CN202615255U - Digital constant current source - Google Patents

Abstract

The utility model discloses a digital constant current source, belongs to a current source, and solves the problems of low precision and inconvenience in manufacturing of the conventional current source. The digital constant current source comprises a sampling resistor, a pre-amplification circuit, a resistance and capacitance (RC) filter circuit, an analog/digital (A/D) conversion circuit, a digital processor, a digital/analog (D/A) conversion circuit, a last stage amplification circuit and a power circuit, wherein the sampling resistor, the pre-amplification circuit, the RC filter circuit and the A/D conversion circuit are sequentially connected in series with one another; the digital processor performs 10-order mid-value filter on a pulse digital signal converted by the A/D conversion circuit, calculates a corresponding voltage output value at the next time according to the pulse digital signal and sends to the D/A conversion circuit for converting the corresponding voltage output value into an analog signal; and the analog signal is amplified by the last stage amplification circuit and is output to an external circuit. The digital constant current source is simple in circuit and high in stability and can precisely and effectively detect and control load current; current which can be adjusted under the precision of +/- 0.5 microampere within a microampere range of 1 to 100 can be controlled; and a user can conveniently execute scientific research and experiment analysis on electrochemical and biomedical engineering.

Description

A kind of digital continuous current source

Technical field

The utility model belongs to current source, particularly a kind of digital continuous current source.

Background technology

Current Control is occupied critical role always in galvanochemistry, modern biotechnology, many chemical reactions are able under the effect of certain intensity currents rapidly, carries out efficiently, and technical fields such as electrophoresis, electrodialysis be unable to do without accurate control and the measurement to electric current especially.In many reactions; The size of electric current can have influence on the ratio of speed, direction and the final reacting product of reaction; The excessive electric current of amplitude of variation can make experimental result become to be difficult to expects that the big electric current that transient flow is crossed may burn out sample, even causes the consequence that is difficult to expect.Therefore, produce a kind of accurately efficiently current source extremely important meaning is arranged in biochemical scientific research.

In view of the vital role of high-precision current source in galvanochemistry, Biochemical Research; From the mid-1970s so far people be devoted to be fit to the exploitation of the high precision constant current current source that galvanochemistry, Biochemical Research uses always; Publication number be CN1213229's " variable current source " constitute by a plurality of weighted currents source, prevent that the precision that foozle causes from reducing, but this circuit is too complicated; Make in a plurality of weighted currents source and debugging all very bothers, and precision is not high yet.Publication number be CN1041230's " current-source arrangement " adopt transistor in a large number, be subject to the influence of manufacturing process and environment for use, in measuring process if temperature changes and may make precision influenced; Though used correcting circuit, the discrete type of circuit structure is introduced external interference easily, and whole be that complicated circuit, volume are comparatively huge.Publication number be CN1038001's " current source technology " adopt NOR circuit and push-pull output stage; This kind device is because the symmetric problem of transistor; Be difficult to produce in batches, in addition, along with environment for use changes; The parameter change of symmetrical transistor is not necessarily consistent, possibly influence measuring accuracy when exceeding preset range.Also there is the requirement that is difficult to reach real-time high-precision in above-mentioned design, and complex equipments is huge, lacks defectives such as human-computer interaction interface.

Summary of the invention

The utility model provides a kind of digital continuous current source, solves the problem that existing current source precision is not high enough and be not easy to make.

A kind of digital continuous current source that the utility model provided comprises sampling resistor, pre-amplification circuit, RC filtering circuit, A/D change-over circuit, digital processing unit, D/A change-over circuit, final stage amplifying circuit and power circuit, it is characterized in that:

Said sampling resistor one end ground connection; The other end connects said pre-amplification circuit input end and load respectively, and sampling resistor is delivered to pre-amplification circuit after converting the current signal of gathering into voltage signal V1, after pre-amplification circuit amplifies voltage signal V1; Send the RC filtering circuit to; Voltage signal after the RC filtering circuit will amplify carries out LPF, delivers to the A/D change-over circuit after the filter out background noise and converts digital signal Vd (n) to, is sent to digital processing unit; Digital processing unit carries out 10 rank medium filterings and calculates next voltage output value V (n+1) constantly according to it digital signal Vd (n), is sent to the D/A change-over circuit and converts simulating signal to, and simulating signal exports external circuit to after the final stage amplifying circuit amplifies; N is the sampling instant of A/D change-over circuit and D/A change-over circuit;

Said power circuit with 220V civil power transformation to ± 15V ,+5V and voltage stabilizing, A/D change-over circuit, digital processing unit, D/A change-over circuit are provided+5V voltage, pre-amplification circuit, final stage amplifying circuit are provided ± 15V voltage.

Described digital continuous current source is characterized in that:

Said digital processing unit connects keyboard and LCD display through the IO interface respectively.

Described digital continuous current source is characterized in that:

It is the Difet type operational amplifier of 100fA level that said pre-amplification circuit adopts bias current;

Said RC filtering circuit adopts single order RC filtering circuit;

Said A/D change-over circuit, D/A change-over circuit adopt 12 analog to digital converter and 12 digital to analog converter respectively;

Said digital processing unit is according to next output voltage values V (n+1) constantly of computes:

$V(n+12)=\frac{V\left(n\right)}{I\left(n\right)}\×I_{\mathrm{set}},$

Initial value V (0) is 2048, when V (n) occurring when equaling 0, then V (n+1) is changed to 2048;

Wherein, I _SetFor required output current value, by keyboard to set up; Current input current value I (n):

$I\left(n\right)=\frac{{\mathrm{Vd}}^{\′}}{4095}\×100\left(\mathrm{\μA}\right),$

The numerical value that Vd ' (n) obtains behind 10 rank medium filterings for digital signal Vd (n) as I (n) when equaling 0, then is changed to 0.01 μ A with I (n).

The utility model circuit is simple, good stability; Sample circuit, pre-amplification circuit, RC filtering circuit, A/D change-over circuit, digital processing unit, D/A change-over circuit, final stage amplifying circuit and power circuit organically are assembled together; Digital processing unit has carried out 10 rank medium filterings to digital signal to be handled; Reduce the burst noise that A/D change-over circuit etc. is introduced under external interference; Can carry out high precision to load current and effectively detect and control, can in 1～100 microampere of scope, realize precision ± 0.5 microampere adjustable Current Control; Digital processing unit is also being undertaken the processing of man-machine interface, can the size that current values and actual current are set be presented on the LCD display; Make things convenient for the user to carry out biomedicine, the corresponding scientific research of galvanochemistry and experimental analysis.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Fig. 2 is the sample circuit synoptic diagram;

Fig. 3 is the pre-amplification circuit circuit diagram;

Fig. 4 is a RC filtering circuit synoptic diagram;

Fig. 5 is an A/D change-over circuit synoptic diagram;

Fig. 6 is a D/A change-over circuit synoptic diagram;

Fig. 7 is a final stage amplifying circuit synoptic diagram;

Fig. 8 is the power circuit synoptic diagram;

Fig. 9 is a single-chip microcomputer mini system plate synoptic diagram.

Embodiment

Below in conjunction with accompanying drawing and embodiment the utility model is further specified.

As shown in Figure 1, the embodiment of the utility model comprises sampling resistor, pre-amplification circuit, RC filtering circuit, A/D change-over circuit, digital processing unit, D/A change-over circuit, final stage amplifying circuit and power circuit; Digital processing unit can connect keyboard and LCD display through the IO interface respectively.Carry out information interaction through SPI (Serial Peripheral Interface (SPI)) bus, parallel bus etc. between the each several part.

Like Fig. 2, shown in Figure 3; The current signal that comes that sampling resistor Rs will gather converts voltage signal into; Sampling resistor R3 one termination simulation ground; Other end A1 connects "+" end and the end of load J5 of the prefix operation amplifier IC1 of said pre-amplification circuit respectively, and the other end B2 of load J5 connects the final stage amplification circuit output end.

Pre-amplification circuit is made up of prefix operation amplifier IC1 and peripheral resistance; Low current signal is input to "+" end of prefix operation amplifier IC1 through sampling resistor Rs; The output terminals A 2 of IC1 and "-" end indirect resistance R4; "-" end of IC1 is through resistance R 3 ground connection, and operational amplifier IC1 adopts the OPA129 chip.

As shown in Figure 4, the RC filtering circuit is the single order RC filtering circuit of resistance R 5 and capacitor C 3 formations; Low current signal gets into the RC filtering circuit through the A2 end and carries out low pass and anti-aliasing filter after pre-amplification circuit amplifies: preposition amplified output signals is divided two-way behind series resistor R5; One the tunnel goes into A/D converter U1 through the A3 termination; Ground is received through capacitor C 3 in another road, current signal behind the RC filtering circuit elimination undesired signals such as ground unrest.

As shown in Figure 5, A/D modular converter employing ADS7818 chip and corresponding decoupling capacitor C4, C5.The A3 end is signal input part, and D1, D2, D3 are respectively the interface of A/D conversion chip and digital processing unit.

As shown in Figure 6, the D/A modular converter adopts DAC7611 chip and respective peripheral circuit.B1 is an analog signal output, and D4, D5, D6 are respectively the interface of D/A conversion chip and digital processing unit.

Among Fig. 2～Fig. 6, triangle is represented simulation ground; Among Fig. 5, Fig. 6, the inverted triangle that four line form is represented digitally; Simulation ground with digitally between link to each other through magnetic bead L1.

As shown in Figure 7, the final stage amplifying circuit is made up of output operational amplifier IC2 and peripheral resistance; The signal of digital processing unit output through D/A conversion back through the B1 port link output operational amplifier IC2 "+" pin, the output terminal B2 of output operational amplifier receives its "-" end through a resistance R 14, "-" end through resistance R 17 to ground; Output operational amplifier IC2 adopts the AD817 chip, and the positive-negative power leads ends connects respectively+15V and-15V.

As shown in Figure 8; Power circuit adopts the LM7805 power supply chip to be used to provide+5V voltage; Adopt LM7815 power supply chip, LM7915 power supply chip be respectively applied for and provide+15V and-15V voltage, each chip pin 1 connects voltage input, pin 2 ground connection; Pin 3 is voltage stabilizing output, and input pin and ground, output pin and ground are connected to the electric capacity of 0.33 μ F and 0.1 μ F respectively.

As shown in Figure 9, digital processing unit is made up of single-chip microcomputer U1, clock circuit, reset circuit, program download interface, 16 * 2LCD display screen, keyboard.Single-chip microcomputer U1, clock circuit, reset circuit and program download interface constitute the minimum system of single-chip microcomputer operate as normal; 16 * 2LCD display screen connects single-chip microcomputer through the I/O mouth, shows current values by Single-chip Controlling.The real-time current digital data that can as required single-chip microcomputer be converted in actual the use sends back to host computer through COM1 and supplies data to preserve, analyze; Single-chip microcomputer U1 adopts the SST89E58RD chip.

Clock circuit is made up of crystal oscillator, and its two ends connect the XTAL1 and the XTAL2 pin of single-chip microcomputer respectively, and the crystal oscillator two ends are respectively through capacitor C 22, and C23 is to ground; Reset circuit adopts the effective RC reset circuit of high level, and the program download interface adopts RXD, TXD and three ports of GND of single-chip microcomputer.16 * 2LCD display screen, keyboard connect single-chip microcomputer through the IO interface respectively.

Claims (3)

1. a digital continuous current source comprises sampling resistor, pre-amplification circuit, RC filtering circuit, A/D change-over circuit, digital processing unit, D/A change-over circuit, final stage amplifying circuit and power circuit, it is characterized in that:

Said sampling resistor one end ground connection; The other end connects said pre-amplification circuit input end and load respectively, and sampling resistor is delivered to pre-amplification circuit after converting the current signal of gathering into voltage signal V1, after pre-amplification circuit amplifies voltage signal V1; Send the RC filtering circuit to; Voltage signal after the RC filtering circuit will amplify carries out LPF, delivers to the A/D change-over circuit after the filter out background noise and converts digital signal Vd (n) to, is sent to digital processing unit; Digital processing unit carries out 10 rank medium filterings and calculates next voltage output value V (n+1) constantly according to it digital signal Vd (n), is sent to the D/A change-over circuit and converts simulating signal to, and simulating signal exports external circuit to after the final stage amplifying circuit amplifies; N is the sampling instant of A/D change-over circuit and D/A change-over circuit;

Said power circuit with 220V civil power transformation to ± 15V ,+5V and voltage stabilizing, A/D change-over circuit, digital processing unit, D/A change-over circuit are provided+5V voltage, pre-amplification circuit, final stage amplifying circuit are provided ± 15V voltage.

2. digital continuous current as claimed in claim 1 source is characterized in that:

Said digital processing unit connects keyboard and LCD display through the IO interface respectively.

3. according to claim 1 or claim 2 digital continuous current source is characterized in that:

It is the Difet type operational amplifier of 100fA level that said pre-amplification circuit adopts bias current;

Said RC filtering circuit adopts single order RC filtering circuit;

Said A/D change-over circuit, D/A change-over circuit adopt 12 analog to digital converter and 12 digital to analog converter respectively;

Said digital processing unit is according to next output voltage values V (n+1) constantly of computes:

Initial value V (0) is 2048, when V (n) occurring when equaling 0, then V (n+1) is changed to 2048;

Wherein, I _SetFor required output current value, by keyboard to set up; Current input current value I (n):

The numerical value that Vd ' (n) obtains behind 10 rank medium filterings for digital signal Vd (n) as I (n) when equaling 0, then is changed to 0.01 μ A with I (n).

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