Hi everyone, just finished my DC-DC amp SMPS project, now i would like to have a go at building an AC to DC SMPS. I will again be using the TL494, driving a half bridge via a gate drive transformer.
The only part of my understanding that im struggling with, is providing 12v auxilary power to the tl494 at startup. I understand that at startup you need to (somehow?) pull up one of the half bridge transistors base, in order to energise the primary and in turn, the auxilary winding.
Surely, one pulse on the auxilary wont be enough to get the tl494 going, also considering that the GDT requires a little current, its difficult?
Also, if the tl494 does manage to startup, i assume that you need to really quickly disable the inital pullup on the chosen half bridge transistor, to avoid shoot-through. Also, if the chosen startup transistor is on for too long, could it not leave saturation issues for when the tl494 kicks in, even with soft start.
At the moment, im considering the option of adding a very small, simplistic self oscillating 12v smps (similar to the sort of smps you might find in a phone charger brick) to the tl494 control board so that it can have its own supply, removing the need for the main transformer to have any auxilary winding, and removing the complication of initial transistor pullup on the half bridge. Would love to hear some relatively simple auxillary ideas 😁.
The only part of my understanding that im struggling with, is providing 12v auxilary power to the tl494 at startup. I understand that at startup you need to (somehow?) pull up one of the half bridge transistors base, in order to energise the primary and in turn, the auxilary winding.
Surely, one pulse on the auxilary wont be enough to get the tl494 going, also considering that the GDT requires a little current, its difficult?
Also, if the tl494 does manage to startup, i assume that you need to really quickly disable the inital pullup on the chosen half bridge transistor, to avoid shoot-through. Also, if the chosen startup transistor is on for too long, could it not leave saturation issues for when the tl494 kicks in, even with soft start.
At the moment, im considering the option of adding a very small, simplistic self oscillating 12v smps (similar to the sort of smps you might find in a phone charger brick) to the tl494 control board so that it can have its own supply, removing the need for the main transformer to have any auxilary winding, and removing the complication of initial transistor pullup on the half bridge. Would love to hear some relatively simple auxillary ideas 😁.
Drew this little smps up that could be dedicated to supplying the tl494:
the R4 10ohm current sensing shunt resistor could always be changed depending on how much current the tl494 will draw, driving its gdt
the R4 10ohm current sensing shunt resistor could always be changed depending on how much current the tl494 will draw, driving its gdt
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A little house keeping supply is a good way to go. I don't have an example handy but I have seen startup resistor/capacitor dividers that are removed from the circuit right after startup. Here is a more appropriate house keeping supply I copied from somewhere and changed to fit my needs. It's frequency and quality is fairly dependent on the transformer.
