MOSFET High side switching at low Voltage

Thread Starter

DanSohan

Joined Jan 6, 2021
18
Hi - had to go back to the drawing board on a battery charger design.

I need to high side switch a 1.5VDC source into a resistive load. I was going to use a P-Channel mosfet, but having trouble finding one that will work below 3V on the source.

Gate signal from arduino nano so a PWM signal at 3.3V
I need to be able to switch 1 to 15V at 6 amps.

Is there any MOSFETs that anyone could recommend for this application? Preferably a PCB through hole package.

Thanks in advanced.
 

TechWise

Joined Aug 24, 2018
143
Why not use an N-channel MOSFET and a high-side driver IC with a bootstrap circuit?

Something like the IRS2117 which comes in a through-hole PDIP package.
 

Thread Starter

DanSohan

Joined Jan 6, 2021
18
yes, the nano boards we have seem to be 3.3V out on the PWMs - I could swap back to an UNO with 5V out, but I was still having trouble with switching the low voltage source.

I have tried low side switching (works great), but this gives me issues with reading voltage and current of load via a low side current sense resistor.
Ideally High side switch was desired.

looked into DCsolid state relays, but many of these have low switching frequencies <100Hz, not ideal for the PWM signal.
 

Veracohr

Joined Jan 3, 2011
738
You can use an N-channel as a high side switch as long as you’re able to generate a high enough gate voltage. That’s why TechWise mentioned a driver IC.
 

Thread Starter

DanSohan

Joined Jan 6, 2021
18
You can use an N-channel as a high side switch as long as you’re able to generate a high enough gate voltage. That’s why TechWise mentioned a driver IC.
I will only have 3 to 5v to work with. Without more supply to provide would the MOSFET driver achieve anything?
 

Veracohr

Joined Jan 3, 2011
738
Yes, a bootstrapped driver circuit creates a voltage higher than the supply voltage. There are plenty of ICs out there to do rhis.
 

Thread Starter

DanSohan

Joined Jan 6, 2021
18
Yes, a bootstrapped driver circuit creates a voltage higher than the supply voltage. There are plenty of ICs out there to do rhis.
ah - great! Wasn't aware of this, last time I used a MOSFET driver is just improved the squarewave. I'll take a look into "booststrap drivers"! Cheers
 

Ian0

Joined Aug 7, 2020
1,121
Do you have a 12V supply available?
If your drain is only at 1.5V, then you don't need a bootstrapped driver, a simple low-side driver like MCP1401/2 will do the job (even though this is technically high-side driving) if it has a supply of 9V or more.
A high-side driver has a minimum operating frequency, something like a MCP1401 will be happy at DC.

You say you want to switch 1.5V, then you say you want to switch 1V to 15V. Could you please clarify?
 

Thread Starter

DanSohan

Joined Jan 6, 2021
18
Do you have a 12V supply available?

You say you want to switch 1.5V, then you say you want to switch 1V to 15V. Could you please clarify?
No, I have the USB power to supply the arduino at 3v3 or 5V if use Uno over Nano.

The charger I would like to build would be adjustable between ~1V and 15V would be great, up to 24V would be ideal! - this supply is isolated from the control circuity. Only the analogue inputs of the Arduino and ground are connected.

After searching bootstrap mosfet on youtube I found this video: https://www.youtube.com/watch/zcQV_ZpK1W8

Implemented the covered design with additional BC548, 1N4148 and 2.2uF Cap and it seems to work perfectly for my application.

Thanks for the advice all! much appreciated.
 

Thread Starter

DanSohan

Joined Jan 6, 2021
18
It will be fine for supplies greater than about 5V, but won't work at all at 1.5V.
You were right, it worked fine initially, but after some additional testing it proved unreliable. I've decided to try another method of current sensing in hope I can use a simple N-Channel MOSFET.
 

Sensacell

Joined Jun 19, 2012
2,673
You don't say anything about the frequency or duty cycle of the switch application?

If it's slow, you can use a charge-pump to generate a low-current -5V negative bias voltage that can turn a PFET on hard, even with 0 volts on the source.
Pull the gate to a negative voltage, makes the source positive.

Clamp the Vgs so it doesn't go over the max Vgs when you have 15 Volts input.
 
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