Current sensing apparatus for resonant tank in an LLC resonant converter
An apparatus comprises a magnetic device coupled to an inductor-inductor-capacitor (LLC) resonant converter, an ac current sensing circuit coupled to the magnetic device, an average current sensing circuit coupled to the ac current sensing circuit and a reference voltage source coupled to the average current sensing circuit, wherein the reference voltage source is configured such that a magnitude of an average signal from the average current sensing circuit is greater than a voltage level of the reference voltage source.
1. A converter comprising:
a switch network coupled to a power source, wherein the switch network comprises a plurality of power switches;
a resonant tank coupled to the plurality of power switches, wherein the resonant tank comprises a series resonant inductor and a series resonant capacitor;
a transformer coupled to the resonant tank;
an output stage coupled to the transformer; and
a current sensing apparatus coupled to the series resonant inductor through a magnetic coupling, wherein the current sensing apparatus is configured to:
generate a detected signal proportional to a current flowing through the series resonant inductor; and
output an average signal of the detected signal.
2. The converter of claim 1 , wherein:
the magnetic coupling is implemented as a signal transformer, and wherein:
a primary side of the signal transformer is the series resonant inductor; and
a secondary side of the signal transformer is coupled to the current sensing apparatus.
3. The converter of claim 2 , wherein:
the current sensing apparatus comprises a reference voltage source, and wherein the reference voltage source is configured so that a magnitude of the average signal is greater than a voltage level of the reference voltage source.
4. The converter of claim 3 , wherein:
the voltage level of the reference voltage source is about 0.8 V.
5. The converter of claim 3 , wherein:
the transformer is a center-tapped transformer.
6. The converter of claim 3 , wherein the current sensing apparatus comprises:
a first resistor having a first terminal coupled to a first side of the secondary side of the signal transformer and a second terminal coupled to a second output of the current sensing apparatus through a second resistor;
a first capacitor coupled between the second terminal of the first resistor and a second side of the secondary side of the signal transformer; and
a second capacitor coupled to the second side of the secondary side of the signal transformer.
7. The converter of claim 3 , wherein the current sensing apparatus comprises:
a first resistor having a first terminal coupled to a second side of the secondary side of the signal transformer;
a first capacitor coupled between a second terminal of the first resistor and a first terminal of a second capacitor; and
the second capacitor having a second terminal coupled to a first side of the secondary side of the signal transformer.
8. The converter of claim 1 , wherein:
the converter is an LLC resonant converter.
9. An apparatus comprising:
a magnetic device coupled to an inductor-inductor-capacitor (LLC) resonant converter;
an ac current sensing circuit coupled to the magnetic device;
an average current sensing circuit coupled to the ac current sensing circuit, wherein a detected signal at an output of the average current sensing circuit is proportional to a current flowing through a series resonant inductor of the LLC resonant converter; and
a reference voltage source coupled to the average current sensing circuit, wherein the reference voltage source is configured such that a magnitude of an average signal from the average current sensing circuit is greater than a voltage level of the reference voltage source, and wherein the reference voltage source is configured to provide an offset on the average signal.
10. The apparatus of claim 9 , wherein:
the magnetic device is a signal transformer, wherein a primary side of the signal transformer is a series resonant inductor of the LLC resonant converter.
11. The apparatus of claim 9 , wherein:
the magnetic device is a signal transformer, wherein a primary side of the signal transformer is a winding of a transformer of the LLC resonant converter.
12. The apparatus of claim 9 , wherein:
the ac current sensing circuit comprises:
a first resistor having a first terminal coupled to a second side of a secondary side of a signal transformer;
a first capacitor coupled between a second terminal of the first resistor and a first terminal of a second capacitor; and
the second capacitor having a second terminal coupled to a first side of the secondary side of the signal transformer; and
the average current sensing circuit comprises:
a rectifier formed by a first diode; and
a resistor-capacitor (RC) filter.
13. The apparatus of claim 12 , further comprising:
a temperature compensation circuit formed by the first diode and a second diode, wherein the second diode and the first capacitor are connected in parallel.
14. The apparatus of claim 9 , wherein:
the ac current sensing circuit comprises:
a first resistor having a first terminal coupled to a first side of a secondary side of a signal transformer and a second terminal coupled to a resistor-capacitor (RC) filter;
a first capacitor coupled between the second terminal of the first resistor and a second side of the secondary side of the signal transformer; and
a second capacitor coupled to the second side of the secondary side of the signal transformer; and
the average current sensing circuit comprises:
a rectifier formed by a first diode; and
the resistor-capacitor (RC) filter.
15. The apparatus of claim 9 , wherein:
an output voltage level of the reference voltage source is in a range from about 0.8 V to about 3.3 V.
16. A method comprising:
providing a resonant converter, wherein the resonant converter comprises:
a switch network coupled to a power source, wherein the switch network comprises a plurality of power switches;
a resonant tank coupled to the plurality of power switches, wherein the resonant tank comprises a series resonant inductor and a series resonant capacitor;
an isolation device coupled to the resonant tank;
an output stage coupled to the isolation device through a rectifier; and
a current sensing apparatus;
detecting an ac signal proportional to a current flowing through the series resonant inductor;
providing a reference voltage source coupled to the current sensing apparatus; and
converting the ac signal into an average current signal, wherein a magnitude of the average current signal is greater than a voltage level of the reference voltage source.
17. The method of claim 16 , further comprising:
providing a temperature compensation circuit coupled to the current sensing apparatus, wherein the temperature compensation circuit is formed by at least one diode.
18. The method of claim 16 , further comprising:
coupling the current sensing apparatus to the series resonant inductor through a signal transformer, wherein a primary side of the signal transformer is the series resonant inductor.
19. The method of claim 16 , wherein:
the isolation device is a power transformer.
20. The method of claim 19 , further comprising:
coupling the current sensing apparatus to the power transformer through a signal transformer, wherein a primary side of the signal transformer is a winding of the power transformer.