Transistor types

Hi all I'm new to arduino and getting back to electronics and im trying to learn about transistors. I want to bu some general purpose type for general logic level use,probably something like 5v triggering voltage and can supply up to 12 volts,no more. Tried to read some datasheets and get to shit bricks...mumbo jumbo... Thank you for help!

These may help:

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&categoryName=cat_10&subCategoryName=Transistors&category=1070

http://electronicsclub.info/transistorcircuits.htm http://www.allaboutcircuits.com/vol_3/index.html http://www.electronics-tutorials.ws/transistor/tran_1.html http://www.electronics-tutorials.ws/transistor/tran_7.html

5v triggering voltage

All transistors are switched on fully when there is 0.7V applied to the base. There is no such thing as a 5V triggering transistor.

and can supply up to 12 volts,no more.

Transistors do not supply voltage. They can only switch current. You have to supply the voltage and the transistor can in effect switch it on and off. Most simple transistors can switch voltages UP TO 60V. That means they can also switch lower voltages if you supply them.

Tried to read some datasheets and get to shit bricks

Try reading this:- http://electronicsclub.info/transistorcircuits.htm

If you are looking for part number recommendations then BC337 (npn) and BC327 (pnp) are good all-rounders, capable of switching up to about 500mA. I suggest you also invest in some logic-level mosfets. IRLU8726pbf is a favourite of mine.

BC337 or 2N2222

Remember to put a 330 ohm resistor between Arduino and transistor base.

IRLU8726pbf is a favourite of mine.

Why? Is it because it can handle alot of current, has low RDS(on), has a built in snubber diode and is a logic level mosfet? Would you please give your interpretation of the graph of figure 1, page 3 of the data sheet. I think this is where it can be determined if it is a logic level mosfet. Do I read correctly that at a low operating temperature, that the mosfet if fully turned on with Vgs at 5v, when Vds is anywhere above around 2v?

  • Scotty

scottyjr:

IRLU8726pbf is a favourite of mine.

Would you please give your interpretation of the graph of figure 1, page 3 of the data sheet. I think this is where it can be determined if it is a logic level mosfet.

Either that, or ... the 'L' in the name.

I read the data sheet for the IRLU8726pbf from Newark's website for International Rectifier:

http://www.irf.com/product-info/datasheets/data/irlr8726pbf.pdf

Figure 1 confirms that, "at a low operating temperature, that the mosfet if fully turned on with Vgs at 5v, when Vds is anywhere above around 2v".

Here are my notes: The 85 amp limit is awsome. The Vt threshold voltage is less than 2.5 volts at -55 degrees C. (Fig. 10) The Reverse Transfer Capacitance is about 10% of the gate capacitance, good.

The Reverse Transfer Capacitance of 205 pF is connected with a 2150pF input capacitance to create a voltage divider. The 9% coupling of drain voltage to gate voltage is good enough for rock and roll. Some devices have 40%, which is not good. Watch that ratio and practice safe specs.

The datasheet quotes a maximum value of Rds(on) at Vgs=4.5v and Id=20A. That means it is good for switching up 20A (subject to thermal considerations) with logic level gate drive. Another reason I like it is that it costs less and takes up less space than most power mosfets, because it is in a smaller package than the usual TO220.

Grumpy_Mike:

5v triggering voltage

There is no such thing as a 5V triggering transistor.

There is if we include MOSFETs …

OK...from all your answers comes up some new Q's: 1.) If transistors switched ate 0.7v,then in order to control it with arduino i just need to write to the base leg\pin HIGH value? or is too much 5v for the base to handle? 2.) What is the difference between NPN and PNP? searched Youtube and looked at some videos-couldn't find adequate explanation and the one on Wiki is a little bit complicated for a begginer like me the one thing i do understand is the one of them is 'switched on'(=connecting the collector and emitter like a switch) when the voltage on the base is high and the second one is switched on when the voltage on the base is low

Did you look at: http://electronicsclub.info/transistorcircuits.htm http://www.allaboutcircuits.com/vol_3/index.html http://www.electronics-tutorials.ws/transistor/tran_1.html http://www.electronics-tutorials.ws/transistor/tran_7.html

1.) If transistors switched at 0.7v,then in order to control it with arduino i just need to write to the base leg\pin HIGH value? or is too much 5v for the base to handle?

npn like 2n2222
Yes. Arduino pin high to resistor 1000 ohms to base of npn transistor. Emitter grounded. Collector to load.

5v is not too much across the 1000 ohm resistor to base. Base is at about 0.8v.
Resistor has about 5.0 - 0.8 = 4.2 volts

2.) What is the difference between NPN and PNP?

npn has emitter grounded
pnp has emitter at 5 volts

npn base at 0mA for off
npn base at 1mA for on

pnp base at -0mA for off
pnp base at -1mA for on

npn collector has voltage above emitter
pnp collector has voltage below emitter

read the links

searched Youtube and looked at some videos-couldn’t find adequate explanation and the one on Wiki is a little bit complicated for a begginer like me
the one thing i do understand is the one of them is ‘switched on’(=connecting the collector and emitter like a switch) when the voltage on the base is high and the second one is switched on when the voltage on the base is low

Sorry for repeating the information in the last post but this might be a bit more palatable packaging of the facts.

1.) If transistors switched at 0.7v,then in order to control it with arduino i just need to write to the base leg\pin HIGH value? or is too much 5v for the base to handle?

A resistor between the pin and base will make it compatible. The resistor does not reduce the voltage as some beginners think, it limits the current which in turn causes a voltage to be dropped across the resistor. This is not the same thing.

2.) What is the difference between NPN and PNP?

A PNP is often called an upside down transistor. You use it to switch things on where you need a source of power, that is you switch the positive. This is called current sourcing.

By contrast an NPN transistor switches the negative, it connects the load to ground it provides a sink for the current. This is called current sinking.

Most of the time it doesn’t matter if you control something with sinking or sourcing, but occasionally it does. So normally you would use an NPN but if you mush have current sourcing you use a PNP.

Kimkash, I cannot stress enough how important it will be to you to read up on those links that LarryD gave you. There are many kinds of transistors. People generally, but not always, mean Bipolar Transistor when they say Transistor. But it is bad form not to specify, it makes it more difficult for people to help you.

For instance, a MOSFET does not require a resistor between the Arduino and its Gate. However, MOSFETs have a large Gate capacitance so if you are trying to use the PWM Analog output of an Arduino to drive it, you may find it gets hotter than you'd thought as it takes time to turn on and off.

A bipolar transistor does require a current limiting resistor from the Arduino pin to the Base lead. You do need to take Beta (current gain) into account, especially when switching larger currents. Bipolar transistor gain goes down when saturated, so with a rated Beta of 100 you might find that you need 1/20th to 1/10th the current going into the Base.

polymorph: For instance, a MOSFET does not require a resistor between the Arduino and its Gate.

Yes it does, and for the same reason as a BJT, ie. to stop more than 40mA coming out of the Arduino pin.

polymorph: Bipolar transistor gain goes down when saturated,

No?

polymorph proposed this advice: "a MOSFET does not require a resistor between the Arduino and its Gate." The following calculation was done to confirm or refute that advice: 2nF gate capacitance on MOSFET is common (2000pF)

Assume 3.6ns rise time for Arduino output

i = c dv/dt i is current from Arduino = 2.8 amps

c = 2x10^-9 F dv = 5 volts dt = 3.6x10^-9 seconds rise time

rise/fall time 3.6ns for SPI pin Atmega328P data sheet page 321

i = (2x10^-9) x 5 / (3.6x10-9) = 2.8 amp

data sheet

https://www.sparkfun.com/datasheets/Components/SMD/ATMega328.pdf

You don’t really think an Arduino can source 2.8A, do you?

Look in that PDF, Pg 340, 27.1.8 Pin Driver Strength. In that section, on Pg 341, see the graph Figure 27-24. I/O Pin Output Voltage vs. Source Current(VCC = 5 V). It only tells part of the story, but if you assume that output current sourcing is linear, then with 4.5V @ 18mA of source current, that would extrapolate to about 180mA max in the initial short-circuited state when an uncharged 2nF capacitor is connected and the output is set to High. Since this decays from 180mA (or whatever the short circuit current max is) to 0mA as the 2nF Gate capacitance charges, you’ll get a much longer rise time.

This link seems to explain it:

I should also point out that while you -can- connect many MOSFET gates directly to an Arduino output, it would be a better idea to use a driver circuit. Because the maximum rated current output of an Arduino is 40mA at any one pin, and driving into a 2nF capacitance is going to cause charge and discharge pulses significantly higher than this. Your Arduino may keep working, but that doesn’t mean it is a good idea or that it is not damaging it.

We seem to be illustrating my point nicely: Read those links that LarryD posted. There is a lot more to know about transistors than can be imparted in a few posts on a forum.