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SN6505B: Driving 2 transformers from single IC

Part Number: SN6505B

Hi,

I am using SN6505BDBVR in one of my application to drive  two transformers ( MPN : 760390014, Ratio 1:1.3) as shown below. Sequence of driving is 

1. MCU enables SN6505 to drive transformer 1  (T1) in full bridge configuration. ( Secondary Load 20mA)

2. After certain time, MCU triggers BSS84P , so that Transformer 2 (T2) sees 3.3V on Vcc pin. ( Secondary Load 50mA)

**Same 3.3V is also given to MCU.

** T2 is placed 10mm away from SN6505 while T1 is placed closed to SN6505. While BSS84P is placed close to T2.

Is there any issue in below schematic while connecting 3.3V to T2 separately as it is not directly connected to VCC pin of SN6505 as shown in the datasheet.

  • Hi Prafulla,

    Thanks for reaching out and for sharing complete details related to your query.

    The approach that you have followed to drive two transformers using one SN6505B sounds good and should work fine. The only concern is the P-FET BSS84P, this doesn't seem to be a power FET and is meant for logic signal switching. Hence, it might not be able to pass enough current to achieve required output voltage and current. The typical RDS(on) of 8Ω drops significant input voltage and hence, transformer might only see about 2.5V thus generating only a poor output voltage.

    Please choose a different MOSFET that is rating 500mA or higher such that the transformer can be reliably powered and desired output voltage / current can be achieved. I hope this answers your question, thanks.


    Regards,
    Koteshwar Rao

  • Hi Rao,

    Thanks for your revert. I will replace BSP84P with suitable MOSFET.

    As Transformer Vcc 3.3V is also given to Microcontroller as digital power supply, will there be any chances that it will disturb the functionality of MCU during any EMI EMC test ?

    Regards,

    Prafulla

  • Hi Prafulla,

    Having a common power supply for MCU and the transformer shouldn't be a problem provided there are sufficient decoupling capacitors used on both device power supply pins.
    EMI / EMC testing can disturb MCU in many ways and those need to be taken care separately. Let me know if you have any further questions, thanks.


    Regards,
    Koteshwar Rao

  • Hi Rao,

    Thanks for your reply !

    Regards,

    Prafulla S.