Elmo Motion Control: Power Supply design notes

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Power Supply design notes

	Capacitors rating
	Rectifying diodes
	Transformer

Capacitors rating

Voltage drop (capacitors only)

For an AC single phase, 60Hz * supply the following rule of thumb holds:

	-	in Amperes
	-	in µF
	-	is the voltage drop of the power supply output

* For 50 Hz network the voltage drop will be 6/5 times VDROP

Simulation example 1

A power supply with 100VAC/50Hz input, 1000µF internal capacitance and a load current of 1A

Simulation example 2

A power supply with 100VAC/50Hz input, 1000µF internal capacitance and a load current of 5A

Simulation example 3

A power supply with 100VAC/50Hz input, 1000µF internal capacitance and a load current of 10A

Simulation example 4

A power supply with 100VAC/50Hz input, 10,000µF internal capacitance and a load current of 10A

Rectifying diodes

Diodes rating

	The current rating of the diodes should exceed the max current requirement of the application.

	Rules of thumb
		In a single phase AC supply (4 diodes) the RMS current rating of each diode should equal to ISUPPLY(max).
		The voltage drop of the diode bridge is 3- 4V

Note:
Calculate and take care for the heat dissipation of the diodes.

Transformer

Transformer output

	Step 1: Calculate the maximum voltage required by the motor for the application.

n max	-	is the max speed of the application.
I motor(max)	-	is the peak current required by the application.

	Step 2: Calculate the minimum DC voltage required from the power supply.

VDROP	-	as calculated in the capacitors rating section.
k	-	is a factor that is typical for each amplifier type.

		For bipolar amplifiers - K=1.1n
		For unipolar amplifiers - K=1.05

	Step 3: Calculate the minimum AC (RMS) voltage required from the transformer:

The above expression takes into account a 10% voltage drop in the transformer. For brushless drives add additional 10% for the inductive impedance.

Note:
If the transformer voltage drop is too high, additional capacitance should be added. Sometime it may be more cost effective to increase the voltage rating of the transformer instead of increasing the capacitance.

Transformer power rating

	The transformer power rating should exceed the power consumption of the servo system:

I motor(max)

is the RMS current required by the application.