Hi, I redrew my circuit showing point X is 24 volts. The mosfet source is 12 volts. I am searching for a transistor circuit that will pulse from 12 to 24 volts to dirve the mosfet gate. Comments are welcome.
Wow! Using a charge pump is the right thing to do, but you made it too complicated. Google, "buck gate drive charge pump."
In any event you'll need a high side driver, better to get IC for that, two diodes, two caps. Since you need a PWM, you can use that for your CP assuming not too much gate charge on the FET, get rid of existing CP. Or just use existing PWM with built in CP, you're done! But if you insist on headaches and perhaps a learning experience do it with all discretes.
Why not use a custom mosfet driver such as an IR2112 supplied by international rectifier Floating channel designed for bootstrap operation • Fully operational to +600V • Tolerant to negative transient voltage dV/dt immune • Gate drive supply range from 10 to 20V • Undervoltage lockout for both channels • 3.3V logic compatible Separate logic supply range from 3.3V to 20V Logic and power ground ±5V offset • CMOS Schmitt-triggered inputs with pull-down • Cycle by cycle edge-triggered shutdown logic
What David sent won't work as is but it's close. Get rid of the lower 1K resistor because the MOSFET must be driven to below say three volts, not 12V. Also you don't need a Baker clamp on the NPN, seriously this is not a power transistor where you have to deal with deep storage and trailing current. Speed isn't an issue. Also the NPN inverts the signal so you'll need a second inversion so use an inverter for that. Otherwise it'll work. You should know that the classic NPN/PNP driver has shoot-through so the driver at 24V will heat up and probably limit the switching to say about 100KHz.
Hi, on page 22 and 23 there seems to be a solution. It looks like Vcc would be replaced by the PMA, but I am not sure. Thank you to everyone for all the suggestions Comments welcome.
Hi, the IR2117 have arrived and I completed all the high current connections of the buck converter. Using a Zener diode as Vcc to power just the nand gate oscillator I was able to illuminate a LED with a quarter turn of the PMA. Not great results but it is a start. I have to test the IR2117 with the oscilloscope to determine if HO is oscillating. I wired the test circuit and used a 12 volt halogen light as a test load and spun the PMA manually. The PMA was very easy to spin until the MOSFET turn on, then I was unable to spin the PMA. I believe the MOSFET is not turning off. My concerns are there is a lot energy stored in the input capacitor and I do not want to harm my oscilloscope. Are there any points I should avoid when testing the circuit????? The chassis ground and each channel ground are a the same common point, is there a safe method to use when testing the circuit with the scope? Comments welcome.
The rectified and filtered output of your three-phase Y is 24 volts correct?
If the center point of the three phase Y is connected to earth ground (same as the oscilloscope AC power ground) that is where you must connect the oscillcope probe ground. This can make it difficult to probe the circuit and get a meaningful measurement.
Or, you can 'float' the oscilloscope by disconnecting the ground prong of the AC plug. I know folks object to this practice but it's common.
If the three phase Y is not grounded (it is floating) to can connect the battery (-) terminal to earth ground and connect the oscillscope probe ground to that point.
Hi, depending on the RPM the output can range from 0 volts to over 60 volts. I found a application note from Fairchild that I am trying to use as a guide line.
I have to read the paper a few times, it is starting to make more sense.
So far the oscillator is working. If I leave the MOSFET out of the circuit and connect Vs of the IR2117 to ground the photo shows input timing signal from 555 timer and output (HO) of IR2117.
When I add the MOSFET the last photo shows the IR2117 will turn on but not off. I am currently working to solve this problem. Comments are welcome and thank you for the help I have been receiving.
Hi, video shows manual operation of PMA and buck converter to a resistive load. The mosfet is turning on during the off cycle of the IR2117. Is there a solution to this problem??? Comments welcome.
A safety margin resistor diode network can be added to the gate, as shown See attached
The purpose of this network is to further delay the turn-on, without affecting the turn-off, thereby inserting some additional dead-time.
The resistor-diode network is also useful in reducing the peak of the current spike during the reverse recovery time.
This has an impact on power losses, as well as dv/dt and EMI.
You can also add a PNP transistor such that the base is attached to the Anode of the diode resistor network , the emitter to the cathode of the diode resistor network and the collector to ground This shuts off the fet completley ensuring that no gate voltage is present during the off cycle
Greetings, I added the larger caps to the boot strap and the ringing is still there but only noticeable at lower RPM’s.
I am still using the 555 timer. I increased the duty cycle to 80% and inverted the output so the duty cycle at the input of the IR2117 is 20% high. I connect a 12 volt 50 watt light and spinning the PMA manually I was able to illuminate the 50 watt light with relative ease. Wow, a shorter duty cycle made all the different. The PMA was much easier to spin and even maintained momentum for a short period when I stopped spinning the PMA.
Without the buck converter I was unable to illuminate the 50 watt load under manual operation.
I am still using the bench power supply to power the IC’s.
Performance has definitely improved.
I still need away to control the duty cycle at different PMA RPM’s and find away to power the IC’s from the battery or PMA. Next step is to try charging the battery. It maybe time to start thinking about adding a micro controller. Thank you for all the suggestions.
The discussion focuses on designing a transistor circuit to pulse a MOSFET gate voltage from 12V to 24V, with the MOSFET source at 12V and the gate requiring a higher voltage drive. Key solutions include using a high-side driver with a bootstrap charge pump, which simplifies the design compared to discrete components. The IR2112 and IR2117 gate driver ICs from International Rectifier are recommended for their floating channel bootstrap operation, wide voltage tolerance, and undervoltage lockout features. Practical issues addressed include ensuring proper gate drive voltage below threshold levels, avoiding shoot-through in transistor drivers, and managing switching frequency limitations due to heating. Additional circuit modifications involve resistor-diode networks and PNP transistors to introduce dead-time and prevent gate voltage during off cycles, reducing EMI and power losses. Testing challenges with oscilloscope grounding and safe measurement practices are discussed. Application notes from International Rectifier and Fairchild Semiconductor provide design guidance, including increasing bootstrap capacitor values to improve performance. Experimental results show improved MOSFET switching and load driving using a 555 timer PWM input with adjusted duty cycles, enabling manual operation of a permanent magnet alternator (PMA) and illumination of resistive loads. Future steps include controlling duty cycle relative to PMA RPM and powering the driver ICs from the battery or PMA output. Summary generated by the language model.
