ahmedragia21
Member
Hi, i tried to switch on/off a fan using this IC but used it as a current source it didnt work , i usd it as a current sink it worked, why that happend ? and why only current sink worked ?
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Hi, i tried to switch on/off a fan using this IC but used it as a current source it didnt work , i usd it as a current sink it worked, why that happend ? and why only current sink worked ?
yea got it thanks , and if it was for current source what would be the difference or the change ?
thanks got it ! , yea PNP would do it because when it saturates it will close on the load and the load will draw current from the supply correct ?
yea got it thanks , and if it was for current source what would be the difference or the change ?
audioguru , cant the uC used as current sinking device and it will output 1.3mA that will feed the ULN2003 ?
by the way , i used an inverter 74HC00 after the uC then fed that to the ULN2003 and it worked.
What load current is the ULN going to sink.?
0.2A
In order to sink current the pin of the MCU would have to be connected to +5V via a resistor.
why ? doesnt when i ouput zero at the pin of the MCU it doesnt act as a current sink ?
Yes its a current sink, BUT where is it going to get the current to sink if there is no current source,... the resistor to +5V supplies the current.
. OK, now this is for current sinking , what configuration should i design to let the MCU source current?
Set the MCU output pin High [+5V], BUT as 'agu' explained it can only source 60µA, which will NOT drive the ULN
I dont know really why the 74HC00 solved the problem
The 74HC00 solves the problem because its CMOS and only requires µAmps to switch it. The output of the 74HC00 has enough current to drive the ULN
i found that the ULN doesnt work with zero Input that's why i made 74HC00 act as an inverter ,would you tell me the theory behind that ?