Quote:
Originally Posted by DIYman
This guy simply powers a camera with a 7808 without heat sinks or caps.
Even if I take the advice you and others have posted, I am still interested in knowing why there is so much variation in the cap values used with a 78xx voltage regulators - particularly when drawing power from similar sources.
Cheers
Doug
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Putting the linear regulator in the battery pack just places a heat (thermal) source in the camera. Moving the regulator out of the battery reduces thermal noise in the DSLR.
The variation in requirement for input caps is due to how each OEM device responds to the capacitive load on the input pin. Since each OEM has their own manufacturing process and quality of dies and taking each others design then variances are common.
Malcom, I made sure I used the appropriate "PI" input and output bandwidth filters as specified by the OEM for my switching regulator (PTN78060WAH)...no issues with noise that I can see. I used their exact specified parts as they were very particular on what to use....maybe I got lucky...maybe I cannot see the noise (more than likely)?
A 7808 will just suffice to power lets say a 450D since higher power usage spike ups and down with the demands of the camera operation...I remember testing one with loads of 500mA and damn they get quite hot! Placing the device on a good heatsink is required.
The
Daniel McCauley pdf on this shows the expected current draw and transients. he suggested using a metal case placing a 7808 against the case (with thermal pad) to dissipate heat.