DC Voltage Regulator (flow), the core function of Electronic Load, power MOS

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DC Voltage Regulator (flow), the core function of Electronic Load, power MOS

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Designers use DC electronic loads to test power supplies, such as solar arrays or batteries, but commercial DC electronic loads are expensive. You only need to use the power MOSFET in its linear zone, you can make your own DC electronic load (figure 1 ). The load uses two simple feedback loops. A power transistor is used as a current source or voltage source in steady-flow mode. The designer uses the Steady-flow mode when describing the characteristics of the voltage source, because in the steady-flow mode, the power supply must provide the current value set in the electronic load. Designers Use the regulator mode with the current source, because the regulator mode forces the power supply to work under the voltage set by the load.

In current mode, rshunt detects iload, and the detected voltage is fed back to the inverse input of the Operational Amplifier ic1a. Because the DC gain of the operational amplifier is very high in the linear feedback work area, the inverse input end must be equal to the non-inverse input end, that is, viref. The amplifier generates its own output value so that the Q2 and Q3 of the mos work in the linear zone, which consumes the power of the power supply. The source pole current value is proportional to the current base quasi viref, that is, iload = viref/rshunt. You can set viref by using a resistance divider connected to a stable voltage reference, or using a D/A converter output from a PC-based I/O Card for flexible configuration.
The voltage operation mode is the same as the current mode, except that the variable detected is the output voltage, Which is attenuated by the divider RA/Rb, therefore, the working voltage of the electronic load is higher than that of the operational amplifier. The detected voltage is fed back to the non-inverse input of ic1b, And the mos work in the active zone again. Load Voltage: vload = vvref × (RA + RB)/Rb.

The ca3240 double op-amp IC1 can work when the input voltage is lower than the negative power supply voltage, which is very useful for single power supply. However, if you have symmetric power supply, you can use any op-amp. Relay K1 switches the working mode through a digital control line of drive Q1. Mos are crucial; you can add this parallel irf150 device to improve current tolerance, because irf150 has a positive temperature coefficient, which allows you to balance the current flowing through two parallel MOS. Because the circuit uses two Enis, the electronic load can withstand 10a current, power consumption is more than 100 W, so it is a good idea to use a radiator and a small fan.
This circuit is suitable for describing the characteristics of photovoltaic cell modules with two power supply modes. When using the current power and PC-based settings, Helios Technology Company (www.heliostechnology.com) of a photovoltaic cell module I-V characteristic curve shows that there is a zone above vmpp (highest point of the voltage, the steep transition corresponds to a voltage source at the power pressure of vmpp (figure 2 ). At a voltage lower than that of vmpp, the PV module is like a current source. Generally, it is very difficult to describe the characteristics of the I-V Characteristic Curve in a simple Current Mode in this flat zone, because the voltage output is very sensitive to the small changes of the current, load in constant voltage mode is a good choice.