A Darlington can never saturate - its worth remembering this when calculating the dissipation at maximum collector current.if i used TP121 npn transistor to control a load that will hold 2Amp . will it need a heatsink?
Maybe. Maybe not.if i used TP121 npn transistor to control a load that will hold 2Amp . will it need a heatsink?
Yes PMW will reduce the power dissipation in the transistor to just switching losses. The frequency does not have to be very high if the load has significant thermal inertia.what is the size of heat sink ?اif i used high frequency PWM , will that solve it?. this type is used in linear power so , i am on the right way.
That chip is for mains operated SMPSUs so you have to watch out for the UVLO, but with 24V you should be OK. There's an internal 30V zener on the Vcc pin so you have to protect it from any spikes on the rail that might exceed that - you'll probably have to use a MOSFET because that's what its designed to drive.the load is a proportional valve . the input signal will range from 0-24v . could i use UC3842 PWM controller.?
but if i used PWM i could replace this npn with a mosfet to hold more current as the operation will be converted to switching , won't it?
Yes, you should use a MOSFET for PWM, but not because it "hold (carries?) more current", it's because a MOSFET has no saturation switching delay, has a lower ON voltage, and requires no steady gate current (just what is required to charge/discharge the gate capacitance), so is generally more efficient as a switch................
but if i used PWM i could replace this npn with a mosfet to hold more current as the operation will be converted to switching , won't it?
but Mosfet is not designed for linear loads. how to use it with PWM will it do the job?Yes, you should use a MOSFET for PWM, but not because it "hold (carries?) more current", it's because a MOSFET has no saturation switching delay, has a lower ON voltage, and requires no steady gate current (just what is required to charge/discharge the gate capacitance), so is generally more efficient as a switch.
PWM gives you the net effect of linear drive while switching the MOSFET either fully on or fully off, so dissipation in the MOSFET is minimal.but Mosfet is not designed for linear loads. how to use it with PWM will it do the job?
please recommend one ULVOso you have to watch out for the UVLO, but with 24V you should be OK. There's an internal 30V zener on the Vcc pin so you have to protect it from any spikes on the rail that might exceed that - you'll probably have to use a MOSFET because that's what its designed to drive.
That's under voltage lock out - the chip you mentioned needs Vcc to reach 16V for it to start, once its running - taking Vcc down to about 10V will cause it to shut down.please recommend one ULVO
i propose the attached sketch . using a comparator will control the current of the mosfet by controlling the width of the duty cycle ,when the input signal changed from 0-24V. i put R1 to control max voltage consequently max current in the valve . i think now we don't need heatsink.
need your comment
What are you feeding into the comparator negative input?i propose the attached sketch . using a comparator will control the current of the mosfet by controlling the width of the duty cycle ,when the input signal changed from 0-24V. i put R1 to control max voltage consequently max current in the valve . i think now we don't need heatsink.
need your comment