Hot!Current draw of blank PIC12F1822, and low power 5V supply from 60V

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PStechPaul
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Re: Current draw of blank PIC12F1822, and low power 5V supply from 60V 2018/02/14 16:26:31 (permalink)
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Here is an image of the simulation with a 500 uF capacitor on the Vdd-Vss lines:
 

 
The MOSFET is only a simple way to simulate the PIC and other circuitry turning on and off (sleep). But I may also need to use a PMOS device to apply and remove power to a Bluetooth device that draws up to 20 mA. However, that may also cause problems because it takes a while to pair and establish communication with the Bluetooth COM port of the computer. But it may be OK, because the final design will not use Bluetooth, or it might be turned on and off manually to observe the SOC of the battery (pack).
 
The prototype I'm building will just monitor a single 12V battery, and I plan to add an I2C LCD character display which should take minimal current. However, I might also consider the Bluetooth Low Energy (BLE) modules which have a peak current of 12.5 mA and average current less than 10 uA:
 
http://www.nordicsemi.com...oth-low-energy/nRF8001
 
It looks like this does not require the high-priced contracts involved with standard Bluetooth, so it would make it possible to market the device at reasonable cost. I should start a new thread if I go in this direction, possibly using the Microchip BLE product.
 
https://www.adafruit.com/product/1697

 
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PStechPaul
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Re: Current draw of blank PIC12F1822, and low power 5V supply from 60V 2018/02/16 02:42:34 (permalink)
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I just found that my HC-05 Bluetooth adapter draws as much as 41-56 mA on start-up and then 12 mA while communicating, and 4 mA while idle. My low power linear regulator can't handle the start-up currents. It will handle 5 mA and probably the 12 mA while communicating, so I may need to use another means to power it, perhaps only for development work. I'll just use a 78L05 for the Bluetooth, and switch it on under control of the PIC using an opto-MOSFET TLP175.

 
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PStechPaul
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Re: Current draw of blank PIC12F1822, and low power 5V supply from 60V 2018/02/25 03:08:05 (permalink)
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I have built the circuit with the regulator shown above, but it is really not good enough for what I need. The I2C LCD display also draws considerable current, and it takes some time for the voltage to stabilize when I switch on the power supply for 1 second every 10 seconds. The Bluetooth takes much longer to power up, pair, and connect, so it will need to be a manually selected option that will allow monitoring of the battery for some period of time and then automatically (or manually) shut down to conserve charge.
 
I'e found several more switching regulators that can do the job, with some trade-offs. An LM2574 handles 37V and the H version handles 57 volts, which is just enough for four fully charged (or charging) batteries at 14V each. However it has an operating current of 5-10 mA and costs about $2.50 to $4.
 
A MAX5033 handles 76V input and puts out 500 mA with 270 uA quiescent current, and costs about $3 in an SO8 package. An MCP16301 handles 30V input and 600 mA output with 2.7 mA quiescent current, for about $1 in an SOT23-6 package. I have some MC34063A devices which handle 40V and 1.5A with 4 mA quiescent current, in a DIP8 or SO8 package for about $0.63. And, finally, I have some UC3843 devices which handle 30V and 500 mA, with 12-17 mA quiescent current, in a DIP8 package for $0.79.
 
For my present design, for a single 12V battery, I can use any of the above, but I'd like to be able to design it so it can handle 4 batteries. Some of the above will do that, but at some expense. So I designed a pre-regulator that efficiently clamps the input voltage to the switching regulator to under 30 or 40 volts when a higher voltage is applied. With a switching regulator, even at 5 volts and 50 mA output, the input will be less than 15 mA, and at worst the pre-regulator will just need to drop 60-30=30V at 15 ma or 450 mW. For the display, I can switch it on for 1 second and off for 10 seconds, and also disable the switching regulator, while the PIC sleeps, drawing its power (300nA for LF device) from a 500 uF capacitor which should be good for about 10 seconds. Or I could just use a 100k resistor and 5V zener and pull up to 100 uA from the battery for the 30 uA sleep current of the standard PIC16F1825.
 
Here is the simulation for the pre-regulator. The LED is not needed, but it might show when the input is greater than the 30-40 volts to the switching regulator.
 


 
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