How to place a capacitor to filter out transient power outage.


Above circuit supposedly has 300ms of power interruption upon switching from input to battery. I want to filter out that transient power outage with a capacitor. My circuit will use 5V at 200mA. Can I just connect a capacitor, maybe 100000uF, parallel to the output terminals?

Pyritism:


Above circuit supposedly has 300ms of power interruption upon switching from input to battery. I want to filter out that transient power outage with a capacitor. My circuit will use 5V at 200mA. Can I just connect a capacitor, maybe 100000uF, parallel to the output terminals?

Consider the voltage on the capacitor will immediately begin to drop from the 5 volts you are using. The more time passes, the lower the voltage. Is this ok for your project?

Paul

Sure. It can tolerate as low as 3.3V, but 3.5V to be on safe side. So, it's 1.5V drop, with 200mA for less than half a second. I think it's around 70mF (70000uF) capacitance?
Problem is, I don't know if I should place a resistor somewhere on the circuit.

Pyritism:
Sure. It can tolerate as low as 3.3V, but 3.5V to be on safe side. So, it’s 1.5V drop, with 200mA for less than half a second. I think it’s around 70mF (70000uF) capacitance?
Problem is, I don’t know if I should place a resistor somewhere on the circuit.

IF the internal resistance of the power supply is great enough, that will limit the charging current. No resistor is necessary. Any resistor will limit the current to your project, as well as limiting the charging current.

You won’t know until you try it!

Paul

Pyritism:
Above circuit supposedly has 300ms of power interruption upon switching from input to battery. I want to filter out that transient power outage with a capacitor. My circuit will use 5V at 200mA. Can I just connect a capacitor, maybe 100000uF, parallel to the output terminals?

Have you tried it, before going and buying capacitors?
Tom... :slight_smile:

If you want to be safe you can place a "large" (i.e. 100Ohm) resistor between the capacitor + and 5V rail and a huge Schottky diode parallel with the resistor to power the load. If the diode is rated for 3A it will have about 200mV forward drop at 200mA forward current. If it is rated for more current the voltage drop will be even less. You do not care about reverse leakage current of the diode for this application so you are limited only by cost and size.

Unless you provide datasheet or product page for the module you are talking about its hard to answer
this question. I would be surprised if there is any switching delay personally…