I'm going to make a PWM high side driver for a solenoid. And now I'm wondering what good or bad happen if I select a 20 kHz PWM frequency instead of 2 kHz?
At 20 Khz I have lower inductance and higher serial resistance that at
2 kHz. Does this lead to more heat in the solenoid coil?And I also assume the driver P-channel MOSFET transistor gets hotter at
20 kHz?Is the coil current step response the same?
Anything else?
The reason for 20 kHz is that it's non audible.
Elektro ha scritto:
I don't known Your application but the only disadvantage is the harmonic emissions in EMC compliance (if it's a power application)
You know the advantages already
Emanuele
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The main drawbacks of low frequency PWM are audible noise and larger ripple current in the inductance. The turn on losses of the switch will be lower, because they take place at the lower minimum current, but the switch off losses are higher because they take place at the higher peak current. But, in general, since many switching losses are a per transient accumulation, lower frequency means lower switching losses.
Higher frequency can raise the core losses through eddy current increase, but this depends a bit on the core material and shape. This effect can be mitigated by adding a low loss (at the fundamental and first few harmonic frequencies) inductor in series with the load, so that most of the high frequency content can be dropped across that, instead of your solenoid. And, the switching losses are higher at higher number of switching events per second. But if other concerns mean that you have to go with the higher frequency, you can move some of those losses to a snubber, to keep the switch cooler. Regardless, at higher switching frequency, turn on and turn off times become more significant, and if you speed those up, dramatically, to keep the losses down, you may have to deal with higher EMI.
As you can see, there are a lot of factors to balance to come up with the optimum switching frequency.
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