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 LPF terlalu rendah?

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sue
Solfers Sejati


Jumlah posting : 1159
Join date : 2009-07-24
Age : 29
Lokasi : Cilacap / Bandung

20100213
PostLPF terlalu rendah?

Tolong kasih masukan,
misal di OCL safari Sby ada LPF pasif 10k dan 1n2, jadi fo = 13kHz. walaupun pasif tapi masih 'benda ini' bekerja kan?
pertanyaan :
Mengapa (cukup banyak mungkin) ampli dikasih LPF 'terlalu rendah'?, Apa manfaatnya? Apa keuntungannya?
Apa ada masalah kalau LPFnya dibuat sedikit lebih tinggi, katakanlah 30kHz ?
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LPF terlalu rendah? :: Comments

Re: LPF terlalu rendah?
Post on Wed Mar 03, 2010 4:24 pm  indra_co_maniz
paragraf keberapa kang membahas input impedance, rumus nilai Zb ngga ketemu Sad
Re: LPF terlalu rendah?
Post on Wed Mar 03, 2010 7:42 pm  sue
So'ir, Zb itu bahasa saya, itu Vin/Input Current

* Input Stages
The input stages of all transistor amps must be able to supply the base current of the Class-A driver. This time, a margin of between 2 and 5 times the expected maximum base current is needed. If the Class-A driver operates with a quiescent current of 8mA, the maximum current will be 12mA (quiescent + driver base current. Assuming a gain of 50 (again), this means that the input stage has to be able to supply 12 / 50 = 240uA, so it must operate at a minimum current of 240uA * 2 = 480uA to preserve linearity.

* Input Current
The input current of the first stage determines the input impedance of the amplifier. Using the above figures, with a collector current of 480uA, the base current will be 4.8uA for input devices with a gain of 100. If maximum power is developed with an input voltage of 1V, then the impedance is 208k (R = V/I).

Since the stage must be biased, we apply the same rules as before - a margin of between 2 and 5, so the maximum value of the bias resistors should be 208 / 2 = 104k. A lower value is preferred, and I suggest that a factor of 5 is more appropriate, giving 208 / 5 = 42k (47k can be used without a problem).
Re: LPF terlalu rendah?
Post on Thu Mar 04, 2010 12:35 pm  indra_co_maniz
Quote :
Using the above figures, with a collector current of 480uA, the base current will be 4.8uA for input devices with a gain of 100

gain 10 atau gain 100 kang ? Sad puyeng juga bahasa linggis pas-pasan... Razz
Re: LPF terlalu rendah?
Post on Fri Mar 05, 2010 10:20 am  sue
"figure"-nya bukan berarti gambar tapi bisa berarti "pernyataan" atas perhitungan-perhitungan sebelumnya.
"gain" disana merujuk ke gain/beta/hFE Tr Q1, bukan gain voltage amplinya mas..


480uA adalah arus di kaki Collector Q1, dan karena dia(Rod Elliott) mengasumsikan gain/beta/hFE dari Q1 adalah 100x, maka Ib (Q1) = 480/100 = 4,8uA.
Re: LPF terlalu rendah?
Post on Fri Mar 05, 2010 10:45 am  indra_co_maniz
iya yah 400 dibagi seratus itu 4 Sad perlu pakai kacamata nih...
thx kang sue..
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LPF terlalu rendah?

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