power supply

[AhmedZafarKhan]

I have designed a 5V ,350mA fixed power supply with a 12 Vrms step down transformer. the voltage across filtering capicitor should be almost peak value i.e 15V or 16V . but I am getting 12 volts across the capacitor why is it so. the supply is loaded.

 

[AnalogKid]

Just like the other forum, not schematic, no useable answers.

 

[AhmedZafarKhan]

sir i have image i can upload it ??

 

[AhmedZafarKhan]

image

 

[alec_t]

Very pretty, but it's not the schematic requested .

 

[AhmedZafarKhan]

SIR I NEVER MADE SCHEMATIC DIAGRAM ON ANY SOFTWARE

 

[AhmedZafarKhan]

SIR I WANT TO KNOW THE REASON WHY VOLTAGE IS DROPED ACROSS FILTERING CAPACITOR
WHEN LOAD IS APPLIED TO THE CIRCUIT

 

[MaxHeadRoom78]

SIR I NEVER MADE SCHEMATIC DIAGRAM ON ANY SOFTWARE

A hand drawn version would be OK.
Or do you mean you never draw the circuit out first?
Max.

 

[Nigel Goodwin]

SIR I WANT TO KNOW THE REASON WHY VOLTAGE IS DROPED ACROSS FILTERING CAPACITOR
WHEN LOAD IS APPLIED TO THE CIRCUIT

As you've been told, you need to post the schematic - we can't just make blind guesses.

 

[AhmedZafarKhan]

I AM DRAWING NOW

 

[alec_t]

The cap voltage drops because the load draws current from it. It would be marvellous if that drop didn't happen: we could then just charge the cap once and have virtually free energy for life .

 

[AhmedZafarKhan]

MAY IT WORK.

 

[Colin]

The voltage is being lost across the top 15R

 

[AhmedZafarKhan]

THERE SHOULD BE 15.6V ACROSS CAPACITOR BUT 12 V ARE MEASURED BY DMM WHY IT HAPPENS EXACT THORY BASED ANSWER NEEDED.

 

[Inquisitive]

Why are you yelling?

 

[large_ghostman]

Why does he have the American bald Eagle wrapped in the Pakistani flag? I am not American but probably not the best choice all things considered. Hi Ahmed no offense intended and welcome

 

[large_ghostman]

Why do you think there should be 15V? The output of the transformer before you even factor in the diodes is only 12V? Although I cant see the schematic very well and its upside down!! Please dont make people download and twist stuff about to help you, there is a sticky on drawing schematics and if your going to do electronics you need to start learning how to draw schematics.

 

[AnalogKid]

What is the current drawn by each of your three loads? Calculate each one and add them up.
What is the current rating for the transformer secondary?
Do you see a problem there?

ak

 

[audioguru]

I notice that the little transformer has no power or current rating. Maybe it is overloaded.
If the mains is really 220V RMS and if the transformer is made by a company who know how to make a good transformer then it will have a 12V RMS sinewave when it has its rated load.
The peak voltage of 12VAC is 16.97V and the diodes in the bridge rectifier will reduce it to 14.97V. The 1 ohm resistor will reduce it to maybe 13.8V. Ripple because the capacitor does not have a very high capacitance might reduce the average output to 12.0VDC.
The Rl load draws 340mA. The zener diode has (12V - 5.1V)/15 ohms minus 340mA= 120mA and heats with 0.6W.
The 12V transformer should be rated at (16.97V X 340mA=) 5.77VA or (5.77VA/12V=) 481mA. Add 15mA of the red LED.

 

[AhmedZafarKhan]

I notice that the little transformer has no power or current rating. Maybe it is overloaded.
If the mains is really 220V RMS and if the transformer is made by a company who know how to make a good transformer then it will have a 12V RMS sinewave when it has its rated load.
The peak voltage of 12VAC is 16.97V and the diodes in the bridge rectifier will reduce it to 14.97V. The 1 ohm resistor will reduce it to maybe 13.8V. Ripple because the capacitor does not have a very high capacitance might reduce the average output to 12.0VDC.
The Rl load draws 340mA. The zener diode has (12V - 5.1V)/15 ohms minus 340mA= 120mA and heats with 0.6W.
The 12V transformer should be rated at (16.97V X 340mA=) 5.77VA or (5.77VA/12V=) 481mA. Add 15mA of the red LED.

thakx