power supply

AhmedZafarKhan · Feb 18, 2016

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 · Feb 18, 2016

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

AhmedZafarKhan · Feb 18, 2016

sir i have image i can upload it ??

AhmedZafarKhan · Feb 18, 2016

image

alec_t · Feb 18, 2016

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

AhmedZafarKhan · Feb 18, 2016

SIR I NEVER MADE SCHEMATIC DIAGRAM ON ANY SOFTWARE

AhmedZafarKhan · Feb 18, 2016

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

MaxHeadRoom78 · Feb 18, 2016

AhmedZafarKhan said:
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 · Feb 18, 2016

AhmedZafarKhan said:
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 · Feb 18, 2016

I AM DRAWING NOW

alec_t · Feb 18, 2016

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 · Feb 18, 2016

MAY IT WORK.

Colin · Feb 18, 2016

The voltage is being lost across the top 15R

AhmedZafarKhan · Feb 18, 2016

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

Inquisitive · Feb 18, 2016

Why are you yelling?

large_ghostman · Feb 18, 2016

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 · Feb 18, 2016

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 · Feb 18, 2016

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 · Feb 18, 2016

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 · Feb 19, 2016

audioguru said:
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

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