AXBB charge pump fault

[driftspin]

Just a quick update...

John repaired the AXBB for me by replacing the faulty Fet. It's all back up and running now. Cheers guys and especially John.

Sent from my SM-G920F using Tapatalk

Good to hear you got it fixed.

Do you know what broke it?

Grtz Bert



Verstuurd vanaf mijn SM-A320FL met Tapatalk

[Voicecoil]

If the FET blew due to back EMF from the relay coil, then it's a bit naughty as the AXBB-E manual shows a direct connection with no added clamp diode Funny, I was just about to email Balazs to ask whether such diodes were included on the board, I'll let you know what he says.

[john swift]

It is not easy to tell what the problem was

a case of no fault found that could of damaged the FET

As the relay worked when the wire from the AXBB output was connected to the -24V supply

you can only suspect either there was an intermittent short connecting the +24V supply to the AXBB output
or
an intermittent open circuit that generated a sustained back emf that over stressed the diode in side of the NTR5198NL-D FET

or may be it was a faulty FET

John

PS

the diode added across the relay coil and a 27ohm resistor in series with the relay coil
will help to protect the AXBB output

the resistor limiting the current if coil is short circuited
and the diode clamping the back emf when the relay is switched off

[john swift]

Hi Voicecoil

The diagram in post 40 shows the signal path through the circuit after the HCPL-2631 opto isolators

the only diode is within the NTR5198NL-D FET

hence my comment in post 30

“Its a pity they had not used a DIL (dual in line ) octal transistor array like the ULN2803
or a new FET array
like the Toshiba TB D62381A series DMOS transistor array
that would enable the user to plug in a replacement “

the Gecko G540 has the same issue with a FET that's soldered in

John

[Voicecoil]

Hi Voicecoil

The diagram in post 40 shows the signal path through the circuit after the HCPL-2631 opto isolators

the only diode is within the NTR5198NL-D FET

hence my comment in post 30

“Its a pity they had not used a DIL (dual in line ) octal transistor array like the ULN2803
or a new FET array
like the Toshiba TB D62381A series DMOS transistor array
that would enable the user to plug in a replacement “

the Gecko G540 has the same issue with a FET that's soldered in

John

Well in that case the manual really should show a clamp diode in parallel with the relay coil IMHO. The intrinsic body diode in the FET will be sod-all use for a coil that's connected between the output and +24 as it'll shoot a long way positive when the FET switches off and over-voltage it in the process. The great thing about drivers like the ULN2803 you mentioned is that they have the clamp diodes built into the chip which makes it a lot less likely that they'll blow. I'll be adding some diodes to all my relay outputs tomorrow.