# Quarter- Wave rectifier?

Discussion in 'General Electronics Chat' started by Vindhyachal Takniki, Feb 12, 2016.

1. ### Vindhyachal Takniki Thread Starter Member

Nov 3, 2014
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1. I have a circuit which has 220Vac/50Hz input which heats up a wire. On full mode, entire 220V is connected to wire, so wire gets heated up quickly. Next mode is half mode, in which I have connected a diode in series, so negative half is clipped & positive half is formed, so wire gets less heated.

2. Is there any way so that power can be further reduced by half, by placing a simple diode or component so that wire gets less heat?

2. ### SLK001 Well-Known Member

Nov 29, 2011
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No - not without extra circuitry.

3. ### hp1729 Well-Known Member

Nov 23, 2015
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Cut the voltage down by a voltage regulator?

4. ### Roderick Young Member

Feb 22, 2015
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If it's a heater, a common way to reduce the heat is to make the element longer, so if you could switch in another heating element in series, that would cut the power way down.

5. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
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Well, clearly, your thread's title has it! -- To wit: please consider a phase control circuit

Best regards
HP

6. ### crutschow Expert

Mar 14, 2008
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One version of what HP is referring to is known as a light dimmer control.

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7. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
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Here's a 'bare bones' phase control implementation --- Note that 'L1' is the load and may be purely resistive --- Moreover, you may generally substitute the Diac with an NE2 if desired...

Note also that, for the given values, R(VR1) ≈ 100kΩ

Best regards
HP

Last edited: Feb 12, 2016
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8. ### crutschow Expert

Mar 14, 2008
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Using an NE2 will mean the Triac can fire no lower than about 90V in the cycle, which would limit the range of power control as compared to a Diac.

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9. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
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Indeed, a diac is a better choice -- that said, NE2s and their ilk often provide acceptable performance where a diac is unavailable -- Interestingly (as an aside), whether owing to reduced ionization potential of the fill gas, or to photoelectric emission of the electrodes, neon lamps (CIP NE2) tend to exhibit significantly higher 'dark' firing EMFs (as much as 100V vs. typically Ca 65V at room-level illumination).

Another point -- While the circuit pictured in my post (above) is functional, I chose it merely to illustrate the principle involved -- good design will incorporate circuitry/techniques suppressive/preclusive of the not inconsiderable electrical noise attendant to such schemes... (you will please pardon the litotes)

Best regards and good luck!
HP

Last edited: Feb 12, 2016
10. ### alfacliff Well-Known Member

Dec 13, 2013
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a single diode in series is called a half wave rectifyer, not a quarter wave. a common way to reduce power, such as to reduce heat on a soldering iron when not in use without having to re heat it up all the way.

11. ### Hypatia's Protege Distinguished Member

Mar 1, 2015
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As I understood the OP, the TS was inquiring as to the 'viability' of a 'quarter wave' rectification scheme applied to 'power limiting'...? Hence my suggestion of a phase control arrangement (in essence an adjustable 'wave chopping' PWM). -- Of course was he to use an SCR (as opposed to a Triac) it could properly be termed an "adjustable fractional wave rectifier" But that'd be missing the point

Best regards
HP