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Tiny DC-DC constant current switching power supply

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TheMerovingian

Sun Feb 13 2011, 04:50PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

I came across those small switchmode constant currend power supplies with buck-boost capabilities and I want to replicate some similar. From photos taken i was able to identify two ICs but with "obscure" markings, one is "101" and the other "7441" do you know something similar? I wasn't able to find anything about these parts. Have anyone reverse-engineered one of these in order to improve their current capabilities and so on?
All i was able to understant is that driver pushes current high side, since the output-ground pin is tied to the input-ground pin. So it must use some specialized switchmode driver ICs...

UPDATE: the 7441 is some reverse polarity protection, so the real switching IC is the "101" (integrated switch probably)

Conundrum

Sun Feb 13 2011, 07:00PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

mc34063 maybe?
i've used one to make an led drive before.
worked well, the only problem was current sharing between the diodes...

Also an idea, some newer LED backlit laptop panels use a 5 pin SOIC as the backlight driver.
says 3A024 on it...
-A

TheMerovingian

Sun Feb 13 2011, 07:21PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

The mc34063 pinout is different but seems a good alternative. Cannot find anything 'bout 3A024 execpt it is a voltage detector of some sorts in the turuta smd handbook

what about those "anonimous" markings... The 101 is a zener in most databases

maybe it is L01 or I01 or even L02 or I02

All i know it is a sot-23 5-pin switching controller of some type Vin min 2.0V , 5.5V Max. , 1.5A max . I don't understant how it can achieve buck boost using a grounded output without inverting the voltage....

Maybe it is boost and down-regulating PWM... (noisy)

Meatball

Sun Feb 13 2011, 10:48PM

Registered Member #2401 Joined: Mon Sept 28 2009, 04:25PM
Location:
Posts: 74

Ah, the flexdrive V5.

If there were anything you could improve on that circuit, Dr Lava himself would have done it already. That circuit is very efficient, and its very flexible, stable, and protected.

Dr Lava sells them all over the place.
He is on photonlexicon I believe, but not active much. Otherwise I would recommend you ask him!

TheMerovingian

Sun Feb 13 2011, 10:59PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Yeah. It would be nice to know what type of amazing controller is he using. A buck boost converter with positive output and grounded negative output is very interesting.

I tried to ask him but I am afraid that he would think that i'm trying to reverse engineer the thing or trying to build my own drivers.. so i doubt he will answer me.... he deleted the markings on the IC in the manual.. so he is not willing to give away his secrets

From the differences with flexdrive V4 i determined that the critical part is the "101" pwm sot-23-5 controller but i could't find it even on the turuta (yet the 2007 edition) smd handbook. THe current sensing resistor is probably a 0.05ohm smd... the rest seems simple (voltage references, filter capacitors). All switching is done by the magical "101" . Probably it also sinchronously rectify the voltage. I will go mad soon

Wolfram

Mon Feb 14 2011, 01:06AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

It might be this

chip.

Steve Conner

Mon Feb 14 2011, 09:54AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

It must be an inverting converter with positive input and negative output. The only buck-boost converters with positive input and positive output are the Cuk and SEPIC, and they both require two inductors, but your board only has one.

The LM3410 doesn't seem to do inverting.

TheMerovingian

Mon Feb 14 2011, 11:24AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

That's why i'm getting mad on it. It also has grounded negative output. How do the hell measures current without a differential amplifier circuit??

Steve Conner

Mon Feb 14 2011, 11:28AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Many of these chips have a differential amp built in for high-side current sensing.

I used to design laser drivers, and mine simply used a differential amp made from an op-amp. The high-end ones used a dedicated current-sense amplifier chip made by Burr Brown, I can't remember the part number.

Conundrum

Mon Feb 14 2011, 12:07PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Shame they don't make a PIC 5 or 6 pin with high current outputs and an A-D.
This would be pretty neat for lasers, etc and also save a lot of hassle when designing small circuits.

-A
#include "1W_laser_sendmeplease_kthx.h"

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