Hello,
I am trying to put a circuit together to operate a solenoid valve using PWM 25kHz, 50% duty at 12V.
I have built a couple of really basic circuits to test this, the first uses a 12V bench supply driving the solenoid (12V 5W 450mA) via a VN1NV04PTR MOSFET on the low side. The MOSFET is driven by a PIC. ( I have used this MOSFET because I wanted the protection features)
The PIC drives the solenoid at the full 100% duty for 1 second (just so I can see what's going on would be shorter normally), then drops to the 50%.
I have also connected a 1R resistor in series with the output of the +12V supply to measure the current via an oscilloscope.
My reason to do these tests is that I want to see the peak current pulses and look at ways to average this, for example I want to use a small SMPS mains converter, that is rated less than the 450mA the solenoid will require at 100%, as it's running at 50% duty.
My issue is this:- When I measure the voltage pulses across the valve using an oscilloscope, I can clearly see just under 12V 100%, then 12V 25Khz 50%, so my assumption is the valve is fully switched on. However when I measure the voltage drops across the 1R, I again can see the same, but the voltage drop is only 250-300mV, this is lower than expected.
I have tried multiple power supplies and MOSFET's and also compared it with a DRV103, the results are identical. So I guess I am not understanding the averaging that is already taking place.
I need to be able to measure/understand this as I want to use the smallest power supply taking into account the average current not the peak current. I figured I would need to put a capacitor say 470uF across the supply to provide the energy required during each pulse, to smooth this, but if I can't measure it correctly I won't know if I have it correct.
If anyone can help me with understanding this I would be grateful.
Thanks.
I am trying to put a circuit together to operate a solenoid valve using PWM 25kHz, 50% duty at 12V.
I have built a couple of really basic circuits to test this, the first uses a 12V bench supply driving the solenoid (12V 5W 450mA) via a VN1NV04PTR MOSFET on the low side. The MOSFET is driven by a PIC. ( I have used this MOSFET because I wanted the protection features)
The PIC drives the solenoid at the full 100% duty for 1 second (just so I can see what's going on would be shorter normally), then drops to the 50%.
I have also connected a 1R resistor in series with the output of the +12V supply to measure the current via an oscilloscope.
My reason to do these tests is that I want to see the peak current pulses and look at ways to average this, for example I want to use a small SMPS mains converter, that is rated less than the 450mA the solenoid will require at 100%, as it's running at 50% duty.
My issue is this:- When I measure the voltage pulses across the valve using an oscilloscope, I can clearly see just under 12V 100%, then 12V 25Khz 50%, so my assumption is the valve is fully switched on. However when I measure the voltage drops across the 1R, I again can see the same, but the voltage drop is only 250-300mV, this is lower than expected.
I have tried multiple power supplies and MOSFET's and also compared it with a DRV103, the results are identical. So I guess I am not understanding the averaging that is already taking place.
I need to be able to measure/understand this as I want to use the smallest power supply taking into account the average current not the peak current. I figured I would need to put a capacitor say 470uF across the supply to provide the energy required during each pulse, to smooth this, but if I can't measure it correctly I won't know if I have it correct.
If anyone can help me with understanding this I would be grateful.
Thanks.