Chippie
Apr 14, 2004, 01:31 PM
Guyz, some of you may remember I constructed a 13.8v 8 amp pwer supply based on a TL 494 switcher with the wound components from a pc power supply( yeah ok I cheated somewhat.... :p ).....
Well the problem now is, I built another exactly the same, same components and same pcb and same inductors etc....well it dont work!!!
The problem seems to be with current sensing, if I power it up with a load via variac, all is well.If I power it up straight from 240v( I'm in the UK remember ;) ) it stalls and doesnt run.
If I start it without a load and straight from the mains, then add the load, all is ok. Puzzlin' aint it.
The current sensing is done by sampling the voltage at the centre tap of the driver transformer T2 and feeding it to the base of Q7, which if turned on then causes pin 4 of the TL494 to be pulled hi......the psu shuts down on hi load
So if you wizards out there could take a look see and mebbe add some comment then perhaps I could resolve this.
I've attached the circuit again to assist your thought processes.....
TIA Chip( failed design engineer.... :rolleyes: )
Well the problem now is, I built another exactly the same, same components and same pcb and same inductors etc....well it dont work!!!
The problem seems to be with current sensing, if I power it up with a load via variac, all is well.If I power it up straight from 240v( I'm in the UK remember ;) ) it stalls and doesnt run.
If I start it without a load and straight from the mains, then add the load, all is ok. Puzzlin' aint it.
The current sensing is done by sampling the voltage at the centre tap of the driver transformer T2 and feeding it to the base of Q7, which if turned on then causes pin 4 of the TL494 to be pulled hi......the psu shuts down on hi load
So if you wizards out there could take a look see and mebbe add some comment then perhaps I could resolve this.
I've attached the circuit again to assist your thought processes.....
TIA Chip( failed design engineer.... :rolleyes: )