RV converter with current mode and voltage mode switching
View Patent ↗A switched mode converter is disclosed that includes mode logic for switching between a voltage mode and a current mode. The converter includes circuitry for sensing current on the primary side of the transformer, load current on the secondary side, and output voltage. When the load current is less than a predetermined value, the output voltage of the voltage mode controller is used to control the duty cycle of a PWM controller. When the load current is greater than a predetermined value, the primary current is used to control the PWM controller. During a light load the converter is voltage controlled and there is no minimum load needed to stabilize the control loop. In a current-mode, the control loop will have a relatively faster transient response and avoid flux imbalance in push-pull topology. The converter provides the advantages of both known voltage controlled and current controlled switched mode converters.
1. A method: for regulating a voltage from an external power supply, the method comprising the steps of:
(a). selectively connecting the external voltage to a high frequency transformer;
(b). rectifying the output of the high frequency transformer defining an output and an output voltage; and
(c) controlling the connection of said external voltage to said high frequency transformer as a function of the voltage of said output voltage and the load current defining a voltage mode and a current mode; and
(d) switching between said current mode and said voltage mode as a function of the load current at said output.
2. The method as recited in claim 1 , wherein step (d) comprises:
(d) operating in said voltage mode when the load current at said output is less than a predetermined value.
3. The method as recited in claim 1 , wherein step (d) comprises:
(d) operating in said current mode when the load current at said output is greater than a predetermined value.
4. A switched mode converter comprising:
a high frequency transformer configured to be selectively coupled to an external power source, said high frequency transformer defining an output and an output signal;
a rectification circuit coupled to said output of said high frequency transformer and rectifying said output signal to produce a load current for charging a battery coupled to said rectification circuit;
a high frequency switching circuit for selectively connecting said external power source to said high frequency transformer;
a pulse width modulator (PWM) for controlling said high frequency switching circuit;
a voltage mode controller for selectively controlling said PWM;
a current mode controller for selectively controlling said PWM; and
a mode switching device for selectively coupling said voltage mode controller and said current mode controller to said PWM defining a voltage mode and a current mode, wherein said mode switching device is configured to selectively couple said voltage mode controller and said current mode controller to said PWM as a function of said DC load current.
5. The switched mode converter as recited in claim 4 , wherein said switch mode converter operates in said current mode when said load current is greater than a predetermined value.
6. The switched mode converter as recited in claim 4 , wherein said switch mode converter operates in said voltage mode when said load current is less than a predetermined value.