Output voltage detection circuit, isolated switching power supply, and semiconductor device
View Patent ↗An output voltage detection circuit is provided for accurately detecting a secondary side output voltage based on a voltage induced to an auxiliary winding in an isolated switching power supply including a transformer having the auxiliary winding. A voltage waveform processing circuit ( 10 - 1 ) processes the waveform of the voltage induced to the auxiliary winding ( 7 - 3 ), a hold circuit ( 10 - 2 ) holds the voltage peak value after the processing, a secondary side current detection circuit ( 24 ) detects a period during which current passes through a secondary side winding ( 7 - 2 ), a correction circuit ( 22 ) performs correction to decrease the peak voltage which has been held by the hold circuit ( 10 - 2 ) during the period, and the corrected voltage is fed back to a control circuit ( 9 ). Meanwhile, a reset circuit ( 23 ) resets, for a fixed period after the current passes through the secondary side winding ( 7 - 2 ), the peak voltage having been held by the hold circuit ( 10 - 2 ).
1. An output voltage detection circuit incorporated into an isolated switching power supply comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding, and
a control circuit for controlling on/off of the switching element,
the output voltage detection circuit generating detection voltage as a detected value of secondary side output voltage based on voltage generated on the auxiliary winding, and feeding back the detection voltage to the control circuit,
the output voltage detection circuit, comprising:
a secondary side current detection circuit connected to the auxiliary winding and detecting a period during which current passes through the secondary side winding,
a voltage waveform processing circuit connected to the auxiliary winding and processing a waveform of the voltage generated on the auxiliary winding,
a hold circuit connected to an output stage of the voltage waveform processing circuit and holding a peak voltage of the voltage having been processed by the voltage waveform processing circuit,
a correction circuit connected to an output stage of the hold circuit, and correcting the peak voltage having been held by the hold circuit and generating the detection voltage in the period having been detected by the secondary side current detection circuit, and
a reset circuit for resetting, for a fixed period of time after the current starts passing through the secondary side winding, the detection voltage having been generated by the correction circuit.
2. The output voltage detection circuit according to claim 1 , wherein the voltage waveform processing circuit includes a diode.
3. The output voltage detection circuit according to claim 2 , wherein the voltage waveform processing circuit has a capacitor for rendering a rising waveform of the voltage generated on the auxiliary winding less steep.
4. The output voltage detection circuit according to claim 1 , wherein the hold circuit includes a diode and a capacitor and outputs voltage across the capacitor.
5. The output voltage detection circuit according to claim 4 , wherein the correction circuit discharges the capacitor included in the hold circuit at a predetermined current value.
6. The output voltage detection circuit according to claim 4 , wherein the correction circuit discharges the capacitor included in the hold circuit at a value of current passing through the auxiliary winding.
7. An isolated switching power supply, comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding,
a control circuit for controlling on/off of the switching element, and
the output voltage detection circuit according to claim 1 ,
the isolated switching power supply further comprising a regulator for generating operating voltage of the control circuit and the output voltage detection circuit based on input voltage applied to the primary side winding.
8. An isolated switching power supply, comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding,
a control circuit for controlling on/off of the switching element, and
the output voltage detection circuit according to claim 2 ,
the isolated switching power supply further comprising a regulator for generating operating voltage of the control circuit and the output voltage detection circuit based on input voltage applied to the primary side winding.
9. An isolated switching power supply, comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding,
a control circuit for controlling on/off of the switching element, and
the output voltage detection circuit according to claim 3 ,
the isolated switching power supply further comprising a regulator for generating operating voltage of the control circuit and the output voltage detection circuit based on input voltage applied to the primary side winding.
10. An isolated switching power supply, comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding,
a control circuit for controlling on/off of the switching element, and
the output voltage detection circuit according to claim 4 ,
the isolated switching power supply further comprising a regulator for generating operating voltage of the control circuit and the output voltage detection circuit based on input voltage applied to the primary side winding.
11. An isolated switching power supply, comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding,
a control circuit for controlling on/off of the switching element, and
the output voltage detection circuit according to claim 5 ,
the isolated switching power supply further comprising a regulator for generating operating voltage of the control circuit and the output voltage detection circuit based on input voltage applied to the primary side winding.
12. An isolated switching power supply, comprising:
a transformer having a primary side winding, a secondary side winding, and an auxiliary winding,
a switching element connected to the primary side winding,
a control circuit for controlling on/off of the switching element, and
the output voltage detection circuit according to claim 6 ,
the isolated switching power supply further comprising a regulator for generating operating voltage of the control circuit and the output voltage detection circuit based on input voltage applied to the primary side winding.
13. The isolated switching power supply according to claim 7 , wherein the control circuit causes the regulator to stop generating operating voltage when the operating voltage generated by the regulator become higher than or equal to a fixed value, and generates operating voltage based on voltage generated on the auxiliary winding.
14. A semiconductor device including the output voltage detection circuit, the control circuit, and the regulator each according to claim 7 , which are formed on a same substrate.
15. A semiconductor device including the output voltage detection circuit, the control circuit, and the regulator each according to claim 8 , which are formed on a same substrate.
16. A semiconductor device including the output voltage detection circuit, the control circuit, and the regulator each according to claim 9 , which are formed on a same substrate.
17. A semiconductor device including the output voltage detection circuit, the control circuit, and the regulator each according to claim 10 , which are formed on a same substrate.
18. A semiconductor device including the output voltage detection circuit, the control circuit, and the regulator each according to claim 11 , which are formed on a same substrate.
19. A semiconductor device including the output voltage detection circuit, the control circuit, and the regulator each according to claim 12 , which are formed on a same substrate.