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| reverse polarity protection |
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| FrankBuss:
I'm creating a PCB for a client for a guitar amp and fuzz, see attached circuit diagram. It should be possible to power it from a 9 V battery and from an external power supply. Note that it uses -9 V and 0 V because of the PNP transistors. Here is a full example of a very similar fuzz. For reverse voltage protection I added some diodes, but how can I protect it, if the power supply is gavanically coupled to the GND of the audio input stage through the output connector? The usual power supply would have the same GND as the audio device. When plugged in the wrong way, the -9 V of the device would be GND, and the GND of the device would be +9 V. This would then short circuit to the GND of the audio device. For protecting the device and for decoupling the battery and external power supply input, I added 2 diodes. For gavanically coupled GNDs, I added the fuse, but the client doesn't like this, because the usual musician might have problems replacing it. Is there a better way to protect this path without a fuse? |
| capt bullshot:
If cost doesn't matter too much, I'd consider a normally open dual pole relay (breaking -9V and GND), closing only when all conditions are met. I'm too lazy ATM to think about it, maybe one could build a similar circuit using MOSFETs instead the relay, don't know if it's worth, since a suitable relay could cost < 1EUR. |
| FrankBuss:
Sounds a bit complicated. I think I will use just use a 100 ohm / 1 W resistor in place of the fuse. This would filter some of the noise of an external power supply as well in combination with C2. |
| Kjelt:
Maybe too simple but why not use a full Graetz bridge and only connect the output to the Vin and GND ? That way there is no chance the - and + will be reversed, only problem is the double diode drop. Also there are these thermal fuses that come back after cooling down, forgot their name, pretty expensive though IIRC. |
| Kasper:
Ti app note slva139 might be useful for this. www.ti.com › lit › slva139PDF Reverse Current/Battery Protection Circuits - Texas Instruments |
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