Do you know the waveforms of ISO 7637 surge at the power port?
Latest update time：2019-11-21
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This time I will talk about the transient conduction anti-interference of BMS power lines. At the same time, I also bought the latest version of ISO7637/ISO 16750 from the Internet, which has been included in the shared standards; I updated the standards, documents and pictures over the weekend. , if necessary, you can leave a message to download; OK, let’s start working.
First, put the information referenced in this article below:
Eliminate Those Automotive Load-DumpCircuit-Protection Headaches
TI ISO 7637 training materials
ISO 7637-1:2015-Definitions and general considerations
ISO 7637-2:2011-Electrical transient conduction along supply lines only
ISO 16750-2:2012-Electrical loads
There are many transient surge interferences in automotive electronic systems, which can affect or even damage electronic equipment, such as the interference sources listed in the table below.
This article only discusses the transient surge interference on the power supply line of automotive electronic equipment.
The transient surge on the power line mainly comes from the energy release of the inductor, and the preceding action is the closing or opening of the switch. Inductance may come from inductive loads, line stray inductance, etc. Don't feel mysterious. This inductance actually exists in the circuit, such as wires, motors, etc.
For these common surges, several more representative surge waveforms were gradually summarized in practice, and then became standards for testing or verification, and eventually evolved into clear requirements of the OEMs and fell into the SOR.
There are a total of eight waveforms: PULSE 1, 2a, 2b, 3a, 3b, 4, 5a, and 5b. They were all included in the ISO 7637-2 standard at first.
Later, PULSE4, 5a, and 5b were included in ISO 16750-2
. The following Let’s start introducing them one by one.
PULSE 1
: This is used to simulate when the product is connected in parallel with an inductive load. If the power supply is suddenly disconnected, the voltage at both ends of the inductive load will be applied reversely to the product's power supply end. This depends on the anti-reverse circuit at the product's power supply to withstand this.
PULSE 2a
: This is used to simulate the stray inductance on the power supply wire harness. As shown in the figure below, due to the disconnection of a parallel load, the current in the stray inductance of the wire harness changes at the power supply point, thereby generating a positive voltage superimposed on the power supply point. This requires a surge clamping device at the product's power supply port.
PULSE 2b
: This is used to simulate when the product is connected in parallel with a DC motor. When the power supply is disconnected, the DC motor becomes equivalent to a generator, generating a positive voltage that is applied to the power supply, a bit like energy recovery.
PULSE 3a
: This is somewhat similar to waveform 1. It simulates the periodic surge impact caused by arcing after disconnection when the power switch is a mechanical switch. The amplitude is both positive and negative, and the speed is very high.
PULSE 3b
: Similarly, this is similar to waveform 2a. It also simulates the periodic surge impact caused by arcing after disconnection when the power switch is a mechanical switch, and the speed is very high.
PULSE 4
: When this simulated starter is powered on and started, due to the large inrush current, there is a large voltage drop on the line, which in turn causes voltage fluctuations at the power supply of the product. To put it bluntly, it is a low-voltage starting problem.
PULSE 5a\5b
: This is the so-called
Load Dump
, and it is also the surge waveform with the largest energy. It simulates the alternator charging the battery with a large current. If the battery is accidentally disconnected, the alternator's output voltage will rise sharply and be applied to the product's power supply.
The difference between waveforms A\B is that waveform B assumes that there is a clamping protection device (clamped to 35V) outside the product; while waveform A does not, all surge energy needs to be resisted by the product itself.
Summarize
:
This time, we summarized several waveforms of transient conduction surges at the BMS power supply. The focus is on understanding the shapes and conditions of generation of several waveforms. It needs to be emphasized that all test parameters need to be negotiated with the OEM. This is a matter of Very important thing; it also passed the 7637 test, but if the test parameters are different, the actual protection circuit will be very different.
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