Error amplifying and frequency compensating circuits and methods
Methods and systems for implementing a closed loop DC-DC converter utilize a compensator to stabilize the output voltage of the DC-DC converter while improving the loop gain in the band of interest. A compensator may be implemented by an operational amplifier and a feedback circuit. The operational amplifier may be configured to receive a fraction of sensed output voltage at the non-inverting terminal and compare the sensed output voltage with the voltage received at the inverting terminal to generate an error signal which is used to determine the duty cycle of a pulse-width modulated signal.
1. A compensation circuit for a dc-dc converter, the compensation circuit comprising:
an amplifier comprising an inverting input coupled to a reference voltage, a non-inverting input coupled to receive a fraction of an output voltage from the dc-dc converter, and an output, wherein the amplifier is operable to generate a first control signal in response to the non-inverting input and inverting input;
a feedback circuit coupled between the amplifier output and the inverting input; and
a subtractor coupled to the reference voltage and the output of the amplifier, wherein the subtractor is operable to receive the first control signal and generate a second control signal, wherein the second control signal is generated by determining a difference of the reference voltage and the first control signal;
wherein the second control signal modulated a duty cycle of the dc-dc converter.
2. The compensation circuit of claim 1 , wherein the feedback circuit further comprises a feedback capacitor connected in parallel with a feedback resistor.
3. The compensation circuit of claim 1 , further comprising a reference voltage source, wherein the reference voltage source is coupled to the inverting input of the amplifier.
4. The compensation circuit of claim 3 wherein the reference voltage is a fixed voltage that controls dc-dc converter output level.
5. The compensation circuit of claim 3 , further comprising passive components coupled between the reference voltage source and the inverting input of the amplifier.
6. The compensation circuit of claim 3 wherein the feedback circuit comprises a low-pass filter having a capacitor coupled between the output and the reference voltage source.
7. The compensation circuit of claim 1 further comprising a resistor divider operable to receive the output voltage from the dc-dc converter and generate the fraction of the output voltage.
8. The compensation circuit of claim 1 further comprising a pulse width modulator coupled to the output of the subtractor and operable to regulate the output voltage based on the second control signal.
9. The compensation circuit of claim 8 wherein the pulse width modulator is further operable to generate binary signals based on the second control signal.
10. The compensation circuit of claim 9 , wherein a duty cycle of the binary signals is controlled by the control signal.
11. The compensation circuit of claim 10 further comprising:
a switch network having a first switching device connected between an inductor and a reference node and a second switching device connected between the inductor and an output capacitor;
wherein the first and second switching devices alternate between a conducting state and a blocking state in response to the binary signals.
12. A method for stabilizing a dc-dc converter, the method comprising:
receiving a fraction of an output voltage from the dc-dc converter at a non-inverting input of an amplifier;
receiving a feedback voltage and a portion of a reference voltage at an inverting input of the amplifier;
generating an output signal from the amplifier in response to the fraction of the output voltage from the dc-dc converter; and
generating a control signal to modulate a duty cycle of the dc-dc converter via a subtractor based on a voltage difference between the reference voltage and the output signal generated by the amplifier.
13. The method of claim 12 , wherein the fraction of the output voltage is generated via a voltage divider.
14. The method of claim 13 , further comprising:
generating a pulse-width modulated signal based on the control signal; and
regulating the output voltage of the dc-dc convertor using the pulse width modulated signal.
15. The method of claim 14 further comprising:
controlling a first switching device and a second switching device using binary signals generated by a pulse width modulator.
16. The method of claim 15 , wherein the second switching device conducts current when the first switching device is in a blocking state.
17. A DC-DC boost converter comprising:
a switch network having a first switching device connected between an inductor and a reference node and a second switching device connected between the inductor and an output capacitor, wherein the first and second switching devices alternate between a conducting state and a blocking state in response to a first binary signal and a second binary signal, respectively;
an output low-pass filter having the output capacitor connected between an output node and the reference node;
a compensation network operable to generate an output signal in correspondence with an output voltage sensed at the output node, wherein the compensation network comprises an amplifier receiving a fraction of the output voltage at a non-inverting terminal of the amplifier and a feedback circuit connected between an output node of the amplifier and a inverting terminal of the amplifier; and
a modulator configured to generate the first and the second binary signals based on a control signal.
18. The dc-dc converter of claim 17 , wherein the second switching device conducts current when the first switching device is in the blocking state.
19. The dc-dc converter of claim 17 , wherein the first switching device is constructed using at least one of a diode, a metal oxide semiconductor field effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), a bipolar junction transistor (BJT), and a thyristor.