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ZL1ANM > FT817 27.04.07 02:14l 32 Lines 831 Bytes #999 (0) @ WW
BID : ZL1ANM81
Read: GUEST DL1RX VE7HFY DG4IAK
Subj: Re: Max current from mic 5v pin?
Path: DB0FHN<DB0FOR<DB0MRW<DK0WUE<7M3TJZ<ON0AR<IW2OAZ<ZL2BAU<ZL1AB
Sent: 070427/0001Z @:ZL1AB.#06.NZL.OC #:59454 [AUCKLAND] FBB7.00i $:ZL1ANM81
From: ZL1ANM@ZL1AB.#06.NZL.OC
To : FT817@WW
>To: ft817@ww
>Subject: Max current from mic 5v pin?
>
>
>As per title.
>
>I wanna build a mic preamp into existing mic case, that's why.
>
>Ta!
>
>- Andy -
>
>G0FTD @ GB7PZT
The MIC jack is J1014. Looking at the '817 circuit diagram, we see
that regulator Q1088 supplies +5v to multiple stages and to the 5v
MIC pin (pin 6) via 10-ohm 1/16W resistor R1414.
It's not possible to calculate the loading on Q1088, and for this
reason I wouldn't attempt to draw more than 10, or at most 20mA
from pin 6. Resistor R1414 should be OK at 20mA, since it will be
dissipating only 4 milliwatts. You should easily be able to design
a pre-amp that consumes 10mA or less. Aim for the least.
73 de Neil ZL1ANM
T4 1.5à24
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