I seconds that.
without this resistor the voltage at low currents will go sky high (~20V)
the 12V is usually close to the maximum current.
Alon.
On 7/14/2010 11:46 AM, Erez D wrote:
The transformer gives 12V DC RMS, The peak voltage however is higher
(but with lower current)
I guess the reason for the resistor is to reduce the peak voltage and
keep it closer to 12V when there is little or no load, or when
connecting the load.
cheers,
erez.
2010/7/14 Shachar Shemesh <shac...@shemesh.biz
<mailto:shac...@shemesh.biz>>
geoffrey mendelson wrote:
I just took a DC adaptor and removed the components that coverted
the AC to DC. I did that for some modems that needed AC but came
without adaptors.
That's what I ended up doing. Now I'm having second thoughts
whether I did that correctly.
The DC adapter had the voltage selector, connected to a diode
bridge, connected to a capacitor and a resistor in parallel to the
connection to the polarity selector. I understand what the diode
bridge and capacitor were doing. The diode bridge was keeping the
positive end of the AC sine wave, and the capacitor was leveling
off the signal. Making it more like a DC line. What I'm not sure
is what the resistor was doing.
This was a 460Ohm resistor, which at 12V would mean about 0.4
Watt. Seems like a lot of wasted energy for a 12Watt power supply.
I checked the output signal after removing all of the above
(resistor included), and a volt meter and an oscilloscope both
shows exactly what I was hoping to see - an AC line giving the
correct voltage. The only problem is that I'm not sure whether it
was correct to remove the resistor.
Thanks,
Shachar
--
Shachar Shemesh
Lingnu Open Source Consulting Ltd.
http://www.lingnu.com
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