FORM 2
THE PATENT ACT 1970
&
THE PATENTS RULES, 2003 COMPLETE SPECIFICATION
(section 10 and rule 13)
1. TITLE OF THE INVENTION:
"Microcontroller based Pulse Width Modulation (PWM) Power Supply for a Circuit Breaker"
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: Larsen & Toubro Limited
Electrical & Automation North Wing, Gate 7, Level 0, Powai Campus, Saki Vihar Road, Mumbai 400 072, INDIA
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in whicl it is to be performed

Microcontroller based Pulse Width Modulation (PWM) Power Supply for a Circuit Breaker
FIELD OF INVENTION:
The present invention relates to circuit breakers and more particularly to a microcontroller based Pulse Width Modulation (PWM) power supply of the circuit breaker.
Background of the invention
The electronic circuit breakers include Molded Case Circuit Breakers (MCCB) and Air Circuit Breakers (ACB) where power supply is required to drive the electronic circuit. The power supply for the electronic circuit is derived from the current transformers which are connected on poles of the circuit breaker.
The power supply can be generated by single phase system or three phase system also. The response will be faster in case of a three phase circuit. Here the MOSFET is used as a power supply controller element. The PWM (Pulse Width Modulation) pulses from the microcontroller are given to the gate of the MOSFET for controlling the power supply.
There is a need to provide a microcontroller based pulse width modulation power supply for a circuit breaker that overcomes all the drawbacks of the prior art.
Objects of the invention
An object of the present invention is to provide a microcontroller based pulse width modulation (PWM, hereinafter) power supply for a circuit breaker.

Another object of the present invention is to provide a microcontroller based PWM power supply for a circuit breaker, which minimizes the use of an extra MOSFET driver 1C.
Yet another object of the present invention is to provide a microcontroller based PWM power supply for a circuit breaker, which minimizes the errors in the PWM signal.
Summary of the Invention
Accordingly, the present invention discloses a microcontroller based pulse width modulation (PWM) power supply for a circuit breaker having an electronic circuit arrangement comprises at least one current transformer that is having a primary winding and a secondary winding for generating an alternating secondary current. The electronic circuit arrangement comprises a bridge rectifier that converts the alternating secondary current into a pulsating direct secondary current. The bridge rectifier connects to a metal-oxide-semiconductor field-effect transistor. The microcontroller generates a plurality of pulse width modulation signals in response to a sensing voltage across a resistor divider connected thereacross. The microcontroller is having an analog to digital converter that converts the sensing voltage into an equivalent digital value. The microcontroller and the metal-oxide-semiconductor field-effect transistor mutually control a voltage across a capacitor mounted thereacross. The resistor divider includes a first pair of resistors connecting across the capacitor for adjusting the sensing voltage. The electronic circuit arrangement comprises a second pair of resistors that includes at least one resistor for limiting a gate current of the metal-oxide-semiconductor field-effect transistor and other resistor for discharging a gate capacitance of the metal-oxide-semiconductor field-effect transistor. The electronic circuit arrangement comprises at least one diode that connects between the capacitor and the metal-oxide-semiconductor field-effect transistor to avoid discharging of the capacitor. The electronic circuit arrangement comprises a zener diode that connects to a

resistor for limiting the current thereof. The resistor drives the metal-oxide-semiconductor field-effect transistor in an over-current condition. The electronic circuit arrangement comprises a pair of diodes that connects to the metal-oxide-semiconductor field-effect transistor to isolate a plurality of gate signals received from the metal-oxide-semiconductor field-effect transistor and the zener diode.
Brief description of the drawings
Figure 1 is a circuit diagram of a microcontroller based PWM power supply for a circuit breaker with a single phase system constructed in accordance with the present invention;
Figure 2 is a circuit diagram of the microcontroller based PWM power supply for the circuit breaker of the single phase system of FIG. 1 with a three phase system constructed in accordance with the present invention; and
Figure 3 is a flow chart showing an operation of the microcontroller based PWM power supply in accordance with the present invention.
Detail description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
Accordingly, the present invention provides an electronic circuit arrangement for a microcontroller based pulse width modulation (PWM, hereinafter) for developing a power supply for a circuit breaker. The present invention minimizes use of an extra driver transistor that is generally required to protect the circuit from over-current in order to reduce components and increasing reliability. Also,

the present invention facilitates PWM pulses to be directly given to a gate of a MOSFET to drive the MOSFET thereby minimizing the use of an extra MOSFET driver IC. Also, the present invention facilitates a microcontroller code that is written to minimize the errors in PWM signals. The circuit of the present invention is also configured to provide protection against the over-current as it contains a zener diode that gets ON at a particular over-current value. Hence, the circuit of the present invention is robust against the over-current. In addition, the MOSFET gives protection against over-current thereby minimizing the need of extra driver transistor.
Referring to Figure 1, an electronic circuit arrangement 100 of a microcontroller based PWM power supply for a circuit breaker with a single phase system is shown. In this one embodiment, the circuit 100 includes a current transformer Tl, a primary winding P1 and a secondary winding S1. The current transformer Tl generates a secondary current 11. The circuit 100 includes a bridge rectifier BR1 that converts the AC secondary current 11 into a pulsating DC current for charging a capacitor C1 such that a rail voltage appears on a rail line 1 and a rail line 2 respectively. The circuit 100 includes a microcontroller M and a metal-oxide-semiconductor field-effect transistor (MOSFET, hereinafter) Ml. The MOSFET Ml is connected across the bridge rectifier BR1 in this one particular embodiment. The voltage stored across a capacitor C1 positioned on a rail 2 is controlled by the microcontroller M and the MOSFET Ml. The microcontroller M is adapted to generate a plurality of PWM pulses by sensing the voltage across a resistor divider 5. The resistor divider 5 consists of a first pair of resistors R2 and R3 that is connected across the capacitor C1. A sense voltage across the resistor divider 5 is available at node 5. The value of sense voltage is configured to be adjusted by adjusting the values of R2 and R3. The voltage across resistor divider 5 is adapted to convert a sense value of the voltage into an equivalent digital value using an analog to digital converter (ADC, hereinafter) of the microcontroller M. This value is adapted to be compared with a fixed reference value. The microcontroller M generates a high pulse as PWM

output via a PWM module 6 if the sense voltage exceeds the fixed reference value. The PWM output is given to a gate of the MOSFET Ml. The MOSFET Ml turns ON to limit the value of secondary current II thereby controlling the rail voltage on line 2. It is understood here that the PWM signal goes high only if the digital equivalent value goes high beyond some pre-determined value and the MOSFET Ml gets on to limit the rail voltage 2. The circuit 100 includes a diode Dl that is connected between the capacitor C1 and the MOSFET Ml for avoiding discharge of the capacitor C1 through the MOSFET Ml. The circuit 100 includes a zener diode Zl that gives protection in case of an over-current. The circuit 100 includes a resistor R4 that is adapted to limit the current to the zener diode Zl. The resistor R4 has a voltage that drives the gate of the MOSFET Ml to turn ON the MOSFET Ml in case of over-current. The circuit 100 includes a pair of diodes D2 and D3 that are connected to the gate of the MOSFET Ml such that the diodes D2 and D3 isolate the gate signals coming from PWM of the controller 6 and the zener diode Zl respectively. A regulator REG converts the rail voltage into the suitable voltage which is required by the microcontroller M. The voltage for the operation of microcontroller M is available at line 3 in this one embodiment. The circuit 100 includes a second pair of resistors, namely Rl and R7. The resistor Rl limits the gate current of the MOSFET Ml. The resistor R7 discharges the gate capacitance of the MOSFET Ml.
As shown in Figure 2, a circuit 100 of a microcontroller based PWM power supply for a circuit breaker is having a single phase system in conjunction with a three phase system 200 In this one alternative embodiment, the circuit 100 includes a plurality of current transformers, a plurality of primary windings, and a plurality of secondary windings. In this one particular embodiment, the circuit 100 includes a first primary winding P1, a second primary winding P2, a third primary winding P3 and a fourth primary winding P4. The circuit 100 includes a first transformer T1, a second transformer T2, a third transformer T3 and a fourth transformer T4. The circuit 100 includes a first secondary winding S1, a second secondary winding S2, a third secondary winding S3 and a fourth secondary

winding S4. The first transformer Tl, the second transformer T2, the third transformer T3 and the fourth transformer T4 respectively generate a first secondary current II, a second secondary current 12, a third secondary current 13 and a fourth secondary current 14. The circuit 100 includes a first bridge rectifier BR1 that converts the AC secondary current 11 into a pulsating DC current. The circuit 100 includes a second bridge rectifier BR2 that converts the AC secondary current 12 into a pulsating DC current. The circuit 100 includes a third bridge rectifier BR3 that converts the AC secondary current 13 into a pulsating DC current. The circuit 100 includes a fourth bridge rectifier BR4 that converts the AC secondary current 14 into a pulsating DC current.
It is understood here that all the secondary currents 11, 12,13, and 14 are connected at a single node 9 after rectification by the bridge rectifiers BR1, BR2, BR3, and BR4 in this one alternative embodiment. The node 4 is considered as a ground. The addition of all the secondary currents 11, 12, 13 and 14 at the single node 9 increases charging time of the capacitor CI that builds up the rail voltage relatively faster than the single phase as illustrated in Figure 1. The three phase system also increases the response of the power supply.
Referring to Figure 3, a flow chart 300 for an operation of the ADC of the microcontroller M in accordance with the present invention is shown. In a first step 10, the ADC performs a function of initialization. In a next step 11, the microcontroller M starts conversion of the ADC. In further step 12, the input to ADC is taken at a pre-determined fixed interval from the resistor divider of R2 and R3 respectively. In this step 12, if it is observed that the ADC conversion is complete then the process moves to a next step 12a else the process returns to the previous step 11. In the step I2a, the ADC conversion value is calculated as a sense voltage (Vsense, hereinafter) and the process moves to a next step 13. In the step 13, it is checked whether Vsense is greater than the fixed reference voltage (Vref, hereinafter). The process moves to a next step 14 if the PWM output goes high (14) else the process moves to a step 15 if the PWM output remains low.

Advantages of the present invention
• The MOSFET Ml is directly driven from the microcontroller M hence the use of MOSFET Gate driver IC is minimized.
• The MOSFET Ml is driven by the zener diode Zl that minimizes use of extra power transistor in ease of over-current conditions such as overload or short-Circuit. This increases reliability and reduces the cost of the circuit 100.
• The microcontroller M is having a coding that minimizes the errors in the PWM controlled signals.
• The circuit 100 advantageously needs the capacitor C1 as the only charging element.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We claim:
1. An electronic circuit arrangement for developing a single phase system or a three phase system based power supply for a circuit breaker, the electronic circuit arrangement comprising:
at least one current transformer having a primary winding and a secondary winding for generating an alternating secondary current;
a bridge rectifier converting the alternating secondary current into a pulsating direct secondary current, the bridge rectifier connecting to a metal-oxide-semiconductor field-effect transistor;
a microcontroller generating a plurality of pulse width modulation signals in response to a sensing voltage across a resistor divider connected thereacross, the microcontroller having an analog to digital converter converting the sensing voltage into an equivalent digital value, the microcontroller and the metal-oxide-semiconductor field-effect transistor controlling a voltage across a capacitor mounted thereacross, the resistor divider having a first pair of resistors connecting across the capacitor for adjusting the sensing voltage;
a second pair of resistors having at least one resistor limiting a gate current of the metal-oxide-semiconductor field-effect transistor, the second pair of resistors having at least one resistor discharging a gate capacitance of the metal-oxide-semiconductor field-effect transistor;
at least one diode connecting between the capacitor and the metal-oxide-semiconductor field-effect transistor for avoiding discharging of the capacitor;
a zener diode connecting to a resistor for limiting the current thereof, the resistor drives the metal-oxide-semiconductor field-effect transistor in an over-current condition; and
a pair of diodes connecting to the metal-oxide-semiconductor field-effect transistor for isolating a plurality of gate signals of the metal-oxide-semiconductor field-effect transistor and the zener diode.

2. The electronic circuit arrangement as claimed in claim 1, wherein the microcontroller is having a coding that minimizes a plurality of errors in the pulse width modulation signals.
3. The electronic circuit arrangement as claimed in claim 1, wherein the circuit includes a regulator that converts the rail voltage into a suitable voltage.