SparkFun Forums

[paulstanely45]

Hey All,

I was looking into using a camera flash circuit for a project, and I came across this tutorial on HowStuffWorks.

http://electronics.howstuffworks.com/camera-flash2.htm

All the logic in this circuit makes sense to me except for the rectifier diode. Did they do that circuit up wrong, or is something not clicking with me? I can't see how the capacitor would ever charge this way :\

[NleahciM]

Hey All,

I was looking into using a camera flash circuit for a project, and I came across this tutorial on HowStuffWorks.

http://electronics.howstuffworks.com/camera-flash2.htm

All the logic in this circuit makes sense to me except for the rectifier diode. Did they do that circuit up wrong, or is something not clicking with me? I can't see how the capacitor would ever charge this way :\

That topology generated a *negative* supply for the camera flash. So the diode is shown in the proper orientation. It's a very elegant topology, in my opinion.

[paulstanely45]

Would you mind elaborating for educational sake? I'm not sure I fully understand what you mean. It still isn't obvious to me how the capacitor would charge, or how the indicator light would come on.

Which side of the capacitor would the charge being collecting on?

[jremington]

Charge always accumulates on both sides of a capacitor, in exactly equal quantity (+ and -). There are two possible orientations, depending on which way the current flows. Most introductory physics textbooks offer a clear explanation.

[RonnyM]

OK. First, the simple circuit and actual device is quite lethal. That cap holds a heart stopping synapse frying amount of energy. That out of the way, here it is...
The diode acts as a one way gate for the current flow. Without it, the voltage would be going both ways with every cycle of the oscillator. It would give you a net charge of zero, and probably kill the cap which has a polarity mark on it for proper operation. The 300 or so volts at the cap terminals is the really dangerous component. The 4Kv secondary on the flash transformer is really only there to give a very short pulse to ionize the gas in the tube, which turns into an excellent conductor for the charge in the cap for a couple of milliseconds.