Hello all,

I only would like to know if there could be any problem when a 5V relay is connected to AT89C51ED2 only across one PNP transistor - BC857. Coil power is 200 mW (5 V * 0,04 A). If the pin goes LOW the base current is about 1 mA that is enougth for collector current up to 100 mA...

There is my schematic:

                                |--------|Pull-up resistor 10k|--------|Vcc|
                                |
|Base|--------|Resistor 4k7|----*---|pin of MCU|

|Emitter|--------|Vcc|

|Collector|----*---|Relay|---*----|GND|
               |             |
               |---|1N4148|--|

I only found divergent opinions on the Internet without final conclusion :-( Darlington is often mentioned but I think this schematic works similarly and in additon it is simpler, isnt it? Thank you very much for you help...