# Buck boost converter for home use (DC load and AC load)

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#### LexenZ

##### New Member
Dear Pros,

I am trying to research on a suitable buck boost converter that is able to power any smartphone of up to 2A and also flexible enough to change to power an ac load (Say maybe a light bulb).

Through my research I found a simple buck boost converter schematic that made use of the LTC3440 chip.
(https://www.circuitstoday.com/buck-boost-converter-circuit)
However, it only has a maximum output of 600mA.

What ic chip/components should I use to further increase the output current if i were to retain the same design?

#### ronsimpson

##### Well-Known Member
What is your input voltage range?
Output voltage is 5V at 2A.
LTC3115 or LTC3118

#### LexenZ

##### New Member
What is your input voltage range?
Output voltage is 5V at 2A.
LTC3115 or LTC3118

Dear Ron,

As I will be hooking up to a solar panel to receive the energy. input voltage range can be about 8V-30V?

My operating voltages for output would be 5V for which you mentioned, as for AC loads to power up bulbs I am unsure of the voltages?

Even though my voltages are low, I would like to be able to showcase the buck boost effect, especially for boost as I wish to see the output voltage being higher than the input voltage(30V max).

With that said, will the current design i provided with the link before be suitable by just replacing your recommended controllers? (LTC3115 or LTC3118)

Regards

John

#### ronsimpson

##### Well-Known Member
What I showed Vin from 3.7 to 40V and Vout to 40V at 2A.
It will not work well at 4V in and 40Vout.

The LTC3440 works at Vin of 2.5 to 5.5V Vout of 2.5 to 5.5V at 600mA

math: assuming the BuckBoost is 100% efficiant.
Power=Power
For the BuckBoost:
5V X 2A = 10watts Power output.
5V x 2A = 10 watts Power input.
10V x 1A= 10 watts Power input.
20V x 500mA = 10 watts input
30V x 333mA = 10 watts input.

Solar panel:
Very bright sun = 30V and 1A = 30 watts.
Dim sun = 20V and 500mA = 10 watts.
very dim sun = 10V and 50mA = 0.5 watts.

Results is at Very bright you have much power and every thing is good. At dim sun things will probably not work. and a very din sun it will not work!
The BuckBoost pulls "power" and if the solar panel can not produce 10 watts then it will pull the panel voltage down to 2.5V and stop working.
I think you need a smarter power supply.
Many cell phones will pull 5V@2A. When the sun is not strong the 5V will drop down and the phone will go to 1A mode. This will help you!

You could probably use a Buck only supply to make the 5V 2A.
I do not know how you are going to make AC. Many kinds of light bulbs will work with AC or DC.

Last edited:

#### LexenZ

##### New Member
What I showed Vin from 3.7 to 40V and Vout to 40V at 2A.
It will not work well at 4V in and 40Vout.

The LTC3440 works at Vin of 2.5 to 5.5V Vout of 2.5 to 5.5V at 600mA

math: assuming the BuckBoost is 100% efficiant.
Power=Power
For the BuckBoost:
5V X 2A = 10watts Power output.
5V x 2A = 10 watts Power input.
10V x 1A= 10 watts Power input.
20V x 500mA = 10 watts input
30V x 333mA = 10 watts input.

Solar panel:
Very bright sun = 30V and 1A = 30 watts.
Dim sun = 20V and 500mA = 10 watts.
very dim sun = 10V and 50mA = 0.5 watts.

Results is at Very bright you have much power and every thing is good. At dim sun things will probably not work. and a very din sun it will not work!
The BuckBoost pulls "power" and if the solar panel can not produce 10 watts then it will pull the panel voltage down to 2.5V and stop working.
I think you need a smarter power supply.
Many cell phones will pull 5V@2A. When the sun is not strong the 5V will drop down and the phone will go to 1A mode. This will help you!

You could probably use a Buck only supply to make the 5V 2A.
I do not know how you are going to make AC. Many kinds of light bulbs will work with AC or DC.

Dear Ron,

Thanks for the info, so i could only make a buck converter only?

As for ac loads, I was thinking of creating a dc-ac inverter to support ac loads.

Regards
John

#### LexenZ

##### New Member
What is your input voltage range?
Output voltage is 5V at 2A.
LTC3115 or LTC3118

Dear Ron,

If I were to use the typical application as the schematics to create it from the link below, I noticed that the ic ship doesn't have "legs" for soldering. Any solutions to that?
https://www.linear.com/product/LTC3118

#### ronsimpson

##### Well-Known Member
This package pretty much kills bread-boarding. If you make a PCB for this ask me how!

But: Did you see this version?

#### LexenZ

##### New Member
This package pretty much kills bread-boarding. If you make a PCB for this ask me how!
View attachment 107487
But: Did you see this version?
View attachment 107488

Thanks for the pcb creation ron!
However, I just need to create using a simple copper board.
I found the chip with legs as shown : https://sg.element14.com/linear-tec...dc-dc-conv-buck-boost-1-2mhz-tssop/dp/2473248

I noticed that all the buck boost claimed ic chips for which the output voltage doesn't go beyond the input voltage. Is this normal?

Regards

#### ronsimpson

##### Well-Known Member
I noticed that all the buck boost claimed ic chips for which the output voltage doesn't go beyond the input voltage. Is this normal?
Buck: Vin>Vout (every part is different but Vin might need to be 3V higher than Vout)
Boost: Vin<Vout (Most have a diode from Vin to Vout so if the IC is not working Vout will be pulled up to almost Vin)
Buck Boost: Vin<=>Vout (will do both jobs)

#### LexenZ

##### New Member
This package pretty much kills bread-boarding. If you make a PCB for this ask me how!
View attachment 107487
But: Did you see this version?
View attachment 107488

Dear Ron,

I finally understood what you mean by killing of bread boarding, the ic chip is extremely small to even be placed in a breadboard.
As such do you have another recommendations for ic chips that has a standard size of being able to put it in the breadboard for testing before soldering commences?

Regards
John

#### ronsimpson

##### Well-Known Member
I never really understood what you are doing.
As I will be hooking up to a solar panel to receive the energy. input voltage range can be about 8V-30V?
My operating voltages for output would be 5V
It will be hard to find a "buck/boost" that has 0.1 inch leads. I can find "buck" that will bread board. But any PWM will not bread board well because of high current and fast edges.

#### LexenZ

##### New Member
I never really understood what you are doing.

It will be hard to find a "buck/boost" that has 0.1 inch leads. I can find "buck" that will bread board. But any PWM will not bread board well because of high current and fast edges.
View attachment 107724

Dear Ron,

Thanks for the recommendation.
Is there such an option to create this kind without using the ic chip (LTC31115) itself? (I would like to use the components such as the one you have attached to create a buck/boost)

Regards
John

#### LexenZ

##### New Member
http://cds.linear.com/docs/en/demo-board-manual/dc1687af.pdf
If you have to test out a buck boost then get this board.

Dear Ron,
Appreciate the quick response!
However , as shown from my link : http://sg.element14.com/linear-tech...ddkey=http:en-SG/Element14_Singapore/w/search
If i were to get it the price is simply too much for me to handle, as such I couldn't afford it.

I found many simple diagrams to build the buck/boost converter with the help of mosfets and zener diodes (Like the one you showed me for buck), however they do not include the values of individual components...... Is there another way?

Regards
John

#### ronsimpson

##### Well-Known Member
I found many simple diagrams to build the buck/boost converter with the help of mosfets and zener diodes
Please post the one you like best.

#### ronsimpson

##### Well-Known Member
I did not study these to see if they will work. The price is good. You probably can not get the parts for the price.
You did not fill in your "location". That helps me know where you can get parts. I think your "ebay" will have the same boards.

#### LexenZ

##### New Member
Please post the one you like best.

This is one of such circuits I would want to create, with the battery (source) provided by a programmable power supply.
However, as shown there are zero values of the components. So.... yea that's where I am at a dead end.

As shown from your links, these are all pre built converters. However, I do not wish to have a pre built one for which I intend to build one by my own.
Is your suggestion meaning that I should get one of these and reverse engineer the process...?

Regards
John

#### ronsimpson

##### Well-Known Member
Your circuit is just a "theory". You also must find a way to open and close SW1 and SW2 at just the right time and at the right duty cycle. There are many pieces missing.

The ebay power supplies are a good way to "bread board". You will have a printed circuit board that you can change parts on.
reverse engineer the process
Yes. Some one in China, took a data sheet example and make it work. They found the parts, probably made some changes. Here it is at a good price. Now you can look at the data sheet and at what China did and you can make changes if you need.

Normally I look at a data sheet and then build one of the examples. Then I make changes. Here China has done this. So much work is done. So far you have only worked on paper. Here you can see some thing work. (maybe not perfect)

#### ronsimpson

##### Well-Known Member
I have not wanted to explain why your project will not work. Here goes.
A buck boost PWM is not smart and will not work well with a solar panel.
To get the most power from a panel you should work at the Max Power Point which is above you battery voltage so "boost" is not needed.
----------------------------------------
Data: 22.1 volts, 2.2 amp, 36 watts, Blue Solaria Co., Ltd..

36 watt panel. (No one has ever got 36 watts) I live at high altitude, 10% humidity, thin air, no clouds and I can't get 36 watts. Close but no 36 watts. I have friends that live sea level, 95% humidity and they get less power. You can not multiply the voltage and current to get power. The voltage is measured with no load and the current is measured into a short.
22.1V open circuit
2.2A at a short
Maximum power point is about 18 volts (2.0A)

Pretend it is a very bright day. Use top green line and top blue line. Top left corner of the graph is 2.2A into a short. (2.2A 0V 0 watts)
Bottom right corner is the open circuit no load point. 22V, 0A 0 watts.
At 18V and 2.0A we get 36 watts. (max power)
If you pulled only 1A you will get 20V and 20 watts.
If you pulled 2.1A you will get 15 volts and 31.5 watts. (down from 36)
If you pull 2.2A the voltage will drop to 0 volts and 0 watts.
What we learned is to pull power until the voltage drops to the MP point. Do not pull any more current.
---------early morning-------- not bright-------
Use the bottom green and blue curve.
Short current is 200mA, open voltage is 19V and the max power point is about 18V.
18V 180mA 3.24 watts is the sweet spot.
If you try to pull anything over 3.24 watts the voltage will fall to zero.
-----------------------------Max Power Point---------------
I looked at several MPPT controllers that are built to charge batteries.
1) max battery voltage. 14.5V for a 12V car battery.
2) max battery current. Your battery probably can handle more than a 2A panel can produce so it could be set to 3A. (mostly not used)
3) max power voltage from panel. In my example 18 volts.
If the battery voltage gets too high the PWM will back down.
If the battery current get too high for the battery the PWM will back down.
The PWM will increase/decrease the power to hold the panel at the best voltage.
--------------------------------------
If the panel voltage drops below 12V (where boost might help) the power level is much less than one watt and not worth the effort.

Hope this helps.

#### LexenZ

##### New Member
I have not wanted to explain why your project will not work. Here goes.
A buck boost PWM is not smart and will not work well with a solar panel.
To get the most power from a panel you should work at the Max Power Point which is above you battery voltage so "boost" is not needed.
----------------------------------------
Data: 22.1 volts, 2.2 amp, 36 watts, Blue Solaria Co., Ltd..

36 watt panel. (No one has ever got 36 watts) I live at high altitude, 10% humidity, thin air, no clouds and I can't get 36 watts. Close but no 36 watts. I have friends that live sea level, 95% humidity and they get less power. You can not multiply the voltage and current to get power. The voltage is measured with no load and the current is measured into a short.
22.1V open circuit
2.2A at a short
Maximum power point is about 18 volts (2.0A)
View attachment 107729
Pretend it is a very bright day. Use top green line and top blue line. Top left corner of the graph is 2.2A into a short. (2.2A 0V 0 watts)
Bottom right corner is the open circuit no load point. 22V, 0A 0 watts.
At 18V and 2.0A we get 36 watts. (max power)
If you pulled only 1A you will get 20V and 20 watts.
If you pulled 2.1A you will get 15 volts and 31.5 watts. (down from 36)
If you pull 2.2A the voltage will drop to 0 volts and 0 watts.
What we learned is to pull power until the voltage drops to the MP point. Do not pull any more current.
---------early morning-------- not bright-------
Use the bottom green and blue curve.
Short current is 200mA, open voltage is 19V and the max power point is about 18V.
18V 180mA 3.24 watts is the sweet spot.
If you try to pull anything over 3.24 watts the voltage will fall to zero.
-----------------------------Max Power Point---------------
I looked at several MPPT controllers that are built to charge batteries.
1) max battery voltage. 14.5V for a 12V car battery.
2) max battery current. Your battery probably can handle more than a 2A panel can produce so it could be set to 3A. (mostly not used)
3) max power voltage from panel. In my example 18 volts.
If the battery voltage gets too high the PWM will back down.
If the battery current get too high for the battery the PWM will back down.
The PWM will increase/decrease the power to hold the panel at the best voltage.
--------------------------------------
If the panel voltage drops below 12V (where boost might help) the power level is much less than one watt and not worth the effort.

Hope this helps.

Dear Ron,

Thank you for the trouble and info you have given me.
As the original idea of me wanting to build that circuit through a simple breadboard process, it was cancelled due to the size of the ic chip.
I was able to follow closely with the circuit and built up everything on the breadboard itself.

However I do have some issues with that circuit.
Is there a way to produce a 5V and 1-2A output to charge smartphones? If so, what are the components to switch out to?
I was thinking of changing the regulator to a higher output current. But i not sure if it works....

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