Power supply with open-loop protection and short-circuit protection
View Patent ↗The power supply according to the present invention comprises a transformer, a power switch, a signal generating circuit, an on-time detection circuit, and a delay circuit. The transformer receives an input voltage and generates an output voltage. The power switch switches the transformer for regulating the output voltage. The signal generating circuit generates a switching signal for controlling switching of the power switch. The on-time detection circuit detects an on-time of the power switch and generates a short-circuit signal. The delay circuit counts to a first delay time or to a second delay time in response to a feedback signal of the power supply and the short-circuit signal to generate a turn off signal for controlling the signal generating circuit to latch the switching signal.
1. A power supply with open-loop protection and short-circuit protection, comprising:
a transformer, receiving an input voltage for generating an output voltage;
a power switch, coupled to the transformer and switching the transformer for regulating the output voltage;
a signal generating circuit, generating a switching signal for controlling switching of the power switch;
an on-time detection circuit, detecting an on-time of the power switch for generating a short-circuit signal; and
a delay circuit, counting to a first delay time or a second delay time in response to a feedback signal of the power supply and the short-circuit signal for generating a turn off signal for the signal generating circuit latching the switching signal;
wherein the delay circuit determines to count to the first delay time or the second delay time in response to the short-circuit signal.
2. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , further comprising a confirmation circuit, confirming the on-time of the power switch being continuously higher than a time threshold and generating a selection signal in response to a reference signal and the short-circuit signal, wherein the delay circuit determines to count to the first delay time or the second delay time in response to the selection signal.
3. The power supply with open-loop protection and short-circuit protection as claimed in claim 2 , wherein the reference signal is correlated to the switching signal.
4. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , wherein the on-time detection circuit detects the on-time of the power switch; when the on-time is lower than a time threshold and the feedback signal is higher than a threshold signal, it means that the power supply is short-circuited and the delay circuit counts to the first delay time in response to the short-circuit signal; when the on-time is higher than the time threshold and the feedback signal is higher than the threshold signal, it means that the power supply is open-looped and the delay circuit counts to the second delay time in response to the short-circuit signal; the first delay time is shorter than the second delay time.
5. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , wherein the on-time detection circuit comprises:
a sawtooth signal generating circuit, generating a sawtooth signal in response to the on-time of the power switch;
a comparator, comparing the sawtooth signal with a threshold signal for generating a duty signal; and
a counting circuit, performing counting in response to a trigger signal and the duty signal and generating the short-circuit signal.
6. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , further comprising:
an oscillator, generating a fundamental clock signal; and
a frequency divider, receiving the fundamental clock signal and frequency-dividing the fundamental clock signal for generating a first clock signal and a second clock signal;
wherein the delay circuit selects the first clock signal or the second clock signal in response to the short-circuit signal for counting to the first delay time or the second delay time in response to the first clock signal or the second clock signal.
7. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , further comprising an oscillator, generating a clock signal, and the signal generating circuit generating the switching signal in response to the clock signal.
8. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , further comprising a feedback detection circuit, generating a pull-high signal in response to the feedback signal of the power supply, and the delay circuit counting to the first delay time or the second delay time in response to pull-high signal and the short-circuit signal.
9. The power supply with open-loop protection and short-circuit protection as claimed in claim 8 , wherein the feedback detection circuit generates the pull-high signal in response to the feedback signal and a threshold signal.
10. The power supply with open-loop protection and short-circuit protection as claimed in claim 1 , further comprising a reset circuit, generating a clear signal in response to a current signal and a power limiting signal of the power supply and the feedback signal for turning off the switching signal.