LM5035: Design problems with half bridge topology using LM5035

Dr. HARIS AHMED

Part Number: LM5035

Hello,

I am using LM5035 IC for my half bridge configuration. The input voltage is 270VDC. Hence, I am supplying VIN to IC by and external 12V supply.

I have few queries:

1.How I can achieve UVLO, RAMP, OVP pin voltage if the grounds are different for IC supply (VIN --12V) and Source Voltage (270VDC). Also need to provide gate isolation using gate drive transformer.

2. How I can obtain differential output voltage using same half bridge topology.

3. If I am using diode at secondary side, then what to do SR1 and SR2 pins. (floating or gnd)

over 1 year ago

0 Hong Huang over 1 year ago

TI__Guru 73355 points

Hi,

1. What do you mean by "the grounds are different"? Please provide your schematics so we can understand what you mean.

2. Which voltage, from where to where, do you want to have? Please show this on your schematics.

3. If SR1 and SR2 not used, then leave the two pins open.

0 Hong Huang over 1 year ago in reply to Hong Huang

TI__Guru 73355 points

Hi,

No communication for a long time. I assume the issues are all resolved. I will close this thread. If you need additional support, you can re-open this thread or create a new thread.

0 Dr. HARIS AHMED over 1 year ago in reply to Hong Huang

Prodigy 30 points

Hi,

I have shared the schematics through mail. However, no response on that yet.
The main query is how I can use LM5035 for 270VDC input voltage to convert into differential +15V and -15V.

The problem I have faced is different grounds.

Let PGND is the input ground associated with 270VDC. DGND is output ground associated with +15V and -15V output.

Now, the LM5035 doesn't withstand on 270VDC input, so I made an isolated auxiliary supply of 12V_AUX to provide the input to LM5035.

The ground associated with 12V_AUX is AGND. Hence, the ground for LM5035 is AGND.

Now, the problem is setting the RAMP, OVP, and UVLO pin. If I connected the resistor divider between 270VDC input with PGND then the ground levels are different PGND and AGND. so, the LM5035 doesn't activate properly.

is there any small circuit using BJT will be used to lower down the input and supply to LM5035 so that a different 12V_AUX is not needed.