LM5033: LM5033：Weak load capacity

min qin

Prodigy 20 points

Part Number: LM5033
Other Parts Discussed in Thread: TL431,

Design parameters:1、full-bridge circuit

2、Output Voltage：±190V

3、Output current：25A

During debugging, the no-load output voltage is normal. When the load reaches 3a, the output voltage is only 22V.

The datasheet indicates that the COMP voltage is between 1.5v-3.5, but when the voltage is within this range, the output voltage can not be stabilized and continues to rise.

So，The current comp voltage setting is 5V

What causes the above problems？

over 4 years ago

0 Steven Mappus1 over 4 years ago

TI__Mastermind 33115 points

Hi,

Thanks for connecting through E2E. If your design is regulating as expected with no load but output voltage is dropping as load current is increased, you need to check the optocoupler feedback and the biasing of the optocoupler/TL431.

Optocoupler biasing and control loop compensation must work together to produce the desired performance. You can have a perfectly designed compensator built around an optocoupler that is not properly biased and the overall response/regulation will be poor. Here are some good references discussing how to properly bias the optocoupler:

Regards,

Steve M

0 min qin over 4 years ago in reply to Steven Mappus1

Prodigy 20 points

Do you have lm5033 as a reference for full bridge circuit (with feedback circuit)？

0 Steven Mappus1 over 4 years ago in reply to min qin

TI__Mastermind 33115 points

Hi,

I searched the internal TI reference design data base and was able to find one LM5033 example showing optocoupler feedback (file attached). This design is for telecom DC/DC so the VIN, VOUT, POUT parameters are not the same as your requirements. However, using the design guidance I provided previously and PMP6946, you should be able to scale for your needs. Good luck with your design and thanks for connecting through TI E2E.

LM5033 PMP6946.zip

Regards,

Steve M

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LM5033: LM5033：Weak load capacity