[amsat-bb] Re: G-5500 7806 regulator question
sv1bsx at yahoo.gr
Sun Aug 17 08:48:13 PDT 2008
Hi Mark, Hi all,
another almost unknown but better and much more accurate combination in
increase the output
of any 78xx regulator is possible by making a divider in the output of 78xx
regulator according to the formula:
R1=VR/0.02 ( where VR the nomimal output of 78xx regulator)
R2=VB/0.025 (where VB the difference in Volts between "nomimal" output
Voltage of 78xx and "request" output Voltage)
---| 78xx |-----o---OUT
-------o-------------- 0V (GND)
Therefore, in case we have a 7805 and we need 6 Volts output:
VR=5 => R1= 5/0.02 = 250 Ohms
VB (Differential Voltage): 6 - 5 = 1
R2 = 1/0.025 = 40 Ohms
You can replace R1, R2 with standard value-resistors:
R2 = 39 Ohms
The R1 is connected between + OUT and GND-Pin of 78xx. The R2 between
GND-Pin of 78xx
and GROUND (see my figure above).
*** HOWEVER, in this case the Hotsink (metal plate) of 78xx MUST BE ISOLATED
from the 0V !!
Just keep in mind that, because the Pin2 is internally connected
to metal-plate of 78xx ! So, if the GND(chassis) is equal to 0V and the
metal plate of
78xx is directly connected to chassis for better cooling, then the R2 is
through the internal connection of 78xx. (and the R1 is now just a...
Finally, in this combination by using divider (or diodes as mentioned by
the 78xx regulators lose the "short-circuit" output protection. That is
only in case where the Pin2 of 78xx is directly connected to 0V (normal
Hope this helps.
73, Mak SV1BSX
----- Original Message -----
From: "Mark L. Hammond" <n8mh at embarqmail.com>
To: <amsat-bb at amsat.org>
Sent: Sunday, August 17, 2008 2:54 AM
Subject: [amsat-bb] G-5500 7806 regulator question
> Hello All,
> It appears that the 7806 voltage regulator in my Yaesu G-5500 control box
> has gone bad; the output is measuring more like 10.8 Volts (!). This
> explains why both position indicators were off by a factor of 2 (e.g.,
> elevation meter showing 90 deg, array pointing 45; azimuth meter showing
> 180 deg, but array pointing 90 deg., and so on).
> Question---has anybody used a 7805 to replace the 7806 regulator in this
> control box?
> I don't have a 7806....so this brings the next question--anybody have a
> 7806 (or 2) that they want to sell?)
> Mark L. Hammond [N8MH]
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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