* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download EE362L, Fall 2006 Isolated Firing Circuit for H
Distributed control system wikipedia , lookup
Electronic musical instrument wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Transmission line loudspeaker wikipedia , lookup
Power inverter wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Ground (electricity) wikipedia , lookup
Control theory wikipedia , lookup
Flexible electronics wikipedia , lookup
Microprocessor wikipedia , lookup
Two-port network wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Control system wikipedia , lookup
Power electronics wikipedia , lookup
Integrating ADC wikipedia , lookup
Regenerative circuit wikipedia , lookup
Schmitt trigger wikipedia , lookup
Switched-mode power supply wikipedia , lookup
EE462L, Spring 2014 Isolated Firing Circuit for H-Bridge Inverter (partially pre-Fall 2009 approach) 1 ! Isolation is needed because we have three separate MOSFET source nodes, and these three nodes are ground references for the respective firing circuits Vdc (source of power delivered to load) A+ One logic signal toggles A+,A– Local ground reference for A+ firing circuit Local ground reference for B+ firing circuit S S S Load A– Local ground reference for A− firing circuit B+ B– S One logic signal toggles B+,B– Local ground reference for B− firing circuit 2 Output of the Comparator Chip Comparator Gives V(A+,A–) wrt. Common (0V) V(A+,A–) +12V from DC-DC chip 1.5kΩ +12V 1.5kΩ –12V 270kΩ Vtri 8 1 Vcont > Vtri Comp 5 1kΩ Vcont 4 Vcont < Vtri Since the comparator compares signals that can be either positive or negative, the comparator must be powered by ±V supply Use V(A+,A–) wrt. –12V 270kΩ Vcont > Vtri –Vcont +24V –12V from DC-DC chip 0V Common (0V) from DC-DC chip Vcont < Vtri 3 Comparator Gives V(B+,B–) wrt. Common (0V) Output of the Comparator Chip V(B+,B–) +12V from DC-DC chip –Vcont > Vtri +12V 1.5kΩ –12V 1.5kΩ 270kΩ Vtri 8 1 Comp 5 1kΩ Vcont 4 Since the comparator compares signals that can be either positive or negative, the comparator must be powered by ±V supply Use V(B+,B–) wrt. –12V 270kΩ –Vcont – Vcont < Vtri –12V from DC-DC chip Common (0V) from DC-DC chip – Vcont > Vtri +24V 0V – Vcont < Vtri 4 The control signals at the open-circuited output of the PWM control circuit are +24V, or 0V When V(A+,A−) is 24V, MOSFET A+ is on, MOSFET A− is off When V(A+,A−) is 0V, MOSFET A+ is off, MOSFET A− is on V(A+,A−) control signal V(B+,B−) control signal MOSFETs B+ and B− work the same way with V(B+,B−) Reference (is −12V from DC-DC chip) DC wall wart AC wall wart (marked with yellow paint) 5 +24V 0V +24V Look for symmetry of pulse centers 0V Save screen snapshot #3 Figure 13. Output control voltage V(A+,A–) on top, and V(B+,B–) on bottom, with respect to protoboard –12V reference, with ma > 0 (the situation shown is where Vcont is positive) +24V 0V +24V Look for symmetry of pulse centers 0V Figure 14. Output control voltage V(A+,A–) on top, and V(B+,B–) on bottom, with respect to protoboard –12V reference, with ma > 0 (the situation shown is where Vcont is negative) 6 Once the MOSFET is connected, this asymmetrical circuit will add blanking by making the turn-on slower than the turn-off. (blanking is the opposite of overlap) Wait until next week One firing circuit for each MOSFET, with each firing circuit mounted on a separate protoboard. Protoboards A– and B – can share a power supply and ground . A + and B + must each use separate power supplies and grounds. Do not connect any of these grounds to the ground of the control circuit. MOSFET G D S 100kΩ Switching diode Overlap is the time that A+ and A− are simultaneously “on,” which should be avoided. Hence, some blanking (time between one turning off and the other turning on) is desirable. 10Ω 1.2kΩ green Grounds (isolated from control circuit) 0.1µF blue 5 4 green Driver 8 A+ and B+ use inverting drivers (1426’s). A– and B– use non inverting drivers (1427’s) . The optocouplers provide an additional inversion. 1 blue red green 5 10kΩ 4 Opto 8 1 Optocoupler is currentcontrolled. Gate current Isolating turns on the transistor, barrier which pulls down the Powered by +12V that is isolated from the collector voltage. PWM control circuit Outline of protoboard blue blue for A+,B+, violet for A–,B– 14mA O+ O– (see Figure 2 for connections) 7 14mA to Opto Input Yields ≈ 0V to Input of Driver Chip, so Inverting Driver Chip Turns MOSFET ON Isolating barrier ! Spec. sheet current transfer ratio 0.2 to 0.3 (times 14mA) +12V 1.2mA (will pull down Vdriver to zero) 14mA from control circuit 10kΩ + To driver Vdriver = 0V – 8 0mA to Opto Input Yields 12V to Input of Driver Chip, so Inverting Driver Chip Turns MOSFET OFF ! Isolating barrier +12V 0mA 0mA from control circuit 10kΩ + Vdriver = 12V – To driver 9 We use the control signals to send 14ma through optocouplers on each of the four firing circuit boards A+ Firing A+ and A− are daisy chained 8” A– Firing O+ O– B+ Firing O+ O– O+ O– O+ O– blue blue violet blue Jack for DC wall wart B– Firing Individual protoboard for each firing circuit violet –12Vdc regulated V(A+,A–) V(B+,B–) Control Circuit from Previous Lab Optically-isolated firing circuits. Mount drivers near the MOSFETs Jack for AC wall wart B+ and B− are daisy chained (for complementary outputs) Figure 2. Physical layout of firing circuits (A+ opto and driver are powered by a +12V isolated DC converter chip. Likewise, B+ is powered by another +12V isolated DC converter chip. A– and B– are powered by the DC wall wart.) So, each 14mA control signal passes through two optocouplers in series 10 With 14mA, the LED of each optocoupler has about 1.6V drop • 24V control signals from the comparators, less 3.2V drop across two series optocoupler LEDs, and with 14mA, requires about 1.5kΩ of resistance in series with the daisy-chained optocouplers • If applied half the time, 24V across a 1.5kΩ resistor would produce about 0.2W. So, it is a good idea to size up to ½W resistors. 11 Thus, you use ½W series resistors between the comparator chip and the output terminals 500Ω trimmer V(A+,A–) V(B+,B–) +12Vdc regulated from 2W, DC converter chip These ½W resistors can get hot - keep them off the surface of the protoboard 1.5kΩ, ½W red 1kΩ High-pass filter to block DC red red 100kΩ 0.01µF 1kΩ 1.5kΩ, ½W Filtered and buffered triangle wave blue 270kΩ Vcont blue 7 1 Waveform Gen. blue 8 0.01µF (freq. control) 2Vdc ated from W, DC erter chip 14 8 Approx 22kHz triangle wave 5 Op Amp 1 8 green 5 1kΩ Comp 4 1 4 violet 10kΩ 9.53kΩ The IC is upside down to minimize wiring clutter –Vcont 1kΩ trimmer 270kΩ 1kΩ blue blue Vcont green violet violet violet Protoboard common connected to 0V output pin 12 Layout of inverter control circuit and isolated firing circuits No MOSFETs connected yet (i.e., the drivers are open-circuited) A+ A− B+ B− DC wall wart AC wall wart (marked with yellow paint) 13 DC converter chip feeds A+ circuit • Keep the 0.1µF capacitors across the drivers to prevent driver failure ground rail fed by wall wart Non-inverting driver for A– (1427’s) 12V rail fed by wall wart 12V rail fed by DC converter chip Inverting driver for A+ (1426’s) ground rail fed by 0V output pin of DC converter chip Zoom-in view of A+ and A– isolated firing circuits • Use the same pattern for B+ and B– • One DC converter chip feeds A+ • Another DC converter chip feeds B+ • Wall wart feeds A− and B− Wall wart feeds A– circuit 14 Side view of A+ and A– isolated firing circuit and single 12V isolated DC-DC converter chip that powers A+ − + wall wart input − + chip output Socket each single DC-DC converter chip, using one half of an 8-pin SIP socket. Carefully break an 8-pin SIP socket in half. Do this by clamping on one-half with your long-nose pliers, and then bending the other half down with your fingers. It should be a clean break. 15 ! Input and Output Voltages of Optocoupler Vcont = 0 (i.e., ma = 0) in this Snapshot Look for Symmetry Among all Four Circuits Opto Input (the 1.5kΩ resistor drops the voltage from 24V to 3.2V) 3.2V V(A+,A–) 0.5V Phototransistor turning on 12V Opto A + output Phototransistor turning off As expected, the opto output is inverted 0V Save screen snapshot #1 This phototransistor turn off delay will limit your PWM operating frequency Different time-constants to avoid shoot-through (i.e. to provide a “dead-time”) 16 Look for Nearly Perfect Alignment Between V(A+,A−) Signal to Optocoupler, and Output of A+ Inverting Driver Chip V(A+,A–) In phase A+ driver output 17 Look for Nearly Perfect Out of Phase Alignment Between V(A+,A−) Signal to Optocoupler, and Output of A− Non-Inverting Driver Chip V(A+,A–) Out of phase A– driver output 18 Now the present circuit based on PCBs: 19 Key new component: IRS21844 20 IRS21844 High output Low output 21 Actual pinout IRS21844 Blanking time and isolation already integrated in a single IC 22