Method and apparatus providing a multi-function terminal for a power supply controller
A method for controlling a power supply is disclosed. An example method includes deactivating the power supply in response to a first current through a first terminal of a power supply controller falling below a first threshold value. The power supply is activated in response to the first current through the first terminal rising above a second threshold value. Deactivating the power comprises causing a power switch coupled to a primary winding of the power supply not to receive a switching waveform for more than one cycle until the power supply is activated.
1. A method for controlling a power supply, comprising:
deactivating the power supply in response to a first current through a first terminal of a power supply controller falling below a first threshold value; and
activating the power supply in response to the first current through the first terminal rising above a second threshold value, wherein deactivating the power supply comprises causing a power switch coupled to a primary winding of the power supply not to receive a switching waveform for more than one cycle until the power supply is activated.
2. The method of claim 1 wherein activating the power supply comprises starting the switching waveform to control the power switch coupled to the primary winding of the power supply.
3. The method of claim 2 wherein starting the switching waveform includes starting a new complete cycle of the switching waveform.
4. The method of claim 1 wherein the second threshold value is greater than the first threshold value.
5. The method of claim 1 further comprising limiting the first current through the first terminal to a maximum value.
6. The method of claim 1 wherein deactivating the power supply includes allowing an existing cycle of the switching waveform to be completed.
7. The method of claim 1 further comprising coupling a switch between the first terminal and ground.
8. The method of claim 1 further comprising coupling a variable resistance between the first terminal and ground.
9. The method of claim 1 , wherein the first current is representative of an input of the power supply, the method further comprising:
dynamically adjusting a current limit of the power switch in response to the first current; and
maintaining a maximum output power of the power supply substantially constant with respect to changes in the input of the power supply.
10. A power supply controller circuit, comprising:
a current input circuit coupled to receive a current representative of an input of a power supply, the current input circuit to generate a current limit adjustment signal in response to the current; and
a control circuit coupled to receive the current limit adjustment signal, the control circuit coupled to dynamically adjust a current limit of a current through a power switch in response to the current limit adjustment signal, wherein a maximum output power of the power supply is maintained substantially constant with respect to changes in the input of the power supply.
11. The power supply controller circuit of claim 10 , wherein the power switch is coupled to a primary winding of the power supply.
12. The power supply controller circuit of claim 10 , wherein the control circuit comprises a pulse width modulation circuit that generates a switching waveform coupled to be received by the power switch to regulate a power supply output.
13. The power supply controller of claim 10 , wherein the control circuit includes a first comparator coupled to compare a signal representative of a current through the power switch with the current limit adjustment signal such that the power switch is disabled in response to an output of the first comparator when the current limit set by the current limit adjustment signal is exceeded.
14. The power supply controller of claim 13 , wherein the control circuit includes a second comparator coupled to compare a ramping signal with a feedback signal representative of the power supply output to regulate the power supply output.
15. The power supply controller circuit of claim 10 , wherein the current limit of the current through the power switch is fixed at a predetermined maximum level when a magnitude of the current is higher than a predetermined value.
16. The power supply controller circuit of claim 10 , further comprising enable/disable logic coupled to the current input circuit to generate an enable/disable signal to deactivate the power supply when a magnitude of the current is below a first threshold value and to activate the power supply when the magnitude of the current rises above a second threshold value.
17. The power supply controller circuit of claim 16 , wherein the control circuit is coupled to prevent a switching waveform from reaching the power switch for more than one cycle in response to the enable/disable signal to deactivate the power supply.
18. The power supply controller circuit of claim 16 , wherein the control circuit includes an oscillator circuit coupled to receive the enable/disable signal, the oscillator circuit to stop generating a switching waveform in response to the enable/disable signal to deactivate the power supply.
19. The power supply controller circuit of claim 18 , wherein the oscillator circuit is to complete an existing cycle of the switching waveform before the oscillator is to stop generating the switching waveform in response to the enable/disable signal to deactivate the power supply.
20. The power supply controller circuit of claim 18 , wherein the oscillator circuit is to start a new complete cycle of the switching waveform if the oscillator circuit is to start generating the switching waveform in response to the enable/disable signal to activate the power supply.