written 3.9 years ago by |
Graphic methaod to obtain CE configuration:
hie=vbib|vc=0=αvbαib|VCEslope=iB(B)−iB(A)VBE(B)−VBE(A)
From input char. curve of VCE=VCE1(constant), then target at QZ drawn will have a slope of 1/hie
∴ Reciprocal of slope of line AB=hie
Parameter hre:
hre=vbvc|ib=0=ΔVBΔVC|ib=constant=αvbαib|IB=VB2−VB1VC2−VC1
From graph of input charac. hre can be determined as a ratio of change in base to emitter voltage to change in collector to emitter voltage. Graph Shown in 52 is used to determine hre. keeping IBQ constant if change in collector to emitter voltage, ΔVC=VCE3−VCE1 then corresponding change in base to emitter voltage ΔVB is found to VBE3-VBE1
∴hre=VCE3−VCE1VBE3−VBE1
In practical ΔVCE is large as compared to ΔVBE & H is different to obtain a accurate value for hre graphically.
Parameter hfe:
hfe=icib|vc=0=ΔicΔib|ib=constant=αicαib|IB=iC2−iC1iB2−iB1|vc
From the output char of a given transistor as shown in fig 5.3 hfe can be expressed as change in Δ IC to Δ IB. hfe is the most important hybrid parameter since H reflect the value of current game of trnsistor on which the amplification property of a transistor depends.
hfe=iC2−iC1iB2−iB1|vc
Parameter hoe:
hoe=icvc|ib=0=αicαvc|ib=0
Graphically, hoe can be determined by determining the slop of tangent drawn or Q point as shown in fig AB is the tangent line drawn on point Q. slope of line AB can give value of hoe.
slope=ic(B)−ic(A)VCE(B)−VCE(A)|iB=ΔicΔVCE|iB
hoe =slope of line or tangent AB.