Flyback switching mode power supply with voltage control and a method thereof
View Patent ↗A controller used to control a flyback switching mode power supply. The flyback switching mode power supply is constructed to charge a capacitor, and includes a rectifying device, a series arrangement of a switch and a primary winding of a transformer for receiving an input voltage, and a secondary winding of the transformer for charging the capacitor via the rectifying device to an output voltage. The controller is configured to sense the output voltage and to turn on the switch when the change of the output voltage over time becomes smaller than a predetermined threshold. By using the controller to sense and use the output voltage across the capacitor to turn on the switch, a controlled flyback switching mode power supply that makes use of voltage control is realized.
1. An integrated circuit comprising:
a flyback switching mode power supply including
an input terminal to receive an input voltage,
an output terminal to provide power to a load coupled to the output terminal,
a rectifying device connected to the output terminal,
a capacitor connected to the output terminal,
a series arrangement of a switch and a primary winding of a transformer, the series arrangement to receive the input voltage, and
a secondary winding of the transformer to provide current to charge the capacitor via the rectifying device; and
a controller to:
monitor a voltage at the capacitor;
calculate a first derivative of the voltage at the capacitor over time;
compare the first derivative to a predetermined threshold; and
turn on the switch in response to determining that the first derivative is less than the predetermined threshold.
2. The integrated circuit according to claim 1 , further configured for turning on the switch for a fixed duration.
3. The integrated circuit as claimed in claim 1 further configured for keeping the switch in an off state when the voltage at the capacitor has reached a predetermined target voltage.
4. The integrated circuit as claimed in claim 3 further configured for connecting the load in parallel with the capacitor for discharging the capacitor into the load after the voltage at the capacitor has reached the predetermined target voltage.
5. The integrated circuit as claimed in claim 1 , further comprising a sensing device to sense the voltage at the capacitor, and a pulse-width modulation unit for turning on and turning off the switch, the sensing device being configured for generating a feedback voltage proportional to the sensed voltage, the pulse-width modulation unit being arranged for receiving the feedback voltage to modulate a duration of the off state of the switch.
6. The integrated circuit as claimed in claim 5 , wherein the sensing device is a resistor ladder electrically connected in parallel with the capacitor for scaling down the voltage at the capacitor into the feedback voltage.
7. The integrated circuit as claimed in claim 5 , wherein the pulse-width modulation unit comprises an analogue to digital converter for converting the feedback voltage into a digital feedback value.
8. The integrated circuit as claimed in claim 1 , wherein the switch of the switching mode power supply is a MOS transistor.
9. The integrated circuit as claimed in claim 1 , wherein the predetermined threshold is less than 0.5 V per 10 us.
10. A capacitive discharge ignition system comprising the capacitor, and the controller as claimed in claim 1 .
11. The capacitive discharge ignition system as claimed in claim 10 , wherein the load in parallel with the capacitor comprises an ignition coil for receiving a charge from the capacitor during an ignition event.
12. The capacitive discharge ignition system as claimed in claim 11 comprising a battery for supplying power to the capacitive discharge ignition system.
13. A method of controlling a flyback switching mode power supply, the flyback switching mode power supply comprising:
an input terminal to receive an input voltage,
an output terminal to provide power to a load coupled to the output terminal,
a rectifying device connected to the output terminal,
a capacitor connected to the output terminal,
a series arrangement of a switch and a primary winding of a transformer, the series arrangement being arranged for receiving the input voltage, and
a secondary winding of the transformer to provide current for charging the capacitor via the rectifying device;
the method comprising:
monitoring a voltage at the capacitor;
calculating a first derivative of the voltage at the capacitor over time;
compare the first derivative to a predetermined threshold; and
turning on the switch in response to determining that the first derivative is less than the predetermined threshold.
14. The method as claimed in claim 13 , further comprising before the comparing:
comparing the voltage at the capacitor with a predetermined target voltage; and
performing the comparing of the change of the voltage at the capacitor over time with the predetermined threshold when the voltage at the capacitor is smaller than the predetermined target voltage.
15. The method according to claim 13 , further comprising turning on the switch for a fixed duration.
16. The method as claimed in claim 13 further comprising keeping the switch in an off state when the voltage at the capacitor has reached a predetermined target voltage.
17. The method as claimed in claim 16 further comprising connecting the load in parallel with the capacitor for discharging the capacitor into the load after the voltage at the capacitor has reached the predetermined target voltage.
18. The method as claimed in claim 13 , further comprising sensing the voltage at the capacitor, turning on and turning off the switch, generating a feedback voltage proportional to the sensed voltage, and receiving the feedback voltage to modulate a duration of the off state of the switch.
19. The method as claimed in claim 18 , further comprising scaling down the voltage at the capacitor into the feedback voltage using a resistor ladder.
20. The method as claimed in claim 18 , further comprising converting the feedback voltage into a digital feedback value.