Simple PT4115 circuit behaving very strangely.

Go To Last Post
25 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

So I built a pt4115 circuit to control my LEDs! it has a 0.12Ohm resistor so it should give me 0.860~ma of current!

 

but the weird thing is that as I turn the votlage fro 0 to 30v on my power supply it goes up to 850 then drops down to 30 and goes up to around 850 and again jumps down but when it goes to 30v it's around 1.2A! it keeps changing if I change the voltage!

 

I attached the pictures!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think your component idents on the board layout have C1 & R1 transposed.

 

Did you build to match the circuit, or to match the idents ... ?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Most examples on the internet show a large bulk cap (100uf) across the supply line, you only have a small bypass cap! ???

 

Jim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

My PSU has some c: i'll add some and try anyway!

 

but it behaves very strangly!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

kamhagh wrote:
My PSU has some c: i'll add some and try anyway!

Sorry that does not count! 

 

Jim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Still goes down after 21.5v and goes up again :|

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

OUCH ok the circuit get's realllly toasty! the pt4115 is burning hot! I made two and both behave the same!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not sure what you mean but I designed it myself! it's pretty much the Datasheet's circuit!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I believe what awneil was pointing out was:

 

David (aka frog_jr)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

kamhagh wrote:

Not sure what you mean but I designed it myself! it's pretty much the Datasheet's circuit!

 

Really? 

 

Your DS must be different, as this one shows a 100uf bulk cap Cin, your circuit is missing it!

It must be close to the chip, any in the Power supply after long leads does not count!

 

A low ESR capacitor should be used for input
decoupling, as the ESR of this capacitor appears in
series with the supply source impedance and lowers
overall efficiency. This capacitor has to supply the
relatively high peak current to the coil and smooth the
current ripple on the input supply. A minimum value of
4.7uF is acceptable if the DC input source is close to
the device, but higher values will improve performance

 

Jim

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think that's only necessary id youre using a rectifier bridge from an ac power sources! (Straight from a transformer) the data sheet said it's not needed if I use a stable power supply and sll that (constant voltage)

Either way I'll add one using some wires tomorrow!

Edit: WOOPS the cap is actually 100uf but not the special kind with low esr (forgot the name). The schematic is wrong. Be it's uf not nf

Last Edited: Mon. Oct 30, 2017 - 09:10 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

frog_jr wrote:
I believe what awneil was pointing out was...

Yes - that's it.

 

And my follow-up question was whether the circuits have been built following the schematic, or following the (incorrect) silk screen 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok I changed it to a tantalum cap and it still behaved the same. 620ma at 12v ( The led consumes 900ma at 10.5v~) then it G
went up to 850ma dropped down and went up to 1.2a! (It gets a bit dimmer after reaching a certain voltage all the sudden!)

And i reached 30v and had a hard attack cause i forgot my cap was eated for 16v~ xD it looked very cool though! Smells nice too! Like flowers.

Last Edited: Mon. Oct 30, 2017 - 11:36 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Schematic! Didn't pay attention to the silk! Plus the part sizes are pretty different so.. c:

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Might I suggest that you stop and examine your circuit and the schematic carefully BEFORE you make post after post showing you haven't done so? And stop with all the exclamation points....we get the hint you are enthusiastic :)

Jim

Edit
While I am at it, your schematic shows a standard diode from Vcc to switch....most of the PT4115 circuits I have worked with use a schocktty diode.

Edit again:
No ground plane for heat radiation and oscillation prevention?

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

Last Edited: Tue. Oct 31, 2017 - 12:15 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

:( i have checked it! The circuit is ok. But I'll do it again tomorrow cause I have horrible attention.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Jim, the part number is a schottky diode.
Is the inductor correct? The current rating of the inductor is critical - get it wrong and i’d expect problems like you’re describing.
Whilst the circuit might look simple, it is actually quite complex. Your pcb is a critical part of the circuit - layout, track size, component type all play a part.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Kartman wrote:
Jim, the part number is a schottky diode.

So it is.....

 

The PCB leaves quite a bit to be desired though, as you describe.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

This is almost the first PCB I've ever designed. I'm a self taught teen ;c So don't expect much from me! it took a month to arrive :| At first it was 3 channels on one PCB (that one had a ground plane and caps close to the IC) but I made a single one since they send 5 and forgot to move changes over :|

Also I just realized my PWM trace goes in middle of my Inductor! could the Inductor be causing noise on the PWM trace ? I could try soldering a wire directly to the PWM pin!

 

Also the Inductor has a very high Resistance! 

SWPA4018S101MT:

DC Resistance is 2.275 max and 1.75 typ! (+30%) SFR is 6.5 Isat is 0.40 typ is 0.44 (Heat rating current is also 0.25 0.41)

It appears that I have ordered the wrong Inductor :| I did check for the Current but I think i may have read the one above or underneath it.

Trying a new Inductor then! will post the results.

Ok with a random non smd coil I found in my closet ( I think it's around the same inductance) and it did drop in current at 20v (at 20v it's almost giving me the current I wanted it to be )

Last Edited: Tue. Oct 31, 2017 - 06:35 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

If you expect your led to draw 800+mA then the inductor has to be rated around twice that. The inductor you’ve used saturates at 400mA and ceases to be an inductor thus giving you the result you’ve observed. The DC resistance of the inductor causes heating, so you want this to be as low as possible but this is a tradeoff vs the physical size.
You’ve now learned a little about inductors.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yaay! Changing it to a random trough hole didn't help. Ill stop being cheap and order some online to see if it helps. Cause it did change the behavior quite a lot.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

if It helps I now have a ds 138 oscilloscope too c:

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think the best thing to do now is to just design a PCB with ground and all that! one more month of shipping :| 

Thanks a lot for your help! I've learned a lot so it was worth waiting a month.

Last Edited: Tue. Oct 31, 2017 - 03:46 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

kamhagh wrote:
one more month of shipping :

 

Take a look at the PM I am writing you

 

JIm

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

kamhagh wrote:
( I think it's around the same inductance

 

There are a bunch of variants on Ali Express of a USD 7  "transistor tester" which also tests:

- Resistors.

- Capacitors.

- Inductors.

- Diode's.

- Led's.

- SCR's.

- Mosfets.

- Triac's.

 

Davey Jones (EEVblog) has done a vid about it and there is also quite a lengthy thread on his forum about all the differen variants of that thing.

(And it uses an ATMEGA328).

 

Or do it yourself:

Build a little pulse gen (AVR or NE555 pdt4115, whatever) and connect and inductor briefly between a known voltage source & GND.

Measure the current with a suitable shunt resistor.

You can calculate the inductance from the slope of the scope trace.

Fun project for beginners and you learn from it.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com