HEAT COUPLED POLYSWITCH WITH REVERSE DISCHARGE DIODE FOR INCREASED SAFETY MARGIN
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Del.icio.us| IP.com Number | IPCOM000008623D |
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| Dated | Mar 1, 1998 UTC | ||
| Size | 3 page(s) (102.0 KB) | ||
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Publication Summary
The reverse discharge protection diode is a series diode on the battery's charger side B+ line which is used to prevent the battery from being discharged in an unplugged charger or outside the charger due to inadvertent shorting of the charger side B+ and B- contacts.| Country | United States |
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| Language | English (United States) |
| Related Person(s) |
(AUTHOR) Joseph Patiño (AUTHOR) Jim Tidwell (AUTHOR) John Fiske (AUTHOR) Alay Mehta |
| Copyright | Motorola Inc. March 1998 |
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MOrOROLA Technical Developments
HEAT COUPLED POLYSWITCH WITH REVERSE DISCHARGE DIODE FOR INCREASED SAFETY MARGIN
by Joseph Patiiio, Jim Tidwell, John Fiske and Alay Mehta
BACKGROUND
The reverse discharge protection diode is a series diode on the battery's charger side B+ line which is used to prevent the battery from being discharged in an unplugged charger or outside the charger due to inadvertent shorting of the charger side B+ and B- contacts.
The polyswitch (PTC) is a resettable fuse which open circuits the battery as a function of tempera- ture and current. The polyswitch is used for short circuit protection (current out) and for charger run- away protection (current in). The polyswitch must not open during charge within the allowable temperature window (45°C max). Additionally, it must not open at 65°C during discharge to allow for proper radio operation.
PROBLEM
1. Depending on the selection of the polyswitch, the polyswitch can open circuit during transmit at 65°C in less than 2 minutes. This could be an user safety problem and radio performance problem.
2. Additionally today's polyswitch will open circuit a 2 amp runaway charger at a battety temperature of approximately 94°C. This high temperature
causes issues with:
a. user safety and
b. battery performance.
The primary reason for this is that the poly- switch has a derating curve that forces the battery designer to select a non-optimum solution to compromise between transmit operation at high temperatures and runaway charger protection.
SOLUTION
By coupling the additional heat generated by the reverse discharge protection diode to the poly- switch, the polyswitch can be manipulated to open at a lower battery tempe...