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I am doing a bench test comparison of the TLVH431CLPR versus LMV431 voltage shunt devices.
The component test using the circuit below resulted in Vref = 1.24v and Vout = 2.5v as expected. So, I am comfortable both the TLVH431 and LMV431 components are working well.
|
Vref |
Vout |
Iref_pin |
TLVH431CLPR |
1.24 |
2.5 |
536 uA |
LMV431 |
1.24 |
2.5 |
535 uA |
Next, I did a bench test with the following circuit. Note the LED will be eventually replaced with an opto-isolator.
The results are shown in the table below.
|
Vref |
Vout |
Iref_pin |
TLVH431CLPR |
0.9 |
1.7 |
708 uA |
LMV431 |
2.45 |
1.53 |
62 uA |
I expected Vref to be about 2.5v for both devices due to the R11 & R22 voltage divider (assuming negligible Iref_pin current) but the TLVH431 has dropped to Vref=0.9v. Note, the Iref_pin is drawing 708 uA for the TLVH431 but only 62 uA for the LMV431.
So, why is the TLVH431 drawing so much Iref_pin current?
Hi Jeff
Both the circuits which you are testing are not same. TLVH431/LM431 is working in regulator mode in first circuit and you are getting proper regulated output.
TLVH431/LM431 are working in comparator mode as you are connecting R11 between supply and Ref pin. Values of R11 and R22 are not proper and there will be very high IREF, that's why the circuit in not working properly. You can go through the app note for more details of open loop design -
Regards
Trailokya