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pika
Joined: 20 Apr 2002
Posts: 184
Helped: 28
Location: Pocket
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 08 Feb 2007 4:46 negative voltage regulator 7908 |
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Vin is 12V and the Vout is -8.2V min.
How to get exactly -8V with 7908?
I need exactly -8.0V.
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zuisti
Joined: 02 Jul 2004
Posts: 48
Helped: 2
Location: Hungary
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08 Feb 2007 11:47 Re: How to get exactly -8V with 7908? |
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You can use a 7906 with a two-resistor divider circuit (for adjust to 8v) to his ground pin.
Sorry, a lot of periods are requiered only there 
.!---------!
-! 7906 !---------*---- out
.!---------!...........!
..... !...!--------!...!
......*--!..........!--! .220 Ohm
......!...!--------!
......!
....!---!
....!....!
....!....! Potenciometer (100 Ohm)
....!---!
......!
-----*----------------- gnd
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nguyennam
Joined: 06 Sep 2006
Posts: 459
Helped: 28
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09 Feb 2007 16:00 Re: How to get exactly -8V with 7908? |
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That 7908 is useless in your case, no way to modify it.
If you insist of using 7908 and need 8.0V you have to buy some 7908 and pick out the right one since the 7908 has the output voltage within the range from -7.68 to -8.32V, typically -8.0V.
But I do not understand why you need -8.0V exactly and with 7908, as in generic requirement of a electronic circuit, the needed supply voltage maybe vary within the range of +/-5% or +/-10% of the nominal value, and the line regulation of the IC is more important than its voltage tolerance, it means -8.2V is good enough for every common use.
nguyennam
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ashad
Joined: 28 Mar 2006
Posts: 307
Helped: 9
Location: Singapore
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03 Mar 2007 13:29 Re: How to get exactly -8V with 7908? |
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| used LM337 or 237 it is negative voltage regulator
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wichayen
Joined: 31 Jan 2007
Posts: 48
Helped: 3
Location: Thailand
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06 Mar 2007 11:15 How to get exactly -8V with 7908? |
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| How much of ampere do you want to supply for -8V. If no need to supply for much of ampere you can use zener diode to regulate -8.2V again.
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06 Mar 2007 11:15 Ads |
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pakitos
Joined: 14 Nov 2005
Posts: 470
Helped: 66
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07 Mar 2007 14:27 Re: How to get exactly -8V with 7908? |
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what is the problem?
you are not able to find the pins?
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