AU2021100313A4 - Fixed off time-based switch mode power supply device - Google Patents

Abstract

The present disclosure relates to a fixed OFF time-based switch mode power supply device. The device comprises a diode equipped with a capacitor for converting alternating current into an unregulated ripples direct current, a high-frequency switch for generating high flux variation to produce alternating current upon switching the unregulated ripples direct current at a range of 15 to 50Hz, a flyback transformer having a primary winding and a secondary winding for generating high voltage sawtooth signals at a relatively high frequency from produced alternating current, a rectifier and filter for generating a regulated direct current, and a feedback circuit for generating a desired direct current output upon producing a feedback signal according to the first output voltage. 19 c.~ 00 0 co I E C-) >0 Cu C u uC otwo 0 u' 0. 5 .- -

Description

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FIXED OFF TIME-BASED SWITCH MODE POWER SUPPLY DEVICE FIELD OF THE INVENTION

The present disclosure relates to a fixed OFF time-based switch mode power supply device. More particularly, the present invention relates to a fixed OFF time-based 30watt switch mode power supply device to obtain a unity input power factor.

BACKGROUND OF THE INVENTION

A switched-mode power supply (switched power supply, SMPS, or switcher) is an electronic power supply that integrates a switching regulator to convert electrical power efficiently. Similar to other power supplies, an SMPS transfers power from a direct current or alternating current source to direct current loads, such as a computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. A hypothetical ideal switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time (also known as duty cycles). In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight. Switching regulators are used as replacements for linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated; switching currents can cause electrical noise problems if not carefully suppressed, and simple designs may have a poor power factor.

Recently, various switch-mode power supplies have adopted an active power factor correction portion to meet the pre-requisites of reduced harmonics and higher efficiency. All these converters are generally fragmented into two segments i.e., single and double stage types depending on their control techniques. In double stage type converters, twin power processing stages are plunged together. First one is for power factor correction and the other one is for regulated output voltage. Although these kinds of converters have very good performance including high power factor and reduced stress on switching components, they usually suffer from disadvantages like poor power conversion efficiency, large component count, high cost when differentiated with single-stage type converters.

In one solution, a measuring output current in a buck SMPS is disclosed. A sample and hold circuit takes a sample of the current flowing through an inductor of a buck switched mode power supply (SMPS) at substantially the middle of the low side portion (50 per cent point during low side switch ON) of the pulse width modulation (PWM) period. This sample of the current through the SMPS inductor during the low side ON 50% point may be considered as the "average" or "DC output" current of the SMPS and taken every time at precisely the same low side ON 50%. A constant current source and sink are used to charge and discharge a timing capacitor whose voltage charge is monitored by a high-speed voltage comparator to provide precise sample timing.

In another solution, a switching-mode power supply (SMPS) having overvoltage cutoff function, and method of cutting off overvoltage and image forming apparatus using the SMPS is disclosed. A switching-mode power supply (SMPS) for an image forming apparatus which may prevent an overvoltage supplied to the SMPS, and damage to circuits in the SMPS in the image forming apparatus. The SMPS includes a rectifying circuit to rectify an alternating-current (AC)voltage input from an external power supply source into a direct current (DC) voltage, a transformer to transform the rectified DC voltage input to a primary coil and output the transformed DC voltage to a secondary coil, the main switch that is connected to the primary coil and switches an output of the transformer, a first overvoltage detecting unit to determine whether the rectified DC voltage is an overvoltage by comparing the rectified DC voltage with a first reference voltage, and a switching control unit to control a switching operation of the main switch based on a result of the determination.

In another solution, a switching mode power supply (SMPS) device, image forming apparatus including the SMPS device, and method of driving the SMPS device. A switching mode power supply (SMPS) device includes a power converting part that converts an input voltage into an output voltage according to a switching signal, and outputs a primitive switching signal for use in varying a frequency of the switching signal based on power drawn by a load receiving the output voltage; a resonant circuit that changes a duty ratio of the primitive switching signal using a variable resonant frequency in accordance with a variance of an impedance of the load; and a signal controlling part that compares a voltage of the primitive switching signal, resonated in accordance with the variable resonant frequency, with a reference voltage, and varies the frequency of the switching signal and outputs the switching signal having the varied frequency when the voltage of the primitive switching signal is maintained below the reference voltage for longer than a reference time.

However, there are various switch-mode power supply devices are available in the market, but these devices are incapable of providing a unity power factor. Furthermore, the existing devices are not able to maintain the desired output at a wide range of alternating current variation. In view of the foregoing discussion, there exists a need for a fixed OFF time-based switch mode power supply device.

SUMMARY OF THE INVENTION

The present disclosure seeks to provide a fixed OFF time-based 30watt switch mode power supply device in which the circuit configuration is simplified and the size and cost are reduced while maintaining a high degree of accuracy in the output voltage to obtain a unity input power factor.

In an embodiment, a fixed OFF time-based switch mode power supply device is provided. The device includes a diode equipped with a capacitor connected to an alternating current source for converting alternating current into an unregulated ripples direct current.

The device further includes a high-frequency switch associated with the diode for generating high flux variation to produce alternating current upon switching the unregulated ripples direct current at 50-60kHz.

The device further includes a flyback transformer having a primary winding and a secondary winding connected with the high-frequency switch for generating high voltage sawtooth signals at a relatively high frequency from produced alternating current.

The device further includes a rectifier and filter attached to the secondary winding of the flyback transformer for generating a regulated direct current. The device further includes a feedback circuit interconnected with the high-frequency switch and rectifier and filter end for generating a desired direct current output upon producing a feedback signal according to the first output voltage.

In an embodiment, the feedback circuit comprises: an output sensor for monitoring the output voltage continuously; an op-amp for generating amplified error signal upon comparing monitored output voltage with a reference signal; a duty cycle controller connected with the op-amp for increasing duty cycle of the output voltage, if the duty cycle of the output voltage is lower than desired duty cycle and decreasing duty cycle of the output voltage, if the duty cycle of the output voltage is higher than the desired duty cycle; a pulse width modulation (PWM) latch for reducing the average power delivered by the duty cycle controller, by effectively chopping it up into discrete parts; and a timer for maintaining the timing of an operation in sync with a system clock or an external clock.

In an embodiment, an optocoupler is interconnected with the output sensor and the op-amp for providing electrical isolation to prevent from short circuit. In an embodiment, a frequency compensator is parallelly connected with the op-amp to avoid the unintentional creation of positive feedback and to control overshoot and ringing in the amplifier's step response, wherein the frequency compensator is also used extensively to improve the bandwidth of single-pole systems.

In an embodiment, fixed off time-based PWM technique is to be implemented using a dedicated L4984D microcontroller to reduce the component count. In an embodiment, the leakage flux is modelled as a leakage inductance, wherein if in case there is no leakage flux, there will be no leakage inductance, wherein the effect of leakage inductance on the operation of the flyback converter is to force a voltage spike to appear across the MOSFET switch when it is turned OFF.

In an embodiment, during ON period of the switch, the current flows through leakage inductor and switch whereas during OFF period, the energy in the transformer core is transferred to the output, but the energy in the leakage inductance cannot be transferred to the output.

In an embodiment, the leakage inductance current starts to flow through the MOSFET, thus charging the capacitor and increasing the voltage across the switch. In an embodiment, depending upon the amount of the energy stored in the leakage inductance related to the amount of leakage flux stored in the transformer, the voltage across the device may exceed the device's ratings resulting in catastrophic failure of the device.

In an embodiment, the energy present in the leakage inductance is recovered and is converted into heat and transferred to output when the switch turns OFF, the voltage across the leakage inductance is Vciamp- VoR and causes the primary side current to slew down in an interval To, , wherein only after To, has elapsed, the secondary side winding takes over the entire primary side current and thereafter turns OFF.

An object of the present disclosure is to develop a fixed OFF time-based switch mode power supply device.

Another object of the present disclosure is to obtain a unity input power factor for the proposed 30 watts SMPS.

Another object of the present disclosure is to maintain a constant output voltage of 12 volts and 2.5 Amp for a large range of input variation from100V-300V.

Another object of the present disclosure is to develop a Fixed off time-based PWM technique is to be implemented using a dedicated L4984D microcontroller to reduce the component count.

Yet another object of the present invention is to deliver an expeditious and cost effective single-output flyback converter of suitable rating for safety and isolation purpose.

To further clarify the advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a block diagram of a fixed OFF time-based switch mode power supply device in accordance with an embodiment of the present disclosure; Figure 2 illustrates a schematic diagram of a fixed OFF time-based switch mode power supply device in accordance with an embodiment of the present disclosure; Figure 3 illustrates a line diagram of a flyback transformer core assembly in accordance with an embodiment of the present disclosure; Figure 4 illustrates a line diagram of a flyback converter with leakage inductance in accordance with an embodiment of the present disclosure; and Figure 5 illustrate a line diagram of a flyback converter with Zener and RCD clamp in accordance with an embodiment of the present disclosure.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

Referring to Figure 1, a block diagram of a fixed OFF time-based switch mode power supply device is illustrated in accordance with an embodiment of the present disclosure. The device 100 includes a diode 102 equipped with a capacitor 104 connected to an alternating current source 106 for converting alternating current into an unregulated ripples direct current. Freewheel diode 102 or Flyback diodes are connected across the active source to prevent from voltage spikes in case of power getting turned off to the devices. There will sharp voltage spike when power to inductive load, i.e., coils and other inductors are turned off.

In an embodiment, a high-frequency switch 108 is associated with the diode 102 for generating high flux variation to produce alternating current upon switching the unregulated ripples direct current at a range of 15 to 50Hz according to the requirement of a load. The range of frequency can be controlled manually. In an embodiment, a flyback transformer 110 is having a primary winding and a secondary winding which is connected with the high frequency switch 108 for generating high voltage sawtooth signals at a relatively high frequency from produced alternating current.

In an embodiment, a rectifier and filter 112 is attached to the secondary winding of the flyback transformer 110 for generating a regulated direct current. The rectifier and filter consisting of a diode and capacitor. In an embodiment, a feedback circuit 114 is interconnected with the high-frequency switch 108 and rectifier and filter 112 ends for generating a desired direct current output upon producing a feedback signal according to the first output voltage.

In an embodiment, the feedback circuit 114 includes an output sensor for monitoring the output voltage continuously. The feedback circuit 114 further includes an op-amp for generating amplified error signal upon comparing monitored output voltage with a reference signal. The feedback circuit 114 further includes a duty cycle controller connected with the op-amp for increasing duty cycle of the output voltage, if the duty cycle of the output voltage is lower than desired duty cycle and decreasing duty cycle of the output voltage, if the duty cycle of the output voltage is higher than the desired duty cycle. The feedback circuit 114 further includes a pulse width modulation (PWM) latch for reducing the average power delivered by the duty cycle controller, by effectively chopping it up into discrete parts. The feedback circuit 114 further includes a timer for maintaining the timing of an operation in sync with a system clock or an external clock.

In an embodiment, an optocoupler is interconnected with the output sensor and the op-amp for providing electrical isolation to prevent from short circuit. In an embodiment, a frequency compensator is parallelly connected with the op-amp to avoid the unintentional creation of positive feedback and to control overshoot and ringing in the amplifier's step response, wherein the frequency compensator is also used extensively to improve the bandwidth of single-pole systems.

In an embodiment, fixed off time-based PWM technique is to be implemented using a dedicated L4984D microcontroller 116 to reduce the component count. The L4984D is a current-mode PFC controller operating with line-modulated fixed-off-time (LM-FOT) control. A proprietary LM-FOT modulator allows fixed-frequency operation for boost PFC converters as long as they are operated in CCM (continuous conduction mode).

In an embodiment, the leakage flux is modelled as a leakage inductance, wherein if in case there is no leakage flux, there will be no leakage inductance, wherein the effect of leakage inductance on the operation of the flyback converter is to force a voltage spike to appear across the MOSFET switch when it is turned OFF.

In an embodiment, during ON period of the switch, the current flows through leakage inductor and switch whereas during OFF period, the energy in the transformer core is transferred to the output, but the energy in the leakage inductance cannot be transferred to the output.

In an embodiment, the leakage inductance current starts to flow through the MOSFET, thus charging the capacitor and increasing the voltage across the switch. In an embodiment, depending upon the amount of the energy stored in the leakage inductance related to the amount of leakage flux stored in the transformer, the voltage across the device may exceed the device's ratings resulting in catastrophic failure of the device.

In an embodiment, the energy present in the leakage inductance is recovered and is converted into heat and transferred to output when the switch turns OFF, the voltage across the leakage inductance is Vciamp - VoR and causes the primary side current to slew down in an interval To, , wherein only after To, has elapsed, the secondary side winding takes over the entire primary side current and thereafter turns OFF.

In an embodiment, A voltage multiplier is connected with the device to convert AC electrical power from a lower voltage to a higher DC voltage, typically using a network of capacitors and diodes. Voltage multiplier is used to generate a few volts for electronic appliances, to millions of volts for purposes such as high-energy physics experiments and lightning safety testing.

Figure 2 illustrates a schematic diagram of a fixed OFF time-based switch mode power supply device in accordance with an embodiment of the present disclosure. Various switch-mode power supplies have adopted an active power factor correction portion to meet the pre-requisites of reduced harmonics and higher efficiency. All these converters are generally fragmented into two segments i.e., single and double stage types depending on their control techniques. In double stage type converters, twin power processing stages are plunged together. First one is for power factor correction and the other one is for regulated output voltage. Although these kinds of converters have very good performance including high power factor and reduced stress on switching components, they usually suffer from disadvantages like poor power conversion efficiency, large component count, high cost when differentiated with single-stage type converters. For all these reasons, two different stages i.e., power factor correction and regulated voltage are integrated into each other to form a single-stage type converter with inbuilt control action has been proposed. Initially, the ac input is to be rectified, then a suitable associated circuitry of the microcontroller 116 is to be designed. The rectified voltage is to be boosted to 350 V using a DC-DC boost converter as shown in Figure 2. The boosted voltage is then fed to the flyback converter.

The switch-mode power supply (SMPS) is a type of power supply that uses semiconductor switching techniques, rather than standard linear methods to provide the required output voltage. The basic switching converter consists of a power switching stage and a control circuit. The power switching stage performs the power conversion from the circuits input voltage, VIN to its output voltage, VOUT which includes output filtering. The major advantage of the switch mode power supply is its higher efficiency, compared to standard linear regulators, and this is achieved by internally switching a transistor (or power

MOSFET) between its "ON" state (saturated) and its "OFF" state (cut-off), both of which produces lower power dissipation. This means that when the switching transistor is fully "ON" and conducting current, the voltage drop across it is at its minimal value, and when the transistor is fully "OFF" there is no current flow through it. So, the transistor is acting as an ideal switch. As a result, unlike linear regulators which only offer step-down voltage regulation, a switch-mode power supply, can offer step-down, step-up and negation of the input voltage using one or more of the three basic switch-mode circuit topologies: Buck, Boost and Buck-Boost. This refers to how the transistor switch, inductor, and smoothing capacitor are connected within the basic circuit.

Figure 3 illustrates a line diagram of a flyback transformer core assembly in accordance with an embodiment of the present disclosure. Figure 3 represents the core assembly of the flyback transformer 110. A suitable core ETD39TH-H 14-Pin is proposed to be selected to design the flyback transformer 110 as shown in Figure 3. The flyback transformer 110 consists of a magnetic core with primary and secondary winding wrapped around the core. The voltage is step-up or step-down depending upon the number of primary and secondary turns in the transformer. When the primary winding is excited by the input voltage, the flux is produced in the core with some leakage out in the air which is termed as leakage flux. It is one of the key parameters to be considered for proper designing of the transformer core.

Figure 4 illustrates a line diagram of a flyback converter with leakage inductance in accordance with an embodiment of the present disclosure. The leakage flux is modelled as a leakage inductance as shown in Figure 4. If in case there is no leakage flux, there will be no leakage inductance. The effect of leakage inductance on the operation of the flyback converter is to force a voltage spike to appear across the MOSFET switch when it is turned OFF. Some of the important parameter to develop the flyback converter is proposed in table 1. Table 1: Important parameters to develop the flyback converter

Selected Parameters Values/Part No Design Target 12 V, 2.5 A Input Voltage Range 335 - 470 V DC

Primary Reflected Voltage (VR) 139 V Primary Inductance 470 uH Switching Frequency(fs) 56 kHz

Iprimary-peak 3.82 A

IprimaryuRMS 1.19 A Core Type ETD39TH-H-14 Pin MOSFET TK1OA80E Clamping Voltage (Vciamp) 350 V

The circuit in Figure 4 shows the leakage inductor in series with the switch. During the ON period of the switch, the current flows through it and inductor. During the OFF period, the energy in the transformer core is transferred to the output, but the energy in the leakage inductance cannot be transferred to the output. The leakage inductance current starts to flow through the MOSFET, thus charging the capacitor and increasing the voltage across the switch. Depending upon the amount of the energy stored in the leakage inductance, which is related to the amount of leakage flux stored in the transformer, the voltage across the device may exceed the device's ratings resulting in catastrophic failure of the device. The energy present in the leakage inductance is recovered and is required to be converted into heat and transfer to output when the switch turns OFF, the voltage across the leakage inductance is V-clamp-VOR and causes the primary side current to slow down in an interval T_on. Only after T_on has elapsed, the secondary side winding can take over the entire primary side current and turn OFF. Transmission finally gets completed. To find the clamping resistor, capacitor and losses following expressions are used.

R 2*Vcamp*(Vcamp-VoR) = 38.4 kO (1) Lik*Iprimarypeak Sw

C 10 = 4.65 nF (2) R*fsw

Where, P= loss in RCD clamp

1 2 Vclamp P= 2* Li * Iprimarypeak2 VclampVOR3 watts (3)

A suitable value of R and C is selected as R= 40 kQ and C= 1OnF.

Figure 5 illustrate a line diagram of a flyback converter with Zener and RCD clamp in accordance with an embodiment of the present disclosure. The flyback converter is composed of a flyback transformer 110, switch, rectifier and filter and the control mechanism to drive the switch and provide regulation. It is a low part count switching converter and relatively easy to make or design. A flyback converter is an isolated switching converter that can be a step-down or step-up configuration. The flyback transformer 110 is not a transformer. A transformer will transfer energy from the primary to secondary ideally real time and perfectly. Flyback transformer on the other hand will store energy on the primary magnetic field and after a certain amount of time, it delivers the energy to the secondary. The role of the switch is to turn ON and OFF the primary circuit which able to magnetize and demagnetize the transformer. The switch is being controlled by the PWM signal which is coming from the selected controller. The rectifier will rectify the voltage on the secondary winding to become a pulsating DC. Another role of the rectifier or the diode is to cut and connect the load from the secondary winding. The rectified voltage is then filtered out by the capacitor to increase the DC level and can be usable by the intended application. The switch plays an important role on how flyback converter works. When the switch is ON, the current will flow from Vin down to the primary ground. This will charge the primary winding and store energy. During this time, the secondary winding has no current flow as the diode is reverse bias. The load demand at this time is supplied by the output capacitance (Cout). The RCD clamp works by absorbing the current in the leakage inductor once the drain voltage exceeds the clamp capacitor voltage. The use of a relatively large capacitor keeps the voltage constant over a switching cycle. The resistor of the RCD clamp always dissipates power. A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" when a certain set reverse voltage, known as the Zener voltage, is reached. Zener diodes are manufactured with a great variety of Zener voltages and some are even variable.

In an embodiment, a complete unit design consisting of microcontroller 116 associated circuitry to obtain unity input power factor, boost converter, a flyback converter, flyback transformer core and clamping design to obtain constant 12 volts DC and 2.5-amp load current. The device electromagnetic interference and compatibility standards to be followed are harmonic current emission: IEC61000-3-2, ESD: IEC-61000-4-2, radiated susceptibility-IEC61000-4-4, surges: IEC61000-4-5, conducted susceptibility-IEC61000-4-6, voltage dips and interruption-IEC61000-4-11, conducted emission: CISPR14-11, and radiated emission: CISPR14-1.

In an embodiment, advantages of the invention include unity input power factor, reduced component count, reduced size of the SMPS, the capability to maintain desired output at a wide range of ac variation, lower cost and higher efficiency. The potential applications of the proposed device are found in televisions, intercom and monitoring systems, computers, refrigerators, air conditioners, led drivers, taxi advertising screen and car audio systems. The device itself is suitable for multiple low power applications such as charging, lighting, speaker etc.

The device developed in accordance with the present disclosure are improved at providing a unity input power factor for the proposed 30 watts SMPS. The device is used to maintain a constant output voltage of 12 volts and 2.5 Amp for a large range of input variation from 100V-300V. The disclosed device develops a Fixed off time-based PWM technique is to be implemented using a dedicated L4984D microcontroller 116 to reduce the component count. The disclosed device delivers an expeditious and cost-effective single output flyback converter of suitable rating for safety and isolation purpose.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims (10)

WE CLAIM

1. A fixed OFF time-based switch mode power supply device, the device comprising: a diode equipped with a capacitor connected to an alternating current source for converting alternating current into an unregulated ripples direct current; a high-frequency switch associated with the diode for generating high flux variation to produce alternating current upon switching the unregulated ripples direct current at a range of 15 to 50Hz; a flyback transformer having a primary winding and a secondary winding connected with the high-frequency switch for generating high voltage sawtooth signals at a relatively high frequency from produced alternating current; a rectifier and filter attached to the secondary winding of the flyback transformer for generating a regulated direct current; and a feedback circuit interconnected with the high-frequency switch and rectifier and filter end for generating a desired direct current output upon producing a feedback signal according to the first output voltage.

2. The device as claimed in claim 1, wherein the feedback circuit comprises: an output sensor for monitoring the output voltage continuously; an op-amp for generating amplified error signal upon comparing monitored output voltage with a reference signal; a duty cycle controller connected with the op-amp for increasing duty cycle of the output voltage, if the duty cycle of the output voltage is lower than desired duty cycle and decreasing duty cycle of the output voltage, if the duty cycle of the output voltage is higher than the desired duty cycle; a pulse width modulation (PWM) latch for reducing the average power delivered by the duty cycle controller, by effectively chopping it up into discrete parts; and a timer for maintaining the timing of an operation in sync with a system clock or an external clock.

3. The device as claimed in claim 1, wherein an optocoupler is interconnected with the output sensor and the op-amp for providing electrical isolation to prevent from short circuit.

4. The device as claimed in claim 1, wherein a frequency compensator is parallelly connected with the op-amp to avoid the unintentional creation of positive feedback and to control overshoot and ringing in the amplifier's step response, wherein the frequency compensator is also used extensively to improve the bandwidth of single pole systems.

5. The device as claimed in claim 1, wherein fixed off time-based PWM technique is to be implemented using a dedicated L4984D microcontroller to reduce the component count.

6. The device as claimed in claim 1, wherein the leakage flux is modelled as a leakage inductance, wherein if in case there is no leakage flux, there will be no leakage inductance, wherein the effect of leakage inductance on the operation of the flyback converter is to force a voltage spike to appear across the MOSFET switch when it is turned OFF.

7. The device as claimed in claim 6, wherein during ON period of the switch, the current flows through leakage inductor and switch whereas during OFF period, the energy in the transformer core is transferred to the output, but the energy in the leakage inductance cannot be transferred to the output.

8. The device as claimed in claim 7, wherein the leakage inductance current starts to flow through the MOSFET, thus charging the capacitor and increasing the voltage across the switch.

9. The device as claimed in claim 8, wherein depending upon the amount of the energy stored in the leakage inductance related to the amount of leakage flux stored in the transformer, the voltage across the device may exceed the device's ratings resulting in catastrophic failure of the device.

10. The device as claimed in claim 9, wherein the energy present in the leakage inductance is recovered and is converted into heat and transferred to output when the switch turns OFF, the voltage across the leakage inductance is Vciamp - VoR and causes

the primary side current to slew down in an interval To, , wherein only after To, has elapsed, the secondary side winding takes over the entire primary side current and thereafter turns OFF.

Alternating Diode 102 Capacitor 104 Current Source 106

High Frequency Flyback Rectifier and Switch 108 Transformer 110 Filter 112

Feedback circuit Microcontroller 114 116

Figure 1

Figure 2

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Figure 5