Universal power load circuit using light bulbs

A universal power load circuit using a light bulb,

　　Improving loads for power supply design and bench testing is often a frustrating and sometimes dangerous endeavor.

process. When you increase high power resistors to their extreme values, they tend to burn the bench and melt the solder joints. Commercially available

There are many electronic loads available, but they are expensive, and it is often unnecessary for the average designer to use such devices with laboratory requirements

accuracy. Incandescent light bulbs are an excellent load, can handle a lot of power, can be packaged in a small package, and require no heat sinking

piece. Furthermore, incandescent bulbs emit light, so you get immediate feedback, much like an analog meter does with a digital meter.

The disadvantage of an incandescent light bulb is that its resistance changes dynamically with the input power. So if incandescent light bulbs were to become a useful

For a current sink, the power entering the load must be controllable over a wide range. There is a simple way to solve this problem

The control problem is to perform pulse width modulation on a MOS field effect power tube connected in series with the load. This design uses a

100W power supply with four output lines of 5V, 12V and ±15V. For the above voltage and power levels, a 50W, 12V light bulb is

A very suitable load. This application requires three light bulbs to be connected in parallel (Figure 1). Many automotive power suppliers sell

50W, 12V light bulb.
　　Because these bulbs screw into regular 115V lamp sockets, you can create an almost unlimited number of load combinations. Instructions for use

Old-fashioned porcelain lampholders wired in parallel allow you to plug any number of light bulbs into the load circuit. The circuit shown in Figure 1 is suitable for output

Negative or positive polarity power supply with voltage of 1~24V and power up to 150W. You just use a 115V bulb and choose the appropriate wattage

The parameters of MOS field effect transistors and other components can be used to load higher voltage power supplies using the same basic method. this circuit

A standard PWM3843 integrated circuit IC1 is used in open loop mode. Potentiometer VR1 controls the duty cycle over the entire range. right

The pulse frequency requirements are not high. If the component parameter values ​​shown in Figure 1 are used, the pulse frequency is approximately 37kHz. The circuit consists of a small

Powered by a modular plug-in transformer, but you can also use any DC source with an output voltage of approximately 18V and an output current of 50mA

source.
　　T1 isolates and drives the power MOS field effect transistor Q1. This transformer allows you to convert negative polarity power supplies as well as positive polarity power supplies

Add load. The various components in the gate circuit can drive Q1 efficiently over a wide range of duty cycles. Choke L1 puts the input

terminal is isolated from the switching pulses in Q1. You can use either an analog current readout or a digital current readout.

This design uses an LED readout removed from an old power supply. You must select a current limit based on power dissipation and ammeter requirements

Resistor R1. In this application, three 0.1Ω, 2W metal oxide film resistors in series can meet the requirements of the ammeter (maximum

The maximum current is 4A). You must attach Q1 to a heat sink suitable for this application. The circuit shown in Figure 1 uses Aavid Corporation (its

530101B00100 heat sink at www.aavid.com ). This is a U-shaped heat sink with dimensions of 1.75 on each side

×175 inches. Where larger current is required, two parallel MOS field effect transistors can be used. The gate drive circuit shown in Figure 1 has

There is enough power to drive two MOS field effect transistors.
　　Figure 1 A circuit using an incandescent bulb as a power supply design test load.