Boost Converter Urgent Help

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Quint24

Member
Joined
Mar 17, 2017
Messages
17
Hey guys. I'm new here. I see that you all are very helpful. I'm currently having a problem with my boost converter design. The requirements are to step up 8-12V to 30V at 1 Amp. I have calculated the values and simulated it and it works. 220uH inductor, irlz44n mosfet, 1n5819 5A schottky, 10uF cap, 30 Ohm 50W load, (3 10Ohms in series). The pwm controller is an attiny45 which supplies 100khz signal to the FET. The feedback loop is a 390k and 33k voltage divider across the load. The problem I am having is that the prototype boosts to well over 50V with no load attached but as soon as I attache the load the output voltage drops to 0.

Your help will greatly be appreciated.
 
wouldn't it be better to just use LM2585-ADJ (150kHz switching freq) or XL6009 (400kHz switching freq)?
lower component count, and smaller board estate.
 
I also thought that but the client specified the components as well as the switching frequency.  So I have to stick by those
 
yeah, nothing beats a cheaper solution (only if it works...) a single LM2587-ADJ ($9) versus a mosfet and a tiny mcu ($1.5 each)
 
Quint24 said:
Hey guys. I'm new here. I see that you all are very helpful. I'm currently having a problem with my boost converter design. The requirements are to step up 8-12V to 30V at 1 Amp. I have calculated the values and simulated it and it works. 220uH inductor, irlz44n mosfet, 1n5819 5A schottky, 10uF cap, 30 Ohm 50W load, (3 10Ohms in series). The pwm controller is an attiny45 which supplies 100khz signal to the FET. The feedback loop is a 390k and 33k voltage divider across the load. The problem I am having is that the prototype boosts to well over 50V with no load attached but as soon as I attache the load the output voltage drops to 0.

Your help will greatly be appreciated.
Click to expand...
It's very difficult to help you without a schemo. Have you done a simulation of your circuit?
 
Hi. This is the schematic. Thanks for all the help guy. I really appreciate it. It works in the sim, ranging from about 28V to 32V which can be tweaked. Oh n John, no matter what load I connect, the output voltage drops to nearly zero. Always below 1 V
 
Quint24 said:
Hey guys. I'm new here. I see that you all are very helpful. I'm currently having a problem with my boost converter design. The requirements are to step up 8-12V to 30V at 1 Amp. I have calculated the values and simulated it and it works. 220uH inductor, irlz44n mosfet, 1n5819 5A schottky, 10uF cap, 30 Ohm 50W load, (3 10Ohms in series). The pwm controller is an attiny45 which supplies 100khz signal to the FET. The feedback loop is a 390k and 33k voltage divider across the load. The problem I am having is that the prototype boosts to well over 50V with no load attached but as soon as I attache the load the output voltage drops to 0.
Click to expand...

The problem with microcontroller-based switching power supply control is that you need to be wise in the ways of switching power supplies in order to write firmware that regulates well under all load conditions. There's more to it than just setting the PWM duty cycle.

i'd just buy the dedicated switching converter or converter controller and be done with it.
 
Quint24 said:
The problem I am having is that the prototype boosts to well over 50V with no load attached but as soon as I attache the load the output voltage drops to 0.
Click to expand...
What voltage source do you use in the real world? Your simulated source is "perfect"; in practice, you need a capacitor in parallels.
Do you have snapshots of the waveforms at the gate and drain of the MOSFET?
 
I don't have a scope with me atm as its night time here. However I can show you those waveforms on Monday if you will still be interested in helping, the voltage source I current used for testing is lm338 regulated pc power supply, giving out 10V
 
Quint24 said:
I don't have a scope with me atm as its night time here. However I can show you those waveforms on Monday if you will still be interested in helping, the voltage source I current used for testing is lm338 regulated pc power supply, giving out 10V
Click to expand...
Then I suspect your voltage source is not stiff enough for supplying the current surges.
 
Thanks guys. I will try again and keep you posted. One more question, should I put a pull up or pull down resistor on the gate?
 
Hey guys. Here's and update on the converter. Currently it's boosting to approx 30V constant. This is with a 5W load and the output current is very low 0.13A. I require 1A. When I put a 50W 30 ohm load on it, the output voltage fluctuates like crazy well below the desired value. I can't figure out why this is happening, any ideas?
 
Quint24 said:
Hey guys. Here's and update on the converter. Currently it's boosting to approx 30V constant. This is with a 5W load and the output current is very low 0.13A. I require 1A. When I put a 50W 30 ohm load on it, the output voltage fluctuates like crazy well below the desired value. I can't figure out why this is happening, any ideas?
Click to expand...
get a scope?

JR
 
Quint24 said:
Hey guys. Here's and update on the converter. Currently it's boosting to approx 30V constant. This is with a 5W load and the output current is very low 0.13A. I require 1A. When I put a 50W 30 ohm load on it, the output voltage fluctuates like crazy well below the desired value. I can't figure out why this is happening, any ideas?
Click to expand...
Have you checked the incoming voltage? Proper operation of a converter requires a stiff power source.
 

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