Soft start power amplifier power supply. Amplifier Soft Start Device

The soft start of the switching power supply protects the power switches from high currents during startup. Large starting currents appear at startup due to the charge of the capacitors. Moreover, the greater the power of the power source, the greater its capacity.

If a 220V lamp is connected in series with the power source alternating current, then when the SMPS is connected to the network, the lamp will flash and go out. The lamp flashes due to the fact that large currents arise in the SMPS when the electrolytes are charged, roughly speaking, these currents tend to the short circuit current, and the resistance decreases. After the completion of the transients, the currents decrease and the lamp goes out.

If an IIP occurs short circuit, the lamp will stay on.

The point is not the lamp. The lamp clearly makes it possible to see the currents flowing during the charging of electrolytes, and also allows you to limit these currents, dissipating power in the form of heat.

A SMPS soft starter is similar to a lamp, the only difference is that this “lamp” is switched on in the circuit for a fraction of a second, and dissipates some power during the transient, and then is switched off from the circuit.

Scheme of soft start SMPS

As you can see from the diagram, the role of the lamp is performed by two series-connected resistors R5 and R6. The power of these resistors is 2 watts. After the completion of the transients (fractions of a second), the relay k1 is activated, shunting the resistors R5 and R6 with its contacts, after which the entire consumed current of the SMPS flows through the relay contacts.

To increase the delay time, it is necessary to increase the capacitance of the capacitor C3.

The relay must be used with a coil designed for voltage 12V and current 30-40mA (coil resistance = 400 Ohm), the contact group must be designed for a current of 10A.

The fuse F1 is optionally 3.15A, you select it depending on the power of the power source connected to the output of the SMPS soft starter.

According to the transistor VT1, I have BD139, you can use BD140, BD875, KT972. Composite transistor.

ARCHIVE:

The soft start circuit provides a delay of about 2 seconds, which allows you to smoothly charge larger capacitors without power surges and blinking home lights. The charge current is limited by the value: I=220/R5+R6+Rt.
where Rt is the resistance of the primary winding of the transformer direct current, Om.
The resistance of resistors R5, R6 can be taken from 15 ohms to 33 ohms. Less - not effective, but more - the heating of the resistors increases. With the ratings indicated on the diagram, the maximum starting current will be limited, approximately: I=220/44+(3...8)=4.2...4.2A.

The main questions that beginners have when assembling:

1. What voltage should electrolytes be set to?
The electrolyte voltage is indicated on the printed circuit board - these are 16 and 25V.

2. What voltage should a non-polar capacitor be set to?
Its voltage is also indicated on the printed circuit board - it is 630V (400V is allowed).

3. What transistors can be used instead of BD875?
KT972 with any letter index or BDX53.

4. Can a non-composite transistor be used instead of the BD875?
It is possible, but it is better to look for a composite transistor.

5. Which relay should be used?
The relay must have a 12V coil with a current of no more than 40mA, and preferably 30mA. Contacts must be rated for a current of at least 5A.

6. How to increase the delay time?
To do this, it is necessary to increase the capacitance of the capacitor C3.

7. Is it possible to use a relay with a different coil voltage, for example 24V?
No, the circuit won't work.

8. Collected - does not work
So this is your mistake. The circuit assembled on serviceable parts starts working immediately and does not require adjustment and selection of elements.

9. There is a fuse on the board, what current should it be used for?
I recommend calculating the fuse current as follows: Ip \u003d (Pbp / 220) * 1.5. The resulting value is rounded up to the nearest fuse rating.

Discussion of the article on the forum:

List of radio elements

This simple device improves the reliability of your radio and reduces network interference when you turn it on.

Any power supply for radio equipment contains rectifier diodes and high-capacity capacitors. At the initial moment of turning on the mains supply, a pulse current jump occurs - while the filter capacitances are being charged. The amplitude of the current pulse depends on the value of the capacitance and the voltage at the output of the rectifier. So, at a voltage of 45 V and a capacitance of 10,000 microfarads, the charging current of such a capacitor can be 12 A. In this case, the transformer and rectifier diodes briefly operate in short circuit mode.

To eliminate the risk of failure of these elements by reducing the inrush current at the time of initial switching on, the one shown in Fig. 1.7 scheme. It also allows you to lighten the modes and other elements in the amplifier for the duration of the transients.

Rice. 1.7

At the initial moment, when power is applied, capacitors C2 and C3 will be charged through resistors R2 and R3 - they limit the current to a value that is safe for the rectifier parts.

After 1 ... 2 seconds, after the capacitor C1 is charged and the voltage on the relay K1 increases to a value at which it will operate and shunt the limiting resistors R2, R3 with its contacts K1.1 and K1.2.

In the device, you can use any relay with a response voltage less than that acting at the output of the rectifier, and the resistor R1 is selected so that the "excess" voltage drops across it. The relay contacts must be rated for the maximum current in the power supply circuits of the amplifier. The circuit uses a relay RES47 RF4.500.407-00 (RF4.500.407-07 or others) with a rated operating voltage of 27 V (winding resistance 650 Ohm; current switched by contacts can be up to 3 A). In fact, the relay is already activated at 16 ... 17 V, and the resistor R1 is selected with a value of 1 kOhm, while the voltage across the relay will be 19 ... 20 V.

Capacitor C1 type K50-29-25V or K50-35-25V. Resistors R1 type MLT-2, R2 and R3 type C5-35V-10 (PEV-10) or similar. The value of the resistors R2, R3 depends on the load current, and their resistance can be significantly reduced.

Rice. 1.8

The second scheme shown in fig. 1.8 performs the same task, but allows you to reduce the size of the device by using a smaller time-setting capacitor C1. Transistor VT1 turns on relay K1 with a delay after capacitor C1 is charged (type K53-1A). The circuit also allows, instead of switching the secondary circuits, to provide a stepped voltage supply to the primary winding. In this case, you can use a relay with only one group of contacts.

The resistance value R1 (PEV-25) depends on the load power and is chosen such that the voltage in the secondary winding of the transformer is 70 percent of the nominal value with the resistor on (47 ... 300 Ohm).

Setting up the circuit consists in setting the delay time for turning on the relay by selecting the value of the resistor R2, as well as choosing R1.

The above schemes can be used in the manufacture of a new amplifier or in the modernization of existing ones, including industrial ones.

Compared to similar devices for two-stage supply voltage supply, given in various magazines, those described here are the simplest.

These two circuits are a power device with a toroidal transformer. Typically, the starting (starting) current is very high for a short period while the smoothing capacitors are charging. This is a kind of stress for capacitors, rectifier diodes and the transformer itself. The fuse may also blow at this point.

The soft start circuit is designed to limit the starting current to an acceptable level. This is achieved by connecting the transformer to the mains through a resistor, which is connected for a short time by means of a relay.

The circuits combine soft start and button control Thus, a ready-made module is obtained that can be used in power amplifiers or in conjunction with other electrical appliances.

Description of soft start circuits

The first circuit is built on CMOS logic chips (4027), and the second on the NE556 integrated circuit, which is 2 combined in one package.

As for the first circuit, it uses a JK flip-flop connected as a T flip-flop.

The T flip-flop is a counting flip-flop. The T-flip-flop has one counting (clocking) input and one synchronizing one.

When the J2 button is pressed, the trigger status changes. During the transition from the off state to the on state, the signal is transmitted through the resistor and capacitor to the second part of the circuit. There, the second JK flip-flop is connected in an unusual way: high level, and the SET pin is used as the input.

You can see in the truth table that when the reset pin is driven high, all other inputs are ignored except for the SET pin. When the SET pin is high, the output is also high and vice versa.

Resistor R6 and capacitor C6 are used to delay the signal at the moment of switching on. At the values ​​indicated in the diagram, the delay is 1 second. If necessary, change the parameters R6 and C6 to change the delay time. Diode VD2 shunts resistor R6, as a result of which, when turned off, the relay turns off without delay.

The second circuit uses the NE556 dual timer. The first timer is used as a pushbutton switch, and the second as a switch associated with the delay created by the elements R5, VD2 and C6.

Resistors R8 - R10 have a resistance of 150 ohms and a power of 10W. They are connected in parallel, resulting in a 50 ohm resistor with a power of 30 watts. On the PCB, two of them are side by side, and the third is in the middle on top of them. The power of the transformer Tr1 is about 5 W with a voltage in the secondary winding of 12-15 V. Connector J1 is used if 12 volt power is needed for other external devices.

Relays K1 and K2 for 12V, the contact groups of which must be designed for switching 220V / 16A. The F1 fuse rating must be selected according to the device that will be connected to the soft starter.

Both circuits have been tested on a breadboard and both work, but the second circuit is prone to interference if the wire to the button is long enough, which in turn leads to false switching.

Most resistors, capacitors and diodes are SMD. Lately I've been using more and more SMD elements in structures because there is no need to drill holes. If you choose to use either of these two printed circuit boards check them carefully because they have not been tested.

(unknown, downloaded: 1,192)

Hello friends!
I once did a ULF with 50,000 microfarad PSU filter capacitors in the shoulder. And I decided to make a smooth start, because. the 5 amp fuse at the input of the transformer periodically burned out when the amplifier was turned on.
I tested different options. There have been various developments in this direction. I settled on the scheme below.

“- Semyon Semyonovich, I told you: without fanaticism!
Amplifier on . The customer lives in a one-room Khrushchev.
And you are still a filter and a filter ... "

THE CONSTRUCTION DESCRIBED BELOW HAS A GALVANIC COMMUNICATION WITH THE NETWORK 220V!
BE CAREFUL!

First, consider the options for the execution of the power part, so that the principle is clear. Then let's move on to the complete scheme of the device. There are two circuits - with a bridge and with two MOSFETs. Both have advantages and disadvantages.

By the way, this property allows you to use the device as a walk-through switch in large rooms or long galleries, corridors, flights of stairs. In parallel, we install several buttons, each of which can independently turn the light on and off. Wherein The device also protects incandescent lamps, limiting the inrush current.
When used in lighting, not only incandescent lamps are acceptable, but also all kinds of energy-saving lamps, LEDs with UPS, etc. The device works with any lamps. For energy saving and LEDs, I put a timing capacitor less than ten times, because they do not need to start as slowly as incandescent lamps.

With a time-setting capacitor (ceramics, a film is better, but an electrolyte is also possible) C5 \u003d 20 μF, the voltage increases non-linearly for about 1.5 seconds. V1 is needed to quickly discharge the timing capacitor and, accordingly, quickly turn off the load.

Between the common wire and the 4th output (Reset to low level) of the timer, you can connect an optocoupler, which will be controlled by some kind of protection module. Then, upon an alarm signal, the timer will be reset and the load (for example, UMZCH) will be de-energized.

Instead of the 555 chip, another control device can be used.

Applied Parts

Unfortunately, the PP drawing has been lost. But the device is so simple that it will not be difficult for those who wish to dilute the signet for their details. Those who want to share their drawing with the world - signal in the comments.

The scheme has been working for me for about 5 years, it has been repeatedly repeated in variations, and has proven itself well.

Thank you for your attention!