I’m trying to find the best way to reduce the voltage from my 41V power supply down to the 21V needed so that I can read the 3.3V output from the MPM3610 buck converter on a Raspberry Pi GPIO pin. I’m trying to use it as a switch so when the output reads either 3.3V or 0V I’ll know the state of the switch. Are there any suggestions about the best way to go about doing this? Thanks.
Hello @robotnik2022 and welcome to the RobotShop community!
Unfortunately, the voltage regulators available in the store have a max input voltage of around 36V, nevertheless, this one might work for you:
Either way, it would be great if you could explain a bit more about what you have in mind as I’m not sure I understood. The MPM3610 is usually used to power 3.3V circuits from a higher-voltage battery or power supply, however, if you don’t have a battery/power supply of 21V or less a better option would be simply getting a 3.3 V DC Regulator.
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A Voltage Divider circuit. Divide by 2.
Half of 48 is 24. Acceptable at that level for most bucks/boosts.
Have the Divider circuit on a logical switch that can be toggled on or off by uProcessor control. Reason for this is that the Divider circuit only needs to be active if the voltage is more then 12v when measured. Half of 24 is 12. So when a reading of 12v or lower is sensed by the uProcessor, it then toggles the Divider circuit to OFF so that a true reading between 12v to 24v can be sensed, Voltages greater then 24v-true, toggles the Divider back on.
In logic the uProcessor already knows if the Divder is on or off since it is controlling it. So if it is ON in logic, whatever is present at the reading, you then multiple that value by 2 for the true voltage on the battery side of the Divider. Use very low ohm resistor on the Divider circuit to pull the line up so that at power up, the Divider is active by way of passives until the uProcessor comes online and gets its first reading. Then it toggles the line up or down and tracks it thereafter, internally.
If the pullup is not present, high voltages will be allowed past the Divider which could be undesirable. So the Divider circuit defaults to active at power up, even with voltages less then 24v. It also ensures that if by chance the uProcessor logic looses track of the switch in logic and High voltages are present on the rail but the switch is off logically, the pull up will be triggered automatically and turn the Divider to on and divide the sensing line until the uProcessor gets its act together logically and regains control of the correct state of the logical switch.
Understand?
Browse Voltage Divider circuits on Electronic sites for how to build one using a few components. The pullup then is just added to it to keep the line pulled HIGH when the uProcessor is not in in controll of it yet, as described. Dividers are simple circuits to toss together. Make sure one you find is able to handle the 48v on the high side of the rail.
Acigan International
Design Division
Hope this helps
Like this:
The uProcessor toggles the 4066 IC on or off and either the battery rail direct is sensed or the Voltage Divider Rail is sensed.
Logical switch on, sense x 2 = ~Battery voltage is via VDC*2, but its higher then 24 volts at the battery.
Logical switch Off, sense is at the Battery and is true voltage.
The VDC can be PCB’d or just solder up the component leads together, inline with the power rail. A tiny breadboard will also do.
The 4066 IC is a generic just for visual purposes. They have pre-4066 values and 4066-post values as part of the actual IC descriptor. The pre and post values will tell you what the switch can handle and its type of IC. You want to locate a 4066 that can deal with the 48v at the switch. Like a telecomm type 4066 class of switch. Examine data sheets and locate one that can handle 48v or more on the switch pins. The IC itself functions 3v or 5v at the control line and internally. But the input lines need to be able to handle the 48v, so pay very close attention to the MAX voltage stats in the data sheets as you locate one.