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AP3302 Pt3 Contents

AP3302 Pt3 Section 2Contents

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AP 3302 Pt. 3

Section 2


Free Running (Astable) Multivibrators

Let us assume that the circuit is oscillating with V1 conducting and V2 cut off but with its grid voltage just about to reach cut-off (say - 5V). Then initially V2a = h.t. (+ 300V); VK is a low value (say + 2V) because of the small current passed by V1; V1gIK is held at zero volts because there is no voltage drop across R1 (see Fig 17a); and V1a is at its low working voltage (say + 30V).

Instant A. V2gIK rises to cut-off...

... V2 conducts causing V2a to fall and VK to rise (because of the increased current from V2 through RK).

... Cl cannot charge instantly so that the sudden rise in VK is developed across R1 (see Fig 17b); V1gIK thus falls as shown and, with point B going negative with respect to point A, V1 cuts off.

... V1a thus rises towards h.t. and this rise is transferred through C2 to cause V2gIK to rise also...

... V2 conducts more heavily, causing V2a to fall further. 


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