Constant voltage source circuit

• US 4,983,905 A
• Filed: 07/05/1989
• Issued: 01/08/1991
• Est. Priority Date: 07/05/1988
• Status: Expired due to Term

• Current Assignee: Fujitsu Microelectronics Limited (Fujitsu Limited)
• Original Assignee: Fujitsu Ten Limited (DENSO Corporation), Fujitsu Limited, Fujitsu VLSI Limited (Fujitsu Limited)
• Inventors: Sano, Yoshiaki, Yasukouchi, Katsuyuki, Fujihara, Susumu, Katagase, Yasuhide, Matsumoto, Takashi, Hanazawa, Toshio
• Primary Examiner(s): Wong, Peter S.
• Application Number:
  US07/375,707
• Time in Patent Office: 552 Days
• Field of Search: 323/274, 323/275, 323/281, 323/299, 323/303
• US Class Current: 323/274
• CPC Class Codes: G05F 1/565 sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor G05F1/563 takes precedence

Abstract

A constant voltage source circuit which is provided with an output transistor (Q₁) for outputting a predetermined output voltage (V₀) in accordance with an input voltage (V_IN) and a differential amplifier (A), and is further characterized in that the circuit further comprises a reference voltage control means which monitors variations of the input voltage (V_IN) and outputs a predetermined constant voltage to the differential amplifier (A) as a reference voltage when the input voltage (V_IN) is higher than, a predetermined voltage level, and a voltage varied in accordance with the variation of the input voltage (V_IN) is output therefrom to the differential amplifier (A) as a reference voltage when the input voltage (V_IN) falls below a predetermined voltage level.

Claims

1. A constant voltage source circuit comprising:

an input terminal for receiving an input voltage;

an output transistor connected to said input terminal for outputting a predetermined output voltage in accordance with said input voltage;

a differential amplifier for controlling said output transistor; and

a reference voltage control means, operatively connected to said differential amplifier and said input terminal, for monitoring variations of said input voltage and for outputting a predetermined constant voltage to said differential amplifier as a reference voltage when said input voltage is higher than a predetermined voltage level, and outputting a voltage varied in accordance with the variation of said input voltage to said differential amplifier as the reference voltage when said input voltage falls below said predetermined voltage level.

2. A constant voltage source circuit according to claim 1, wherein said reference voltage control means further comprises a first reference voltage supply means for supplying said predetermined constant voltage to said differential amplifier (A) when said input voltage (V_IN) is higher than the predetermined voltage level and a second reference voltage supply means for supplying said voltage varied in accordance with the variation of said input voltage (V_IN) to said differential amplifier (A) when said input voltage (V_IN) falls below the predetermined voltage level.

3. A constant voltage source circuit according to claim 1, wherein said reference voltage control means further comprises a reference voltage supply means for supplying said predetermined constant voltage to said differential amplifier (A) when said input voltage (V_IN) is higher than the predetermined voltage level and a bias voltage supply means for supplying a bias voltage varied in accordance with the variation of said input voltage (V_IN) to said reference voltage supply means so as to provide said voltage (V_RB) varied in accordance with the variation of said bias voltage to said differential amplifier (A) when said input voltage (V_IN) falls below the predetermined voltage level.

4. A constant voltage source circuit according to claim 1, wherein said circuit further comprises a ripple elimination means for eliminating a ripple accumulated in said input voltage (V_IN).

5. A constant voltage source circuit according to claim 1, wherein said output transistor (Q₁) comprises a transistor.

6. A constant voltage source circuit according to claim 2, wherein said circuit further comprises a ripple elimination means for eliminating a ripple accumulated in said input voltage (V_IN).

7. A constant voltage source circuit according to claim 3, wherein said circuit further comprises a ripple.

8. A constant voltage source circuit according to claim 2, wherein said output transistor (Q₁) comprises a transistor.

9. A constant voltage source circuit according to claim 3, wherein said output transistor (Q₁) comprises a transistor.

10. A constant voltage source circuit according to claim 1, wherein said output transistor (Q₁) comprises a pair of transistors connected by a Darlington connection.

11. A constant voltage source circuit according to claim 1, wherein said output transistor (Q₁) comprises a pair of transistors connected by an inverted Darlington connection.

12. A constant voltage source circuit according to claim 2, wherein said output transistor (Q₁) comprises a pair of transistors connected by a Darlington connection.

13. A constant voltage source circuit according to claim 2, wherein said output transistor (Q₁) comprises a pair of transistors connected by an inverted Darlington connection.

14. A constant voltage source circuit according to claim 3, wherein said output transistor (Q₁) comprises a pair of transistors connected by a Darlington connection.

15. A constant voltage source circuit according to claim 3, wherein said output transistor (Q₁) comprises a pair of transistors connected by an inverted Darlington connection.