Claims:We Claim:
1. An auxiliary circuit for regulating hysteresis in an over temperature protection circuit, the auxiliary circuit comprising of:
a programmable chip (1) for regulating an input signal based on a preset temperature, the programmable chip having a plurality of pins each for an input and an output;
a hysteresis arrangement (2) operatively coupled to the programmable chip (1) through at least one pin each on the input and the output, wherein the arrangement (2) is configured to operate based on a threshold input received from the input pin on the programmable chip (1); and
a voltage divider arrangement (3) sandwiched between the programmable chip (1) and the hysteresis arrangement (2), wherein the voltage divider arrangement (3) is configured to operate between a predefined range of temperature,
wherein the said operation of the voltage divider arrangement (3) regulates the operation of the hysteresis arrangement (2).
2. The auxiliary circuit as claimed in claim 1, wherein the voltage divider arrangement comprises of at least one thermistor capable of operating over a given range of temperature and at least one resistor of a preset value, wherein the said thermistor and the said resistor is connected in a series connection.

3. The auxiliary circuit as claimed in claim 1, wherein the voltage divider arrangement is connected in parallel with the hysteresis arrangement.

4. The auxiliary circuit as claimed in claim 1, wherein the hysteresis arrangement comprises of a MOSFET configured to operate as a switch and connected in series with a resistor of a preset value.

5. The auxiliary circuit as claimed in claim 1, wherein the value of the thermistor of the voltage divider arrangement is altered with the change in the temperature, the changed value of the thermistor changes the net voltage across the voltage divider arrangement leading to change in the state of the hysteresis arrangement.

6. The auxiliary circuit as claimed in claim 1, wherein the predefined range of temperature is about 95oC to about 105oC.

7. The auxiliary circuit as claimed in claim 1, wherein the hysteresis is 10°C.

8. The auxiliary circuit as claimed in claim 1, wherein the auxiliary circuit is used for shutdown and auto recovery applications.

Bangalore RANI MADANAN
3rd September 2021 (INTELLOCOPIA IP SERVICES)
AGENT FOR APPLICANT

, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10 & Rule 13]

AN AUXILIARY CIRCUIT FOR REGULATING HYSTERESIS IN AN OVER TEMPERATURE PROTECTION CIRCUIT

CENTUM ELECTRONICS LTD.
#44, KHB INDUSTRIAL AREA,
YELAHAKA, BANGALORE – 560106,
KARNATAKA, INDIA.

AN INDIAN NATIONAL

THE FOLLOWING SPECIFICATION DESCRIBES THE NATURE OF THE INVENTION AND PARTICULARLY THE MANNER IN WHICH IT IS TO BE PERFORMED.

AN AUXILIARY CIRCUIT FOR REGULATING HYSTERESIS IN AN OVER TEMPERATURE PROTECTION CIRCUIT

FIELD OF INVENTION
The invention generally relates to the field of electronic circuits and particularly to an auxiliary circuit for regulating hysteresis in an over temperature protection circuit.
BACKGROUND
An over temperature protection circuit in a converter is a protection circuit that shuts down the power supply when the internal temperature exceeds a threshold limit. The over temperature protection circuit is used to monitor and generate a signal that starts the shutdown process at high temperatures. The over temperature protection circuits that are available in the art generally works by switching power supply and a MOSFET based temperature circuit.
In one of the circuits known in the art, the temperature protection circuit for switching power supply controls temperature of the circuit during abnormal conditions by using a temperature detector and a switch connected to control electrode for controlling drive signal via switch during temperature detection. In another circuit known in the art, the MOSFET based temperature circuit controls temperature of the circuit by utilizing a pulse width modulation controller, where pulse width modulator produces square wave with variable ON to OFF ratio for detecting temperature of the circuit via the MOSFET without using current sensing resistor.
The currently available solutions have drawbacks in terms of inability to accurately function without stable reference and inability to control hysteresis value thereby limiting in advancement. Another drawback in available solutions is the requirement of more PCB area. Hence, there is a need of a circuit that could regulate hysteresis value and occupy less space of PCB for good functioning.

BRIEF DESCRIPTION OF DRAWINGS
So that the manner in which the recited features of the invention can be understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG.1 shows an auxiliary circuit for regulating hysteresis in an over temperature protection circuit, according to an embodiment of the invention.
SUMMARY OF THE INVENTION
The present invention is intended to solve problems as indicated by the above presented background and state-of-the-art. In particular, the invention solves a problem of regulating hysteresis in an over temperature protection circuit. An advantage gained by the invention is that it is simple and compact, by the fact that it comprises few components, and can be realized very economically. This can be used in commercial, industrial, defence and MIL applications wherever over temperature protection is required to protect the devices from the over temperature.
The invention provides an auxiliary circuit for regulating hysteresis in an over temperature protection circuit. The auxiliary circuit includes a programmable chip for regulating an input signal based on a preset temperature, the programmable chip having a plurality of pins each for an input and an output. A hysteresis arrangement is operatively coupled to the programmable chip through at least one pin each on the input and the output. The hysteresis arrangement is configured to operate based on a threshold input received from the input pin on the programmable chip. A voltage divider arrangement is sandwiched between the programmable chip and the hysteresis arrangement, wherein the voltage divider arrangement is configured to operate between a temperature range, wherein the said operation of the voltage divider arrangement regulates the operation of the hysteresis arrangement.
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.
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.
Various embodiments of the invention provide an auxiliary circuit for regulating hysteresis in an over temperature protection circuit. The auxiliary circuit includes a programmable chip for regulating an input signal based on a preset temperature, the programmable chip having a plurality of pins each for an input and an output. A hysteresis arrangement is operatively coupled to the programmable chip through at least one pin each on the input and the output. The hysteresis arrangement is configured to operate based on a threshold input received from the input pin on the programmable chip. A voltage divider arrangement is sandwiched between the programmable chip and the hysteresis arrangement, wherein the voltage divider arrangement is configured to operate between a temperature range, wherein the said operation of the voltage divider arrangement regulates the operation of the hysteresis arrangement. The invention finds its application in temperature protection circuits for providing shutdown and auto recovery operation during over temperature, under voltage, over voltage and short circuit. Embodiments of the present invention shall be described below in detail with reference to the accompanying figure.
FIG.1 shows an auxiliary circuit for regulating hysteresis in an over temperature protection circuit, according to an embodiment of the invention. The auxiliary circuit includes a programmable chip 1 for regulating an input signal based on a preset temperature. In one example of the invention, the preset temperature is an ambient temperature that is 25oC. In another example of the invention in respect of burn-in or thermal cycling application, the preset temperature is 55 oC. In one embodiment of the invention, the programmable chip is a Supervisory Comparator Integrated Circuit, AU3 IC. The programmable chip 1 is provided with a plurality of pins each for an input and an output. The output (pin 3) of programmable chip 1 drives a diode AD2 to shutdown the circuit during over temperature, under voltage, over voltage and short circuit condition, by isolating it from other related circuits, thereby providing protection. The programmable chip 1, depending upon the voltage at input (pin 6) and the ambient temperature, generates high or low signal as output to regulate shutdown through AD2.
Each pin of AU3 IC has a weak internal pull-up to VCC (pin8) and a strong pull-down to ground. Since it has weak internal pull-up, an external pull-up resistor AR38 is used to pull output above VCC voltage. Overvoltage Logic Output (pin3) asserts low when the VL input voltage (pin6) is above threshold (500mV). The external pull-up resistor AR38 allows these pins to have open drain.
The auxiliary circuit includes an input supply and bypass capacitor section 4. The input supply and bypass capacitor section 4 includes a bypass capacitor AC23. An input of 4.7V is given as supply to the AU3 IC. The bypass capacitor AC23 shorts AC signals to the ground to filter out AC ripples in the DC signal to produce clean and pure DC signal. The auxiliary circuit further includes a TMR Reset section 5, wherein the pin 5 is tied to ground through a capacitor AC22. It can be used wherever delay is needed in some applications.
A hysteresis arrangement 2 is operatively coupled to the programmable chip 1 through at least one pin each on the input and the output. The hysteresis arrangement 2 is configured to operate based on a threshold input received from the input (pin 6) on the programmable chip 1. The hysteresis arrangement 2 comprises of a MOSFET AM2 configured to operate as a switch and connected in series with a resistor AR27 of a preset value. In one example of the invention, whenever the input (pin6) crosses the threshold voltage (500mV), it swings its output immediately without any holdup or hysteresis band. This sudden change can cause malfunction in converter turn-on and turn-off and may damage the converter permanently. Hence it is required to use hysteresis for proper operation of the converter.
A voltage divider arrangement 3 is sandwiched between the programmable chip 1 and the hysteresis arrangement 2. The voltage divider arrangement 3 is connected in parallel with the hysteresis arrangement 2. The voltage divider arrangement 3 is configured to operate between a predefined temperature range. The predefined temperature range described herein is between 95oC and 105oC. The operation of the voltage divider arrangement 3 regulates the operation of the hysteresis arrangement 2. The voltage divider arrangement includes at least one thermistor capable of operating over a given range of temperature and at least one resistor of a preset value. In one embodiment of the invention, the said thermistor and the said resistor are connected in a series connection. The value of the thermistor of the voltage divider arrangement 3 is altered with the change in the temperature, the changed value of the thermistor changes the net voltage across the voltage divider arrangement 3 leading to change in the state of the hysteresis arrangement 2.
In one example of the invention, the voltage divider arrangement 3 includes a thermistor AR25, a resistor AR24 and a resistor AR26 connected in a specific manner to form a resistor divider network. AR25 is a 10K thermistor. Initially, at ambient temperature (25°C), the value of thermistor is 10K and decreases as temperature increases. Hence at ambient temperature, the divider voltage at pin6 of AU3 is around 2.85V. Voltage at input (pin6) is much higher than internal reference voltage (500mV). Hence, output (pin3) is pulled low. When temperature of converter rises to 105°C, the value of thermistor becomes 833Ω. Now the voltage at input (pin6) becomes lower than threshold voltage (500mV). Hence output (pin3) is pulled-up and given to shutdown circuit through diode as shown in FIG.1. AR26 is used to trim the AR24 value to get precise voltage at pin6 in case of variation in resistor tolerance.
Table-1 shows a reference designator with component type and component value implemented in the circuit.

Table-1: Material for circuit
Reference Designator Component Type Component Value
AU3 Supervisory comparator IC LTC2912-2
AC23 Bypass capacitor 1uF
AR24 Resistor 6.49KΩ
AR25 Thermistor 10KΩ
AR26 Resistor 100KΩ
AR27 Resistor 3.3KΩ
AM2 MOSFET DMG3418L
AR38 Resistor 4.7KΩ
AC22 Capacitor NA (open)
AD2 Signal diode PMEG4010ER (40V,1A)

Working
In an example embodiment, a voltage supply (4.7V) is powered to AU3. Initially, at ambient temperature (25°C), the value of thermistor AR25 is 10K and decreases as temperature increases. Hence, at ambient temperature, the divider voltage at pin6 of AU3 IC is around 2.85V. Voltage at input (pin6) is much higher than internal reference voltage (500mV). Hence, output (pin3) is pulled low. When temperature of converter rises to 105°C, the value of thermistor becomes 833Ω and the voltage at input (pin6) becomes lower than threshold voltage (500mV). Hence, output (pin3) is pulled-up and given to shutdown circuit through diode AD2 as shown in FIG.1.
One resistor AR27 is connected in series with MOSFET AM2 and which is parallel to AR25 thermistor. Whenever input (pin6) crosses the threshold voltage (500mV), it swings its output immediately without any holdup or hysteresis band. This sudden change can cause malfunction in converter turn-on and turn-off and may damage the converter permanently. Hence, it is recommended to use some hysteresis for proper operation.
When temperature of converter rises to 105°C, the value of thermistor becomes 833Ω. Now the voltage at input (pin6) becomes lower than threshold voltage (500mV). Hence output (pin3) is pulled-up and inturn shutdown the converter through shutdown circuit. If converter is in shutdown mode, temperature starts decreasing and immediately it may start again if input (pin6) voltage crosses 500mV. Hence, to avoid such immediate turn-on, hysteresis method is implemented. Higher output voltage (pin3) drives the gate of MOSFET AM2 and conducts. Due to the MOSFET AM2 turn-on, AR27 resistor becomes parallel to AR25 thermistor (effective resistance becomes 665Ω) which makes this divider voltage still lesser and thus provide the hysteresis. During normal ambient operation, output (pin3) will be low and MOSFET will not conduct. This AR27 can be adjusted as per requirement. In this application, the hysteresis provided is 10°C.
Hence, the invention provides protection through shutdown and auto recovery operation during over temperature, under voltage, over voltage and short circuit. The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Reference Numerals
Programmable chip 1
Diode section AD2
Pull-up resistor AR38
Hysteresis arrangement 2
Voltage divider arrangement 3
Input supply & capacitor section 4
TMR reset section AC22