Error amplifier and DC-DC converter and the method thereof

• US 20040160270A1
• Filed: 08/12/2003
• Published: 08/19/2004
• Est. Priority Date: 02/18/2003
• Status: Active Grant

• Current Assignee: Aimtron Technology Corp. (Global Mixed-Mode Technology Inc.)
• Original Assignee: Aimtron Technology Corp. (Global Mixed-Mode Technology Inc.)
• Inventors: Chen, Yung-Chih, Tzeng, Guang-Nan, Chen, Tien Tzu
• Granted Patent: US 6,911,867 B2
• Time in Patent Office: Days
• US Class Current: 330/10
• CPC Class Codes: H03F 1/303 using a switching device H03F1/305, H03F3/005, H03F3/38 take precedence
• CPC Class Codes: H03F 2203/45526 the FBC comprising a resistor-capacitor combination and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45546 the IC comprising one or more capacitors feedback coupled to the IC
• CPC Class Codes: H03F 2203/45601 the IC comprising one or more passive resistors by feedback
• CPC Class Codes: H03F 2203/45684 the LC comprising one or more buffers or driving stages not being of the emitter respectively source follower type, between the output of the dif amp and the output stage
• CPC Class Codes: H03F 3/38 DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers switched capacitor amplifiers H03F3/005
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence

Abstract

The DC-DC converter of the present invention sets the soft start function in the error amplifier. With soft start added, the error amplifier'"'"'s output voltage will follow the slowly ascending soft start voltage when the DC-DC converter is enabled. Then the soft start looses control over the error amplifier when the soft start voltage exceeds the steady state value of the error amplifier'"'"'s output voltage. And meanwhile, the amplifier'"'"'s input will take over the control. By doing so, the present invention significantly eradicates or reduces jitters caused by the output voltage of the error amplifier and the DC-DC converter.

Claims

1. An error amplifier, comprising:

a soft start signal;

an input signal;

a reference voltage;

an output signal converging to a steady state voltage;

a first amplification stage for amplifying the difference between the reference voltage and the input signal;

a clamp stage for clamping the output signal to the soft start signal when the soft start signal is smaller than the steady state voltage;

a buffer stage for driving the output signal; and

a second amplification stage including a first transistor controlled by the first amplification stage and a second transistor controlled by the clamp stage, wherein the outputs of the first transistor and second transistor are electrically connected to the buffer stage.

2. The error amplifier of claim 1, wherein the input signal is generated by a voltage divider.

3. The error amplifier of claim 1, wherein the clamp stage compares the input signal or output signal with the soft start signal.

4. The error amplifier of claim 1, wherein the first transistor is enabled when the soft start signal is larger than the steady state voltage, and the second transistor is enabled when the soft start signal is smaller than the steady state voltage.

5. An error amplifier, comprising:

a soft start signal exhibiting a slowly ascending characteristic when the error amplifier is enabled;

an output signal converging to a steady state voltage;

an input signal;

a reference voltage;

a clamp stage for clamping the output signal to the soft start signal when the soft start signal is smaller than the steady state voltage; and

an error amplification module for amplifying the difference between the reference voltage and the input signal when the soft start signal is larger than the steady state voltage.

6. The error amplifier of claim 5, wherein the clamp stage compares the input signal or output signal with the soft start signal.

7. The error amplifier of claim 5, further comprising a buffer stage, wherein the input of the buffer stage is connected to the clamp stage and the error amplification module, and the output of the buffer stage is connected to the output signal.

8. The error amplifier of claim 5, wherein the clamp stage and the error amplification module alternately output through a set of switching transistors.

9. A DC-DC converter, comprising:

an error amplifier recited as in claim 5;

a PWM comparator, one input of the PWM comparator connected to the error amplifier and another input connected to an oscillation curve; and

a driver connected to the PWM comparator for driving external electronic components of the DC-DC converter.

10. The DC-DC converter of claim 9, wherein the output of the error amplifier is between the maximal and minimal voltages for adjusting duty cycles.

11. The DC-DC converter of claim 9, wherein the output of the driver feeds back to the input of the driver through a voltage divider.

12. A DC-DC converting method, comprising the steps of:

providing a soft start signal and a reference voltage connected to an error amplifier, wherein the soft start signal ascends gradually when the error amplifier is enabled and the output of the error amplifier converges to a steady state voltage;

clamping the output of the error amplifier to the soft start signal when the soft start signal is smaller than the steady state voltage; and

amplifying the difference between the reference voltage and the input of the error amplifier when the soft start signal is larger than the steady state voltage.