Commit 31fee49a authored by Alex Shure's avatar Alex Shure

MOSFETs

parent a12268d3
......@@ -11,9 +11,16 @@ Needed for precise ADC measurements. 2.56V?
### Switching
1. n-channel MOSFET switching the negative rail, while a common conductor is tied to the positive rail and possibly earth grounded. This will reduce the overhead for gate drivers, charge pumps or p-channel mosfets as switches. What are the downsides to this approach?
1. n-channel MOSFET switching the negative rail, while a common conductor is tied to the positive rail and possibly earth grounded. This will reduce the overhead for gate drivers, charge pumps or p-channel mosfets as switches. What are the downsides to this approach? Voltage sensing will be difficult as the MCU and ADC will be tied at the low side, not floating. A differential sensing with a common voltage higher than the maximum bus voltage is needed.
2. p-channel MOSFET on positive rail. More expensive, Rds worse, but common GND at 0V.
potential MOSFETs:
n-Channel
CSD18540Q5B
### Current Sensing
1. MOSFET Vds sensing. Only valid if the consumer is a pure current source or current sink. What happens if the gate is discharged and Vds rises to 50V? The following amp and ADC will go into saturation, this needs some more thought. High impedance line from the amp, limited with a diode (crowbar)? Possible if the input impedance is high enough. Temperature drift.
......@@ -41,9 +48,15 @@ Unplugging a consumer with an inductive load or a high current flow will result
8bit with integrated ADC should be sufficient. ESP8266 with integrated WiFi is inexpensive but has high power demands.
### Power Supply
For logic power a low Iq buck converter. Best with synchronous rectification, few external parts. Potential candidates: TPS54061 (0.09 mA), LM5156 (0.01 mA), LM5009A (0.5 mA), all types up to 60 Vin and about 150mA output.
If the n-channel MOSFET is switched at the high side a gate driver is needed. Power supply for the gate driver can be derived from the 3.3 V logic power if the gate driver can bootstrap it's high potential from that. Although a driver might charge and discharge the FET gate with 1..2A, the charge time is sufficiently low and can be buffered by caps. For a very low switching frequency (ie. using the FET as a power switch) this is fine. When the FET is used to throttle the output (e.g. via BAM / bit ampltitude modulation), the gate driver needs more power.
### Communication
Wireless: NRF24L01+ or WiFi with ESP8266
However, everything should be passive first and work plug and play without having a communication channel.
### Optional Display
......@@ -60,4 +73,4 @@ Small OLED
![](/cad/Wall Socket v4 inside.png)
![](/cad/Wall Socket v4 side2.png)
![](/cad/Wall Socket v4 front2.png)
\ No newline at end of file
![](/cad/Wall Socket v4 front2.png)
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