Control of the output power of a DC-DC converter upon varying the switching frequency
AssigneeSGS-Thomson Microelectronics S.A.
InventorsClaudio Adragna, Giuseppe Gattavari, Mauro Fagnani
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Abstract
The power output of a static DC--DC converter employing a current mode PWM controller is controlled upon the varying of the switching frequency, by detecting the sawtooth signal produced by the local oscillator generating a DC signal with an amplitude inversely proportional to the frequency. The power output is controlled by alternatively clamping the output voltage of the error amplifier of the PWM controller at a voltage proportional to the amplitude of the DC signal, or by offsetting the signal present on the current sensing resistor by a voltage corresponding to the difference between a constant voltage and the DC signal.
Claims33
A method of controlling the power output of a static DC--DC converter of a type comprising a current mode PWM controller, the current mode PWM controller comprising an oscillator including a resistor-capacitor (R-C) circuit connected between a node at a reference voltage and ground, and an error amplifier having an output voltage referred to a pre-established voltage, the method comprising the steps of:
- detecting a periodic signal produced by the oscillator on the capacitor of the R-C circuit and generating a DC signal having an amplitude inversely related to a frequency of the periodic signal;
- and
- clamping the output voltage of the error amplifier at a voltage having an amplitude related to the amplitude of the generated DC signal.
A method of controlling the power output of a static DC--DC converter of a type comprising a current mode PWM controller and a power switch connected thereto, the current mode PWM controller comprising an oscillator including a resistor-capacitor (R-C) circuit connected between a node at a reference voltage and ground, a current sensing resistor functionally connected in series with the power switch, and a current control circuit using the current sensing resistor, the method comprising the steps of:
- detecting a periodic signal produced by the oscillator on the capacitor of the R-C circuit and generating a DC signal having an amplitude inversely related to a frequency of the periodic signal;
- and
- offsetting a signal present on said current sensing resistor by a voltage corresponding to a difference between a constant voltage and the generated DC signal.
A current mode PWM controller comprising:
- an oscillator including a resistor and a first capacitor defining a resistor-capacitor (R-C) circuit coupled between a node at a reference voltage and ground;
- an error amplifier of an output voltage referred to a pre-established voltage;
- and
- a current control circuit comprising a current sensing resistor to be functionally connected in series with a power switch, and control means for controlling an output power by varying a switching frequency of the power switch, said control means comprising
- a detecting and generating circuit for detecting a periodic signal produced on the first capacitor of said R-C circuit and for generating a DC signal having an amplitude inversely related to a frequency of the periodic signal, and
- a clamp stage for clamping the output voltage of said error amplifier at a voltage level related to the DC signal.
A current mode PWM controller comprising:
- an oscillator including a resistor and a first capacitor defining a resistor-capacitor (R-C) circuit coupled between a node at a reference voltage and ground;
- an error amplifier of an output voltage referred to a pre-established voltage;
- and
- a current control circuit comprising a current sensing resistor to be functionally connected in series with a power switch and control means for controlling an output power by varying a switching frequency of the power switch, said control means comprising
- a detecting and generating circuit for detecting a periodic signal produced on the first capacitor of said R-C circuit and for generating a DC signal having an amplitude inversely related to a frequency of the periodic signal, and
- an offset circuit for offsetting a signal present on said current sensing resistor by a voltage corresponding to a difference between a constant voltage and the oscillator DC signal.
A power supply for a scanning circuit of a cathode ray tube operating at varying frequencies of synchronization and comprising:
- a static DC--DC converter comprising a current mode PWM controller, said current mode PWM controller comprising
- an oscillator including a resistor and a first capacitor defining a resistor-capacitor (R-C) circuit coupled between a node at a reference voltage and ground;
- an error amplifier of an output voltage referred to a pre-established voltage;
- and
- a current control circuit comprising a current sensing resistor to be functionally connected in series with a power switch and control means for controlling an output power by varying a switching frequency of the power switch, said control means comprising
- a detecting and generating circuit for detecting a periodic signal produced on the first capacitor of said R-C circuit and for generating a DC signal having an amplitude inversely related to a frequency of the periodic signal, and
- a clamp stage for clamping the output voltage of said error amplifier at a voltage level related to the DC signal.
A power supply for a scanning circuit of a cathode ray tube operating at varying frequencies of synchronization and comprising:
- a static DC--DC converter comprising a current mode PWM controller, said current mode PWM controller comprising
- an oscillator including a resistor and a first capacitor defining a resistor-capacitor (R-C) circuit coupled between a node at a reference voltage and ground;
- an error amplifier of an output voltage referred to a pre-established voltage;
- and
- a current control circuit comprising a current sensing resistor to be functionally connected in series with a power switch and control means for controlling an output power by varying a switching frequency of the power switch, said control means comprising
- a detecting and generating circuit for detecting a periodic signal produced on the first capacitor of said R-C circuit and for generating a DC signal having an amplitude inversely related to a frequency of the periodic signal, and
- an offset circuit for offsetting a signal present on said current sensing resistor by a voltage corresponding to a difference between a constant voltage and the DC signal.
Dependencies are inferred from the claim text.