Compensating on-time delay of switching transistor in switching power converters

1. A power converter comprising:

a transformer coupled to a power source;

a switch coupled to the transformer for coupling or decoupling the power source to or from a load of the power converter; and

a switch controller coupled to the switch for controlling on-times and off-times of the switch, the switch controller determining a time difference between an actual on-time of the switch in a first switching cycle and an intended on-time of the switch for the first switching cycle and adjusting the intended on-time of the switch for a second switching cycle subsequent to the first switching cycle based upon the time difference.

2. The power converter of claim 1 , wherein the switch controller determines the actual on-time of the switch in the first switching cycle by determining a duration of a current through the switch generating a voltage exceeding a predetermined threshold voltage.

3. The power converter of claim 1 , wherein the switch controller controls the on-times and the off-times of the switch by generating a pulse signal controlling the switch, the pulse signal having first logic levels and second logic levels, and the intended on-time of the switch for the first switching cycle corresponds to a duration of the pulse signal in the first logic level during the first switching cycle.

4. The power converter of claim 1 , wherein the switch controller adjusts the intended on-time of the switch for a second switching cycle by reducing the intended on-time of the switch for the second switching cycle by the time difference between the actual on-time of the switch in the first switching cycle and the intended on-time of the switch for the first switching cycle.

5. The power converter of claim 1 , wherein the switch controller determines the time difference between the actual on-time of the switch in the first switching cycle and the intended on-time of the switch for the first switching cycle in numbers of cycles of a predetermined clock signal.

6. A power converter comprising:

a transformer coupled to a power source;

a switch coupled to the transformer for coupling or decoupling the power source to or from a load of the switching power converter;

a pulse generator generating a control pulse signal for controlling on-times and off-times of the switch, the control pulse signal having first logic levels during which the switch is turned on and second logic levels during which the switch is turned off; and

delay compensation circuitry for adjusting an intended on-time of the switch for a second switching cycle subsequent to a first switching cycle based upon a time difference between an actual on-time of the switch in the first switching cycle and an intended on-time of the switch for the first switching cycle.

7. The power converter of claim 6 , further comprising a comparator outputting a comparison pulse being in a first logic level while a voltage level corresponding to current through the switch exceeds a predetermined threshold voltage and being in a second logic level while the voltage level corresponding to the current through the switch does not exceed the predetermined threshold voltage.

8. The power converter of claim 7 , wherein the delay compensation circuitry includes a counter counting numbers of cycles of a predetermined clock signal during which the comparison pulse is in the first logic level to determine the actual on-time of the switch in the first switching cycle.

9. The power converter of claim 6 , wherein the delay compensation circuitry adjusts the intended on-time of the switch for the second switching cycle by reducing the intended on-time of the switch for the second switching cycle by the time difference between the actual on-time of the switch in the first switching cycle and the intended on-time of the switch for the first switching cycle.

10. A method of controlling a power converter, the power converter including a transformer coupled to a power source, a switch coupled to the transformer for coupling or decoupling the power source to or from a load, and a switch controller coupled to the switch for controlling on-times and off-times of the switch, the method comprising:

determining a time difference between an actual on-time of the switch in a first switching cycle and an intended on-time of the switch for the first switching cycle; and

adjusting the intended on-time of the switch for a second switching cycle subsequent to the first switching cycle based upon the time difference.

11. The method of claim 10 , further comprising determining the actual on-time of the switch in the first switching cycle by determining a duration of a current through the switch generating a voltage exceeding a predetermined threshold voltage.

12. The method of claim 10 , further comprising generating a pulse signal controlling the on-times and the off-times of the switch, the pulse signal having first logic levels and second logic levels, and the intended on-time of the switch for the first switching cycle corresponding to a duration of the pulse signal in the first logic level during the first switching cycle.

13. The method of claim 10 , wherein adjusting the intended on-time of the switch for the second switching cycle comprises reducing the intended on-time of the switch for the second switching cycle by the time difference between the actual on-time of the switch in the first switching cycle and the intended on-time of the switch for the first switching cycle.

14. The method of claim 10 , wherein the time difference between the actual on-time of the switch in the first switching cycle and the intended on-time of the switch for the first switching cycle is determined in numbers of cycles of a predetermined clock signal.