# Boost converter

Thread Starter

#### Tam2020

Joined Jan 26, 2023
3
Hello!

I am looking for a circuit that can boost the voltage of 1 V to approximately 5V and give me as an output current something like 250 mA. The whole idea is that I want to use solar cells to power a line following robot. I will not use any battery. Given that solar cells have little voltage and a lot of current then I thought of using a Boost Converter (circuit with timer circuit 555 or with LTC 3429 )to give me a voltage that I need. Now I can get 5.5 v but my output voltage will be 5 mA which is not enough to drive the robot forward. I am not that much sure about the load resistor (the will be DC Motor Dagu DG02S-2M with 48:1 Gear, 3V - angular with double sided shaft). But I have tested with 1000 ohm.

I really appreciate any help. Thanks a lot

#### Alec_t

Joined Sep 17, 2013
13,337
Welcome to AAC.
Even if the boost circuit were 100% efficient, the solar cells would have to provide 5V x 0.25A = 1.25W and a current of 1.25A. Can they do that?
The standard 555 needs a minimum supply voltage of 4.5V, so wouldn't work as the boost converter.

Thread Starter

#### Tam2020

Joined Jan 26, 2023
3
Welcome to AAC.
Even if the boost circuit were 100% efficient, the solar cells would have to provide 5V x 0.25A = 1.25W and a current of 1.25A. Can they do that?
The standard 555 needs a minimum supply voltage of 4.5V, so wouldn't work as the boost converter.
when we had the lamp close to (25 cm of) the solar cells then we got 0.63 V and 5 A. but I will use 2 solar cells so I think in this case these values becomes 1.26 V and 10 A.
Is there another solution, maybe another circuit that you recommended?
Thanks a lot

#### Jerry-Hat-Trick

Joined Aug 31, 2022
232
when we had the lamp close to (25 cm of) the solar cells then we got 0.63 V and 5 A. but I will use 2 solar cells so I think in this case these values becomes 1.26 V and 10 A
If you use two solar cells you can maybe get twice the power = volts x amps but you can't double both! How about using 7 solar cells in series to get 4.4V?

Thread Starter

#### Tam2020

Joined Jan 26, 2023
3
If you use two solar cells you can maybe get twice the power = volts x amps but you can't double both! How about using 7 solar cells in series to get 4.4V?
They are too big. and the other problem is that 7 of them will give me really huge amount of current

#### Alec_t

Joined Sep 17, 2013
13,337
the other problem is that 7 of them will give me really huge amount of current
No. If they are in series the current will be that of a single cell.

#### moses essien

Joined Jan 27, 2023
1
Welcome to AAC.
Even if the boost circuit were 100% efficient, the solar cells would have to provide 5V x 0.25A = 1.25W and a current of 1.25A. Can they do that?
The standard 555 needs a minimum supply voltage of 4.5V, so wouldn't work as the boost converter.
I wish to know how many MA

#### DickCappels

Joined Aug 21, 2008
9,632
Your life will be much easier if you choose a higher voltage solar panel to start with. For one thing in general buck converters are more efficient than boost converters.

#### Papabravo

Joined Feb 24, 2006
19,874
Hello!

I am looking for a circuit that can boost the voltage of 1 V to approximately 5V and give me as an output current something like 250 mA. The whole idea is that I want to use solar cells to power a line following robot. I will not use any battery. Given that solar cells have little voltage and a lot of current then I thought of using a Boost Converter (circuit with timer circuit 555 or with LTC 3429 )to give me a voltage that I need. Now I can get 5.5 v but my output voltage will be 5 mA which is not enough to drive the robot forward. I am not that much sure about the load resistor (the will be DC Motor Dagu DG02S-2M with 48:1 Gear, 3V - angular with double sided shaft). But I have tested with 1000 ohm.

I really appreciate any help. Thanks a lot
What you don't know about boost converters is that as you increase the boost ratio beyond 2.5 to 3.0 they become very squirrely and difficult to control. You are proposing a boost ratio of 5, which as others have pointed out will require at least a 5-fold increase in input current if you can make one that is 100% efficient. On top of that if you have no other power source than the solar cells, then making the control circuits and finding components to work at that level will be a challenge.

#### BobTPH

Joined Jun 5, 2013
6,319
Can you link to the solar panel you are using?

#### Papabravo

Joined Feb 24, 2006
19,874
I did not do a complete design for this illustration, but rather threw some components together to illustrate the problem. The boost ratio of 5 requires a nominal duty cycle of 80%. Using such a duty cycle is problematic because the slope of the output voltage vs duty cycle transfer function is very steep. This means small changes in duty cycle result in large changes in output voltage. The design was for a boost ratio of 5, but in reality, the result was a disappointing 4, and a corresponding reduction in the available current to approximately 205 mA.

#### tindel

Joined Sep 16, 2012
909
It's probably better to put your solar arrays in series instead of parallel and buck down. High currents are not desired in most applications.

#### MisterBill2

Joined Jan 23, 2018
14,280
How about selecting a motor that uses a lower voltage?? If it can operate directly from the solar cells that is even more efficient.
And keep in mind that while there are a lot of great brains available here they are all limited by the severe effects of reality. They can not exceed 100% efficiency for any design.

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