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Discrete reset circuit for a microcontroller powered by a rechargeable battery Disclosure Number: IPCOM000010468D
Publication Date: 2002-Dec-05
Document File: 1 page(s) / 20K

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ID 612478

Discrete reset circuit for a microcontroller powered by a rechargeable battery

In rechargeable shavers and other electronic devices microprocessors are used. Microprocessors need a reset circuit in order to start properly when the power supply has been dropped below a minimum level. In rechargeable battery applications a simple RC-reset in combination with an edge sensitive reset input can not be used due to the battery characteristics (very slow upcoming voltage when charged). Level sensitive reset ICs can be used to overcome this problem. In this disclosure a cheap alternative discrete solution is presented in the accompanying circuit diagram.

The circuit is based on a latch which is build around the transistors Q2 and Q3. When the microcontroller is in operation, Q3 conducts and as a result the reset port of the microcontroller is high (in this case the reset is active low).

When the battery voltage Vbatt drops below a certain voltage transistor Q1 will be activated by the microcontroller through an push-pull Output. As a result the state of the latch will change and the microcontroller is reset and the push-pull Output releases transistor Q1 which does not conduct anymore.

When the battery voltage Vbatt rises again (due to charging) the voltage on the basis of transistor Q2 will rise. At a certain voltage level, mainly determined by the values of the resistors R3, R4, R5 and the characteristics of transistor Q2, the latch will switch again and releases the rese...