lm317 always breaks down

我在山东玩51

lm317 always breaks down [Copy link]

 

OUT is the access bus terminal. The bus is a centralized device, but the copied device is generally not powered. However, the LM317 will burn out after a long time. The phenomenon is that VIN VOUT breaks down or is close to breaking down. I can't analyze the reason for the time being. Please analyze it.

accon

MUB-like circuit? How is the heat dissipation of 317? I think it is just too hot because of too much power.

qwqwqw2088

How long will it take to burn out? Load size

The reasons for load startup shutdown and normal use are different

我在山东玩51

accon posted on 2020-7-20 07:27 MUBs-like circuit? How is the heat dissipation of 317? I think it is just too hot because of the high power.

Yes, it is the mbus circuit

我在山东玩51

accon posted on 2020-7-20 07:27 MUBs-like circuit? How is the heat dissipation of 317? I think it is just too hot because of the high power.

The heat dissipation is directly attached to the board surface and the current is about 200-400MA

chineseboyzxy

The input voltage is too high, close to the maximum value, and the transient high voltage is definitely more than 40V.......

我在山东玩51

chineseboyzxy posted on 2020-7-20 08:12 The input voltage is too high, close to the maximum value, and the transient high voltage is definitely more than 40V.......

317 seems to only require the voltage difference not to exceed 40V, and there is no maximum input voltage limit

qwqwqw2088

The load current is not large, it should be caused by the moment of DC power supply disconnection

maychang

I am playing 51 in Shandong. Posted on 2020-7-20 09:28 317 seems to only require the voltage difference not to exceed 40V. There is no maximum input voltage limit

In the original poster's diagram, when Q4 is turned on, the entire input voltage is applied between pins 3 and 1.

maychang

I am playing 51 in Shandong. Posted on 2020-7-20 07:50 The heat dissipation is directly attached to the board surface, and the current is about 200-400MA

When Q4 is saturated and turned on, the output voltage is 1.25V plus Q4 saturation voltage drop (a few tenths of a volt). If the current is 400mA, the power consumption of the tube is 32V*0.4A=12.8W. This power consumption is not small. Even if the time is very short, it may cause damage to the LM317.

chineseboyzxy

I am playing 51 in Shandong. Posted on 2020-7-20 09:28 317 seems to only require the voltage difference not to exceed 40V. There is no maximum input voltage limit

Please read the data sheet carefully several times...

小~明

Can't you lower the voltage?

accon

Your current solution is to reduce the rated output current or replace the DC-DC with a 100V MOS.

qwqwqw2088

What is the output V?

The reason why the pressure difference is too large and the heat power consumption

To power the mbus circuit, we need to figure out what the maximum current and power can be provided to each slave device node through the MBUS bus.

我在山东玩51

qwqwqw2088 Published on 2020-7-21 07:43 What is the output voltage? The voltage difference is too large, which causes heat and power consumption. To power the mbus circuit, we must understand that the MBUS bus is used to power each slave device node...

18-24v