which will be better linear IC circuit or SMPS?

Thread Starter

rahulb

Joined Jun 5, 2019
39
Hi Everyone,

I am designing a blinker for led strips.

please check the design below :

blinker circuit.png

The 4017 ic resets after three counts.

The timer 555 and 4017 circuit is powered by 9v supply and the mosfets are powered by a 12v, 2 amp supply.

My question is about the 9v supply. Which type of supply will be better to power the blinker part of the circuit using 12v 2amp smps supply which I am using for the mosfets.

1. A linear circuit probably with LM317.

2. A buck converter

3. or a simple voltage divider circuit?

thanks
 

AlbertHall

Joined Jun 4, 2014
11,498
Forget the voltage divider, that isn't going to work.
If you feed the LM317 from the 12V supply it will not use much power compared to the LEDs and will do the job.
You could use a buck converter but in this case I don't think the extra cost and complexity would be justified.
 

Irving

Joined Jan 30, 2016
2,058
LM317 or LM7809 will work, the current draw of those ICs is so small that the loss savings don't justify the additional cost of a buck converter.

A voltage divider or better, a shunt regulator with a 9v zener or a TL431 would work.

But why not run the CMOS off the 12v as well?

What was behind your choice of MOSFETs?
 

Thread Starter

rahulb

Joined Jun 5, 2019
39
LM317 or LM7809 will work, the current draw of those ICs is so small that the loss savings don't justify the additional cost of a buck converter.

A voltage divider or better, a shunt regulator with a 9v zener or a TL431 would work.

But why not run the CMOS off the 12v as well?

What was behind your choice of MOSFETs?
hi,

when I am using 12v for the blinker circuit. the mosfets are not switching on and off.

I chose mosfets according to availability. I needed a mosfet which can run on 12v and can be used for 2 amps current.

one question:

If I use 7809, will I need to use resistor before it as the smps power supply is 2 amps?

thanks
 

AlbertHall

Joined Jun 4, 2014
11,498
If I use 7809, will I need to use resistor before it as the smps power supply is 2 amps?
No, it will only draw whatever current it needs to feed the logic.

Incidentally, it would be better to connect the MOSFET sources to ground, and connect the LEDs between the drains and +12V.
Are the LEDs designed for 12V?
 

Thread Starter

rahulb

Joined Jun 5, 2019
39
Incidentally, it would be better to connect the MOSFET sources to ground, and connect the LEDs between the drains and +12V.
Are the LEDs designed for 12V?
hi,

thanks for reply.

actually there are three strips of red, green and blue. they share a common neutral. yes, they are designed for 12v, I calculated resistor for each strip.

thanks
 

djsfantasi

Joined Apr 11, 2010
7,825
hi,

thanks for reply.

actually there are three strips of red, green and blue. they share a common neutral. yes, they are designed for 12v, I calculated resistor for each strip.

thanks
If they are designed for 12V operation, I suspect that the strip includes current limiting resistors. Why did you add another resistor?
 

AlbertHall

Joined Jun 4, 2014
11,498
In the circuit that you show, with the logic powered from 9V, you will get a good bit less than 12V across the LEDs, probably about 6V.
 

djsfantasi

Joined Apr 11, 2010
7,825
Isn’t the IRL840 an N channel MOSFET? The circuit shown uses them to switch +12V. He needs a P channel MOSFET and driver that can switch with 9V.
I may be wrong...
 

eetech00

Joined Jun 8, 2013
2,568
Hi

The circuit should work with the mosfets you have, but you have the mosfets connected wrong.
Connect the source to ground and the drain to the LED-, LED + should go to +12v (so the load is connected between the drain and +12).

You don't need the regulator. Run the entire circuit using a 12v supply.
Connect a bypass cap (0.1uf) across the power supply pins of the 555 and the 4017
 

djsfantasi

Joined Apr 11, 2010
7,825
Hi

The circuit should work with the mosfets you have, but you have the mosfets connected wrong.
Connect the source to ground and the drain to the LED-, LED + should go to +12v (so the load is connected between the drain and +12).

You don't need the regulator. Run the entire circuit using a 12v supply.
Connect a bypass cap (0.1uf) across the power supply pins of the 555 and the 4017
The three LED strips are connected together with a common cathode. They aren’t independent strips. Thus the TS can’t switch ground as you suggested. Hence, different (P channel) MOSFETs are necessary.
 

Dodgydave

Joined Jun 22, 2012
10,050
Hi

The circuit should work with the mosfets you have, but you have the mosfets connected wrong.
Connect the source to ground and the drain to the LED-, LED + should go to +12v (so the load is connected between the drain and +12).

You don't need the regulator. Run the entire circuit using a 12v supply.
Connect a bypass cap (0.1uf) across the power supply pins of the 555 and the 4017
He's switcing Positive supply to Common ground loads, so your idea won't work, he needs Pfets.
 
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