Hi,
I have designed a circuit which will be powered by 4-20mA current loop. As per my guesstimate I do not need more power at 3.3V and hence this should suffice. The circuit is based on shunt regulator TLV431B as shown below:
I have not shown a Micro connection but the Output of Opamp U3C (Pin # 7) goes to the ADC input of the Micro.
1. Based on the the datasheet the min Vref required at TLV431B is 1.234V. With this potential divider values I set that.
The output goes to 4.2V for any value of current between 4 to 20mA both inclusive. The I disconnected U2, U3 from the connection so only TLV431 is on the board but output remains unchanged.
2. The datasheet also refers to value of Vk at Ik = 10mA. With this at 4mA the output voltage is 2.5V and at 20mA it is 4.5V.
3. I replaced TLV and resistor divider by LM385-2.5 and the circuit work just fine. But then the micro needs 3.3V.
Please suggest what I could be potential problem?
Regards,
Girish
I have designed a circuit which will be powered by 4-20mA current loop. As per my guesstimate I do not need more power at 3.3V and hence this should suffice. The circuit is based on shunt regulator TLV431B as shown below:
I have not shown a Micro connection but the Output of Opamp U3C (Pin # 7) goes to the ADC input of the Micro.
1. Based on the the datasheet the min Vref required at TLV431B is 1.234V. With this potential divider values I set that.
The output goes to 4.2V for any value of current between 4 to 20mA both inclusive. The I disconnected U2, U3 from the connection so only TLV431 is on the board but output remains unchanged.
2. The datasheet also refers to value of Vk at Ik = 10mA. With this at 4mA the output voltage is 2.5V and at 20mA it is 4.5V.
3. I replaced TLV and resistor divider by LM385-2.5 and the circuit work just fine. But then the micro needs 3.3V.
Please suggest what I could be potential problem?
Regards,
Girish