The Importance Of Current Sense Resistor In Switch Mode Power Supply

1. The current sense resistor is usually located in https://shunts.com/ the switch mode power supply area. A more recent version of monitor-the b+ (boost) circuit also has this current sense resistor. If you repair electronic devices specifically the switch mode power materials, the current sensing resistor is connected to the source pin of power FET (field impact transistor) and the other end to HOT GROUND. The worth of the current sense resistor is in the series of 0.1 ohms to about 1 ohm. The worths depend on the design of each power supply. In screen power supply where pulse width modulation (PWM) IC UC3842 are utilized. Pin 3 of this power ic is called I-sense which suggests current sense and this pin is connected to source pin of POWER FET. The function of this current sense circuit is for overcurrent defense. This circuit generally samples the voltage drop throughout a resistor in series with the changing FET transistor. If the current rises abnormally due to some brief circuit in the secondary side such as a shorted secondary diode or horizontal output transistor (HOT), the voltage will exceed a referral level and shut down the pulse generator which is the PWM IC. This circuit supplies defense to components in case an issue occurs. In some cases where overload happen-the power area will blow and most of the time the elements changed are the fuse, power feed, PWM IC, Zenner diode and current sense resistor. Do you understand that a little change in this current sense resistor worth have a fantastic effect on the secondary output? A little change in worth say from 0.22 ohm to 0.44 ohm can cause your output voltage to drop into half! I have seen a lot of repairers can't discover this type of issue (low output voltage) due to that they used an analog or digital meter that does not have the low ohms range. You can't distinguish if the low ohms resistor has its worth altered by utilizing typical meters. I personally utilize the Penis Smith ESR Meter which has the capabilities to check resistor worth to 0.01 ohm! If you do not have this the special meter you might just direct change the current sense resistor to see if the generated secondary output will back to typical voltage. Another idea is that if the current sense resistor in the display B+ circuit has actually changed the worth it will trigger the output in the boost circuit to end up being low and you will have a small width display and obviously, the high voltage will end up being low also. Instead of 24Kv, it ends up being 15-18Kv. The current sense resistor is generally located in the switch mode power supply section. If you repair electronic equipment particularly the switch mode power products, the current picking up resistor is linked to the source pin of power FET (field result transistor) and the other end to HOT GROUND. The worth of the current sense resistor is in the variety of 0.1 ohms to about 1 ohm. In some cases where overload happen-the power area will blow and most of the time the elements altered are the fuse, power feed, PWM IC, Zenner diode and current sense resistor.