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How to drive a proportional solenoid from PWM?
To be clear, I’ll assume the problem is to control a 24 V 2 A solenoid proportionally from a 5 V digital PWM output. The PWM duty cycle is intended to be roughly the solenoid drive level. A 24 V supply with at least 2 A capability is available. Since you need considerable current, a FET is easier to drive in this case.
Can a MOSFET drive a PWM via NPN?
If you want to use a MOSFET the Si2318DS is suitable. It’s a 40V FET which can drive 3A at less than 4V V G S. R D S ( O N) is 45m Ω, so at 2A it will only dissipate 180mW. That sounds safe, but when you’re going to PWM this will rise due to switching losses. At 300Hz this will not really be a problem, however.
Can a NPN be used as a low side switch?
A NPN as low side switch would work, but even assuming a generous gain of 50 for a power transistor that can handle 2 A, that still requires 40 mA base current. That is more than can be expected from a ordinary digital output, so would require additional gain.
Do you need a NPN to drive a FET?
A 24 V supply with at least 2 A capability is available. Since you need considerable current, a FET is easier to drive in this case. A NPN as low side switch would work, but even assuming a generous gain of 50 for a power transistor that can handle 2 A, that still requires 40 mA base current.
How does a solenoid coil work with MOSFET?
Both Q1 and Q2 transistors increase the input signal to higher. Then the signal flows to G of both MOSFET. The full current flows the solenoid. Then, R8, R9, VR1, and Q3 are the current adjusting section. The D1- diode protects the current spike or high voltage turns back from the solenoid coil.
What causes MOSFET to run with low current?
It causes MOSFET runs with low current and not very hot. Both Q1 and Q2 transistors increase the input signal to higher. Then the signal flows to G of both MOSFET. The full current flows the solenoid. Then, R8, R9, VR1, and Q3 are the current adjusting section.
Do you need FET to pulse modulate solenoid?
It serves no purpose (other than to waste power) if you are going to pulse modulate the solenoid. It would be good to place a 5k ohm resistor from the gate to ground to ensure your uP can turn off the FET. If you still have problems, you may wish to switch to a logic level FET after confirming the high output voltage of your uP port.
Do you need a voltage drop for a solenoid?
Usually you’ll use a common emitter configuration, where the solenoid comes at the place of R1. In that case you’ll need R2. If your microcontroller runs at 5V and you’re using the KSD1222 (see below), you’ll have a voltage drop of 5V – 2V = 3V across R2. You’ll need at least 2mA, but let’s play safe and give it 10mA.
What should the voltage drop be on a microcontroller?
If your microcontroller runs at 5V and you’re using the KSD1222 (see below), you’ll have a voltage drop of 5V – 2V = 3V across R2. You’ll need at least 2mA, but let’s play safe and give it 10mA. Then R2 should be maximum 3V/10mA = 300 Ω. If you want to use a MOSFET the Si2318DS is suitable.