Synchronous rectifier control for synchronous boost converter
View Patent ↗A synchronous boost DC/DC conversion system comprises an input for receiving a DC input voltage, an output for producing a DC output voltage, a power switch controllable to adjust an output signal of the conversion system, and an inductor coupled to the input. A synchronous rectifier is configurable to create a conduction path between the inductor and the output to provide the inductor discharge. A control circuit is provided for controlling the synchronous rectifier as the input voltage approaches the output voltage, so as to adjust average impedance of the conduction path over a discharge period of the inductor.
1. A synchronous boost DC/DC conversion system, comprising:
an input for receiving a DC input voltage, to which an inductor is coupled,
an output for producing a DC output voltage,
a power switch controllable to adjust an output signal of the conversion system,
a synchronous rectifier configurable to provide a conduction path between the inductor and the output, and
a control circuit for controlling the synchronous rectifier as the input voltage approaches the output voltage, so as to adjust average impedance of the conduction path over a discharge period of the inductor,
wherein the control circuit is configured to continuously increase the average impedance as the input voltage approaches the output voltage.
2. A synchronous boost DC/DC conversion system, comprising:
an input for receiving a DC input voltage, to which an inductor is coupled,
an output for producing a DC output voltage,
a power switch controllable to adjust an output signal of the conversion system,
a synchronous rectifier configurable to provide a conduction path between the inductor and the output, and
a control circuit for controlling the synchronous rectifier as the input voltage approaches the output voltage, so as to adjust average impedance of the conduction path over a discharge period of the inductor,
wherein the control circuit is configured to incrementally increase the average impedance as the input voltage approaches the output voltage.
3. A synchronous boost DC/DC conversion system, comprising:
an input for receiving a DC input voltage, to which an inductor is coupled,
an output for producing a DC output voltage,
a power switch controllable to adjust an output signal of the conversion system,
a synchronous rectifier configurable to provide a conduction path between the inductor and the output, and
a control circuit for controlling the synchronous rectifier as the input voltage approaches or exceeds the output voltage, so as to adjust average impedance of the conduction path over a discharge period of the inductor,
wherein the synchronous rectifier comprises a synchronous switch provided between the inductor and the output, and the control circuit is configured to gradually reduce a conduction period of the synchronous switch as the input voltage approaches the output voltage.
4. A synchronous boost DC/DC conversion system, comprising:
an input for receiving a DC input voltage, to which an inductor is coupled,
an output for producing a DC output voltage,
a power switch controllable to adjust an output signal of the conversion system,
a synchronous rectifier configurable to provide a conduction path between the inductor and the output, and
a control circuit for controlling the synchronous rectifier as the input voltage approaches or exceeds the output voltage, so as to adjust average impedance of the conduction path over a discharge period of the inductor,
wherein the synchronous rectifier comprises a synchronous switch provided between the inductor and the output, and the control circuit is configured to supply a pulse-width modulation (PWM) signal to the synchronous switch so as to reduce a conduction period of the synchronous switch as the input voltage approaches the output voltage.
5. The system of claim 4 , wherein the synchronous switch is connected in parallel to a shunting element having impedance higher than impedance of the synchronous switch in a conduction state.
6. The system of claim 4 , wherein the synchronous switch includes a P-channel MOSFET element having a gate configured for receiving the input voltage during a reset portion of a switching cycle to provide reverse voltage in order to reset current flowing through the inductor.
7. The system of claim 4 , wherein the control circuit comprises a pulse width modulator for producing the PWM signal having a duty cycle variable with a threshold voltage.
8. The system of claim 7 , wherein the threshold voltage corresponds to a difference between the input voltage and the output voltage.
9. The circuit of claim 8 , wherein the threshold voltage is proportional to a difference between the input voltage and a sum of the output voltage and a first offset voltage.
10. The system of claim 8 , wherein the control circuit comprises a transconductance amplifier for generating output current proportional to the threshold voltage.
11. The system of claim 8 , wherein the pulse width modulator comprises a comparator for comparing a sawtooth signal with a signal corresponding to the threshold voltage to produce a signal for controlling the synchronous rectifier.
12. A method of converting a DC input voltage into a DC output voltage using a power switch, inductor and a synchronous rectifier, the method comprising the steps of:
controlling the power switch to adjust the output voltage, and
as the input voltage approaches the output voltage, adjusting average impedance of the synchronous rectifier over a discharge period of the inductor,
wherein the average impedance is adjusted so as to continuously increase the average impedance as the input voltage approaches the output voltage.
13. A method of converting a DC input voltage into a DC output voltage using a power switch, inductor and a synchronous rectifier, the method comprising the steps of:
controlling the power switch to adjust the output voltage, and
as the input voltage approaches the output voltage, adjusting average impedance of the synchronous rectifier over a discharge period of the inductor,
wherein the average impedance is adjusted so as to incrementally increase the average impedance as the input voltage approaches the output voltage.
14. A method of converting a DC input voltage into a DC output voltage using a power switch, inductor and a synchronous rectifier, the method comprising the steps of:
controlling the power switch to adjust the output voltage, and
as the input voltage approaches the output voltage, adjusting average impedance of the synchronous rectifier over a discharge period of the inductor,
wherein the average impedance is adjusted so as to reduce a conduction period of the synchronous rectifier as the input voltage approaches the output voltage.