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L6203 LED indication issue used for peltier heating/Cooling

Question asked by Vaibhav Pawar on Mar 1, 2018
Latest reply on Mar 20, 2018 by Vaibhav Pawar

We are using L6203 IC in production with annual consumption of 400 Nos. The product where it is used in biomedical instrument used for blood analysis and diagnosis. IC L6203 is used for controlling temp of peltier from 3 set poins (25,30 and 37 °C) and temp can be changed to any values either 25,30,37 °C from its earlier set value ( either heating or cooling )


Temp is sensed using LM35 temp sensor and using analog circuitry it is assigned to EN, IN1 and IN2 pin of L6203 to achieve set temp.


Attached schematics and in design, D6(red) is indication of heating and D7 is indication of cooling.


As per our observation when it is heating , D6 (red) is glowing.

when is is cooling , D7(green) is glowing.


But after stabilizing temp to set value, 4 conditions are observed  ( only D6 is ON, only D7 is ON, Both LED ON, Both LED OFF ), but temp is controlled correctly as per provided settings.


So please guide us "why LED indication is different when set temp is achieved"? Otherwise L6203 is operating correctly to heat or cool as per settings. Only problem is of indication.