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555 Motor Speed Controller

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Zero999:

--- Quote from: Bulb on April 23, 2019, 06:28:45 pm ---Waveforms looks good. I would recommend to put a snubber in parallel with load and use of UF4007 diode instead of 1N4007. Reason for it is voltage spikes on load and MOSFET. This voltage spikes are high (double of power supply voltage) and can hurm MOSFET if higher currents and voltages are used. With snubber you can reduce voltage spikes.
What is snubber and how to dimension it is discraibed in this pdf https://www.illinoiscapacitor.com/pdf/Papers/RC_snubber.pdf
Snubber is RC circuit connected in paralled with inductive load and purpose of it is to reduce voltage spikes caused by fast switching of mosfet (or any other switch).

No, R7 is not needed. Output of NE555 is also totem pole configuration (there are two transistors, one switch to positive power supply input and other to negative power supply side (gnd)) but it can deliver max +/- 0.25A. With external totem pole you can achive higher currents (like +/-0.5A) that are useful for fast switching of MOSFET.

Nice work  :-+

--- End quote ---
Using a faster diode such as the UF4007 is a good idea.

No snubber is required, because the freewheeling diode short circuits any back-EMF pulses.

In this case, a snubber would just dissipate power and reduce the efficiency of the circuit.

The downside with having an external emitter follower is it reduced the voltage swing of the 555 timer. R7 isn't needed, but it may turn off faster with it.

iMo:
TV310G is 150ns max recovery time and 15pF and UF4007 is 75ns and 17pF. Otherwise both are the similar spec.
I would use the TVR10G in your app when the diode in my junkbox..
PS: answered a Q which has disappeared already.. :)

mike_mike:

--- Quote from: imo on April 26, 2019, 09:37:18 am ---PS: answered a Q which has disappeared already.. :)

--- End quote ---
Yes, I deleted the message because I think that I could find a better diode for this project, if I will search in some old equipment...

mike_mike:
I found RG10 diode in that old TV.
I checked the Datasheet and it says that the trr is 50ns and 100ns for RG10 and 75ns for UF4007.
In this situation, it is safe to use RG10 as replacement for UF4007 ?

iMo:
I think yes. RG10 is 400V/1A and fast enough imho.

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