BUCK CONVERTER WITH A STABILIZED SWITCHING FREQUENCY
A switchable buck-converter with zero voltage switching capability includes a non-linear inductor having an inductance as a function of a load current to allow for a constant switching frequency operation of the switchable buck-converter.
1 . A switchable buck-converter with zero voltage switching capability comprising a non-linear inductor having an inductance as a function of a load current to allow for a constant switching frequency operation of the switchable buck-converter.
2 . The switchable buck converter according to claim 1 , comprising: an output stage for generating an output voltage according to a control signal and an input voltage via a switching element comprising a high-side switch and a low-side switch, each switch having respective first and second main terminals and a respective control terminal driven by a respective driver of the switchable buck converter configured according to the control signal;
the first main terminal of the low-side switch being connected to ground of the output stage;
the second main terminal of the low-side switch and the first main terminal of the high-side switch being connected to a switch node of the output stage;
the second main terminal of the high-side switch being connected to an input voltage terminal of the output stage;
the output stage comprising the non-linear inductor connected to the switch node and an output capacitor connected to ground of the output stage;
the buck-converter being operable in a charge phase with the high-side switch being switched on and the low-side switch being switched off;
the buck-converter being further operable in a discharge phase with the high-side switch being switched off and the low-side switch being switched on;
the drivers being configured to implement zero voltage switching by allowing an inductor current flowing to the switch node such that a voltage drop across the high-side switch is nearly zero when switching from the discharge phase to the charge phase.
3 . The switchable buck-converter according to claim 2 , wherein the low-side driver is configured to implement zero voltage switching by keeping the low-side switch switched on to allow the inductor current flowing to the switch node to reach a value of sufficient magnitude to drive a potential of the switch node back to the input voltage prior to switching on the high-side switch.
4 . The switchable buck-converter according to claim 2 , wherein the low-side driver is configured to implement zero voltage switching by keeping the low-side switch switched on until the inductor current flowing to the switch node exceeds a pre-determined value.
5 . The switchable buck converter according to claim 2 , wherein the low-side driver is configured to implement zero voltage switching by keeping the low-side switch switched on until a voltage drop across the low-side switch exceeds a threshold.
6 . The switchable buck converter according to claim 5 , wherein the low-side driver comprises
means for sensing the voltage drop across the low-side switch;
a comparator for comparing the voltage drop across the low-side switch against the threshold and
a latch for latching a drive signal of the low-side driver until the voltage drop across the low-side switch exceeds the threshold.
7 . The switchable buck-converter according to claim 6 , wherein the threshold has a value allowing zero voltage switching over a full input voltage range.
8 . The switchable buck converter according to claim 1 , wherein the non-linear inductor has an inductance in function of an inductor current such that the inductance reduces as the inductor current increases.
9 . The switchable buck converter according to claim 8 , wherein the non-linear inductor comprises a magnetic material.
10 . The switchable buck converter according to claim 9 , wherein the magnetic material exhibits a saturating relationship between flux density and magnetic field strength.
11 . The switchable buck converter according to claim 10 , wherein the non-linear inductor comprises a core of magnetic material and is configured to operate in a controlled saturation region of the magnetic material.
12 . The switchable buck converter according to claim 10 , wherein the non-linear inductor comprises soft saturation magnetic material compositions.
13 . The switchable buck converter according to claim 11 , wherein the non-linear inductor is configured such that its inductance as a function of the inductor current corresponds to a pre-calculated inductance.
14 . The switchable buck converter according to claim 13 , wherein the pre-calculated inductance results in an inductor current to allow for a constant frequency operation of the buck converter.
15 . The switchable buck-converter according to claim 2 , wherein the control signal is a pulse width modulation signal and wherein a drive signal of the high-side switch corresponds to the PWM signal and the drive signal of the low-side switch corresponds to the complement of the PWM signal.
16 . The switchable buck converter according to claims 12 , wherein the non-linear inductor is configured such that its inductance as a function of the inductor current corresponds to a pre-calculated inductance.
17 . The switchable buck converter according to claim 16 , wherein the pre-calculated inductance results in an inductor current to allow for a constant frequency operation of the buck converter.