Hi Group,
Around the middle of December, the Batteroo team announced that they were having problems with a new IC designed for this application:
Dear Indiegogo supporters,
I want to take this opportunity to wish you and your families Happy Holidays and a wonderful New Year full of happiness, joy, and prosperity. I also want to give you another summary update with regards to our product shipment.
With each passing day, we are getting closer and closer to shipping your Batterisers. As you may recall, we initially planned to ship the 500 milli-amp beta version of the Batteriser; however, we made a strategic decision to deliver Batterisers with a new IC (Integrated circuit) capable of driving 1300 milli-amps of steady state current. We did this because the new version will make Batteriser more compatible with a wider range of devices, and we want to give our backers the absolute best final product that we believe they deserve. Unfortunately, in the construction of the updated Batteriser IC, we encountered unexpected technical fabrication process related issues which caused us to miss our estimated November shipping date....
So what would it take to do this?
Here is a little Boost Converter Maths:
Iout (MAX) = (Isw(peak) – (Iripple/2)) Vin/(Vout + Vdiode)
Iripple is normally chosen to be Iout x 0.4
(40% ripple current)
Rearranging to get the peak switch current:
Isw(max) = 1.2 x Iout(max) x ((Vout + Vdiode)/Vin)
So if we have:
Iout(max) = 1A (less than the 1300mA above)
Vout = 1.5V
Vin(min) = 0.8V
Vdiode = 0.1V (synchronous rectifier)
Isw(max) = 1.2 x 1 x ((1.5 + 0.1)/0.8V)
Isw(max) = 2.4A
If I recalculate for 1300mA
I get Isw(max)= 3.12A
This is a big switch.
Now to the IC design. One of the first, and really successful, low-voltage, integrated circuits was designed by the late, great Bob Widlar. The IC is the LM10. It is reported that it took Widlar a long time ( 5 years) to develop this IC. For the young kids, the LM10 is a combination of 200mV (sub-bandgap) reference and a rail-to-rail op-amp that work down to a Vin of 1.2V. The LM10 and the similar LT1635 are still in production after 30+ years.
To drive a switch either BJT or MOSFET from the input (0.8V) is going to be difficult. It is possible to drive the switch with power from the output (1.5V) once the circuit has started.
There are some BOOST ICs that will start from a very low voltage (the LTC3108 will start from just 20mV). This is achieved with depletion mode devices. There are more ICs that will start from 0.5V
I wonder how 'Uncle Bob's' IC is working?
(I am surprised one of the supports of the IGG campaign has asked for an update on the mid-December report.)
Regards,
Jay_Diddy_B