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What is a DC choke? 

A choke is another name for an inductor used as a power supply filter element. Similar in appearance to a small transformer, a choke tends to resist change in current flow. For this reason, it is used together with capacitance to form a filter for DC power supplies.

Why do I need to put current through a dc choke?

A transformer or choke that is designed to carry a DC current must be properly tested to ensure that it will work correctly in the final assembly. This testing must be carried out with the current applied to ensure that it works properly in the final assembly.

The choke must have inductance to smooth the output current of the power supply with the DC output current of the power supply flowing at the same time.
If the choke is incorrectly manufactured, then a normal inductance test will not detect a fault. The best way to test any transformer or choke that carries a DC current while in use is to test inductance when DC current is present.

It is important that these measurements are taken both during the design phase and the production phase. During design, measuring inductance with DC Bias can confirm design calculations and prove the design margin before saturation. In the production phase, these measurements will confirm that the correct number of turns have been wound and that the core is of the right material and properly gapped.

Why not use an ordinary DC power supply?

A typical bench power supply has large smoothing capacitors at its output. This presents a low impedence, Z, to the LCR meter. One solution is to use large inductors to keep the dc impedence low, but to present a large ac impedence to the LCR meter.

The inductor solution has a number of problems:

• Big and Heavy
• Different value inductors are required at different frequencies
• Must route LCR meter to the DC Bias supply (inconvenient)

The solution?

Voltech's DC1000 DC Bias unit is used to characterize wound components that are intended for use in high current
DC power supplies and DC-to-DC converters. It applies bias current to transformers and chokes for impedance testing under working conditions.

Smooth, linear power is delivered to the inductor under precision microprocessor control. Programming is performed on the front panel via a speed sensitive rotary control, or via a RS232 link. The key to the versatility of the DC1000 is its unique and proprietary current compensation technique that virtually eliminates the effect of the DC1000’s impedance on the measurements made by the LCR meter.

• works with almost any LCR meter.
• Easy to use with rotary knob to set the current, and a clear display of set and actual current.
• stackable to 250A (up to 10 DC Bias units in parallel)