Claims: We Claim:
1. An adaptive protection circuit for a power converter, the circuit comprising:
an amplifier configured for amplifying a certain portion of the input current;
a linearly variable reference voltage generator which is dependent on the input voltage; and
a comparator having two inputs, the first input connected to the output of the amplifier and the second input connected to the variable reference voltage generator, wherein the comparator is configured to generate a shutdown signal;
Wherein the shutdown signal turns off the signal from a pulse wave modulating circuit, thereby protecting the power converter during overload, over the entire input voltage range.
2. The circuit as claimed in claim 1, wherein the linear variable reference voltage generator generates a linearly variable reference voltageby averaging gate voltage of a pulse wave modulating circuit.
3. The circuit as claimed in claim 1, wherein the power converter can be a DC/DC or an AC/DC converter

Bangalore NARENDRA BHATTA HL
20 June 2018 (INTELLOCOPIA IP SERVICES)
AGENT FOR APPLICANT
, Description:AN ADAPTIVE PROTECTION CIRCUIT FOR A POWER CONVERTER

FIELD OF INVENTION
The invention generally relates to the field of power converters and particularly to linearized current limiting circuit for power converters.
BACKGROUND
Power converters can convert one form of electric power to another form and also can convert one voltage level to another voltage level. The converters provide any type of the required voltage at the desired magnitude. Power converters include converters and switch-mode converters. The switch-mode converters implements pulse width modulation or pulse frequency modulation. The modulation methods are implemented together with a switch mode controller and protection components. The protection components avoid permanent damage of the power converter and other connected circuits. The components can provide protection against increased voltage, temperature, current and power. Currently available protection circuits are those designed for fixed input voltage and input current and do not provide protection for a wide range of variable input voltage.
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 a schematic diagram of an adaptive protection circuit for a power converter, according to an embodiment of the invention.
SUMMARY OF THE INVENTION
The invention provides an adaptive protection circuit for a power converter. The circuit includes an amplifier, a linearly variable reference voltage and a comparator. The amplifier is configured for amplifying a certain portion of the input current. The linearly variable reference voltage generator is dependent on the input voltage. The comparator has two inputs, the first input connected to the output of the amplifier and the second input connected to the variable reference voltage generator. The comparator is configured to generate a shutdown signal. The shutdown signal turns off the signal from a pulse wave modulating circuit, thereby protecting the power converter during overload, over the entire input voltage range. The power converter can be a DC/DC or an AC/DC converter.
The circuit provides a mechanism to limit the input over current, at any input voltage, within the tolerance band, for complete range of input voltage. The reference voltage of the comparator is varied to linearize the over current protection limit for wide range of input voltage. The nominal input current reduces when the input voltage increases, therefore the comparator reference is also made variable.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide a protection circuit for a power converter at varying range of input voltage.
FIG.1 shows a schematic diagram of an adaptive protection circuit for a power converter, according to an embodiment of the invention. The circuit comprises of an amplifier 101, a linearly variable reference voltage generator 102 and a comparator 103.
The amplifier 101 and the comparator 103 include, but are not limited to, op-amps. The amplifier 101 receives input from, but is not limited to, a current transformer secondary 104. A circuit arrangement 105 is connected to positive terminal of the amplifier 101. The linearly variable reference voltage generator 102 includes, but is not limited to, a resistor 107, a resistor 108, a resistor 111, a capacitor 109 and a Zener diode 110. The linearly variable reference voltage generator 102 receives input from a pulse width modulation circuit 106 and a reference voltage 112. First end of the resistor 107 is connected to the pulse width modulation circuit 106 .The resistor 108, the capacitor 109 and Zener diode 110 are connected parallel to each other and its first common point is connected to second end of the resistor 107 and first end of the resistor 111, the second common point is grounded. The second end of the resistor 111 is connected to the reference voltage 112. First input of the comparator 103 is connected to output of the amplifier 101 and second input is connected to the linearly variable reference voltage generator 102.
The amplifier 101 amplifies output current received from the current transformer 104. The circuit arrangement 105 feeds positive signal from the current transformer secondary 104 to positive terminal of the non-inverting amplifier 101. The linearly variable reference voltage generator 102 generates a variable reference voltage on averaging gate voltage of the pulse width modulation circuit 106 using resistor 107 and resistor 108. The generated variable reference voltage corresponds to input voltage variation. The resistor 111 compensates the input voltage variation and aids startup by acting as pull up resistor. The capacitor 109 is used to average the gate voltage 106 and the Zener diode 110 limits maximum value of the reference voltage112. The comparator 103 compares output from the amplifier 101 with a variable reference voltage from the linearly variable reference voltage generator 102 and generates a shutdown signal 113. The shutdown signal 113 during conditions of overcurrent, overload, fault and short circuit shuts down signal from the pulse width modulating circuit 106 to protect a power converter.
For example, the tables shown depict the performance of the protection circuit in comparison with traditional circuit for output loads: 10V/1A, 15V/1A, 7.5V/3A, 20V/0.5A, 20V/0.5A and 10V/2.8A. The protection circuit gives better over current protection limit compared to the old circuit for various input voltages at different output load.
Output Load: 10V/1A, 15V/1A, 7.5V/3A
Normal condition Overload condition With old circuit Overload condition With new circuit
Vin (V) Iin @ Nom. Load (A) Pin @ Nom. Load (W) Iin @ OCP Triggering point (A) Pin @ triggering point (W) OCP limit (%) Iin @OCP Triggering point (A) Pin @ triggering point (W) OCP limit (%)
20 3.08 61.6 3.86 77.2 125.3 3.86 77.2 125.3
28 2.37 66.36 3.86 108.08 162.9 3.07 85.96 129.5
36 1.88 67.68 3.86 138.96 205.3 2.4 86.4 127.7
42 1.64 68.88 3.86 162.12 235.4 2.07 86.94 126.2
50 1.41 70.5 3.86 193 273.8 1.7 85 120.6

Output Load: 20V/0.5A, 20V/0.5A, 10V/2.8A
Normal condition Overload condition With old circuit Overload condition With new circuit
Vin (V) Iin @ Nom. Load (A) Pin @ Nom. Load (W) Iin @ OCP Triggering point (A) Pin @ Triggering point (W) OCP limit (%) Iin @ OCP Triggering point (A) Pin @ triggering point (W) OCP limit (%)
20 3.01 60.2 4.01 80.2 133.2 4.01 80.2 133.2
28 2.25 63 4.01 112.28 178.2 3.1 86.8 137.8
36 1.74 62.64 4.01 144.36 230.5 2.33 83.88 133.9
42 1.56 65.52 4.01 168.42 257.1 2.07 86.94 132.7
50 1.34 67 4.01 200.5 299.3 1.76 88 131.3

The invention provides an adaptive protection circuit for a power converter. The power converter as described herein and as illustrated through the accompanying drawing provides input overcurrent protection, output short circuit protection and output overload protection, for varying input voltage range.

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.