# Tag Info

49

When a channel exists in a MOSFET, current can flow from drain to source or from source to drain - it's a function of how the device is connected in the circuit. The conduction channel has no intrinsic polarity - it's kind of like a resistor in that regard. The intrinsic body diode inside the MOSFET is in parallel with the conduction channel, however. When ...

37

The physical size of a capacitor is a function of the thickness of the dielectric (among other things). Early on, it was discovered that the oxides of certain metals (aluminum and tantalum in particular) made good dielectrics, and could be made very thin through a chemical process — orders of magnitude thinner than other dielectrics such as waxed/...

34

Below is the pinout for the receptacle: GND TX1+ TX1- Vbus CC1 D+ D- SBU1 Vbus RX2- RX2+ GND | | | | | | | | | | | | =+====+====+====+====+====+====+====+====+====+====+====+= | | | | | | | | | | | | GND RX1+ RX1- Vbus SBU2 D- D+ CC2 Vbus TX2- TX2+ GND You will note that all ...

27

This is a very handy reverse polarity protection scheme. A P channel MOSFET turns on when $V_{gs}$ is negative, probably starting around -3V to -5V. When power is switched on, $V_{gs}=0V$. This is where the parasitic diode drawn across the MOSFET in the datasheet comes into play (drawn for explanation purposes only, do not put a diode between the drain ...

27

Yes it does conduct in either direction. Due to the body diode, most discrete MOSFETs cannot block in the reverse direction, but the channel will conduct in either direction when the gate is biased "on". If you want to conduct and block in both directions you need two MOSFETs in series. MOSFETs used as near-perfect rectifiers are usually used in the ...

26

Relax... It will work just fine. Make sure to orient the positive terminal towards the input pin of the regulator (pin #1). To be extra sure, use two in parallel (since you have them anyway!) to reduce the equivalent series resistance (ESR). That's just a precaution since I haven't read your datasheet and electrolytic types can be higher ESR than ceramics....

24

Two mnemonic technique I'll mention. Both technique I've learnt from someone else, many-years ago. We can easily remember, anode is abbreviated as A, and Cathode as K. That is standard, and easy to remember. Now , Write a K Now, just fill in the blanks to make it a diode. Now , the side of diode, where K was drawn, is Cathode (K). By default, the ...

24

This image: Is just a drawing, it has no meaning. It does not represent the radiation pattern of an antenna in any way ! Basically all antennas radiate (and receive) the EM waves in all directions. However, depending on the design it might not radiate and receive in some direction very well but it might do so in a different direction very well. Those are ...

19

Can I use a non-polarized capacitor with the same voltage and capacitance instead of these polarizing capacitors? Electrically speaking, non-polarized capacitor is always better than a polarized one. Yes, you can always replace with a non-polarized capacitor with exactly same rating. But there is an assumption hidden here: Provided you can find one that's ...

18

One other answer that nobody else has mentioned is this: If you power a circuit through a bridge rectifier, then the entire circuit must be allowed to "float" with respect to any other "ground" in the system. If you were to connect the negative output of the bridge to "system ground" and then hook up the "AC" inputs the wrong way, you'd short out the power ...

17

Conventional current flows from Drain to Source in an N Channel MOSFET. The arrow shows body diode direction in a MOSFET with a parsitic diode between source and drain via the substrate. This diode is missing in silicon on saphire. 2a is a JFet so different topology. 2d is a MOSFET with no body diode. I've never seen one ...

17

There is no reason why a DC polarity reversal should take place, and the warranty can basically blame it on the user. If the device is battery powered, the use of a standard, convention-adhering battery holder with clear markings should prevent such a thing from ever happening. Even users who don't look at markings are trained to put the flat part of an AA ...

16

I just measured a Lithium battery with unknown polarity with a digital multimeter and got the following measurement. The same results should apply for other DC sources: I hypothesized that the negative result may have meant that I'd attached the positive (red) lead of the multimeter to the negative lead of the battery. To confirm this hypothesis I flipped ...

16

A NPN transistor basically is a stack of three differently doped areas of a semiconductor. The first is N-doped, the middle P-doped and the last N-doped. So yes, on the first sight, you can swap collector and emitter, and the transistor might still work. But there's more magic: A real transistor is optimized to fulfill its specs when connected correctly, i....

16

Since the product you purchased has no background information, you can't be certain. However, the convention for these stacked-disk type capacitors is polarity mark points to negative lead. This is the same as is the convention with conventional electrolytic capacitors. For example, the Eaton KR-5R5V474-R: Has its datasheet show: Similarly, for the ...

14

The main problem with a diode bridge is the fact that you always have two diodes in series with your circuit, and this creates a voltage drop of about 1.4 V between the power source and the load. The power loss is simply this voltage drop multiplied by the load current. It also means that you cannot connect the negative side of the load, which you might ...

13

The bigger problem you're likely to run into is operation under forward bias conditions. Schottky diodes still have a voltage drop under forward bias, say 0.25V. That means at 100mA, you're dissipating 25mW of power. Better than a standard silicon diode, but not great especially for a battery constrained device. A better way to get reverse bias protection ...

13

The main reason is efficiency. The diodes have a fixed voltage drop, that is a property of semiconductors. As the current flowing through the diodes starts to increase, an proportional amount of power is wasted as heat. See this answer for a more efficient reverse polarity protection scheme using a P channel MOSFET.

12

In the case of the 7805, which is unconditionally stable, the type and value of the capacitors is not very important- as the note says, you can leave them out entirely and it will 'work' and will not oscillate. It will work better with the minimum capacitances shown and will be happy with much bigger caps (47uF on the input and 1uF-10uF on the output- ...

11

I'm assuming the type of circuit you are thinking of is this: - For use on your battery powered circuit I see little to say against it. A couple of things though; you need to pick a FET with low $V_{GS(threshold)}$ so that the device is still offering a tiny volt drop at low battery voltages AND you'll need a FET with low $R_{DS(on)}$ so that at 30mA (...

11

The outer cylinder is negative with the inner surface being positive. The tip connects to a Maxim One-Wire memory in the power supply that is read by the computer to obtain information such as power supply capability, serial number etc. Be VERY careful if you probe the cable, if you accidentally short the centre pin to the inner cylinder it may destroy the ...

10

A TEC is polarized in the sense that how it is connected matters. If you want to be able to heat and cool an element then a full Hbridge will work. This will allow you to pump current both directions across a TEC's terminals. If you apply a positive voltage to a TEC in one polarization then side A will get warm and side B will cool. If you then reverse ...

9

If you want your circuit to be tolerant of over-voltage, you will have to specify up to which voltage, because your protection circuit must be built to withstand that voltage. If you can afford the drop a diode bridge is a sure way to be polarity independent. You can eliminate the drop by using a relay. For over-current you will have to decide what to do ...

9

Note that in case (a) the ratio of the currents is negative while in (b) it is positive but the secondary current arrows are reversed. They both, effectively, say the same thing. I've never seen it expressed as in (a) but I can see that it may make some sense to present an ideal transformer with current in from both sides as neither side is then assumed to ...

9

It really depends on the kind of antenna. Google will probably answer this with pictures better than I will (Google "antenna radiation pattern"). You will distinguish in shape of radiation mainly 2 kinds of antenna: Directional: They radiate most of its energy in one direction (front) , some of it in the opposite direction (back) and a little portion of ...

9

Murata has a site specifically about that "polarization" mark. It isn't so much polarization as that the chip its self is in some way asymmetrical so that it changes its electrical properties depending on how it is mounted. Depending on how you place those parts, the effective value of the inductor may go up or down a bit. Presumably, you can place an ...

8

Use of electrolytic caps makes about no sens for Ci1 and Ci2 and only for Co if your Vcc is hundreds of volts. ie the leakage characteristics of an ecap will trash any precision you may hope for (and quite a lot that you don't hope for.) And, 0.1 uF is such a small value for an ecap that you probably need a special licence these days to buy one, if anyone ...

8

It is entirely per component manufacturer, and when the PCB is manufactured some companies will ask that component placement overlays are given with designators are provided and polarity marks for all polarized components are shown. It's also a good idea to make a couple of test boards and hand solder and get familiar with the components to identify this ...

8

Yes, they have polarity and it has to be right to work- the output needs to be biased positive with respect to the ground terminal. The ground/GND terminal should be common with the case, so you can check polarity with a multimeter. Here, from a Panasonic Datasheet, is a typical arrangement: The two diagrams you show are equivalent, one is just drawn ...

8

This question has gone from a 'simple project query' to a good example in both question asking and design, by the addition of key information buried in added comments. The added-in-comments advice that This is for use with a 2S LiPo battery, and It is for use with a small robot is of utterly immense relevance to the question and to the answer and should ...

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