Screech New Member Jan 26, 2004 #1 Must you always use a resistor between most ic's out pin and a transistor? Egin 3 of 555 to an npn transistor. Say I need 200 milliamps going to base of tansistor mj150013. The 555's output can supply 200 milliamps. Can I run the 555's output to the transistor without a resistor? Will that cause the ic to short (as current flows from base to emitter(earth)). does the tranny act as a load from base to emitter? Think I'm going on and on. Thanks
Must you always use a resistor between most ic's out pin and a transistor? Egin 3 of 555 to an npn transistor. Say I need 200 milliamps going to base of tansistor mj150013. The 555's output can supply 200 milliamps. Can I run the 555's output to the transistor without a resistor? Will that cause the ic to short (as current flows from base to emitter(earth)). does the tranny act as a load from base to emitter? Think I'm going on and on. Thanks
L ljcox Well-Known Member Jan 26, 2004 #2 Resistors to stop shorts Yes, you need a resistor in order to limit the base current to a safe level. What collector current do you want? The base current only needs to be about one tenth of the collector current in order to saturate the transistor. 200mA seems a bit much. I don't know whether the 555 can source this much. Len
Resistors to stop shorts Yes, you need a resistor in order to limit the base current to a safe level. What collector current do you want? The base current only needs to be about one tenth of the collector current in order to saturate the transistor. 200mA seems a bit much. I don't know whether the 555 can source this much. Len
Nigel Goodwin Super Moderator Most Helpful Member Jan 26, 2004 #3 Yes, you need a current limiting resistor - otherwise you are effectively connecting the base emitter junction of the transistor straight across the supply rails - shorting them together.
Yes, you need a current limiting resistor - otherwise you are effectively connecting the base emitter junction of the transistor straight across the supply rails - shorting them together.
R Russlk New Member Jan 27, 2004 #4 The problem is that the 555 can output a minimum of 200 mA, typically it will output much more, possibly damaging the transistor.
The problem is that the 555 can output a minimum of 200 mA, typically it will output much more, possibly damaging the transistor.
Screech New Member Jan 27, 2004 #5 That transistor is a 5 amp one. Its hFE is 25 so 5000mA/25 =200mAmps. I only nead 4amps: 4000/25=160milliamps so I'm going to supply it with a bit more then 160milliamps, with a resistor. Thanks for answering my question guys.
That transistor is a 5 amp one. Its hFE is 25 so 5000mA/25 =200mAmps. I only nead 4amps: 4000/25=160milliamps so I'm going to supply it with a bit more then 160milliamps, with a resistor. Thanks for answering my question guys.