what's up with this snubber?

Thread Starter

m1ch43l

Joined Aug 16, 2012
62
I've a snubber circuit/clamp circuit. Basically it's a cap and resistor in parallel.
I have a supply of 23v and wish it to hover around 12-14v for my circuit that requires max 100mA.
My circuit has 2 smaller circuits each supplied from the main line by a filter circuit
resistor 100ohms and 16v 470uF cap.
The problem is that the first snubber (which according to some equations from ehow.com needs a min of 125ohm 694pF clamp circuit (with or without diode) clamping an initial burst of 25v at 10KHz). Soldering them only ends up with a faint pop from my 555s. To temporarily counter this problem and create a vdrop of 10v from the supply, I run a fan parallel to my circuit and I end up with 14v for my circuit. That's good. However, I intend to run the circuit on its own. I use 1 3Kohm 10nF cap clamp circuit and according to the simulator that should have me 13v on the circuit supply. On the circuit, there's berely no change: 23v which is too high. I try with 33K resistor and still voltage is way up (after some time).
What gives?
 

crutschow

Joined Mar 14, 2008
23,155
If I understand you correctly, you want to reduce the supply current from 23V to around 12-14V for your circuit. For that you shouldn't use a series resistor since the voltage will vary with the circuit load (ehow is not giving you good information on that). Instead use a voltage regulator, such as an LM317 or a series resistor with a 12V zener to ground.
 

Thread Starter

m1ch43l

Joined Aug 16, 2012
62
Will it take care of the initial spikes of v>25? Don want to burn more 555's: they aren't readily sourceable here...
 

bountyhunter

Joined Sep 7, 2009
2,498
I use 555 devices in auto and motorcycle electrics which get hit with nasty voltage spikes. The safe way to protect them is to use an R-C filter to the 555 power terminal and also a zener clamp on the 555 power pin to ground.
 

Thread Starter

m1ch43l

Joined Aug 16, 2012
62
Clamped a 1N4148 parallel to my circuit input to ground and pretty much burnt 1 555 I decided to sacrifice. I'm currently looking into the reverse breakdown v of this diode.
BTW, where should the diode be...after the RC snubber or before it, relative to the voltage source?

When you say 'power pin' are you suggesting I place this diode at pin8 to ground?
 
Last edited:

Thread Starter

m1ch43l

Joined Aug 16, 2012
62
My bad, 1N4148 has breakdown voltage of 75 and/or 100 (clarify?). Zeners are scarce here so the fan idea will have to do. Thanks gents.
 

Thread Starter

m1ch43l

Joined Aug 16, 2012
62
Instead use a voltage regulator, such as an LM317 or a series resistor with a 12V zener to ground.
Hadn't paid close attention to this...seems I need to learn as many zeners and their BV for my projects. Thanks alot cruts.:D
 
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