SIMETRI, Jurnal Ilmu Fisika Indonesia Volume 1 Nomor 1(C) Mei 2012

Bondgraph Model of A Current Amplifier

Assaidah

Physics Department, FMIPA, University of Sriwijaya, Southern Sumatra, Indonesia; e-mail: ias aca@yahoo.com

Abstract: A bondgraph model of a current amplifier had been done. The simulation used 20-sim version 4.0 and

compared with the simulation result of Orcad program. Some adjustment of the constant values of bondgraph symbol

is needed to yield the same result. By setting the proper ratio of R3 and R4 (Resistance of Op Amp) in the bondgraph

model , the same simulation result with Orcad program can be achieved.

Keywords: bondgraph model, amplifier, simulation

Received : 2 April 2012; Accepted : 20 Mei 2012

1 INTRODUCTION

A physical system can be represented by symbolsand lines, identifying the power flow paths. The

lumped parameter elements of resistance, capacitanceand inertance are interconnected in an energy conserv-ing way by bonds and junctions resulting in a net-work structure, named Bond Graph. The languageof bond graphs aspires to express general class physi-cal systems through power interactions. The factors ofpower i.e., Effort and Flow have different interpreta-tions in different physical domains as shown in Table1. To describe the flow and effort path, bond witharrow line (to show the direction) is used [3].

Another symbols are also used to express the phys-ical process i.e : R as energy dissipation, C as energystorer and I as inertia component in a dynamic sys-tem. In electrical case, these symbols (R, C and I)are used to show the real meaning of them self, whereR is a symbol for Resistor, C for Capasitor and I forInductor. Such as an amplifier, the circuit can be rep-resented using the bondgraph model.

1.1 Amplifier Circuit

An amplifier circuit had been made using Orcad Pro-gram (Figure 2). It used Howland Current configu-ration to produce a constant current source. It hadbeen proved that this circuit is stable over a largerfrequency range, simpler, smaller and can be improvedwhen better op-amp become available [4].

The input of amplifier is 100 mV of AC Voltage.LM675 application is chosen since it is suitable forhigh power supply. R11 and R12 are feedback resistor(Rf) of the amplifier. To get the proper amplification,Rf is set to 10.100 Ω and Ri (input resistance) is setto 2.2 KΩ. To avoid drop voltage, R14 should be verysmall so it is set to 4.7 Ω. With such setting, current

output of the circuit of 0.1 mA can be yielded.

2 BONDGRAPH MODEL OF THEAMPLIFIER CIRCUIT

The amplifier circuit can be modeled with bondgraphas shown in figure 3. Sine is the AC voltage signal asthe input. MSe is needed to connect the input (as en-ergy source) to the circuit’s component. By considerthe effort and flow (in this case voltage and current),the 0 and 1 junction will show at which point the volt-age is the same or different, either the current. The0 junction means the voltage value is the same butthe current is different. While the 1 junction meansvice versa. Besides, the direction of the arrow shouldbe drawn carefully following the current flow in thecircuit. Otherwise, the simulation will not work.

The bondgraph model for Op-Amp is shown insidethe triangle. R3 is the input resistance and R4 isthe output resistance of the Op-Amp. The parame-ter value of these two resistor should be set properlyto get the correct output of amplification process. Inthis case, the parameter value of R3 and R4 are set to100 and 0.1 .

3 SIMULATION RESULT

The bondgraph model is made using 20-Sim programversion 4.0. After the model is finish by setting eachsuitable parameter of the circuit’s component, thenthe simulation can be run. As the result, the bond-graph simulation (Figure 4) is similar with the simu-lation result using Orcad Program (Figure 5).

4 CONCLUTION

Bondgraph can model dynamic system effectively in-clude electrical system. For an amplifier circuit, one

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should be careful with the Op-Amp model for thebondgraph symbol besides consider current flow di-rection to obtain the correct simulation result.

Acknowledgement

This paper is part of result study during internship pro-

gram at GIST (Gwangju Institute Science and Technol-

ogy), Republic of Korea, under Professor Sun-Kyu Lee su-

pervision. Many thanks to him and also to CISS (Com-

mittee International Student and Scholarship) at GIST as

the internship committee.

REFERENCES

[1] AJ Wilson et al ; A comparison of modified Howlandcircuits as current generators with current mirror typecircuits

[2] Samantaray, A.K. 2005. About Bondgraphs.http://www.bondgraph.info (August 9,2008)

[3] Su Zhao. 2005. Modelling of an electromechanicallyactuated spindle system with considering bidirectionalbearing compliance. Thesis graduate school of MechatronicDepartment, Republic of Korea : Gwangju InstituteScience and Technology

[4] W Wang. A Comprehensive study on current sourcecircuit

Table 1: Effort and Flow interpretation in Physical domains

Systems Effort (e) Flow (f )

Mechanical Force (F ) Velocity (v)

Torque (τ) Angular velocity (ω)

Electrical Voltage (V ) Current (i)

Hydraulic Pressure (P ) Volume flow rate (dQ/dt)

Thermal Temperature (T ) Entropy change rate (ds/dt)

Pressure (P ) Volume change rate (dV/dt)

Chemical Chemical potential (µ) Mole flow rate (dN/dt)

Enthalpy (h) Mass flow rate (dm/dt)

Magnetic Magneto-motive force (em) Magnetic flux (φ)

Figure 1: A Howland Current Amplifier Circuit

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Figure 2: Bondgraph model of the Current Amplifier

Figure 3: The Simulation result of the bondgraph model for the amplifier

Figure 4: The simulation result of amplifier circuit in Orcad

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