LM2576: I have a question about power circuits. Using a relay and power divide.

Hello,

An engineer has been assigned to this thread. They will get back to you about this soon.

Regards,

Rahil

Hi Jiho,

Zener can theoretically be used - however, the power rating of the zener will be the limiting factor here. You will have to properly rate your passives.

Can you share your system block diagram - it will be easier to analyse your system and implementation? We may also need to consider the back emf from the motors that you have. 

Also, TI has battery charger, relay driver and motor driver devices - these may help greatly simplify your implementation. 

Thanks,

Best Regards,

Taru 

Hi Taru.

I appreciate your reply.

I can share our team's system block diagram. but, the total system block diagram has mobile applications, server communication, and others. I thought it was too big, so I just prepared a hardware system block diagram.

This is our team's hardware system block diagram.

I thought it might be helpful to understand this block diagram, so I prepared the contents and schematics ver 1.

The topic is "Mobile Camara Module using object tracking based remote control". this module is on a camera tripod with one mobile. two mobile communications of object tracking. After communicating mobile and this module using Bluetooth.

If a module has signal reception of Bluetooth data(like coordinate or switch by applications). the end effector is a combined mobile and is moved by motors.

This hardware form is a module that can be combined with camera tripods. So, I design this block Diagram. battery[packed Li-ion battery] charging by external powers. using charging module(TYE-BCM01). and I thought it should be separate battery's charge and discharge. so, I used a relay. relay is checked for external power. If checked the external power. charging the battery. but, external power isn't checked. the battery is connected to internal power.

Motor, sensor, switch, and Bluetooth signal these all most data's worked by a microprocessor. I/O worked 3.3[V]. but, some peripherals don't work that. So, I used 74LV1T34 level shifter IC. it can make 3.3[V] to 5[V], then I used these signals control motors.

The below schematic is ver 1. It is designed by a hardware system block diagram.

thank you for reading these long words.

Regards.

Jiho

Hi Jiho,

Thanks for the details! Let me go through the entire system and get back to you. 

Thanks,

Best Regards,

Taru

Hi Jiho,

Thanks for sharing - few references/comemnts that I can help you with are:

1. You can refer to this battery charger reference design: https://www.ti.com/tool/PMP30963 (Here you can take inspiration from the battery charger circuit for your design and also the switchover circuit). Since you are taking an input of 5V and have a 2s Li Ion battery - you may want to look at this Buck Boost battery charger: https://www.ti.com/product/BQ25731. You can also use this to have a system that can work with both Battery and power plugged in (I am not sure if that is a use case here - what would change is that you will have to use a buck-boost converter here - since your input power rail and your internal system rails are both 5V). 

2.The LDO that you have chosen may not be the best approach - To Switch down from 7.4V to 5V at 1A - there is power loss of 2.4W - which may lead to thermal issues and is also not the best solution when you are designing battery operated systems.

3. You can avoid generating two different 5V rail and use just one! I am not too sure what the LDO and the Buck Converter are powering but seems like you are turning on/off these power stages for different loads. What, in my opinion, would be better is to use load switches. You turn On/off the loads according to your system operation and Enable/ Disable using load switches.

From your first post about having these two for different current limits - what exactly is the application? Is one LDO powering one motor and the buck is powering the other two? What exactly are the loads being driven by these two power converter? 

4. you can look at these low side switches to drive your relays: https://www.ti.com/power-management/power-switches/low-side-switches/products.html#sort=248;desc&. 

Hope this helps - good luck for your project. 

Thanks,

Best Regards,

Taru

Hi Taru.

I appreciate your reply.
And I apologize for replying too late.

Reply to your question, LDO has an operating power for the MCU with peripherals. It supplies MCU, sensors, Bluetooth module and etc. Buck is supplying power for motor systems: 2 servo motors, 1 step motor, and level shifters.

After I read your reply changed the circuits. I found another LDO on the evaluation board. So, I deleted the LDO in the circuit and used another LDO on the evaluation board. And I wanted to change the relay to load switches. But, project deadline is on May 20, 2025. So I don't have testing time for load switches(and 2 weeks ago started mid-term exam. It ended yesterday. Time is too short...). It's a shame that I didn't use the load switch before.

I regret that I was not able to reflect much of the advice you gave me.
But, this time I gained many circuit knowledge. I appreciate it a lot.

Thankfully, I had the opportunity to join the firmware and hardware team for a robotics project. This time, let's use this knowledge to make better power systems.

Said again, I apologize that I was not able to reflect much of the advice you gave me. But I learned so much about power circuit systems. I appreciate it a lot.

Thank you for reading this comment. And taking for time to answer my question.

The day you read this comment, I hope you have a nice day. :D

Best Regards.
Jiho