Boost convertor

Thread Starter

gokulpradeep010

Joined Jun 2, 2021
33
Hi all,
I am trying to build a boost convertor ckt using LT3757A for 24V to (180V,0.1A). I am getting the required voltage, but my voltage drops to 65V when a load is connected.
inductor- API Delven 220uH,
Mosfet - IRLI640GPBF,(200V)
Output capacitor( 4.7uF, 250V ESR 490m), KEMET
 
Last edited:

BobaMosfet

Joined Jul 1, 2009
1,850
Hi all,
I am trying to build a boost convertor ckt using LT3757A for 24V to (180V,.1mA). I am getting the required voltage, but my voltage drops to 65V when a load is connected.
inductor- API Delven 220uH,
Mosfet - IRLI640GPBF,(200V)
Output capacitor( 4.7uF, 250V ESR 490m), KEMET
That most likely would mean the load is taking more current than your Boost Converter is providing- Make sure you understand how much current the load demands.
 

Papabravo

Joined Feb 24, 2006
16,825
Building a boost converter with a ratio of 7.5 to 1 is going to be a challenge regardless of anything else you do. I'm uncertain if this enterprise has any chance of success. Do you have some reason to be hopeful? Certainly a ratio in the neighborhood of 3-4 is reasonable.
 

ronsimpson

Joined Oct 7, 2019
1,474
inductor- API Delven 220uH
Part number. Will it work at 1 to 2 amps? Is it saturating? Send picture.

The LT3757 current limits when pin 5 gets to 0.108 volts. There is a 0.09 ohm resistor on pin 5. 0.1 ohm is easy math. There will be 1A average through the transistor so the peak is above the 1A limit.

I know you are current limiting. Try 1/2 the load and see if it regulates.
Many people do not check for saturation on inductors.
 

Thread Starter

gokulpradeep010

Joined Jun 2, 2021
33
Part number. Will it work at 1 to 2 amps? Is it saturating? Send picture.

The LT3757 current limits when pin 5 gets to 0.108 volts. There is a 0.09 ohm resistor on pin 5. 0.1 ohm is easy math. There will be 1A average through the transistor so the peak is above the 1A limit.

I know you are current limiting. Try 1/2 the load and see if it regulates.
Many people do not check for saturation on inductors.
The part number is:


4590R-224K



1627888797357.png
 

ronsimpson

Joined Oct 7, 2019
1,474
I think you are trying to pull 2X too much current.
The IC is current limiting and the inductor is right at saturation. 1.2A
-----edited-----
The fact your voltage drops to 65V from 180 suggests you are 2.5X maybe 3X too much current.
 
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