Hi, in High Frequency Inverters, Voltage is First Boosted to 311 VDC using push pull converters, then it converter to AC using SPWM and couple MOSFETs or IGBTs.
to maintain the 311VDC, the PWM IC such as SG3525 is getting feedback from the rectified voltage which is the 311VDC.
The point is.. that I found two ways of getting the feedback, the first one is done by just a voltage divider circuit [just couple resistors to reduce the 311VDC to around 4VDC], which is controlling the Duty Cycle of the PWM Circuit Which is Controlling the push pull MOSFETs, this method is found mainly on most of the circuits that I found online.
but when I was checking the Commercial Design of Inverters, I found that they were using op-amp as a comparator [including the voltage divider for the comparator circuit] and isolation optocoupler and the output signal is then goes to the PWM IC, which is just turning the PWM ON with 100% duty Cycle, or OFF, as Shown Here:
When I tried the First Method, Which is controlling the Duty Cycle, I Found that the MOSFET's Temperature was Raising Dramatically, Without Loading the Circuit, Actually there is Many Probabilities that may Cause that, but my scope here is just related to the Feedback only...
so, the question is:
1- What is the Difference between the Two Methods? does it just for Isolation?
2- Does the Feedback Method do something with the Temperature/Efficiency of the Circuit?
I mean, Maybe when the MOSFETs is cooling when they are turned OFF [on second method]? while the first Method is just reducing the duty cycle and not turning off the PWM completely, which is doing something with the crossover losses I guess?
some Extra Information:
- Switching Frequency = ~33Khz
- Dead time is Taken in Consideration with the Used MOSFET and Checked with the Oscilloscope
- Soft Start is Taken in Consideration
- The Whole Circuit was Build on the Breadboard, I know that there is may be noise etc..., But I just wanted to check the Feedback Method Before Making the Prototype on the Vero Board [Then I will make the Prototype PCB, but later]
- This is very close to the actual Push Pull Converter Circuit, the only difference that I removed the Feedback here
Very Thankful for Reading my Questions. Waiting for your Answer
to maintain the 311VDC, the PWM IC such as SG3525 is getting feedback from the rectified voltage which is the 311VDC.
The point is.. that I found two ways of getting the feedback, the first one is done by just a voltage divider circuit [just couple resistors to reduce the 311VDC to around 4VDC], which is controlling the Duty Cycle of the PWM Circuit Which is Controlling the push pull MOSFETs, this method is found mainly on most of the circuits that I found online.
but when I was checking the Commercial Design of Inverters, I found that they were using op-amp as a comparator [including the voltage divider for the comparator circuit] and isolation optocoupler and the output signal is then goes to the PWM IC, which is just turning the PWM ON with 100% duty Cycle, or OFF, as Shown Here:
When I tried the First Method, Which is controlling the Duty Cycle, I Found that the MOSFET's Temperature was Raising Dramatically, Without Loading the Circuit, Actually there is Many Probabilities that may Cause that, but my scope here is just related to the Feedback only...
so, the question is:
1- What is the Difference between the Two Methods? does it just for Isolation?
2- Does the Feedback Method do something with the Temperature/Efficiency of the Circuit?
I mean, Maybe when the MOSFETs is cooling when they are turned OFF [on second method]? while the first Method is just reducing the duty cycle and not turning off the PWM completely, which is doing something with the crossover losses I guess?
some Extra Information:
- Switching Frequency = ~33Khz
- Dead time is Taken in Consideration with the Used MOSFET and Checked with the Oscilloscope
- Soft Start is Taken in Consideration
- The Whole Circuit was Build on the Breadboard, I know that there is may be noise etc..., But I just wanted to check the Feedback Method Before Making the Prototype on the Vero Board [Then I will make the Prototype PCB, but later]
- This is very close to the actual Push Pull Converter Circuit, the only difference that I removed the Feedback here
Very Thankful for Reading my Questions. Waiting for your Answer