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university:courses:electronics:switched-cap-power-supplies [09 Apr 2018 22:51] – Figure resizing Mark Thorenuniversity:courses:electronics:switched-cap-power-supplies [25 Jun 2020 22:07] (current) – external edit 127.0.0.1
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 ====== Activity 1: Switched Capacitor Voltage Inverter ====== ====== Activity 1: Switched Capacitor Voltage Inverter ======
 +===== Theory and Simulation =====
 Some op-amp circuits can operate on a single supply, with the op-amp negative supply pin connected to ground. However there are applications that benefit from the use of a "split" supply with voltages of opposite polarity referred to circuit ground, for example, with the op-amp's supply pins connected to positive 5V and negative 5V. Such a supply can be created by using two 9-V batteries, an LM7805 positive regulator, and an LM7905 negative regulator. But this extra battery is an inconvenience - when is the last time you saw a product that required TWO 9V batteries? Some op-amp circuits can operate on a single supply, with the op-amp negative supply pin connected to ground. However there are applications that benefit from the use of a "split" supply with voltages of opposite polarity referred to circuit ground, for example, with the op-amp's supply pins connected to positive 5V and negative 5V. Such a supply can be created by using two 9-V batteries, an LM7805 positive regulator, and an LM7905 negative regulator. But this extra battery is an inconvenience - when is the last time you saw a product that required TWO 9V batteries?
  
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 <WRAP centeralign> Figure 6. clk_bar Parameters</WRAP> <WRAP centeralign> Figure 6. clk_bar Parameters</WRAP>
  
-Each source outputs 3 microsecond pulses with a 10 microsecond period. The only difference is that V3 is delayed by 5us - this produces a "non-overlapping clock", which allows switches to be alternately turned on and off, and never on at the same instant. Running the simulation, and probing and q_bar, shows what's going on:+Each source outputs 3 microsecond pulses with a 10 microsecond period. The only difference is that V3 is delayed by 5us - this produces a "non-overlapping clock", which allows switches to be alternately turned on and off, and never on at the same instant. Running the simulation, and probing clk and clk_bar, shows what's going on:
  
 {{ :university:courses:electronics:sw_cap:nonoverlapping_clocks.png?400 |}} {{ :university:courses:electronics:sw_cap:nonoverlapping_clocks.png?400 |}}
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 When S3 and S4 close, C1 and C2 are placed in parallel, so the 5uc is then divided among two 1uF capacitors, resulting in a voltage of -2.5V. Subsequent charge / discharge cycles drive the output voltage closer to its final value of nearly -5V. The 1k load resistor prevents the output from ever reaching exactly -5V, but if the switching is fast enough, it can come close. When S3 and S4 close, C1 and C2 are placed in parallel, so the 5uc is then divided among two 1uF capacitors, resulting in a voltage of -2.5V. Subsequent charge / discharge cycles drive the output voltage closer to its final value of nearly -5V. The 1k load resistor prevents the output from ever reaching exactly -5V, but if the switching is fast enough, it can come close.
  
 +===== Circuit Construction and Testing =====
 +With the simulation understood, let's move on to actual components. Open the //LT1054_inverter.asc// schematic from the zip file in LTspice. Construct the circuit on a breadboard, following the LTspice schematic.
  
-With the simulation understood, let's move on to actual components. Open the //LT1054_inverter.asc// schematic from the zip file in LTspice. Construct the circuit on a breadboard, following the LTspice schematic: +{{ :university:courses:electronics:sw_cap:lt1054_inverter_schematic.png?600 |}} 
- +<WRAP centeralign> Figure 11. Inverter Breadboard circuit</WRAP>
-{{ :university:courses:electronics:sw_cap:1054_inverter.zip |}}+
  
 Build the following breadboard circuit for the voltage inverter. Build the following breadboard circuit for the voltage inverter.
  
-{{ :university:courses:electronics:sw_cap:lt1054_inverter_breadboard.png?600 |}} +{{ :university:courses:electronics:sw_cap:lt1054_inverter_breadboard.png |}} 
-<WRAP centeralign> Figure 11. Inverter Breadboard circuit</WRAP>+<WRAP centeralign> Figure 12. Inverter Breadboard circuit</WRAP>
  
 The circuit can also be soldered on a "Perma Proto" solderable breadboard from Adafruit, which matches the layout of typical solderless breadboards. The circuit can also be soldered on a "Perma Proto" solderable breadboard from Adafruit, which matches the layout of typical solderless breadboards.
  
 {{ :university:courses:electronics:sw_cap:lt1054_inverter.jpg?600 |}} {{ :university:courses:electronics:sw_cap:lt1054_inverter.jpg?600 |}}
-<WRAP centeralign> Figure 12. Inverter Circuit Soldered on PermaProto board</WRAP>+<WRAP centeralign> Figure 13. Inverter Circuit Soldered on PermaProto board</WRAP>
  
 Connect a voltmeter (or M2K in voltmeter mode) between circuit ground and the OUT pin of the LT1054, and Apply 5V to the IN pin. The voltmeter should read close to -5V. Connect a voltmeter (or M2K in voltmeter mode) between circuit ground and the OUT pin of the LT1054, and Apply 5V to the IN pin. The voltmeter should read close to -5V.
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 Set Scopy to Oscilloscope mode, with the following settings: Set Scopy to Oscilloscope mode, with the following settings:
  
-  * Timebase: 200us/div+  * Timebase: 250us/div
   * CH1, CH2: 1V/div   * CH1, CH2: 1V/div
   * Triggering: Ch1, -1V, Falling Edge, Single Shot mode.   * Triggering: Ch1, -1V, Falling Edge, Single Shot mode.
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 Momentarily short LT1054 pin 1 (FB) to ground. This disables the LT1054. Release FB; this allows the LT1054 to operate again, and produces a "clean" turn-on transient. You should see a waveform similar to the figure below: Momentarily short LT1054 pin 1 (FB) to ground. This disables the LT1054. Release FB; this allows the LT1054 to operate again, and produces a "clean" turn-on transient. You should see a waveform similar to the figure below:
  
-{{ :university:courses:electronics:sw_cap:lt1054_inverter_turn_on_scopy.png?600 |}} +{{ :university:courses:electronics:sw_cap:lt1054_inverter_turn_on_scopy.png |}} 
-<WRAP centeralign> Figure 13. LT1054 Inverter Startup Scopy Measurement</WRAP>+<WRAP centeralign> Figure 14. LT1054 Inverter Startup Scopy Measurement</WRAP>
  
 Run the LTspice simulation, and probe the corresponding nodes. You should see results similar to the figure below: Run the LTspice simulation, and probe the corresponding nodes. You should see results similar to the figure below:
  
 {{ :university:courses:electronics:sw_cap:lt1054_inverter_turn_on_ltspice2.png?600 |}} {{ :university:courses:electronics:sw_cap:lt1054_inverter_turn_on_ltspice2.png?600 |}}
-<WRAP centeralign> Figure 14. LT1054 Inverter Startup LTspice Simulation</WRAP>+<WRAP centeralign> Figure 15. LT1054 Inverter Startup LTspice Simulation</WRAP>
  
 This shows reasonable correlation between the simulation and actual measurements. This is a good thing, but it's always important to keep in mind that: This shows reasonable correlation between the simulation and actual measurements. This is a good thing, but it's always important to keep in mind that:
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 {{ :university:courses:electronics:sw_cap:lt1054_inverter_turn_on_ltspice_w_cap_current.png?600 |}} {{ :university:courses:electronics:sw_cap:lt1054_inverter_turn_on_ltspice_w_cap_current.png?600 |}}
-<WRAP centeralign> Figure 15. LT1054 Inverter Startup Simulation w/ Capacitor Current</WRAP>+<WRAP centeralign> Figure 16. LT1054 Inverter Startup Simulation w/ Capacitor Current</WRAP>
  
 If you built this circuit up on a PermaProto board, you can put it in a box and use it with your next project that requires a split (positive and negative) power supply. If you built this circuit up on a PermaProto board, you can put it in a box and use it with your next project that requires a split (positive and negative) power supply.
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 ====== Activity 2: Charge Pump Voltage Doubler ====== ====== Activity 2: Charge Pump Voltage Doubler ======
 +===== Theory and Simulation =====
 Another useful power conversion function is producing a high voltage from a lower voltage, which was demonstrated in the second half of Experiment 0. The LT1054 switches are not configured in a way that will perform this function directly, but we can use the LT1054 to drive a "charge pump" to double the input voltage. Once again, let's start with a close to ideal simulation to illustrate the idea. Open the //switch_cap_pump_doubler.asc// schematic from the zip file in LTspice. Another useful power conversion function is producing a high voltage from a lower voltage, which was demonstrated in the second half of Experiment 0. The LT1054 switches are not configured in a way that will perform this function directly, but we can use the LT1054 to drive a "charge pump" to double the input voltage. Once again, let's start with a close to ideal simulation to illustrate the idea. Open the //switch_cap_pump_doubler.asc// schematic from the zip file in LTspice.
  
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 {{ :university:courses:electronics:sw_cap:switch_cap_pump_doubler_phase_0.png?500 |}} {{ :university:courses:electronics:sw_cap:switch_cap_pump_doubler_phase_0.png?500 |}}
-<WRAP centeralign> Figure 16. Doubler Phase 0</WRAP>+<WRAP centeralign> Figure 17. Doubler Phase 0</WRAP>
  
 **clk_bar** asserts, turning on S1. The lower terminal of C1 is driven to Vusb, and the Pump node is driven to Vusb plus another Vusb (minus a diode drop.) **clk_bar** asserts, turning on S1. The lower terminal of C1 is driven to Vusb, and the Pump node is driven to Vusb plus another Vusb (minus a diode drop.)
  
 {{ :university:courses:electronics:sw_cap:switch_cap_pump_doubler_phase_1.png?500 |}} {{ :university:courses:electronics:sw_cap:switch_cap_pump_doubler_phase_1.png?500 |}}
-<WRAP centeralign> Figure 17. Doubler Phase 1</WRAP>+<WRAP centeralign> Figure 18. Doubler Phase 1</WRAP>
  
 The result is that Vout is "pumped" to 2X Vusb, minus two diode drops. Probing Vout and Pump confirms this: The result is that Vout is "pumped" to 2X Vusb, minus two diode drops. Probing Vout and Pump confirms this:
  
 {{ :university:courses:electronics:sw_cap:switch_cap_pump_doubler_waveforms.png?600 |}} {{ :university:courses:electronics:sw_cap:switch_cap_pump_doubler_waveforms.png?600 |}}
-<WRAP centeralign> Figure 18. Doubler Startup LTspice Simulation</WRAP>+<WRAP centeralign> Figure 19. Doubler Startup LTspice Simulation</WRAP> 
 + 
 +As with the inverter circuit, the output takes several clock cycles to reach its final value due to charge sharing.  
 +===== Circuit Construction and Testing ===== 
 +With the simulation understood, let's move on to actual components. Construct the LT1054 doubler circuit, following the LTspice schematic //LT1054_doubler.asc// from the zip file.
  
-As with the inverter circuit, the output takes several clock cycles to reach its final value due to charge sharingWith the simulation understood, let's move on to actual componentsConstruct the LT1054 doubler circuit, following the LTspice schematic //LT1054_doubler.asc// from the zip file.+{{ :university:courses:electronics:sw_cap:lt1054_doubler_schematic.png?600 |}} 
 +<WRAP centeralign> Figure 20Doubler Schematic</WRAP>
  
 Build the following breadboard circuit for the voltage inverter. Build the following breadboard circuit for the voltage inverter.
  
-{{ :university:courses:electronics:sw_cap:lt1054_doubler_breadboard.png?600 |}} +{{ :university:courses:electronics:sw_cap:lt1054_doubler_breadboard.png |}} 
-<WRAP centeralign> Figure 19. Doubler Breadboard circuit</WRAP>+<WRAP centeralign> Figure 21. Doubler Breadboard circuit</WRAP>
  
 The circuit can also be soldered on a "Perma Proto" solderable breadboard from Adafruit, which matches the layout of typical solderless breadboards. The circuit can also be soldered on a "Perma Proto" solderable breadboard from Adafruit, which matches the layout of typical solderless breadboards.
  
 {{ :university:courses:electronics:sw_cap:lt1054_boost.jpg?600 |}} {{ :university:courses:electronics:sw_cap:lt1054_boost.jpg?600 |}}
-<WRAP centeralign> Figure 20. Doubler Circuit Soldered on PermaProto board</WRAP>+<WRAP centeralign> Figure 22. Doubler Circuit Soldered on PermaProto board</WRAP>
  
 Connect a voltmeter (or M2K in voltmeter mode) between circuit ground and the OUT pin of the LT1054, and Apply 5V to the IN pin. The voltmeter should read close to +8.6V. Connect a voltmeter (or M2K in voltmeter mode) between circuit ground and the OUT pin of the LT1054, and Apply 5V to the IN pin. The voltmeter should read close to +8.6V.
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 Set Scopy to Oscilloscope mode, with the following settings: Set Scopy to Oscilloscope mode, with the following settings:
  
-  * Timebase: 200us/div+  * Timebase: 250us/div
   * CH1, CH2: 1V/div   * CH1, CH2: 1V/div
   * Triggering: Ch1, +5V, Rising Edge, Single Shot mode.   * Triggering: Ch1, +5V, Rising Edge, Single Shot mode.
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 Momentarily short LT1054 pin 1 (FB) to ground. This disables the LT1054. Release FB; this allows the LT1054 to operate again, and produces a "clean" turn-on transient. You should see a waveform similar to the figure below: Momentarily short LT1054 pin 1 (FB) to ground. This disables the LT1054. Release FB; this allows the LT1054 to operate again, and produces a "clean" turn-on transient. You should see a waveform similar to the figure below:
  
-{{ :university:courses:electronics:sw_cap:lt1054_doubler_turn_on_scopy.png?600 |}} +{{ :university:courses:electronics:sw_cap:lt1054_doubler_turn_on_scopy.png |}} 
-<WRAP centeralign> Figure 21. LT1054 Doubler Startup Scopy Measurement</WRAP>+<WRAP centeralign> Figure 23. LT1054 Doubler Startup Scopy Measurement</WRAP>
  
  
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 {{ :university:courses:electronics:sw_cap:lt1054_doubler_turn_on_ltspice.png?600 |}} {{ :university:courses:electronics:sw_cap:lt1054_doubler_turn_on_ltspice.png?600 |}}
-<WRAP centeralign> Figure 22. LT1054 Doubler Startup LTspice Simulation</WRAP>+<WRAP centeralign> Figure 24. LT1054 Doubler Startup LTspice Simulation</WRAP>
  
-Note that there is a noticeable qualitative difference between the Scopy measurement and the LTspice simulation; the measured rampup appears more linear, while the LTspice rampup appears more exponential.+//Note that there is a noticeable qualitative difference between the Scopy measurement and the LTspice simulation; the measured rampup appears more linear, while the LTspice rampup appears more exponential.//
  
 ====== TBD: Activity 3: Voltage Divider ====== ====== TBD: Activity 3: Voltage Divider ======
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 ===== Questions: ===== ===== Questions: =====
  
 +<WRAP round download>
 +**Lab Resources:**
 +  * Fritzing files: [[downgit>education_tools/tree/master/m2k/fritzing/switch_cap_bb | switch_cap_bb]]
 +  * LTSpice files: [[downgit>education_tools/tree/master/m2k/ltspice/switched_cap_ltspice| switch_cap_ltspice]]
 +</WRAP>
  
 **Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]** **Return to Lab Activity [[university:courses:electronics:labs|Table of Contents]]**
  
university/courses/electronics/switched-cap-power-supplies.1523307069.txt.gz · Last modified: 09 Apr 2018 22:51 by Mark Thoren