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Old 20th December 2006, 03:08 AM   #1
sunny is offline sunny  India
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Default How to decrease this voltage?

Hi Friends,
I have Yamaha PSR-3000 electronic keyboard and it needs 16 volts switching power supply and i dont have company adapter and at present i have another switching power supply adapter of 19 volts DC of 3.42 Amperes and my keyboard requires 16 volts DC,2.4 Amperes.
So what resistor i should i use in series to get 16 volts,2.4A from 19 volts,3.42 power supply?Your help is highly appreciated and please give the resistor value and its wattage.

Thanks,
SUNNY.
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Old 20th December 2006, 07:05 AM   #2
Elvee is offline Elvee  Belgium
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Hi

Use 3 or 4 BY255 diodes in series; that way you won't ruin the output impedance.
LV
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Old 20th December 2006, 07:31 AM   #3
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you can decrease the highside resistor of the feedback divider resistors
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Old 20th December 2006, 06:58 PM   #4
cerrem is offline cerrem  United States
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Quote:
Originally posted by hqeepower
you can decrease the highside resistor of the feedback divider resistors

NO...
Actually you want to adjust the LOWER resistor in the divider ...
The upper resistor usually plays a role in the loop compensation network. Adjusting the lower resistor is a safer bet..due to the vurtual ground....
There are many variables not known.... especially if we have an opto-coupled flyback, which is typical for these crappy supplies...If that is the case you can have to be carefull what you adjust since these supplies are usually not much phase margin to begin with...
Your quickest and safe solution are adding the diodes....
Chris
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Old 26th December 2006, 11:17 AM   #5
sunny is offline sunny  India
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Hello Friends,
I have played my keyboard for the christmas programmes very well using the modified switching power supply.I have connected four 6A4 diodes in series on positive line and i'm getting 16.5 volts at the keyboard.
Now another problem has started,the four 6A4 doides are getting too hot and they are burning my fingers if i touch them,I can't understand why the dodes are getting very hot ?The current rating of diodes are 10A and my keyboard requires only 2.5 A.
Is there any solution to this problem?

Thanks,
SUNNY.
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Old 27th December 2006, 05:13 AM   #6
paulb is offline paulb  Canada
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They should be getting maybe about 25 degrees C hotter than the air temperature.
http://www.rectron.com/data_sheets/6a05-6a10.pdf
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Old 27th December 2006, 07:00 AM   #7
sunny is offline sunny  India
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I'm looking for 10Amps rectifier diode.Please suggest a low cost 10 A diode.

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SUNNY.
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Old 29th December 2006, 07:41 AM   #8
Elvee is offline Elvee  Belgium
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Quote:
Originally posted by sunny
Hello Friends,
I have played my keyboard for the christmas programmes very well using the modified switching power supply.I have connected four 6A4 diodes in series on positive line and i'm getting 16.5 volts at the keyboard.
Now another problem has started,the four 6A4 doides are getting too hot and they are burning my fingers if i touch them,I can't understand why the dodes are getting very hot ?The current rating of diodes are 10A and my keyboard requires only 2.5 A.
Is there any solution to this problem?

Thanks,
SUNNY.

You have to dissipate more than 6W; there is no way of doing that without releasing some heath. The diodes can happily withstand temperatures of up to 125C, but if you don't want to burn your fingers, you've to spread the power dissipated on a larger area, by using a heatsink or something playing a similar role.
LV
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Old 31st December 2006, 10:33 PM   #9
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Default 10a diode

you could parallel 4 3a diodes, or scavenge one of those to-220 diodes from a junked tv or PC power supply.

best "quick and dirty" way to turn 22vdc into 18vdc

make sure the 3055 is heat sinked. you might want a 10uf cap across the zener too....
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