Low voltage current source/start-up circuit

• US 4,837,496 A
• Filed: 03/28/1988
• Issued: 06/06/1989
• Est. Priority Date: 03/28/1988
• Status: Expired due to Term

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Erdi, George
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): Sterrett, Jeffrey
• Application Number:
  US07/173,758
• Time in Patent Office: 435 Days
• Field of Search: 323/315, 323/316
• US Class Current: 323/315
• CPC Class Codes: G05F 3/20 using diode- transistor combinations G05F3/18 takes precedence

Abstract

A start-up circuit/current source includes a first current path including serially connected first field effect transistor, first resistor, first bipolar transistor, and second resistor. A second current path includes a second field effect transistor, a second bipolar transistor, and a third resistor. The base electrodes of the first and second bipolar transistors are interconnected, and the base and collector of the second bipolar transistor are shorted together. A first current source includes a bipolar transistor serially connected through the third resistor, the base of the third bipolar transistor connected to the first current path. A second current source can be provided including a fourth bipolar transistor serially connected with a fourth resistor and with the base of the fourth transistor connected to a common terminal of the first resistor and first bipolar transistor. The two field effect transistors can be replaced by two equal resistors or by a single field effect transistor serially connected with a two-collector PNP bipolar transistor which provides the equal currents for the two current paths. The current source is independent of supply voltage and the magnitude of the currents in the two current paths so long as the currents are equal. Accordingly, the circuit is independent of poorly-controlled currents in field effect transistors so long as the currents are equal.

Claims

1. A start-up/current source circuit providing current source outputs that are independent of power supply voltage and start-up currents comprising

first and second voltage potentials,

first and second current paths connected between said first and second voltage potentials for conducting equal currents, said first current path including a first bipolar transistor serially connected with a first resistor and said second current path including a second bipolar transistor serially connected with a second resistor, said first and second resistors being equal, the base and collector of said second transistor being connected, the emitter of said second transistor being larger than the emitter of said first transistor and the bases of said first and second transistors being connected, said first and second current paths further including first and second field effect transistors serially connected with said first and second bipolar transistors and said first and second resistors, respectively, the currents through said first and second field effect transistors being equal, and

a first current source including a third bipolar transistor serially connected with said second resistor, the base of said third transistor being connected to said first current path.

2. The circuit as defined by claim 1 and further including a third resistor equal to each of said first and second resistors and serially connected in said first current path between said first field effect transistor and said first transistor, a second current source including a fourth bipolar transistor serially connected with a fourth resistor, the base of said fourth transistor being connected to a common terminal of said third resistor and said first bipolar transistor, the base of said third transistor being connected to a common terminal of said first field effect transistor and said third resistor.

3. A start-up/current source circuit providing current source outputs that are independent of power supply voltage and start-up currents comprising

first and second voltage potentials,

first and second current paths connected between said first and second voltage potentials for conducting equal currents, said first current path including a first bipolar transistor serially connected with a first resistor and said second current path including a second bipolar transistor serially connected with a second resistor, said first and second resistors being equal, the base and collector of said second transistor being connected, the emitter of said second transistor being larger than the emitter of said first transistor and the bases of said first and second transistors being connected, a field effect transistor serially connected with a two-collector bipolar transistor, wherein said first current path includes one collector of said two-collector bipolar transistor, and said second current path includes the other collector of said two-collector bipolar transistor and said field effect transistor, currents through said first and second current paths being equal,

a first current source including a third bipolar transistor serially connected with said second resistor, the base of said third transistor being connected to said first current path.

4. The circuit as defined by claim 3 wherein said first, second, and third bipolar transistors are NPN transistors and said two-collector bipolar transistor is a PNP transistor.

5. A start-up/current source circuit providing current source outputs that are independent of power supply voltage and start-up currents comprising

first and second voltage potentials,

first and second current paths connected between said first and second voltage potentials for conducting equal currents, said first current path including a first bipolar transistor serially connected with a first resistor and said second current path including a second bipolar transistor serially connected with a second resistor, said first and second resistors being equal, the base and collector of said second transistor being connected, the emitter of said second transistor being larger than the emitter of said first transistor and the bases of said first and second transistors being connected,

fourth and fifth bipolar transistors and a field effect transistor, wherein said first and second current paths are connected to said fourth and fifth bipolar transistors, respectively, and through said field effect transistor to said first voltage potential, currents through said first and second current paths being equal, a first current source including a third bipolar transistor serially connected with said second resistor, the base of said third transistor being connected to said first current path.

6. The circuit as defined by claim 5 wherein said first, second, and third bipolar transistors are PNP transistors and said fourth and fifth bipolar transistors are matched NPN transistors.