Hi All,
I recently posted about a 555 pwm circuit for controlling rgb led panels using mosfets.

My question is, which 555 or 556 circuit would you recommend? There are so many. Something stable, trouble free and can run 24/7 without heat problems. The led panels are 5V. I have 5v and 12v supplies available.

Thanks very much.

 

Where is the circuit?

 

Oops I meant thought, not posted. I don't have a specific one. I'd like to know which one you'd recommend. There are a lot of circuits and most of them have very few differences.

I just need one that can do as close to 0-100% brightness as possible.

 

Go to check -- NE555 Pulse Generator and PWM adjustable circuit.

 

Thanks Scott. So I can drive 5V led panels from the mosfet with separate 5v supply while still using 12v for the 555 circuit?

 

You can using +5V for 555 and MOSFET and led panels.
You also can using +12V for 555 and +5V for MOSFET and led panels, but using +12V is for 555 is unnecessary, why you need to do that?

 

I thought the 555 needed 6-15v? If I can use 5V, then I'm happy. Thanks for your help!!

 

I thought the 555 needed 6-15v? If I can use 5V, then I'm happy. Thanks for your help!!

555 - 3~15V, NE555 Vout = Vcc-1.4V = 3.6V when Vcc =+5V.
If the MOSFET is a logic Vgs=4.5V type then the NE555 Vout needs to add one npn and one pnp stage to raise the voltage close to +5V, and the output from C of pnp to drive the Vgs of MOSFET.

 

I almost forgot that you need to using the pwm signal, so the one is like the preview posted as #8 or using the power more than +7V for NE555, maybe using a 78L08 to be the regulator from +12V or directly connects to +12.

 

Thanks. The previews only go up to number 7? You say I need a pnp stage for a logic level mosfet. Do you have a schematic or link to a stage I can add?

 

If you want to power the NE555 with +5V then you will need one npn and one pnp(because the output needs the same phase with the input) and the circuit as fig-07 that it is shown on the right top in the below page.
The Transistor's Sink And Source

Another method is that I haven't try yet below, probably it can be works, if the Vout(c of Q1) can't goes high when the Vout of NE555 goes high then the R1 should be increase to 2.2K or a little more.

 

Ah I see. That's adding more components though. What if I powered the 555 from my 12V supply? Then I would have to use a different mosfet (not logic level), yes? I have a few IRF540 sitting at home.

Would I need a resistor between the 555 and gate? And a gate to source resistor?

 

Ah I see. That's adding more components though. What if I powered the 555 from my 12V supply? Then I would have to use a different mosfet (not logic level), yes? I have a few IRF540 sitting at home.

A logic level Vgs to 12V is ok, you can in series with a 1~10K resistor.

Would I need a resistor between the 555 and gate? And a gate to source resistor?

If you meant that the new circuit then no needs.
When the Ne555 output is high then the current will be flows through from +5V → diode → R1 → Vbc → Vgs(MOSFET).

When the Ne555 output is low then the current of Vgs(MOSFET) will be flows through from Vgs → Vce(Q1) → NE555 output (now it is as grounded).

 

I'll try with 12V supply first. I'm looking at the first pwm circuit in your link. Is that right? I'll try it tonight.

 

Here's a PWM circuit that goes from 0% (full off) to 100% (continuously on) duty-cycle using an LM339 or LM393 comparator.
It can operate readily with a 5V supply.

 

crutschow does that circuit need the 4050 to drive a logic level mosfet? I'm trying to keep the component count to a minimum.

 

Hi All,
I recently posted about a 555 pwm circuit for controlling rgb led panels using mosfets.

My question is, which 555 or 556 circuit would you recommend? There are so many. Something stable, trouble free and can run 24/7 without heat problems. The led panels are 5V. I have 5v and 12v supplies available.

Thanks very much.

The text book 555 PWM uses 2 of them, one as a monostable and the other as a VF oscillator triggering it. As you increase the number of fixed width pulses - they occupy more of the time.

A single 555 can do PWM if you use separate charge and discharge Rt and steering diodes. Easy if you use a pot to vary PWM, but gets complex if you want to control it with an input signal - if you're using a micro; you can programme that to output variable pulse rate to drive the monostable stage.

 

Hi Ian. No micro. Just using a pot to vary pwm output to a mosfet. One 555 per channel is preferred, but if I have to use a 556 to have the double 555 circuit, then so be it.

 

I'll try with 12V supply first. I'm looking at the first pwm circuit in your link. Is that right? I'll try it tonight.

If you use cmos type as TLC555 or HA17555 or ICM 7555 then the output will be close to +5V and no needs to use +12V.

 

Hi Ian. No micro. Just using a pot to vary pwm output to a mosfet. One 555 per channel is preferred, but if I have to use a 556 to have the double 555 circuit, then so be it.

With a pot - you shouldn't have any difficulty with the single 555 and steering diodes.