I am playing around with design of a ISM remote control and I have a dilemma on the power supply section of it, I would be very interested in your suggestions and views.
Referring to the very simplified diagram, relevant sections are as follows:
Battery is a LI-ion 18650 3V7 3A
MCU is a low power/voltage PIC operates down to 2V
TX module works at 3V7 max @ 125mA
The battery fully charged can be as high as 4V2 this is the main issue as the TX module max Vin is 3V7. I know the simplest way is to put a diode in series and drop a little across that, but I will be wasting power as the design is to have the battery last for a couple of years at least before a recharge is required. I don’t particularly need rechargeable battery but the 18650 is the only battery that fits the bill in terms of V/I, and physically being easy to remove from the unit to charge. I can’t put a socket for recharging as the IP rating would be an issue and don’t want to do wireless charging as it would complicate it unnecessarily.
At the moment I have Q1 representing a low voltage 3A high side switch that can be switched via the MCU, I could put 2 of these one with a diode in series to drop the excess and one without. The MCU is connected directly to the battery and R1/R2 feed the A/D of the PIC for voltage measurement once the battery V has dropped to 3V7 then I can switch the path to the switch without diode. Battery V is also monitored so that once it drops to 3V the switch would not be operated so that to avoid battery damage as battery would need to be charged. Operating cycle would be once a week or something like that so that battery would last for a very long time. As I couldn’t find a non-rechargeable battery that would give me 3V7 & around 2-3A I ended up with 18650.
No very efficient way, also the logic high out of the PIC would be above VCC of the TX modules. Would appreciate any thoughts on this.
Referring to the very simplified diagram, relevant sections are as follows:
Battery is a LI-ion 18650 3V7 3A
MCU is a low power/voltage PIC operates down to 2V
TX module works at 3V7 max @ 125mA
The battery fully charged can be as high as 4V2 this is the main issue as the TX module max Vin is 3V7. I know the simplest way is to put a diode in series and drop a little across that, but I will be wasting power as the design is to have the battery last for a couple of years at least before a recharge is required. I don’t particularly need rechargeable battery but the 18650 is the only battery that fits the bill in terms of V/I, and physically being easy to remove from the unit to charge. I can’t put a socket for recharging as the IP rating would be an issue and don’t want to do wireless charging as it would complicate it unnecessarily.
At the moment I have Q1 representing a low voltage 3A high side switch that can be switched via the MCU, I could put 2 of these one with a diode in series to drop the excess and one without. The MCU is connected directly to the battery and R1/R2 feed the A/D of the PIC for voltage measurement once the battery V has dropped to 3V7 then I can switch the path to the switch without diode. Battery V is also monitored so that once it drops to 3V the switch would not be operated so that to avoid battery damage as battery would need to be charged. Operating cycle would be once a week or something like that so that battery would last for a very long time. As I couldn’t find a non-rechargeable battery that would give me 3V7 & around 2-3A I ended up with 18650.
No very efficient way, also the logic high out of the PIC would be above VCC of the TX modules. Would appreciate any thoughts on this.
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