current value of the current, and updates the current limit signal according to the maximum current value and an ideal current limit value.

Abstract: Switching mode power supplies (SMPS) that can operate in a control mode for a normal load condition and operate with a burst-mode controller for a light load condition are disclosed herein. In one embodiment, a method for controlling the switching mode power supply includes when the load is in a light load condition, the switching mode power supply is controlled by a burst-mode controller.

Abstract: An adaptive pulse width control power conversion device includes a pulse width adjustable pulse frequency module (PFM) control circuit, a pulse width modulation (PWM) control circuit, a PWM/PFM switching unit, a switching circuit, and a load status detection circuit. When the power conversion device is to be switched from a PWM mode to a PFM mode, pulse width of a series of PFM control signals is sequentially adjusted from a low value to a high value according to a predetermined pulse width increment until an optimum pulse width is determined and thereafter, an output voltage is supplied to a load in the PFM mode, whereby ripple of output voltage in the PFM mode can be improved and improved stability of output of the power conversion device is realized.

Abstract: An ultralow no-load conduction loss DC converter includes a DC power source, a transformer having a first winding, a first MOSET and a PWM controller at the primary side and a second winding, a third winding, a drive control unit, a rectifier unit and a second MOSFET at the secondary side. The second MOSFET, the drive control unit and the rectifier unit constitutes a combination circuit electrically coupled between one end of the second winding and one end of the third winding. The second MOSFET has set therein a body diode. The second winding and the second MOSFET forms a combination circuit electrically connected to a load. Thus, the decision to turn off the drive control unit is made at the secondary side so that non-load conduction loss can be minimized.

Abstract: A system including a switch configured to supply power to a load. A first comparator is configured to compare a first current through the switch to a first threshold. A second comparator is configured to compare the first current through the switch to a second threshold. The second threshold is greater than the first threshold. A current control module is configured to turn off the switch (i) for a first duration in response to the first current through the switch being greater than or equal to the first threshold and (ii) for a second duration in response to the first current through the switch being greater than or equal to the second threshold. The current control module is configured to adjust the second duration based on a difference between an estimated current through the load and a desired current through the load.

Abstract: A controller for use in a power supply includes a clock coupled to output a clock signal. The clock signal determines a frequency. A modulator is coupled to receive the clock signal. The clock signal is divided into N cycles within the power supply. N is an integer greater than one. The modulator is coupled to receive N feedback signals from N output circuits during each respective one of the N cycles to control conduction times of a primary switch during each respective one of the N cycles to regulate N outputs of a power supply. Each of the N feedback signals is representative of a respective one of N output voltages of a respective to one of the N outputs of the power supply.

Abstract: A frequency limitation method used in quasi-resonant control of a switching regulator is disclosed. The switching frequency is limited through setting a minimum time limit, such as a minimum switching period or a minimum OFF time. The minimum time limit may be a first time limit or a second time limit. The minimum time limit is changed into another value if the minimum voltage point approaches the minimum time limit point, so as to eliminate the audible noise.

Abstract: A charging device for charging a battery pack, having a control circuit for a switched-mode power supply transformer assigned to the charging device, the transformer having at least one primary winding switchable using a power switch and at least one first secondary winding for generating an electrical output voltage for charging the battery pack, the output voltage having a first amplitude which is predefinable by a control unit and adjustable using a first voltage limiting control loop. The transformer has at least one second secondary winding for generating at least one electrical auxiliary voltage having a second amplitude which is predefinable by the control unit and adjustable using a second voltage limiting control loop in order to at least reduce an energy feed assigned to an operation of the control circuit from the primary winding to the secondary windings in a standby mode of the control circuit.

Abstract: Disclosed are a switch controller, a switch control method, a converter using the same, and a driving method thereof. A first voltage is generated by using a voltage that is input to an input terminal, and a soft start signal is generated by using the first voltage during a soft start duration. A switching operation is controlled by using the soft start signal during the soft start duration.

Abstract: A novel switching hysteretic power converter is presented. The converter includes the generation of a synthetic ripple signal and a feedback network to combine a signal in phase with the inductor current with a signal proportional to the regulated output voltage. The presented approach provides a switching boost converter with a much simpler control method with respect to conventional inductive boost power converters. The hysteretic control provides stable operation in all conditions with excellent load and line transient response. Furthermore the hysteretic control allows high frequency switching, reducing the size and cost of the passive components. The presented converter includes the Discontinuous Conduction Mode of operation to achieve very high efficiency at light loads. The presented approach can also be applied to buck switching power converters with excellent performance in terms of transient response, stability, efficiency and operation at high switching frequencies.

Abstract: A control device for regulating the constant output current of a flyback converter, the control device adapted to control the on time period and the off time period of a primary winding switch and including a first circuit adapted to multiply a first signal representative of current flowing through the primary winding and a second signal representative of an input voltage and outputting a signal representative of the multiplication, a second circuit adapted to compare the output signal of the first circuit and a third signal representative of the direct output voltage, the control device determining, on the basis of the output signal of the second circuit, the on time period and the off time period of the switch so that the output signal of the first circuit is equal to the signal representative of the direct output signal to have the output current of the flyback converter constant.

Abstract: A flyback DC-DC converter is disclosed herein. The flyback DC-DC converter includes a controller, an input switching circuit, a transformer and an output switching circuit. The input switching circuit is controlled by the controller and thus controls power supply to the transformer. The transformer is equipped with a first secondary winding to provide the output voltage, a second secondary winding that forms a feedback loop together with a voltage divider, and a third secondary winding to control the output switching circuit.

Abstract: A Buck converter may include an input for connecting a DC voltage source; an output for connecting an LED; and a diode, an inductor and a main switch; wherein the diode and the main switch are coupled in series, wherein the inductor is coupled between the connecting point for the diode and the main switch, and a first output connection, wherein the converter further includes: a first auxiliary switch supplied with a first voltage; and a second auxiliary switch supplied with a second voltage, wherein the first auxiliary switch and the second auxiliary switch are coupled to the main switch such that the first voltage stipulates the switch-off time for the main switch and the second voltage stipulates the switch-on time for the main switch.

Abstract: A buck converter for providing a current for an LED includes an input for connection of a DC voltage source; an output for connection of the LED; and a Buck diode, a Buck inductor and a Buck main switch which has a control electrode, a working electrode and a reference electrode. The diode and the main switch are coupled in series, wherein the connecting point between the diode and the main switch is coupled to the second output connection. The converter includes: an auxiliary winding which is coupled to the inductor and has a connection which is coupled to the second input connection and a connection which is coupled to the control electrode of the switch, wherein the auxiliary winding is coupled to the inductor such that, when current is flowing through the switch, a current is provided through the auxiliary winding to the control electrode of the switch.

Abstract: Embodiments of the invention provide a DC/DC converter. The DC/DC converter includes a transformer, a switch controller and a driver controller. The transformer has a primary winding coupled to a power source, a first secondary winding provides a first output voltage to a first load, and a second secondary winding provides a second output voltage to a second load. The switch controller is coupled to the primary winding and controls a first switch coupled to the primary winding to control input power to the primary winding and to regulate the first output voltage based on a power requirement of the first load. The driver controller is coupled to the second secondary winding and generates a pulse modulation signal to alternately turn on and turn off a second switch coupled to the second secondary winding to regulate the second output voltage based on a power requirement of the second load.

Abstract: We describe a switch mode power supply (SMPS) current regulation system comprising: a current sense signal input sensing a primary current of the SMPS; a voltage sense input to receive a voltage sense signal from a primary or auxiliary winding; a switch drive signal input to receive a drive signal; a timing signal generator coupled to said voltage sense input and to said drive signal input to generate a timing signal T0 indicating a duration of a period for which current is flowing through said primary winding and a timing signal T1 indicating a duration of a period for which current is flowing through said secondary winding; and a regulator to provide an output current regulation signal responsive to an average of the current sense signal multiplied by a ratio of T1 to T0, and wherein T0 and/or T1 are generated responsive to the voltage or current sense signal.

Abstract: In a switching power converter, PWM mode and PFM mode are separated into two independent control sections with the control voltage range in each control section determined independently. Each of the PWM and PFM modulation modes cannot operate continuously beyond its boundaries, thereby forming a control gap between the two control sections within which no continuous operation is allowed. In order to supply a load condition within the control gap, the power supply operates at the two boundaries of the control gap. Transition between PWM and PFM modes occurs fast, with low output voltage ripple. No limitation needs to be imposed on the control voltage range in each of the PWM and PFM control sections, because the control parameters in the PWM and PFM control sections need not be matched to one another, due to separation of the PWM and PFM modes by the control gap.

Abstract: A switching power supply device includes: a transformer that has a primary winding and a secondary winding; a switching element connected to the primary winding of the transformer; a control circuit that controls the switching element to be turned on/off in a case where a voltage is inputted to the primary winding of the transformer, and thereby induces a voltage in the secondary winding of the transformer; and a rectifying/smoothing circuit that rectifies and smoothes the voltage induced in the secondary winding of the transformer, and outputs the rectified and smoothed voltage to a load.

Abstract: A switching power converter detects low load conditions based on the ratio of a first peak current value for peak current switching in constant voltage regulation mode to a second peak current value for peak current switching in constant current regulation mode. The power supply load is considered to have a low load if the ratio is lower than a predetermined threshold. Once a low load condition is detected, the switching frequency of the switching power converter is reduced to a level that minimizes switching loss in the power converter. In addition, the switching power converter also adjusts the switching frequency according to the sensed input line voltage. An offset is added to the switching period to reduce the switching frequency of the switching power converter, as the input line voltage is increased.

Abstract: An example controller for use in a power supply regulator includes a switch signal generator, a modulation circuit, and a multi-cycle modulator circuit. The modulation circuit modulates the duty cycle of a pulse width modulated switching signal to provide a fixed peak switching current in the switch during light load conditions and a variable peak switching current during load conditions other than the light load condition. The multi-cycle modulator circuit enables the switch signal generator to provide a switch signal uninterrupted if the load condition is other than the light load condition and disables the switch signal generator for a first time period and then enables the switch signal generator for a second time period when the load condition is the light load condition. The multi-cycle modulator circuit adjusts the first time period in response to the feedback signal to regulate the output.

Abstract: A switching DC to AC power converter includes an automatic zero voltage switching (ZVS) mode controller. The automatic zero voltage switching mode controller may adjust a ZVS dead-time in accordance with a range of load currents being supplied by the power converter that range from quiescent conditions to a predetermined loading level of the power converter. The variable ZVS dead-time may be larger nearer to quiescent conditions, and become progressively smaller as load currents increase. Outside a predetermined range of load currents, the variable ZVS dead-time may be disabled or minimized.

Abstract: A power supply includes a transformer having a primary winding and one or more secondary windings. The power supply also includes a primary switch coupled to the primary winding, a control unit coupled to control the primary switch, and N output circuits each to provide a respective one of N output voltages. N is an integer greater than one. Each of the N output circuits also includes a feedback circuit to produce a respective feedback signal representative of the respective one of N output voltages to the control unit to regulate the respective one of N output voltages. The power supply also includes a switching arrangement coupled to the N output circuits. The switching arrangement is to selectively couple each of at least N?1 of the N output circuits to a respective one of the one or more secondary windings during a respective time period.

Abstract: The present invention relates to a frequency modulation device and a switching mode power supply using the frequency modulation device. To prevent electro-magnetic interference (EMI), it is required to slightly vary a switching operation frequency in an SMPS operation. In some embodiments, at least one first signal having a predetermined cycle is generated, a second signal corresponding to a level of a first signal is generated at a turn-off time of a switch, a first reference voltage having at least two different levels is generated according to the second signal, and an oscillator signal for increasing along a first slope during a first period and decreasing along a second slope during a second period between the first reference voltage and a second reference voltage having a level that is different from the first reference voltage is generated.