# A voltage booster without capacitor

1. Aug 31, 2008

### Truthlover

Hello i just want to know if it's possible to do 5V with a 1.5V battery without any capacitor

Thanks

2. Sep 1, 2008

### Staff: Mentor

Are you familiar with the boost topology DC-DC? Why do you not want an output smoothing cap? What is the application that you have in mind?

3. Sep 1, 2008

### Truthlover

I have to run a 4.8V DC motor with a 1.5V battery. The motor is used to propulse a little car.

4. Sep 1, 2008

### Staff: Mentor

Look at the Simple Switcher boost DC-DC circuits at National Semiconductor:

http://www.national.com/analog

Click on the design helper at the right of the page, and input your voltage and current requirements. The calculator will help you design the circuit. You can generally buy the parts from Digikey.com

You should also calculate how long the motor will run on that 1.5V battery. Assume about 85% efficiency for the boost stage (the National calculator may guesstimate the efficiency for you -- I'm not sure if it will), and check the A*Hr rating of the 1.5V battery. BTW, when you spec the input voltages for the calcultor, keep in mind that the range for an alkaline battery is about 1.65V fresh, and 0.8V mostly gone. Other battery types will have different discharge curves. Check the battery manufacturer websites for datasheets.

I think the calculator will provide you with an output capacitor value. I'm still not sure why you don't want to have a cap at the output. If you still have questions after using the calculator, post them here and we'll try to help.

5. Sep 2, 2008

### Truthlover

This is very good but i want to know if it's possible tu use the booster without capacitor. it's a constraint.

6. Sep 2, 2008

### Truthlover

In example: is it possible to use this boost converter without the cpacitor if not what will happen

7. Sep 2, 2008

8. Sep 2, 2008

### Staff: Mentor

You tell us. What is the function of the capacitor in the standard boost DC-DC converter circuit? What happens as you make the capacitor larger, or smaller?

There are at least two effects of decreasing the output capacitor size. Can you tell us what they are?

Why do you have this constraint? Is it coming from someone who does not have an understanding of electronics? Or is it being posed as an advanced puzzle by someone who knows of an elegant non-standard solution?

9. Sep 3, 2008

### Truthlover

it is posed as an advanced puzzle by someone who knows of an elegant non-standard solution. It's like a challenge. so i have to find a way to do 5V with a 1.5V battery without any capacitor.

10. Sep 3, 2008

### chroot

Staff Emeritus
You'll need some kind of reactance, but it doesn't have to be capacitance. You can build a voltage multiplier with inductors, too -- they're just larger and heavier and more expensive.

- Warren

11. Sep 5, 2008

### chaoseverlasting

12. Sep 5, 2008

### Redbelly98

Staff Emeritus
13. Sep 5, 2008

### Truthlover

Thank you chroot for your advice it worked. And yes chaoseverlasting i could run the motor with 1.5v but it was also a question of speed.

14. Sep 5, 2008