UCC24624: Questions regarding the scope of use of this IC

You could use UCC24612 which is for driving flyback SR. 

Do you still want to use UCC24624 for the flyback?

Regards

Manikanta P

Hello Mr. Manikanta

This is Kurata from Hinox.

Thank you very much for your answer.

I knew how easy it was to use the UCC24624 and had an evaluation board on hand, so I decided to use the flyback method instead.

I connected it and tested it.

For 5V output applications, for simplicity, the IC power supply (VDD) is supplied from the output voltage.

Since the synchronous rectification operation stops when the output is short-circuited, the drive FET will overheat.

To prevent this, the power supply for the synchronous rectifier IC must be connected to another auxiliary power supply (self-biasing with a separate winding).

Since it has to be extracted, it results in wasted power consumption and reduces conversion efficiency.

So I would like to ask you the following question.

① Considering this, does the proposed UCC24612 have the function to solve these problems?

② Considering the above, is this UCC24612 the best choice?

③ UCC24612 has two synchronous rectification connections: high side SR and low side SR.

Whichever option I choose, will the problem of the drive FET overheating during an output short circuit mentioned above be solved?

④How many volts can be used for the line voltage of the transformer output winding and the DC output voltage of the circuit to be used?

Please let me know again.

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

Hello,

Are you using the SR driver in high side or low side rectifier in your flyback design?

Regards,

Hello Mr. Manikanta

This is Kurata from Hinox.

Thank you very much for your answer.

I received a reply, but I couldn't understand the meaning of the question, "Are you using an SR driver?"

Currently, the output rectification of flyback power supplies uses silicon Schottky diode rectifiers.

We are considering changing the SR driver to a synchronous rectifier circuit using FETs to improve efficiency.

This is the answer to the first question when considering using UCC24624, and was recommended as an alternative by Mr. Manikanta.

I am planning to consider using UCC24612 for the first time.

Therefore, I am unsure whether to choose high-side SR or low-side SR as shown in the examples in this data sheet.

This time, if we set the condition that SR does not overheat even when the output is short-circuited, the Vcc power supply of SR will be

It needs to be maintained.

This is an application example of the UCC24612 data sheet, but when the low side SR is short-circuited, Vcc becomes zero V,

I think synchronous rectification is not possible.

If we use high-side SR, we expect that Vcc will be maintained even in the event of a short circuit, and synchronous rectification will continue.

Is it safe to assume that with this high-side SR, conduction loss will not increase significantly and overheating will not occur? 　

Please let me know about questions ①~④ that I asked you last time.

Hello,

Your inquiry is under review and I will get back to you shortly.

Regards,

Hello,

Please see my comments below.

I received a reply, but I couldn't understand the meaning of the question, "Are you using an SR driver?"

> I asked if you are using the synchronous  rectifier in a high side or low side application.  This is where in a flyback design if the the rectifier is the high side or low side.  I believe the data sheet has examples of these, if not the evaluation module does.

Evaluation Module:  https://www.ti.com/lit/pdf/sluubp3

Currently, the output rectification of flyback power supplies uses silicon Schottky diode rectifiers.

We are considering changing the SR driver to a synchronous rectifier circuit using FETs to improve efficiency.

This is the answer to the first question when considering using UCC24624, and was recommended as an alternative by Mr. Manikanta.

> The UCC24624 with a dual driver could be used for driving FETs in parallel in a flyback or an LLC.

I am planning to consider using UCC24612 for the first time.

Therefore, I am unsure whether to choose high-side SR or low-side SR as shown in the examples in this data sheet.

> I would use the FET on the low side it is easier to setup and requires the least amount of circuitry.

This time, if we set the condition that SR does not overheat even when the output is short-circuited, the Vcc power supply of SR will be

It needs to be maintained.

>To help with this I would use a flyback that is powered of the aux winding of the main transformer.  In this way when you short the output VCC will not be powered by the aux winding.  The VCC or VDD capacitor will be discharged disabling the flyback controller by triggering ULVO.  The other option is to use a flyback controller with short circuit protection in its control circuitry..

This is an application example of the UCC24612 data sheet, but when the low side SR is short-circuited, Vcc becomes zero V,

> If you short the SR driver the flyback controller should cycle by cycle current limit protecting the SR.

I think synchronous rectification is not possible.

If we use high-side SR, we expect that Vcc will be maintained even in the event of a short circuit, and synchronous rectification will continue.

> This is not true and the VCC capacitor will not remain charged.

Revisited questions:

① Considering this, does the proposed UCC24612 have the function to solve these problems?

> I think if you use the SR in the low side with flyback controlled with an Aux winding it will prevent SR over heating.

> Consider using a flyback controller with over current/short circuit protection.  TI has many to choose from at the following link.

https://www.ti.com/power-management/acdc-isolated-dcdc-switching-regulators/flyback-controllers/products.html

② Considering the above, is this UCC24612 the best choice?

> Using an SR driver will make a design more efficient compared to using diodes.

> The flyback controller can prevent the SR from over heating when the output is short circuited.  The SR driver will not solve this problem.

③ UCC24612 has two synchronous rectification connections: high side SR and low side SR.

Whichever option I choose, will the problem of the drive FET overheating during an output short circuit mentioned above be solved?

>If you are going to use an SR instead of a diode, I would recommend using the low side approach due to it taking less components.

>Please note the driver itself will not prevent over heating.  Recommendations were made above on how to prevent heating of the SR with an output short circuit.

④How many volts can be used for the line voltage of the transformer output winding and the DC output voltage of the circuit to be used?

>  This will be based on the transformer turns ratio and the UCC24612 absolute maximum ratings of VD, VS and VDD.  The following ratio will help you determine this.  VA is the voltage across transformer winding NA and VB is the voltage across transformer VB.

VA/VB = NA/NB

Regards,