INPUT PROTECTION CIRCUIT

• US 20090268356A1
• Filed: 04/23/2009
• Published: 10/29/2009
• Est. Priority Date: 04/25/2008
• Status: Active Grant

• Current Assignee: Philips IP Ventures B.V. (Koninklijke Philips N.V.)
• Original Assignee: Access Business Group International LLC (Alticor Incorporated)
• Inventors: Baarman, David W., Mollema, Scott A., Blaha, Mark A., Zeik, Andrew C., Liff, Dale R.
• Granted Patent: US 8,259,428 B2
• Time in Patent Office: Days
• US Class Current: 361/37
• CPC Class Codes: H02H 9/042 comprising means to limit the absorbed power or indicate damaged over-voltage protection device

Abstract

A voltage clamp protection circuit to protect against overvoltage conditions where there is insufficient current to blow a fuse. The voltage clamp protection circuit includes a voltage clamp and a thermal cutoff. The voltage clamp clamps any overvoltage to a clamping voltage. If an overvoltage condition persists for too long the voltage clamp dissipates a sufficient amount of heat to activate the thermal cutoff creating an open circuit that protects the rest of the circuit. The voltage clamp protection circuit may be used in combination with a variety of other protection circuits to provide increased protection.

Claims

1. A protection circuit comprising:

a thermal cutoff, wherein in response to being heated to a threshold temperature, said thermal cutoff creates an open circuit in said protection circuit;

a voltage clamp electrically and thermally coupled to said thermal cutoff, wherein said voltage clamp is adapted to clamp an input voltage to a desired level in response to an overvoltage condition and dissipate energy to said thermal cutoff in the form of heat.

2. The protection circuit of claim 1 wherein, in response to said overvoltage condition persisting, said voltage clamp dissipates a sufficient amount of heat to reach said threshold temperature.

3. The protection circuit of claim 1 wherein, in response to said overvoltage condition persisting, said voltage clamp dissipates a sufficient amount of heat to reach said threshold temperature before said voltage clamp malfunction.

4. The protection circuit of claim 1 wherein said thermal cutoff is capable of creating an open circuit when there is insufficient power to activate an electrical fuse.

5. The protection circuit of claim 1 wherein said thermal cutoff and said voltage clamp are operational without input from a microcontroller.

6. The protection circuit of claim 1 wherein said thermal cutoff and said voltage clamp are operational without a power source.

7. The protection circuit of claim 1 wherein said voltage clamp is a transient voltage suppressor.

8. The protection circuit of claim 1 further comprising thermal adhesive, wherein said thermal adhesive assists in the transfer of heat from said voltage clamp to said thermal cutoff.

9. An inductively powered secondary circuit comprising:

a secondary coil for receiving inductive power at an input voltage;

a secondary load in electrical communication with said secondary coil; and

a protection circuit electrically connected between said secondary coil and said secondary load, said protection circuit including;

a thermal cutoff, wherein in response to being heated to a threshold temperature, said thermal cutoff electrically disconnects said secondary load from said secondary coil;

a voltage clamp electrically and thermally coupled to said thermal cutoff, wherein said voltage clamp is adapted to clamp said input voltage to a desired level in response to an overvoltage condition and dissipate energy to said thermal cutoff in the form of heat.

10. The inductively powered secondary circuit of claim 9 wherein, in response to said overvoltage condition persisting, said voltage clamp dissipates a sufficient amount of heat to reach said threshold temperature.

11. The inductively powered secondary circuit of claim 9 wherein, in response to said overvoltage condition persisting, said voltage clamp dissipates a sufficient amount of heat to reach said threshold temperature before said voltage clamp malfunctions.

12. The inductively powered secondary circuit of claim 9 wherein said thermal cutoff is capable of disconnecting said secondary load from said secondary coil when there is insufficient power to activate an electrical fuse.

13. The inductively powered secondary circuit of claim 9 wherein said thermal cutoff and said voltage clamp are operational without input from a microcontroller.

14. The inductively powered secondary circuit of claim 9 wherein said thermal cutoff and said voltage clamp are operational without a power source.

15. The inductively powered secondary circuit of claim 9 wherein said voltage clamp is a transient voltage suppressor.

16. The inductively powered secondary circuit of claim 9 further comprising thermal adhesive, wherein said thermal adhesive assists in the transfer of heat from said voltage clamp to said thermal cutoff.

17. An inductively powered secondary circuit comprising:

a secondary coil; and

a secondary load in electrical communication with said secondary coil;

an electrical fuse electrically connected between said secondary coil and said secondary load, wherein said electrical fuse disconnects said secondary load from said secondary coil in response to a large transient;

a microprocessor controlled field effect transistor connected between said secondary coil and secondary load, wherein said field effect transistor disconnects said secondary load from said secondary coil in response to detection of a fault condition; and

a voltage clamp protection circuit including;

a thermal cutoff, wherein in response to being heated to a threshold temperature, said thermal cutoff electrically disconnects said secondary load from said secondary coil; and

a voltage clamp electrically and thermally coupled to said thermal cutoff, wherein said voltage clamp is adapted to clamp said input voltage to a desired level in response to an overvoltage condition and dissipate energy to said thermal cutoff in the form of heat.

18. The inductively powered secondary circuit of claim 17 wherein, in response to said overvoltage consistent persisting, said voltage clamp dissipates a sufficient amount of heat to reach said threshold temperature.

19. The inductively powered secondary circuit of claim 17 wherein, in response to said overvoltage condition persisting, said voltage clamp dissipates a sufficient amount of heat to reach said threshold temperature before said voltage clamp malfunctions.

20. The inductively powered secondary circuit of claim 17 wherein said thermal cutoff is capable of disconnecting said secondary load from said secondary coil when there is insufficient power to activate an electrical fuse.

21. The inductively powered secondary circuit of claim 17 wherein said thermal cutoff and said voltage clamp are operational without input from a microcontroller.

22. The inductively powered secondary circuit of claim 17 wherein said thermal cutoff and said voltage clamp are operational without a power source.

23. The inductively powered secondary circuit of claim 17 wherein said voltage clamp is a transient voltage suppressor.

24. The inductively powered secondary circuit of claim 17 further comprising thermal adhesive, wherein said thermal adhesive assists in the transfer of heat from said voltage clamp to said thermal cutoff.