Variable reference signal generator used with switching mode power supply and the method thereof

Patent metadata

Field	Value
Publication number	US-9841779-B2
Application number	US-201514937853-A
Country	US
Kind code	B2
Filing date	Nov 10, 2015
Priority date	Nov 21, 2014
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

A reference signal generator used with a switching mode power supply which converts an input voltage to an output voltage. The reference signal generator provides a reference signal consisting of a constant voltage signal and a variable voltage signal which is varying according to a duty cycle of the switching mode power supply during a startup period of the switching mode power supply and is varying according to a ratio of the input voltage at an end of the startup period to the input voltage of real time after the startup period.

First claim

What is claimed is:

1. A reference signal generator used with a switching mode power supply, wherein the switching mode power supply converts an input voltage to an output voltage, comprising:
a constant voltage generator configured to provide a constant voltage signal;
a voltage convert circuit having an input terminal configured to receive the input voltage, a first output terminal configured to provide a startup voltage converted digital signal indicative of the input voltage during a startup period of the switching mode power supply, and a second output terminal configured to provide a real time voltage converted digital signal indicative of the real time input voltage;
a duty cycle convert circuit, having an input terminal configured to receive a duty cycle signal indicative of a duty cycle of the switching mode power supply, and an output terminal configured to provide a duty cycle converted digital signal indicative of the duty cycle of the switching mode power supply; and
a variable voltage generator having a first input terminal coupled to the first output terminal of the voltage convert circuit to receive the startup voltage converted digital signal, a second input terminal coupled to the second output terminal of the voltage convert circuit to receive the real time voltage converted digital signal, a third input terminal coupled to the output terminal of the duty cycle convert circuit to receive the duty cycle converted digital signal, and an output terminal configured to provide a variable voltage signal based on the startup voltage converted digital signal, the real time voltage converted digital signal and the duty cycle converted digital signal;
wherein during the startup period of the switching mode power supply, a value of the variable voltage signal is directly proportional to the duty cycle of the switching mode power supply, and after the startup period of the switching mode power supply, the value of the variable voltage signal is directly proportional to the ratio of the input voltage at the end of the startup period to the real time input voltage, and wherein a reference signal is generated based on a sum of the constant voltage signal and the variable voltage signal.

2. The reference signal generator of claim 1 , wherein the constant voltage generator comprises:
a reference current source having an input terminal configured to receive an internal power supply and an output terminal configured to provide a preset reference current;
a reference resistor having a first terminal and a second terminal, wherein the first terminal is coupled to the output terminal of the reference current source to receive the preset reference current; and
a compensation resistor coupled between the second terminal of the reference resistor and a ground reference;
wherein the preset current provided by the reference current source flows through the reference resistor and the compensation resistor to generate the constant voltage signal across the reference resistor and the compensation resistor.

3. The reference signal generator of claim 1 , wherein the voltage convert circuit comprises:
a comparison circuit including N comparators, wherein each comparator has a first input terminal, a second terminal and an output terminal, and wherein the first input terminals of the comparators respectively receive threshold signals with different values, the second input terminals of the comparators receive the input voltage, and the output terminal of each comparator provides a digit to finally form the real time voltage converted digital signal; and
a latch circuit having an input terminal coupled to the output terminal of the comparison circuit to receive the real time voltage converted digital signal, a control terminal configured to receive a startup complete signal indicating a end of the startup period of the switching mode power supply, and an output terminal configured to provide the startup voltage converted digital signal based on the real time voltage converted digital signal and the startup complete signal;
wherein N is an integer and N>1.

4. The reference signal generator of claim 1 , wherein the duty cycle convert circuit comprises:
a frequency-voltage converter having an input terminal configured to receive the duty cycle signal and an output terminal configured to provide a voltage signal indicating the duty cycle of the switching mode power supply based on the duty cycle signal;
a comparison circuit having N comparators, wherein each comparator has a first input terminal, a second terminal and an output terminal, and wherein the first input terminals of the comparators respectively receive threshold signals with different values, the second input terminals of the comparators receive the voltage signal, and the output terminal of each comparator provides a digit to finally form the duty cycle converted digital signal;
wherein N is an integer and N>1.

5. The reference signal generator of claim 2 , wherein the variable voltage generator comprises:
a compensation current source having a first control terminal configured to receive the startup voltage converted digital signal, a second control terminal configured to receive the real time voltage converted digital signal, and an output terminal configured to provide a compensation current based on the startup voltage converted digital signal and the real time voltage converted digital signal; and
the compensation resistor having a first terminal coupled to the output terminal of the compensation current source to receive the compensation current, a second terminal coupled to the second terminal of the reference resistor, a third terminal connected to the ground reference and a control terminal configured to receive the duty cycle converted digital signal;
wherein the compensation current flows through part of the compensation resistor to generate the variable voltage signal, and the reference signal is provided at the connection node of the reference current source and the reference resistor.

6. The reference signal generator of claim 2 , wherein the variable voltage generator comprises:
a compensation current source having a first control terminal configured to receive the startup voltage converted digital signal, a second control terminal configured to receive the real time voltage converted digital signal, a third control terminal configured to receive a duty cycle converted digital signal, and an output terminal configured to provide a compensation current based on the startup voltage converted digital signal, the real time voltage converted digital signal and the duty cycle converted digital signal; and
the compensation resistor having a first terminal coupled to the output terminal of the compensation current source to receive the compensation current, a second terminal connected to the ground reference;
wherein the reference signal is provided at the connection node of the reference current source and the reference resistor.

7. The reference signal generator of claim 4 , wherein the frequency-voltage converter comprises:
a current source having a first terminal coupled to an internal power supply, and an output terminal configured to provide a preset current;
a first duty cycle switch, having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the second terminal of the current source to receive the preset current, the control terminal is configured to receive a high-side control signal of the switching mode power supply;
a logic circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is configured to receive the high-side control signal, the second terminal is configured to receive a l

Assignees

• Monolithic Power Systems Inc

Inventors

• Wang Yiwei
• Li Yike

Classifications

• G05F3/262 Primary

  using field-effect transistors only · CPC title

• H02M7/217

  using semiconductor devices only · CPC title

• G05F3/26

  Current mirrors · CPC title