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Old 5th April 2013, 06:21 AM   #1
limono is offline limono  United States
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Default Voltage regulator adjustment

What would be the simplest way to increase voltage in HV section from 250V to 300V ? TIA , L
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Old 5th April 2013, 06:31 AM   #2
UV101 is offline UV101  England
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You could try lowering the 500r between pins 2 & 3 of the lm317 but it will depend on the input voltage as to if you can get to 300v.
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Old 5th April 2013, 07:39 AM   #3
limono is offline limono  United States
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Input voltage is 350V. Load current is less than 10mA . I think it's possible.
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Old 5th April 2013, 09:13 AM   #4
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The formula is always the same. 1.24V times the gain + the tiny amount of the adj current. Either do as UV101 suggests or increase the 100k resistor. Dropping the 500 ohms is probably the better of the two as it adds a bit of current draw and will likely lead to less variation with load.
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Old 5th April 2013, 09:18 AM   #5
lineup is offline lineup  Sweden
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Change the 100k resistor in LM317 to 120k.
Or add 20k to the 100k resistor.
This should give like 300V output
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Old 5th April 2013, 10:18 AM   #6
AndrewT is offline AndrewT  Scotland
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with 10uF on the adj pin you must add diode protection from adj to out.
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Old 5th April 2013, 01:56 PM   #7
limono is offline limono  United States
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OK , Thank You guys .If I find 120k/5W in my junk bin ,I'll try it first . If not I lower 500R a little bit , easier to get small wattage resistor. And LM317 has hefty heatsink so upping current want be a problem either.
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Old 5th April 2013, 04:19 PM   #8
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For 10mA you really should use a HV regulator.
The LM317 will work but you have a huge gain (120k/500R) which means the regulation gets worse in the same ratio.

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Old 5th April 2013, 10:49 PM   #9
limono is offline limono  United States
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Actually it's 1.7mA for a channel so 3.4 mA for both . I didn't want to mess with it too much. ( the psu unit ) I don't know why people who made it went for Maida regulator . I put Cree Shottky rectifier diodes , dropped resistor from 500R to 420R and it took care of the business. I will listen to it a little (sounds pretty good )and than maybe go passive with chokes and tube gas regulators . Thank you for your help. Best Regards, L
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