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現在2147件がヒットしています。check
This is Sasaki in charge of power supply dock technology.
In this column, I would like to introduce some examples of problems related to power supplies that I encountered multiple times during various customer support sessions.
In this column,
We will solve problems while checking the "Problems that are likely to fall into power supply design" introduced in .
By all means everyone
While looking back, think together where the cause is.
Why does the power supply not start up properly?
One day, I received an inquiry that "the board does not start even when the power is turned on."
After talking to the customer, I learned that the board would not start because the power supply IC was repeatedly turning on and off.
(It seems necessary to check the problems that are likely to occur in power supply design one by one.)
First, let me check the power supply circuit.
Regarding the output part, are you using a large capacity capacitor? (See column 6)
home. Since we are using the manufacturer's recommended circuit diagram as is, we do not use large capacitors.
Here is the reason why the power turns on and off repeatedly when using a large capacity capacitor.
[Power supply column] No. 6 A power supply that repeatedly turns on and off at startup!
Next, check the voltage.
Was the measured voltage pre-biased? (Refer to the 4th column)
Yes, it is not pre-biased.
The reason why the power supply repeatedly turns on and off when the voltage is in a pre-biased state is here.
[Power supply column] No. 4 If you repeatedly turn it on and off, the power will not turn on...! ?
So that's it. . Let's check the operation of all the power supplies, including the current.
Check the operation of the power supply
As a result of checking, it was found that the current value flowing to the power supply IC reached the overcurrent limit.
It seems that the overcurrent protection was working because of that, and the power supply was repeatedly turning on and off.
Even so, why was the current flowing enough to reach the overcurrent limit?
How did you calculate the load current estimate?
Calculated with the maximum current value when all ICs on the board are operating.
I have confirmed this with the manufacturer, so I'm pretty sure.
Hmm. . .
So what about the value of the rush current at startup?
All devices have maximum inrush current, but they do not exceed the overcurrent limit.
Then, check the power supply sequence.
Are you following the power supply sequence recommended by the power supply IC manufacturer?
･･･.
Actually, I didn't follow the recommended power supply sequence.
But we checked it during the prototype evaluation, and there were no particular problems, so it's okay, right?
No. Unfortunately, I think this is where the problem is.
Many people tend to do this, but it is very dangerous to judge that there is no problem by checking at the time of evaluation.
It is very important to apply the manufacturer's recommended power supply sequence so that trouble does not occur during mass production.
It's was so. . .
I definitely thought it wouldn't be a problem.
Could you check it again by creating a sequence with power supply enable control?
After checking, it turned out that the change in the power supply sequence was the cause.
After adapting the power supply sequence recommended by the manufacturer, the trouble disappeared.
Cause of power supply IC repeatedly turning on and off
A change in the power supply sequence caused the current to reach the overcurrent limit.
The point of this time
Use the power supply sequence recommended by the manufacturer.
(It is extremely dangerous to make judgments based on confirmation during evaluation.)
Click here for recommended articles/materials
[Power Supply Column] Part 4: What happens when you repeatedly turn the power on and off? The power won't start up...!?
[Power Supply Column] Part 6: Power supplies that repeatedly turn on and off during startup!
List of Power Supply Columns
Frequently Asked Questions about Power Supplies