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GregTN

Question about a circuit

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Will both of these circuits yield the same results?  I know a single 20K would be better but I had several 10K on hand.

F1B8731F-D993-4482-BBC5-54E653F29915.jpeg

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Yup, same total resistance in circuit.

 

What's the load and the desired effect?

 

It may be better to use X rated capacitors to reduce the power dissipation.

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13 minutes ago, Crossy said:

Yup, same total resistance in circuit.

 

What's the load and the desired effect?

 

It may be better to use X rated capacitors to reduce the power dissipation.

It is actually part of a larger circuit that I am trying to fit on a circuit board and the top schematic works much nicer.  Thanks so much for the help.

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It will be same total resistance in the circuit, but it will depend on what the load is.

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Posted (edited)

.

Edited by GregTN

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The actual circuit uses a 64K 1 watt resister (I had several 33k 2 watts on hand), a couple of diodes and the purpose is to light an LED from 220 ac.  I just used the above pictures to simplify the question.  Don’t laugh to hard at the completed project as I am definitely a rookie but love the hobby.

8B672B55-F183-4262-B901-AE9D8A012A46.jpeg

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Posted (edited)

Totally with you about the fun hobby side of things but your little circuit dissipates around 2.4W from the two 10K resistors and less than 4mW of power for light (they are only ON for half of each mains cycle).

 

It would be MUCH safer to use a 5v USB supply and a 470 Ohm resistor - and the LED would be on continuously.

 

Edited by sandbox
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3 hours ago, GregTN said:

The actual circuit uses a 64K 1 watt resister (I had several 33k 2 watts on hand), a couple of diodes and the purpose is to light an LED from 220 ac.  I just used the above pictures to simplify the question.  Don’t laugh to hard at the completed project as I am definitely a rookie but love the hobby.

8B672B55-F183-4262-B901-AE9D8A012A46.jpeg

Do you have capacitor 100n (marked 104) on hand?  Use that in series with one resistor and the led, and the led in parallel with diode other way around.

 

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2 hours ago, Metropolitian said:

Do you have capacitor 100n (marked 104) on hand?  Use that in series with one resistor and the led, and the led in parallel with diode other way around.

 

You mean, do you have a 100n capacitor of suitable voltage rating and be careful of voltages left on capacitors after disconnection.


Eg 100n-400V in series with 500Ω inrush limit + diodes

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Thanks so much for all the suggestions.  Considering all the good advice I will search out some small neon lamps and replace the LED’s.  Space is limited and I had some spare parts and a lot of time on hand.  Here are a couple of pictures of the almost finished product.

2170C3EC-7A12-44FB-96EC-5164B28476CE.jpeg

52DEC4B5-A9FD-44B7-B064-0AAD2D9F88D4.jpeg

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2 hours ago, Jan Dietz said:

I would keep the LEDs but go for a capacitative (reactance) voltage dropper, as per the APP note.

 

Thank you very much for the information and link.

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Do it like this:-

 

RDaRk.jpg

 

Get an "X" rated capacitor suitable for AC mains use anything around 0.1 - 0.22u will do the trick. 

https://www.aliexpress.com/item/32947949184.html

 

0.1u will give you about 32k + the 4.7k => about 6mA through the LED

0.22u will give you about 14k + the 4.7k => about12mA through the LED

 

The 4.7k will dissipate 0.2W or 0.6W respectively.

 

Capacitive reactance calculator here if you want to try other capacitors / currents  

http://www.sengpielaudio.com/calculator-RC.htm

 

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5 hours ago, Crossy said:

Do it like this:-

 

RDaRk.jpg

 

Get an "X" rated capacitor suitable for AC mains use anything around 0.1 - 0.22u will do the trick. 

https://www.aliexpress.com/item/32947949184.html

 

0.1u will give you about 32k + the 4.7k => about 6mA through the LED

0.22u will give you about 14k + the 4.7k => about12mA through the LED

 

The 4.7k will dissipate 0.2W or 0.6W respectively.

 

Capacitive reactance calculator here if you want to try other capacitors / currents  

http://www.sengpielaudio.com/calculator-RC.htm

 

Thank you Crossy.

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