opamp amplifier and microcontroller circuit.......

[jit_singh_tara]

Dear frnds ,
I m using a circuit where a step down transformer rated for 350mA is used .

It is giving 2 windings:
a. 9-0-9 volts.
b. 0-12 volts .

now I am using following voltage regulators
LM7805 , LM7809 , LM7909 ON 9-0-9 winding of the transformer .

The controller is driving 8 seven segment displays from 5V.
and other +9V and -9V are driving the opamp section which involves 3 opamps as OP07 and 1 opamp as lm324.

now the problem is I checked current consumption on 5V supply as 135 mA when the microcontroller is running and all displays are glowing ....the current fluctuates around 135 mA as tje display values changes .this also reflects on the +9V regulator output . its value varies around 7.5 V to 8V which is not desirable .-9V regulator voltage is fixed.can anyony explain why this is happening .
one more thing when the controller is erased the voltage on 9V regulator shows 9V Full.

I am powering both 5v and 9v regulator from the same input capacitor after the bridge .

help plz .

 

[barry]

schematic????

 

[Yosmany325]

Please, put the schematics of that circuit. Maybe what is happening is too much load on positive side of your circuit, that causes a voltaje drop. Also, the 7809/7805 need atleast 3V above the output voltage. Yosmany325.

 

[jit_singh_tara]

plz find the attached file.....



- - - Updated - - -

plz find the attached file.....

 

[jayanth.devarayanadurga]

Use secondary with 12-0-12 and 12-0.

 

[jit_singh_tara]

how much input voltage is required if i want full 8v output from lm7808 .

- - - Updated - - -

well for that i need to use transformer with 12-0-12 v winding neway....
If i need to use +9V -9V and +5V supplies in my ckt then :
a. should i generate +5V from +9V regulator or should i connect it directly to bridge which will dissipate more heat in lm7805.
b. if i connect lm7805 in output of lm7809 will the voltages be stable .+9v and +5v.

 

[wp100]

Hi,

As Yosmany325 said earlier you need a minimum 2 to 3 volts higher input than the desired output

Do you have to run your op amps a +- 9v ? they can both run down to +-3v, so you could use just 2 regs, a 7805 and 7905

Your psu is the heart of your circuit, any short comings in its design will soon be followed by circuit failures / incorrect operation.

 

[jit_singh_tara]

barry......
i have posted the schematic