# How to regulate voltage using TIP122

#### kithul godage Vijitha

Joined Aug 8, 2017
7
I want to create small circuit for regulate when the higher than 14V DC.. Please help me if you can..

#### ScottWang

Joined Aug 23, 2012
7,327
How is the input V/I?
How is the Vout?

#### crutschow

Joined Mar 14, 2008
31,538
Need regulation accuracy, maximum current, maximum input voltage.
What does it do below 14v?

#### kithul godage Vijitha

Joined Aug 8, 2017
7
Need regulation accuracy, maximum current, maximum input voltage.
What does it do below 14v?
actually I hope to use this to Alternator, for charge the lead acid batteries. then 200Ah batteries are connect as parallel so I want to charge the batteries without over charging. because I want regulate alternator output, using TIP122.

#### kithul godage Vijitha

Joined Aug 8, 2017
7
How is the input V/I?
How is the Vout?
actually I hope to use this to Alternator, for charge the lead acid batteries. then 200Ah batteries are connect as parallel so I want to charge the batteries without over charging. because I want regulate alternator output, using TIP122.

Input voltage is not constant value. it will change according to RPM of alternator. maximum current 80A.

#### cmartinez

Joined Jan 17, 2007
7,914
actually I hope to use this to Alternator, for charge the lead acid batteries. then 200Ah batteries are connect as parallel so I want to charge the batteries without over charging. because I want regulate alternator output, using TIP122.

Input voltage is not constant value. it will change according to RPM of alternator. maximum current 80A.
How many TIP122 do you have with you? Because a single of those transistors is only capable of handling 5A at most. And that's under ideal conditions. You'd end up with a rather inefficient circuit with numerous components to accomplish what you want.

There are other options out there, such as MOSFETS. Is the use of TIP122 for your application a must?

Last edited:

#### ScottWang

Joined Aug 23, 2012
7,327
actually I hope to use this to Alternator, for charge the lead acid batteries. then 200Ah batteries are connect as parallel so I want to charge the batteries without over charging. because I want regulate alternator output, using TIP122.

Input voltage is not constant value. it will change according to RPM of alternator. maximum current 80A.
The circuit can't be that simple, because you want to build the batteries charger with high current.

#### crutschow

Joined Mar 14, 2008
31,538
Normally alternators have a voltage regulator.
Doesn't yours?

#### kithul godage Vijitha

Joined Aug 8, 2017
7
How is the input V/I?
How is the Vout?
Normally alternators have a voltage regulator.
Doesn't yours?
yes of course it has a regulator, But I want to build new one

#### kithul godage Vijitha

Joined Aug 8, 2017
7
The circuit can't be that simple, because you want to build the batteries charger with high current.
How many TIP122 do you have with you? Because a single of those transistors is only capable of handling 5A at most. And that's under ideal conditions. You'd end up with a rather inefficient circuit with numerous components to accomplish what you want.

There are other options out there, such as MOSFETS. Is the use of TIP122 for your application a must?
it doesn't matter. I want to just create a circuit for apply Alternator. I haven't idea how to use MOSFET for regulate the voltage. please send me your idea. It will more helpful to me.

#### ScottWang

Joined Aug 23, 2012
7,327
Voltage regulator for Alternator:

Vin = input voltage unknown (range?).
Iin = input current 80A.
Vout = input voltage unknown (14V?).
Iout max = 80A * eff% = ? A (80A?)

12V Batteries:

Iout max = 200Ah
Vout = 14V

#### crutschow

Joined Mar 14, 2008
31,538
yes of course it has a regulator
Then use that to give the desired output voltage.
It will be more efficient and take less parts.

#### kithul godage Vijitha

Joined Aug 8, 2017
7
Then use that to give the desired output voltage.
It will be more efficient and take less parts.
out put voltage must be 14V

#### kithul godage Vijitha

Joined Aug 8, 2017
7
Voltage regulator for Alternator:

Vin = input voltage unknown (range?).
Iin = input current 80A.
Vout = input voltage unknown (14V?).
Iout max = 80A * eff% = ? A (80A?)

12V Batteries:

Iout max = 200Ah
Vout = 14V
yes I want to charge 12 V Batteries

#### crutschow

Joined Mar 14, 2008
31,538
out put voltage must be 14V
And how is that not achievable by regulating the alternator output voltage?

#### dl324

Joined Mar 30, 2015
15,511
actually I hope to use this to Alternator, for charge the lead acid batteries. then 200Ah batteries are connect as parallel so I want to charge the batteries without over charging. because I want regulate alternator output, using TIP122.
14V is not optimum for charging 12V lead acid batteries, nor is charging them in parallel.

Go to batteryuniversity.com and study the requirements before you try to build a charger. You'll find that you need a timer and multiple voltages.