# which type of dc to dc converter to use to convert 5V, 80mA input to 3V 300mA output?

#### ashokraj

Joined Feb 1, 2018
117
Hi,
I am working on a solar panel whose output maximum specifications are 6V, 100mA ( nearly 0.6watt). Practically these values came to 5v, 80mA when tested in afternoon sun. I want to run a motor whose operating voltage is (3~12V), no load current is 180mA. I would like to know what are the ready to available module I can use to make this possible. I have little knowledge of DC to DC converters. In this example do I have to use Step down converter or buck boost converter ? Usually I am with an impression that power can neither be created no destroyed so in the buck converter the voltage reduces and current amplifies so I can use it. Am i right ?

There are different types of buck converters available I would like to know how to select the right one for my application?

1. LM2596 in this they mentioned output current as 2A. does it mean it supplies 2A at any output irrespective of input and output voltage ?
2. AMS1117 in this they mentioned ouput current as 800mA . does it mean it supplies 800mA in definetely !!?

As I need more current than the input current I have eliminated the option of boost converter which increases the voltage and decreases current at the input.

#### Yaakov

Joined Jan 27, 2019
3,523
A magical one?

You have 5V at 80mA which is .4W you want 3V at 300mA which is .9W

Where will the extra half Watt come from?

All conversions from one voltage to another have to choose between current and voltage. You have a certain amount of power, which is expressed in Watts, and you can use that budget, minus the unavoidable conversion losses, to shuffle the voltage and current outputs but you can never get more than you put in and in fact always have to get somewhat less out.

#### Yaakov

Joined Jan 27, 2019
3,523
One more thing, you can use time as well. If you charge a battery or capacitor you can get higher currents than the input but only for the amount of time you charge minus losses. So if you charged, say, a supercap at some rate for some given time then you could have your higher current for some time after charging and do it again.

But you can't get more out than you put in, ever.

#### bertus

Joined Apr 5, 2008
21,557
Hello,

You can never get more on the output than you put in.
You will need about 200 mA at the 5 V input at a high efficiency of 90%

Bertus

#### trebla

Joined Jun 29, 2019
431
If you want get 3V and 300mA out then you need put in at least 5V and 230mA if converter efficiency is 70% or better

#### ashokraj

Joined Feb 1, 2018
117
One more thing, you can use time as well. If you charge a battery or capacitor you can get higher currents than the input but only for the amount of time you charge minus losses. So if you charged, say, a supercap at some rate for some given time then you could have your higher current for some time after charging and do it again.

But you can't get more out than you put in, ever.
hi, when you say a super capacitor can I use 1000uF electrolytic capacitor?

#### Yaakov

Joined Jan 27, 2019
3,523
hi, when you say a super capacitor can I use 1000uF electrolytic capacitor?
It wouldn’t run a motor for more than a fractional second. A super cap is something different.

A super cap would be more like 5F, or more. You can search for super capacitors online, lots of information. They are a bit like super fast charging batteries.

#### ashokraj

Joined Feb 1, 2018
117
Dick, he wants more power out than he is putting in.
I will add another solar panel in series, so the input power can be 10V, 80mA = 0.8 watt, in this situation if I keep 3.3V at the output I could get a 240mA!!!

In this scenario which module is more recommended to use , AMS1117 or LM2596 mentioned in the post, any method/ procedure which I can find out.

#### Yaakov

Joined Jan 27, 2019
3,523
I will add another solar panel in series, so the input power can be 10V, 80mA = 0.8 watt, in this situation if I keep 3.3V at the output I could get a 240mA!!!

In this scenario which module is more recommended to use , AMS1117 or LM2596 mentioned in the post, any method/ procedure which I can find out.
The LM2596 buck converter will be more efficient than the LDO but it requires more external components.

#### sghioto

Joined Dec 31, 2017
2,395
AMS1117 in this they mentioned output current as 800mA . does it mean it supplies 800mA in definetely !!?
This means the LDO can handle up to 800ma, it does not supply current. If you connect two panels in series and use the LDO the current output is only what the solar panels can deliver safely which is still only 80ma.
What you really need is a 5 volt 5 watt panel, then you can drive the motor directly.

#### Yaakov

Joined Jan 27, 2019
3,523
This means the LDO can handle up to 800ma, it does not supply current. If you connect two panels in series and use the LDO the current output is only what the solar panels can deliver safely which is still only 80ma.
What you really need is a 5 volt 5 watt panel, then you can drive the motor directly.
EDIT: Ignore this response, it's the result of divided attention and it completely irrelevant.

My bad for not noticing the deficit in the LDO specs. He can't use the LM1117 because he still needs too much current. It looks like a 7805 might be a good choice, for some values of "good choice".

Last edited:

#### sghioto

Joined Dec 31, 2017
2,395
Lost me here. What difference would a 7805 make if the panels can only deliver 80 ma.

#### Yaakov

Joined Jan 27, 2019
3,523
Lost me here. What difference would a 7805 make if the panels can only deliver 80 ma.
I am doing too many things at once. To untangle the confused state I put myself into to make that post would require years of therapy. Let's just say I entered an alternate reality where you said something different than you actually did and I responded to a third thing when I got the thing you didn't say even wronger.

#### trebla

Joined Jun 29, 2019
431
Maybe the AP63203 fits to your requirements.

#### BobaMosfet

Joined Jul 1, 2009
1,850
Hi,
I am working on a solar panel whose output maximum specifications are 6V, 100mA ( nearly 0.6watt). Practically these values came to 5v, 80mA when tested in afternoon sun. I want to run a motor whose operating voltage is (3~12V), no load current is 180mA. I would like to know what are the ready to available module I can use to make this possible. I have little knowledge of DC to DC converters. In this example do I have to use Step down converter or buck boost converter ? Usually I am with an impression that power can neither be created no destroyed so in the buck converter the voltage reduces and current amplifies so I can use it. Am i right ?

There are different types of buck converters available I would like to know how to select the right one for my application?

1. LM2596 in this they mentioned output current as 2A. does it mean it supplies 2A at any output irrespective of input and output voltage ?
2. AMS1117 in this they mentioned ouput current as 800mA . does it mean it supplies 800mA in definetely !!?

As I need more current than the input current I have eliminated the option of boost converter which increases the voltage and decreases current at the input.