Week #15: (12/14-16) Voltage Regulators & Power Converters, Practical Considerations, Course Wrap-Up

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Week #15: (12/14-16) Voltage Regulators & Power Converters, Practical Considerations, Course Wrap-Up

Post by rjagodowski »

Voltage Regulators, DC-to-DC Converters, Linear & Switching Power Supplies

LM340/78XX Series Linear Regulators

Understanding How Voltage Regulators Work

Here's a link on What is a DC-to-DC Converter?

RBBA-3000 Series 3 kW buck-boost converter has 98% efficiency.

RBBA-3000 and it's Datasheet. Here's the pdf of the datasheet:
RBBA3000_Datasheet_DC-DC Converter.pdf
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Here's a quick note about the differences between classical linear power supplies and switched mode power supplies (SMPS) aka switching power supplies. Difference between linear & switching power supplies. Note the use of the term "pulse width modulation". It is a concept used in many aspects of power control.

Thermal Management of Components:

Understanding Semiconductor Thermal Resistance Data Here's the pdf of this link: Here's a tutorial from Analog Devices on Thermal Design Basics. This applies mostly to ICs, but the thermal concepts are similar for all electronic devices.

This link presents How to Select a Heat Sink. The thermal analysis for proper heat sink selection is rather complex and usually reserved for engineering-level analysis. Therefore, we won't really attempt to work through the process. However, by looking at the various charts & graphs, you should be able to get a sense for some of the considerations designers must use when specifying a system to remove heat, including convection, ducting, heatsink, thermal compounds and liquid cooling systems. For a technician, the moral of the story is that any heat dissipating equipment removed as part of a service must be replaced. Thermal compounds should be re-applied with fresh compound of the proper type.

1N4000 Series Rectifier Diodes from Vishay Semiconductor.

Using some typical 1N400X values, if there is 0.75 volts across a forward biased 1N400X diode with an average current of 1.0 Amps, the diode will be dissipating 0.75 Watts. Using the 50 ohms thermal resistance from Junction to Ambient, gives (50 *C/W) x (0.75W) = 37.5 *C temperature difference. That means if the ambient temperature is 25 *C, the junction temperature will be about 62.5 *C (25 *C + 37.5 *C). (In *F, ambient is about 77 *F and the junction temp would be about 144.5 *F) From the spec sheet, the maximum junction temperature is spec'd at 150*C, so this device should be able to handle this current continuously. These are all approximate calculations, but it does give a technician a rough idea as to whether or not the device will be subjected to excessive junction temps. (As a note, the 25 *C/W thermal resistance with the JL subscript is a figure to be used as a "best case" for heat removal. This assumes that a heatsink is properly applied and any additional cooling needed is also proper. It's an "ideal" spec, not the typical. That is why the 50 *C/W number was used in our calculations.)

1n47xx Series Zener Diodes from Vishay Semiconductor.

Another example: Look up a 1N4739 to find it's zener voltage rating (9.1). How much power will this device dissipate with 100 mA through it at it's zener voltage? (910 mW). From the data sheet, how much above ambient temperature will the junction be with 100 mA flowing through the diode? (100.1 *C). If the ambient temperature is 40 *C, what is the approximate junction temp with this current? (140.1*C) Can this zener diode survive with this current flowing through it at 40 *C ambient temp? (Most likely it should, max. junction temp is spec'd at 175 *C, and it should remain below that. But it IS getting close. Note that the Maximum power rating for this series is 1300 mW, so it is operating below that maximum as well.) (NOTE: The Kelvin and Celsius scales have the same slope, just different y-intercepts. Therefore the 110 *K/W thermal spec is equivalent to 110 *C/W.)

2N3904 NPN Transistor Data Sheet We'll look at a variety of specs, but one graph to note is Fig. 15, which shows how the (normalized) DC Current gain varies with temperature.

Lastly, a comparison of a bipolar transistor amplifier and an op-amp amplifier in terms of power supply regulation. The op-amp offers much better regulation. The bipolar transistor will reflect power supply changes in it's gain/output voltage.

"New" Technologies in Semiconductor Devices:

Difference Between GaN and SiC Transistors:
Difference between GaN and SiC Transistors.pdf
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