# SIM card power supply design, from 3V/50mA into 2.7V/10..100mA

I am designing a SIM card with RF radio included. The radio with its CPU needs minimum 2.7V to run. The current consumption is my problem: - for a period of 50msec (during transmission), it requires 100mA or more - for the same period afterwards, there is an idle period where it needs less than 10mA

The SIM card is plugged into any cell phone, which supplies on the SIM connector 3V/50mA guaranteed.

My idea is to take advantage of my radio idle period, charge something up, and add that charge to my high demand period.

In short: - supply to SIM card from the phone is 3V / 50mA (no more current allowed) - the SIM circuit requires 2.7V minimum, but the consumption needs to alternate between 10/100mA (50mA supply is not sufficient)

Sound like 'just add a capacitor'... but here is my last obstacle: SIM card is TINY, we have a total of about 8 x 10mm

We have tried to use a charge-pump to hold the 2.7V for as long as possible, but unless we are wrong, the capacitance needed is 1mF which we do not see how to do in the small size we have available.

Anybody has any smart idea how to solve this?

• I don't really understand what product that is.Are you're making a converter? – Daniel Tork Feb 17 '17 at 20:09
• Are you making the SIM card? What exactly are you making? Please be more specific. – Daniel Tork Feb 17 '17 at 20:12
• I updated the text. Should I write there more? – EmbeddedGuy Feb 17 '17 at 20:13
• Well let's see. You say something about a converter(in the title).Then, you specify "a product". You state that "you need more current" so that make me think that this circuit has a converter on it, but it can't output more current? There's a mess in my head. Help me get rid of it by specifying: – Daniel Tork Feb 17 '17 at 20:18
• Do you have a converter for the product? Is the voltage ok?More details about product like the entire setup: SIM card with wi fi adapter and bluetooth module for example. – Daniel Tork Feb 17 '17 at 20:20