View source for Generate pwm using ic 555: Add a diode

== Method 2; Longer low time: Add a Diode ==

<gallery>
Ic555 diode.pdf| The schematics. 
555 diode Ranalysis.png| The simulations.
</gallery>

The added diode <math>D</math> shorts the out the resistor <math>R_2</math> during the charging cycle; thus the capacitor charges directly from <math>R_1</math> removing <math>R_2</math>, though a small leakage current will flow through it. The constants are modified due to the voltage drop of <math>D</math>.

<math>
\begin{align}
T_\text{on} &= 0.8 R_1 C \\
T_\text{off} &= 0.7 R_2 C \\
f &= \frac{1.44}{(R_1 + 2R_2)C}
\end{align}
</math>

<math>
pwm% = \frac{ T_\text{on} }{ T_\text{on} + T_\text{off}} = \frac{0.8 R_1 C}{0.8 R_1 C + 0.7 R_2 C } 
</math>


The simulation file: [[File:555 diode 300 300.circuitjs.txt]]