problem with a rectifier

[Kevin Weddle]

I think you are terribly wrong Audioguru. I have in fact experienced this phenomen. Please enlighten me. It does make sense that the resistance of the diode is part of the filtering RC. When the voltage of mains reaches peak, the capacitor is charged. This is a peak to peak result that is filtered by the RC. Don't think of it as a capacitor that is just charged when the voltage rises enough. This is a ripple that is filtered.

 

[audioguru2]

Kevin,
A rectifier with a filter cap isn't an RC low pass filter.
The cap simply charges very quickly through the low resistance of the transformer and extremely low impedance of the rectifier, then discharges into the load between charge pulses from the rectifier.
The exponentially dropping voltage of the filter cap is powering the load most of the time and the rectifier is reverse-biased and doing nothing. Using a "better" rectifier won't make any difference.

With a true RC low pass filter with a series resistor feeding a filter cap to ground, the cap's voltage never reaches the peak voltage of the input like a filter cap's voltage being fed from a rectifier does.

 

[shekhar_dandya]

Hi AudioGuru,
Thanks for the soldering tips.I did not make a PCB for my circuit.I just used a general purpose board that provides only mechanical stability to components and soldering pads to adhere the components to the board.
As far as your high power X'mitter speculation goes,I have our city 's TV transmitter as well as our local radio's FM X'mitter nearby i.e about 50-60 km away.Could that distance be a problem?
Well the big prob is I don't have a CRO to watch the effect.

Anyway if you say that this isn't going to cause any problem to power small electronic circuits (cordless phones,radios/tapes etc)I will leave the problem as it is.

Thanks all of you for your cooperation and patiently replying my silly questions.
-Shekhar

 

[audioguru2]

Hi Shekhar,
50-60km is too far away to cause your DMM to give false readings. A high power transmitter less than 1km would.

I have two DMM's. They both always give similar and correct readings on AC and DC. Yours must be defective.

 

[shekhar_dandya]

Hi Audioguru,
That may be the case. I have a rather cheap DMM with only 2 ranges for a.c 750V,200V.
So I just wanted to confirm that my circuit is not at fault.Can I continue using the circuit? Or else this false signal(If it exists) may damage the load?
-Shekhar

 

[audioguru2]

Hi Shekhar,
One of my DMM's is also very cheap (about $7.00US) and it works perfectly.
You won't know if your power supply project works properly unless you measure it with a meter that works well.