# Which of the following represents the correct relationship between collector to emitter cut-off current (ICEO) of a transistor and collector to base c

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Which of the following represents the correct relationship between collector to emitter cut-off current (ICEO) of a transistor and collector to base cut-off current (ICBO)?

(Assume: 'x' is the CB current gain of the transistor)

1. IECO = ICBO
2. IECO = x ⋅ ICBO
3. IECO = ICBO/(1 - x)
4. IECO = ICBO/ (1 + x)

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Correct Answer - Option 3 : IECO = ICBO/(1 - x)

Expression of Collector current in CE configuration:

In CE configuration, IB is input current and IC is output current.

We know that,

IE = IB + IC …. (1)

In CB cofiguration, The expression of collector current is written as,

IC = xIE + ICBO …. (2)

From equation (1) and (2),

IC = x (IB + IC) + ICBO

IC (1 – x) = αIB + ICBO

$I_C=\frac{x}{1-x}I_B+\frac{1}{1-x}I_{CBO}$…. (3)

From equation (3), it is apparent that if IB = 0, the collector current will be equal to the collector to emitter cut-off current (ICEO).

This is abbreviated as ICEO, meaning Collector-Emitter current with base open.

IECO = ICBO/(1 - x)