MAINFRAME Why Switched FICON? (Switched FICON vs. Direct ...
Troubleshooting Switched Mode Power Supplies (Presented at EELive!)
-
Upload
rohde-schwarz -
Category
Engineering
-
view
691 -
download
11
description
Transcript of Troubleshooting Switched Mode Power Supplies (Presented at EELive!)
![Page 1: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/1.jpg)
Troubleshooting Switched Mode Power Supplies
![Page 2: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/2.jpg)
SMPS | 2
Agenda
l Switched mode power supply background l Measurement points l Voltage and current waveforms
l Maximizing measurement accuracy l Averaging, high resolution decimation l Sampling rate
l Analyzing common issues l Improper inductor size l EMI l Load transient behavior
![Page 3: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/3.jpg)
Modern Power Supplies: Inductors, Capacitors and Fast Switches
ı Use ‘Lossless’ Components, In ‘Switching’ Operation Inductors store energy, and can deliver the energy at higher or lower
voltage than input Capacitors store energy between ‘pumping’ operations of inductors ı Replace Linear Series Pass And Shunt Regulators Linear regulators turn excess voltage into thermal energy Efficiencies can be very high – as little as 2% to 3% “wasted” energy ı Effectively ‘Variable Transformer’ Operation Able To Provide Increase/Decrease, Or Both, In Voltage Able To Operate Over Wide Ranges Of Input Voltage
01.04.2014 3
![Page 4: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/4.jpg)
Power Supply – Evolution Instead of “Burning” Excess Voltage, SMPSs Use Inductors and Capacitors to “Transform” the Voltage. In a Buck (Down-) Converter, the Inductor “input” is switched between voltage source and ground
01.04.2014 4
Currents And Voltages Change Direction / Polarity, At High Speed… Dynamic Circuits, Where Oscilloscopes Excel At Measurement!
![Page 5: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/5.jpg)
Understanding What to Measure ı Understanding Power Flow and Topology The Basic SMPS - Buck Converter Topology – Current Flow
01.04.2014 5
A diode or transistor may replace one switch
![Page 6: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/6.jpg)
Understanding What to Measure ı The Basic SMPS - Buck Converter Topology The “Switches” are typically implemented as internal, or external, FET’s, or
IGBT’s in high-power applications.
01.04.2014 6
Shunt resistor
![Page 7: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/7.jpg)
Power Flow and Topology
01.04.2014 7
Vswitch
Iinductor Vout
Note the slope in Vswitch Related to the slope in inductor current Proportional to the internal switch and current-sense resistance
Measure V1 and I1 Measure V2 and I2
Use V1 -V2 / I2-I1 To calculate switch resistance
![Page 8: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/8.jpg)
SMPS | 8
Maximizing measurement accuracy l Large dynamic range required for accurately measuring
switching voltage and current l On state is tens to hundreds (even thousands) of volts l Off state is often only several mV to a few volts l Typical 8-bit A/D provides approximately 39 mV on a 10 V scale
l Three possibilities to improve signal to noise l Use waveform averaging l High resolution decimation (trade off sample rate and bandwidth for
S/N) l Overdrive instrument front end
Resolution enhancement (B = bits) due to averaging
![Page 9: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/9.jpg)
SMPS | 9
Noise reduction using averaging
1 mV on 10 V scale (13.3 bits) 50 averages
Zoom of this segment
![Page 10: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/10.jpg)
SMPS | 10
High Resolution Mode
l Combine consecutive samples from A/D converter with weighting
l Preserves real time sampling – no smearing of dynamic signals
l Reduces bandwidth based on decimated sampling rate
l Compatible with segmented memory so that each cycle can be analyzed
Combine samples for each point
![Page 11: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/11.jpg)
SMPS | 11
High Resolution Decimation Mode
Decimate 10 Gs/s to 1 Gs/s ~ 500 MHz BW 4.6 mV on 10 V scale (11.1 bits)
![Page 12: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/12.jpg)
SMPS | 12
Combining averaging and high resolution mode
Decimate 10 Gs/s to 1 Gs/s 50 averages ~ 500 MHz BW 500 uV on 10 V scale (14.3 bits)
![Page 13: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/13.jpg)
SMPS | 13
Slew Rate and Vertical Resolution
N bits 2N levels
Sampling rate = F Resolution = 1/F
![Page 14: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/14.jpg)
SMPS | 14
Slew Rate and Vertical Resolution
N bits 2N levels
Sampling rate = F Resolution = 1/F
![Page 15: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/15.jpg)
SMPS | 15
Slew Rate and Vertical Resolution
l Both vertical and horizontal resolution are critical l High slew rates l Measuring short, high amplitude peaks that could damage active
components l 10 V/ns = 1 V per sample @ 10 Gs/s l 10 V/ns = 5 V sample @ 2 Gs/s l Compare to digitizer range
l 39 mV @ 8 bits l 9.7 mV @ 10 bits
l Measurement resolution can be limited by the sampling rate
![Page 16: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/16.jpg)
SMPS | 16
Viewing Multiple Waveforms
![Page 17: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/17.jpg)
SMPS | 17
But the Resolution is Reduced by Half…
Full scale waveform
Half scale waveform
![Page 18: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/18.jpg)
SMPS | 18
Using Multiple Grids
![Page 19: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/19.jpg)
SMPS | 19
Current Measurements
Shunt resistor
![Page 20: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/20.jpg)
SMPS | 20
Current Measurements
Current probe
Shunt resistor
![Page 21: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/21.jpg)
SMPS | 21 SMPS | 4
Inductor Current Waveform
Vg = Vin V = Vout
![Page 22: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/22.jpg)
SMPS | 22 SMPS | 4
Inductor Current Waveform
Vg = Vin V = Vout
![Page 23: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/23.jpg)
SMPS | 23
Analyzing the Inductor Current
Ts = 950 ns D = 0.35 L = 2.2 µH Vin – Vout = 3.2V 2*∆I = 3.2*950e-9*0.35 (2.2e-6) = 484 mA
Predicted current ripple:
20 ohm resistive load (90 mA load current)
![Page 24: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/24.jpg)
SMPS | 24
Analyzing the Inductor Current
Measured current ripple: 2*∆I = 680 mA Equivalent Inductance: L = 950e-9*.35*3.2/0.680 = 1.56 uH
5 ohm resistive load (360 mA load current)
![Page 25: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/25.jpg)
SMPS | 25
Using Math Waveforms to Identify Saturation l Create math waveform = integral(VL/L) l Ideal current ripple is linear
Measured I(t)
Computed I(t)
![Page 26: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/26.jpg)
Output Voltage Ripple The Basic SMPS – 1.4 MHz Buck Converter – Vout Ripple Spectrum
01.04.2014 26
Iinductor
Vout
Spikes at multiples of Fswitch
![Page 27: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/27.jpg)
Output Voltage Ripple – No Load
01.04.2014 27
![Page 28: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/28.jpg)
Output Voltage Ripple – Small Load
01.04.2014 28
![Page 29: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/29.jpg)
Output Voltage Ripple – Large Load
01.04.2014 29
![Page 30: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/30.jpg)
EMI – Large Load
01.04.2014 30
Vout
Near field probe
![Page 31: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/31.jpg)
Understanding Power Flow and Topology The Basic SMPS - Buck Converter – Load Transient – Well-Damped Response, Little Overshoot
01.04.2014 31
ILoad Vout
![Page 32: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/32.jpg)
Load Transient Response inductor current linearity and output voltage ripple
01.04.2014 32
Red = Vout Blue = IL
![Page 33: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/33.jpg)
Load Transient Response ı 1% to 100% load shift with 5 V input ı 4 µs recovery time ı Higher Vin-Vout delivers more current to load
01.04.2014 33
Red = Vout Blue = IL
![Page 34: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/34.jpg)
Load Transient Response
ı 1% to 100% load transient with 3.3 V input ı 9 µs recovery ı Smaller Vin – Vout slows down response
01.04.2014 34
Red = Vout Blue = IL
![Page 35: Troubleshooting Switched Mode Power Supplies (Presented at EELive!)](https://reader034.fdocuments.us/reader034/viewer/2022050919/546eed4cb4af9fc3268b482d/html5/thumbnails/35.jpg)
SMPS | 35
Summary
l Switched mode power supply voltages are dynamic with very high voltage swings
l Oscilloscope performance is critical for making accurate measurements l Both sampling rate (bandwidth) and resolution are important l Averaging techniques are used to enhance resolution when required
l Trouble shooting techniques l Analyzing output ripple voltage and EMI l Observing inductor current l Using spectrum analysis