ln004 - pwm driver for asymmetric motors (v5.1)
TRANSCRIPT
LN004 / JohnStone / 2013-02-20
V1
Page 2 of 26
Exzerpt
This document describes a fast switching FET driver circuit dedicated to asymmetric motors.
List of Contents
Scope of this document: ............................................................................................. 4
Basic Knowledge ........................................................................................................ 4
Overview ..................................................................................................................... 6
Circuit ......................................................................................................................... 7
Opto (Section C) ...................................................................................................... 7
Signal Conditioning & Power on Disable (Section D) .............................................. 8
FET driver (Section E) ........................................................................................... 10
FET Stage (Section F) ........................................................................................... 12
Circuit Board ............................................................................................................. 15
Bread board .............................................................................................................. 17
Assembly .................................................................................................................. 17
Wiring Procedure ...................................................................................................... 18
Precautions at Different Circuit Areas ....................................................................... 19
Basic Testing of the Circuit ....................................................................................... 23
Some Hints out of the Forum .................................................................................... 23
Testing and Tuning ................................................................................................... 25
Further knowledge .................................................................................................... 25
APPENDIX ............................................................................................................... 26
Page 3 of 26 Author
Name: John Stone
Profession: Engineer in electronics and humble apprentice in radiant science
Location: Somewhere in a rural area in the global village
The author performs this research in order to bring honor to the creator and help protect his creation.
Disclaimer
The contents described herein are for education only. You are not encouraged to replicate items
described herein. The author takes no responsibility for any damage, injury or other disadvantage
occurring.
Policies:
Anybody is encouraged to copy and forward this document at will as long as the content is not
modified.
Quotations are allowed unmodified only with added reference (title and version) and internet link if
possible.
Intellectual Properties
As far as the author is aware there are no facts described herein pending to any intellectual property
being protected.
All contents are open source and MUST NOT be patented or claimed to be private in any way.
Glossary
FET field effect transistor
Page 4 of 26
Scope of this document:
Due to the fact that many members of energetic forum are not educated in electronic
matters this document shall help anybody to build a high quality driver dor own
experiments.
Basic Knowledge
The notions below were published in Energetic Forum by the author in Oct. 2012.
Everybody shall understand that the matter is far complicated but these notions may
suffice in order to get the basic understanding for building drivers like presented
herein.
“1. FETs are modern electric valves with some very superior properties compared to
transistors. This makes them a primary choice in order to switch high currents along low
loss.
But FETs will perform well only if they are kept within their area of wellness.
Unfortunately many of you do not now these conditions and therefore you torture them
without any malicious intention.
2. Any valve performs well only if you switch it fast. Any intermediate state will perform
excessive losses. You experienced it before if a switch (valve) in your home does not
perform well and the contacts get hot - and possibly ignite your home. So the question
is: How do we get FETs hurry up in their switching time.
3. FETs are extremely fast electric valves. They can perform (but not easily) within ps
(picoseconds = 10 power -12 seconds) - But they show up some drawbacks we need to
take in account.
4. For better understanding let's recall the connections of a FET (exactly a N-FET). This is
the type we usually use. The leg being connected to electrical minus or GND or ground is
called the "source". The leg where you connect your load is called "drain". Where you
control the FET is the "gate".
5. The abbreviation FET stands for Field Effect Transistor. This term tells you that you
can change the state of ON /Off by controlling an electric field within the structure of the
FE-Transistor - see additionally This might give you the notion that a FET will not draw
current but the field will be sufficient. This notion is true and false at same time - sorry -
given at what time you look at your FET.
6. Gate capacitance: There is no FET (or transistor) without it (app. 1nF = 1 nanaofarad).
As you possibly know a capacitance is a bin for electrons where you can put them in and
extract them later on (in reality it is not - but let's take it as thinking model). We charge
a capacitor and discharge it. In this respect it behaves like a rechargeable battery. If you
have lots of current you can charge it within short time and if you have a weak power
supply you need to wait long time in order to use the charged object.
Now please understand that you can have no natural feeling of what is slow or fast for a
FET and what currents will flow. All this matter defies your daily experience and therefore
we need to talk about it.
7. Charging a capacitance is no linear job but the more charge you have gathered in the
Page 5 of 26 cap the slower it will increase its voltage. So please understand that it will be no good
idea to supply your FET driver with 12V while your FET needs 10V for full ON state.
Additionally your driver will eat up some voltage and supply somewhat less than your
battery supplies.
And beware of long thin wires - they will kill the rest of your switching quality.
For discharge you unfortunately have no negative voltage in order to speed up the cycle.
Then the low driver stage needs to be strong enough.
8. Oscillations are another enemy of your FETs. As you learned above every transition
generates losses and you can imagine that some additional oscillations (wires are
inductance, capacitance and act along FET capacitance) will add losses and eat up
performance of your PWM circuit. These oscillations may go up to MHz! But there is a
drug for this - an additional resistor (10....30 Ohm) - look forward to schematic coming
soon.
9. Now let's recall some usual nominal properties of a FET.
Threshold voltage for ON state : higher than ca. 10V
Threshold voltage for OFF state: lower than ca. 4V
This tells you that you need to travel as fast as possible through the lossy zone between
4V and 10V and vice versa and additionally exceed the thresholds by some volts in order
to stay in a secure zone.
The bad news is that you do not have a certain amount of loss once only but at every
transition ON/OFF and OFF/ON. The frequency of 10 KHz tells you i.e. that a FET will
experience 20000 times pulses of heat every second because of switching only. Imagine
these facts like driving your car without oil in the engine /gear -> friction + heat +
damage.
I do not want to derange you with math. If you want to know more see this calculator.
Any way you can understand that if we have a weak, slow current source as driver and
possibly no good conductors it will take longer time to switch a FET ON/OFF.
As you own no oscilloscope it is of no value for you to enter into calculations and figures.
Let's focus on what we can do in order to enhance your FET driving.
10. There are some other facts to be considered but stay with this knowledge for now.
Page 6 of 26
Overview
The FET driver described herein incorporates an opto coupler at input in order to
separate the PWM generator from the noisy driver circuit. A simple opto will not
transfer clean signals with steep edges. Therefore the opto output feeds aome gates
for signal conditioning along power on disable. Both measures are necessary in order
to prevent stress and damage of the FET stage itself.
An essential part of this circuit is the FET driver itself being able to charge and
discharge the gate capacitance very fast. This action requires high current flow and
builders shall provide conductors with corresponding diameter in this section.
The final FET stage contains some protection means from high voltage.
An overcurrent protection is not designed in this version of circuit but can be added
later on.
Page 7 of 26
Circuit
This circuit was tuned in order to serve as safe unit for research purpose at
asymmetric motors. Some simplifications can be performed before using it in real
use. Anybody untrained person is warned to modify it. Low performance might result.
Please consult the corresponding forum for further knowledge.
Opto (Section C)
The input connector at left hand side provides aresistor and opto with separated
leads on a post each in order to be easily adapted to the PMW generator. If this
circuit is not connected the FETs are – for safety controlled to switched off.
Activating the opto at input will draw pin 3 at output to 5V performing as HIGH signal
to the signal conditioning stage.
Pin 6 at connector is not connected to the circuit. It sits there just in case you need to
connect PSU from generator.
Page 8 of 26
Signal Conditioning & Power on Disable (Section D)
The gates are of Schmitt trigger type. They prevent randomly switching at output if
noisy signals are fed at input.
The circuit serves as power on disable in order to protect the setup from unsolicited
switching. After switch on C18, R4, D3 disable the gate pin 10 up to the time when
the capacitor is being charged above the switching level of the gate. In case of power
off procedure the diode enables fast discharge of the capacitor in order to be
prepared soon for next switch on procedure.
Gate IC4d performs as simple inverter. There are two gates left in IC4.They can be
used for later additions. All inputs are tied to +5V in order to prevent unsolicited
switching and noise.
Page 9 of 26 Note: The voltage for this circuit is 5V fed by a separated voltage regulator LM7805.
This measure was chosen in order to prevent any crosstalk of the noisy circuitry
originating from FET switching.
Builders are advised to not omit capacitors shown in the diagram. They are essential
in order to provide smooth DC voltage. Every type of capacitor performs in a certain
proprietary frequency range. Thus a cluster of capacitors covers a wider range of
frequencies. They get charged / discharged at spikes and crosstalk and load
changes as well.
Page 10 of 26
FET driver (Section E)
FET drivers are designed for sudden source / sink of several amps. This special type
performs 12A within 50ns. Special precautions were taken by the manufacturer in
order to prevent crosstalk form output to input. Input section was separated from
output section.
C17 / C2 guarantee smooth DC voltage for input circuitry. This cluster is being fed
from 12V regulator and this is the only connection to the output cluster.
Same procedure at GND connections. input separated from output – one single lead
in-between.
You are advised to solder this IC to PCB directly (no socket) in order to guarantee
maximum current flow.
The LED D1 performs as monitor for switching actions.
Page 11 of 26
The circuit gets 12V from a separated voltage regulator LM7812. It is advised to feed
this regulator by a galvanically separated PSU i.e. a simple socket charger.
This regulator feeds the 5V regulator as well (see baove).
Page 12 of 26
FET Stage (Section F)
R8, R9 shall prevent spurious oscillations at FET side. They grow up along gate
capacitance and inductivity of the leads between driver and FET. Therefore it is
essential to have them as short as possible. The resistor values need to be
determined at the setup itself. You are advised to check before with wire jumpers
only.
The drawback of these resistors is -> they prevent high currents to flow and thus
reduce the switching speed. The resistors should be of metal film type or SMD.
Normal carbon resistors contain a helical structure and thus add inductance to the
gate (danger of oscillations)
C9 / D2 and C15/D7 perform as overvoltage protection for the gate. In order to
separate the capacitance and its influence to switching speed, overvoltage is being
fed through low capacitance diodes 1N4148 (D1, D6). Once C9 or C15 is charged
Page 13 of 26 there is no further interaction with the gate, except in case of overvoltage. Then D2
will conduct and prevent damage to the gate.
D4, D5, D8, D9 perform as overvoltage protection for the DS junction. They conduct
in case of overvoltage and feed charge to the gate. Thus the FET will open again for
short time and conduct the overvoltage to GND. The double diode design is intended
in order to reduce capacitance by series connection of the diode capacitance.
NOTE: This protection was designed for these specific FETs in diagram (600V). The
values for these diodes need to be adapted to about 80% of maximum voltage drain /
source.
K2, K3 are contacts for connecting meters.
This circuit shows no high current contacts because builders will have very different
arrangements for FETs along heat sinks. The FETs were prepared to be assembled
on bottom side in order to give space for extensive heat sinks if requested.
Mounting FETS off PCB is not recommended because the wiring from driver to gates
and source pins needs to be AS SHORT AS POSSIBLE.
NOTE:
It is essential to perform the connections from driver to FETS exactly like shown
below. Else low switching performance will be observed.
Please note this current path marked in red and blue will perform up to 12A for short
time. It needs to be performed EXACTLY like in layout below. Wires need to be
covered with massive solder.
Page 14 of 26
Page 15 of 26
Circuit Board
As component placing and wiring are in some extent essential, this setup shall serve
as template for easy building and proper function.
The circuit board below was setup primary for replicating the circuit on a breadboard
(instruction below) but may be built as true PCB.
Page 16 of 26
Please note the FETs are positioned mirrored in order to get gate pins as close
together as possible. Thus heat sinks shall be applied on both sides.
Page 17 of 26
Bread board
The board was developed in 1/10” (2.54mm) pitch. Thus any commercial breadboard
(“pad per hole”) board may be used.
The dimensions are about 94mm x 64mm
Assembly
Step 1:
• Print the assembly print in scale 1:1 on paper. (template in correct size-> see
appendix)
• Check if dimensions ore OK, else correct your printer setup.
• Adjust the printout on the breadboard: holes in board shall fit to fiducial marks.
• Fix paper with pins on corners through holes first and then with glue.
• Puncture the assembly holes.
• Assemble a cluster of components at a time (not all at once) i.e. 12V voltage
regulator along related components.
• Ceramic 100nF capacitors were used of different pitch. You may use all the
same and bend wires conforming the corresponding hole distance.
• Proceed with wiring (see next paragraph).
• After wiring finished proceed with next cluster.
Page 18 of 26
Wiring Procedure
The wiring was performed like a single sided circuit board. The position of
components was guided by having short and well-arranged wiring. The layout may be
used as printed template for marking wires soldered. (see pic below – bottom view)
Perform short wires first. Blank wires may be used there.
For some longer wires insulated ones may be advised.
Wiring: bottom view
Page 19 of 26
Precautions at Different Circuit Areas
Some circuit areas need to be wired with massive wire in order to allow high
amperage to flow in time.
GROUNDs
The GND wires related to gate drive are marked in pink color. Be advised to perform
those wires at left hand side from driver as massive wires in order to let up to 12A
flow.
The gate resistors shall be accompanied by ground lines in order to prevent
oscillations and spurious nose.
Hint: Solder thin blank wires and cover them with solder later on in order to get
massive metal connections. Pause in-between in order to not kill components by
heat.
Remember the jumper (grey line above)
Page 20 of 26 GATE DRIVE
Same procedure like above
Page 21 of 26 DIGITAL GROUND
This part may be wired without covering with solder like above.
Page 22 of 26 FET (SOURCE / DARIN)
Source and drain pins are prepared for high curents up to 300A peak. Conducting
such current can not be performed by simple PCB or wiring. Thus the wiring for
source and drain will be done differently – off PCB surfce at top side.
Note: Soldering needs to be done hot and fast in order to prevent damage inside the
FETS ba heat.
It is essential to perform this “triangle” for drain wires (connected to load later on)
symmetrically in order to load both FETs equally.
Same procedure for wires to source pins at FET. Keep both triangles well insulated.
The circuit might be loaded up to 650V.
Page 23 of 26
Basic Testing of the Circuit
After assembly and wiring thorough testing shall be performed. It is advised to do
testing step by step. The input needs to be controlled either by a frequency generator
or by a simple toggle switch. All sections shall be tested.
• 12V regulator (note: regulators of type 78xx need minimum 2 volts higher at
input than their output rating)
• 5V regulator
• Opto part
• Signal conditioning / power on disable
• FET driver
• FET stage (add a resistive load (i.e. 20W bulb / 12V) and do not exceed 12V
voltage at load for safety of the circuit in case of malfunction) Check for steep
edges and missing oscillations at switching time. In case of oscillations gate
resistors need to be added and increases up to smooth switching.
Some Hints out of the Forum
Link
1. Action: Do not use coils in the very first switch on but a resistor or car lamp or similar ohmic load. Calculate the max. current at permanently switched on stat to not be grater than 80 % of the max. current out of data sheet. Mount your FETs on a heatsink. Check: At every test check temperature. 2. Action: Attatch the overvoltage protection to FETs 3. Action: Start with 12V first. 4. Action: Operate the FET stage manually first - disconnect from generator. Thus you can measure with simple DVM and thoroughly. 5. Action: Connect input lead to GND. Check: Measure if your FETs have less than 1 V on gate. Light at output OFF! If not: measure where the the voltage originates. 6. Action: Connect input lead to 12V Check: Measure if FETs have 10V minimum at gate. Light at output ON! If not: search for the loss of voltage. 7. Action: Connect generator with low frequency ca. 1Hz Check: Watch function: on / off / on ...... 8. Action: Add in series to bulb at output a coil. Replace the output load by a moderate coil. Attach a neon (overvoltage protection) across SD of the FET. 9. Action: Operate generator faster i.e. 100Hz. Connect a home brew peak detector,
Page 24 of 26 connect DVM. Check: If neon lights at this step you have too big coil or too low frequency. Wait DVM reading being stable. Now you have the exact peak voltge less 0.6V beacuse of the diode. Action: Discharge the cap from peak detector after every check. 10. Action: Remove the bulb at output. and connect coil between Battery and FET directly. Repeat #9. 11. Action: Increase battery voltage or use bigger coil (or motor). Repeat #8 Check. Neon on? procede with #12. If you have now not your final load increse load step by step until neon gets on dimmly. 12. Action: Neon is now on dimmly while FET stage running. Note the peak voltage. 13. Action: Check the data sheet for max. voltage DS. Take 80% of this voltage and devide it by the neon voltage + 1V noted before. The integer number is the number of SAME neons you can connect in series between DS of FET in order to get a reliable protection from overvoltage. Check. Neons shall not light up at all while normal operation. Measure the peak voltage to be below 80% of FET voltage and note the voltage red. 14. Action: Discionnect overvoltge protection (cap/resistor) Check: Recheck like #13. 15: Increase freqeuncy step by step. Check: Temperature, neons to be off, voltge at peak detector.... Hint: - When operating assymetric motors high voltage spikes are intended. Therefore neones shall light for exceptional protection only. If the lihgt up you should replace FETs by higher rated components. Calculate the cont of neons again (#13) - Recheck overvoltage protection if you make your FETs switch faster as well. The calculation for voltage spikes depends on switching speed as well. They are build up by load voltge, amps being switched off and switching speed. Small 12V motors can develop spikes up to 150V and more. An ignition coil being fed with 12V / 3A will produce up to 300V spikes. - Your setup will not be protected while you read this text. YOU MUST DO IT YOURSELF!
Page 25 of 26
Testing and Tuning
Once the driver board proved to perform basic functions it needs to be tested at
dedicated load. Remember the advice to start tuning with removed gate resistors and
added wire jumpers.
It is essential to test the driver board with resistive load only because any inductivity
oscillates at switching time and will override deadly self-oscillations at gates.
Resistive load: Get a bulb from car head lamp H4 (or two H7), parallel filaments and connect as load with short wires. You can pulse it at 36V with 40% duty and get plenty of amps for testing while not overloading the bulb.
Check for smooth switching like above.
Recheck if the overvoltage diodes fit to max. voltage of the FETs used.
Further knowledge
This driver is being discussed in Energetic Forum “my-motors-got-me-tap-into-radiant-energy” starting with post # 1745.
~o0o~
Page 26 of 26
APPENDIX
Opto
couple
r
5V
supply
Section
B:
12V
supply
Section
A:
Pow
er
FE
Ts
Section F
:F
ET
driver
Section E
:D
igital gate
sS
ection D
:S
ection
C:
500
V
300A
sin
gel p
ulse
100A
con
tinuo
us
V5.1
1K
R8
1K
R7
LE
D r
ed 3
mm
D11
1N4007 D10
1K
R6
1K
R5
P6KE250CA
D9
P6KE250CA
D8
K3
K1X
02
K2
K1X
02
P6KE15
D7
100nF
C15
10K
R4
23:2
708
.02.
13
20:1
508
.02.
13
Mon
ster
Driv
er -
V5.1
- 20
1302
08 p
rere
leas
e.T3
001
130,
00%
Ver
sion
:
Cha
nge:
Pro
ject
: Asy
met
ric U
fo M
otor
Item
: Mon
ster
Driv
er
She
et: 1
/1...
...
File
:
Sca
le:
+5V
+5V
100nF C2
100nF C7
P6KE250CA
D5
P6KE250CA
D4
P6KE15
D2
1R
R3
1R
R9
1N4148
D6
IPW60R041C6
T2K
1K
1X06
1µF C18
+
1N4148D3
100nF
C9
IPW60R041C6
T1V
_GE
N
K8
K1X04
1µF
C5+
1N4148
D1
1K R2
+12
V
1µF C17 +
1µF C10+
10µF C3+
470
R1
+5V
+5V
+5V
100nFC1
1µF
C14+
1µF
C11 +
+12
V
100nFC13
100nFC12
100nFC8
100nFC4
VC
CV
CC
MIC
4452Y
N
IC7
GN
DO
UT
2O
UT
1
GN
DN
CIN
10µFC6+
7812
IC6
GND
INO
UT
7805
IC5
GND
INO
UT
SFH
617A
-3
IC3
E CKA
IC4
IC4b
74H
C132N
IC4d
74H
C132N
IC4c
74H
C132N
IC4a
74H
C132N
OP
TO
_K
OP
TO
_A
Rout
Rin
V_G
EN
AU
X_P
WR
GN
DG
ND
GN
D
GN
DG
ND
GN
D
IN
MD5.1 - BOM prereleasePos Cont Name Value Case DATASHEET
1 5 R2,R5,R6,R7,R8 1K 0207
2 1 D10 1N4007 D_RM12,7_DM3
3 3 D1,D3,D6 1N4148 DO35 http://datasheet.octopart.com/1N4148-Fairchild-datasheet-521777.pdf
4 2 R3,R9 1R 0204_MET for tuning only
5 6 C5,C10,C11,C14,C17,C18 1µF C_ELKO_RM5,08_DM6 pitch 5.08 mm / diameter 6mm / voltage > 20V
6 1 R4 10K 0207
7 2 C3,C6 10µF D6R2,54_ELKO pitch 2.54 mm / diameter 6mm / voltage > 20V
8 1 IC4 74HC132N DIL14 http://focus.ti.com/lit/ml/mpdi002c/mpdi002c.pdf
9 2 C2,C7 100nF 3X13R7,62 same like next line! but bent for pitch 7.62 mm for use at MIC4452YN
10 7 C1,C4,C8,C9,C12,C13,C15 100nF 6X3R5,08 pitch 5.08 mm / diameter 6mm / voltage > 20V
11 1 R1 470 0207
12 1 IC5 7805 TO220 http://datasheet.octopart.com/L7812CV-STMicroelectronics-datasheet-10835933.pdf
13 1 IC6 7812 TO220 http://datasheet.octopart.com/L7812CV-STMicroelectronics-datasheet-10835933.pdf
14 2 T1,T2 IPW60R041C6 TO247 http://datasheet.octopart.com/IPW60R041C6-Infineon-datasheet-10026896.pdf
15 2 K2,K3 K1X02 1X02
16 1 K8 K1X04 1X04
17 1 K1 K1X06 1X06
18 1 D11 LED red 3mm LED_3MM_RED
19 1 IC7 MIC4452YN DIL8 http://datasheet.octopart.com/MIC4452YN-Micrel-datasheet-12335.pdf
20 2 D2,D7 P6KE15 DO15 http://datasheet.octopart.com/P6KE15A-STMicroelectronics-datasheet-14475.pdf
21 4 D4,D5,D8,D9 P6KE250CA DO15 http://datasheet.octopart.com/P6KE250CA-Fairchild-datasheet-3040.pdf
Please buy diodes above fitting to the Vds of your FETs. These ones refer to T1/T2 . Both diodes in series shall be well below the max. Voltage of your FETs!
22 1 IC3 SFH617A-3 DIL4 http://datasheet.octopart.com/SFH617A-3-Vishay-datasheet-8399721.pdf
63,5 mm93,9
8 m
m
63,5
mm
93,98 mm