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NPN to PNP control? Answered

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So as I get into this project the circuit keeps building and now I once again have another problem that I can't figure out. As the title hopefully suggests I am using a NPN PN2222A trans. to control a PNP 2N3906 The idea was to use the 5v from a Ardinuo UNO to control a 12v. Currently I am testing with a 9v I had on hand. I thought it would pretty straight forward but every time I supply power to the NPN it creates the short needed to turn on the LED, but once I cut the power the LED stays on until I create another short (using a probe) uphill of the NPN. The only thing I can think of is that the LED doesn't the resistance needed for the power to re-saturated the PNP. Any thoughts?
I will admit  haven't done any of the math needed yet for the resistors.

Also can someone send me a link to the programs you use for drawing the layouts so I can move past MSpaint?

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icengBest Answer (author)2015-10-08

The way to start if you don't know the relay current is to turn the PNP as much as it can be. The spec sheet indicates 100 ma with a gain of 30. That means the base current needs 100/30 =10/3 = 3.34 ma I'm going to, round up to 5 ma. Then find a Resistor that can allow 5 ma at 12-o.3-o.3 = 11.4v

The formula for R = Vr / I = 11.4V / .005A = 2280 ohms round to a real value = 2.2K

NEXT,

Now lets turn the NPN fully on.. The spec sheet indicates 150 ma with a gain of 50. That means the base current needs 150/50 =15/5 = 3 ma again round up to 5 ma. Then find a Resistor that can allow 5 ma at 4 V ......

R = Vr / I = 4 V / .005 = 800 ohms nearest real value is 750 ohms.

Finally what is the 2.2k Resistor Power = V x I =12 V x .005 A .06 watt

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iceng (author)iceng2015-10-09

Thanks for the best answer.

Wanted to show you a simpler drive for your coil.

Regards,

A

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steveastrouk (author)iceng2015-10-10

Some micros reset with all their outputs high, like the 8052, an NPN/PNP circuit can have the advantage that its off when the input is high.

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Jayccob (author)iceng2015-10-08

ok, this looks like what I am working on. I just got the coils so I will be testing this out, Thanks.

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Jayccob (author)2015-10-06

**Edit**

I finally came across Yenka for th diagram part of the question.

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iceng (author)2015-10-20

IF you are smoking the 2N3906 PNP there are two possible causes.

A] The relay is using more current then the PNP is capable of supplying.

B] Or the reactive diode is wired backwards.

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steveastrouk (author)2015-10-07

the resistors on the NPN collector are the wrong way round, and the 10k should be more like 2.2k

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iceng (author)2015-10-06
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iceng (author)iceng2015-10-06

And a simpler voltage driver for you.

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iceng (author)iceng2015-10-06

The math to size the LED resistor is

R = V / I = (9 - 3.3 - 0.3) / .02 = 5.4 / .02 = 270 ohm

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Jayccob (author)iceng2015-10-06

I am new to drawing the diagrams, so in the real circuit it is facing the right way, and I need to be able to control the LED (which is a place holder for a magnetic coil, easier to check if it is working with the LED) uphill of the LED. I need to be controlling the ground and power of a grid, but I am using an Ardunio and need to pretty much step-up the 5v to control the PNP. I don't understand why this set-up isn't working.

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