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Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
I am sure everyone is sick of these types of questions but I just can not get a good gate drive transformer. I got the Fair-Rite 5977006401 Type 77 core from easternvoltageresearch (who I am very grateful for) but after trying out the new core it still results in the same thing, the chip still gets hot.
I am using this circuit still , at one point I tried using a BJT buffer stage but it made audio modulation sound bad but the chip stayed cool.
I have some UCC37321's and UCC37322's lying around but I am not sure how to correctly connect them to the circuit.
Below is the transformer I have made out of the core, it uses insulated bell wire in a tri-filier configuration. 12 turns and 1:1:1. I have used electrical tape to make sure it is tightly pressed against the core to help reduce leakage inductance.
Does anyone know why it is drawing so much idle current? 80mA @50khz. And would those UCC chips be a good choice as a buffer stage? Also the duty cycle of the chip reads around 45%, is that bad?
Thanks and I apologise as this topic has been discussed to death.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Steve Conner wrote ...
Is the 80mA reading with the MOSFETs connected to the GDT secondaries? If so it seems reasonable.
This is with no MOSFET's connected, just to the chip outputs via 1uF capacitor. It was taken with my multimeter measuring the AC current of the GDt primary coil.
But regardless of how accurate my meter is the chip still gets hot.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
That ic is rated for 1 watt. How fast are you driving it and what is the gate capacitance? And voltage for that matter. The ka3525 is only rated for 500mA. It would be really easy to overheat it in this application.
Use the ic to give a high and low signal to feed into the ucc's. I have count that that line of chips is just bout indestructible if you don't mistreat them(dc blocking cap and maybe a resistor). Thy are extremely simple chips to hook up. Just look at the data sheet.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
ben123324 wrote ...
That ic is rated for 1 watt. How fast are you driving it and what is the gate capacitance? And voltage for that matter. The ka3525 is only rated for 500mA. It would be really easy to overheat it in this application.
Use the ic to give a high and low signal to feed into the ucc's. I have count that that line of chips is just bout indestructible if you don't mistreat them(dc blocking cap and maybe a resistor). Thy are extremely simple chips to hook up. Just look at the data sheet.
The high idle current draw happens without the mosfets even connected though.
I had a look in the datasheet for the UCC3732x's but it does not show how to connect the two together which is why I am asking here.
Registered Member #4146
Joined: Tue Oct 18 2011, 02:01AM
Location: Wisconsin, U.S.A
Posts: 56
Since the ka3525 looks to have inverting outputs you would need 2 noninverting ucc's as in 2 ucc37321's and you can connect them using this schematic as a reference just remember to use 2 of the same ucc and you should be good to go
edit: Make sure instead of connecting the inputs of the chips together as one like shown you just run 1 output of the ka3525 into each ic pin 2 and you can leave pin 3 disconnected
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
HB wrote ...
Since the ka3525 looks to have inverting outputs you would need 2 noninverting ucc's as in 2 ucc37321's and you can connect them using this schematic as a reference just remember to use 2 of the same ucc and you should be good to go
edit: Make sure instead of connecting the inputs of the chips together as one like shown you just run 1 output of the ka3525 into each ic pin 2 and you can leave pin 3 disconnected
So something like this? (BTW the UCC37322's are the non-inverting ones. I only have the plastic DIP package ones.
Can they use the same 15v supply as the chip or do they need a separate supply? and does it matter if I use a 1uF DC blocking capacitor or does it need to be a smaller 0.1uF in this setup?
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
HB wrote ...
Yep that should work and sorry for the misinformation about the non inverting ones to early in the day for me to think clearly yet lol.
Haha no problem, thanks I will give it a go. Just regarding the capacitors that go on the chips, it says to use ceramic but I don't have any of that size. Can I use film caps instead or will it cause problems? and it says to use a 0.1uF DC blocking cap in series with the primary coil, I currently have a 1uF in there. Is that too large for the chips to handle?
Thanks, and hopefully I don't end up blowing up any UCC chips this time.
Registered Member #4146
Joined: Tue Oct 18 2011, 02:01AM
Location: Wisconsin, U.S.A
Posts: 56
I'm not 100% sure on the decoupling caps i used tantalum caps but i have had decent success with film on some projects. All i can say is give it a go. As far as the DC blocking cap i don't see why the 1uf wouldn't work, again trial and error if anything it will be a learning experience.
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Another half-bridge gate drive transformer problem
