enter image description here enter image description here I find some random issues that is still unknown. I'm using mean well SMPS 12v, 3A for supply and charging 2 cell battery 7.4v with a charging current 1.2A. The supplies are parallel which is switched by LTC4412 power path controller.

The issue I'm getting in my product: When turning on the AC supply device stops working and runs only when the battery supply is present.

This issue doesn't happen in all the devices. In some similar devices it rarely occurs and in some devices it is frequent. The AC voltage observed is 230v (L & N) 30v in (G & N). What might be the issue in the input side?

  • \$\begingroup\$ Way too little information! Post schematic. Clearly define “not working”. Post oscillograms. \$\endgroup\$ – winny Jun 21 '19 at 9:25
  • \$\begingroup\$ The schematic is huge. Shall I share only the power input part? \$\endgroup\$ – PCBLearner182 Jun 21 '19 at 10:43
  • \$\begingroup\$ @winny , 'Not working' . When turning on the AC supply micro controller does not start and when turning off circuit takes battery power and controller starts. \$\endgroup\$ – PCBLearner182 Jun 21 '19 at 12:52
  • \$\begingroup\$ Find out why. Does Vcc drop? When? How fast? Why? Does UVLO trip? When? Why? Is reset pulled high? When? Why? And so on. \$\endgroup\$ – winny Jun 21 '19 at 16:51

If the Meanwell supply is a voltage source rather than an LED current source, then the voltages must be closely match to the load, which is not the case here.

When you drive 12V 3A limit with some C source to a 6.4V low battery the current across the switch is too high to regulate and it shuts down.

Thus your voltage in and out must be closer matched to supply a charge current limited by RdsOn, delta V/Rs with Rs including battery ESR( e.g. 50mx2=100mOhm), Supply (<10mOhm, depending on load regulation error deltaV/Delta I) and current limit of supply after a surge 2A.

Beware that you do not use current sensing Rs to battery, so you cannot regulate CC and CV with cutoff when you have an external load current during charging. Warning !

Alternatively you can create a buck regulator to step down the voltage using PWM with supply suitable choke and clamp diode by storing the current I*t between pulses.

  • \$\begingroup\$ The switch is a push button switch of 12V, 2A. The battery charging unit takes 1.3A max and if the internal circuit takes more than 800mA at any time will it cause a problem on device functionality ? \$\endgroup\$ – PCBLearner182 Jun 24 '19 at 9:23

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