Open the (mosfet) gate!

When used in the same configuration, both NPN and PNP will invert the signal. Inversion is a function of circuit topology. A common emitter circuit inverts. The common base and common collector circuits do not invert.

Ok thanks. I'll look into the common collector circuit then.

Michael

Just drive it with the Arduino output. That should be fine.

George H.

The common collector configuration provides no voltage gain, only current gain. Will that work for you?

The common emitter configuration provides no current gain, but provides voltage gain.

The bottom line is driving MOSFETs has been done before and optimized. Why reinvent the wheel?

Ah. That explains a lot. No.

To make it fun, and to learn something new.

I suppose I'll try using the inverting common emitter and just update my Arduino code with analogWrite( 255 - value ).

Thanks,

Michael

...

That's what I'm doing now, with an IRLZ34N.

Yeah, perhaps adding a PN2222 to amplify the voltage will introduce more losses than the Rds,on loss I'm taking by operating at just 5V (below Vgs,max).

I found this. Pretty. $0.57 for one, Rds,on = 6.2 mOhm (~10 mOhm at 5v).

Michael

That is certainly a valid reason.

I'm a bit confused. Is this a discrete control or a proportional control? What exactly is this controlling?

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It's controlling a coolant pump motor. If I look over at the thermometer a nd the temperature is too high, I type say for instance a "6" on my laptop, and it sends a 60% PWM duty cycle to the pump motor to send cooling water. It's laughable for now, but it took me a year to get the dang thing built , and it works for now. Someday I'll get around to getting a thermistor (m aybe from the car's coolant sensor) and installing it, and getting some PID control in there. Someday.

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Where does the analog output come in?

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Does this clarify?

Michael

Not really. If you are driving this with a PWM signal, that is just on or off with variable timing. That would normally be driven by writing a one or a zero to an I/O pin. Writing an integer to a DAC gives signal with many values that will turn the drive on to a range of strengths which is pretty much the opposite of PWM. Or are you calculating a value of 0 or 255 and nothing in between to drive the DAC?

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Oh, I guess the Arduino is unique then.

Here's a description of analogWrite.

Michael

No, it's not unique, I'm just not familiar with the libraries for the Arduino. This one is called "analog" when it is actually PWM. I expect it uses PWM hardware built into the MCU chip you are using. There is no DAC, it is a counter/timer instead.

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To get a PWM frequency of greater than ~500 Hz, I might have to use these f unctions anyway :p

Michael

I can't imagine a PWM timer would only work up to 500 Hz. Rather than relying on canned I/O routines, I suggest you read the data sheet for your device and program the PWM counter directly. I think the library code is leaving out a *lot* of capability.

What are the source/sink current specs on the Arduino output pin? ...Jim Thompson

It looks like 20 mA per pin. The Arduino Uno that I'm using uses an ATmega328p.

Michael

I don't think that is the relevant spec. That number if a guaranteed spec for continuous operation. To determine the rise/fall time of the gate voltage you need to know the *actual* current over the range of voltage as the gate capacitance charges. They may have a curve showing this, but it won't be a single number.