i use this schematic The problem is that transistors heat when load is given in the output
Output is rectified and smoothed
I dont know adding or removing components in the circuit
Please help me

 

More details will get you a more detailed response.

With 3,200 pf of input capacitance and 1K pullups, no wonder they are getting hot.

The TL494 was designed before high power MOSFETs came into existence, and was intended to drive bipolar transistors. More modern power supply controllers are able to drive gates directly.

You can probably use the TL494 and the MOSFETs together if you put a gate driver between the two.

If you can't get an integrated gate driver, the circuit below should be almost as good:

 

I would use a Tip126/7 totem pole pair.

 

Thanks for the replies
I understand tl494 cannot drive mosfets directly
Can ka3525 drive mosfet directly?
If so
I made this circuit from ka3525

Output is rectified and smoothed
With no load output voltage is 350v
When i put load (100w lamp) two mosfets heat very fast
Transformer can handle 500watt
Is there any problem in this circuit?
Plz hemp me

 

It should be fine for driving MOSFETs, but be careful not to exceed the maximum gate drive for your FETs.

I did not check the circuit carefully because I am having a lot of trouble following it.

It is a good idea to put some resistance in series with the gate leads (20 or 30 ohms for starters) to suppress ringing.

You said the transistors get hot quickly -that might be fine. How hot? What about the heatsink (devrees per watt)?

 

Thanks but i missed 15 ohms resistor in this picture
there are two resistors (15 ohm) for each transistor in this circuit
But the problem the same

 

How hot? What kind of heatsink?

 

No heatsink for transistors but must not be heat for this load in 5 seconds

 

I have another circuit from tl494 but it is made in china i checked this circuit without heatsinks with 100watt lamp load . Transistors is a little warm only
It is also 500watt 12 to 220 inverter
But my inverter transistors gets hot

 

From the small amount of information available I can see that your average input current is more than 5 amps for each transistor. You probably need a heatsink.

Can you measure or estimate the case temperature?

What MOSFETs are you using?

What is the switching frequency?

 

Irf3205 mosfet
And f= 69000

 

How hot?

 

Very hot
I have no thermometer
You cant hold the transistor 5 sec

 

Have you got email or telegram,whatapp or imo to speak with you for also other problems in electronics

 

The MOSFETs have a very low RDon so I suspect that though they may feel hot to the touch they should not be very painful (ideally 15° to 25° above ambieint.

If you have an oscilloscope have a look at the risetime of the gate voltage and the saturation voltage on the drain. Those might offer a clue to what's causing the extra dissipation.

 

is from gate driver pin
is from drain pin
Above pictures in no load state

With load this is from drain pin

 

From the SG3525 datasheet (assumed similar to the KP3525), the output stage drops about 2V when sourcing/sinking only 100mA and is rated for 500mA absolute maximum. If your gate resistors are as low as 15Ω the peak gate current will theoretically be ~800mA. It is therefore likely that the IC is being overloaded, cannot provide enough current to charge the gate capacitance quickly, and/or cannot drive the gate at a high enough voltage for full turn-on of the FET.

 

From Alec_t's post, slow turn-on and turn-off because of limited gate drive can certainly be the case of your excess dissipation. You might have to add a gate driver to this circuit too.

Good! you have a scope at your disposal! The waveforms shows do not look at all like what would be expected. They both should be good approximations of rectangular waveforms. A little sloppieness or "garbage" is expected but the roughly rectangular shape is not apparent. Two things that might cause this come to mind:

1. Scope probe shield not grounded at the circuit under test or at the scope, or

2. Scope probe not properly compensated. This short article may be of help.

A clean image of the waveforms would be useful in confirming Alec_t's diagnosis.

 

Thanks Alec and DickCappels
Yes my oscilloscope probe is simple cable , nothing in it capacitor and resistor . Only cable.
So. Does waveform not look like rectangular shape?
I must make scope probe
After i make it i will show waveforms to you ok