Would like to have this circuit upgraded to use MOSFET's

[infoman3302]

This circuit must handle 40 amps @ a maximum of 20 volts.
Thank you for any suggestions.

 

[Joe G]

add the P channel mosfets in the 12V line (source), feed the gates of the fet's with the transistors going to ground, (add a 10k pull up resistor to the fet gates) feed the fet outputs (drains) to the coils.

 

[ronv]

What do you want the circuit to do? It almost looks like a load box? In any case I think D1 is backwards.

 

[Joe G]

you're spot on ronv, the diode might let a lil' bit of the juice go straight to ground, could it be the reason for needing 40 amps????

 

[infoman3302]

ronv..... you are correct. D1 is backwards in my schematic, sorry.
Also, diode has a 40v & 20a rating. I apologize for my mistakes.
Thank you Joe G for your suggestion. If it's not too much trouble, could you post the schematic of your suggested circuit. I am a novice and need all the guidance people are willing to give.

 

[alec_t]

Can you tell us the purpose of the circuit? Is it for providing a regulated voltage/current to the coils? Or are the coils just a convenient load for testing the supply? Or are the coils motor windings? Or........?

 

[infoman3302]

Can you tell us the purpose of the circuit? Is it for providing a regulated voltage/current to the coils? Or are the coils just a convenient load for testing the supply? Or are the coils motor windings? Or........?

It is to provide current to the coils.....

 

[4pyros]

This isn't for a coil gun is it?

 

[infoman3302]

This isn't for a coil gun is it?

No......

 

[infoman3302]

Is this the correct schematic lay out as Joe G suggested?
Also, can some one suggest which MOSFET's to use for Q1 & Q2?
Thank you.

 

[alec_t]

Besides the FETs being upside-down, that isn't quite the circuit Joe suggested and it won't be suitable if you need to switch the FETs on and off rapidly. What signal are you applying to the input?

 

[infoman3302]

Besides the FETs being upside-down, that isn't quite the circuit Joe suggested and it won't be suitable if you need to switch the FETs on and off rapidly. What signal are you applying to the input?

MOSFET's upside down? Where did I go wrong? Those are P- Channel FET's right? As for Joe G's circuit, I thought I did what he said but you are the person of knowledge, not me. That's why I'm here..... to get the help I need. FET's do need to be switched on and off rapidly.

 

[Joe G]

a RANDOM picture I Google'd, input would be labeled "MCU" . also resistors and part numbers may need to be changed

 

[Joe G]

also there is a good explanation of what you may need to know about fet drivers in this artical
converter using logic level mosfet

 

[4pyros]

To run them in parallel you may need current sharing resistors.

 

[infoman3302]

I'd like to thank every one for their input on this topic........ gonna try some things and I'll post the results in the next few days.

 

[Nigel Goodwin]

Just as a matter of interest why do you consider MOSFET's an 'upgrade'?.

The original circuit is pretty naff, but that's down to poor design, not the use of bipolar devices.

 

[Joe G]

I agree w/ Nigel. Tip darlington transistors also came to my mind..

 

[Nigel Goodwin]

I agree w/ Nigel. Tip darlington transistors also came to my mind..

I wasn't my thought

My thought was PNP transistors, with the coils driven from the collectors - giving far less loss - darlingtons are high loss devices anyway, and not terribly suited to switching applications (as the collectors are joined together there's not enough drive for the output section).

To maintain the HIGH = ON switching format, simply use an NPN transistor to feed the PNP's, also giving you much better base drive. There should also be low value balancing resistors in each PNP emitter (as there should have been in the original NPN emitters).

 

[infoman3302]

More information for this circuit.........
Input will be a 1.562 khz frequency....... Vcc and input voltage will be from 12-20v

Will this work?