Electrical transmission or interconnection systems – Plural supply circuits or sources – Substitute or emergency source
Reexamination Certificate
2000-01-27
2001-10-09
Tso, Edward H. (Department: 2838)
Electrical transmission or interconnection systems
Plural supply circuits or sources
Substitute or emergency source
Reexamination Certificate
active
06300690
ABSTRACT:
The invention relates to an apparatus which is electronically switched on and off. The invention may be applied, for example, in a mobile phone which can be switched on and off by depressing a power key.
An apparatus can be electronically switched on in the following manner. A power-on circuit initially provides a power-on signal. A power supply derives a power supply voltage from an electrical power source in response to the power-on signal. A feedback path upholds the power-on signal on the basis of the power supply voltage. It seems that U.S. Pat. No. 5,404,578 describes a car telephone is switched on in this manner.
It is an object of the invention to provide better user satisfaction. The invention takes the following aspects into consideration. In an apparatus as described in the preceding section, the following problem may occur. It may happen that the electrical power source is temporarily disconnected from the power supply, for example, due to a shock or a vibration. Such an event will hereinafter be referred to as a power cut. A power cut will cause a drop in the power supply voltage. Since the feedback path upholds the power-on signal on the basis of the power voltage, a power cut may cause the power-on signal to be lost. In that case, the power supply will not provide the power supply voltage once the power cut has ended, because there is no power-on signal any more. Thus, the apparatus is unintentionally switched off as a result of the power cut. This will generally annoy a user. It will particularly annoy a user, for example, when the apparatus is a mobile phone which the user carries in his pocket. If the mobile phone is switched off unintentionally, the user cannot be reached via his mobile phone whereas he or she is unaware of this.
In accordance with the invention, the feedback path for upholding the power-on signal on the basis of the power supply voltage, comprises a hold circuit for upholding the power-on signal for a least a period of time following a drop in the power supply voltage. Accordingly, in the case of a relatively short power cut, the power supply will still receive the power-on signal once the power cut has ended. As a result, the apparatus will automatically be switched on once the power cut has ended. Consequently, the invention prevents that, in the case of a relatively short power cut, the apparatus is switched off unintentionally. Thus, the invention provides more user satisfaction.
Another advantage of the invention relates to the following aspects. In principle, it is possible to prevent an unintentional switch-off by coupling a capacitor between the output of power supply which provides the power supply voltage, and signal ground. Such a power supply capacitor will delay, in effect, a drop in the power supply voltage as a result of a power cut. Accordingly, the feedback path will continue to uphold the power-on signal for a certain period of time. However, since the power supply capacitor will be discharged by power-consuming circuitry, it needs to have a relatively high capacitance value in order to sufficiently delay a drop in the power supply voltage. Since, according to the invention, the hold circuit upholds the power-on signal following a drop in the power supply voltage, there is no need to delay the drop. Consequently, any power supply capacitor need not have a relatively large capacitance value. It generally holds that the smaller the capacitance value of a capacitor, the cheaper and the smaller the capacitor is. Thus, the invention is advantageous in terms of size and cost.
REFERENCES:
patent: 5055703 (1991-10-01), Schornack
patent: 5404578 (1995-04-01), Kuge et al.
patent: 5551007 (1996-08-01), Oda
Halajian Dicran
Tso Edward H.
U.S. Philips Corporation
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