Light an LED, Power a motor, this simple - ish circuit will accommodate all you constant current needs using NE555 chips! This is a great way to learn about electronics and although not as efficient as using a pre made buckpuck, this is more fun, cheaper and hopefully you'll learn something too!
Step 1: Intro
To build on breadboard a circuit which will control the current across a load by using pulse width modulation for maximum power efficiency.
To operate the circuit the user will plug the circuit into a power supply; this will keep the load at a constant predetermined current.
Spec (don't worry about these bits yet, i will explain what these numbers mean later)
Power supply voltage: 15V,0V,-15V
Astable Frequency: 60KHz
Astable Space Period: 16Âµs
Astable Mark Period: 0.7Âµs
Monostable Period: 8Âµs (half the period of the astable)
Reference Voltage: 2mV
Output current: 2mA
1. Astable oscillates when circuit is connected to power supply.
2. Falling edge of the astable will trigger the monostable.
3. Monostable will stay high for a variable period; this period is modulated by the difference amplifier.
4. Mosfet switches and allows current to flow.
5. Current Set circuit uses LC to smooth out the voltage into a DC flow.
6. Output is high, LED comes on.
7. Current in load gets too high.
8. Difference amplifier attempts to make this the same as the reference by changing its output.
9. Output of difference amplifier drops.
10. Period of monostable decreases.
11. Monostable on for less time per astable oscillation.
12. Mosfet switches on for less time.
13. After smoothing the voltage is less.
14. Less current across the load.
15. Difference amplifier output rises.
16. Monostable period increases.
Here is a diagram where i have split the project down into 'manageable' chunks, i will explain each chunk individually to help with the build.