| ??? 07/18/06 14:49 Read: times |
#120483 - Alternatives Responding to: ???'s previous message |
Asok Sankar Rudra said:
Dear Members,
Can I drive a 12 Volts 400 Ohms relay (like LEONE SC5-S-DC12V OR GOODSKY RW-SH-112D)by a '51 microcontroller working at 5 Volts? I normally use 5 Volts 100 Ohms relays (GOODSKY GS-SH-205T-DS) with a BC557/8B and a 10 KOhms resistance connected between the port pin and the base. The collector goes to ground and the emitter to the relay coil, the other end of which is connected to the Vcc +5Volts,the usual IN4148 is across the coil.This unisolated arrangement works faultless even with inductive loads like fridge. When the same arrangement is used with 12Volts relay connected to 12v,the relay is put on only once by the microcontroller as desired, by clearing the port pin;but the relay cannot be put off by setting high the port pin.It appears that the transistor is leaking.Since the whole arrangement is on a transformerless platform,I would not like to fiddle and adjust bias.What is the proper design or shall I forget 12 Volts relays in this context? With best regards, A.S.Rudra As an alternative to a discrete component solution, you may wish to consider a highly integrated driver. Take a look at this thread: http://www.8052.com/forum/read.phtml?id=91200 Erik and I both commented on the use of integrated drivers. In particular, you might want to look at these messages: http://www.8052.com/forum/read.phtml?id=91206 http://www.8052.com/forum/read.phtml?id=91376 http://www.8052.com/forum/read.phtml?id=91397 --Sasha Jevtic |
