I wanted to dim my room LED lighting with a potentiometer, and decided on creating a solution from scratch to make it more fun and educative. I decided to go with the fairly well-known 555 PWM circuit. To decrease size and for learning purposes I decided on using surface-mount components for the first time. The reason I wanted to make this 555 PWM circuit is actually just to see if I could solder SMD components on home-etched PCB’s, and to see how hard it actually is.
Working with breadboards is really great, and you can very easily prototype your circuit and swap out components. However, after a while you might want something more permanent, so you grab the good old perfboard, and things get a lot more nasty, with wires sticking out everywhere. After having some experience with PCB milling, I wanted to give etching a shot. And having plenty of soldering experience, I decided on using surface-mount components.
To make soldering easier, I decided on using 1206 resistors and capacitors, except for the 22µF tantalum capacitor used for the Vcc line. Also not having a solder mask will make things a bit more messy, I had to use some external flux to make sure the solder flowed nicely.
- Operates at roughly 1Khz
- Voltage range 5v – 30v
- 100mV ripple @ 1A
- At least 2A continuous current without heat sink on MOSFET
- Duty cycle from ~10% – ~90%
As you can see, the duty cycle is not that good. It doesn’t go fully off or on, I already saw this on the breadboard, but decided it didn’t matter because I wanted a simple circuit with average performance.
Here are some snapshots of the schematic, circuit, and soldered PCB:
This was very fun for a first etching and SMD-soldering project, but there are plenty of improvements to be made. First of all, the duty cycle is really bad. It doesn’t fully switch on or off. I’ll probably go for an Op-amp circuit next time, because I had good results with that in the past. The voltage ripple is decent, but could be better. Another cap wouldn’t hurt. Also you can see some dirty, white stains on the PCB, this is because of my overpriced SMD soldering flux I got from Conrad. Fortunately I got some premium no-clean flux for my next project!
Eagle files: 555-PWM-SMD.zip
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