strobing signal/fast switching

[bruno]

Hello, OK I'm new to this forum and was hoping for some advice. I'm building a circuit to flash some LED's. I need a flash rate of 18Hz with a duration of 2ms. I'm using a 555timer to send a pulse to a led driver which controls multiple high power LED's. With the astable circuit i changed R1 to 850Mohms, R2 to 1Mohms and a capacitor of .1uF as a 555component calculator told me and it doesn't work! Are these values wrong? I'm not even sure if a 555 is the right thing to use. Any advice as to how I can achieve this kind of pulse rate would be much appreciated....HELP!

 

[ericgibbs]

Hello, OK I'm new to this forum and was hoping for some advice. I'm building a circuit to flash some LED's. I need a flash rate of 18Hz with a duration of 2ms. I'm using a 555timer to send a pulse to a led driver which controls multiple high power LED's. With the astable circuit i changed R1 to 850Mohms, R2 to 1Mohms and a capacitor of .1uF as a 555component calculator told me and it doesn't work! Are these values wrong? I'm not even sure if a 555 is the right thing to use. Any advice as to how I can achieve this kind of pulse rate would be much appreciated....HELP!

hi,
The mark/space ratio you require can be realised using a 555.

Look at this image, the diodes/resistor change the ratio.