Claims:We Claim:
1. An improved circuit for varying the output voltage of a buck converter using an external command, the improved circuit comprising of:
an external voltage source (7) for supplying an analog voltage command (7a);
a differential amplifier (8) connected to the external voltage source (7) for obtaining differential output from the supplied analog voltage command (7a);
an error amplifier (9) having a first input terminal (9a) connected an output (8a) of the differential amplifier (8) and a second input terminal (9b) connected to an output (6a) of a voltage divider (6) for generating an error signal; and
a buck converter integrated circuit (3) connected to an output (9c) of the error amplifier (9) for varying the output voltage of the buck converter based on the error signal.
2. The circuit as claimed in the claim 1, wherein the analog voltage command (7a) is a DC voltage command.
3. The circuit as claimed in the claim 1, wherein the first input terminal (9a) is configured for receiving a minimum reference voltage
4. The circuit as claimed in the claim 1, wherein the minimum reference voltage is obtained by adding the differential output with a 2.5V reference voltage.
5. The circuit as claimed in the claim 1, wherein the error signal is generated by comparing the minimum reference voltage with respect to the output voltage.
6. The circuit as claimed in the claim 1, wherein the output voltage can be reduced linearly when the analog voltage command (7a) is reduced from 5V to 0V.

Bangalore RANI MADANAN
01st January 2021 (INTELLOCOPIA IP SERVICES)
AGENT FOR APPLICANT
, Description:AN IMPROVED CIRCUIT FOR VARYING THE OUTPUT VOLTAGE OF A BUCK CONVERTER USING AN EXTERNAL COMMAND
FIELD OF INVENTION
The invention generally relates to the field of DC-DC converter and particularly to an improved circuit for varying the output voltage of a buck converter using an external command.
BACKGROUND
Normally buck converters are designed for generating a constant output voltage based on a fixed reference. In order to design variable output voltage buck converter, the voltage divider resistors need to be changed internally. As it is very difficult to internally change the voltage divider resistors, there is a requirement for an external circuit for varying the output voltage of the buck converter with ease. One of the systems known in the art discloses a power converter with output voltage control by using PWM command. The PWM command signal is coupled to an N channel MOSFET and the MOSFET is directly connected to a feedback voltage divider resistor for setting the output voltage. The disadvantage associated with the system is that there is chance of generation of more noise due to the use of the PWM command signal directly in the feedback path. Further, a complex circuitry is required for generating the PWM command signal corresponding to the output voltage. Hence there is need for an improved circuit for varying the output voltage of a buck converter by using an external command.

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.1shows a block diagram of an improved circuit for varying the output voltage of a buck converter using an external command, according to an embodiment of the invention.
FIG.2 shows a schematic diagram of an improved circuit for varying the output voltage of a buck converter using an external command, according to an embodiment of the invention.
SUMMARY OF THE INVENTION
The invention provides an improved circuit for varying the output voltage of a buck converter using an external command. The improved circuit includes an external voltage source for supplying an analog voltage command. A differential amplifier is connected to the third voltage source for obtaining a differential output from the supplied analog voltage command. An error amplifier having a first input terminal and a second input terminal are connected to an output of the differential amplifier and an output of a voltage divider respectively for comparing a minimum reference voltage with respect to the output voltage. The minimum reference voltage is obtained by adding the differential output with a 2.5V reference voltage. The error amplifier generates an error signal based on the comparison. An output of the error amplifier is connected to the buck converter integrated circuit for varying the output voltage of the buck converter integrated circuit based on the error signal.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide an improved circuit for varying the output voltage of a buck converter using an external command.
FIG.1 shows a block diagram of an improved circuit for varying the output voltage of a buck converter using an external command, according to an embodiment of the invention. The buck converter includes a first voltage source 1 for supplying VCC and a second voltage source 2 for supplying Vin. A buck converter integrated circuit 3 is connected to the first voltage source1. Electronic switches 4 are connected to the buck converter integrated circuit 3. An inductor 5 is connected to the electronic switches 4 and a voltage divider 6 is coupled to the inductor 5. The improved circuit includes an external voltage source 7 for supplying an analog voltage command 7a. In one example of the invention, the analog voltage command 7a is a DC voltage command. A differential amplifier 8 is connected to the third voltage source 7 for obtaining a differential output from the supplied analog voltage command 7a. A fixed reference voltage of 2.5V is generated from the first voltage source 1. The 2.5V reference voltage is added with the differential output of the differential amplifier for setting a minimum reference voltage, when the analog voltage command 7a is 0V. An error amplifier 9 having a first input terminal and a second input terminal are connected to an output of the differential amplifier 8 and an output of the voltage divider 6, respectively. The error amplifier 9 compares the minimum reference voltage with respect to the output voltage and generates an error signal. An output of the error amplifier 9 is connected to the buck converter integrated circuit 3 for varying the output voltage of the buck converter integrated circuit 3 based on the error signal.
FIG.2 shows a schematic diagram of an improved circuit for varying the output voltage of a buck converter using an external command, according to an embodiment of the invention. The buck converter includes a first voltage source 1 (not shown) for supplying VCC and a second voltage source 2 (not shown) for supplying Vin. A buck converter integrated circuit 3 is connected to the first voltage source 1. Electronic switches 4 are connected to the buck converter integrated circuit 3. An inductor 5 is connected to the electronic switches 4 and a voltage divider 6 is coupled to an output of the inductor 5. The improved circuit includes an external voltage source 7(not shown) for supplying an analog voltage command 7a. In one example of the invention, the analog voltage command is a DC voltage command. A differential amplifier 8 is connected to the third voltage source 7 for obtaining differential output from the supplied analog voltage command 7a. An error amplifier 9 having a first input terminal 9a and a second input terminal 9b are connected to an output 8a of the differential amplifier 8 and an output 6a of the voltage divider 6 respectively. The voltage divider 6 includes a series connected resistors, R17 and R18.A fixed reference voltage of 2.5V is generated from the first voltage source 1 and supplied to the first input terminal 9a of the error amplifier 9 through resistors R8 and R9. The 2.5V reference voltage is added with the differential output of the differential amplifier 8 for setting a minimum reference voltage, when the analog voltage command 7a is 0V. The first input terminal 9a has the sum of the differential output and 2.5 V reference voltage. A capacitor C4 is connected to the first input terminal 9a of the error amplifier 9 for providing smooth minimum reference voltage. The error amplifier 9 compares the minimum reference voltage with respect to the output voltage and generates an error signal. An output 9c of the error amplifier 9 is connected to the buck converter integrated circuit 3. The buck converter integrated circuit 3 varies the duty cycle based on the error signal. The varied duty cycle varies the output voltage.The output voltage can be reduced linearly when the analog voltage command 7a is reduced from 5V to 0V. In one example of the invention, the circuit can be used with an external digital command by increasing the value of a capacitor C4 for making the external digital command to smooth DC voltage.

Table-1 shows the electrical readings taken with the circuit of the present invention, when the external analog command is 5V.

Table-1:External analog command: 5V
Input Voltage (Volts) Input Current (Amps) Output Voltage (Volts) Output Current (Amps) Input Power (Watts) Output Power (Watts) Efficiency (%)
100.00 0.03 20.35 0.1 2.70 2.04 75.38
99.88 0.55 20.35 2.5 54.43 50.88 93.47
99.79 0.85 20.35 3.9 85.02 79.35 93.33

Table-2 shows the electrical readings taken with the circuit of the present invention, when the external analog command is 3.22V.
Table-2:External analog command: 3.22V
Input Voltage (Volts) Input Current (Amps) Output Voltage (Volts) Output Current (Amps) Input Power (Watts) Output Power (Watts) Efficiency (%)
100.00 0.03 17.79 0.1 2.50 1.78 71.16
99.90 0.48 17.79 2.5 48.15 44.48 92.36
99.82 0.75 17.79 3.9 75.06 69.38 92.42

Table-3 shows the electrical readings taken with the circuit of the present invention, when the external analog command is 1.5V.
Table-3:External analog command: 1.5V
Input Voltage (Volts) Input Current (Amps) Output Voltage (Volts) Output Current (Amps) Input Power (Watts) Output Power (Watts) Efficiency (%)
100.00 0.03 15.32 0.1 2.90 1.53 52.83
99.92 0.42 15.33 2.5 41.97 38.32 91.32
99.85 0.66 15.32 3.9 65.60 59.75 91.08

Hence, the improved circuit varies the output voltage of the buck converter without changing voltage divider resistors. The circuit is simple and can be used in all applications where variable output is required. 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.