# Function generator transistor testing

#### Nubz

Joined Apr 12, 2015
8
My function generator outputs around 10mA @ 4.7V max , I would like to drive some transistors some bipolar and some mosfets with it for testing purposes, what is the best way to amplify the signal. Using single transistor or darlington or maby something else? In other words I need more current , and more voltage for mosfets.

#### ScottWang

Joined Aug 23, 2012
7,238
Using totem pole bjt driver, you can use +V, 0V or +V, 0V, -V.
You can also add a pot to adjust the input voltage level.

You can provide the voltage for totem pole bjt driver as +6V, 0V or +6V, 0V, -6V, or +9V, 0V, or +9V, 0V, -9V.

#### crutschow

Joined Mar 14, 2008
30,080
What are the waveforms and their maximum frequency?

#### Nubz

Joined Apr 12, 2015
8
Using totem pole bjt driver, you can use +V, 0V or +V, 0V, -V.
You can also add a pot to adjust the input voltage level.

You can provide the voltage for totem pole bjt driver as +6V, 0V or +6V, 0V, -6V, or +9V, 0V, or +9V, 0V, -9V.
Interesting, what transistors should I use for such a low current (10mA). I understand I need a pnp and an npn bjt.

What are the waveforms and their maximum frequency?
Square, sine and dc is what I am interested in, max frequency up to 5Mhz

#### ScottWang

Joined Aug 23, 2012
7,238
Interesting, what transistors should I use for such a low current (10mA). I understand I need a pnp and an npn bjt.
2N3904(NPN) and 2N3906(PNP).

#### upand_at_them

Joined May 15, 2010
905
So you're going to make him deal with crossover distortion?

#### ScottWang

Joined Aug 23, 2012
7,238
So you're going to make him deal with crossover distortion?
I just thought the TS might be want to using it with square wave to do the test, if he doesn't then maybe he can using LM380 or LM386.

#### upand_at_them

Joined May 15, 2010
905
How about an LM6181 or LM7171?

Last edited:

#### ian field

Joined Oct 27, 2012
6,536
So you're going to make him deal with crossover distortion?
I've seen some op-amp designs that directly drive a complementary-symetry pair with the bases tied together, crossover seems adequately reduced by including the transistor pair in the NFB loop to make an over all voltage follower.

The clever bit is finding an op-amp with bandwidth to match the function generator.

#### ScottWang

Joined Aug 23, 2012
7,238
How about an LM6181 or LM7171?
They are designed for high frequency as video amp and higher load as 50-Ω or 75-Ω, if the function generator is a AF as 20Hz ~20KHz then these two chips is not a appropriate amp.

LM386 - LM386 Low Voltage Audio Power Amplifier.
LM6181 - LM6181 100 mA, 100 MHz Current Feedback Amplifier.
LM7171 - LM7171 Very High Speed, High Output Current, Voltage Feedback Amplifier.

#### ian field

Joined Oct 27, 2012
6,536
They are designed for high frequency as video amp and higher load as 50-Ω or 75-Ω, if the function generator is a AF as 20Hz ~20KHz then these two chips is not a appropriate amp.

LM386 - LM386 Low Voltage Audio Power Amplifier.
LM6181 - LM6181 100 mA, 100 MHz Current Feedback Amplifier.
LM7171 - LM7171 Very High Speed, High Output Current, Voltage Feedback Amplifier.
The LM386 has been widely dubbed; "The cockroach of audio amplifiers" - they're fairly noisy.

#### Nubz

Joined Apr 12, 2015
8
Thank you all, I am grateful for the much needed advice.

#### ScottWang

Joined Aug 23, 2012
7,238
The LM386 has been widely dubbed; "The cockroach of audio amplifiers" - they're fairly noisy.
Since the cockroach can be live longer ...
If using it for audio sine wave with 4.7 Vin then it's ok, not use it as 0.2V.

#### ScottWang

Joined Aug 23, 2012
7,238
If you using the amplifier to test the bjt and mosfet as switch function, then maybe you just need +V, 0V totem pole bjt driver, the +V as 12V, 18V, 24V.