I would like to add small form factor OVP (Over voltage protection) circuit after my power JACK. Could you please any one help me on this, because we have similar kind of 2 adapters one is 5V and another one is 12V. So by mistaken we will connect and power-up 5Volt circuit through 12 Volt adapter. So i need to add OVP circuit.
please guide me: my idea about series resistor with 5.1V zener diode, Voltage break down is 5.1V and power peak pulse max 75Watts it will accept max 5A current
shall i implement this?
Best Answer
You could use a P-channel MOSFET as a series switch, with its gate pulled to ground by a comparator. Bypass the comparator's positive supply pin with a 0.1uF capacitor to ground. Provide a reference for the comparator's non-inverting input with a 5.6V Zener diode and current limiting resistor. Sample the DC supply at the comaparator's inverting input. The comparator will switch the MOSFET off when the input rises above ~5.6V.
This schematic is an example using half of an LM393N comparator (1), a 1N5232B Zener diode and an IRFU5305 P-channel MOSFET. The power and comparator elements of the LM393N are split into three sections in this schematic; just pay attention to the pin numbers as they relate to the 8-DIP package.
The MOSFET won't dissipate more than 260mW at 2A, so you shouldn't need a heatsink if the ambient temperature is reasonable.
If you use different components, ensure that your MOSFET's gate-source voltage (Vgs) is well above 12V, and that your comparator can operate with a supply from 5V to above 12V. There are lots of options in both through-hole and surface mount components.
MOSFET power dissipation in watts (W) equals current (I) squared times MOSFET on-resistance (Rdson): W = I x I x Rdson. Use the maximum Rdson value in the datasheet.
MOSFET junction temperature rise (Tr) without a heatsink equals power dissipation (W) times junction-to-ambient thermal resistance (RΦja): Tr = W x RΦja.
MOSFET junction temperature (Tj) equals ambient temperature (Ta) plus junction temperature rise (Tr): Tj = Ta + Tr. Keep junction temperature well below the datasheet maximum.