Programmable feedback voltage pulse sampling for switched power supplies
View Patent ↗Disclosed is a method and apparatus that includes a power supply having a primary coil and a secondary coil. The secondary coil generates an output voltage and a feedback voltage related to the output voltage. The feedback voltage is sampled at a time instant that is digitally controllable. The output voltage is determined from the feedback voltage.
1. A circuit-implemented method for determining an output voltage of an isolated flyback power supply having a primary coil and a secondary coil, said secondary coil for generating said output voltage and for inductively generating a feedback voltage related to said output voltage, said method comprising:
determining a digitally controllable time instant using a time delay based on a value stored in a register;
sampling said feedback voltage at the digitally controllable time instant; and
determining said output voltage from said sampled feedback voltage.
2. The method of claim 1 wherein said time instant is specified by a register.
3. The method of claim 1 comprising digitally controlling a switch that controls said feedback voltage.
4. The method of claim 1 wherein said feedback voltage spikes before leveling off into a plateau.
5. The method of claim 4 wherein said sampling said feedback voltage occurs at the start of said plateau.
6. A circuit-implemented method for an isolated flyback power supply having (a) on a primary side, (i) a primary coil, (ii) a controller having a clock signal having a period, and (iii) a switch connected to the primary coil and controlled by the controller and (b) on a secondary side, a secondary coil, the method comprising:
setting a delay parameter D corresponding to an integer multiple of the period of the clock signal;
configuring, based on the delay parameter, the controller to sample, on the primary side, a feedback voltage, proportional to a voltage across the secondary coil, D periods of the clock signal after a turn-off time;
at a turn-on time before the turn-off time, turning on the switch;
at the turn-off time, turning off the switch to generate the feedback voltage; and
sampling the feedback voltage D periods of the clock signal following the turn-off time.
7. The method of claim 6 , wherein the configuring step comprises configuring a digital delay chain to delay the sampling by D periods of the clock signal.
8. The method of claim 6 , wherein the sampling step comprises analog-to-digital conversion.
9. The method of claim 8 , wherein the analog-to-digital conversion comprises converting a value of the feedback voltage into a digital word for further digital processing.
10. The method of claim 6 , wherein the controller is configured to sample the feedback voltage exactly once between the turn-off time and a subsequent turn-on time.
11. The method of claim 6 , wherein the configuring step is performed by a high-level control and software interface.
12. The method of claim 11 , wherein the high-level control and software interface comprises a set of registers, wherein the delay parameter is stored in the set of registers.
13. The method of claim 6 , further comprising dynamically changing the delay parameter D.
14. The method of claim 6 , wherein:
the configuring step comprises configuring a digital delay chain to delay the sampling by D periods of the clock signal;
the sampling step comprises analog-to-digital conversion;
the analog-to-digital conversion comprises converting a value of the feedback voltage into a digital word for further digital processing;
the controller is configured to sample the feedback voltage exactly once between the turn-off time and a subsequent turn-on time;
the configuring step is performed by a high-level control and software (HLCS) interface; and
the HLCS interface comprises a set of registers, wherein the delay parameter is stored in the set of registers.