Electronics > Beginners
555 Motor Speed Controller
Bulb:
Hello!
If I may, I would advice you to put two transistor for driving MOSFET in totem pole configuration. For example https://electronics.stackexchange.com/questions/299552/what-is-the-purpose-of-this-pull-up-resistor-in-totem-pole
Also, I would recommended of using UF4007 diode instead of 1N4007 for flayback diode. Also with totem pole configuration you can try out to reduce gate resistance and observer output wave forms of voltage across MOSFET. Decreasing reistance you speed up switching and reduce switching losses.
Edit:
If i see good (from scope wave forms), your switching frequency is 160kHz. You should reduce it to a round of 5kHz to 20kHz and all should work just fine. Then, totem pole isnt needed.
Buf if you are intresed in reasherce you can build one totem pole driver just for analayzing. Also, here are switching losses small, but if you use for example higher voltage sorce (for example 100V), switching losses also increase.
Hope it helped.
mike_mike:
I tried the attached schematic, based on the information from: https://www.quora.com/What-is-the-purpose-of-a-MOSFET-gate-driver
The results are as following:
1. On the Base of the 2 transistors (PNP and NPN): 0673.jpg
2. On the Gate of the Mosfet: 0675.jpg
3. On the RLoad: 0676.jpg
The power supply of the entire circuit was 12Vdc.
1. Please have a look at the attached screen shots and tell me what you think.
2. Can you please explain why the Vpp is 35.6V in the first screenshot, why it is 34.4V in the second and why it is 24V in the third while the supply voltage is only 12V in all 3 cases ?
Bulb:
--- Quote from: mike_mike on April 22, 2019, 08:00:13 pm ---I tried the attached schematic, based on the information from: https://www.quora.com/What-is-the-purpose-of-a-MOSFET-gate-driver
The results are as following:
1. On the Base of the 2 transistors (PNP and NPN): 0673.jpg
2. On the Gate of the Mosfet: 0675.jpg
3. On the RLoad: 0676.jpg
The power supply of the entire circuit was 12Vdc.
1. Please have a look at the attached screen shots and tell me what you think.
2. Can you please explain why the Vpp is 35.6V in the first screenshot, why it is 34.4V in the second and why it is 24V in the third while the supply voltage is only 12V ?
--- End quote ---
This is good example when using high switching frequency, good MOSFET driver is need. This wave forms are now :-+
I recommend of reduceing frequency around 20kHz. You can keep it higher than 20kHz to reduce sound noise of PWM.
To sum, this wave forms now look good.
Edit:
High voltage spikes are due parasitic inductens of traces. To reduce it, you can increas a gate resitance. At 10 ohm resistance, mosfet is fast switching and voltage across indactens is raisng very fast, U_inductor = L*di/dt. Adding a capacitor close in DC bus, neer the load can also help to remove parasitic inductance. But tehnici you cant eliminate parasitic inductance.
soldar:
Yeah, 160 KHZ seems unnecessarily high. Probably 40 KHz would work better in reducing switching and other losses.
Bulb:
One more thing I forgot... Peak current through BC338 and complement transistor is around peak apsolte curret for that transistor. Beacuse, at 10 Ohm resistance at gate, peak current is around 1A. So, for selected transistor in totem pole configuration I advice of puting gate resistance of around 20Ohms (for example series combination of two 10 ohms resistors).
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