parallel connection of TPS40120

Deepak Bansal

Other Parts Discussed in Thread: TPS40120, UCC39002, TPS40210

One of project needs high o/p current. So I connected three TPS40120 in parallel. As shown below: (below shown is 2 parallel DC-Dc, similarly I connected three in parallel)

But when I connected them , almost all load current was taken by one TPS.

After that I made connection by connecting diode as shown below:

It allows current to be shared by Dc-Dc. But still one of device still share very low amount of current around 100 ma only. While individually all works fine at low o/p current.

My question is :

1. Why after connecting diode current get shared, while by simple connecting them in parallel current passes by one device only.

2. Is there any method by which current can be made to equally pass through all devices.

over 13 years ago

0 Lisa Dinwoodie over 13 years ago

TI__Genius 15910 points

Admittedly, I am not specifically familiar with the TPS40120 but TI does offer a Load Share Controller, the UCC39002, that is designed to parallel multiple independent power supplies and current share with up to 1% current share accuracy. You may want to take a look at it to see if it can be used to meet your load sharing needs.

0 Deepak Bansal over 13 years ago in reply to Lisa Dinwoodie

Expert 2395 points

Many thanks for your reply.I will check the controller.

But can you tell me why after connecting diodes current gets shared in two boards.While by shorting directly all the current was taken by one unit only.

0 Na Kong over 13 years ago in reply to Deepak Bansal

TI__Genius 17240 points

Hi Deepak,

TPS40120 is the VRM10.0 compliant programmable feedback divider. Could you confirm it is the device in your application?

Regards,

0 Deepak Bansal over 13 years ago in reply to Na Kong

Expert 2395 points

Na Kong

Yes it the same device. My company sourced it from TI's distributors. I checked it also.

Kindly reply at the earliest.

0 Na Kong over 13 years ago in reply to Deepak Bansal

TI__Genius 17240 points

Hi Deepak,

Your circuit is not clear to me. What is your PWM controller? Is it possible for you to provide the schematic of the circuit?

Regards,

0 Lisa Dinwoodie over 13 years ago in reply to Deepak Bansal

TI__Genius 15910 points

For details on load sharing, Unitrode Power Supply Design Seminar 800 has a topic called Load Sharing with Paralleled Power Supplies that has a very good discussion on the various load sharing techniques (http://www.smps.us/Unitrode2.html). Also, there are some application notes on the TI website (U-163 and U-129) that discuss load sharing.

0 Deepak Bansal over 13 years ago in reply to Lisa Dinwoodie

Expert 2395 points

Hi Lisa,

Many thanks for your reply. I will go through the same.

Regards

Deepak Bansal

0 Deepak Bansal over 13 years ago in reply to Na Kong

Expert 2395 points

Na Kong,

Below is the schematic of my circuit. I have to increase the output current. Therefore I connected them by using diode at the output as posted earlier. But still there is poor sharing of current. Kindly help.

Thanks & Regards

Deepak Bansal

0 Na Kong over 13 years ago in reply to Deepak Bansal

TI__Genius 17240 points

Hi Deepak,

It seems you are using TPS40210 (not TPS40120) in a non-isolated flyback converter. By adding diode at the output, if the voltage feedback connection point is before the diode, then the load current information of each supply will be read by the controller because of the voltage drop on diode. The one delivering higher current will read higher output voltage. The controller will try to reduce the duty cycle to cause the output current reduce, or vice versa. Effectively, the load current gets shared between the paralleling supplies.

For accurate load sharing, please check out UCC39002 and the references that Lisa has recommended.

Regards,

0 Deepak Bansal over 13 years ago in reply to Na Kong

Expert 2395 points

Na Kong

Many thanks for your prompt reply. Regrets for silly mistake in TPS40210-TPS40120.

Thanks & Regards

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parallel connection of TPS40120