Controlling a 5V pump with 3.3V

Thread Starter

xfeseab

Joined Jan 26, 2024
2
Hello,

I want to control a 5V pump with a 3.3V signal using NodeMCU-32S. The pump can draw current up to 120 mA. I have tried transistors like BC547 but failed. What should I consider when choosing a transistor to trigger 5V or more using a 3.3V signal in such cases?

My English is not very good, I apologize for spelling mistakes.

Thank you in advance for your help.
 

sghioto

Joined Dec 31, 2017
5,390
BC547 is only rated at 100ma
Use a 2N2222A or equivalent.
Show the schematic of how you connected the BC547.
Do you want to switch high side or low side?
 

jkhusky1587

Joined Feb 6, 2024
6
id recommend using a low side FET. you just need one with a maximum Vgs(th) that's a decent amount below your signal level. for example AO3400 maximum Vgs(th) is 1.45v which is plenty below 3.3v. 2.5v is cutting it close, but 1.45v is well below where you need it to be. AO3416 is a similar option with an even lower maximum Vgs(th). both AO3400 and AO3416 are widely available on aliexpress for like $0.01 each

the connections are very simple, here's a simulation link http://tinyurl.com/26a5jjc9
 

Thread Starter

xfeseab

Joined Jan 26, 2024
2
BC547 is only rated at 100ma
Use a 2N2222A or equivalent.
Show the schematic of how you connected the BC547.
Do you want to switch high side or low side?
I will post the schematic as soon as possible. What are the advantages and disadvantages of low side and high side? Thank you for your answers.

id recommend using a low side FET. you just need one with a maximum Vgs(th) that's a decent amount below your signal level. for example AO3400 maximum Vgs(th) is 1.45v which is plenty below 3.3v. 2.5v is cutting it close, but 1.45v is well below where you need it to be. AO3416 is a similar option with an even lower maximum Vgs(th). both AO3400 and AO3416 are widely available on aliexpress for like $0.01 each

the connections are very simple, here's a simulation link http://tinyurl.com/26a5jjc9
Gate-Source Voltage value for AO3400 seems to be +-12V. Gate Threshold value is between 0.65V and 1.45V. I don't quite understand how to use these values when choosing a MOSFET. Does the Gate Threshold value here mean the value at which the MOSFET starts to conduct, and the Gate-Source Voltage means the maximum value we can apply to the Gate? Will applying 3.3V to the gate damage this MOSFET? Please excuse my ignorance. Thank you for your answers.
 

jkhusky1587

Joined Feb 6, 2024
6
What are the advantages and disadvantages of low side and high side? Thank you for your answers.
Low side is easier to control and low side FETs (N-Channel) are cheaper/more available/more capable than high-side (P-Channel) FETs. There are no material advantages to P-Channel, but sometimes you need to use them or sometimes they're more convenient to use.

Does the Gate Threshold value here mean the value at which the MOSFET starts to conduct
yes
and the Gate-Source Voltage means the maximum value we can apply to the Gate?
yes
Will applying 3.3V to the gate damage this MOSFET?
no
 

MisterBill2

Joined Jan 23, 2018
18,535
Switching as stated will be simple with an NPN transistor like the 2N2222A, or an equivalent bipolar transistor. The pump must be connected between the positive 5 volt supply and the transistor collector, with the 5 volt return side (negative) connected to the emitter. The 3.3 volt control voltage must be connected to the transistor base, and the 3.3. volt negative also connected to the emitter.
A resistor may be required in series with the base connection to limit the base current, I have not calculated if that will be required.
I see no need to post a circuit this simple.
 
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