Happy new year guys,


My circuit is running on following battery, which has maximum pulse current of upto 400 mA. As with most embedded devices, my device spends most of its time in sleep state consuming uAs of current. But, roughly around every 2 hours, device need to drive a servo, which requires either 5V or upto 600 mA of current for couple of seconds. I tried placing a 1000 uF capacitors parallel to battery to help supply higher pulse current, but solutions doesn't seem to be reliable enough. Now I am thinking 2 approaches here.


https://uk.farnell.com/eve/er34615/battery-lithium-3-6v-d/dp/1973584


1. Boosting the current in my circuit, with a current boost IC, but as I understand it would have effect on the battery voltage, considering battery starting voltage is 3.6V and I need minimum of 3.3V for my circuit to operate.

2. Second solution would be to somehow boost the voltage with boost converter for only 2 seconds when servo is demanding higher voltage.

Your thoughts on this will be very welcome.

 

1000 microfarads is not enough. deltaV * Cx = i * t ==> Cx> 0.6A * 2s / 0.3V ==> Cx = 4 Farades. If you use a step-up stabilizer up to 5V and allow a voltage drop of 5V of 1.5V, then Cx = 0.6 * 2 / 1.5 = 0.8Farad. In my development I used a 1.5Faradx5V supercapacitor.

 

1000 microfarads is not enough. deltaV * Cx = i * t ==> Cx> 0.6A * 2s / 0.3V ==> Cx = 4 Farades. If you use a step-up stabilizer up to 5V and allow a voltage drop of 5V of 1.5V, then Cx = 0.6 * 2 / 1.5 = 0.8Farad. In my development I used a 1.5Faradx5V supercapacitor.

With supercapacitor, you mean ordinary cap with capacitance in range of Farads instead of Micro farads ?

 

What about the "normal" capacitor you said! Although in appearance they can be (just as they cannot) are similar to oxide capacitors. You can read about them on the Internet.

 

Below is the LTspice simulation of the circuit with the simulated battery limited to 400mA and a 2.5F buffer capacitor.
The 2s, 600mA load pulse from the motor drops the voltage from 3.3V to ≈3.1V.

 

What about the "normal" capacitor you said! Although in appearance they can be (just as they cannot) are similar to oxide capacitors. You can read about them on the Internet.
View attachment 167470

Below is the LTspice simulation of the circuit with the simulated battery limited to 400mA and a 2.5F buffer capacitor.
The 2s, 600mA load pulse from the motor drops the voltage from 3.3V to ≈3.1V.

View attachment 167476

How does this changes if load current for 2s is reduced to within 300 - 400 mAs