TNY280 CC\CV charger
Hi everyone,
having new PI Expert, I've tried to design a CC/CV charger for 7.2V NiMH battery.
It wasn't a big thing to biuld a cicrcuit, however it doesn't want to work properly. Simply speaking: current doens't reach calculated 2Amps. Circuit just samples output with regular packets of "bursts" (I can see them on a scope).
I have a question to someone who ever did such a charger before:
what voltage you enter in PI Expert output section having in mind, that fully loaded NiMH cell can reach 1,55V while dead drops down to 1V per cell???
This really confuses me and I think this is a problem.
So: if my battery is 7.2V nominal but 9.3V fully loaded - which voltage to choose?
thanks in advance,
Pauli
Comments
Hi there,
I'm back with screen shot from oscill. I put there on it some comments to explain what is happening.
Some additional notes: when no load applied output voltage stays at desired level, here 9.3V.
As soon as battery is connected, output voltage drops down to that voltage present at battery and circuit seems to start every 2sec to "recover".
After disconnecting the load, output voltage drops down for some reason and then backs again to 9.3 Volts.
I don't use aux winding, as PI claims it's not needed to power the chip.
Hope now it's more clear.
Greetings,
Pavel
ok this confirms what I was saying earlier. The fact that these bursts occur every 2 s confirm that the chip is in auto-restart. This is happening because the control loop path is somehow open...
Please check your prototype and verify that the chip is receiving feedback (check for open components, cold solder joints etc)
Hi,
I have discovered what was wrong: a TVS diode was damaged! As it happened without any significant side effects like burn blow or smoke, I didn't suspect this component to be malfunctionig...
This component comes right from the shelf so to be honest I'm really surprised :(
Maybe I did something bad during building and powering, but now it's solved.
Last qestion comes out of this: is a RCD clamp more reliable?
with compliments,
Pavel
Can you send me a waveform showing these "bursts" you are referring to? Most likely the power supply is in the auto-restart mode which is a self protection mode that the chip enters into when it detects some fault condition. This fault condition most likely is that your feedback loop is open. Would you double check your connects (watch for cold solder joints etc)