LED driver question

Thread Starter

psoke0

Joined Mar 31, 2017
187
hi guys. i have a curcuit that im simulating in ltspice. here it is

led.png


the 80 leds drops Average of 281v . resistor is dropping Average of 15v . and the transistor dropping average of 13,7v . well because its PWM average values is okay for the transistor to run at that voltage. but at On time the peak voltage shows transistor is dropping 141v. is the transistor will burn like this or not because its breakdown voltage is 55v . can you guys help me please. thank you
 

Ian0

Joined Aug 7, 2020
5,163
I wouldn‘t recommend it, but a there will be a voltage below which the LEDs do not conduct, probably about 2.5V, so you might just get away with a 110V transistor. (Compare with nixie tubes which can be driven with 50V drivers, because they don’t conduct below 150V).
400V MOSFETs are cheap, why take the risk?
By the way, 310V looks like rectified 220V AC to me. What would happen if your mains supply were 242V? I bet there’s a 10% tolerance on it.
 

Thread Starter

psoke0

Joined Mar 31, 2017
187
I wouldn‘t recommend it, but a there will be a voltage below which the LEDs do not conduct, probably about 2.5V, so you might just get away with a 110V transistor. (Compare with nixie tubes which can be driven with 50V drivers, because they don’t conduct below 150V).
400V MOSFETs are cheap, why take the risk?
By the way, 310V looks like rectified 220V AC to me. What would happen if your mains supply were 242V? I bet there’s a 10% tolerance on it.
thanks for the answer. yes it is rectifed mains of 220 :) i just wanted to learn what should i consider in this type of curcuits. like is the average or peak voltage important here. or is it both . i think its both. because if the average is above max volt rating then u cant use it anyway . but the peak is above u cant use it either i think
 

Thread Starter

psoke0

Joined Mar 31, 2017
187
Hello,

You must use a mosfet with a much higher breakdown voltage as the IRFZ44.
Have a look at the BUZ90 or BUZ380.

Bertus
yeah i didnt have it so i thought what is the important thing here if i use this mosfet should i consider average or peak voltage thats why i posted here to learn from you guys about this
 
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