How to Simple cc/cv boost converter / adding cc/cv

Thread Starter

bigjoncoop

Joined Feb 1, 2019
158
I'm looking for a relatively "simple way" of creating a constant current constant voltage boost converter circuit.

Or if it would be cheaper or easier to add cc/cv to a cheap pre-made boost converter...

I know there are existing boost converters with cc/cv for really cheap but the problem is there all fairly large and are normally there spec are way more then need.

My parameters are:
Input: 5v
Output: 8.4v-6.8v or upto 26v (if possible and still be relatively small)
Current: 2a

Thx guys for your input
 

Papabravo

Joined Feb 24, 2006
16,118
I'm looking for a relatively "simple way" of creating a constant current constant voltage boost converter circuit.

Or if it would be cheaper or easier to add cc/cv to a cheap pre-made boost converter...

I know there are existing boost converters with cc/cv for really cheap but the problem is there all fairly large and are normally there spec are way more then need.

My parameters are:
Input: 5v
Output: 8.4v-6.8v or upto 26v (if possible and still be relatively small)
Current: 2a

Thx guys for your input
You cannot have both features simultaneously.
Adding these features to an existing design requires that you firs understand the existing design to see if it is possible. It may not be possible in all cases.
 

Dodgydave

Joined Jun 22, 2012
9,951
I would buy one readymade for the output that you need, but you need to know that if you want say 26V at 2A out, that's 52W so your input current at 5V s going to be 10A plus...

You can't have cc and cv at the same time..
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
158
@Dodgydave
@Papabravo

I don't quite understand what you mean by you can't have CC & CV at the same time?

There are a ton of cc/cv buck converters and boost converters available...

All I'm trying to do is make one as small as possible, also without trim pots and just using a fixed resistors in order to set cc cv...

I am also looking to do the same with a buck converter also.
 

ronsimpson

Joined Oct 7, 2019
1,227
Many people don't understand cc/cv.
Output: 8.4v-6.8v or up to 26v (if possible and still be relatively small)
Current: 2a
The 2A part is easy. There will be a amplifier looking at current and as soon as you reach 2A it will reduce the duty cycle.
In the same way there will be a amplifier looking at the voltage and keeping the output below some voltage.
Battery charging: The power supply will put 2A (at a low voltage) into the battery. (current regulation) Think car battery. As soon as the battery voltage reaches ma. (14.5V) the current will start dropping because the voltage topped out at 14.5V. The supply now is not watching current but watching voltage.
LED: LEDs should be driven with a regulated current. The supply will regulate at 2A and the voltage could be in the 6.8 to 8.4 range depending on LED voltage and temperature. If the LED breaks the supply will increase too much. Maybe break the supply. So a over voltage limit is on the supply. At 10V or "26V" the supply will go into CV mode and stop sending power out.

What are you powering? It makes a different.
 

Papabravo

Joined Feb 24, 2006
16,118
@Dodgydave
@Papabravo

I don't quite understand what you mean by you can't have CC & CV at the same time?

There are a ton of cc/cv buck converters and boost converters available...

All I'm trying to do is make one as small as possible, also without trim pots and just using a fixed resistors in order to set cc cv...

I am also looking to do the same with a buck converter also.
It's pretty simple really, I'm surprised you were not aware of Ohm's Law.
If you have a constant voltage supply, the load will set the current according Ohm's law. You CANNOT set the current independently.
If you have a constant current supply, the load will set the voltage according to Ohm's law. You CANNOT set the voltage independently.
There are no extant buck converters that are both cv and cc at the same time.
 

ronsimpson

Joined Oct 7, 2019
1,227
Ohms Law gets complicated when the load is non linear. Like a LED.
There are many LED power supplies (boost or buck) that are CC/CV.

Even a bench power supply is CV in that you can set it to 12V and CC in that you can set it to never go beyond 2A. These supplies will almost never see CC and CV at the same time. The output (in my example) will all ways be in a box bordered by 12V and 2A.
Some Arc Welders are CC/CV.
 

Delta Prime

Joined Nov 15, 2019
998
My parameters are:
Input: 5v
Output: 8.4v-6.8v or upto 26v (if possible and still be relatively small)
Current: 2a
Hello there:)
You had to throw in parameters...You have got to start somewhere right? Buck, Boost
know there are existing boost converters with cc/cv for really cheap but the problem is there all fairly large and are normally there spec are way more then need
I designed them that way for a living ,not my fault that's how my superiors want it.If they want a purple elephant I give them...my purple elephant.
If you 86 the 5 volts at over 10 amps input
then you can see my purple elephant. Which is two linear power supplies in parallel one constant voltage the other constant current, that's my purple elephant.
The LT3081’s unique current-source reference and voltage-follower output amplifier make it possible to connect two linear regulators in parallel for up to 3A and over 24V of adjustable current and voltage output control. Linear regulators at the output suppress output ripple without requiring large output capacitors, resulting in a truly flat DC output.cv.png
 
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