Vlado391
Newbie
Hello,
I'm trying to build a 12V to 220VDC 100W converter with TL494. For input source i'm using 150W 220VAC-12VDC smps. The load is a light bulb.
Works fine when the input voltage is low (maximum duty cycle) - efficiency around 92%.
After increasing it the waveform of the drains getting awful. The efficiency drop to 70 percent and the transistors starts heating up. The input current stay almost constant. Under 0.15 duty cycle its even disgusting for looking. For some reason the drain voltage of the first transistor dying when the other switching off. No matter what is the duty cycle, the drain voltage stay the same. Maybe thats why the input current stay constant. I already tried with different transistors, IC and transformer - same result.
Currently i'm using an EI-33 transformer from old ATX power supply. It's working in half-bridge so i'm expecting 155V, but it's around 65-70V. The middle point is connected to VCC and the two 12V to the drains.
I'm using optocouplers for driving the transistors, because I didn't have any complementary transistors. I tried even with dual power supply to shut down the transistors (+-12), but with no effect.
For explaining the problem in his best i added a potentiometer on DTC pin and removed all feedbacks.
YELLOW (gate)
BLUE (drain)
Questions:
1. What may be the reason for this? What i'm getting wrong?
2. Why the drain voltage is 2 times bigger than the supply voltage?
3. Why the output voltage of EI-33 is only 70V?
Thanks in advance!
I'm trying to build a 12V to 220VDC 100W converter with TL494. For input source i'm using 150W 220VAC-12VDC smps. The load is a light bulb.
Works fine when the input voltage is low (maximum duty cycle) - efficiency around 92%.
After increasing it the waveform of the drains getting awful. The efficiency drop to 70 percent and the transistors starts heating up. The input current stay almost constant. Under 0.15 duty cycle its even disgusting for looking. For some reason the drain voltage of the first transistor dying when the other switching off. No matter what is the duty cycle, the drain voltage stay the same. Maybe thats why the input current stay constant. I already tried with different transistors, IC and transformer - same result.
Currently i'm using an EI-33 transformer from old ATX power supply. It's working in half-bridge so i'm expecting 155V, but it's around 65-70V. The middle point is connected to VCC and the two 12V to the drains.
I'm using optocouplers for driving the transistors, because I didn't have any complementary transistors. I tried even with dual power supply to shut down the transistors (+-12), but with no effect.
For explaining the problem in his best i added a potentiometer on DTC pin and removed all feedbacks.
YELLOW (gate)
BLUE (drain)
Questions:
1. What may be the reason for this? What i'm getting wrong?
2. Why the drain voltage is 2 times bigger than the supply voltage?
3. Why the output voltage of EI-33 is only 70V?
Thanks in advance!