2-channel dimmer from NE555 + LM358?

Question

I have a 12-24 V dimmer for LED strips like this: https://www.circuitlab.com/editor/#?id=c8m48y

^{simulate this circuit – Schematic created using CircuitLab}

I want to understand a couple of issues about it:

1. Does it utilize only 1 channel of LM358?
2. Copying the schematic analogous to R4, VA1, R5, R6, R7, Q1 and MOSFET to a second channel (unit) of LM358 I can get the second dimmable channel for another LED strip? If yes - would it be also up to 8A?
3. I can use the same output after R2 as a negative input to the second channel of LM358?
4. What is the PWM frequency? \$ 1 / ( C3 * R2) \$ or \$1 / ( C3 * ( R3 + R2))\$ ?

Thank you!

Answer 1

1. Yes it only uses one of the op-amps and there are two in the same package.
2. Assuming your power supply can handle the power drawn from them then yes. As long as you don't hook up the LED strip to the same MOSFET.
3. Yup, Op-amps have infinite input impedance so they won't effect your circuit.*
4. I believe the frequency won't be either of the ones you state. However I may be wrong.

\begin{align} t_{dicharge} &= (0.693 * C3 * R2 * R3) \\ t_{discharge} &= (0.693 * 2 * R2) \end{align}

adding them together

\begin{align} T &= 0.693 * C3 * (R3 + 2*R2) \end{align}

convert to frequecny

\begin{align} F &= \frac{1}{T} = \frac{1}{(0.693 C3 (R3 + 2R2))} \end{align}

*Well, high enough that it shouldn't effect your case.