Power converter with inductor current monitoring circuit based on inductor voltage
A current monitoring circuit for use with an inductor having a magnetizing phase and a de-magnetizing phase is presented. The current monitoring circuit has a voltage controlled oscillator and a first counter. The voltage controlled oscillator generates a clock signal based on a voltage across the inductor. The first counter generates a counter value using the clock signal. The current monitoring circuit may be implemented as part of a switched mode power supply having an inductor coupled to a pair of power switches and a controller adapted to generate a control signal to control the pair of power switches based on the counter value.
1 . A current monitoring circuit for use with an inductor having a magnetizing phase and a de-magnetizing phase, the current monitoring circuit comprising:
a voltage controlled oscillator adapted to generate a clock signal based on a voltage across the inductor; and
a first counter configured to generate a counter value using the clock signal.
2 . The current monitoring circuit as claimed in claim 1 , wherein the counter value is proportional to an inductor current through the inductor.
3 . The current monitoring circuit as claimed in claim 1 , wherein the clock signal has a frequency proportional to an absolute value of the voltage across the inductor.
4 . The current monitoring circuit as claimed in claim 1 , wherein the voltage controlled oscillator comprises:
a voltage to current converter adapted to convert the voltage across the inductor into a current signal; and
a current controlled oscillator adapted to generate the clock signal based on the current signal.
5 . The current monitoring circuit as claimed in claim 4 , wherein the current controlled oscillator comprises a ring oscillator.
6 . The current monitoring circuit as claimed in claim 5 , wherein the ring oscillator comprises a NAND gate coupled to a plurality of inverters.
7 . The current monitoring circuit as claimed in claim 1 , wherein the clock signal is configured to control a counting frequency of the first counter.
8 . The current monitoring circuit as claimed in claim 1 , wherein the first counter counts up or down based on a polarity of the voltage across the inductor.
9 . The current monitoring circuit as claimed in claim 8 , wherein during the magnetizing phase the first counter is counting up from a first counter value to a second counter value, and during a de-magnetizing phase the first counter is counting down from the second counter value to the first counter value.
10 . The current monitoring circuit as claimed in claim 1 , comprising a second counter.
11 . The current monitoring circuit as claimed in claim 10 , wherein during the magnetizing phase the second counter counts from an initial counter value to an end counter value, and during the de-magnetizing phase the first counter counts from the initial counter value to the end counter value.
12 . The current monitoring circuit as claimed in claim 10 , wherein the first and second counters are ripple counters.
13 . The current monitoring circuit as claimed in claim 1 , wherein the voltage to current converter comprises a first circuit configured to generate a current signal during the magnetizing phase, and a second circuit configured to generate a current signal during the de-magnetizing phase.
14 . A switched mode power supply comprising:
an inductor coupled to a pair of power switches;
a current monitoring circuit comprising a voltage controlled oscillator adapted to generate a clock signal based on a voltage across the inductor; and a first counter configured to generate a counter value using the clock signal; and
a controller adapted to generate a control signal to control the pair of power switches based on the counter value.
15 . The switched mode power supply as claimed in claim 14 , wherein the voltage controlled oscillator comprises:
a voltage to current converter adapted to convert the voltage across the inductor into a current signal; and
a current controlled oscillator adapted to generate the clock signal based on the current signal.
16 . The switched mode power supply as claimed in claim 14 , wherein the pair of power switches comprises a first power switch and a second power switch, the controller being operable in three states: a first state during which the first power switch is on, while the second power switch is off to magnetize the inductor, a second state during which the first power switch is off while the second power switch is on to de-magnetize the inductor and a third state during which the first and second power switches are both off.
17 . The switched mode power supply as claimed in claim 16 , wherein during the first state the counter value increases from a first counter value to a second counter value, and when the counter value reaches the second counter value the controller starts operating in the second state during which the counter value decreases from a second counter value to a first counter value.
18 . The switched mode power supply as claimed in claim 16 , wherein in the third state the controller is configured to disable the voltage to current converter and the oscillator and to reset the first counter.
19 . The switched mode power supply as claimed in claim 14 , comprising a second counter wherein during a magnetizing phase of the inductor, the second counter counts from an initial counter value to an end counter value, and during de-magnetizing phase of the inductor, the first counter counts from the initial counter value to the end counter value.
20 . The switched mode power supply as claimed in claim 19 , wherein the controller is configured to change state when the counter value reaches the end value.
21 . The switched mode power supply as claimed in claim 14 , comprising a calibration circuit configured to calibrate the counter value and to calculate an absolute value of the current through the inductor.
22 . The switched mode power supply as claimed in claim 14 , wherein the power supply has a switching frequency, and wherein the voltage controlled oscillator operates at a frequency greater than the switching frequency.
23 . A method of monitoring an inductor current comprising:
generating with a voltage controlled oscillator a clock signal based on a voltage across the inductor; and
generating with a first counter a counter value using the clock signal to monitor the inductor current.
24 . The method as claimed in claim 23 , wherein the inductor is coupled to a pair of power switches of a switched mode power supply, the method further comprising:
generating a control signal to control the pair of power switches based on the counter value.