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Registered Member #3905
Joined: Mon May 23 2011, 09:26AM
Location: Hungary
Posts: 16
Hi,
I have a problem with my driver which is Wards Universal with a few modifications (not all the components are available in my country).
The 5V regulator usually gets quite hot after 5 minutes (without any interrupter turn on pulse) , and the 24V regulator gets really hot when the driver gets feedback and the coil starts to resonate. I use a 5cm diameter toroid (14 turns UTP) and it drives a full bridge of SKM200GB125D without highside driver.
I attached the board.
I dont have the schematic for the board because it's 80% wards schematic... ]driver2.2.pdf[/file]
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
How much voltage are you dropping across the regulator? If you are using a 24 volt transformer then you are putting 33 volts into the regulator and it is dissipating all but 5 volts of that as heat. I am not sure what you are using but if you are using a 24 volt transformer I would recommend using the center tap and only apply half that voltage to the 5 volt regulator and it will run cooler. Still I would use a heat sink though.
Registered Member #3905
Joined: Mon May 23 2011, 09:26AM
Location: Hungary
Posts: 16
Hi,
Thanks for your reply. Yes, I'm using a 24V transformer, but I don't have any center tap on it. Is there any other way that I can solve this problem without changing transformer?
Efficiency of your linear regulator = 5V / 33V = 15%, the other 85% of that is converted to heat in your regulator.
The easiest is to add another wall adapter for the 5V. You can also consider a switch mode regulator to improve the efficiency for that kind of voltage drop.
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Another option would be in how you layout your regulators. Put the largest first then take voltage from that and input it to the next largest and then take voltage from that one and input it to your smallest or the 5 volt regulator. Then you drop the voltages in a sequence.
So you would have the 24 volt regulator feeding the 9 volt regulator and the 9 volt regulator feeding the 5 volt regulator.
That should work ok and help keep the 5 volt regulator cooler and then you wont need the center tap.
Put a big resistor in series with the input of the 7805 such that you drop it down to a manageable lower voltage for the 7805 say 9V. So now all that heat is dissipated in the resistor instead of the 7805.
So 33V - 9V = 24V is the drop. Divide that by the current needed by 7805 gives you the value of the resistor and 24V * the current gives you the (minimum) wattage rating.
Add a filter cap after the resistor for the 7805 and you are set.
Do you know how much current is being drawn from the 24v regulator? Another option might be to run two 24v regs in parallel or you could just ad a small heat sink how much room do you have available on your PCB?
Or add heatsink + a small CPU fan to the 24V regulator. ;) Just a tiny bit of airflow from a fan and it'll make a lot of difference to the amount of heat that a heat sink can handle.
Between the 33V input and the 24V output, you have about 9V which should be able to power a small 12V fan. There is always the 5V from the 7805. ;)
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Regulators heating in Wards Universal driver
