Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. The HV7100 is an integrated PWM speed controller for driving. 24V and 48V DC. HV7100 drives a high side external P-channel FET, allowing the use of fans. I have a Mosfet driver (see attached diagram). This device can handle currents upto 1A. The 5V input is from a microcontroller PWM pin (100% duty cycle for measurements). I connected the output of the Mosfet to a motor and the motor to ground (with appropriate protection diode). The motor only drew 300mA. I then short-circuited the output to measure the maximum current but that was still about 300mA. The Mosfet power supply is from a 8V 0.8A ac-dc adaptor. How can I force more current through the Mosfet? Does this mean I cannot get 0 - 1.5A linearly with a Vg of 0 - 5V? You might be able to measure up a single mosfet specimen and create a table of Vgs values for your range of 0-1.5A Id, then output that (perhaps via a resistive voltage divider) for your one-off design. Otherwise you need to put a low res series resistor and measure the voltage created by the Id. App store for mac computers. This voltage would then be fed back to your PIC (after amplification and/or level shifting) at one of the ADC inputs, thus creating a servo loop by letting the output level sent to the gate be adjusted to give the currently desired Id. Note that a number of mosfet makers have special models with an Id sensing output included on the mosfet chip, saving the need and cost for the extra current sensing resistor. The only practical way of making multiple units is by having a feedback from the outputs as this takes care of the variations between Vgs and Id that exist between each individual mosfet. Then you have to decide which tolerance your design requires as this tells you which precision the resistor(s), Vref, and op-amp(s) have to meet together with the errors in the PIC's ADC. ORIGINAL: PIC I would have liked to increase Vg linearly from 0 - 5V, and have that correspond to Id of 0 - 1.5A. The gate threshold voltage Vth is 2.5V (max) for the above device. At 2.8V the drain current is slightly above 1A. Does this mean I cannot get 0 - 1.5A linearly with a Vg of 0 - 5V? I don't think that is what you want to do. ![]() ![]() If you are just trying to control the speed of the fans, you want to use PWM for this. The MOSFET is just a switch, it is either full on or full off. You control the average current by the percentage of time they are on. This is called the duty-cycle of the PWM. You set up a PWM at some freqency, say 10Khz. During the year there should be no contact between them whatsoever. Vasu then meets Sandhya, a widow who teaches him Hindi. After such a period, if they still want to be together, they can get married. Vasu moves to Hyderabad, and they both initially suffer due to the separation. Vasu and Sapna reluctantly agree to the condition and decide to separate. Ek duje ke liye mp3 download. The the duty-cycle is set so that it is on somewhere between 0 and 100us corresponding to 0% and 100% duty cycle. The reason for doing it this way is to avoid dissapating power in the MOSFET. If you are contolling the MOSFET linearly, at 50% power you are wasting 50% of the power in the MOSFET. With the fan at 12V, this would be.5A * 6V drop = 3Watts that goes into heat in the device requiring heat-sinking. If you control the power by PWM, there is virtually no power dissapated in the MOSFET, so it probably does not even need a heat sink.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |