i want to add a second circuit that is partially controlled by first circuit.
first circuit will control main power.
circuit 1 will feed power to circuit 2 and both can turn off 1 LED in each circuit.
will use 2 on-off-on switches.
thanks a million.




Mods Note:
Cut off the useless part of the circuit file, also negated image.
@crutschow

 

i need to cutoff the last LED in circuit instead of the first.
will this still work?
thanks
dear mods
how do i cutoff the unnecessary border stuff and what is negated image?
i'm an old codger that doesn't know all this computer stuff.
thanks

Mod:
Negative image, means black > white, white > black, makes it easier to view, improves your chances of getting help.
I am a very old codger.
Eric

 

I see no ground path for the LEDs' currents.

 

Q3 is drawn the wrong way round , or you're using the wrong fet, the internal diode will pass the Negative supply, .
No negative path for the leds, or do they get their supply from the 2861 device L1,2?

 

crut
this is the same circuit we worked on a while back.
i just copied it over for second half and deleted the Q3 polarity protection stuff since it isn't needed twice.
i thought the LEDs were grounded through the PWM chip.
remember my ignorance on electronics?

dave
Q3 is for reverse polarity protection.
it's a Nchannel mosfet. DMN6140
passing to ground is ok when power is connected correctly.

all help appreciated.

 

this is the same circuit we worked on a while back.

Okay, it's coming back to me.

i need to cutoff the last LED in circuit instead of the first.
will this still work?

No, it needs to be the top LED for that circuit to work.
But the order of the LEDs is immaterial.
Just put the LED you want to cutoff on top.

 

ugghhh
my board layout gets a lot more complicated to get the lighting effect i want.
oh well, guess it's back to the drawing board.
if it's not too much trouble, can you explain why it won't work on last LED?
is it because this is a PNP and the lower side is going to ground instead of still having a positive voltage?
thanks

 

if it's not too much trouble, can you explain why it won't work on last LED?

The LED switch is a P-MOSFET and its source terminal must be connected to the most positive voltage to get the proper Vgs voltage for switching it on and off..

(To clarify, NPN's and PNP's are bipolar transistors. MOSFETs are either n-channel or p-channel.)

 

finally got my circuit boards.
the gate voltage checks high or low as it should depending on power connection but the Pfet is conducting all the time on both LEDs that have Pfets.
i even reversed the source and drain and it still conducts all the time either way and i tried new Pfets in both locations.
when i remove the Pfet, the LED turns on.
i'm using DMP4065S
https://www.mouser.com/datasheet/2/115/DMP4065S-537770.pdf
only pulling 400mA
what's this dummy doing wrong?
thanks

 

finally got my circuit boards.
the gate voltage checks high or low as it should depending on power connection but the Pfet is conducting all the time on both LEDs that have Pfets.
i even reversed the source and drain and it still conducts all the time either way and i tried new Pfets in both locations.
when i remove the Pfet, the LED turns on.
i'm using DMP4065S
https://www.mouser.com/datasheet/2/115/DMP4065S-537770.pdf
only pulling 400mA
what's this dummy doing wrong?
thanks

Any chance you did your board layout for the wrong pinout? Some pin arrangements are so close to standardized that people assume they are 100% standard, and in fact they're not.

Here's a thread where some alternate pinouts were discussed:
https://forum.allaboutcircuits.com/...ackage-going-to-have-the-same-pin-out.116676/

 

i switched the source and drain with same result.
looking down on the part with single lead up, i have gate as left pin of the 2 pins on down side.
using ohm meter with no power to board, with positive on drain, negative on source, it reads 2.5m.
with positive on source, negative on drain, it shows open.
with 12volt power input on high switch position, it shows 12volt on gate, 12 volt on source, 9 on drain. LED has about 3Vf but is not lighted.
with power on low switch position, gate show .05v, source and drain show 12v.
its like when gate is high, voltage is going through the LED but it is still not lighted.
this is over my head.
thanks

 

voltage is going through the LED but it is still not lighted.

Have you tried replacing that LED, or testing that LED outside of this circuit? Any chance that LED is damaged or defective?

If I'm understanding that portion of the circuit, all of the MOSFET pin voltages you described sound correct in both positions, which makes me think the board layout and MOSFET are working properly.

I'm intrigued, but probably not clever enough to be helpful. Hopefully someone more experienced will jump in!

 

yes i removed and replaced both LEDs.
new LEDs gave same result.
i tested the removed LEDs and both were good.
thanks

 

yes i removed and replaced both LEDs.
new LEDs gave same result.
i tested the removed LEDs and both were good.
thanks

Cool. I see now that you mentioned in an earlier post that the LEDs worked when you removed the FETs, so I should've known the LEDs weren't the problem.

Sorry I don't have any more insights. I did try running an LTSpice simulation of the key portion of the schematic (albeit with substitute parts cause I don't have all the right part models) and everything worked as expected in simulation.

Maybe if you share pics of your board layout we'll see something that's not obvious from the descriptions so far. Otherwise I've got nothing. Hopefully @crutschow will have some ideas.

 

board has mask so u can't see circuits.
i built half this circuit with just 3 LEDs earlier and it worked as it should.
don't know what's happening with double circuit.
thought it might get feedback or something through some of the zeners or tvs diodes.
what i can't understand is the correct voltage drop but LED doesn't light.
thanks

yes cruts is a wizard.
wish i was a 10th as sharp.

 

i can't understand is the correct voltage drop but LED doesn't light.

An LED will indicate a voltage drop with very little current, so low that the LED doesn't light.
Even the current from the multimeter 10meg input may be sufficient.

Compare all the voltages between the good circuit and the bad circuit.
Any significant difference should point you to the problem.

 

Maybe something to do with imperfect grounding through the reverse polarity protection MOSFET? With inductors and high speed switching, imagine there's a lot of potential for odd voltages, overshoot, ringing, etc. in unpredictable places.

Maybe try bypassing that MOSFET and providing really beefy grounding connections everywhere?

Also, do you have a scope? Can you look at the gate voltage and source voltage with a scope (preferable both at the same time, maybe in differential mode?) Maybe the average voltage readings with a DMM are good but there are transients you're not seeing that are making your PFETs misbehave.

I really have no idea - just more brainstorming.

 

i removed reverse polarity mosfet, zeners, and tvs diodes with same result.
i also built another of the 3 LED version and it works as should.
starting to think there is a wrong circuit somewhere but why would both sides not work?
i'm redesigning board using the exact same 3 LED circuit and just copying, rotating, and connecting power and ground.
if this doesn't work, i give up.

cruts continues to over estimate my abilities...lol

thanks again.

 

UPDATE
got the new circuit board and it works as should.
THANKS again CRUTSCHOW and others.
this site and it's members are the greatest.

 

UPDATE
got the new circuit board and it works as should.
THANKS again CRUTSCHOW and others.
this site and it's members are the greatest.

Congrats! Glad you got it sorted out.