System, method and apparatus to transition between pulse width modulation and pulse-frequency modulation in a switch mode power supply
AssigneeMicrochip Technology Incorporated
InventorScott C. Dearborn
Life of this patent
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Abstract
A switch mode power supply (SMPS) has optimized efficiency over an entire operating range, from no load to full load, by transitioning between pulse frequency modulation (PFM) and pulse width modulation (PWM) for control of the SMPS depending upon load current. Accurate, smooth, and seamless transitions between PFM and PWM modes of operation occur at a preset load current(s). PFM operation improves efficiency during light load conditions, and PWM has better efficiency at higher load currents. This is advantageous in battery powered applications, and thereby results in a longer time before battery replacement or recharge is necessary.
Claims22
A switch mode power supply (SMPS) using pulse-density modulation (PDM) control or pulse-width modulation (PWM) control, said SMPS comprising:
- a switch mode power supply (SMPS) converter;
- and
- a load determination circuit for detecting when a load current reaches a transition current value, comprising:
- a PWM error generator generating a PWM demand signal,
- a threshold generator generating a PDM demand signal;
- a hysteretic comparator receiving a current sense signal and being operable to enable the PWM error generator and the PDM threshold generator dependent on the current sense signal;
- and
- a fixed frequency oscillator and power circuit driver receiving th PWM demand signal and the PDM demand signal, wherein, when the PWM error generator and PDM threshold generator are enabled, the fixed frequency oscillator and power circuit driver outputs fixed frequency pulses or pulse width modulated pulses having said fixed frequency depending on whether the PWM error generator generates a duty cycle demand signal.
A method for controlling a switch mode power supply (SMPS) using pulse-density modulation (PDM) control or pulse-width modulation (PWM) control, said method comprising the steps of:
- determining a load current of a switch mode power supply (SMPS) converter;
- comparing the load current to a transition current value;
- providing pulses having a fixed frequency and a predetermined pulse width;
- if the load current is below the transition current value;
- performing a pulse density modulation of said fixed frequency pulses;
- and if the load current is equal or above the transition current value then performing a pulse width modulation of said pulses having a fixed frequency.
Dependencies are inferred from the claim text.