Top 10 practical tips you should know about power

For power products, you should know 10 practical tips

simple ways to improve your operation and measurement ability

tip 1 use remote sensing to compensate for the influence of load leads

when the power supply leaves the factory, its adjustment sensing end is usually connected to the output end. Doing so will limit the voltage regulation ability of the power supply, even in very short leads. Using longer leads or higher gauge numbers will make the adjustment capability worse (Figure 1). Compared with the 0.2m Ω output impedance of 10A power supply, the impedance of copper lead is:

AWG wire gauge Resistance M Ω/ft (20oC)

22 16.1

20 10.2

18 6.39

16 4.02

14 2.53

12 1.59

10 0.999

if the load is connected to the power supply with a relay, the adjustment ability will be even worse

remote sensing is to amplify the internal feedback of the power supply and adopt tepex surface layer, which can significantly improve the rigidity. The sensing end of the device is directly connected to the load, so that the power supply can adjust the output at the load end, rather than at its own output end (Fig. 2). The voltage compensates the resistance of the load lead, relay or connector through the necessary offset, so as to maintain a constant load voltage

to realize remote sensing, disconnect the connection between the output end and the sensing end. Use shielded twisted pair cable to connect the power sensing terminal to the sensing point on the load (do not use shielding as an sensing conductor). Ground one end of the shield and hang the other end in the air

the induced current is usually less than 10mA. As a general rule, you should keep the voltage drop in the induction line less than 20 times the temperature coefficient of the power supply (usually expressed in mv/° C). It is easy to meet this requirement by using shielded two-wire cables

tip 2 charge and discharge the battery in a short time

the constant current mode of using the power supply (Figure 1) is a simple method to recharge the battery, which can achieve 100% charging. However, slow charging is a major disadvantage of this method. Since the charging current is only a fraction of the rated ampere hour of the battery, it will take hours to charge

pulse charging is also called transient mode, which can shorten the charging time and charge the battery to more than 90% capacity (Figure 2). The electronic load acts as a switch to provide current pulses (note that you can also program constant current charging with the electronic load). Figure 3 shows a typical pulse charging current waveform

to simulate the battery leakage current, you can also program the electronic load to discharge the battery with a constant current or pulse current waveform. In some cases, pulse discharge makes the battery much like the energy-saving characteristics of the product. For example, simulating the battery discharge of a cell is extremely complex, because it has various working modes - standby, dial-up, call. You can also use the electronic load to establish the required three state discharge current waveform as shown in Figure 3

prompt 3 use the remote disable feature to improve safety

remote disable provides a safe method to disconnect the power supply in response to some specific working conditions or to protect the system operator (such as the response to the unexpected opening of the cabinet door or someone pressing the emergency button)

remote inhibit (RI) is the input to the power supply, and the output is prohibited when the RI end is pulled down to low (Figure 1). Short circuit the normally open switch to disconnect the power output. You can also use a logic chip with open collector transistor output to replace the switch. Figure 1 also shows a discrete fault indicator (DFI). When the power supply detects a user-defined fault, you can use it as a signal to inform the operator or other components in the system

DFI signal can be generated under almost any working condition. For example, to generate DFI signal when the load drags too much current, you can enable the overcurrent protection (OCP) mode, program the power supply, generate DFI signal when entering the constant current mode, and then program the maximum current usually pulled out by the load. If the load current exceeds the maximum value, the DFI output is low, which disables the power supply and informs the operator of the overcurrent condition (or provides other user-defined functions), without involving the system bus or interrupting the system controller

you can also daisy chain DFI and RI as shown in Figure 2. If a power supply detects a fault, all power supplies in the system will be disabled. With this method, you can connect unlimited power supplies together

tip 4 eliminate the noise of low-level measurement

there are several different sources of noise in low-level measurement; It is easier to eliminate noise than to filter it out. Please check the following noise sources:

1 Power supply

using low-noise power supply is naturally the best way to remove measurement noise. Linear power supply has low common mode noise current, and generally works at low frequency. However, you can also successfully use the switching power supply with low common mode current included in the index. As a rule of thumb, common mode currents exceeding Ma can cause trouble. Mastering the contents of this prompt can minimize this problem

2. The connection of the DUT to the power supply

eliminates the ground loop to minimize conductive noise. Ideally, there should be only one grounding point. In the rack system, multi-point grounding is inevitable, and the DC distribution path isolated from other conduction paths will carry the ground current. If necessary, float the power supply (do not directly ground either end. Adding baycusan? C 1010 to the formula can make the hair in an extremely wet and dry environment)

for output lines and induction lines, shielded twisted pair can be used to minimize radiation pickup (Electrical and magnetic pickup). To ensure that the shield does not carry current, only one end of the shield should be grounded, preferably the grounding point on the power supply (Figure 1). The common mode noise current of the power supply can be minimized by balancing the ground impedance of the positive and negative outputs. It is also necessary to balance the ground impedance of the positive and negative input terminals of the DUT. Magnetic coupling or capacitive leakage provides the return path of high-frequency noise ground loop current. To balance the ground impedance of the DUT at your test frequency, put the common mode choke