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I am currently using PWM and MOSFET driving like this. T1 is a gate driver transformer (GDT.) T2 generates high voltage.

enter image description here

Now I am planning to replace the SG3525 with a microcontroller which works on 5V. The PWM output will have only 5V and moreover will not have enough current to drive the primary of GDT. My system prefers the gate drive transformer itself. How can I drive this?

JRE
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UB_Roy
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    Are you using a 1:1:1 GDT? If yes, are your MOSFETs happy with Vgs=5V? – Rohat Kılıç Aug 14 '21 at 14:38
  • (*I am planning to replace the SG3525*) Sounds like your plan doesn't make a whole lot of sense. – Andy aka Aug 14 '21 at 14:43
  • @RohatKılıç currently SG3525 works on 12Volts and 1:1:1 GDT basically works there – UB_Roy Aug 14 '21 at 14:53
  • @Andyaka May I know why? "Replace" means I will change the entire PWM Circuitry. – UB_Roy Aug 14 '21 at 14:54
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    You need to explain why you are wanting to replace it given that there doesn't appear to be a great case for making that decision @UB_Roy – Andy aka Aug 14 '21 at 14:58
  • If you will have only a 5V source with the MCU-based circuit then the Vgs of the HB MOSFETs will be 5V. I don't know what MOSFETs are you using, so I'm not sure if they will be fully on with Vgs=5V. Ordinary MOSFETs may cause you some trouble with Vgs=5V if the load current is relatively high because their Rds will be relatively high for Vgs=5V even if their threshold is 4V. So, Use either a 1:2:2 GDT to have Vgs=10V (and thus, lower Rds) or use logic-level MOSFETs if you don't have a chance to replace the GDT. – Rohat Kılıç Aug 14 '21 at 15:04
  • @RohatKılıç I am not planning to Drive the MOSFETS with 5V, I am looking for a method to change the 5V outputs of MCU to 12V and Drive The GDT. I think something like a H Bridge. GDT also I can change, if needed. But that wont solve the issue as MCU pins cannot provide enough current drive to fast switch the Gate even if we use 1:2:2. ( or I think so) – UB_Roy Aug 14 '21 at 15:07
  • @Andyaka I want to add more features like current sensing and other protections plus one display. So I though If I introduce a MCU I can have more control over all operations including PWM. – UB_Roy Aug 14 '21 at 15:09
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    @UB_Roy Why not use a center-tapped transformer, ground or tie the center-tap to Vsupply, and just drive alternating ends? Fewer transistor switches, less to worry over (no shoot-through, for example.) – jonk Aug 14 '21 at 17:38
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    @jonk Yes! Seems a very good idea! Center Tap tied +12V and two ends alternatively pulled down by two transistors from MCU PWM pins. Is there any pitfalls which I am overlooking? – UB_Roy Aug 14 '21 at 17:50
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    @UB_Roy No pitfalls. It's a technique that has been used for longer than I've been alive. And the planet's population has ***quadrupled*** in that time. This used to be used in the back seat or trunk of old cars in order to generate the hundreds and sometimes thousands of volts required for vacuum tube plates in ham radio setups. It's an ancient technique. Works good. You will be happy. – jonk Aug 14 '21 at 18:02
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    @jonk Thank you! Just by adding a winding and two transistors, I don't have to worry about many otherwise popping up issues. Moreover I am free from current limits of Drive pins which I had to take care of even in 3525. This will make my GDT and MOSFET part independent of PWM circuitry. I can Plug PWM MCU signals without worrying about Voltage or current levels . I may have to change some resisters, but still convenient. – UB_Roy Aug 14 '21 at 18:20
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    @UB_Roy Like I said, you'll be happy. :) I honestly don't know why someone else didn't suggest it. Must be glaucoma-day. ;) What's your frequency of operation? – jonk Aug 14 '21 at 18:25
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    @UB_Roy Also, if you want to see how it was done *back in the day* look at [this Youtube video by Carlson](https://youtu.be/bROZ4hGisgM). Watch the whole thing. It is very educational. Also, if you want, you can jump forward to [this point in the same video](https://youtu.be/bROZ4hGisgM?t=1201) where he pulls out and repairs the key item used back then -- a vibrating relay (vibrator.) It's very interesting. And I used to use these, myself. Still have a few! – jonk Aug 14 '21 at 18:34

2 Answers2

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Since you can use a 1:2:2 GDT as stated in the comments, a simple solution would be to use a totem-pole for each MCU output:

schematic

simulate this circuit – Schematic created using CircuitLab

A totem-pole output is a simple push-pull output with high input impedance and low output impedance.

Remember that you may need AC coupling at the primary and thus DC restoration at the secondary. I didn't show them in the simplified schematic above.

Rohat Kılıç
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There are lots of driver chips like MC4426 .These chips take a low volt logic signal and put out a rail to rail swing at the supply volts of say 15VDC .The internal mosfets have low RDS on so peak drive currents in the ampere range are possible .IUf you google dual lowside mosfet driver you will have lots to choose from .

Autistic
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  • They are dual low side MOSFET drivers. But I think we have limitations to drive Gate drive transformers with more current. See this line from datasheet "They can withstand up to 500mA of reverse current (either polarity) without latching" That means we cannot drive a GDT with more than 500mA. (Please Correct me if I am wrong" – UB_Roy Aug 15 '21 at 05:03