Winding a Gate Drive Transformer

[MOSFET KILLER]

I have two IRFP460 N-Channel MOSFETs, I want to wire them in a halfbridge. I have a variable frequency source at 40% duty cycle with limited current. I also have FBT cores and several small ferrite toroids. I need to know how I can wind a gate drive transformer to drive these two MOSFETs.

MOSFET datasheet Here

 

[smanches]

Why do you want to drive them with transformers instead of directly? If you need isolation, and opto-isolator would probably be easier. Transformers are usually only used if you have to do LONG runs on the gate trace/line, or for certain amplifier drivers.

 

[Sceadwian]

A basic opto isolator won't allow the gate to be driven at higher than the supply voltage if that voltage isn't already supplied smanches, he'd need a photovoltaic isolator.

Something like Digi-Key - PVI5033RPBF-ND (Manufacturer - PVI5033RPBF) were designed specifically for the posters needs.

It's basically the same thing as a common optoisolator except there are a lot more diodes in series which allows for completely isolated voltage driving of the gate relative to the source lead and it will always provide the voltage relative to the source without a supply. They're a bit expensive though.

 

[smanches]

I was referring in general as to why he wants a transformer specifically, as opposed to using general opto-isolated drivers. I was basically meaning what you detailed, I just didn't detail it.

 

[Sceadwian]

Well lets wait for Mosfet Killer to respond then, I have a hunkering as you probably do that he doesn't even know what he actually needs yet.

 

[MOSFET KILLER]

I will need galvanic isolation on my gate drives to prevent the main supply from shorting out, that is why I thought GDT. An optoisolator would work but only for lower frequencies. This is to replace my induction heater which operates at about 150 kHz, out of the range of my optoisolators. I could use transformers to couple my driver circuits to my oscillator and use floating supplies to power the drivers. I also thought I could use a transformer to replace the alternating push-pull outputs of my recently exploded SG3524 by winding two secondaries of oppisite polarity. But I heard that gate drive transformers do not always work well with PWM so maybe galvanically isolated drivers are the way to go. I already have two 12V regulated power supplies built on a circuit board so all I need to do is build the drivers. Also, on another topic is there a way I could replace my blown SG3524 with discrete components. I could do PWM with a comparator and capacitor, would a 555 be any good at higher frequencies?

 

[ronsimpson]

It takes many parts to replace a SG3524.
I often use gate drive transformers. They do not work as duty cycle approaches 0 or 100%.
The galvanic isolator outputs 1 uA and will not work at 150khz. The edges should be 2 to 5 amps.
Digikey has a gate drive transformer GDE25-2. Try Coilcraft.

 

[MOSFET KILLER]

I have drawn a schematic for the drivers. T1 couples the driver to the oscillator and is clipped by diodes D1 and D2. U1 turns Q1 on which turns on Q2 and Q3 which drive the MOSFET gate. The power supplies are seperate to keep the drivers isolated. Would this drive the MOSFET gate with enough current to turn it on?

 

[ronsimpson]

Don't use LM393. Use a "gate drive IC" to replace IC+Q1-3.
or
If you have to use the LM393; the (-) input should be at 6 volts or 1/2 supply. Add two resistors.
or
Remove LM393 + Q1. Drive the base of Q2,Q3 directly from the transformer.
If you do this you will find that the two diodes are in parallel with the B-C diodes in Q2,Q3. I have used this circuit with out the diodes, just using the B-C diodes.

 

[ronsimpson]

If you want to use Q2, Q3 with out LM393 look at ZXGD3003E6. There are biger versions.
or
Look at IXDN409, IXDD409 to replace LM393 & Q1-3.

 

[MOSFET KILLER]

T1 is a homemade transformer wired with CAT-5 wire, it is not going to have the best signal, that is the reason for the 393. I will make a voltage devider for the (-) input on the LM393 with two 1K resistors. I would use a driver IC but I do not want to wait 3 weeks for E-bay and I also want to know how to do this with discrete components. I will try to drive the base of the transistors with the coupling transformer but I doubt that the signal will be good enough to drive the MOSFETs.

 

[tcmtech]

The IRF 21XX series of gate drive IC's could cure a lot of problems as well. Doing PWM through a gate drive transformer is common place in welder and plasma cutter power supplies but its not a simple process. Dedicated driver IC's are needed for the transformers and clamping circuitry is needed on the gates themselves.

 

[Madarasi]

Simple Gate Drive circuit



This simple circuit, which I downloaded some time back, works great. I have tested this at around 120kHz., with literally zero rise time / fall times. If you are using half bridge, then you would require two, though. No isolated power supplies required. 3524 outputs may not have enough drive and you need to use a transistor drive. (I had used 3825 while experimenting which have 1A totempole drivers).

 

[indulis]

Look on page 30.

https://www.electro-tech-online.com/custompdfs/2010/02/slup169.pdf