1
\$\begingroup\$

I am trying to figure out one of two ways to switch off the power in my circuit using an LM2596-5.0 switching regulator.

Option 1: In the datasheet it says you can pull the regulator ON/OFF pin to VCC to turn it off, with a loss of 80uA.

I'm using an SPDT switch, so if I choose the above option, the regular's input capacitor will remain charged, and won't the battery drain?

Option 2 is a more traditional way, leave the regulator ON/OFF pin tied to ground (datasheet says this will turn the regulator on), and the SPDT switches all of the power to the circuit, which charges the capacitor up and I'm sure eventually this might wear out the switch's contacts, despite it being rated for 5 Amps. The circuit consumes less than 50mA average, but I'm assuming that capacitor wants to charge quickly, hence my concern.

In either Option 1 or 2, I'm avoiding a parasitic loss on a voltage divider as shown in my schematic. Option 2 would avoid the 80uA loss if I use the regulator's shutdown feature, but in my application I don't need to worry about 80uA loss.

I see in the datasheet for the LM2596 that if I choose my Option 1 it would truly be a 'soft' start, which would extend the switch life? (not really an issue I'm thinking, due to the switch's rating, but I may be wrong?)

Can someone help me decide what would work best? Thank you.

BVCC is battery voltage which is connected to the common/center pin of the SPDT switch, the top pin of the switch is connected to the common/center pin when the switch actuator points downwards.

1st schematic showing Option 1:

enter image description here

1nd schematic showing Option 2:

enter image description here

\$\endgroup\$
  • 1
    \$\begingroup\$ so if I choose the above method, the regular's input capacitor will remain charged, and won't the battery drain? No, not if you use a decent capacitor there. A 680 uF cap should leak much less than the 80uA of the LM2596. \$\endgroup\$ – Bimpelrekkie Mar 3 '17 at 10:44
  • \$\begingroup\$ If the toggle switch can handle the current then I see no reason not to go for the simplest which is option 2. And you avoid that 80uA which may not be a problem but I'd avoid it anyway. \$\endgroup\$ – Bimpelrekkie Mar 3 '17 at 10:45
  • \$\begingroup\$ The capacitor would be a 35V Panasonic FK V series, pretty good quality I think. \$\endgroup\$ – klcjr89 Mar 3 '17 at 10:46
  • \$\begingroup\$ @FakeMoustache how will the capacitor affect the switch's contacts? Or will it not at all? \$\endgroup\$ – klcjr89 Mar 3 '17 at 10:47
  • 1
    \$\begingroup\$ What kind of comment is that? Plenty was stated in my question about concern with switch life, and asking if the regulator is soft-start or not. I already found out the regulator is soft-start in the datasheet just now. \$\endgroup\$ – klcjr89 Mar 3 '17 at 11:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.