Iscariah
Newbie level 1
- Joined
- Feb 26, 2013
- Messages
- 1
- Helped
- 0
- Reputation
- 0
- Reaction score
- 0
- Trophy points
- 1,281
- Activity points
- 1,294
Hello everyone!
I have bad 12v to 220V converter which I'm trying to repair. My friend reversed the supply leads on it some time ago and it doesn't work since then.
It's classic push-pull converter with two transformers, and 3 IC's ( 2 PWM and 1 quad comparator). PWM chips are 7500's which i replaced with TL494 and comparator is D339. So, first TL494 switches transformers up to 220V DC and second makes AC out of it. I don't understand why is necessary to have quad comparator for this circuit when TL494's have their own double error amplifier...
Anyway, I didn't have time to write down whole circuit schematic because things get little complicated around that comparator and besides that I need just basic boost up to 220V without AC conversion.
I realised that first TL494 which boosts up to 220V have a constant maximum duty cycle which makes short circuit everytime I power up converter.
Shorting error amplifier pins (with feedback and dead time pin also) to groung still didn't dropped duty cycle a bit so I'm confused because only thing that produces duty cycle is error amplifier voltage. Does anyone have some info where to look for a bug? Thanx
I have bad 12v to 220V converter which I'm trying to repair. My friend reversed the supply leads on it some time ago and it doesn't work since then.
It's classic push-pull converter with two transformers, and 3 IC's ( 2 PWM and 1 quad comparator). PWM chips are 7500's which i replaced with TL494 and comparator is D339. So, first TL494 switches transformers up to 220V DC and second makes AC out of it. I don't understand why is necessary to have quad comparator for this circuit when TL494's have their own double error amplifier...
Anyway, I didn't have time to write down whole circuit schematic because things get little complicated around that comparator and besides that I need just basic boost up to 220V without AC conversion.
I realised that first TL494 which boosts up to 220V have a constant maximum duty cycle which makes short circuit everytime I power up converter.
Shorting error amplifier pins (with feedback and dead time pin also) to groung still didn't dropped duty cycle a bit so I'm confused because only thing that produces duty cycle is error amplifier voltage. Does anyone have some info where to look for a bug? Thanx
