# Tag Info

31

An AC waveform consists of a (ideally, mostly) sinusoidal waveform that crosses zero voltage and current periodically. All wiring has stray inductance, and when contacts are opened the inductance will cause a rise in voltage until there's an arc across the contacts. There's plasma in the arc that makes the impedance between the contacts much lower than air, ...

29

The gate source is essentially a capacitor. So with this high resistor, it would take a very long time to charge. The MOSFET will only turn on when the gate capacitor is charged above some level (the threshold voltage), so you will have very slow switching. The reason gate drivers are often used is because they are able to quickly charge the gate capacitor (...

25

OR is a logical function - the output is high when either input is high. ORing is simply a way of saying perform the logical OR of a set of signals. In the context of power supplies, when ORing is used, the output (the device) is powered by whichever supply typically has the highest voltage. A simple power OR gate can be made by diodes in series with each ...

23

If wires were 100% reliable and had zero resistance, there would be no difference between the neutral (groundED conductor) and the safety ground (groundING conductor). Neither condition applies, however. Even if the neutral-grounded and safety-grounding conductors are connected at the breaker panel, a current-drawing appliance some distance from the box ...

23

When you open a switch, typically you get a spark. It may be a small spark you don't see, but it is still there. If there is enough current flowing at the time you open the switch, and if there are long wires or inductors connected, then that spark will turn into a full-on arc that bridges the gap and allows current to flow even though the switch is open or ...

21

Big resistors on the gate slow down the switching of the MOSFET. This is OK when you are using the MOSFET as a switch (ON-OFF) but when you're driving a motor at a 20kHZ frequency and above, switching should be fast to minimize the heat losses (switching faster means less power lost). Note that the resistor you see at the gate is not intended to only protect ...

20

This circuit is for a buck converter. If you look into the working of the buck converter, this diode is essential for the purpose of voltage conversion. What happens is that, during Toff duration, inductor current cannot change instantaneously, hence, a freewheeling path is required when the transistor inside the IC is switched off. That is why this diode ...

19

The primary purpose of soldermask is to prevent solder from going where you don't want it to go. I'm sure you're well aware of this. The problem is that the solder burns right through superglue with no trouble at all, and the vapors are nasty. If you breathe it in it could cause respiratory issues, and if you get the vapors in your eyes they will burn for ...

18

There's only any point in trying to protect a circuit with a fuse if there is enough headroom between the operating current, and the fault current, to ensure that the fuse won't blow in normal operation, and will blow under fault conditions. Unfortunately, once you have included all the tolerances, there is no current level you can choose that is ...

18

As others have said, you shouldn't have a problem as long as you double check your code. If you do get it wrong, by and large the ATMega IO pins will limit themselves to about ~80mA due to internal resistance of the MOSFETs (value found by experiment). This is not good for the chip, but as long as you don't leave it in this condition for an extended period,...

18

If you're building a few for personal use, I'd say it's not worth it unless part of your goal is to learn power supply design techniques and principles. Even then, it's much safer to get a wall wart to convert your line to, say, 12VAC for safety. If you're planning to go into production with it, you should consider your volumes first. The lion's share of ...

17

Having a power fuse blow on the circuit that is going to the engine starter can result in a serious safety issue, especially in marine systems where the inability to start the engine can mean limited or no navigation capabilities. On cars, it can mean not being able to start in an emergency situation. Some cars used to have it. I once rear ended an old ...

16

TL;DR: The ground wire is a safety feature to keep you safe in case things aren't working right. You have a neutral wire as a current conducting wire to provide power. You have the ground wire as a safe ground point for equipment with conductive (metal) housings and as a safe short circuit path for current when things go bad. Now, some background. In ...

15

It is explained in the/a datasheet of the LM2576: https://www.onsemi.com/pub/Collateral/LM2576-D.PDF In short, the circuit you mention is a buck converter, and the diode is called a catch diode. Below the excerpt:

14

As I guessed in my comment, it's a Gas Discharge Tube. As Dave Tweed says, it's an overvoltage protection device, or more precisely, it protects against high voltage spikes as opposed to long term faults. Here's an excerpt from a Littlefuse datasheet: GDTs function as switches which dissipate a minimum amount of energy and therefore handle currents ...

14

Don't. Just use one TP4056 and connect both cells in parallel after balancing them first. Don't connect batteries with more than 0.2V difference in parallel as this can risk fire and explosions (excessive charging current from one to another). This will work because Lithium cells have a wide voltage range. So when connected in parallel they will self-balance....

14

You specified a current draw of 800mA. The voltage drop is 12-5=7V thus the regulator will consume 0.8*7=5.6 Watts. That will likely burn your regulator from the board. Even if you take a different type and a heat sink, you don't want a big heat source in your car. I strongly suggest you use a ready-made 5V switching regulator. They come in a bit larger ...

14

Fuses are used for over-current protection, first please diagnose the mistake what causing the fuse to blow (like any shortages, overloading or some faults) and solve that before you replace new fuse. As long the voltage of fuse is more than the system voltage. you can use it. Since, what you are saying is right.. fuses protects the system/equipment from ...

13

For the purpose as you describe it, you need just to cover your exposed traces and re-work. This is not a "solder mask". The best and standard way is to use "conformal coating", found in electronics stores. It comes in several different flavors, acrylic, silicone, urethane, etc. Any type will serve your purpose well and much better than the super glue.

12

Crayola makes easy to use non-toxic biodegradable food safe solder mask in a variety of colors. You can find it in the toy section at most stores. I have used it for masking when wave soldering. It works great and easily comes off with a little elbow grease. Superglue, as has been mentioned can give off toxic, potentially fatal, fumes when heated.

12

It's pretty simple: The Zener diode voltage is at (or slightly above) the normal Vcc voltage. For example, a 5.6V Zener for a 5V Vcc. When Vcc is below the Zener voltage, no current flows through the diode, and the 1k resistor keeps the base of T1 low. No current flows through the collector to the emitter of the transistor. When Vcc is higher than the ...

11

The usual approach is on the AC line (inserted into your N\$93 net) before the bridge, which will protect the power supply if the bridge rectifier fails short. Assuming there is bulk capacitance after this bridge rectifier, you will need to use a slow-blow fuse so that the inrush current doesn't destroy it. If the capacitance is very large, you will want to ...

11

Voltage dividers work great if and only if all of the current that flows through R1 also flows through R2. simulate this circuit – Schematic created using CircuitLab However, as soon as another current path forms between the resistors, the divider no longer works. Since some of the current is diverted away from R2, the voltage drop changes. What's ...

11

You should be cautious but not terrified about it. Setting a pin output and driving it to the other direction will cause a lot of current to flow, but it also does not blow up in smoke immediately. You could for example power the device with current limited labotatory supply when bringing up a design so these kind of errors cause even less damage. I'd be ...

11

M1 could blow up if the Gate Source voltage is too much. Autoelectric systems are full of spikes. Place a zener between gate source of M1 to clamp the gate below the gate source rating. For example if the Vgs rating is 20VDC then a 18Volt zener would suffice. Load inductance is always present. This causes drain voltage spikes at turnoff which could exceed ...

11

Basically it's a power zener diode circuit. The zener begins turning on the BJT when sufficient voltage is across the line. The transistor takes current and the more that the line voltage tries to rise above the zener voltage (plus a Vbe drop of around 1 volt max), the more current is taken by the BJT. The BD139 can handle currents up to a few amps and that ...

11

If you understand the body diode then you should see that if you apply significant negative voltage to the input the body diode needs to block or it will pass the incorrect polarity to the output, probably destroying the circuitry it is connected to. In normal operation (positive input) the body diode is shunted by the Rds(on) channel resistance of the ...

10

Edit: Re-interpreting the value shown on the datasheet. The resistance shown is not M$\Omega$, much lower, more like 3400 ohms based on the change in the switching times with external gate resistor. This does in fact really slow the switching when the gate charge is high, such as the 1.6ms minimum off switching time with a 15V 1.5A load. The asymmetric ...

10

Protection of electronic equipment is normally defined in IEC 61000 standard. It includes protection against ESD (61000-4-2), immunity to EFT (61000-4-4), 61000-4-5 (lightening surge immunity), etc. The standard is a collective wisdom of what kind of surges are typically there, and defines several classes of equipment protection. Here is an example from ...

10

The real problem is not the unprotected USB port, the real problem is that your device puts you and your devices at risk of being connected to higher-voltage, relatively high-current sources. You can solve transient overvoltage with clamping diodes, but these won't help if you power supply is strong enough – they will just fail, and then you're in the same ...

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