Switching converter and lighting device using the same
A switching converter includes: an output circuit including a switching transistor, an inductive element, and a rectifying element configured to rectify a current flowing to the inductive element; a control circuit having a monitor terminal, and configured to drive the switching transistor such that a voltage of the load becomes close to a reference voltage when a voltage of the monitor terminal is higher than the reference voltage, and to drive the switching transistor such that a voltage of the load becomes close to a voltage of the monitor terminal when a voltage of the monitor terminal is lower than the reference voltage; and an abnormality protection circuit configured to monitor a state of the load, the control circuit, peripheral circuits, and the switching converter, and to pull down a voltage of the monitor terminal to a voltage lower than the reference voltage when abnormality is detected.
1. A switching converter for supplying power to a load, comprising:
an output circuit comprising a switching transistor, an inductive element, and a rectifying element configured to rectify a current flowing to the inductive element;
a control circuit having a monitor terminal, and configured to drive the switching transistor such that an electrical state of the load becomes close to a target state corresponding to a reference voltage when a voltage of the monitor terminal is higher than the reference voltage, and to drive the switching transistor such that an electrical state of the load becomes close to a state corresponding to a voltage of the monitor terminal when a voltage of the monitor terminal is lower than the reference voltage; and
an abnormality protection circuit configured to monitor a state of at least one of the load, the control circuit, peripheral circuits, and the switching converter, and to pull down a voltage of the monitor terminal to a voltage lower than the reference voltage when abnormality is detected,
wherein the abnormality protection circuit comprises a first resistor and a switch installed in series between the monitor terminal and a ground, and is configured to turn on the switch when the abnormality is detected, and
wherein the abnormality protection circuit further comprises a thermistor and a second resistor sequentially installed in series between a power line and the ground, and is configured to turn ON and OFF of the switch based on a result of comparison between a voltage of a connection node of the thermistor and the second resistor and a predetermined threshold voltage.
2. The switching converter of claim 1 , wherein the thermistor is a negative temperature coefficient (NTC) thermistor, and is arranged on a potential side higher than the second resistor, and
the switch is an NPN-type bipolar transistor or an N-channel metal oxide semiconductor field effect transistor (MOSFET) having a control terminal to which the voltage of the connection node of the thermistor and the second resistor is input.
3. The switching converter of claim 1 , wherein an electrical state of the load corresponds to a current flowing through the load.
4. The switching converter of claim 1 , wherein the control circuit comprises a comparator or an error amplifier having a first inverting input terminal connected to the monitor terminal, a second inverting input terminal configured to receive the reference voltage, and a non-inverting input terminal configured to receive a feedback signal indicating an electrical state of the load, and configured to compare a lower value, among a voltage of the first inverting input terminal and a voltage of the second inverting input terminal, with the feedback signal or amplify an error between the lower value and the feedback signal.
5. The switching converter of claim 1 , wherein the control circuit comprises a quasi-resonant (QR) type modulator.
6. The switching converter of claim 1 , wherein the load is a semiconductor light source.
7. The switching converter of claim 1 , wherein the output circuit comprises:
an output capacitor installed between an input line and an output line;
a diode having a cathode connected to the input line;
an inductor installed between the output line and an anode of the diode; and
the switching transistor installed between the anode of the diode and the ground.
8. The switching converter of claim 1 , wherein the output circuit has a flyback-type topology.
9. The switching converter of claim 1 , wherein the output circuit has a topology of a buck converter or a boost converter.
10. A lighting device, comprising:
a semiconductor light source; and
the switching converter of claim 1 , configured to light the semiconductor light source.
11. The lighting device of claim 10 , further comprising:
a rectifying circuit configured to rectify an AC voltage; and
a smoothing capacitor configured to smooth an output voltage of the rectifying circuit to supply the same to an input line of the switching converter.
12. A switching converter for supplying power to a load, comprising:
an output circuit comprising a switching transistor, an inductive element, and a rectifying element configured to rectify a current flowing to the inductive element;
a control circuit having a monitor terminal, and configured to drive the switching transistor such that an electrical state of the load becomes close to a target state corresponding to a reference voltage when a voltage of the monitor terminal is higher than the reference voltage, and to drive the switching transistor such that an electrical state of the load becomes close to a state corresponding to a voltage of the monitor terminal when a voltage of the monitor terminal is lower than the reference voltage; and
an abnormality protection circuit configured to monitor a state of at least one of the load, the control circuit, peripheral circuits, and the switching converter, and to pull down a voltage of the monitor terminal to a voltage lower than the reference voltage when abnormality is detected,
wherein the abnormality protection circuit comprises a first resistor and a switch installed in series between the monitor terminal and a ground, and is configured to turn on the switch when the abnormality is detected, and
wherein the control circuit further comprises a bias circuit configured to bias the first resistor through the monitor terminal.
13. The switching converter of claim 12 , wherein the bias circuit comprises a current source configured to supply a predetermined current to the first resistor through the monitor terminal.
14. The switching converter of claim 12 , wherein the bias circuit comprises a third resistor connected to the monitor terminal.
15. A lighting device, comprising:
a semiconductor light source; and
a switching converter configured to receive a DC input voltage to light the semiconductor light source,
wherein the switching converter comprises:
an output circuit comprising a switching transistor, an inductive element, and a rectifying element;
a control circuit having a current detection terminal configured to receive a feedback signal indicating a driving current flowing through the semiconductor light source and a monitor terminal, and configured to drive the switching transistor such that the feedback signal becomes close to a reference voltage when a voltage of the monitor terminal is higher than the reference voltage, and to drive the switching transistor such that the feedback signal becomes close to a state corresponding to a voltage of the monitor terminal when the voltage of the monitor terminal is lower than the reference voltage;
a first resistor and a transistor sequentially installed in series between the monitor terminal and a ground; and
a negative temperature coefficient (NTC) thermistor and a second resistor sequentially installed in series between a power line and the ground, and
wherein a voltage of a connection node of the NTC thermistor and the second resistor is input to a control terminal of the transistor.