diode circuit protection

[blanik]

i did some searching around for circuit protection... found interesting stuff (i blew a 4558 in my TS just by changing the battery...  )

the interesting device for me is the diode in parallel between the +9V in and ground, does it suck battery power like the "series" version?

R.

[R.G.]

I hope you found the polarity protection articles at GEO - http://www.geofex.com.

A series diode is good - but you lose 0.6V from your 9V battery, which reduces your headroom and your effective battery life.

A reverse biased diode is what most companies use. It is placed with anode to ground and cathode to +9 on negative ground pedals. When the power supply is correct, it does nothing because it's reverse biased. When the power supply is backwards, it tries to pull the battery down to 0.6V, effectively shorting the battery. This is OK if the polarity reversal is momentary, and harsher if the battery is left connected or if there's a wrong-polarity power adapter connected. Then the battery may overheat and vent or the diode may short from overheating. Still it's cheap and prevents some damage.

The series MOS transistor protector circuit at GEO is really good: much lower voltage loss than a series diode, but not destroyed by long time reversal. The only really bad thing about it is the $0.50 cost of the MOSFET.

The "Cheap - and Good" protector is a version of the series protector done with cheap NPN transistors.

[The Tone God]

No which is one advantage of this design and is usually my chosen method of protection. Of course there is a downside. If an AC source is used or the diode you choose is not capable of handling the load when it blows it can go to a short condition and take other parts down.

Edit: Too slow. R.G. beat me.

Andrew

[boyersdad]

What about using a 9.1v zener from +9 to ground?

[Seljer]

What about using a 9.1v zener from +9 to ground?

thats the same deal for wrong polarity, it just protects from too high voltages as well

[boyersdad]

What about using a 9.1v zener from +9 to ground?

thats the same deal for wrong polarity, it just protects from too high voltages as well

Right, but would it drain as much or any current?

[blanik]

thanks for the reply RG, i did read your article on geo before posting i learned all i needed to form an opinion..
the mosfet sounds interesting but i need protection for really short/quick reverse polarity, like if i'm fumbling in the dark to change a battery and push it wrong side on the batt. snap for a couple of secs before realizing it's backwards... so the +9V to grnd diode sound simple an cost effective for me... i can even solder this directly to the 9V input jack without bothering finding a place on the board... and since all my DIY and commercial stuff is the same polarity (boss type) my chances of feeding reverse ploarity for a long period is very slim...

R.

[blanik]

any prefered type of diode? any type of 1N400X ? should i prefer full black diode or glassy transparent type?

R.

[R.G.]

1N400x is what is almost universally used. You want tough - rectifier style, high peak currents, not glass body signal diodes.

[blanik]

excellent!       thanks!!    a diode is wayyy cheaper than a new opamp... 

R