hi.
I'm desiging switch mode power supply using the "LM2576-ADJ"
As much as I know the ON/OFF pin is only the switch on and off the lm2576. how can I make it also control the output current? it doesnt make senes to me.The most easiest and cheapest way I can suggest you to play with On/OFF pin of LM2576. Use any open collector voltage comparator (eg. LM339) and limit your current by swithing On/Off of your regulator.
mine is 2576 not 2676.LM2676 has a so called "cycle-by-cycle current limiting" function. By driving its ON/OFF pin with a PWM signal, you could force the output to OFF state till the end of the current (internal) clock period, thus reducing the internal PWM duty cycle. But, once again, you still need some external components for that.
As much as I know the ON/OFF pin is only the switch on and off the lm2576. how can I make it also control the output current? it doesnt make senes to me.
Current is depend upon load. Therefore, you can set the Maximum current limit through comparator. As soon your load current crosses the limit ur regulator switched off.
if I put 15V in, the output should be 15V, and that I can adjust the output current, and not the output voltage like most of the schematics I saw. Vin = Vout, Iout = set by potentiometer.
15V was an example. the voltage is going to change and I'm aware of the voltage drop and the other things.This way, you can at best implement "hick-up" current limiting but no continuous limiting.
You should observe the minimal voltage drop and maximal buck converter duty cycle of different switch mode ICs. LM2576 has e.g. 1.4 V typical saturation voltage and 98 % duty cycle limitation, so you won't get more than 13.3 V output.
Do you mean a linear current regulator? You can make it using a MOSFET, an OP, a shunt and some additional components.I wonder if there is some type of "current regulator" that works like a voltage regulator, but that can control the current and not the voltage.
Adjust the limited current, and not fixed load, its for a power supply so anything can be connected and I need to LIMIT the current that is following. lets say I connect an LED to the power supply, it can be anything but for an example LED, and I want to limit the current to 20mA, or 30mA, or 3A. so I need adjustable current limiting circuit.To adjust current to a fixed load you have to increase the voltage to force more current to flow. Or decrease the voltage to limit the current.
Current = Voltage / Resistance
The resistance is your load.
And the resistance is fixed, so you can only adjust the voltage to change the current.
What is the "set off" pin and what is the "monitor" pin?
I thought some things to be self-explanatory...What is the "set off" pin and what is the "monitor" pin?
Yes, according to suitable circuit parameters, e.g. MOSFET and shunt rating. Generally considering ohms law.it is supposed to give me adjustble current limit up to 3A?
thanks for your help. I would wait to see if someone have other options that works better or just easier.I thought some things to be self-explanatory...
"set off" - a means to switch the output off
"monitor" - a line that indicates if the circuit is operating in current limit or not
Yes, according to suitable circuit parameters, e.g. MOSFET and shunt rating. Generally considering ohms law.
Designing the circuit for 3A range makes it difficult to set e.g. 20 mA exactly. Not a property of the circuit in particular but of the involved component parameters, e.g. OP offset voltage.
Another general remark. Operating a linear current limiter at higher currents involves large power dissipation for the output transistor (P = I*V). The monitor/set off lines may cooperate with a circuit that shuts the circuit down after a certain time of continuous limiting.
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