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Author Topic: Zener diode help  (Read 4375 times)

magnetman12003

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Zener diode help
« on: March 25, 2016, 02:47:01 PM »
i have heard you can use a Zener diode instead of a resistor to drop voltage.
I have a 110 DC power supply and wish to drop the voltage anywhere from 90 to 73 volts.
What Zener diode can do this job?


All help appreciated.
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pomodoro

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Re: Zener diode help
« Reply #1 on: March 25, 2016, 04:44:45 PM »
Quote from: magnetman12003 on March 25, 2016, 02:47:01 PM
i have heard you can use a Zener diode instead of a resistor to drop voltage.
I have a 110 DC power supply and wish to drop the voltage anywhere from 90 to 73 volts.
What Zener diode can do this job?


All help appreciated.

Its not the best system but for example 110-90 =20v.  So you need a zener of 20v or a string of smaller values that add up to 20v. The average current expected times the 20v is how much the zener must dissipate. For 1 amp you're looking at
20w. Using many smaller zeners in series spreads the wattage. 4x5.1v zeners only need to dissipate 4w at 1A. Still a lot. Simply buy zeners with a higher wattage than required. The better system to use is shown at picture 3 of this link. You need one low power zener and the power is dissipated by a power transistor.
http://www.bristolwatch.com/ele/zener_power_supply.htm
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verpies

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Re: Zener diode help
« Reply #2 on: March 25, 2016, 06:02:11 PM »
Quote from: pomodoro on March 25, 2016, 04:44:45 PM
Its not the best system but for example 110-90 =20v.  So you need a zener of 20v or a string of smaller values that add up to 20v.
Not in this circuit.
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AlienGrey

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Re: Zener diode help
« Reply #3 on: March 25, 2016, 11:01:04 PM »
Quote from: magnetman12003 on March 25, 2016, 02:47:01 PM
i have heard you can use a Zener diode instead of a resistor to drop voltage.
I have a 110 DC power supply and wish to drop the voltage anywhere from 90 to 73 volts.
What Zener diode can do this job?


All help appreciated.

You can amplify a zener diode with a transistor, simply put the diode between the Collector and the base but make sure the transistor can handle the current and the voltage or pop! but you could make some kind of protection or soft start, but as we don't know what you're doing who knows ?
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BootBoyer

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Re: Zener diode help
« Reply #4 on: March 31, 2016, 08:51:38 PM »
So you need a zener of 20v or a string of smaller values that add up to 20v. The average current expected times the 20v is how much the zener must dissipate. For 1 amp you're looking at
20w. Using many smaller zeners in series spreads the wattage. 4x5.1v zeners only need to dissipate 4w at 1A. Still a lot. Simply buy zeners with a higher wattage than required. The better system to use is shown at picture 3 of this link. You need one low power zener and the power is dissipated by a power transistor.
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