DC Buck & Boost

takao21203

Joined Apr 28, 2012
3,702
I've been building smps circuits for a while, including a 400w tl494 buck converter and lm 2576 with external transistor for high voltage.

Firing a photo flash would saturate the gate drive transformer, turning off the lm2576.

I learned a lot but realised it would take more and more space. I stopped with it again.

Without experience you have to try a lot of parts and ideas, see most of them failing.

You need equipment set up too for powering, testing and measuring.

Too much effort to get good efficiency let's say 80 or more percent. Too much heat other wise, need for specialised parts like transformers.

So actually mostly I use ready made modules.
 

Thread Starter

bumba000

Joined Oct 7, 2015
97
I got it! Full PWM control. Anything from 100hz to 20kHz for sure. If that's working (and it is) I can go as high as I'd like in any increments as I'd like. I found a PWM library for arduino! Trouble is, without a load attached the voltage can go clear up to 22v or so. I attach a 1.5ohm or 0.5ohm load the voltage goes down to 2 - 2.4. Can not get it to go higher.
 

Thread Starter

bumba000

Joined Oct 7, 2015
97
ok, this is just crazy.
Attach battery to circuit and Vout is 3.61
Attach 1.5ohm load and Vout goes down to 3.1
PWM at just about any hz or Khz and Vout goes down more as far as 2.2.

What is going on here? It's like I'm in the twilight zone or something...
Without the load, Vout can go as high as 20v or so.
 

Thread Starter

bumba000

Joined Oct 7, 2015
97
Got it! Okay folks ( Tindel!! ) even the schematic that I drew correctly I connected incorrectly. I promise it's right now. And it works even better. I've got to agree to sleep before I pass out at my battle station. I have more work ahead tomorrow with my pwm. Vout is rising now with load attached. Even the 0.5ohm load! Oh my goodness. 4 Pages.

Thanks again, John :)
 

takao21203

Joined Apr 28, 2012
3,702
Yes inductors need right parameters

Permissible dc current
Saturation at given frequency
Stored energy
Physical construction

In general for more than 4 amps a transformer is smaller and easier to control larger currents.

Here's an expert that knows the trade of these circuits
http://www.joretronik.de

I do have useful information even if I dont always write yesyes posts so there could be disagree.
 

Thread Starter

bumba000

Joined Oct 7, 2015
97
O'kay folks - I can not seem to find a good frequency and duty cycle here. I've tried just about everything from 22000hZ (22kHZ) to 1000000hZ (1mHZ) in increments of 2000hZ (2kHZ) at duty cycles from 20 to 60. Nothing seems to perform really anywhere near a store bought device. I am using an 18650 battery charged to 4.2V with a 0.5ohm load. When I connect the load the voltage at the load drops to 2.6. When I activate the PMW I have gotten it to climb to 3.2 but no higher.

I have rebuilt the circuit using parts from a store bought device and I can not seem to get to the performance of the store bought device. What could I possibly be missing here. Please...

Thank You, John
 

Thread Starter

bumba000

Joined Oct 7, 2015
97
I guess in all of the excitement I forgot to post back. While I still have no oscilloscope to measure the frequency, the settings I'm using should have it between 30kHz and 40kHz. I have also eliminated the 10 and 12 inch wiring. I've gone with heavier shorter wiring and it's working great. I did have a bad experience with a battery charger I am working into the equation a few days ago and have smoked my last mosfet. I'm waiting on more mosfets to arrive and in the meantime I've been able to get the charger worked out. Next will be measuring the actual output current. I can see that I can reach voltages above 5v which was the target. I am seeing the performance I was looking for, I just need to measure the amps out so that I may adjust the settings to be more accurate with the actual output.

Thanks everyone, John
 
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