POWER CONVERTER
LLC power converters are disclosed that operate in the soft switching region and are defined by a range of frequencies within which soft switching occurs. The LLC power converters include an LLC tank circuit in which the values of the inductors and the capacitors are scaled by a frequency scaling factor and a power scaling factor based on selected design parameters for the LLC power converter. The switching frequency of the disclosed LLC power converters can be varied by an output voltage to switching frequency controller.
1 . An LLC tank circuit with a design maximum input voltage and design output voltage, the LLC tank circuit, comprising:
a first inductor;
a second inductor electrically coupled in series with the first inductor; and
a capacitor electrically coupled in series with the first inductor and the second inductor,
wherein values of the first inductor, the second inductor, and the capacitor are selected such that the design output voltage is maintained over a range of input voltages from at least 65% to 100% of the design maximum input voltage with an efficiency of at least 90% at maximum design load over the input voltage range 65%-100%.
2 . The LLC tank circuit of claim 1 , wherein the first inductor includes a parasitic inductance.
3 . The LLC tank circuit of claim 1 , wherein the first inductor is a discrete inductor.
4 . The LLC tank circuit of claim 1 , wherein the first inductor has a first inductance and the second inductor has a second inductance that is 9 times greater than the first inductance.
5 . The LLC tank circuit of claim 4 , wherein the applied load is applied across the second inductor.
6 . The LLC tank circuit of claim 5 , wherein the applied load is applied directly across the second inductor.
7 . The LLC tank circuit of claim 5 , wherein the applied load is applied by turn-ratio winding that is coupled to the second inductor.
8 . The LLC tank circuit of claim 1 , wherein the design output voltage is maintained over the range of input voltages from 20% to 100% of the design maximum input voltage when the applied load varies between the maximum design load and no load.
9 . The LLC tank circuit of claim 1 , wherein a frequency of the LLC converter stage is fixed between a first limit and a second limit, the first limit defined by resonant frequency peaks formed by a frequency of the first inductor, the second inductor, and the capacitor and the second limit defined by resonant frequency peaks formed by a frequency of the first inductor and the capacitor.
10 . The LLC tank circuit of claim 1 , wherein an inductive phase angle is maintained through the range of input voltages.
11 . The LLC tank circuit of claim 1 , wherein the values of the first inductor, the second inductor, and the capacitor are selected such that the design output voltage is maintained over a range of input voltages from 50% to 100% of the design maximum input voltage.
12 . The LLC tank circuit of claim 1 , wherein the values of the first inductor, the second inductor, and the capacitor are selected such that the design output voltage is maintained over a range of input voltages from 25% to 100% of the design maximum input voltage.
13 . The LLC tank circuit of claim 1 , wherein an applied load varies between the maximum design load and 50% of the maximum design load.
14 . An LLC converter stage with a design maximum input voltage and design output voltage, the LLC converter stage comprising:
an output voltage to switching frequency controller;
a first inductor;
a second inductor electrically coupled in series to the first inductor; and
a capacitor electrically coupled in series with the first inductor and the second inductor,
wherein values of the first inductor, the second inductor, and the capacitor are selected such that the design output voltage is maintained over a range of input voltages from at least 65% to 100% of the design maximum input voltage, with an efficiency of at least 90% at maximum design load over the input voltage 65%-100%.
15 . A method of operating an LLC tank circuit, comprising:
selecting values for an LLC kernel that includes:
a first inductor;
a second inductor electrically coupled in series with the first inductor; and
capacitor electrically coupled in series with the first inductor and the second inductor,
wherein values of the first inductor, the second inductor, and the capacitor are selected such that the design output voltage is maintained over a range of input voltages from at least 65% to 100% of the design maximum input voltage with an efficiency of at least 90% at maximum design load over the input voltage range 65%-100%;
adjusting values of the first inductor, the second inductor, and the capacitor by a frequency scaling factor that is a ratio of a maximum frequency of the kernel and a minimum frequency of the kernel; and
further adjusting the frequency adjusted values of the first inductor, the second inductor, and the capacitor by a power scaling factor that is a ratio of a peak power output of the kernel at maximum line and a peak power output when the maximum design load is applied to the kernel.
16 . The method of claim 14 , further comprising:
providing an output voltage to switching frequency controller; and
operating the output voltage to switching frequency controller based on the output voltage measured from the LLC tank circuit.