Light emitting module and thermal protection method
View Patent ↗Proposed is a light emitting module ( 1 ), comprising a semiconductor light emitting device ( 10 ) and a thermal switch ( 20 ). The thermal switch ( 20 ) is arranged to protect the device ( 10 ) from over heating. At elevated temperatures the junction of the device ( 10 ) may reach a critical level causing catastrophic breakdown of the device. According to the invention, the thermal switch is arranged to shunt the semiconductor light emitting device. This is especially advantageous as the thermal protection offered by the switch ( 20 ) correlates directly to the (junction) temperature of the device ( 10 ).
1. A light emitting module comprising:
a semiconductor light emitting device having a junction, and
a thermal switch device having two terminals and two states: a conducting state that effectively creates a short circuit between the two terminals and a non-conducting state that effectively creates an open circuit between the two terminals, wherein:
the thermal switch device is arranged in parallel with, and in thermal contact with, the light emitting device and is configured to enter the conducting state at and above a predetermined shunt temperature, protecting the junction from reaching a critical, higher temperature under operating conditions, and
the thermal switch device comprises a HCTE (High Coefficient of Thermal Expansion) material with a coefficient of thermal expansion αh and a LCTE (Low Coefficient of Thermal Expansion) material with a coefficient of thermal expansion αl, and αh>αl.
2. The light emitting module of claim 1 , wherein the HCTE material comprises a metal and the LCTE material comprises a ceramic.
3. The light emitting module of claim 1 , wherein the thermal switch device comprises a bimetallic element.
4. The light emitting module of claim 1 , wherein the HCTE material is provided in two parts, the parts arranged at a distance from each other forming a gap.
5. The light emitting module of claim 4 , wherein the gap is arranged to have a predetermined size based on the shunt temperature.
6. The light emitting module of claim 1 , wherein the thermal switch device is positioned adjacent to the semiconductor light emitting device.
7. The light emitting module of claim 1 , wherein the semiconductor light emitting device comprises a light emitting diode or a laser diode.
8. The method of claim 1 , including fabricating conductive patterns on a common substrate to contact n and p regions of the light emitting device; wherein the thermal switch device is coupled to these conductive patterns.
9. A method to protect a semiconductor light emitting device from overheating comprising:
providing the semiconductor light emitting device having a junction;
providing a thermal switch device having two terminals and two states; a conducting state that effectively creates a short circuit between the two terminals and a non-conducting state that effectively creates an open circuit between the two terminals,
coupling the thermal switch device in parallel and in thermal contact with the light emitting device, and
fabricating the light emitting device and the thermal switch device on a common substrate
wherein the thermal switch device is configured to enter the conducting state at and above a predetermined shunt temperature, protecting the junction from reaching a critical, higher temperature under operating conditions, and
providing the thermal switch device includes fabricating a first conductive element and a second conductive element on a surface, and a distance between the first and second conductive elements determines a switching point of the thermal switch device to and from the conducting state.
10. A method to protect a semiconductor light emitting device from overheating comprising:
providing the semiconductor light emitting device having a junction;
providing a thermal switch device having two terminals and two states; a conducting state that effectively creates a short circuit between the two terminals and a non-conducting state that effectively creates an open circuit between the two terminals, and
coupling the thermal switch device in parallel and in thermal contact with the light emitting device,
wherein the thermal switch device is configured to enter the conducting state at and above a predetermined shunt temperature, protecting the junction from reaching a critical, higher temperature under operating conditions, and
the thermal switch device comprises a HCTE material with a coefficient of thermal expansion oh and a LCTE material with a coefficient of thermal expansion αl, and αh>αl.
11. The method of claim 10 , wherein the HCTE material comprises a metal and the LCTE material comprises a ceramic.
12. The method of claim 10 , wherein the thermal switch device comprises a bimetallic element.
13. The light emitting module of claim 1 , wherein the thermal switch device is positioned adjacent to the semiconductor light emitting device.
14. The light emitting module of claim 2 , wherein the thermal switch device is positioned adjacent to the semiconductor light emitting device.
15. The light emitting module of claim 4 , wherein the thermal switch device is positioned adjacent to the semiconductor light emitting device.
16. The light emitting module of claim 2 , wherein the HCTE material is provided in two parts, the parts arranged at a distance from each other forming a gap of a predetermined size based on the shunt temperature.
17. The light emitting module of claim 3 , wherein the HCTE material is provided in two parts, the parts arranged at a distance from each other forming a gap of a predetermined size based on the shunt temperature.
18. The method of claim 10 , including fabricating conductive patterns on a common substrate to contact n and p regions of the light emitting device; wherein the thermal switch device is coupled to these conductive patterns.
19. The method of claim 9 , wherein the thermal switch device comprises a bimetallic element.
20. The method of claim 9 , wherein the thermal switch device comprises a HCTE material with a coefficient of thermal expansion αh and a LCTE material with a coefficient of thermal expansion d, and αh>αl.