Claims:We Claim:

1. A connector drop compensation circuit to improve load regulation, the circuit comprising:
a secondary winding of a transformer magnetically coupled to a primary winding, the secondary winding having a secondary winding magnetizing inductance, wherein during ON period energy will be stored in the transformer and transferred to secondary winding during OFF period;
an output diode and snubber section electrically connected with the transformer, wherein the output diode and snubber section has a rectifier diode (D1)and during forward biased allows the current to flow from the transformer;
a storagesection electrically connected with the output diode and snubber section, the storage section stores the energy at the output capacitors (C1, C2, and C3) transferred from the transformer and supply the energy to load during on period of primary switch.
a voltage divider circuitusing resistors (R1, R2) electrically connected with the storage to provide reference voltage when output voltage reaches the desired output voltage; and
a voltage drop compensator element (R4) is added in series with ground reference in a feedback loop section, the feedback loop section for isolation between the input and output section,
wherein, at no-load condition, current through voltage drop compensator elementR4 will be zero and difference voltage across voltage drop compensator elementR4 will be negligible thereby desired output voltage will be available at load end as connector losses also zero,
wherein, when difference voltage acrossvoltage drop compensator element R4 increases as output current increases, the voltage at feedback reference (Rfb) starts decreasing linearly, and due to this feedback system raise the output voltage accordingly and thereby compensate for connector drop to maintain load regulation well within the required specification.

2. The circuit as claimed in claim 1, wherein the voltage divider circuit including a first resistor (R1) and a second resistor (R2), where R1 and R2 are selected such that to provide reference voltage when output voltage reaches the desired output voltage.

3. The circuit as claimed in claim 1, wherein the second resistor R2 is connected to one end of the voltage drop compensator element R4 and other end of voltage drop compensator element R4 is connected as ground reference.

4. The circuit as claimed in claim 1, wherein at the voltage drop compensator element R4, whenever output current is zero, there will be no voltage drop across voltage drop compensator elementR4 and both the voltages (before and after R4) are same, wherein when the output current increases, the drop across voltage drop compensator elementR4 increases which makes the potential difference.

5. The circuit as claimed in claim 1, wherein the energy transferred from the transformer recharges the output capacitors C3, C1, C2 and supplies the load across Vout, and wherein RC snubber R5 & C5 is used to reduce the stress voltage on diode D1.

6. The circuit as claimed in claim 1, further comprising:
a feedback voltage (Rfb) to provide feedback to primary side control, and wherein RC network (R3, C4) connected across R1 is used for reducing the transient overshoot of output voltage.

7. The circuit as claimed in claim 1, wherein when current flows through R4, it sees voltage difference across it and RFb voltage reduces which forces the feedback loop to increase the output voltage.

8. The circuit as claimed in claim 1, wherein the voltage drop compensator elementR4 is a variable resistor which is adjusted for efficient regulation.

9. The circuit as claimed in claim 1, wherein the feedback loop section is a TL431 based type3 network and an optocoupler for isolation between input and output section.

10. The circuit as claimed in claim 1 is used in applications where tight output load regulation are required.

Bangalore RANI MADANAN
5 May 2021 (INTELLOCOPIA IP SERVICES)
AGENT FOR APPLICANT

, Description:DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the figures 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. 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. 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.
It will be understood that when an element or layer is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it can be directly on, connected to, or coupled to the other element or layer or intervening elements or layers that may be present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Spatially relative terms, such as “detection,” or “capture, and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the structure in use or operation in addition to the orientation depicted in the figures.
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, circuits and examples provided herein are illustrative only and not intended to be limiting.
Embodiments of the present invention will be described below in detail with reference to the accompanying figures.
FIG. 1 shows a connector drop compensator circuit to improve load regulation in SMPS, according to one embodiment of the present invention. In an example embodiment, the circuit is further divided into multiple blocks for detailed understanding. The circuit mainly includes a secondary winding of transformer, an output diode and snubber section, an output capacitor section, a voltage divider circuit section, a voltage drops compensator element, and a feedback loop section. The secondary winding of transformer, i.e. L1 which shows the secondary winding inductance of flyback transformer. In flyback topology, during ‘ON’ period energy will be stored in transformer and transferred to secondary winding (L1) during ‘OFF’ period. The secondary winding of transformer is electrically connected to the output diode and snubber section. In this section whenever secondary voltage Vs=(Ns/Np) *Vp is positive, rectifier diode D1 becomes forward biased and allows the current to flow from the transformer. The energy transferred from the transformer recharges the output capacitors C3, C1, C2 and supplies the load across Vout.RC snubber R5 & C5 is used to reduce the stress voltage on diode D1. The output diode and snubber section is further electrically connected to the output capacitor section. In this section, the output capacitors C3, C1, C2 to store energy and supply the energy to load during on period of primary switch. The output capacitor section is further connected to the voltage divider circuit section. In this section, the voltage divider circuit using resistors R1 & R2. In an example embodiment, R1 and R2 values are selected in such way that it gives 2.5V reference voltage when output voltage reaches the desired output voltage (3.3V). This feedback voltage (Rfb) is then fed to TL431 reference regulator (U2) to give feedback voltage to primary side control. RC network R3, C4 connected across R1 is used for reducing the transient overshoot of output voltage.
The voltage divider circuit section is further electrically connected to a voltage drop compensator element. In this section, where resistor (R4) is added in series with ground path to make the potential voltage difference. In an example embodiment, whenever output current is zero, there will be no voltage drop across R4 resistor and both the voltages (before and after R4) are same. But as output current increases, the drop across R4 increases. This makes the potential difference. Hence as shown in FIG. 1, voltage divider circuit resistor R2 bottom is connected to one end of R4 and other end of R4 is connected as ground reference for TL431 (U2) in feedback loop section.
Moreover, when current flows through R4, it sees voltage difference across it and RFb voltage reduces. This forces the feedback loop to increase the output voltage. For example, considering connector resistance is 5mO, suppose if using 3 pins for live and 3pins for returns. Total voltage drop across connector becomes 26.66mV (3.3V-0.0266=3.27V). Apart from this, PCB track losses also contribute. Hence it is always difficult to meet tight regulation for lower output voltages like 1% of output voltage. Hence it is needed to compensate that drop to maintain desired output at load end. Based on required compensation voltage, value of R4 can be adjusted. Practically this connector drop was more. Hence compensated 40mV (R4=5mO for 8A) for better regulation.
The voltage drops compensator element is further connected to a feedback loop section. In this feedback loop compensation section which involves the TL431 based feedback loop type3 network and optocoupler for isolation between input and output section. Voltage divider feedback (RFb) voltage is given to TL431 (U2), whenever output voltage reaches desired voltage (3.3V), U2 gets conducted and current flows through resistor R6 and photodiode of optocoupler (U1). Current transfer ratio of U1 will drive the base of opto transistor and produce corresponding voltage at emitter point (R9-R10 junction). This voltage (CTR*R10) can be varied by changing the value of R10 to suitable for PWM operation. R9 resistor is implemented in series with feedback path to PWM. This resistor proves immunity for noises in path. Further, R7 resistor is implemented to ensure that minimum 1mA current will flow through U2 for proper operation of TL431. R8, C6, C7 is connected for loop stabilization of converter to set desired gain and phase margin.

The below Table-1 shows the bill of materials used in circuit.

Reference Designator Component Type Component Value
L1 Secondary winding of transformer L1=1.35uH
D1 Output diode SBR40U45CT (45V,40A)
C5 Snubber capacitor 3.3nF
R5 Snubber resistor 1.5O
C1, C2, C3 Output capacitor 100uF
R3 Resistor 500O
C4 Capacitor 1nF
R1 Resistor 3.24KO
R2 Resistor 9.76KO
R4 Resistor 5mO
R6 Resistor 33O
R7 Resistor 470O
R8 Resistor 1KO
C6 Capacitor 1uF
C7 Capacitor TBD (open)
U2 2.5V ref voltage regulator ZHT431FMTA
U1 Isolated optocoupler SFH1690CT
R9 Resistor 10KO
R10 Resistor 1KO

Working
In an example embodiment, when secondary winding voltage is positive, output diode D1 becomes forward biased and allows current to flow through it to recharge the output capacitors (C1, C2, C3). As output increases, divider voltage Rfb (junction of R1&R2) also start increases. Until this point reaches the 2.5V, U2 (TL431) will not conduct and will not give any feedback to primary control PWM. When output reaches desired output voltage (3.3V), Rfb point becomes 2.5V and U2 gets conducted. Current will flow through R6, photodiode of optocoupler and U2. This photodiode current will drive the base terminal of opto-transistor and provide the feedback voltage at emitter point which is given to PWM of primary side to vary the duty cycle.
During no load condition, there will be no drop across resistor R4 as no current flow through it. Hence it works as normal circuit operation. When load current increases, drop across R4 increases and divider voltage Rfb decreases linearly. During this, connector drop increases and will get reduced voltage at load end. This decreased in Rfb voltage forces the TL431(U2) to correct the loop and try to get desired 2.5V reference at Rfb point by increasing the output voltage little higher side. This whatever increased voltage will compensate the connector drop voltage and maintain the desired output voltage (3.3V) at load end.
While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.
The figures 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.
Reference Numerals
Secondary Winding of Transformer 1
Output diode & Snubber section 2
Output Capacitor Section 3
Voltage divider circuit section 4
Voltage drops compensator element 5
Feedback loop section 6