The AM Forum

Hello, Been working on the rf deck a couple of nights now, and was going to make a low voltage test. When I connected 12v to the driver vcc bus,  my lab psu pegged the needle at almost 5 amps and dropped the voltage to about 1,5v. Number of 414's is 2, and that is without drive. Checked the vcc bus for shorts to ground but there are none. I'll have to admit that these are 414's off ebay, fakes maybe?

Is there a short on the output of the IXDD?  That could do it.

Normally, when not actually switching the IXDD414/614 draws virtually no current at all.

...or does the input pin not have a resistor to ground?  I'm guessing that would make the output go high continuously and draw lots of current.  I think I made that mistake once somewhere along the way. 

Jon

Okay, thanks for the tips. Had of course forgotten the resistors at the inputs, added those this morning, but still no improvement in terms of no signal current draw. Tried lifting the output pins from the gate buses, no change. Lifting the EN pins from the driver vcc bus made the excessive current draw stop (as it should be i suppose), and by driving the inputs high, the devices start to conduct... Either I´m missing something very easy, or these devices are some fake crap. Probably something easy, that wouldn´t be the first time ;)

Hmmm.. you could have bad devices .... but... a few checks first.

There should be a resistor (around 200 to 300 ohms) in SERIES with each input pin of both of your IXDD414s.  This helps stop parasitics.  The inputs should be pulled low with no input.  A resistor to ground (ahead of the series resistor which should be the last thing in the circuit) may be necessary as well and is recommended unless the input is absolutely pulled low with no input.

Have you put a scope on the ixdd414s just to make sure there isn't some type of oscillation taking place?  Probably a long shot, but worth a try.  If there is any input at all, particularly at a high frequency, you can see lots of current, depending on the frequency of course.

Let us know!

Regards,  Steve

Oh the other thing I notice is that you only have 2 cores in your transformer.  This may very well be inadequate.  4 cores may be OK - you might have to use 2 turns in the primary - you'll have to measure or figure the inductance relative to the output impedance of the 2 MOSFETs in parallel.

Thanks Steve, will try that. As for the output transformer, that's just one of them, installed the other after picture was taken. Hopefully, those will be enough with 100w carrier

You may need 4 cores PER module just to get enough inductance if nothing else.  It may be that 2 turns may be necessary.

Please replace them with something NOT from ebay!

I looked just now, and only see two sellers.


"Polida2008" , is probably one of the top 'fake parts' sellers on ebay.


And "Janeh2100" is pretty likely selling fakes as well.

Ha, mine was from "janeh2100", gave up on those and ordered a couple of TC4452's ( was in stock here in sweden) from a well known supplier. I'll let you know how it turns out.

Well if you are going to change drivers anyway you might consider using NCP81074 drivers. They have rise and fall times of 4ns vice 22ns for the TC4452, and are inexpensive, use 1 per FET for best results. And while you are at it get some C3M0280090D SiC FETs also, 150pf gate easy to drive, very fast and inexpensive.  Speed really matters for best performance and efficiency.  Happy building.

73s  Nigel

If you really give up......

I've still got a couple tubes of them.

Actually I probably only have a few IXDD414, and a large quantity of IXDD614 ( same thing )

So let me know if you need some....

Yes. Got it to generate rf from one phase of the transmitter with a very weak psu and loads of clipleads, they all get warm and cosy :) The TC drivers did the trick, Now on to a sturdier 24v psu to try the modulator and a more permanent deck to house the thing, then on to the final 80v psu :)

I Have the same problem with current and getting HOT, i use IXDD NOT from Ebay. I found out that MOSFET gate capacitance to which IXDD drive is 3500 pf. Maybe its fake MOSFET.

I agree with statement to not use fake components on Switcher, you will not get the power efficiency you are expecting.

73s Agus