# 220V voltage to digital voltage

Discussion in 'General Electronics Discussion' started by Alef, Apr 29, 2013.

1. ### Alef

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0
Apr 29, 2013
I use two LDOs to obtain digital voltages. Finally I get 3.3V at the end.
However, when I connected something, such wifi module, which must be driven by 3.3V, the voltage at that terminal drops down to 1.9V.

I am beginner in electronics design. My only knowledge tells me I should add an extra capacitor at the terminal, but I don't know what value should it be...

Or, if there any solution to such problem? Please see the attached.

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2. ### BobK

7,682
1,688
Jan 5, 2010
You need a diode to ground, parallel to the zener to conduct in the negative half of the AC cycle. Also, the .47uF capacitor is going to limit the current to about 40ma. How current do you require?

Bob

3. ### Alef

3
0
Apr 29, 2013
I haven't considered the current output of 3V3 regulator before adding the wifi module...
I think I should increase the output current as much as possible in order to supply 3.3V at the output of the 3V3 LDO with the wifi module connected. Can you suggest a way to increase the voltage at the output of the 3V3 LDO?

4. ### duke37

5,364
771
Jan 9, 2011
I do not think that a diode across the zener is necessary but it will not hurt, the zener will do the job.

5. ### BobK

7,682
1,688
Jan 5, 2010
I think you are right duke, the zener itself would conduct in the opposite direction. I guess I was thinking about a different circuit for off-line transformerless supplies, which did have two diodes.

Bob

6. ### Alef

3
0
Apr 29, 2013
I think I should increase the output current as much as possible in order to supply 3.3V at the output of the 3V3 LDO with the wifi module connected. Can you suggest a way to increase the voltage at the output of the 3V3 LDO?

7. ### BobK

7,682
1,688
Jan 5, 2010
How much current does your combined circuit need? To up the current you will have to raise the value of the capacitor and possibly raise the power handling capability of the zener.

Bob