Hello everyone,
I have a circuit powered by a 9V adapter. I will use a voltage regulator. How can I adjust the power supply circuit to protect the PCB from overvoltage and overcurrent, such as fuses, diodes, capacitors etc.? Are there any examples?
And which step-down voltage regulator do you recommend?
Circuit ICs work with 5V & 3.3 V, and the maximum current drawn is 500mA.
Well first of all, your selections of components need to fit your supply voltage. If you have 9 Volt coming in, there should be no parts of your PCB that are not rated for this.
If you have components that are current sensitive, such as LEDs, then you need to put resistors before or behind them.
So you want to generate two different output voltages from the 9V input?
Either you find an IC that has two different output voltages, or you need two different ones with all the components necessary (capacitors, inductors and so on).
You might want to share your schematics to get further help
Lots of examples for all of them - just do a quick search on Google.
Fuses are to protect your wiring, they blow after your circuit has failed.
Diodes protect against reverse polarity (a common user error, connecting the wires the wrong way around), you can also use a pMOS for this. More efficient. At <500 mA a diode will do just fine, especially if it's before your on-board regulator so the voltage drop doesn't matter.
Capacitors are for filtering voltage spikes and dips, as are inductors, you may combine them to create a pi filter. If you are dealing with a lot of noise - especially if the source is your circuit itself - you may want to place a common mode choke in your power supply line.
Overvoltage protection: depends on what you want to protect against, exactly. High voltage spikes can be dealt with using TVS diodes or MOVs (the latter are mainly for filtering mains). Longer lasting and lower levels of overvoltage need more complex circuits, see Google for examples.
Overcurrent circuits you can also easily find on Google. Again these do not protect your circuit, if there's an overcurrent situation it usually means your circuit is at fault.
The main thing you have to ask yourself: what kind of protection does your circuit need? What likely real life scenarios are there for your product's use case that may cause issues?
For the power supply: buck converter for the 5V supply (stepping down the 9V supply); linear regulator for the 3.3V supply (stepping down the 5V supply) especially if that's <200 mA or so. A nicer solution would be to use a 5V supply, then you only need a regulator for the 3.3V.
I do it the easy way, I figured that by the time I purchased the parts, built and calibrated I had almost enough to buy a Lab Power Supply, so I did. Turns out it was the best for me, I now have several and they have saved me many times.
I don't know how that's going to protect a project from things like overvoltage (by you setting the power supply to a too high voltage), or reverse voltage (by you connecting the wires incorrectly).
By the way, considering the parts for these protection circuits cost no more than about USD 0.20 per project (for that reason I routinely add it to my designs), I'd love to know where you got a so cheap and presumably decent quality lab power supplies.
I've been using these buck converters. I built an input/output board to solder onto to the connection pads. It has locations for a fuse and double diode on the input and inductor, resistor and capacitor for filtering on the output.
Ignore the component values
With a Lab supply I have the correct voltage and a current limit to protect me from reverse voltage. Both can be set before connecting and on my units it is in bright Red numerals. You still need a power source for the buck converters and a meter to set the voltage and current, a bit more involved then when the meters are built in. Yes you can also set the buck converter for to much voltage.
The Lab Supply is for use in the Lab for testing and debug, not the vehicle. By the time the module gets in the vehicle it is working and ready to tolerate reverse power, 24V jump, temperature, etc.
I'm not sure I could secure a benchtop lab supply under the dash of a vehicle or would want to leave it powered on 24/7 outdoors in a dry-box.
Point is, a lab supply is great in the lab. However, most projects don't stay in the lab.
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