Linear voltage regulator with selectable light and heavy load paths
View Patent ↗A light-load power transistor and a heavy-load power transistor are connected in parallel between an input voltage and an output voltage. The light-load power transistor has a smaller current driving capability, i.e. a smaller dimension of a current path. During a light-load mode, only is the light-load power transistor activated to reduce the current consumption caused by an error amplifier, thereby enhancing the efficiency. When a detection current signal is higher than a threshold current signal, the heavy-load power transistor is additionally activated through a gate control circuit by a mode selection circuit, thereby achieving a sufficient current driving capability.
1. A linear voltage regulator comprising:
a light-load transistor having a gate and a light-load current path coupled between an input voltage and an output voltage;
an error amplifier for generating an error signal in response to a reference voltage signal and a feedback voltage signal representative of the output voltage, the error signal controlling the gate of the light-load transistor;
a heavy-load transistor having a gate and a heavy-load current path coupled between the input voltage and the output voltage;
a gate control circuit coupled to the gate of the heavy-load transistor; and
a mode selection circuit coupled between the error amplifier and the gate control circuit for generating a detection current signal representative of a current flowing through the light-load transistor such that when the detection current signal is larger than a predetermined threshold current signal, the mode selection circuit allows the error signal to control the gate of the heavy-load transistor through the gate control circuit.
2. The linear voltage regulator according to claim 1 , wherein:
when the detection current signal is smaller than the threshold current signal, the mode selection circuit prevents the error signal from controlling the gate of the heavy-load transistor through the gate control circuit.
3. The linear voltage regulator according to claim 2 , wherein:
when the detection current signal is smaller than the threshold current signal, the mode selection circuit causes the gate of the heavy-load transistor to be coupled to the input voltage through the gate control circuit.
4. The linear voltage regulator according to claim 1 , wherein:
the heavy-load transistor has a current driving capability larger than that of the light-load transistor.
5. The linear voltage regulator according to claim 1 , wherein:
the heavy-load transistor has a dimension larger than that of the light-load transistor.
6. The linear voltage regulator according to claim 1 , wherein:
the gate control circuit includes a first transmission gate and a second transmission gate, which are controlled by the mode selection circuit such that when the first transmission gate is made conductive, the input voltage controls the gate of the heavy-load transistor through the first transmission gate, and when the second transmission gate is made conductive, the error signal controls the gate of the heavy-load transistor through the second transmission gate.
7. The linear voltage regulator according to claim 6 , wherein:
when the detection current signal is smaller than the threshold current signal, the mode selection circuit makes the first transmission gate conductive.
8. The linear voltage regulator according to claim 6 , wherein:
when the detection current signal is larger than the threshold current signal, the mode selection circuit makes the second transmission gate conductive.
9. The linear voltage regulator according to claim 1 , wherein:
the mode selection circuit includes:
a current sensing unit for generating the detection current signal, and
a current comparing unit for comparing the detection current signal and the threshold current signal.
10. The linear voltage regulator according to claim 9 , wherein:
the current comparing unit is implement by a current comparator having a hysteresis effect.