Voltage monitor circuit (reverse polarity protection with high voltage cut-off)

I want to make a circuit which performs these tasks:1) Protect the load against reverse polarity.2) Protect the load against over voltage.Load = Raspberry piReason for this circuit - Pi is not directly being powered through the USB jack. There will be a DC jack where the users are supposed to plug in a 5V 2A power supply with circular pin. Ultimately this will be given to the micro-USB jack. This is being done because Pi is inside a casing and it's not possible to expose the micro-USB port directly.I have come up with this circuit:How I think i...Read more

P-MOSFET allowed some reverse current, L7805CV destroyed. Why?

I was experimenting with reverse voltage protection using a P-channel MOSFET. I hooked up an IRF9510PBF in the following configuration (diagram from Nick Gammon's site, will change if requested):When I hooked up the 12 V power source backwards to see what would happen, the first thing I noticed was that the output voltage (labeled LOAD) was -1 V instead of 0 V. However, it had very little current capacity—I think it put around 1.4 µA through a 470 ohm resistor. Next, I hooked up the load, a L7805CV 5V regulator, to see what would happen. There ...Read more

Reverse Polarity Protection: Is this method safe!

Consider the above circuit. The N-channel MOSFET has been used as a low side switch to provide reverse polarity protection. A capacitor charges to the 12V supply(battery) voltage and subsequently the supply terminals are reversed. Since the capacitor will hold its charge for a certain period of time, it is therefore able to keep the MOSFET Vgs well above the minimum threshold voltage of 2.8V. As such on reversal, the capacitor discharges and settles its voltage to 2.8V after which the MOSFET turns off completely thereby disconnecting the circui...Read more

Reverse polarity protection using MOSFET - what is the voltage drop after it?

I am using this schematic for reverse polarity protection of an IC (bq78412). However the same IC has an ADC that senses the source voltage and appears not to be tolerant to reverse voltage either. Since the IC is measuring the voltage with +-0.5% at 12V I assume that it would not harm if I measure the voltage after the MOSFET since according to the data sheet its Rds(on) is about 0,082 Ohm at Id = - 3A. The total current consumption of the IC is 3,2 mA. So I assume a voltage drop of 0,082*0,0032= 0,2624 mV which is way below 0,5%*12V = 60 mV.I...Read more

Reverse voltage protection circuit explanation

Considering this circuit :(The complete schematic can be found following this link - page 23)It is connected on the return path of an IC to provide reverse-voltage protection.I understand that D11 zener diode set Vgs to 7.5V when Vdd is positive (24VDC) so Q1 nMOSFET is ON and when Vdd becomes negative with respect to the supply ground, Q1 is turned OFF and disconnect the return path.But what is the D2 Schottky diode for ?...Read more

Rapidly reverse polarity of electromagnet

Please forgive my zero knowledge of electronics.I have asked my people what I thought was a simple question but I just get bogged down with endless questions which I can't answer.Expressing the situation as simply as possible.I wish to use a couple of electromagnets about 2 or 3 inches long. I wish to change the polarity of both magnets simultaneously about 20 times a second.Question: Can anyone advise what device I require?...Read more