Is the power of the resistor enough? Please help me analyze it.

Knight97538

Is the power of the resistor enough? Please help me analyze it. [Copy link]

 

The following figure shows the pulse voltage waveform across a chip resistor. Does the power of the resistor meet the requirements?

吾妻思萌

I calculated that it was almost enough, but you have to leave a margin. The master would say 2 or even 3 times.

maychang

What is the value of the resistance of the OP? It is not enough to know that the voltage across the two ends is 42V and the pulse duty cycle.

chunyang

How to judge without even knowing the resistance value!

chunyang

Azuma Simeng posted on 2022-8-8 14:27 I think it’s almost enough, but you have to leave a margin. The master would say 2 times or even 3 times~

Tell us how you “total the total”?

天天1

Are you kidding me? You didn't even mention the resistance value.

秦天qintian0303

The package is not small, the pulse is not high, yeah, it should work

吾妻思萌

Azuma Simeng posted on 2022-8-8 14:27 I calculated it and it’s almost enough, but you have to leave a margin. The master will say 2 times or even 3 times~

Tell me how you "calculated"?

Just make a random calculation

baopodao

A resistor of 1K or above is sufficient. If heat dissipation is a concern, choose a resistor of 2K or above.

Fred_1977

The current parameter is the key. The current depends on how big your resistance is. Use Ohm's law to calculate it.

Knight97538

Fred_1977 posted on 2022-8-8 18:53 The current parameter is the key. The current depends on how big your resistance is. Use Ohm's law to calculate it.

470

Please leave the teacher's calculation formula

Knight97538

Tiantian1 posted on 2022-8-8 15:04 You are here to make fun of me. You don’t even mention the resistance value.

470

Please leave the teacher's calculation formula

maychang

Knight97538 posted on 2022-8-9 09:23 470 Euros, please leave the teacher's calculation formula

470 ohms, the average power dissipation of this resistor is greater than 0.25W at a voltage of 42V and a duty cycle of 2.2/16.8. So the conclusion is "does not meet the requirements".

maychang

Knight97538 posted on 2022-8-9 09:22 470 Euros, please leave the teacher's calculation formula

"Please leave the teacher's calculation formula"

Fred_1977 said in the original post: Ohm's law.

qwqwqw2088

This kind of pulse square wave power, whether it is the average value or the RMS value, should be calculated in combination with the duty cycle.

qwqwqw2088

Then, check whether the resistor package meets the power requirements.

1206 1/2W
1210 3/4W
2512 1W
This is the relationship between the size and power of most chip resistors

chunyang

There are two points to note when selecting the resistor power in the pulse signal circuit:

1. The transient peak power cannot exceed the tolerance limit of the resistor.

2. The average power cannot exceed the rated power dissipation of the resistor.

The above two points must be met at the same time, which is a mandatory requirement. In addition, the heat dissipation conditions and the impact of temperature rise on the resistor itself, the surrounding area and the system, and this is a long-term impact, must also be considered. Therefore, even if the two points mentioned above are met, an appropriate margin must be left. For resistors with higher power consumption, appropriate materials must be considered, not just any resistor that only meets the power requirements.

chunyang

Regarding the original poster's situation, first calculate the two points mentioned in the previous post, and then judge according to the other matters mentioned in the previous post. If you want to improve your ability as soon as possible, it is most important to think for yourself, rather than asking for ready-made answers.

chunyang

qwqwqw2088 posted on 2022-8-9 13:44 Then, see if the resistor package meets the power requirements 1206 1/2W 1210 3/4W 2512 1W This is the size and power of most chip resistors...

The rated power parameters in the manual of conventional surface mount resistors (thick film process) are not like this. The rated power dissipation of the E96 series resistors in 1206 package at 70 degrees Celsius is indeed only 1/4W, and the E24 series is only 1/8W. This is what the manual of chip resistors I have on hand indicates. You have to read the manual. The general information on the Internet is not accurate.

chunyang

qwqwqw2088 posted on 2022-8-9 13:44 Then, see if the resistor package meets the power requirements 1206 1/2W 1210 3/4W 2512 1W This is the size and power of most chip resistors...

I checked Fenghua Hi-Tech's conventional surface mount resistors, and the corresponding "conventional power series" and "enhanced power series" in Fenghua Hi-Tech's manual are 1/8W and 1/4W respectively. For alloy process surface mount resistors, the 70-degree rated power of the 1206 package can only reach 1/2W.