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Author Topic: I have a problem with the LULU  (Read 3016 times)

Offline Mr.ArchVile

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I have a problem with the LULU
« on: October 22, 2016, 0325 UTC »
The MOSFET is getting hot when I connect direct DC to modulation PIN of the LuLu Board.

But when I used a Cap in series with the Mod pin, it stay cool.

I think though this is a trade off in power.

I included a drawing.

Offline Stretchyman

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Re: I have a problem with the LULU
« Reply #1 on: October 26, 2016, 2115 UTC »
Ok we have resolved this problem off board.

An antenna of the correct impedance must be connected to any transmitter before power is applied. That or a 50 ohm dummy load.

There is no need to connect a capacitor as shown as that will simply block DC and only pass current when modulation is applied. To be honest I have no idea how that would turn out but I suspect not well!

However, Thanks for posting this as it's clear that I need to provide more instructions with my kits.

I will be making a video in the near future!

Hope that this will explain everything!

Hopefully!

'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline Mr.ArchVile

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Re: I have a problem with the LULU
« Reply #2 on: October 26, 2016, 2354 UTC »
Stretchy should the mosfet give off any heat at all?


Offline Stretchyman

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Re: I have a problem with the LULU
« Reply #3 on: October 27, 2016, 1225 UTC »
Yes, of course but it's reasonably efficient as it's class E. Worst case is 85% efficiency so then 15% loss, so at 10W o/p that's 1W5 of heat and 4 times that on mod peaks. It does NOT need a Massive heatsink, just mount in a metal case and bolt to that with the supplied insulating kit.

The IRF510 (o/p FET) is easy to drive but has a fairly pants on resistance of 0R5. This is what causes the loss, as if it was 0R it would be the perfect switch.

Class E tries to be the perfect switch as it's either on or off, so S/C or O/C (Short/Open Circuit). As long as you switch quick and have a low on resistance and you have a efficient amp.

An amplifier is just a switch, that's all!

Sooper simple once you get your head round a few basic principles!

Wierd I know but this is RF at its most basic and efficient of modes, you simply cannot beat class E, it's the Biz. It truly is!
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)