Deeply understand the new high-power test power supply and fully control the rules of the game!

When it comes to high-power adjustable voltage-regulated power supplies with an output of more than 10A, readers who have come into contact with them will think of: a huge power transformer with taps, a large radiator, multiple high-power adjustment tubes fixed on it, at least 10W instrument fans that keep turning to dissipate heat, and a control panel with dense components, which is enough to reflect the complexity of its structure. It is a rather spectacular instrument. Many switches, potentiometers, complex settings and LED or LCD display devices seem to have a high-tech flavor.

However, from the perspective of basic structure, the series voltage regulator circuit lacks creativity. It is still the first-class circuit in large power supplies. Its low efficiency and high power consumption of the regulator tube are still criticized by people.

Can we use a high-frequency switching power supply with high efficiency and low power consumption? The answer is that in many occasions, such as brushless motor detection, it cannot be used normally. The reason is very simple. The output of the switching power supply is not pure. It has no effect when it is connected to a resistive load, but it is unable to cope with a load with a large pulsation in PWM mode.

This is also the main reason why large power supplies now mainly use series-stabilized structures. Of course, manufacturers have also made a lot of efforts, such as using tapped output power transformers to reduce the power consumption of the adjustment tube. When the external voltage demand changes, the relay controls the tracking adjustment and automatically adjusts the tap position. This greatly reduces the power consumption of the adjustment tube and improves the system efficiency.

Of course, it also makes the originally not simple structure more complicated.

Large-scale voltage-stabilized power supplies with conventional structures are difficult to imitate by the majority of electronics enthusiasts, including many manufacturers with insufficient technical capabilities.

Why can't we be creative and create a large power supply with a simple structure and practicality? First of all, we must make a breakthrough in the basic concept. There is a way.

The company I used to work for is a brushless motor manufacturer that produces 24V-36V/200W bicycle motors. Each motor must undergo a load operation test, which requires an adjustable 12V-45V, maximum 20A test adjustable voltage regulated power supply. This task fell on me. For this.

After considering many structures, we finally decided to use a 30A/380V AC voltage regulator module as the control device. It is connected in series to the primary side of the power transformer, and the secondary side of the transformer rectifies and filters to output the corresponding DC voltage.

This module is a bidirectional thyristor full-angle control type, with a control voltage of 0-5V, and the control part is insulated from the switch part. Moreover, the heat sink is insulated from the internal components. There are many brands, and I use the products of Hangzhou Xizi Solid State Relay Factory.

Control scheme design: The control voltage is set by the 5V power supply with a potentiometer voltage divider, and is sent to the module input after being compared with the output DC voltage sampling signal. In addition, when a large current is detected during operation, the protection circuit will randomly act, shut down the module and self-lock until the reset button is pressed to release it.

The power transformer uses a 1KW, 220V input, 45V output control transformer. In order to avoid the waveform distortion caused by thyristor regulation, abnormal heating and machine vibration, many long-term simulation tests were conducted. The results showed that except for a slight vibration of the transformer at low voltage and high current, there were no other abnormal signs. It proves that the transformer can operate under the thyristor voltage regulation condition.

1. Circuit components are introduced as follows

UT is a 50N380V single-phase voltage regulating thyristor module. Its working mode is zero-crossing triggering, and the control voltage 0-5V controls the conduction angle. It shares a 200X120 aluminum finished heat sink with the rectifier module, and a 12V/0.45A fan is used as a forced air cooling source. B1 is a 1KW/220V control transformer, with a secondary of 45V, L1 and C1 are 8A power filters, K2 is a double-pole 10A power switch, and C3 and R1 are vibration elimination components. D1-D4 are full-wave rectifier diode modules. C4 is a large-capacity electrolytic capacitor, and RL is a dummy load resistor.

LM2576ADJ, D5, L1, C6, R2, R3 form a 12V regulated power supply. It supplies power to the fan, ICl, and 7805. 7805, C7, and C8 are 5V regulator components. The basic circuit is shown in Figure 1.

Readers can see that: the circuit structure is very simple, and its electrical performance also meets the parameter requirements of the motor test power supply, which can output 20-42V DC voltage: after adjusting the voltage value. When the current changes from 0~18A. The voltage change rate is 0.55V. Although this is a bit larger than the precision voltage regulator which only changes by 0.15V, it can meet the test requirements, because for the manufacturer. The power supply is nothing more than a quantitative test tool, and the first requirement is to have a strong and durable structure: in fact, the power supply meets this requirement very well. One of the power supplies performed so well that it set a record of not needing repair for three years! 2. Circuit Introduction

In the figure, the 220 power phase line is input to the primary end of B1. The other end of the primary is connected to one side of the module thyristor, and the other side of the thyristor is connected to the neutral line. The thyristor is turned on after the AC waveform passes zero. Its conduction angle. It is controlled by the input level of the control end. When the input voltage amplitude is 0V, the conduction angle is 0, and when the input is 5V, the full angle is turned on. Therefore, the change of the control voltage causes the AC voltage input to the primary to change accordingly. Since the primary and secondary of B1 have a fixed ratio, the voltage coupled to the secondary changes. After rectification and filtering, a DC voltage of the expected amplitude is obtained. It should be noted that the reason why the capacity of the voltage regulator module is selected with a large margin is that the module drives an inductive load. When working in the wave cutting state, the withstand voltage and current values ​​must have a large margin.

The 12V power supply consists of LM2576HV, D5, L1, C6, etc.:

The input power supply is allowed to vary between 7-60V. No additional input power supply is required from the input voltage. Another reason for directly taking the working power supply is to realize the power failure protection condition, after the short circuit and overcurrent protection are activated.

When the working power fails, the 12V power supply and the 5V power supply lose power successively, causing the system to shut down and stop working. The mechanism is described in detail later.

The stable 12V voltage is also used to supply the 12V fan, ICl and the next level 5V regulated power supply.

IClA, R12, R13, W1, and R14 form a voltage setting signal processing circuit. The signal is transmitted to the IClB non-inverting terminal and compared with the feedback signal input to the IClB inverting terminal. IClB outputs the control signal to the module control terminal. IClA works in follower mode.

IClB works in subtractor mode. It can be seen that the setting signal is amplified 1.4 times after subtracting the voltage feedback signal. Its gain is determined by the ratio of R15, R16, R19, and R18, and R18=R16, R15=R19. If the design increases the gain, it may cause over-compensation, and the output voltage will rise when the load current increases.

IClD, R6, R7, R8, and C10 form a W conversion amplifier circuit.

Its gain is " times. IClC, R9, R10 and R11 form a comparator. Once the current signal passes through I/O, the converted and amplified voltage is greater than the reference signal at the inverting input end of IClC. IClC quickly flips to a high level. At this time, D6 charges C9, and C9 turns on 7002 through R17.

The control voltage output by IClB is pulled down to 0, causing the module thyristor side to turn off quickly. At this time, the secondary voltage disappears and the working power supply voltage is zero.

12V and 5V also discharge to zero due to the short delay of each level of filter capacitor.

Although the 220 power supply is not turned off at this time, the system is in a power-off state.

The current consumption of the whole machine is only the leakage current of the module thyristor side. If you want to restart in a short time, you need to press K1 to discharge C9, and then close and open the power switch K2 again.

The setting of D6 and C9 prevents the IC1C from repeatedly flipping when the 12V power supply is not powered off, causing the module to repeatedly switch on and off, resulting in damage to the device! Due to the unidirectional power supply of D6 and the storage effect of C9, the module remains in a closed state for a certain period of time, so that there is ample time for the system to lose power or eliminate faults.

One of the uses of this power supply is to test the durability of brushless motors. It works around the clock and is often unattended at night. Short circuits often occur due to motor damage or controller damage. The above power-off protection scheme can better protect the safety of the equipment and avoid unnecessary power consumption.

When there is no such requirement: the 12V power supply is powered by an independent power supply. After the system is protected, it can maintain self-locking for a long time, and it is very convenient to reset. Just press K1 to work again. There is no need to operate the power switch K2. Therefore, the working conditions after using an independent power supply are completely different from the former!

Under the premise that everything must be subject to actual needs, electronic design has great flexibility. It can be said that unit circuits are basic elements. All elements have their own characteristics. The key lies in understanding the depth and optimizing the combination. This is the rule of the game to win!