Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

Issue with boost driver

GBD

New member
Joined
Oct 25, 2010
Messages
805
Likes
71
Points
0
Ive made a boost converter style driver for a lab 445nM build. but I seem to have some issues with the output.

This driver is okay to run without a load, as my design just turns off the driver after too high voltage on the output, and likewise for the input (but also low limit to prevent the battery from draining too much).

but now when I put a load, I have it set to 4.8V, but just as I load it, the whole output sags down to 4.2V, and after that it will continue to go lower.
(went right down to the original input voltage).

this was tested with a dummy load of a 1ohm 5W resistor and 6 1n series diodes in series with it.

the battery itself is fine btw, stays at simular voltage levels and draws the appropriate current. ive also tested it yet again with a lab supply, and still the same results.

if anyone has any ideas to why its behaving in this manner, id love to hear your input. :confused:
 

ped

Well-known member
Joined
Nov 25, 2008
Messages
5,003
Likes
709
Points
113
If its a lab build, why are you using a boost driver??
Boost driver's are for single Li-Ion (and similar) batteries to boost the voltage as some (405nm & 445nm) diodes require 4v + to run , surely if its a labby, its being run from a PSU?
 

GBD

New member
Joined
Oct 25, 2010
Messages
805
Likes
71
Points
0
Well, id guess it should be called a portable. reason I called it this is because this is a battery powered lab (3.7V) and is in a bulky box...

yeah.. this is a portable.. nevermind. (im just used to the term portable bieng something like a hand held host in the general shape of a flashlight/pointer)
 
Last edited:

qumefox

New member
Joined
Mar 26, 2010
Messages
3,234
Likes
117
Points
0
You'd really have to post your schematic if you truly want assistance with this. Otherwise it's like asking a mechanic to fix a car blindfolded.
 

GBD

New member
Joined
Oct 25, 2010
Messages
805
Likes
71
Points
0
You'd really have to post your schematic if you truly want assistance with this. Otherwise it's like asking a mechanic to fix a car blindfolded.
Yes my bad. Do grant me a break though, I was posting this yesterday at 1AM :eek:

Here is the part of the schematic that seems to be doing something wrong, but ive yet to figure out.

The CLK (provided by a 555 timer) is oscillating properly, and is of no issue. but as ive stated in the first post, there is an issue somewhere in the boost circuit. I just cant pinpoint it yet.

In the circuit I included the gate driver's basic scheme, and the overvoltage cuttoff comparator. (If the output voltage gets too high, the driver will shut off via an AND gate)



If anyone is still unclear of anything, please let me know and Ill do my best to correct it.
 

qumefox

New member
Joined
Mar 26, 2010
Messages
3,234
Likes
117
Points
0
Hmm. If it were me, i'd start with eliminating all non-necessary components. Your voltage comparators, all the rectifier diodes, etc. Just start with the basics.. The basic boost circuit and it's PWM drive, and get that behaving properly on a test load, then once that's dealt with, start with re-adding the filtering to clean up the output, then worry about your voltage comparators and logic lastly.

Breadboards are your friends on projects like these. :D


Though after looking at it more.. It seems your missing some stuff. This appears to be a voltage control converter. What you need to be building for LD control one that does current control. And it seems like you'd need at least one more comparator for that.

This is an example of one, but there are more if you google.

 
Last edited:

GBD

New member
Joined
Oct 25, 2010
Messages
805
Likes
71
Points
0
Well, at the moment Im using current control via the 555. I think using an error amp, or even getting an IC to do it for me would be a supperior approach.

luckly, after stripping apart my circuti down to the bare boost driver (CLK to gate, only an inductor and diode) and using a dummy load. suddenly my voltage stoped dropping!

but as soon as I add my comparator circuit, it drops again. what gives? I ask.

the comparator circuit turned out to be just fine and working properly, but the voltage regulator circuit for my referance, I discovered that the IC had an issue with it. so my voltage referance on the + side was dropping down from 3.3V and lower, which meant that it was tricked into thinking that the voltage on the output must be too high, shutting off the driver, and so on so forth it contiued.

the solution: I replaced the regulator with a more relaible one, now I have a consistant referance and so far no issues. to vary the current, I have to mess with the gate driver.

IMO, in the future I will invest in a chip to do this mess for me rather then having to build a circuit from scratch..

Thanks for your advice qumefox! +1 for you.
 




Top