I wish to power LM239 comparator from a +5V single supply and use the open-collector output to switch a 24V load (resistor plus LED). Is this permissible?


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    \$\begingroup\$ Yes, if you look at the datasheet schematic (Figure 6) you can see the output is a single NPN transistor capable of withstanding 36 V and sinking 20 mA. \$\endgroup\$ – Jack Creasey Apr 13 '17 at 23:21
  • \$\begingroup\$ And this supply voltage is completely separate from the other +5V supply. What about supply sequencing? \$\endgroup\$ – mcintoda Apr 17 '17 at 1:04
  • \$\begingroup\$ +5 VCC should be up before the high voltage supply or else there is a chance of momentary high dissipation in the output transistor. \$\endgroup\$ – Jack Creasey Apr 17 '17 at 1:48

Since you have an open collector, the voltage used at the collector is independent from Vcc. Therefore, you can connect the collector to 24V supply, as long as you limit the current to 20ma max. In calculating the max current, assume the transistor is a short, so your limiting resistor should not be less that 1.2K ohms.


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