Charge device reduced in size and power consumption

A charge device comprising:

• a battery connected between a first power supply terminal and a first contact;
• a first transistor connected between the first contact and a second contact;
• a resistor connected between the second contact and a second power supply terminal;
• a second transistor connected between the first contact and the second power supply terminal;
• an operation amplifier having an inverted input terminal thereof connected to the second contact and a non-inverted input terminal thereof connected to a constant voltage source;
• and
• potential providing means for providing respective gates of the first and second transistors with one of an electric potential at the first power supply terminal, an electric potential at the second power supply terminal and an electric potential at an output of the operation amplifier.

A charge device comprising:

• a battery connected between a first power supply terminal and a contact;
• a transistor connected between the contact and a second power supply terminal;
• an adapter connected between the first and second power supply terminals;
• a first detection means for comparing a voltage of the battery and a voltage of a constant voltage source to detect which thereof is higher;
• a second detection means for detecting whether or not the adapter is supplying a voltage between the first and second power supply terminals;
• and
• a control means for responding detection results of the first and second detection means to provide a gate of the transistor with one of an electric potential at the first power supply terminal, an electric potential at the second power supply terminal and a bias potential between the electric potential at the first power supply terminal and the electric potential at the second power supply terminal.

A charge device comprising:

• a battery connected between a first power supply terminal and a first contact;
• a first transistor connected between the first contact and a second contact;
• a resistor connected between the second contact and a second power supply terminal;
• a second transistor connected between the first contact and the second power supply terminal;
• an adapter having a positive pole and a negative pole, the adapter being operative to provide a voltage between the first and second power supply terminals and generate a detection signal, as a voltage is applied between the positive pole and the negative pole;
• a first operation amplifier having an inverted input terminal thereof connected to the first contact and a non-inverted input terminal thereof connected to a first constant voltage source;
• a second operation amplifier having an inverted input terminal thereof connected to the second contact and a non-inverted input terminal thereof connected to a second constant voltage source;
• a control means for responding to a combination of an output signal of the first operation amplifier and the detection signal to provide an active level to one of first, second and third control signals;
• a first buffer for responding to the active level of the first control signal to interconnect the first power supply terminal with respective gates of the first and second transistors;
• a second buffer for responding to the active level of the second control signal to interconnect the second power supply terminal with the respective gates of the first and second transistors;
• and
• a third buffer for responding to the active level of the third control signal to interconnect an output terminal of the second operation amplifier with the respective gates of the first and second transistors.