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  1. A

    voltage regulators!!

    Think of a transformer rated as 9V/2A, after rectification the current will be reduced to for example 1.95 Amps then that is the max DC current can be supplied by the power supply. If you connect it with 3 Ohms resistor how much current will be delivered to the load? By ohm's low 9/3 = 3 Amps...
  2. A

    5v to run a 12v electronic relay?

    Hello SunnySkyguy So i understood that, the capacitor pumps with opposite voltage to the coil for a short time at starting of NPN transistor goes on and after that the capacitor discharges through the NPN transistor because it has low resistance, means you just need pulse for pushing the coil up...
  3. A

    5v to run a 12v electronic relay?

    I want to analysis the operation mechanism of the circuit i made simulation to note how much volt will be devolved across the coil with power supply 6V and input voltage to NPN transistor 1.5. Suppose if the 1.5V is not applied to the NPN transistor and transistor is in off mode and in...
  4. A

    Transistor base current for this circuit ... Help

    I understood from your words if the transistor in saturation mode the hFE does not matter, but my simple question, how did calculated the Vce=0.05 V to know the transistor in saturation mode ?
  5. A

    Transistor base current for this circuit ... Help

    Hi godfreyl As your calculation on Ib= 7.6mA, you ignored the influence of the hFE and the value is big according if for example the hFE = 40 as min. value, the Ic would be 40*7.6 = 304 mA
  6. A

    Transistor base current for this circuit ... Help

    on transistor datasheet BD139 i have max rates , and from calculations as example i have ic= 10 mA how can i extract the Hfe from datasheet according to my calculations, and in the datsheet there is min. values according to test conditions and there is typical characteristics but i am confused...
  7. A

    Transistor base current for this circuit ... Help

    Hello I have this simple current source circuit and the current source through the collector is controlled by voltage drop across the transistor base emitter and resistor R5 Ic=Ie = Vbe/R5 but i want to know how much current flowing through the base and diodes ? The current flow through the...
  8. A

    How to calculate protecting resisotor betwen power supply and load ?

    I have question about, if i have a load (example Microcontroller) needs max constant voltage dc = 5 V and max constant current 100 mA and i have a power supply can supply only 5 v dc with max current 1 A How to calculate the protection resistance that should be connected between microcontroller...
  9. A

    how to make code protection for PIC

    Hello I want to make code protection for pic16f876, but i dont know how, i am using picbasic pro. so any idea? and if i make a code protection, can i erase the code protection and read the pic again ? Thank you
  10. A

    pic16f84A and 7-segments flicker, why?

    i am still sticking around the problem, i searched in internet for finding solution but nothing, all i would like to know when one of the 7-segments blinking and the other does not, as i said before, i used 2 digit 7-segments. i noticed maybe problem because of interrupt, because the interrupt...
  11. A

    pic16f84A and 7-segments flicker, why?

    hello i have a problem i could not solve it. my simple program counts from 00 to 33 and start again and using two 7-segments . The program counts with no problem, but the problem is, when i test it with ISIS Proteus, one of 7-segments flashes and the other one does not (i.e counts normally...
  12. A

    microcontroller parallel programming, how?

    i want to make a project , but this project dependence on 2 timers working at the same time. i want enable then at the same time the first one i named as (main timer) and duration is 30 minutes it will enable another timer counts for 5 minutes and relay too for and takes a rest for 50 seconds...
  13. A

    helo with flow meter water based PIC16f876

    help with flow meter water based PIC16f876 i want to build washing machine control system, but i am confusing on a device, that is flow meter water. i saw analog one on an industrial washing machine and takes hot water from boiler and the device reads the volume and send it to control system...
  14. A

    introduction to parallel EEPROM structure ???

    Hello everyone i want to learn how to program memory chips specially EEPROM , but i am not understanding timing diagram yet, so i want simplicity full introduction of memory structure from simple blocks (flip flops and so on) to advanced . I have HN58C256A parallel memory but i am confused on...
  15. A

    Heat sink with transistor

    Thank you for your replay But i want to know, is there any reference for using heatsink if the watts passed the margin? i mean if the watts for example 5 w or less how do i know i must attach heat sink any criteria for helping?? Thanks
  16. A

    Heat sink with transistor

    I am a little confused when should i use heat sink or not using it. For example if i want to design power amplifier or control servo motor and i use power transistor, and if transistor runs at IC = 1 A and VCE=10 V the power dissipation = 10 W . So how to know if that transistor needs heat sink...
  17. A

    questions on Sealed lead acid battery

    Thank you all for reply do you mean if i use 18 volt maybe the charging volt arise and exceeding more than 12 ?? so if i use 13 volt and diode in series the voltage drop will be 13 -0.7 = 12.3 v to insure that when volt starts to rise up it the diode will open , so using diode as switch. Is...
  18. A

    questions on Sealed lead acid battery

    Hello Friends i am confusing about using Sealed acid battery and i have some questions, but before i ask i would to put what i am understanding to find out if i am right or wrong i have lead acid battery 12 v/ 7.5 AH i want to use it for lighting 12 leds Red color red color led VF = 2 V...
  19. A

    When a heatsink is required on transistor ?

    @ keith1200rs i am still confused yet "65W is what the TRANSISTOR can dissipate if you hold the case at 25C" case at 25C ,so it should be at 25C despite of ambient temperature ??? i mean the ambient maybe at different temperature high or low so i understand from that : the transistor can...
  20. A

    When a heatsink is required on transistor ?

    TIP41 NPN in datasheet i see following Continuous device dissipation at max 25ºC case temperature (see note 1) Ptot 65 W Continuous device dissipation at max 25ºC free air temperature (see note 2) Ptot 2 W so what is the difference between p = 65 W and P = 2 W ? and which one should i use...

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