# Hi everyone, I want to know the counterpart BJT for iRF630 and iRF9630. For my school experiment.

#### iamprincejoy

Joined Aug 7, 2017
25
Just for my experiment subject.
Thank you for helping.

#### crutschow

Joined Mar 14, 2008
27,718
MOSFETs don't really have BJT counterparts, since their operational characteristics are so different.
What do you want the BJTs to do?

#### Raymond Genovese

Joined Mar 5, 2016
1,658
Oh wow, I am going to watch this topic just to learn something.

NPN and PNP counterparts for N- and P-channel mosfets? Apples and oranges?
I suppose that one would pick a common characteristic or two to at least *try* to base the counterpart claim on.
Maybe power dissipation, or maybe continuous current, e.g. - continuous drain current vs Ic?

What do you think?

#### phranzdan

Joined Aug 4, 2017
40
HI: The IRF630 is rated at 200 volts and 9 amps with an Rdson of about 0.4 ohms. The IRF9630 is rated at 200 volts and 6 amps with Rdson at 0.8 ohms max. Understanding that the drive requirements are different for bipolar versus mos, you would need to select a bipolar device with a BVceo of at least 200 volts and a 6 to 8 amp current rating. The other parameter is Rdson. Take an IRF630 switching 5 amps. The dissipation in the device would be 5 squared X .4 or about 10 watts with the device biased at 10 volts Vgs. The 200 volt Bipolar Device dissipation would depend on the Vcesat. Say we used a forced beta of 10 then the base current at 5 amps would be 500ma. I don't have my old transistor manuals, but I'm guessing the Vcesat would be about 1.5 to 2 volts. The dissipation in the collector emitter junction would be P=EI or 2 x 5.5 = 11 watts. Note that the Vcesat of BJT's gets higher as the voltage rating increases since the resistivity of the silicon increases. This just a simple case of finding a BJT with similar ratings to a Power Mosfet. We also should note that the Rdson can be reduced by using higher cell density Power Mos. Another device, the IGBT(Insulated Gate Bipolar Transistor) combines the best of both worlds with a MOS gate and a bipolar structure in the collector emitter. These are commonly used in switching applications such as switch mode power supplies and Generators. I hope this helps a little.

#### crutschow

Joined Mar 14, 2008
27,718
Without knowing what the transistors are used for, it's kind of a crapshoot as to what BJTs would work in place of those MOSFETs.

#### iamprincejoy

Joined Aug 7, 2017
25
MOSFETs don't really have BJT counterparts, since their operational characteristics are so different.
What do you want the BJTs to do?

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#### iamprincejoy

Joined Aug 7, 2017
25
Thats the schematic diagram for our experiment, my professor, he wants to replace the mosfet with bjt.
As I observe in experiment the irf630 is for positive cycle sine wave and the irf9630 is for negative cycle sine wave.

#### GopherT

Joined Nov 23, 2012
8,012
Thats the schematic diagram for our experiment, my professor, he wants to replace the mosfet with bjt.
As I observe in experiment the irf630 is for positive cycle sine wave and the irf9630 is for negative cycle sine wave.
That amplifier is a mess if intended for audio signals.
Mosfets don't work well in that application - especially without your feedback loop going all the way from the op amp to the mosfet output (which will require more changes).

What are you trying to do? Simply amplify an audio signal?

#### Jazz2C

Joined May 27, 2016
52
Just for my experiment subject.
Thank you for helping.
There aren't counterparts of field effect transistors among junction transistors! They're two entirely different semiconductor topologies! It looks to me like your assignment is to design an equivalent circuit around BJTs which isn't the same as the BJTs being equivalent to the FETs!

That amplifier is a mess if intended for audio signals.
Mosfets don't work well in that application - especially without your feedback loop going all the way from the op amp to the mosfet output (which will require more changes).
Tnx for that! I knew it couldn't be just me!

#### iamprincejoy

Joined Aug 7, 2017
25
That amplifier is a mess if intended for audio signals.
Mosfets don't work well in that application - especially without your feedback loop going all the way from the op amp to the mosfet output (which will require more changes).

What are you trying to do? Simply amplify an audio signal?
Yes sir, To amplify audio signal, in our experiment we are using audio generator for our audio input.
My professor want to replace the mosfet with BJT but the op amp is still there.
And he said that ones we have replace a BJT we need to prove the computation.

#### GopherT

Joined Nov 23, 2012
8,012
Yes sir, To amplify audio signal, in our experiment we are using audio generator for our audio input.
My professor want to replace the mosfet with BJT but the op amp is still there.
And he said that ones we have replace a BJT we need to prove the computation.
You say he is a professor. I assume he is not a professor of electrical engineering. What kind of research?

#### iamprincejoy

Joined Aug 7, 2017
25
You say he is a professor. I assume he is not a professor of electrical engineering. What kind of research?
what he want is to replace the circuit with transistorize.
He let us to research for the circuit.

Last edited by a moderator:

#### GopherT

Joined Nov 23, 2012
8,012
Start over and try something like this. It is not perfect but it is simple.

Also, my schematic does not show the +/-12v to power the op amp.

Also, the bjt need some biasing and help with cross over distortion, hence the diodes and resistors.

Also, I pulled the feedback loop all the way to the output speaker to improve performance.

#### iamprincejoy

Joined Aug 7, 2017
25
Start over and try something like this. It is not perfect but it is simple.

Also, my schematic does not show the +/-12v to power the op amp.

Also, the bjt need some biasing and help with cross over distortion, hence the diodes and resistors.

Also, I pulled the feedback loop all the way to the output speaker to improve performance.

View attachment 134058
What is the value for transistor and diode sir?

#### GopherT

Joined Nov 23, 2012
8,012
What is the value for transistor and diode sir?
MJF122 and MJF127 - many other Darlington BJT with gain over 1000 and more than 1 amp collector current.

1N4148 or 1N914 - many others are possible.

#### Bordodynov

Joined May 20, 2015
2,906
If Darlington's transistors are used, then it is probably better to use four diodes, rather than two diodes.

#### GopherT

Joined Nov 23, 2012
8,012
If Darlington's transistors are used, then it is probably better to use four diodes, rather than two diodes.
Yes
I realized that when i answered the OP's question but work got in the way.

NOTE: use two diodes in series for each diode shown in schematic.

#### Jazz2C

Joined May 27, 2016
52
what he want is to replace the circuit with transistorize.
He let us to research for the circuit.
Your prof gave you a bogus starting point! He's either totally inept or he's testing your powers of observation I've met plenty of each so beware!

#### JoeJester

Joined Apr 26, 2005
4,390
Your prof gave you a bogus starting point! He's either totally inept or he's testing your powers of observation I've met plenty of each so beware!
I think he was just plain LAZY and put in two MOSFETS where there were transistors in the original schematic.