DC/DC Boost Converter not handling Load

[LukeKnepp]

Hello Everyone,

I built the circuit below with the PAM2423 Boost converter IC.... Here is the datasheet.
I am wanting to use it to get about 3-4 Amps of current at 5V out of a 12,000mAH Li-ion Battery Pack, which will put out between 3V and 4.2V....

I built this exact circuit with only 2 small changes...
R1 = 33k ohm to get 5.3V output
L1 = 4.7uH

So, I hooked it up, and it looks like it works great, putting out 5.3V and everything...
Until I put on a small, 200mA load... Then, with the input at 4.2V, the output was at 5.1V - a 200mA drop, and at 3V input, the output was at like 4.1V!!!!

I think it is probably the Comp pin circuit that is the issue, and I know very little about Compensation pins....

Any help would be greatly appreciated!!!!

 

[ronsimpson]

Which PAM242X do you have.
PAM2421 max switch current is 3A, PAM2422 = 4.5 PAM2423 = 5.5A.
5 volts at 4A = 20 watts = 3.6 volts at 6.67A measured at dc.
If the duty cycle was 50%. Then the switch will se 13A at 50% but the current has a slope so you need to use a IC good for 20A.
You need a part 4 times bigger than a PAM2423. My guess is you are only getting about 1A out.

Next thing is you need a inductor L1 that can handle 20A.

The circuit you posted 3.6V at 3.2A to 12V at 800mA will probably take the PAM2423 to do the job.

 

[LukeKnepp]

Which PAM242X do you have.

I answered that in my first post...

I built the circuit below with the PAM2423 Boost converter IC.... Here is the datasheet.

Next thing is you need a inductor L1 that can handle 20A.

I have a 17A inductor here, so that will work for me, since I will not be needing more than about 2.5A, I just want to make sure I am large enough....

You need a part 4 times bigger than a PAM2423.

I have been looking for anything that will work.... Probably a switching regulator will not be large enough....

I was looking at switching controllers... Does the controller have a maximum output current, or does it not matter, as long as the MOSFET is large enough?
Here are a few of the ones I was looking at...
https://www.analog.com/media/en/technical-documentation/data-sheets/1872fa.pdf

https://www.onsemi.com/pub/Collateral/NCV8878-D.PDF

https://www.diodes.com/assets/Datasheets/ZXSC410_420.pdf

 

[LukeKnepp]

I was looking at switching controllers... Does the controller have a maximum output current, or does it not matter, as long as the MOSFET is large enough?

 

[Diver300]

I was looking at switching controllers... Does the controller have a maximum output current, or does it not matter, as long as the MOSFET is large enough?

A controller won't have a maximum current, as the regulator's output current passes through the MOSFET. The choice of MOSFET is quite involved.

 

[Diver300]

I'm not sure if you will achieve 4 A output with the PAM2423, but it should do a lot better than you achieved. What diode are you using? The SS34 is too small for 4A, but should have been OK with a 200 mA load. You need a schottky diode as normal diodes just aren't fast enough.

 

[unclejed613]

in case you missed it, look at the output in the schematic. it says "12V/800mA"

 

[ronsimpson]

I am wanting to use it to get about 3-4 Amps

I will not be needing more than about 2.5A,

I made a little boost supply just to look at. Vin 3.0V (low voltage) Vout=12V Iout=1A
MOSFET current is the blue trace. Turn on at 3.8A and turns off at 5.5A. The diode will turn on at 5.5A and off at 3.8A.
Here we reached 5.5A which is the max current for the PAM2423 at only 1A output current. Inductor current reaches 5.5A also.

Hope this helps explain current flow in a boost supply.
RonS

 

[LukeKnepp]

Okay, thanks for the illustration, ronsimpson....

So, if I get me a small Controller, like the LTC3872 that you are using, and I get me the correct MOSFET(s), then I could build me my step up converter that would be capable of putting out 3 amps at 5 volts?

If I would get me a 20A MOSFET, like the AO4576, and a big inductor, like this one, and a diode like this one, then I would have my converter?