Why a PWM with NE555?
This tiny but powerful circuit generates a PWM with the "oldschool"-timer-IC NE555. This PWM is not a static but a dynamic one adjusted by P1.
The working frequency is defined by C4. The lesser the capacity of C4 the higher the frequency of the circuit. The working frequency is calculated by approximation: f = 100e3
* C4. This in mind it is very easy to generate blinking frequencies with capacity in the µF area.
The second part of the circuit provides the load control. In this case a LED. A powermosfet in a TO220 case presents the output stage. His gate is driven by set of bipolar transistors. They take care of the appropriate control voltage and a proper slew rate regardless of the frequency. The diode makes sure that the gate capacity is quickly discharged during the off-time of the PWM.
The circuit can be supplied with voltages from 5V to 12V. It is reasonable to choose the supply voltage according to the quantity and the configuration of the used LEDs. For example a cheap wall plug is a good supply voltage source. The circuit was developed for a Luxeon power LED but it can also be used to drive a fan.