Hi everyone, I need your help for my circuit project. I want to know the value for the resistor and capacitor so that I get the 3 amperes output. Thanks for helping

 

Walk it back from what you want to what you need.

How much current do you want going through the regulator when you have 3 A being delivered to the load?

 

Walk it back from what you want to what you need.

How much current do you want going through the regulator when you have 3 A being delivered to the load?

I have a 220/12v 2A transformer, can I use it?

 

This is a better current boost circuit.
Nat Semi Voltage Regulator Handbook:

 

I have a 220/12v 2A transformer, can I use it?

Not for 3A.

 

This is a better current boost circuit.
Nat Semi Voltage Regulator Handbook:
View attachment 134433

i need a 3 amperes output, what must be the value of the resistor? and I have a 2 amperes transformer, can I use the transformer? many thanks

 

Hello,

You can NOT draw 3 A from a 2 A transformer.

Bertus

 

i need a 3 amperes output, what must be the value of the resistor?

Rearranging the divider equation from above and assuming maximum of 1A in the regulator:
\( \small \frac{I_1}{I_{REG}}=\frac{R_2}{R_1} => \frac{R_2}{R_1} = 2 \)
You want to use low value resistors to minimize wasted power, e.g. R2 = 0.2Ω, R1 = 0.1Ω.

I have a 2 amperes transformer, can I use the transformer?

No. A non-center tapped transformer would provide a little over 1A; 1.1A from the equation above.

 

Hello,

You can NOT draw 3 A from a 2 A transformer.

Bertus

thanks about that sir, how about I use 3a transformer, its works now?

 

thanks about that sir, how about I use 3a transformer, its works now?

No. Transformer secondary current needs to be 1.8X the load current; 5.4A minimum.

 

ah ok, I will use a 3 ampere transformer, is it ok?

No. 3A/1.8 = 1.67A

 

No. 3A/1.8 = 1.67A

Now I understand, 6 Amperes transformer how big is that?

 

Now I understand, 6 Amperes transformer how big is that?

That would be twice what the 3A transformer would provide.