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Strange startup waveform on 7805 vReg and spikes on 5V output.
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tom66:
I usually add a small TVS to inputs of systems like this where the input is very low impedance, to provide additional attenuation of this effect.  Typically sized to break down before the regulator chip does!
David Hess:

--- Quote from: Psi on August 10, 2022, 04:20:06 am ---But I'm not liking those spikes above 12V.
Is that caused by the sharp edge of the switch combined with some inductance on the wires to the 7805?
--- End quote ---

Yep.


--- Quote ---I think maybe I just need a high ESR cap on the input. 
The ceramics are probably adding too much low ESR capacitance?
--- End quote ---

Yep, yep.

If a small input capacitance is used, then the inductance back to the source can cause spikes like that.  The solution is to add some bulk capacitance, like a 47 or 100 microfarad aluminum electrolytic, close to the regulator's input terminal.

I think Bob Pease discussed this or a very similar problem.
Psi:
Anyone know what causes the step response?
David Hess:

--- Quote from: Psi on August 11, 2022, 04:36:44 am ---Anyone know what causes the step response?
--- End quote ---

Poorly implemented current limiting might do that.
Psi:

--- Quote from: David Hess on August 11, 2022, 08:14:40 am ---
--- Quote from: Psi on August 11, 2022, 04:36:44 am ---Anyone know what causes the step response?
--- End quote ---

Poorly implemented current limiting might do that.

--- End quote ---

Hmm, i was powering it from a GWinstek psu,  will try a battery.
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