Hi Mark, Hi all,
another almost unknown but better and much more accurate combination in order to 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)
In ----------- ---| 78xx |-----o---OUT ----------- | | R1 o----------| | R2 | -------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: R1=220+27 Ohms 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 by-passed through the internal connection of 78xx. (and the R1 is now just a... bleeder !)
Finally, in this combination by using divider (or diodes as mentioned by others) the 78xx regulators lose the "short-circuit" output protection. That is available only in case where the Pin2 of 78xx is directly connected to 0V (normal connection).
Hope this helps.
73, Mak SV1BSX
----- Original Message ----- From: "Mark L. Hammond" n8mh@embarqmail.com To: amsat-bb@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?)
Thanks,
Mark L. Hammond [N8MH]
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