Methods and systems of operating power converters
Operating power converters. Some of the methods include: storing energy in a transformer arranged for flyback operation, the storing by making conductive a primary switch coupled to a primary winding of the transformer; and then ceasing the storing of energy; determining on time of the primary switch during the storing of energy, the determining creates a value indicative of charge time; transferring energy from the transformer to a load through a secondary winding of the transformer; measuring discharge time of the energy from the transformer during the transferring, the measuring of the discharge time creates a value indicative of discharge time; calculating a value indicative of output voltage of the power converter using the value indicative of charge time and the value indicative of discharge time; and then compensating a charge time of a subsequent energy storage cycle, the compensation based on the value indicative of output voltage.
1. A method of operating a power converter comprising:
storing energy in a transformer arranged for flyback operation, the storing by making conductive a primary switch coupled to a primary winding of the transformer; and then ceasing the storing energy;
determining on time of the primary switch during the storing energy, the determining creates a value indicative of charge time;
transferring energy from the transformer to a load through a secondary winding of the transformer;
measuring a discharge time of the energy from the transformer during the transferring, the measuring of the discharge time creates a value indicative of discharge time;
calculating a value indicative of output voltage of the power converter using the value indicative of charge time and the value indicative of discharge time, the calculating without measuring an output voltage and without sensing through an auxiliary winding; and then
compensating a charge time of a subsequent energy storage cycle, the compensation based on the value indicative of output voltage.
2. The method of claim 1 , wherein determining the on time of the primary switch further comprises measuring the on time based on a drive signal provided to the primary switch.
3. The method of claim 1 , wherein calculating the value indicative of output voltage further comprises calculating the value indicative of output voltage using a value indicative of an input voltage.
4. The method of claim 1 , wherein calculating the value indicative of output voltage further comprises calculating the value indicative of output voltage based on a value indicative of input voltage and a turns ratio of the transformer.
5. The method of claim 1 , wherein compensating the charge time in a subsequent energy storage cycle further comprises compensating the charge time in an immediately subsequent energy storage cycle.
6. The method of claim 1 , wherein compensating the charge time in a subsequent energy storage cycle further comprises changing a peak current setpoint for a subsequent energy storage cycle, the peak current setpoint triggers the end of an energy storage cycle.
7. A primary-side controller for a power converter, the primary-side controller comprising:
a gate terminal and a drain terminal;
the primary-side controller configured to:
assert the gate terminal; and then
de-assert the gate terminal;
create a value indicative of change time based on assertion of the gate terminal and de-assertion of the gate terminal;
determine an end time of a discharge cycle based on a voltage on the drain terminal falling below a threshold amount;
create a value indicative of discharge time of a discharge cycle based on the end time;
calculate a value indicative of output voltage using the value indicative of charge time and the value indicative of discharge time; and
compensate a charge time used in a subsequent de-assertion of the gate terminal based on the value indicative of output voltage.
8. The primary-side controller of claim 7 , further comprising:
a current-sense terminal; and
wherein when the primary-side controller de-asserts the gate terminal, the primary-side controller is further configured to:
measure a value indicative of primary current by way of the current-sense terminal; and
de-assert the gate terminal when the value indicative of primary current reaches a peak current setpoint.
9. The primary-side controller of claim 7 , wherein when the primary-side controller creates the value indicative of discharge time, the primary-side controller is further configured to determine a start time as at least one selected from a group comprising: a time at which the gate terminal is de-asserted; and at time at which a voltage on the drain terminal rises above predetermined threshold.
10. The primary-side controller of claim 7 , wherein calculating the value indicative of output voltage is performed without measuring an output voltage.
11. The primary-side controller of claim 10 , further comprising:
a measurement terminal; and
wherein when the primary-side controller calculates the value indicative of output voltage, the primary-side controller is further configured to:
determine a ratio of the value indicative of charge time and the value indicative of discharge time; and
calculate the value indicative of output voltage based on the ratio and a voltage on the measurement terminal indicative of input voltage and a turns ratio of a transformer.
12. A power converter comprising:
a primary side comprising:
a primary winding of a transformer;
a primary field effect transistor (FET) coupled to the primary winding, the primary FET defining a gate, a drain, and a source;
a primary-side controller defining a drain terminal coupled to the drain of the primary FET, a gate terminal, and a measurement terminal, the gate terminal coupled to the gate, and the measurement terminal coupled to an input voltage;
a secondary side comprising:
a second winding of the transformer;
a secondary rectifier coupled to the secondary winding and arranged for flyback operation;
wherein the primary-side controller is configured to:
assert the gate terminal to create an energy storage cycle; and then
de-assert the gate terminal to end the energy storage cycle;
create a value indicative of charge time of the energy storage cycle;
determine an end time of a discharge cycle based on a voltage on the drain terminal falling below a threshold amount;
create a value indicative of discharge time of a discharge cycle based on the end time;
calculate a value indicative of output voltage using the value indicative of charge time and the value indicative of discharge time; and
compensate a charge time used in a subsequent de-assertion of the gate terminal based on the value indicative of output voltage.
13. The power converter of claim 12 , wherein the primary-side controller further comprises:
a current-sense terminal coupled to a sense node defined between the primary FET and a sense resistor; and
wherein when the primary-side controller de-asserts the gate terminal, the primary-side controller is further configured to:
measure a value indicative of primary current by way of the current-sense terminal; and
de-assert the gate terminal when the value indicative of primary current reaches a peak current setpoint.
14. The power converter of claim 12 , wherein when the primary-side controller creates the value indicative of discharge time, the primary-side controller is further configured to determine a start time as at least one selected from a group comprising: a time at which the gate terminal is de-asserted; and at time at which a voltage on the drain terminal rises above predetermined threshold.
15. The power converter of claim 12 , wherein calculating the value indicative of output voltage is performed without measuring an output voltage.
16. The power converter of claim 15 , wherein when the primary-side controller calculates the value indicative of output voltage, the primary-side controller is further configured to:
determine a ratio of the value indicative of charge time and the value indicative of discharge time; and
calculate the value indicative of output voltage based on the ratio and a voltage on the measurement terminal indicative of input voltage and a turns ratio of the transformer.
17. The power converter of claim 16 further comprising a voltage divider defining a node coupled to the measurement terminal, resistance of the voltage divider are indicative of a turns ratio of the transformer.