ELECTRICAL CONSTANT CURRENT CIRCUIT, ELECTRICAL CONSTANT CURRENT SOURCE, MEASUREMENT ARRANGEMENT

Abstract

An electrical constant current circuit (CCC) in particular for supplying electrical power to a sensor, the circuit (CCC) including a power supply input terminal (INT), a constant current output terminal (OUT), a first transistor (TRF), and a shunt-type voltage reference (RVS), wherein the base of the first transistor (TRF) is biased by the shunt-type voltage reference (SVR) in series with the base-emitter junction of the second transistor (TRS), wherein the emitter of the first transistor (TRF) is connected to the power supply input terminal (INT) via a current set resistor (RST), wherein the collector of the first transistor (TRF) is connected to the output terminal (OUT) through a Schottky diode (SKD). For the improved temperature stability, initial accuracy, drop out voltage and power consumption embodiment provides that the circuit (CCC) includes a second transistor (TRS) in the line between the base of the first transistor (TRF) and the shunt-type voltage reference (SVR), wherein the second transistor's (TRS) base and collector are connected to the first transistor's (TRF) base.

Claims

1. An electrical constant current circuit for supplying electrical power to a sensor, the circuit comprising: a power supply input terminal; a constant current output terminal; a first transistor; and a shunt-type voltage reference; wherein a base of the first transistor is biased by the shunt-type voltage reference in series with a base-emitter junction of a second transistor, wherein the first transistor (TRF) emitter is connected to the power supply input terminal via a collector resistor, wherein a collector of the first transistor is connected to the constant current output terminal, and wherein the circuit comprises the second transistor in a line between the base of the first transistor and the shunt-type voltage reference, wherein a base of the second transistor and a collector of the second transistor are connected to the base of the first transistor, wherein the first transistor and the second transistor are identical, wherein the first transistor and the second transistor are both part of a matched-pair dual transistor, wherein a capacitor is connected in parallel to the series association of the shunt type voltage reference and the diode-connected transistor.

2. (canceled)

3. The circuit of claim 1, wherein the shunt-type voltage reference is a micropower precision shunt-type voltage reference with a power consumption in a range of microwatts.

4. The circuit of claim 1, wherein a Schottky diode is provided at the constant current output terminal to avoid reverse current.

5. The circuit of claim 1, further comprising: a ground reference of the shunt-type voltage reference connected to a ground of a power supply via the base-emitter junction of the second transistor in series with a grounding bias resistor.

6. An electrical constant current source, the electrical constant current source comprising: a constant current circuit comprising: a power supply input terminal; a constant current output terminal; a first transistor; a shunt-type voltage reference; wherein a base of the first transistor is biased by the shunt-type voltage reference in series with a base-emitter junction of a second transistor, wherein an emitter of the first transistor is connected to the power supply input terminal via a collector resistor, wherein a collector of the first transistor is connected to the constant current output terminal, and wherein the circuit comprises the second transistor in a line between the based of the first transistor and the shunt-type voltage reference, wherein a base of the second transistor and collector are connected to the base of the first transistor, wherein the first transistor and the second transistor are identical, wherein the first transistor and the second transistor are both part of a matched-pair dual transistor; a power supply, supplying power to the constant current circuit.

7. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 depicts a schematic diagram of an electrical constant current source including a constant current circuit according to an embodiment.

[0022] FIG. 2 depicts a measured temperature stability of the circuit in the temperature chamber according to an embodiment.

DETAILED DESCRIPTION

[0023] FIG. 1 depicts a schematic diagram of an electrical constant current source CCS including a constant current circuit CCC. The constant current circuit CCC for supplying electrical power to a sensor SNR receives the operation power from a (for example regulated) DC power supply POS.

[0024] The circuit CCC includes a power supply input terminal INT and a constant current output terminal OUT. A first transistor TRF and an identical second transistor TRS are provided as a matched-pair dual transistor MDT. The transistors are configured such that the first transistor's TRF emitter is connected to the power supply input terminal INT via a-current set resistor RST; the first transistor's TRF base is biased by the shunt-type voltage reference SVR via the second transistors emitter-base-line (base-emitter junction); the second transistor's TRS base is connected to its collector and to the first transistor's TRF base; the first transistor's TRF collector is connected to the output terminal OUT via a Schottky diode SKD, and an optional noise reduction capacitor CNR connected in parallel to the shunt-type voltage reference SVR in series with the base-emitter junction of the second transistor TRS.

[0025] In the circuit CCC, the transistor TRF is the main pass element and equates the voltage across the reference voltage SVR plus the base-emitter voltage of the second transistor TRS to the voltage across the current set resistor RST and its base-emitter voltage VTRF such that:

[00001]$VSVR+V\mathrm{TRS}=V\mathrm{RST}+V\mathrm{TRF}$

[0026] Employing the matched-pair dual transistor MDT perfectly cancels out VTRS and VTRF and their drifts due to the ambient temperature variations and self-heating of the transistor. This mechanism results in significant improvement on temperature drift and the accuracy of the circuit. Due to the cancellation of the VTRS by VTRF, and neglecting the base currents inequality of transistors (<50 A), the output [Iout] current is:

[00002]$\mathrm{Iout}=\frac{V_{SVR}+\left(V_{TRF}-V_{TRS}\right)}{R_{ST}}\frac{V_{SVR}}{R_{ST}}$

[0027] The drop-out voltage [VDO] of the circuit is: VDO=VSVR+VTRF CEsat+VSKD where the VTRF CEsat is the collector-emitter saturation voltage of the TRF and VF is the forward voltage of the diode SKD. The optional capacitor CNR is used for noise reduction and power supply rejection ratio [PSRR] improvement in high frequencies.

[0028] FIG. 1 depicts a schematic diagram of an embodiment.

[0029] FIG. 2 depicts the measured temperature stability in the temperature chamber. Over a wide range of 40 C. to 100 C. the temperature drift is about 3.96 mA-4.09 mA which is approximately 1.5% (this result is achieved with a 50 ppm/ C. set resistor (Rset), further improvement possible by choosing a lower thermal coefficient resistor).

[0030] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present description. Thus, whereas the dependent claims depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

[0031] While the present description has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.