January 6, 2013 at 16:05Design a power source for an energy-intensive portable device
Good day to all habrazhitel.
This post belongs to the “Do it yourself” section and describes a simple (in my opinion) way of solving the problem of nutrition control.
In my spare time, I pick a hefty boombox with a soldering iron in the case of the ancient Soviet tape recorder Electronics 211 Stereo , the task is to assemble a portable unit with full minced meat, sufficient sound output and working duration for going out into the countryside, exercising in the gym and for voicing the garage. Here are the requirements that I put forward when developing the device for its power supply:
- stable power for my built-in digital 5-volt devices with an average current of at least 1A - an outdated PDA, player, as well as external devices - USB and SD flash drives, hard drive;
- power amplifier power supply voltage from 11 to 18V;
- autonomous power supply sufficient for continuous operation of the device at maximum volume with constant performance;
- external power from the network 220 volts;
- external power from the vehicle’s on-board network;
- electronic power management;
- zero battery power consumption in standby mode;
- control of battery discharge Li-Ion batteries with a warning about the discharge and auto power off;
- selection of parts, if possible, from waste elements (places in the boombox body with a large excess).
In my opinion, all the development points were successfully implemented, partly except for the last - I still had to spend $ 6.2 on the purchase of the moduleeffective DC-DC converter , another $ 13.2 respectively batteries 4 pcs. and a $ 2.8 4-piece battery box . The remaining parts were soldered from burned motherboards and ancient Soviet iron in stock.
Now the actual development steps themselves.
In the text of the article I will not indicate the designation of the used parts, they are given on the diagrams for convenience.
1. The choice of the primary source of autonomous power.
The primary power source is 4 Li-Ion batteries18650 with a capacity of 2500 mAh without built-in charge / discharge control. After exploring the Internet for the possibility of charging a battery of 4 sequentially connected batteries, it turned out that this task is not trivial, and in fact it was decided to charge the batteries separately with an external charger - thus, their service life will be maximum. For one battery, the recommended cut-off voltages are lower and upper 2.75V and 4.2V, respectively; for an assembly of 4 batteries, the lower cut-off voltage should be 11V. Compliance with the operating rules for discharging and charging batteries ensures long-term operation of the battery, so you should not neglect them in any case. The maximum voltage of a charged battery can be 16.8V, the average operating voltage is 14.8V.
2. Implementation of the primary nutrition scheme.
The Elektronika 211 Stereo tape recorder has a stabilized power supply according to the scheme of a zener diode and a composite emitter follower, which is easily tuned to a voltage of 17V with a sufficient load current (in a dashed box in the diagram). At the maximum possible battery charge of 16.8V, power isolation and reverse polarity protection is achieved by switching the Schottky diode in series with the battery and connecting the circuit directly to the output capacitors of the standard power supply. A battery current leak does not occur in the absence of mains power, since the base-emitter junction of the full-time stabilizer transistor will be switched in the opposite direction. An external 12 ... 14V power connector for a car is inserted into the battery circuit break, the design of which includes a battery circuit breaker,
3. Select a key element for power supply.
An MTN3302 n-channel high-power field effect transistor was found on a burned motherboard as a key element . The open channel resistance is 10 milliohms, the transistor opens with a gate voltage relative to a source of the order of 4V and higher, and the maximum drain-source voltage is 30V. With a switched voltage of 13 V at a load of 27 Ohms, the drain-source voltage of the open transistor was vanishingly small. Similar transistors can be found on any motherboard.
4. Implementation of electronic on / off load and battery discharge control.
Given the implementation of primary power supply circuits, the key must switch voltage from 11 to 18V, and also have control circuits that will not consume current when the key is open.
The voltage source of the reference voltage is a Zener diode D814G for 11V, connected from the key drain in series with a quenching resistor to the power plus. The choice of a zener diode is determined by a wide range of operating currents, which cannot be provided by a low-power analogue. The voltage at the quenching resistor is monitored by a silicon pnp transistor, if the voltage is close to zero, the transistor closes and the circuit switches itself off. With the control transistor open (which means that the supply voltage is not lower than 11 volts), the voltage of the key transistor is supplied to the gate of the key transistor through a divider with high-resistance resistors, which keeps it open.
The key state switching circuit is made on the basis of a charge accumulator on the capacitor, which is connected between the power plus and the key drain through high-resistance resistors. When the key is open, the capacitor is charged, and the potential of its negative electrode relative to the source approaches zero, and vice versa - when the key is closed, the capacitor discharges through the load resistance and the potential of its negative electrode relative to the source approaches the supply voltage. Since the charge and discharge time of the storage capacitor to the threshold value of the switching voltage relative to the source of 4V must be balanced, a separate diagram of the charge / discharge of the capacitor using a diode and an additional resistor is shown. When you press the power button, the charge accumulated on the capacitor opens or closes the key,
5. Low battery indicator.
For the indicator to work, it is necessary to monitor the supply voltage level in the same way as the control transistor in step 4 does, i.e. you can use the finished part of the circuit with a zener diode, already implemented in step 4. It is also necessary to take into account that the discharge indicator should glow from the level of the supply voltage equal to approximately 12V or lower until the key is closed. The indicator amplifier is assembled on the basis of a cascade of two germanium transistors according to the scheme with common emitters with a positive feedback circuit for organizing hysteresis (provides a sharp inclusion of the indicator when passing the threshold value). Germanium transistors were chosen based on the fact that the base-emitter junctions of such transistors open at a significantly lower voltage drop than silicon ones,
6. The choice of voltage converter DC-DC 5V.
I found an interesting device from the Chinese - VMP3203. This is a finished assembly, incorporating almost all the necessary elements for use with a minimum of strapping. The conversion efficiency on the datasheet is about 95%. The maximum output current is 3A at a voltage of 5V. Input voltage range 8 - 24V. I have not yet tested the ripple of the output voltage, because the general assembly of the structure is not finished.
Eventually:electronic power management scheme, providing power to both digital devices and a power amplifier. The circuit monitors the discharge of the battery and warns of low voltage on the batteries, uses both autonomous and external power. The discharge of battery power is eliminated due to the zero current consumption of the switched off device. The vast majority of parts are taken from carefully organized ducks and dead motherboards. Profit!
UPD1An error was made when redrawing the circuit from a bunch of wires. The diode in the overcharge circuit of the open / close capacitor key has been reversed, corrected. The positive feedback resistor in the amplifier circuit of the battery low voltage indicator was selected more accurately (200k instead of 75k). If interested, I can lay out the wiring and photos of the finished circuit board.
This post belongs to the “Do it yourself” section and describes a simple (in my opinion) way of solving the problem of nutrition control.
In my spare time, I pick a hefty boombox with a soldering iron in the case of the ancient Soviet tape recorder Electronics 211 Stereo , the task is to assemble a portable unit with full minced meat, sufficient sound output and working duration for going out into the countryside, exercising in the gym and for voicing the garage. Here are the requirements that I put forward when developing the device for its power supply:
- stable power for my built-in digital 5-volt devices with an average current of at least 1A - an outdated PDA, player, as well as external devices - USB and SD flash drives, hard drive;
- power amplifier power supply voltage from 11 to 18V;
- autonomous power supply sufficient for continuous operation of the device at maximum volume with constant performance;
- external power from the network 220 volts;
- external power from the vehicle’s on-board network;
- electronic power management;
- zero battery power consumption in standby mode;
- control of battery discharge Li-Ion batteries with a warning about the discharge and auto power off;
- selection of parts, if possible, from waste elements (places in the boombox body with a large excess).
In my opinion, all the development points were successfully implemented, partly except for the last - I still had to spend $ 6.2 on the purchase of the moduleeffective DC-DC converter , another $ 13.2 respectively batteries 4 pcs. and a $ 2.8 4-piece battery box . The remaining parts were soldered from burned motherboards and ancient Soviet iron in stock.
Now the actual development steps themselves.
In the text of the article I will not indicate the designation of the used parts, they are given on the diagrams for convenience.
1. The choice of the primary source of autonomous power.
The primary power source is 4 Li-Ion batteries18650 with a capacity of 2500 mAh without built-in charge / discharge control. After exploring the Internet for the possibility of charging a battery of 4 sequentially connected batteries, it turned out that this task is not trivial, and in fact it was decided to charge the batteries separately with an external charger - thus, their service life will be maximum. For one battery, the recommended cut-off voltages are lower and upper 2.75V and 4.2V, respectively; for an assembly of 4 batteries, the lower cut-off voltage should be 11V. Compliance with the operating rules for discharging and charging batteries ensures long-term operation of the battery, so you should not neglect them in any case. The maximum voltage of a charged battery can be 16.8V, the average operating voltage is 14.8V.
2. Implementation of the primary nutrition scheme.
The Elektronika 211 Stereo tape recorder has a stabilized power supply according to the scheme of a zener diode and a composite emitter follower, which is easily tuned to a voltage of 17V with a sufficient load current (in a dashed box in the diagram). At the maximum possible battery charge of 16.8V, power isolation and reverse polarity protection is achieved by switching the Schottky diode in series with the battery and connecting the circuit directly to the output capacitors of the standard power supply. A battery current leak does not occur in the absence of mains power, since the base-emitter junction of the full-time stabilizer transistor will be switched in the opposite direction. An external 12 ... 14V power connector for a car is inserted into the battery circuit break, the design of which includes a battery circuit breaker,
3. Select a key element for power supply.
An MTN3302 n-channel high-power field effect transistor was found on a burned motherboard as a key element . The open channel resistance is 10 milliohms, the transistor opens with a gate voltage relative to a source of the order of 4V and higher, and the maximum drain-source voltage is 30V. With a switched voltage of 13 V at a load of 27 Ohms, the drain-source voltage of the open transistor was vanishingly small. Similar transistors can be found on any motherboard.
4. Implementation of electronic on / off load and battery discharge control.
Given the implementation of primary power supply circuits, the key must switch voltage from 11 to 18V, and also have control circuits that will not consume current when the key is open.
The voltage source of the reference voltage is a Zener diode D814G for 11V, connected from the key drain in series with a quenching resistor to the power plus. The choice of a zener diode is determined by a wide range of operating currents, which cannot be provided by a low-power analogue. The voltage at the quenching resistor is monitored by a silicon pnp transistor, if the voltage is close to zero, the transistor closes and the circuit switches itself off. With the control transistor open (which means that the supply voltage is not lower than 11 volts), the voltage of the key transistor is supplied to the gate of the key transistor through a divider with high-resistance resistors, which keeps it open.
The key state switching circuit is made on the basis of a charge accumulator on the capacitor, which is connected between the power plus and the key drain through high-resistance resistors. When the key is open, the capacitor is charged, and the potential of its negative electrode relative to the source approaches zero, and vice versa - when the key is closed, the capacitor discharges through the load resistance and the potential of its negative electrode relative to the source approaches the supply voltage. Since the charge and discharge time of the storage capacitor to the threshold value of the switching voltage relative to the source of 4V must be balanced, a separate diagram of the charge / discharge of the capacitor using a diode and an additional resistor is shown. When you press the power button, the charge accumulated on the capacitor opens or closes the key,
5. Low battery indicator.
For the indicator to work, it is necessary to monitor the supply voltage level in the same way as the control transistor in step 4 does, i.e. you can use the finished part of the circuit with a zener diode, already implemented in step 4. It is also necessary to take into account that the discharge indicator should glow from the level of the supply voltage equal to approximately 12V or lower until the key is closed. The indicator amplifier is assembled on the basis of a cascade of two germanium transistors according to the scheme with common emitters with a positive feedback circuit for organizing hysteresis (provides a sharp inclusion of the indicator when passing the threshold value). Germanium transistors were chosen based on the fact that the base-emitter junctions of such transistors open at a significantly lower voltage drop than silicon ones,
6. The choice of voltage converter DC-DC 5V.
I found an interesting device from the Chinese - VMP3203. This is a finished assembly, incorporating almost all the necessary elements for use with a minimum of strapping. The conversion efficiency on the datasheet is about 95%. The maximum output current is 3A at a voltage of 5V. Input voltage range 8 - 24V. I have not yet tested the ripple of the output voltage, because the general assembly of the structure is not finished.
Eventually:electronic power management scheme, providing power to both digital devices and a power amplifier. The circuit monitors the discharge of the battery and warns of low voltage on the batteries, uses both autonomous and external power. The discharge of battery power is eliminated due to the zero current consumption of the switched off device. The vast majority of parts are taken from carefully organized ducks and dead motherboards. Profit!
UPD1An error was made when redrawing the circuit from a bunch of wires. The diode in the overcharge circuit of the open / close capacitor key has been reversed, corrected. The positive feedback resistor in the amplifier circuit of the battery low voltage indicator was selected more accurately (200k instead of 75k). If interested, I can lay out the wiring and photos of the finished circuit board.