Abstract: A cellular telephone charging circuit using a dry battery and capable of displaying a charging operation by a light-emitting diode (LED) when the charging operation is actually carried out is provided. The cellular telephone charging circuit using the dry battery as a power supply and including a boost switching regulator that supplies a predetermined charging power to a charging terminal of a cellular telephone, includes: the LED for displaying the charging operation; a control circuit that generates an ON and OFF control signal for driving a boost chopper included in the boost switching regulator; a chopper ON-period detection circuit that detects an ON-period of the boost chopper; and an LED lighting circuit that drives the LED when the ON-period detected by the chopper ON-period detection circuit reaches a predetermined value.

Abstract: A battery charger for a portable telephone in which the whole of it is simply and lightly formed and with which a battery of the portable telephone can be securely charged is provided.

Abstract: An auxiliary power source device for a portable electronic instrument is formed of a main body, an attaching terminal disposed, at one side of the main body, which is detachably fitted into an external connection terminal of the portable electronic instrument to provide electricity to the same, a battery disposed in the main body and connected to the attaching terminal, and an elastic engaging member disposed at a side portion of the attaching terminal. When the attaching terminal is fitted into the external connection terminal, the engaging member is engaged with an inner wall of the external connection terminal by an elastic force of the engaging member. In case a battery of the portable electronic instrument is dead, the auxiliary power source device can be securely connected to the portable electronic instrument by an easy operation, so that the battery of the portable electronic instrument can be charged, or the portable electronic instrument can be used immediately.