A circuit capable of obtaining constant current in a large temperature range

Abstract

This invention relates to the field of electronic technology and describes a circuit capable of achieving constant current over a wide temperature range. It consists of a constant voltage section and a constant current section. The constant current section is a conventional circuit, and the output of the constant voltage section is connected to the input of the constant current section. The constant voltage section includes a Zener diode, an adjustable resistor, a resistor, an operational amplifier, and a transistor. The Zener diode can be an LED or a standard Zener diode. If the constant voltage section has a constant voltage point relative to VCC, the transistor is a PNP type. In this case, if the Zener diode is an LED, its anode is connected to VCC, and its cathode is connected to the positive input of the operational amplifier and a fixed terminal of the adjustable resistor. Other connection relationships can be adjusted accordingly. Ideally, the current through the Zener diode should be between 0.1 mA and 10 mA. This invention was developed through experimentation. The circuit based on this invention can achieve constant current over a wide temperature range.

Description

Technical Field

[0001] This invention belongs to the field of electronic technology, specifically relating to a circuit that can obtain constant current over a wide temperature range. Background Technology

[0002] Existing constant current source circuits have a narrow operating temperature range. For example, when we need a stable constant current source to make test equipment, we use a common LED and a resistor to ground to form a voltage regulator circuit, plus a conventional constant current circuit. We find that when the output is set to 250 microamps, it drifts by more than 10 microamps when a hot air blower blows it. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a circuit that can obtain constant current over a wide temperature range.

[0004] The circuit of this invention is characterized by:

[0005] a. It consists of a constant voltage section and a constant current section. The constant current section is a conventional circuit, and the output terminal of the constant voltage section is connected to the input terminal of the constant current section.

[0006] b. The constant voltage section includes a Zener diode, an adjustable resistor, a resistor, an operational amplifier, and a transistor. The Zener diode can be a light-emitting diode or a general-purpose Zener diode.

[0007] c. If the constant voltage section has a constant voltage point relative to VCC, then the transistor is a PNP type. In this case, if the Zener diode is an LED, then the positive terminal of the LED is connected to VCC, and the negative terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. If the Zener diode is a conventional Zener diode, then the negative terminal of the Zener diode is connected to VCC, and the positive terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. The adjustable terminal of the adjustable resistor is connected to either of its own fixed terminals. The other fixed terminal of the adjustable resistor is connected to one end of the resistor and the C-pin of the transistor to become the output terminal of the constant voltage section. The other end of the resistor is grounded. The B-pin of the transistor is connected to the output pin of the operational amplifier, and the E-pin is connected to the negative input terminal of the operational amplifier.

[0008] d. If the constant voltage section is constant voltage point to ground, then the transistor is NPN type. In this case, if the Zener diode is an LED, then the negative terminal of the LED is grounded, and the positive terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. If the Zener diode is a conventional Zener diode, then the positive terminal of the Zener diode is grounded, and the negative terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. The adjustable terminal of the adjustable resistor is connected to either of its fixed terminals. The other fixed terminal of the adjustable resistor is connected to one end of the resistor and the C-pin of the transistor to become the output terminal of the constant voltage section. The other end of the resistor is connected to VCC. The B-pin of the transistor is connected to the output pin of the operational amplifier, and the E-pin is connected to the negative input terminal of the operational amplifier.

[0009] Preferably, the adjustable resistor has a resistance value twice that of the main resistor, thus facilitating its use.

[0010] When using this invention, the current through the Zener diode is preferably between 0.1 mA and 10 mA.

[0011] The technology of this invention was obtained through experimentation.

[0012] The beneficial effects of this invention are: by using the circuit of this invention, constant current can be obtained over a wide temperature range. Attached Figure Description

[0013] Figure 1 The electrical schematic diagram is for an example. Detailed Implementation

[0014] See Figure 1 Examples of implementations.

[0015] The circuit in this example consists of a constant voltage section 1 and a constant current section 2. The constant current section 2 is a conventional circuit. The output terminal of the constant voltage section 1 is connected to the input terminal of the constant current section 2. The constant voltage section 1 is a constant voltage point relative to VCC. Transistor Q1 is a PNP type, and Zener diode D1 is an LED. Its anode is connected to VCC, and its cathode is connected to both the positive input terminal of operational amplifier IC1 and one end of variable resistor R1. The adjustable terminal of R1 is connected to one end of resistor R2. The other end of R1 is connected to both one end of R2 and pin C of Q1, thus becoming the output terminal of the constant voltage section. The other end of R2 is grounded. Pin B of Q1 is connected to the output pin of IC1, and pin E of Q1 is connected to the negative input terminal of IC1. The current through the Zener diode is 0.1 mA to 10 mA. The resistance of R1 is 10 kΩ, and the resistance of R2 is 5.1 kΩ.

[0016] Using the circuit in this embodiment, 10 channels of 250 microamp constant current are driven in parallel (10 channels of electronic detonator ignition resistor measurement, requiring 1.6 ohms ± 0.3 ohms, with a measurement error of ± 0.01 ohms). After being tested in a high-temperature chamber at 80 degrees Celsius and a low-temperature chamber at -40 degrees Celsius, the drift is less than 1 microamp in the temperature range of -20 degrees Celsius to +50 degrees Celsius.

[0017] During debugging, it was found that at a certain temperature, adjusting R1 could raise the current source to a maximum point. After over-adjustment, the current would drop again (actually the maximum point of constant voltage). The stable operating range of the constant current source is centered on the temperature during debugging. That is, when the temperature is high (low), the stable range of the constant current source will be higher (lower).

Claims

1. A circuit capable of obtaining constant current over a wide temperature range, characterized in that: a. It consists of a constant voltage section and a constant current section. The constant current section is a conventional circuit, and the output terminal of the constant voltage section is connected to the input terminal of the constant current section. b. The constant voltage section includes a Zener diode, an adjustable resistor, a resistor, an operational amplifier, and a transistor. The Zener diode can be a light-emitting diode or a common Zener diode. c. If the constant voltage section has a constant voltage point relative to VCC, then the transistor is a PNP type. In this case, if the Zener diode is an LED, then the positive terminal of the LED is connected to VCC, and the negative terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. If the Zener diode is a conventional Zener diode, then the negative terminal of the Zener diode is connected to VCC, and the positive terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. The adjustable terminal of the adjustable resistor is connected to either of its own fixed terminals. The other fixed terminal of the adjustable resistor is connected to one end of the resistor and the C-pin of the transistor to become the output terminal of the constant voltage section. The other end of the resistor is grounded. The B-pin of the transistor is connected to the output pin of the operational amplifier, and the E-pin is connected to the negative input terminal of the operational amplifier. d. If the constant voltage section is constant voltage point to ground, then the transistor is NPN type. In this case, if the Zener diode is an LED, then the negative terminal of the LED is grounded, and the positive terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. If the Zener diode is a conventional Zener diode, then the positive terminal of the Zener diode is grounded, and the negative terminal is connected to the positive input terminal of the operational amplifier and one fixed terminal of the adjustable resistor. The adjustable terminal of the adjustable resistor is connected to either of its fixed terminals. The other fixed terminal of the adjustable resistor is connected to one end of the resistor and the C-pin of the transistor to become the output terminal of the constant voltage section. The other end of the resistor is connected to VCC. The B-pin of the transistor is connected to the output pin of the operational amplifier, and the E-pin is connected to the negative input terminal of the operational amplifier. e. The resistance of the adjustable resistor is twice the resistance of the resistor mentioned above, and the current through the Zener diode is 0.1 mA to 10 mA.

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